Free-piston Stirling device

Abstract

The present invention provides a free piston Stirling device that can be easily manufactured by reducing manufacturing steps. The free piston Stirling device is a free piston Stirling refrigerator (1), which has a piston (5) as a reciprocating body that can reciprocate in the axial X direction of a first cylinder (3), a first leaf spring (11) as an elastic body for controlling the reciprocating motion of the piston (5), a connecting body (13) that connects the piston (5) to the movable part of the first leaf spring (11), and a support arm (25) as a support body that supports the fixed part of the first leaf spring (11) when its positional relationship with the first cylinder (3) is fixed. Since the piston assembly (6) has a movable mass mp as a hammer body and a mounting part (30) on the connecting body (13) on which the washer (31) is mounted, and the mounting part (30) is set in a position where the washer (31) can be mounted when the piston assembly (6) is assembled, it is easy to manufacture by reducing the steps of disassembly and reassembly.

Description

Technical Field

[0001] The present invention relates to an invention of a free piston Stirling device. Prior Art

[0002] Conventionally, as such a free piston Stirling device, there is known a device having a cylinder; a piston and a displacer as reciprocating bodies that can reciprocate axially in the cylinder; a leaf spring as an elastic body that controls the reciprocating motion of the piston and the displacer; sleeves and opening bolts, rods and nuts as connecting bodies that connect the piston and the displacer to the central portions of the movable parts of the leaf spring respectively; a fixed shaft, spacers and nuts as a support body that supports the outer peripheral portion of the fixed part of the leaf spring in a state where the positional relationship with the cylinder is fixed (for example, refer to Patent Document 1). Moreover, in such a free piston Stirling device, by optimizing the resonance frequency determined by the spring constant of the leaf spring and the movable mass with the piston assembly and the displacer assembly, the operation in a state of maintaining the phase difference between the piston and the displacer becomes easy. Thus, in order to adjust the resonance frequency of the piston assembly and the displacer assembly, in Patent Document 1, a method of adding an additional weight (equivalent to the hammer body of the invention of the present application) through washers is adopted. Prior Art Documents Patent Documents

[0003] Patent Document 1: Japanese Patent Application Laid-Open No. 2004-309080 Summary of the Invention Problems to be Solved by the Invention

[0004] In Patent Document 1, after assembling the piston assembly and the displacer assembly, fixing these piston assembly and displacer assembly on a fixing table different from the Stirling device, applying a minute vibration, measuring their respective resonance frequencies, calculating the additional weight, once disassembling the piston assembly and the displacer assembly from the fixing table and decomposing them, and integrating the washers as the additional weight with the piston assembly and the displacer assembly. It should be noted that adding washers to the piston assembly is performed by sandwiching the washer together with the leaf spring between the hub hole of the sleeve as the connecting body for fixing the piston to the leaf spring and the opening bolt when screwing them together. Similarly, adding washers to the displacer assembly is performed by sandwiching the washer together with the leaf spring between the rod and the nut when screwing the rod as the connecting body for fixing the displacer to the leaf spring and the nut together. That is, in Patent Document 1, steps of assembling, resonance frequency measurement, decomposition, and reassembly must be taken, which is not only time-consuming and laborious during manufacturing, but also there is a problem of increasing the risk of component breakage due to the increase in steps.

[0005] Therefore, the object of the present invention is to provide a free-piston Stirling device. This device solves the aforementioned problems and reduces manufacturing steps while also lowering the risk of component breakage. The means to solve the problem

[0006] The free-piston Stirling device described in claim 1 of this invention has... cylinder, A reciprocating body can reciprocate along its axial direction within the cylinder. The elastomer controls the reciprocating motion of the reciprocating body. Connector, which connects the reciprocating body to the movable part of the elastic body and A support body, which supports the fixing part of the elastic body in a state where its positional relationship with the cylinder is fixed, wherein, The free-piston Stirling device further has: The hammer body is used to adjust the movable mass of the reciprocating body and the connecting body. The mounting part is provided on the connecting body or reciprocating body and is used to mount the hammer body. The mounting part is positioned in a position where the hammer body can be mounted after the cylinder, reciprocating body, elastic body, connecting body and support body have been assembled.

[0007] Furthermore, in claim 2 of the present invention, the free piston Stirling device, in claim 1, wherein the elastic body is a leaf spring, and the mounting portion is provided on the side opposite to the reciprocating body.

[0008] Furthermore, in the free piston Stirling device described in claim 3 of the present invention, in claim 2, the mounting portion and the reciprocating body are configured to be coaxial, and the hammer body is mounted coaxially with respect to the mounting portion.

[0009] Furthermore, in the free piston Stirling device described in claim 4 of the present invention, in claim 3, the hammer body is one or more washers, the mounting part is an internal thread member and an external thread member that engages with the internal thread member, and the one or more washers can be clamped by the engagement of the external thread member with the internal thread member.

[0010] Furthermore, in the free piston Stirling device described in claim 5 of the present invention, in claim 3, the hammer body is an external thread member, the mounting portion is an internal thread member, the external thread member can be screwed with the internal thread member, and any one of the external thread members with different weights can be screwed with the internal thread member. Advantages of the Invention

[0011] The free piston Stirling device described in claim 1 of the present invention, by having the above-described structure, can adjust the movable mass in the state where the cylinder, the reciprocating body, the elastic body, the connecting body, and the support body are assembled. Therefore, it is possible to reduce the steps of disassembly and reassembly and facilitate manufacturing. At the same time, by reducing the steps, the risk of component damage can be reduced.

[0012] It should be noted that by setting the elastic body as a leaf spring and arranging the mounting portion on the side opposite to the reciprocating body of the leaf spring, it is possible to easily adjust the movable mass in the state where the cylinder, the reciprocating body, the elastic body, the connecting body, and the support body are assembled.

[0013] In addition, by setting the mounting portion and the reciprocating body coaxially and mounting the hammer body coaxially with respect to the mounting portion, the reciprocating motion of the reciprocating body can be performed with good balance.

[0014] In addition, by using the hammer body as a washer, the mounting portion as an internal thread member and an external thread member screwed with the internal thread member, and clamping the washer by the screwing of the external thread member and the internal thread member, according to the different numbers of sheets and / or masses of the washers, the movable mass can be easily adjusted.

[0015] Furthermore, by using the hammer body as an external thread member, the mounting portion as an internal thread member, screwing the external thread member with the internal thread member, and screwing any one of the external thread members with different weights with the internal thread member, by selecting any one of the external thread members for screwing, the movable mass can be easily adjusted. Brief Description of the Drawings

[0016] [Figure 1] is an external view of the free piston Stirling device of the present invention. [Figure 2] is a schematic view of the piston assembly of the free piston Stirling device of the present invention. [Figure 3] is a schematic diagram of the displacement assembly of the free piston Stirling device of the present invention. [Figure 4] is an explanatory diagram illustrating the adjustment of the movable mass of the piston assembly in the first embodiment of the present invention. [Figure 5] is an explanatory diagram illustrating the adjustment of the movable mass of the displacement assembly in the first embodiment of the present invention. [Figure 6] is an explanatory diagram illustrating the adjustment of the movable mass of the piston assembly in a free piston Stirling device representing the second embodiment of the present invention. [Figure 7] is an explanatory diagram illustrating the adjustment of the movable mass of the displacement assembly in a free piston Stirling device representing a second embodiment of the present invention. [Figure 8] is an explanatory diagram illustrating the adjustment of the movable mass of the piston assembly in a free piston Stirling device representing the third embodiment of the present invention. [Figure 9] is an explanatory diagram illustrating the adjustment of the movable mass of the displacement assembly in a free piston Stirling device representing the third embodiment of the present invention. [Figure 10] is an explanatory diagram illustrating the adjustment of the movable mass of the piston assembly in a free piston Stirling device according to the fourth embodiment of the present invention. [Figure 11] is an explanatory diagram illustrating the adjustment of the movable mass of the displacement assembly in a free piston Stirling device according to the fourth embodiment of the present invention. [Figure 12] is an explanatory diagram illustrating the adjustment of the movable mass of the piston assembly in a free piston Stirling device according to the fifth embodiment of the present invention. Implementation

[0017] The first embodiment of the present invention will be described below based on Figures 1 to 5. The free-piston Stirling refrigerator 1 is the free-piston Stirling device of the present invention (hereinafter simply referred to as the Stirling refrigerator). It should be noted that, for ease of explanation, although a γ-type device is illustrated in this example, other forms such as a β-type device may also be used. Inside the sealed outer casing 2, the Stirling refrigerator 1 includes a first cylinder 3, a second cylinder 4, a piston assembly 6, and a displacement assembly 8. The piston assembly 6 has a piston 5 that acts as a reciprocating body within the first cylinder 3, capable of reciprocating along its central axis X direction, and the displacement assembly 8 has a displacement device 7 that acts as a reciprocating body within the second cylinder 4, capable of reciprocating along its central axis X direction.

[0018] The outer casing 2 has a cylindrical portion 9 and a body portion 10. The front end of the cylindrical portion 9 is a heat-absorbing portion 9C, and its base end is a heat-dissipating portion 9H. The cylindrical portion 9 also houses the second cylinder 4, a portion of the displacement assembly 8, and heat exchangers (not shown) on the heat-absorbing side, a regenerator, and heat exchangers (not shown). The body portion 10 houses the first cylinder 3, a piston assembly 6, a portion of the displacement assembly 8, and the stator of a linear motor (not shown).

[0019] The piston assembly 6 will be described in detail. The piston assembly 6 is configured to include the piston 5, a first leaf spring 11 serving as an elastic body for controlling the reciprocating motion of the piston 5 within the first cylinder 3, a mover 12 of the linear motor that applies driving force to the piston 5, and a connecting body 13 for fixing the piston 5 and the mover 12 to the first leaf spring 11. The piston 5 is formed in a cylindrical shape. Furthermore, an internal thread (not shown) is formed on the base end side of the piston 5. The mover 12 is configured to have a cylindrical, non-magnetic synthetic resin frame 14, and a cylindrical permanent magnet 15 fixed to the frame 14. A circular through-hole 16 is formed on the base end side of the frame 14. The inner diameter of the through-hole 16 is smaller than the outer diameter of the piston 5. The connecting body 13 is configured to have a connecting body 17 and a nut 18. The connecting body 17 is configured to have a first external thread (not shown), a second external thread 19, a large diameter portion 20, a small diameter portion 21, and an internal thread 22. The first external thread is configured to engage with the internal thread (not shown) of the piston 5 through the through hole 16. That is, the outer diameter of the first external thread is smaller than the inner diameter of the through hole 16. On the other hand, the outer diameter of the large diameter portion 20 is larger than the inner diameter of the through hole 16. Therefore, by threading the first external thread of the connecting body 17 into the internal thread of the piston 5 through the through hole 16, the mover 12 is clamped by the piston 5 and the connecting body 17. While a central through hole 23 is formed in the center of the first leaf spring 11, a plurality of peripheral through holes 24 are formed on the outer periphery. The inner diameter of the central through hole 23 is larger than the outer diameter of the second external thread 19 and smaller than the width opposite to the nut 18. Therefore, the second external thread 19 can pass through the central through hole 23 of the first leaf spring 11. Furthermore, with the second external thread 19 passing through the central through hole 23, the first leaf spring 11 is clamped by the connecting body 17 and the nut 18 by screwing the nut 18 onto the second external thread 19. Thus, the piston assembly 6 is configured.

[0020] The first leaf spring 11 is supported by a support arm 25, which serves as a support. In detail, this is achieved by screwing a screw 26 through the outer peripheral through-hole 24 of the first leaf spring 11 and into the internal thread 27 of the support arm 25, thus clamping the outer periphery of the first leaf spring 11 between the support arm 25 and the screw 26. Furthermore, the support arm 25 is integrally formed with the first cylinder 3 via a flange 28. Therefore, the positional relationship between the support arm 25 and the first cylinder 3 is fixed. This means that the positional relationship between the outer periphery of the first leaf spring 11 supported by the support arm 25 and the first cylinder 3 is fixed. That is, the outer periphery of the first leaf spring 11 becomes a stationary fixed portion, while the central portion of the first leaf spring 11 becomes a movable portion that moves with the reciprocating motion of the piston 5.

[0021] An internal thread 22, coaxial with the second external thread 19, is formed on the side of the connecting body 17 constituting the piston assembly 6 opposite to the piston 5. That is, on the side of the connecting body 17 opposite to the piston 5, the second external thread 19 is formed on the outer side, and the internal thread 22 is formed on the inner side. The front end of the connecting body 17 having the internal thread 22 is an internal thread member. A bolt 29, as an external thread member, is screwed into the internal thread 22. Moreover, the mounting part 30 is formed by these internal thread members having the internal thread 22 and the bolt 29, as external thread members. That is, the mounting part 30 is provided on the side of the first leaf spring 11 opposite to the piston 5. Furthermore, by screwing the internal thread 22 and the bolt 29 together, a washer 31, which serves as the hammer body, can be clamped between the connecting body 17 and the bolt 29.

[0022] Next, the method for adjusting the resonant frequency fp of the piston assembly 6 in this embodiment will be described. First, the spring constant kp is pre-measured by pre-installing the outer periphery of the first leaf spring 11 on a measuring fixture (not shown) and applying stress. It should be noted that the measuring fixture is in the same positional relationship as the support arm 25. Furthermore, the spring constant kp is not measured for all first leaf springs 11, but for each manufacturing batch. Generally, the resonant frequency f of a vibration system consisting of a reciprocating object and an elastic body connected to that object is expressed by the following formula. f = (1 / 2π)√(k / m) In this formula, k is the spring constant of the elastic body, and m is the movable mass. Therefore, the target resonant frequency fpt of the piston assembly 6 is expressed by the following formula. fpt=(1 / 2π)√(kp / mp) Since the target resonant frequency fpt and the spring constant kp of the first leaf spring 11 have been determined, the movable mass mp of the piston assembly 6 can be calculated. Here, the movable mass mp is the sum of the mass m5 of the piston 5, the mass m12 of the mover 12, the mass m17 of the connecting body 17, the mass m18 of the nut 18, the mass m29 of the bolt 29, the mass m11 of the portion of the first leaf spring 11 excluding the periphery, and the mass m31 of the n-piece washer 31. m5, m12, m17, m18, m29, and m31 were measured in advance. However, these mass measurements were not performed on all components, but rather on a batch basis. Furthermore, m11 is a calculated value. Therefore, the above formula is rewritten as follows. fpt=(1 / 2π)√(kp / (m 5+m 12+m 17+m 18+m 29+m 11+nm 31)) It should be noted that in this example, as shown in Figure 4(b) which serves as the standard, although n=2, the value of n can also be varied depending on the value of kp. Since the piston 5, the mover 12, and the connecting body 17, which constitute the majority of the movable mass mp, are manufactured with high precision, the original tolerances are small. Furthermore, although the nut 18, bolt 29, and washer 31 are standard parts, their small mass means that differences in mass have a relatively small impact on the resonant frequency fp. Calculatedly, this can bring the resonant frequency fp of the piston assembly 6 close to the target resonant frequency fpt; however, in reality, the resonant frequency fp sometimes deviates from the target resonant frequency fpt by more than the allowable range. Thus, when the resonant frequency fp deviates from the target resonant frequency fpt by more than the allowable range, this can be addressed by increasing or decreasing the number of washers 31. When it is necessary to reduce the value of the movable mass mp, for example, as shown in Figure 4(a), the number of washers 31 can be reduced to one. Furthermore, when it is necessary to increase the value of the movable mass mp, for example as shown in Figure 4(c), the number of washers 31 can be increased to three. In this way, by adjusting the number of washers 31 held when the bolt 29 is screwed onto the internal thread 22, the value of the movable mass mp can be adjusted, and the resonant frequency fp of the piston assembly 6 can be made close to the target resonant frequency fpt. It should be noted that by reducing the thickness of the washers 31, the adjustment steps for the movable mass mp can be precisely defined.

[0023] It should be noted that in the free-piston Stirling refrigerator 1, since the coaxiality of the piston 5 and the first cylinder 3 needs to be highly precise, if the piston assembly 6 is disassembled to adjust the movable mass mp, the coaxiality of the piston 5 and the first cylinder 3 needs to be readjusted during reassembly. However, as described above, since the mounting part 30 is located on the side opposite to the piston 5 of the first leaf spring 11, even when the piston assembly 6 is supported by the support arm 25 and the piston 5 is inserted into the first cylinder 3, the movable mass mp can be adjusted simply by removing the bolt 29 from the piston assembly 6 and adjusting the number of washers 31. That is, without compromising the coaxiality of the piston 5 and the first cylinder 3, the resonant frequency fp can be easily made close to the target resonant frequency fpt.

[0024] The displacement assembly 8 will now be described in detail. The displacement assembly 8 is configured to include the displacement device 7, a second leaf spring 32 serving as an elastic body for controlling the reciprocating motion of the displacement device 7 within the second cylinder 4, and a connecting body 33 for fixing the displacement device 7 to the second leaf spring 32. The displacement device 7 is cylindrical. The connecting body 33 is configured to have a rod 34 and a first nut 35. The rod 34 is configured to have a rod body 36 in the shape of a round bar and an external thread 37 provided on the side of the rod body 36 opposite to the displacement device 7. Furthermore, the rod body 36 is coaxially connected to the displacement device 7. It should be noted that the outer diameter of the external thread 37 is smaller than the outer diameter of the end of the rod body 36 on the side opposite to the displacement device 7. A central through hole 38 is formed in the center of the second leaf spring 32, and a plurality of peripheral through holes 39 are formed on the outer periphery. The inner diameter of the central through hole 38 is formed to be larger than the outer diameter of the external thread 37, and smaller than the outer diameter of the end of the rod body 36 opposite to the displacement device 7 and the width opposite to the first nut 35. Therefore, the external thread 37 can pass through the central through hole 38 of the second leaf spring 32. Furthermore, with the external thread 37 passing through the central through hole 38, the second leaf spring 32 is held by the rod body 36 and the first nut 35 by screwing the first nut 35 into the external thread 37. Thus, the displacement device assembly 8 is configured.

[0025] The second leaf spring 32 is supported by a support arm 40, which serves as a support. In detail, this is achieved by screwing a screw 41, which passes through a through hole 39 on the outer periphery of the second leaf spring 32, into the internal thread 42 of the support arm 40, thus clamping the outer periphery of the second leaf spring 32 between the support arm 40 and the screw 41. Furthermore, the support arm 40 is fixedly positioned within the body portion 10 of the housing 2. Additionally, the second cylinder 4 is also fixedly positioned within the cylindrical portion 9 of the housing 2. Therefore, the positional relationship between the support arm 40 and the second cylinder 4 within the housing 2 is fixed. This means that the positional relationship between the outer periphery of the second leaf spring 32, supported by the support arm 40, and the second cylinder 4 is fixed. That is, the outer periphery of the second leaf spring 32 becomes a stationary fixed portion, while the central portion of the second leaf spring 32 becomes a movable portion that moves with the reciprocating motion of the displacement device 7.

[0026] The front end of the external thread 37 of the rod 34 constituting the displacement assembly 8 is an external thread member that forms part of the mounting portion 43. Furthermore, a second nut 44, which is an internal thread member forming part of the mounting portion 43, is screwed onto the external thread 37. That is, the mounting portion 43 is located on the side of the second leaf spring 32 opposite to the displacement assembly 7. Furthermore, by screwing the external thread member having the external thread 37 and the second nut 44, which is an internal thread member, a washer 45, serving as a hammer body, can be clamped between the first nut 35 and the second nut 44.

[0027] Next, the method for adjusting the resonant frequency fd of the displacement assembly 8 in this embodiment will be described. First, the spring constant kd is pre-measured by pre-installing the outer periphery of the second leaf spring 32 on a measuring fixture (not shown) and applying stress. It should be noted that the measuring fixture is positioned in the same manner as the support arm 40. Furthermore, the spring constant kd of the second leaf spring 32 is not measured for all of them, but for each manufacturing batch. Similar to the piston assembly 6, the target resonant frequency fdt of the displacement assembly 8 is expressed by the following formula. fdt=(1 / 2π)√(kd / md) Since the target resonant frequency fdt and the spring constant kd of the second leaf spring 32 have been determined, the movable mass md of the displacement assembly 8 can be calculated. Here, the movable mass md is the sum of the mass m7 of the displacement device 7, the mass m34 of the rod 34, the mass m35 of the first nut 35, the mass m44 of the second nut 44, the mass m32 of the portion of the second leaf spring 32 excluding the peripheral portion, and the mass m45 of the n washers 45. m7, m34, m35, m44, and m45 were measured in advance. However, these mass measurements were not performed on all components, but rather on a batch basis. In addition, m32 is a calculated value. Therefore, the above formula is rewritten as follows. fdt=(1 / 2π)√(kd / (m 7+m 34+m 35+m 44+m 32+nm 45)) It should be noted that in this example, as shown in Figure 5(b) which serves as the standard, although n=2, the value of n can also vary depending on the value of kd. Since the displacement device 7 and the rod 34, which constitute the majority of the movable mass md, are manufactured with high precision, the original tolerances are small. Furthermore, although the first nut 35, the second nut 44, and the washer 45 are standard parts, their small mass means that differences in mass have a relatively small impact on the resonant frequency fd. Calculatedly, this can make the resonant frequency fd of the displacement device assembly 8 close to the target resonant frequency fdt, but in reality, sometimes the resonant frequency fd deviates from the target resonant frequency fdt by more than the allowable range. Thus, when the resonant frequency fd deviates from the target resonant frequency fpt by more than the allowable range, this can be addressed by increasing or decreasing the number of washers 45. When it is necessary to reduce the value of the movable mass md, for example, as shown in Figure 5(a), the number of washers 45 can be reduced to one. Furthermore, when it is necessary to increase the value of the movable mass md, for example as shown in Figure 5(c), the number of washers 45 can be increased to three. In this way, by adjusting the number of washers 45 held when the second nut 44 is screwed onto the external thread 37, the value of the movable mass md can be adjusted, and the resonant frequency fd of the displacement assembly 8 can be made closer to the target resonant frequency fdt. It should be noted that by reducing the thickness of the washers 45, the adjustment steps for the movable mass md can be precisely defined.

[0028] It should be noted that in the free-piston Stirling refrigerator 1, since the coaxiality of the displacement device 7 and the second cylinder 4 needs to be highly precise, if the piston assembly 8 is disassembled to adjust the movable mass md, the coaxiality of the displacement device 7 and the second cylinder 4 needs to be readjusted during reassembly. However, as described above, since the mounting part 43 is located on the side opposite to the displacement device 7 of the second leaf spring 32, even with the piston assembly 8 supported by the support arm 40 and the displacement device 7 inserted into the second cylinder 4, the movable mass md can be adjusted simply by removing the second nut 44 from the piston assembly 8 and adjusting the number of washers 45. That is, without compromising the coaxiality of the displacement device 7 and the second cylinder 4, the resonant frequency fd can be easily made close to the target resonant frequency fdt.

[0029] Thus, by adjusting the number of washers 31 installed on the piston assembly 6 and the number of washers 45 installed on the displacement assembly 8, the resonant frequency fp of the piston assembly 6 can be made close to the target resonant frequency fpt, ​​and the resonant frequency fd of the displacement assembly 8 can also be made close to the target resonant frequency fdt. Furthermore, by placing the mounting part 30 on the side opposite to the piston 5 of the first leaf spring 11, the resonant frequency fp can be easily adjusted even when the piston assembly 6 is supported by the support arm 25 and the piston 5 is inserted into the first cylinder 3. Similarly, by placing the mounting part 43 on the side opposite to the displacement 7 of the second leaf spring 32, the resonant frequency fd can be easily adjusted even when the displacement assembly 8 is supported by the support arm 40 and the displacement 7 is inserted into the second cylinder 4. Therefore, since it is not necessary to disassemble the piston assembly 6 after measuring its resonant frequency fp, as was done previously, not only is the risk of component damage during assembly and disassembly (specifically, damage to threads, collisions or friction between components and other objects) reduced, but the movable mass mp can also be adjusted without compromising the coaxiality of the piston 5 and the first cylinder 3, which has already been adjusted once. Similarly, since it is not necessary to disassemble the displacement assembly 8 after measuring its resonant frequency fd, not only is the risk of component damage during assembly and disassembly reduced, but the movable mass md can also be adjusted without compromising the coaxiality of the displacement 7 and the second cylinder 4, which has already been adjusted once. Furthermore, since the mounting portions 30 and 43 are coaxially arranged with the piston assembly 6 and the displacement assembly 8, respectively, the washers 31 and 45, which serve as hammer bodies, can be coaxially mounted relative to the mounting portions 30 and 43. The weight of the piston assembly 6 and the displacement assembly 8 is well balanced, thereby enabling the reciprocating motion of the piston 5 and the displacement assembly 7 to be performed in a well-balanced manner. Moreover, by using the washers 31 and 45 as hammer bodies and adjusting the number of washers 31 and 45 held, the resonant frequency fp of the piston assembly 6 and the resonant frequency fd of the displacement assembly 8 can be easily adjusted.

[0030] Hereinafter, the second embodiment of the present invention will be described based on Figures 1 to 3 and Figures 6 and 7. It should be noted that since the structures of the piston assembly 6 and the displacement assembly 8 are common to those of the first embodiment, their descriptions are omitted, and the adjustment of the movable masses mp and md will be described instead.

[0031] An internal thread 22 is formed coaxially with the second external thread 19 on the side of the connecting body 17 constituting the piston assembly 6 opposite to the piston 5. That is, on the side of the connecting body 17 opposite to the piston 5, the second external thread 19 is formed on the outer side, and the internal thread 22 is formed on the inner side. The front end of the connecting body 17 having the internal thread 22 is an internal thread member. A bolt 29, which is an external thread member, is screwed into the internal thread 22. Moreover, these internal threads 22 and bolt 29 constitute a mounting portion 30. That is, the mounting portion 30 is provided on the side of the first leaf spring 11 opposite to the piston 5. Furthermore, by screwing the internal thread member having the internal thread 22 into the bolt 29, which is an external thread member, a washer 51, which is a hammer body, can be clamped between the connecting body 17 and the bolt 29. It should be noted that the washer 51 is any one of a variety of washers with different diameters (51a, 51b, 51c...).

[0032] Next, the method for adjusting the resonant frequency fp of the piston assembly 6 in this embodiment will be described. First, the spring constant kp is pre-measured by pre-installing the outer periphery of the first leaf spring 11 on a measuring fixture (not shown) and applying stress. It should be noted that the measuring fixture is positioned in the same manner as the support arm 25. Furthermore, the spring constant kp of the first leaf spring 11 is not measured for all of them, but for each manufacturing batch. Generally, the resonant frequency f of a vibration system consisting of a reciprocating object and an elastic body connected to that object is expressed by the following formula. f = (1 / 2π)√(k / m) In this formula, k is the spring constant of the elastic body, and m is the movable mass. Therefore, the target resonant frequency fpt of the piston assembly 6 is expressed by the following formula. fpt=(1 / 2π)√(kp / mp) Since the target resonant frequency fpt and the spring constant kp of the first leaf spring 11 have been determined, the movable mass mp of the piston assembly 6 can be calculated. Here, the movable mass mp is the sum of the mass m5 of the piston 5, the mass m12 of the mover 12, the mass m17 of the connecting body 17, the mass m18 of the nut 18, the mass m29 of the bolt 29, the mass m11 of the portion of the first leaf spring 11 excluding the periphery, and the mass m51 of the washer 51. m5, m12, m17, m18, m29, and m51 were measured in advance. However, these mass measurements were not performed on all components, but on a batch basis. In addition, m11 is a calculated value. Therefore, the above formula is rewritten as follows. fpt=(1 / 2π)√(kp / (m 5+m 12+m 17+m 18+m 29+m 11+nm 51)) It should be noted that, in this example, as shown in the standard Figure 6(b), although the washer 51 is a medium-diameter washer 51b, any of the washers 51a, 51b, 51c, ... can be selected depending on the value of kp. The piston 5, the mover 12, and the connecting body 17, which account for the majority of the movable mass mp, are manufactured with high precision, resulting in small original tolerances. Furthermore, although the nut 18, bolt 29, and washer 51 are standard parts, their small mass means that differences in mass have a relatively small impact on the resonant frequency fp. Calculatedly, this can bring the resonant frequency fp of the piston assembly 6 close to the target resonant frequency fpt; however, in reality, the resonant frequency fp sometimes deviates from the permissible range of the target resonant frequency fpt. Therefore, when the resonant frequency fp deviates from the permissible range of the target resonant frequency fpt, ​​this is addressed by changing the type of washer 51 installed. When it is necessary to reduce the value of the movable mass mp, for example as shown in Figure 6(a), the washer 51 is changed to a washer with a smaller diameter (51a). Conversely, when it is necessary to increase the value of the movable mass mp, for example as shown in Figure 6(c), the washer 51 is changed to a washer with a larger diameter (51c). Thus, by adjusting the value of the movable mass mp by selecting the type of washer 51 that clamps the bolt 29 when it is screwed onto the internal thread 22, the resonant frequency fp of the piston assembly 6 can be made close to the target resonant frequency fpt. It should be noted that by reducing the diameter difference between the washers 51 (51a, 51b, 51c, ...), the adjustment steps for the movable mass mp can be precisely formulated.

[0033] It should be noted that in the free-piston Stirling refrigerator 1, since the coaxiality of the piston 5 and the first cylinder 3 needs to be highly precise, if the piston assembly 6 is disassembled to adjust the movable mass mp, the coaxiality of the piston 5 and the first cylinder 3 needs to be readjusted during reassembly. However, as described above, since the mounting part 30 is located on the side opposite to the piston 5 of the first leaf spring 11, even when the piston assembly 6 is supported by the support arm 25 and the piston 5 is inserted into the first cylinder 3, the movable mass mp can be adjusted by simply removing the bolt 29 from the piston assembly 6 and appropriately selecting the type of washer 51 (51a, 51b, 51c, ...). That is, the resonant frequency fp can be easily made close to the target resonant frequency fpt without compromising the coaxiality of the piston 5 and the first cylinder 3.

[0034] The front end of the external thread 37 of the rod 34 constituting the displacement assembly 8 is an external thread member that forms part of the mounting portion 43. Furthermore, a second nut 44, which is an internal thread member and forms part of the mounting portion 43, is screwed onto the external thread 37. That is, the mounting portion 43 is located on the side of the second leaf spring 32 opposite to the displacement assembly 7. Furthermore, by screwing the external thread member with the external thread 37 and the second nut 44, which is an internal thread member, a washer 52, which serves as the hammer body, can be clamped between the first nut 35 and the second nut 44. It should be noted that the washer 52 can be any of a variety of washers with different diameters (52a, 52b, 52c, ...).

[0035] Next, the method for adjusting the resonant frequency fd of the displacement assembly 8 in this embodiment will be described. First, the spring constant kd is pre-measured by pre-installing the outer periphery of the second leaf spring 32 on a measuring fixture (not shown) and applying stress. It should be noted that the measuring fixture is positioned in the same manner as the support arm 40. Furthermore, the spring constant kd of the second leaf spring 32 is not measured for all of them, but for each manufacturing batch. Similar to the piston assembly 6, the target resonant frequency fdt of the displacement assembly 8 is expressed by the following formula. fdt=(1 / 2π)√(kd / md) Since the target resonant frequency fdt and the spring constant kd of the second leaf spring 32 have been determined, the movable mass md of the displacement assembly 8 can be calculated. Here, the movable mass md is the sum of the mass m7 of the displacement device 7, the mass m34 of the rod 34, the mass m35 of the first nut 35, the mass m44 of the second nut 44, the mass m32 of the portion of the second leaf spring 32 excluding the peripheral portion, and the mass m52 of the washer 52. m7, m34, m35, m44, and m52 were measured in advance. However, these mass measurements were not performed on all components, but rather on a batch basis. In addition, m32 is a calculated value. Therefore, the above formula is rewritten as follows. fdt=(1 / 2π)√(kd / (m 7+m 34+m 35+m 44+m 32+m 52)) It should be noted that, in this example, as shown in the standard Figure 7(b), although the washer 52 is a medium-diameter washer 52b, any of the washers 52a, 52b, 52c, ... can be selected depending on the value of kd. The displacement device 7 and rod 34, which account for the majority of the movable mass md, are manufactured with high precision, resulting in small original tolerances. Furthermore, although the first nut 35, the second nut 44, and the washer 52 are standard parts, their small mass means that differences in mass have a relatively small impact on the resonant frequency fd. Calculatedly, this can bring the resonant frequency fd of the displacement device assembly 8 close to the target resonant frequency fdt; however, in reality, the resonant frequency fd may sometimes deviate from the permissible range of the target resonant frequency fdt. Therefore, when the resonant frequency fd deviates from the permissible range of the target resonant frequency fdt, this is addressed by changing the type of washer 52 installed. When it is necessary to reduce the value of the movable mass md, for example as shown in Figure 7(a), the washer 52 is changed to a washer with a smaller diameter (52a). Conversely, when it is necessary to increase the value of the movable mass md, for example as shown in Figure 7(c), the washer 52 is changed to a washer with a larger diameter (52c). Thus, by adjusting the value of the movable mass md by selecting the type of washer 52 that clamps the second nut 44 when screwed onto the external thread 37, the resonant frequency fd of the displacement assembly 8 can be made close to the target resonant frequency fdt. It should be noted that by reducing the diameter difference between the washers 52 (52a, 52b, 52c, ...), the adjustment steps for the movable mass md can be precisely formulated.

[0036] It should be noted that in the free-piston Stirling refrigeration unit 1, since the coaxiality of the displacement device 7 and the second cylinder 4 needs to be highly precise, if the displacement device assembly 8 is disassembled to adjust the movable mass md, the coaxiality of the displacement device 7 and the second cylinder 4 needs to be readjusted during reassembly. However, as described above, since the mounting part 43 is located on the side opposite to the displacement device 7 of the second leaf spring 32, even with the displacement device assembly 8 supported by the support arm part 40 and the displacement device 7 inserted into the second cylinder 4, the movable mass md can be adjusted by simply removing the second nut 44 from the displacement device assembly 8 and appropriately selecting the type of washer 52 (52a, 52b, 52c, ...). That is, the resonant frequency fd can be easily made close to the target resonant frequency fdt without compromising the coaxiality of the displacement device 7 and the second cylinder 4.

[0037] Thus, by selecting the type of washer 51 installed on the piston assembly 6 (51a, 51b, 51c, ...) and the type of washer 52 installed on the displacement assembly 8 (52a, 52b, 52c, ...), the resonant frequency fp of the piston assembly 6 can be made close to the target resonant frequency fpt, ​​and the resonant frequency fd of the displacement assembly 8 can also be made close to the target resonant frequency fdt. Furthermore, by providing the mounting part 30 on the side of the first leaf spring 11 opposite to the piston 5, the resonant frequency fp can be easily adjusted even when the piston assembly 6 is supported by the support arm 25 and the piston 5 is inserted into the first cylinder 3. Similarly, by providing the mounting part 43 on the side of the second leaf spring 32 opposite to the displacement 7, the resonant frequency fd can be easily adjusted even when the displacement assembly 8 is supported by the support arm 40 and the displacement 7 is inserted into the second cylinder 4. Therefore, since it is not necessary to disassemble the piston assembly 6 after measuring its resonant frequency fp, as was done previously, not only is the risk of component damage during assembly and disassembly (specifically, damage to threads, collisions or friction between components and other objects) reduced, but the movable mass mp can also be adjusted without compromising the coaxiality of the piston 5 and the first cylinder 3, which have already been adjusted once. Similarly, since it is not necessary to disassemble the displacement assembly 8 after measuring its resonant frequency fd, not only is the risk of component damage during assembly and disassembly reduced, but the movable mass md can also be adjusted without compromising the coaxiality of the displacement 7 and the second cylinder 4, which have already been adjusted once. Furthermore, since the mounting portions 30 and 43 are coaxially arranged with the piston assembly 6 and the displacement assembly 8, respectively, the washers 51 and 52, which serve as hammer bodies, can be coaxially mounted relative to the mounting portions 30 and 43. This allows for good weight balance between the piston assembly 6 and the displacement assembly 8, enabling balanced reciprocating motion of the piston 5 and the displacement assembly 7. Moreover, by using the washers 51 and 52 as hammer bodies and clamping them with washers of different diameters (51a, 51b, 51c, ..., 52a, 52b, 52c, ...), the resonant frequency fp of the piston assembly 6 and the resonant frequency fd of the displacement assembly 8 can be easily adjusted.

[0038] The third embodiment of the present invention will be described below based on Figures 1 to 3, 8, and 9. It should be noted that since the structures of the piston assembly 6 and the displacement assembly 8 are common to the first and second embodiments, their descriptions are omitted, and the adjustment of the movable masses mp and md will be described instead.

[0039] An internal thread 22 is formed coaxially with the second external thread 19 on the side of the connecting body 17 constituting the piston assembly 6 opposite to the piston 5. That is, on the side of the connecting body 17 opposite to the piston 5, the second external thread 19 is formed on the outer side, and the internal thread 22 is formed on the inner side. The front end of the connecting body 17 having the internal thread 22 is an internal thread member. A bolt 29, as an external thread member, is screwed into the internal thread 22. Moreover, the mounting part 30 is formed by these internal thread members having the internal thread 22 and the bolt 29, as external thread members. That is, the mounting part 30 is provided on the side of the first leaf spring 11 opposite to the piston 5. Furthermore, by screwing the internal thread 22 into the bolt 29, a washer 61, which serves as a hammer body, can be clamped between the connecting body 17 and the bolt 29. It should be noted that the washer 61 is any one of a variety of washers with different thicknesses (61a, 61b, 61c...).

[0040] Next, the method for adjusting the resonant frequency fp of the piston assembly 6 in this embodiment will be described. First, the spring constant kp is pre-measured by pre-installing the outer periphery of the first leaf spring 11 on a measuring fixture (not shown) and applying stress. It should be noted that the measuring fixture is in the same positional relationship as the support arm 25. Furthermore, the spring constant kp is not measured for all first leaf springs 11, but for each manufacturing batch. Generally, the resonant frequency f of a vibration system consisting of a reciprocating object and an elastic body connected to that object is expressed by the following formula.

[0041] f = (1 / 2π)√(k / m)

[0042] In this formula, k is the spring constant of the elastic body, and m is the movable mass. Therefore, the target resonant frequency fpt of the piston assembly 6 is expressed by the following formula. fpt=(1 / 2π)√(kp / mp) Since the target resonant frequency fpt and the spring constant kp of the first leaf spring 11 have been determined, the movable mass mp of the piston assembly 6 can be calculated. Here, the movable mass mp is the sum of the mass m5 of the piston 5, the mass m12 of the mover 12, the mass m17 of the connecting body 17, the mass m18 of the nut 18, the mass m29 of the bolt 29, the mass m11 of the portion of the first leaf spring 11 excluding the periphery, and the mass m61 of the washer 61. m5, m12, m17, m18, m29, and m61 were measured in advance. However, these mass measurements were not performed on all components, but rather on a batch basis. Furthermore, m11 is a calculated value. Therefore, the above formula is rewritten as follows. fpt=(1 / 2π)√(kp / (m 5+m 12+m 17+m 18+m 29+m 11+m 61)) It should be noted that, in this example, as shown in the standard Figure 8(b), although the washer 61 is a medium-thickness washer 61b, any of the washers 61a, 61b, 61c, ... can be selected depending on the value of kp. The piston 5, the mover 12, and the connecting body 17, which account for the majority of the movable mass mp, are manufactured with high precision, so the original tolerances are small. Furthermore, although the nut 18, bolt 29, and washer 61 are standard parts, their small mass means that differences in mass have a relatively small impact on the resonant frequency fp. Calculatedly, this can bring the resonant frequency fp of the piston assembly 6 close to the target resonant frequency fpt, ​​but in reality, the resonant frequency fp sometimes deviates from the target resonant frequency fpt by more than the allowable range. Therefore, when the resonant frequency fp deviates from the target resonant frequency fpt by more than the allowable range, this is addressed by changing the type of washer 61 installed. When it is necessary to reduce the value of the movable mass mp, for example as shown in Figure 8(a), the washer 61 is changed to a thin washer (61a). Conversely, when it is necessary to increase the value of the movable mass mp, for example as shown in Figure 8(c), the washer 61 is changed to a thick washer (61c). Thus, by adjusting the value of the movable mass mp by selecting the type of washer 61 that clamps the bolt 29 when it is screwed onto the internal thread 22, the resonant frequency fp of the piston assembly 6 can be made close to the target resonant frequency fpt. It should be noted that by reducing the thickness difference between the washers 61 (61a, 61b, 61c, ...), the adjustment steps for the movable mass mp can be precisely formulated.

[0043] It should be noted that in the free-piston Stirling refrigerator 1, since the coaxiality of the piston 5 and the first cylinder 3 needs to be highly precise, if the piston assembly 6 is disassembled to adjust the movable mass mp, the coaxiality of the piston 5 and the first cylinder 3 needs to be readjusted during reassembly. However, as described above, since the mounting part 30 is located on the side of the first leaf spring 11 opposite to the piston 5, even with the piston assembly 6 supported by the support arm 25 and the piston 5 inserted into the first cylinder 3, the movable mass mp can be adjusted by simply removing the bolt 29 from the piston assembly 6 and appropriately selecting the type of washer 61 (61a, 61b, 61c, ...). That is, the resonant frequency fp can be easily made close to the target resonant frequency fpt without compromising the coaxiality of the piston 5 and the first cylinder 3.

[0044] The front end of the external thread 37 of the rod 34 constituting the displacement assembly 8 is an external thread member that forms part of the mounting portion 43. Furthermore, a second nut 44, which is an internal thread member and forms part of the mounting portion 43, is screwed onto the external thread 37. That is, the mounting portion 43 is located on the side of the second leaf spring 32 opposite to the displacement assembly 7. Furthermore, by screwing the external thread member with the external thread 37 and the second nut 44, which is an internal thread member, a washer 62, which serves as the hammer body, can be clamped between the first nut 35 and the second nut 44. It should be noted that the washer 62 is any one of several washers with different thicknesses (62a, 62b, 62c, ...).

[0045] Next, the method for adjusting the resonant frequency fd of the displacement assembly 8 in this embodiment will be described. First, the spring constant kd is pre-measured by pre-installing the outer periphery of the second leaf spring 32 on a measuring fixture (not shown) and applying stress. It should be noted that the measuring fixture is positioned in the same manner as the support arm 40. Furthermore, the spring constant kd is not measured for all second leaf springs 32, but for each manufacturing batch. Similar to the piston assembly 6, the target resonant frequency fdt of the displacement assembly 8 is expressed by the following formula. fdt=(1 / 2π)√(kd / md) Since the target resonant frequency fdt and the spring constant kd of the second leaf spring 32 have been determined, the movable mass md of the displacement assembly 8 can be calculated. Here, the movable mass md is the sum of the mass m7 of the displacement device 7, the mass m34 of the rod 34, the mass m35 of the first nut 35, the mass m44 of the second nut 44, the mass m32 of the portion of the second leaf spring 32 excluding the peripheral portion, and the mass m62 of the washer 62. m7, m34, m35, m44, and m62 were measured in advance. However, these mass measurements were not performed on all components, but rather on a batch basis. In addition, m32 is a calculated value. Therefore, the above formula is rewritten as follows. fdt=(1 / 2π)√(kd / (m 7+m 34+m 35+m 44+m 32+m 62)) It should be noted that, in this example, as shown in Figure 9(b) which serves as the standard, although the washer 62 is a medium-thickness washer 62b, any of the washers 62a, 62b, 62c, ... can be selected depending on the value of kd. The displacement device 7 and rod 34, which account for the majority of the movable mass md, are manufactured with high precision, resulting in small original tolerances. Furthermore, although the first nut 35, first nut 44, and washer 62 are standard parts, their small mass means that differences in mass have a relatively small impact on the resonant frequency fd. Calculatedly, this can bring the resonant frequency fd of the displacement device assembly 8 close to the target resonant frequency fdt; however, in reality, the resonant frequency fd may sometimes deviate from the target resonant frequency fdt by more than the allowable range. Therefore, when the resonant frequency fd deviates from the target resonant frequency fdt by more than the allowable range, this can be addressed by changing the type of washer 62 installed. When it is necessary to reduce the value of the movable mass md, for example as shown in Figure 9(a), the washer 62 is changed to a thin washer (62a). Conversely, when it is necessary to increase the value of the movable mass md, for example as shown in Figure 9(c), the washer 62 is changed to a thick washer (62c). Thus, by selecting the type of washer 62 that is held when the second nut 44 is screwed onto the external thread 37, the value of the movable mass md can be adjusted, thereby making the resonant frequency fd of the displacement assembly 8 closer to the target resonant frequency fdt. It should be noted that by reducing the thickness difference between the washers 62 (62a, 62b, 62c, ...), the adjustment steps for the movable mass md can be precisely formulated.

[0046] It should be noted that in the free-piston Stirling refrigeration unit 1, since the coaxiality of the displacement device 7 and the second cylinder 4 needs to be highly precise, if the displacement device assembly 8 is disassembled to adjust the movable mass md, the coaxiality of the displacement device 7 and the second cylinder 4 needs to be readjusted during reassembly. However, as described above, since the mounting part 43 is located on the side opposite to the displacement device 7 of the second leaf spring 32, even with the displacement device assembly 8 supported by the support arm part 40 and the displacement device 7 inserted into the second cylinder 4, the movable mass md can be adjusted simply by removing the second nut 44 from the displacement device assembly 8 and appropriately selecting the type of washer 62 (62a, 62b, 62c, ...). That is, without compromising the coaxiality of the displacement device 7 and the second cylinder 4, the resonant frequency fd can be easily made close to the target resonant frequency fdt.

[0047] Thus, by selecting the type of washer 61 (61a, 61b, 61c, ...) installed on the piston assembly 6 and the type of washer 62 (62a, 62b, 62c, ...) installed on the displacement assembly 8, the resonant frequency fp of the piston assembly 6 can be made close to the target resonant frequency fpt, ​​and the resonant frequency fd of the displacement assembly 8 can also be made close to the target resonant frequency fdt. Furthermore, by providing the mounting part 30 on the side opposite to the piston 5 of the first leaf spring 11, the resonant frequency fp can be easily adjusted even when the piston assembly 6 is supported by the support arm 25 and the piston 5 is inserted into the first cylinder 3. Similarly, by providing the mounting part 43 on the side opposite to the displacement 7 of the second leaf spring 32, the resonant frequency fd can be easily adjusted even when the displacement assembly 8 is supported by the support arm 40 and the displacement 7 is inserted into the second cylinder 4. Therefore, since it is not necessary to disassemble the piston assembly 6 after measuring its resonant frequency fp, as was done previously, not only is the risk of component damage during assembly and disassembly (specifically, damage to threads, collisions or friction between components and other objects) reduced, but the movable mass mp can also be adjusted without compromising the coaxiality of the piston 5 and the first cylinder 3, which has already been adjusted once. Similarly, since it is not necessary to disassemble the displacement assembly 8 after measuring its resonant frequency fd, not only is the risk of component damage during assembly and disassembly reduced, but the movable mass md can also be adjusted without compromising the coaxiality of the displacement 7 and the second cylinder 4, which has already been adjusted once. Furthermore, since the mounting portions 30 and 43 are coaxially arranged with the piston assembly 6 and the displacement assembly 8, respectively, the washers 61 and 62, which serve as hammer bodies, can be coaxially mounted relative to the mounting portions 30 and 43. This allows for good weight balance between the piston assembly 6 and the displacement assembly 8, enabling balanced reciprocating motion of the piston 5 and the displacement assembly 7. Moreover, by using the washers 61 and 62 as hammer bodies and selecting any of the washers (61a, 61b, 61c, ..., 62a, 62b, 62c, ...) of different thicknesses for clamping, the resonant frequency fp of the piston assembly 6 and the resonant frequency fd of the displacement assembly 8 can be easily adjusted.

[0048] The fourth embodiment of the present invention will now be described based on Figures 1 to 3 and Figures 10 and 11. It should be noted that since the structures of the piston assembly 6 and the displacement assembly 8 are common to those of the first to third embodiments, their descriptions are omitted, and the adjustment of the movable masses mp and md will be described instead.

[0049] An internal thread 22 is formed coaxially with the second external thread 19 on the side of the connecting body 17 constituting the piston assembly 6 opposite to the piston 5. That is, on the side of the connecting body 17 opposite to the piston 5, the second external thread 19 is formed on the outer side, and the internal thread 22 is formed on the inner side. The front end of the connecting body 17 having the internal thread 22 is an internal thread member. A bolt 29, as an external thread member, is screwed into the internal thread 22. Moreover, the mounting part 30 is formed by these internal thread members having the internal thread 22 and the bolt 29, as external thread members. That is, the mounting part 30 is provided on the side of the first leaf spring 11 opposite to the piston 5. Furthermore, by screwing the internal thread 22 into the bolt 29, a washer 51, which serves as a hammer body, can be clamped between the connecting body 17 and the bolt 29. It should be noted that the washer 51 is any one of a variety of washers with different diameters (51a, 51b, ...).

[0050] Next, the method for adjusting the resonant frequency fp of the piston assembly 6 in this embodiment will be described. First, the spring constant kp is pre-measured by pre-installing the outer periphery of the first leaf spring 11 on a measuring fixture (not shown) and applying stress. It should be noted that the measuring fixture is in the same positional relationship as the support arm 25. Furthermore, the spring constant kp is not measured for all first leaf springs 11, but for each manufacturing batch. Generally, the resonant frequency f of a vibration system consisting of a reciprocating object and an elastic body connected to that object is expressed by the following formula. f = (1 / 2π)√(k / m) In this formula, k is the spring constant of the elastic body, and m is the movable mass. Therefore, the target resonant frequency fpt of the piston assembly 6 is expressed by the following formula. fpt=(1 / 2π)√(kp / mp) Since the target resonant frequency fpt and the spring constant kp of the first leaf spring 11 have been determined, the movable mass mp of the piston assembly 6 can be calculated. Here, the movable mass mp is the sum of the mass m5 of the piston 5, the mass m12 of the mover 12, the mass m17 of the connecting body 17, the mass m18 of the nut 18, the mass m29 of the bolt 29, the mass m11 of the portion of the first leaf spring 11 excluding the periphery, and the mass m51 (m51a, m51b, ...) of the washer 51. m5, m12, m17, m18, m29, and m51 (m51a, m51b, ...) were measured in advance. However, these mass measurements were not performed on all components, but rather on a batch basis. Furthermore, m11 is a calculated value. Therefore, the above formula is rewritten as follows. fpt=(1 / 2π)√(kp / (m 5+m 12+m 17+m 18+m 29+m 11+xm 51a+ym 51b)) It should be noted that, in this example, as shown in Figure 10(b) which serves as the standard, although the washer 51 consists of two small-diameter washers (51a) (x=2, y=0), the number and type of washers 51a, 51b, ... can be varied depending on the value of kp. The piston 5, the mover 12, and the connecting body 17, which constitute the majority of the movable mass mp, are manufactured with high precision, resulting in small original tolerances. Furthermore, although the nut 18, bolt 29, and washer 51 are standard parts, their small mass means that differences in mass have a relatively small impact on the resonant frequency fp. Calculatedly, this can bring the resonant frequency fp of the piston assembly 6 close to the target resonant frequency fpt; however, in reality, the resonant frequency fp sometimes deviates from the target resonant frequency fpt beyond the permissible range. Therefore, when the resonant frequency fp deviates from the target resonant frequency fpt beyond the permissible range, the number and type of the installed washers 51 are changed to address this. When it is necessary to reduce the value of the movable mass mp, for example as shown in Figure 10(a), the washer 51 is replaced with a washer with a smaller diameter (51a) (i.e., x=1, y=0). Conversely, when it is necessary to increase the value of the movable mass mp, for example as shown in Figure 10(c), the washer 51 is replaced with a washer with a smaller diameter (51a) and a washer with a larger diameter (51b) (i.e., x=1, y=1). Thus, by adjusting the number and type of the washers 51 held when the bolt 29 is screwed onto the internal thread 22, the resonant frequency fp of the piston assembly 6 can be brought close to the target resonant frequency fpt. It should be noted that by reducing the difference in diameter or thickness between the washers 51 (51a, 51b, ...), the adjustment steps for the movable mass mp can be precisely formulated.

[0051] It should be noted that in the free-piston Stirling refrigerator 1, since the coaxiality of the piston 5 and the first cylinder 3 needs to be highly precise, if the piston assembly 6 is disassembled to adjust the movable mass mp, the coaxiality of the piston 5 and the first cylinder 3 needs to be readjusted during reassembly. However, as described above, since the mounting part 30 is located on the side of the first leaf spring 11 opposite to the piston 5, even when the piston assembly 6 is supported by the support arm 25 and the piston 5 is inserted into the first cylinder 3, the movable mass mp can be adjusted by simply removing the bolt 29 from the piston assembly 6 and appropriately changing the number and type (51a, 51b, ...) of the installed washers 51. That is, without compromising the coaxiality of the piston 5 and the first cylinder 3, the resonant frequency fp can be easily made close to the target resonant frequency fpt.

[0052] The front end of the external thread 37 of the rod 34 constituting the displacement assembly 8 is an external thread member that forms part of the mounting portion 43. Furthermore, a second nut 44, which is an internal thread member forming part of the mounting portion 43, is screwed onto the external thread 37. That is, the mounting portion 43 is located on the side of the second leaf spring 32 opposite to the displacement assembly 7. Furthermore, by screwing the external thread member having the external thread 37 and the second nut 44, which is an internal thread member, a washer 52, which serves as the hammer body, can be clamped between the first nut 35 and the second nut 44. It should be noted that the washer 52 is any one of several washers with different diameters (52a, 52b, ...).

[0053] Next, the method for adjusting the resonant frequency fd of the displacement assembly 8 in this embodiment will be described. First, the spring constant kd is pre-measured by pre-installing the outer periphery of the second leaf spring 32 on a measuring fixture (not shown) and applying stress. It should be noted that the measuring fixture is positioned in the same manner as the support arm 40. Furthermore, the spring constant kd is not measured for all second leaf springs 32, but for each manufacturing batch. Similar to the piston assembly 6, the target resonant frequency fdt of the displacement assembly 8 is expressed by the following formula. fdt=(1 / 2π)√(kd / md) Since the target resonant frequency fdt and the spring constant kd of the second leaf spring 32 have been determined, the movable mass md of the displacement assembly 8 can be calculated. Here, the movable mass md is the sum of the mass m7 of the displacement device 7, the mass m34 of the rod 34, the mass m35 of the first nut 35, the mass m44 of the second nut 44, the mass m32 of the portion of the second leaf spring 32 excluding the peripheral portion, and the mass m52 (m52a, m52b...) of the washer 52. m7, m34, m35, m44, and m52 (m52a, m52b...) were measured in advance. However, these mass measurements were not performed on all components, but rather on a batch basis. Furthermore, m32 is a calculated value. Therefore, the above formula is rewritten as follows. fdt=(1 / 2π)√(kd / (m 7+m 34+m 35+m 44+m 32+xm 52a+ym 52b)) It should be noted that, in this example, as shown in Figure 11(b) which serves as the standard, although the washer 52 consists of two small-diameter washers (52a) (x=2, y=0), the number and type of washers 52a, 52b, ... can be varied depending on the value of kd. The displacement device 7 and the rod 34, which constitute the majority of the movable mass md, are manufactured with high precision, resulting in small original tolerances. Furthermore, although the first nut 35, the second nut 44, and the washer 52 are standard parts, their small mass means that differences in mass have a relatively small impact on the resonant frequency fd. Calculatedly, this can bring the resonant frequency fd of the displacement device assembly 8 close to the target resonant frequency fdt; however, in reality, the resonant frequency fd may sometimes deviate from the target resonant frequency fdt by more than the allowable range. Therefore, when the resonant frequency fd deviates from the target resonant frequency fdt by more than the allowable range, the number and type of the installed washers 52 are changed to address this. When it is necessary to reduce the value of the movable mass md, for example as shown in Figure 11(a), the washer 52 is changed to a washer with a smaller diameter (52a) (i.e., x=1, y=0). Conversely, when it is necessary to increase the value of the movable mass md, for example as shown in Figure 11(c), the washer 52 is changed to a washer with a smaller diameter (52a) and a washer with a larger diameter (52b) (i.e., x=1, y=1). Thus, by changing the number and type of the washers 52 held when the bolt 29 is screwed onto the internal thread 22, the value of the movable mass md can be adjusted, thereby making the resonant frequency fd of the displacement assembly 8 closer to the target resonant frequency fdt. It should be noted that by reducing the difference in diameter or thickness between the washers 52 (52a, 52b, ...), the adjustment steps for the movable mass md can be precisely formulated.

[0054] It should be noted that in the free-piston Stirling refrigeration unit 1, since the coaxiality of the displacement device 7 and the second cylinder 4 needs to be highly precise, if the displacement device assembly 8 is disassembled to adjust the movable mass md, the coaxiality of the displacement device 7 and the second cylinder 4 needs to be readjusted during reassembly. However, as described above, since the mounting part 43 is located on the opposite side of the second leaf spring 32 to the displacement device 7, even with the displacement device assembly 8 supported by the support arm part 40 and the displacement device 7 inserted into the second cylinder 4, the movable mass md can be adjusted by simply removing the second nut 44 from the displacement device assembly 8 and appropriately selecting the number and type (52a, 52b, ...) of the installed washers 52. That is, without compromising the coaxiality of the displacement device 7 and the second cylinder 4, the resonant frequency fd can be easily made close to the target resonant frequency fdt.

[0055] Thus, by changing the number and type (51a, 51b, ...) of the washers 51 installed on the piston assembly 6 and the number and type (52a, 52b, ...) of the washers 52 installed on the displacement assembly 8, the resonant frequency fp of the piston assembly 6 can be made close to the target resonant frequency fpt, ​​and the resonant frequency fd of the displacement assembly 8 can also be made close to the target resonant frequency fdt. Furthermore, by placing the mounting part 30 on the side of the first leaf spring 11 opposite to the piston 5, the resonant frequency fp can be easily adjusted even when the piston assembly 6 is supported by the support arm 25 and the piston 5 is inserted into the first cylinder 3. Similarly, by placing the mounting part 43 on the side of the second leaf spring 32 opposite to the displacement 7, the resonant frequency fd can be easily adjusted even when the displacement assembly 8 is supported by the support arm 40 and the displacement 7 is inserted into the second cylinder 4. Therefore, since it is not necessary to disassemble the piston assembly 6 after measuring its resonant frequency fp, as was done previously, not only is the risk of component damage (specifically, damage to threads, collisions or friction between components and other objects) associated with assembly and disassembly reduced, but the movable mass mp can also be adjusted without compromising the coaxiality of the piston 5 and the first cylinder 3, which have already been adjusted once. Similarly, since it is not necessary to disassemble the displacement assembly 8 after measuring its resonant frequency fd, not only is the risk of component damage associated with assembly and disassembly reduced, but the movable mass md can also be adjusted without compromising the coaxiality of the displacement 7 and the second cylinder 4, which have already been adjusted once. Furthermore, since the mounting portions 30 and 43 are coaxially arranged with the piston assembly 6 and the displacement assembly 8, respectively, the washers 51 and 52, which serve as hammer bodies, can be coaxially mounted relative to the mounting portions 30 and 43. This allows for good weight balance between the piston assembly 6 and the displacement assembly 8, enabling balanced reciprocating motion of the piston 5 and the displacement assembly 7. Moreover, by using the washers 51 and 52 as hammer bodies and by changing the number and type of washers (51a, 51b, ..., 52a, 52b, ...) with different diameters, the resonant frequency fp of the piston assembly 6 and the resonant frequency fd of the displacement assembly 8 can be easily adjusted.

[0056] The fifth embodiment of the present invention will now be described based on Figures 1 to 3 and Figure 12. It should be noted that since the structure of the piston assembly 6 is common to that of the first to fourth embodiments, its description is omitted, and the adjustment of the movable mass mp will be described instead.

[0057] The internal thread 22 is formed coaxially with the second external thread 19 on the side of the connecting body 17 constituting the piston assembly 6 opposite to the piston 5. That is, on the side of the connecting body 17 opposite to the piston 5, the second external thread 19 is formed on the outer side, and the internal thread 22 is formed on the inner side. The front end of the connecting body 17 having the internal thread 22 is an internal thread member. The mounting part 71 is thus formed by the internal thread member. That is, the mounting part 71 is provided on the side of the first leaf spring 11 opposite to the piston 5. Furthermore, a bolt 72, which is an external thread member, is screwed into the internal thread 22. Moreover, the bolt 72 is referred to as a hammer. It should be noted that the bolt 72 is any one of a variety of bolts with different lengths (72a, 72b, 72c, etc.).

[0058] Next, the method for adjusting the resonant frequency fp of the piston assembly 6 in this embodiment will be described. First, the spring constant kp is pre-measured by pre-installing the outer periphery of the first leaf spring 11 on a measuring fixture (not shown) and applying stress. It should be noted that the measuring fixture is in the same positional relationship as the support arm 25. Furthermore, the spring constant kp is not measured for all first leaf springs 11, but for each manufacturing batch. Generally, the resonant frequency f of a vibration system consisting of a reciprocating object and an elastic body connected to that object is expressed by the following formula. f = (1 / 2π)√(k / m) In this formula, k is the spring constant of the elastic body, and m is the movable mass. Therefore, the target resonant frequency fpt of the piston assembly 6 is expressed by the following formula. fpt=(1 / 2π)√(kp / mp) Since the target resonant frequency fpt and the spring constant kp of the first leaf spring 11 have been determined, the movable mass mp of the piston assembly 6 can be calculated. Here, the movable mass mp is the sum of the mass m5 of the piston 5, the mass m12 of the mover 12, the mass m17 of the connecting body 17, the mass m18 of the nut 18, the mass m72 of the bolt 72, and the mass m11 of the portion of the first leaf spring 11 excluding the periphery. m5, m12, m17, m18, and m72 were measured in advance. However, these mass measurements were not performed on all components, but rather on a batch basis. In addition, m11 is a calculated value. Therefore, the above formula is rewritten as follows. fpt=(1 / 2π)√(kp / (m 5+m 12+m 17+m 18+m 11+m 72)) It should be noted that, in this example, as shown in Figure 12(b) which serves as the standard, although the bolt 72 is a medium-length bolt 72b, any of the bolts 72a, 72b, 72c, ... can be selected depending on the value of kp. The piston 5, the mover 12, and the connecting body 17, which account for the majority of the movable mass mp, are manufactured with high precision, so the original tolerances are small. In addition, although the nut 18 and bolt 72 are standard parts, their small mass means that the difference in mass has a relatively small impact on the resonant frequency fp. Calculatedly, this can make the resonant frequency fp of the piston assembly 6 close to the target resonant frequency fpt, ​​but in reality, the resonant frequency fp sometimes deviates from the target resonant frequency fpt beyond the allowable range. Thus, when the resonant frequency fp deviates from the target resonant frequency fpt beyond the allowable range, the type of bolt 72 installed is changed accordingly. When it is necessary to reduce the value of the movable mass mp, for example, as shown in Figure 12(a), the bolt 72 is changed to a shorter bolt (72a). Furthermore, when it is necessary to increase the value of the movable mass mp, for example as shown in Figure 12(c), the bolt 72 can be changed to a longer bolt (72c). In this way, by selecting the type of bolt 72 screwed onto the internal thread 22 to adjust the value of the movable mass mp, the resonant frequency fp of the piston assembly 6 can be made closer to the target resonant frequency fpt. It should be noted that by reducing the length difference between the bolts 72 (72a, 72b, 72c, ...), the adjustment steps for the movable mass mp can be precisely formulated.

[0059] It should be noted that in the free-piston Stirling refrigerator 1, since the coaxiality of the piston 5 and the first cylinder 3 needs to be highly precise, if the piston assembly 6 is disassembled to adjust the movable mass mp, the coaxiality of the piston 5 and the first cylinder 3 needs to be readjusted during reassembly. However, as described above, since the mounting part 71 is located on the side of the first leaf spring 11 opposite to the piston 5, even when the piston assembly 6 is supported by the support arm 25 and the piston 5 is inserted into the first cylinder 3, the movable mass mp can be adjusted by simply removing the bolts 72 (72a, 72b, 72c, ...) from the piston assembly 6 and exchanging them with the other bolts 72 (72a, 72b, 72c, ...). That is, the resonant frequency fp can be easily made close to the target resonant frequency fpt without compromising the coaxiality of the piston 5 and the first cylinder 3.

[0060] Thus, by selecting the type (72a, 72b, 72c, ...) of bolts 72 installed on the piston assembly 6, the resonant frequency fp of the piston assembly 6 can be made close to the target resonant frequency fpt. Furthermore, by placing the mounting portion 71 on the side opposite to the piston 5 of the first leaf spring 11, the resonant frequency fp can be easily adjusted even when the piston assembly 6 is supported by the support arm portion 25 and the piston 5 is inserted into the first cylinder 3. Therefore, since it is not necessary to disassemble the piston assembly 6 after measuring its resonant frequency fp as in the past, not only is the risk of component damage (specifically, damage to threads, collisions or friction between components and other objects) associated with assembly and disassembly reduced, but the movable mass mp can also be adjusted without compromising the coaxiality of the piston 5 and the first cylinder 3, which has already been adjusted once. Furthermore, since the mounting portion 71 is coaxially arranged with the piston assembly 6, the bolt 72, which serves as the hammer body, can be coaxially mounted relative to the mounting portion 71, and the weight of the piston assembly 6 can be well balanced, thereby enabling the reciprocating motion of the piston 5 to be well balanced. Moreover, by using the bolt 72, which has an external thread, as the hammer body and the mounting portion 71 as the internal thread 22, the bolt 72 can be screwed into the internal thread 22, and at the same time, any one of the various bolts 72 (72a, 72b, 72c, ...) with different weights can be screwed into the internal thread 22, thereby easily adjusting the movable mass mp.

[0061] It should be noted that the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the present invention. For example, in the fourth embodiment, although the movable mass mp and md can be adjusted by combining washers 51a, 51b, ... or washers 52a, 52b, ... with different diameters, the movable mass mp and md can also be adjusted by combining washers 61a, 61b, ... or washers 62a, 62b, ... with different thicknesses. Furthermore, the movable mass mp and md can also be adjusted by combining washers with different diameters and different thicknesses. Additionally, in the above embodiments, although the mass can be adjusted by using hammers of different sizes, the mass can also be adjusted by using hammers of different materials. Furthermore, in the above embodiments, although the reciprocating body and the connecting body can be separate structures, the reciprocating body and the connecting body can also be an integral structure.

[0062] 1: Free-piston Stirling Refrigeration Unit (Free-piston Stirling Device) 2: Outer shell 3: First cylinder 4: Second cylinder 5: Piston (reciprocating body) 6: Piston assembly 7: Displacement device (reciprocating body) 8: Displacement Components 9: Cylindrical section 10: Ontology part 11: First leaf spring (elastic body) 12: Motion 13: Connector 14: Framework 15: Permanent magnets 16: Through hole 17: Connecting body (internal threaded component) 18: Nut 19: Second external thread 20: Large diameter part 21: Small diameter section 22: Internal thread 23: Central through hole 24: Through hole in the outer perimeter 25: Support arm (support body) 26: Screws 27: Internal thread 28: Flange portion 29: Bolt (externally threaded component) 30: Installation Department 31: Washer (Hammer Body) 32: Second leaf spring (elastic body) 33: Connector 34: Rod 35: First Nut 36: Main body of the rod 37: External thread (external thread component) 38: Central through hole 39: Through hole in the outer perimeter 40: Support arm (support body) 41: Screw 42: Internal thread 43: Installation Department 44: Second nut (internal thread component) 45: Washer (Hammer Body) 51, 51a, 51b, 51c……: Washers (hammer body) 52, 52a, 52b, 52c……: Washers (hammer body) 61, 61a, 61b, 61c...: Washers (hammer bodies) 62, 62a, 62b, 62c...: Washers (hammer bodies) 71: Installation Department 72, 72a, 72b, 72c...: Bolts (externally threaded components, hammer bodies) f: Resonance frequency fp: Resonance frequency of piston assembly 6 fpt: Target resonant frequency of piston assembly 6 fd: Resonance frequency of displacement assembly 8 fdt: Target resonant frequency of displacement assembly 8 k: Spring constant of the elastic body kp: Spring constant of the first leaf spring 11 kd: Spring constant of the second leaf spring 32 m: movable mass mp: Movable mass of piston assembly 6 md: Movable mass of displacement assembly 8

Claims

1. A free-piston Stirling device, comprising: The device comprises: a cylinder; a reciprocating body capable of reciprocating along its axial direction within the cylinder; an elastic body controlling the reciprocating motion of the reciprocating body; a connecting body connecting the reciprocating body to a movable part of the elastic body; and a support body supporting a fixed part of the elastic body when its positional relationship with the cylinder is fixed. The free-piston Stirling device further includes: a hammer for adjusting a movable mass comprising the reciprocating body and the connecting body; and a mounting part disposed on the connecting body or the reciprocating body for mounting the hammer, wherein the mounting part is positioned such that the hammer can be mounted without compromising the coaxiality of the cylinder and the reciprocating body when the cylinder, the reciprocating body, the elastic body, the connecting body, and the support body are assembled.

2. The free-piston Stirling device as described in claim 1, wherein, While the elastic body is a leaf spring, the mounting part is located on the side opposite to the reciprocating body of the leaf spring.

3. The free-piston Stirling device as described in claim 2, wherein, The mounting part and the reciprocating body are configured to be coaxial, and the hammer body is mounted coaxially with respect to the mounting part.

4. The free-piston Stirling device as described in claim 3, wherein, The hammer body is one or more washers, and the mounting part is an internal threaded member and an external threaded member that engages with the internal threaded member. The engagement of the external threaded member with the internal threaded member can clamp the one or more washers.

5. The free-piston Stirling device as described in claim 3, wherein, The hammer body consists of several external threaded components, and the mounting part is an internal threaded component. The external threaded components can be screwed into the internal threaded component, and any one of the multiple external threaded components with different weights can be screwed into the internal threaded component.

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