Cryogenic refrigerator and method of operating a cryogenic refrigerator

Abstract

To provide a novel technology which can asynchronously and simultaneously operate a plurality of cold heads.SOLUTION: A cryogenic refrigerator 10 comprises: a compressor 12; a plurality of cold heads 14 which are connected to the compressor 12 in parallel therewith; a pressure sensor 48 for measuring the pressure of a working gas at a supply side to the plurality of cold heads 14 from the compressor 12, or at a collection side to the compressor 12 from the plurality of cold heads 14; and a controller 50 constituted so as to acquire individual pressure waveform data measured by the pressure sensor 48 with respect to each of the plurality of cold heads 14 when the cold heads 14 are individually operated, and to asynchronously and simultaneously operate the plurality of cold heads 14 on the basis of the individual pressure waveform data.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a cryogenic refrigerator and a method for operating a cryogenic refrigerator.

Background Art

[0002] In a multi-system refrigerator having a plurality of refrigerators, when the opening and closing timings of the pressure switching valves of these refrigerators coincide when the refrigerators are operated simultaneously, the refrigeration performance may deteriorate. Conventionally, in order to avoid this, it is known to make the operating frequencies of the refrigerators different by using inverters provided in each refrigerator and make the valve timings asynchronous.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The above-described method cannot be applied to a cryogenic refrigerator not equipped with an inverter.

[0005] One exemplary object of an aspect of the present invention is to provide a new technique that enables asynchronous simultaneous operation of a plurality of cold heads.

Means for Solving the Problems

[0006] According to one aspect of the present invention, the cryogenic refrigerator includes a compressor, a plurality of cold heads connected in parallel to the compressor, a pressure sensor that measures the pressure of the working gas on the supply side from the compressor to the plurality of cold heads or on the recovery side from the plurality of cold heads to the compressor, and a controller configured to acquire individual pressure waveform data measured by the pressure sensor when each of the plurality of cold heads is operated individually, and to operate the plurality of cold heads simultaneously and asynchronously based on the individual pressure waveform data.

[0007] According to one aspect of the present invention, a method for operating a cryogenic refrigerator is provided. The cryogenic refrigerator comprises a compressor and a plurality of cold heads connected in parallel to the compressor. The method comprises measuring the pressure of the working gas for each of the plurality of cold heads during the individual operation of the cold heads, either on the supply side from the compressor to the plurality of cold heads or on the recovery side from the plurality of cold heads to the compressor, and operating the plurality of cold heads simultaneously and asynchronously based on the pressure waveform obtained from the measurement.

[0008] Furthermore, any combination of the above components, or any substitution of components or expressions of the present invention between methods, apparatus, systems, etc., is also valid as an embodiment of the present invention. [Effects of the Invention]

[0009] According to the present invention, multiple cold heads can be operated simultaneously and asynchronously. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram showing a cryogenic refrigerator according to an embodiment. [Figure 2] This is a schematic diagram showing a cryogenic refrigerator according to an embodiment. [Figure 3] This flowchart shows an example of an operating method for a cryogenic refrigerator according to an embodiment. [Figure 4] This flowchart shows another example of an operating method for a cryogenic refrigerator according to the embodiment. [Modes for carrying out the invention]

[0011] The embodiments for carrying out the present invention will be described in detail below with reference to the drawings. In the description and drawings, identical or equivalent components, members, and processes are denoted by the same reference numerals, and redundant descriptions will be omitted as appropriate. The scale and shape of the illustrated parts are set for convenience to facilitate the explanation and are not to be interpreted restrictively unless otherwise specified. The embodiments are illustrative and do not limit the scope of the present invention in any way. Not all features or combinations thereof described in the embodiments are necessarily essential to the invention.

[0012] Figures 1 and 2 are schematic diagrams showing a cryogenic refrigerator 10 according to an embodiment. The cryogenic refrigerator 10 is, as an example, a two-stage Gifford-McMahon (GM) refrigerator. Figure 1 shows the external appearance of the cryogenic refrigerator 10, and Figure 2 shows the internal structure of the cryogenic refrigerator 10.

[0013] The cryogenic refrigerator 10 comprises a compressor 12 and a plurality of cold heads 14 connected in parallel to the compressor 12. The compressor 12 is configured to recover the working gas of the cryogenic refrigerator 10 from the cold heads 14, pressurize the recovered working gas, and supply the working gas back to the cold heads 14. The plurality of cold heads 14 may include at least two cold heads 14, namely a first cold head 14a and a second cold head 14b. The cold heads 14 are also called expanders. The working gas is also called the refrigerant gas and is usually helium gas, but other suitable gases may be used.

[0014] The cold head 14 comprises a refrigeration cylinder 16, a displacer assembly 18, and a refrigeration housing 20. The refrigeration housing 20 is coupled to the refrigeration cylinder 16, thereby forming an airtight container that houses the displacer assembly 18. The internal volume of the refrigeration housing 20 may be connected to the low-pressure side of the compressor 12 and maintained at a low pressure.

[0015] The refrigeration cylinder 16 has a first cylinder 16a and a second cylinder 16b. The first cylinder 16a and the second cylinder 16b are, for example, cylindrical members, with the second cylinder 16b having a smaller diameter than the first cylinder 16a. The first cylinder 16a and the second cylinder 16b are arranged coaxially, and the lower end of the first cylinder 16a is rigidly connected to the upper end of the second cylinder 16b.

[0016] The displacer assembly 18 includes a first displacer 18a and a second displacer 18b. The first displacer 18a and the second displacer 18b are, for example, cylindrical members, with the second displacer 18b having a smaller diameter than the first displacer 18a. The first displacer 18a and the second displacer 18b are arranged coaxially.

[0017] The first displacer 18a is housed in the first cylinder 16a, and the second displacer 18b is housed in the second cylinder 16b. The first displacer 18a is reciprocable in the axial direction along the first cylinder 16a, and the second displacer 18b is reciprocable in the axial direction along the second cylinder 16b. The first displacer 18a and the second displacer 18b are connected to each other and move as a single unit.

[0018] In this book, for the purpose of explaining the positional relationship between the components of the cryogenic refrigerator 10, for the sake of convenience, the side closer to the top dead center of the axial reciprocating motion of the displacer will be denoted as "upper", and the side closer to the bottom dead center will be denoted as "lower". The top dead center is the position of the displacer where the volume of the expansion space is maximum, and the bottom dead center is the position of the displacer where the volume of the expansion space is minimum. During the operation of the cryogenic refrigerator 10, a temperature gradient occurs where the temperature decreases from the upper side to the lower side in the axial direction, so the upper side can also be called the high-temperature side and the lower side can be called the low-temperature side.

[0019] The first displacer 18a houses the first regenerator 26. The first regenerator 26 is formed by filling, for example, a wire mesh of copper or other appropriate first regenerator material into the cylindrical main body of the first displacer 18a. The upper lid and lower lid of the first displacer 18a may be provided as separate members from the main body of the first displacer 18a, and the upper lid and lower lid of the first displacer 18a are fixed to the main body by appropriate means such as fastening or welding, whereby the first regenerator material may be housed in the first displacer 18a.

[0020] Similarly, the second displacer 18b houses the second regenerator 28. The second regenerator 28 is formed by filling, for example, a non-magnetic regenerator material such as bismuth, a magnetic regenerator material such as HoCu2, or other appropriate second regenerator material into the cylindrical main body of the second displacer 18b. The second regenerator material may be formed into granules. The upper lid and lower lid of the second displacer 18b may be provided as separate members from the main body of the second displacer 18b, and the lower lid of the upper lid of the second displacer 18b is fixed to the main body by appropriate means such as fastening or welding, whereby the second regenerator material may be housed in the second displacer 18b.

[0021] The displacer assembly 18 forms an upper chamber 30, a first expansion chamber 32, and a second expansion chamber 34 inside the refrigerator cylinder 16. For heat exchange with a desired object or medium to be cooled by the cryogenic refrigerator 10, the cold head 14 includes a first cooling stage 33 and a second cooling stage 35. The upper chamber 30 is formed between the upper lid portion of the first displacer 18a and the upper portion of the first cylinder 16a. The first expansion chamber 32 is formed between the lower lid portion of the first displacer 18a and the first cooling stage 33. The second expansion chamber 34 is formed between the lower lid portion of the second displacer 18b and the second cooling stage 35. The first cooling stage 33 is fixed to the lower portion of the first cylinder 16a so as to surround the first expansion chamber 32, and the second cooling stage 35 is fixed to the lower portion of the second cylinder 16b so as to surround the second expansion chamber 34.

[0022] The first regenerator 26 is connected to the upper chamber 30 through an operating gas flow path 36a formed in the upper lid portion of the first displacer 18a, and is connected to the first expansion chamber 32 through an operating gas flow path 36b formed in the lower lid portion of the first displacer 18a. The second regenerator 28 is connected to the first regenerator 26 through an operating gas flow path 36c formed from the lower lid portion of the first displacer 18a to the upper lid portion of the second displacer 18b. Further, the second regenerator 28 is connected to the second expansion chamber 34 through an operating gas flow path 36d formed in the lower lid portion of the second displacer 18b.

[0023] First seals 38a and second seals 38b may be provided so that the operating gas flow between the first expansion chamber 32, the second expansion chamber 34, and the upper chamber 30 is guided to the first regenerator 26 and the second regenerator 28 rather than the clearance between the refrigerator cylinder 16 and the displacer assembly 18. The first seal 38a may be mounted on the upper lid portion of the first displacer 18a so as to be disposed between the first displacer 18a and the first cylinder 16a. The second seal 38b may be mounted on the upper lid portion of the second displacer 18b so as to be disposed between the second displacer 18b and the second cylinder 16b.

[0024] The cold head 14 also includes a pressure switching valve 40 and a drive motor 42. The pressure switching valve 40 is housed in the refrigerator housing 20, and the drive motor 42 is mounted on the refrigerator housing 20.

[0025] As shown in Figure 2, the pressure switching valve 40 comprises a high-pressure valve 40a and a low-pressure valve 40b, and is configured to generate periodic pressure fluctuations within the refrigeration cylinder 16. The working gas outlet of the compressor 12 is connected to the upper chamber 30 via the high-pressure valve 40a, and the working gas inlet of the compressor 12 is connected to the upper chamber 30 via the low-pressure valve 40b. The high-pressure valve 40a and the low-pressure valve 40b are configured to open and close selectively and alternately (i.e., when one is open, the other is closed). High-pressure (e.g., 2-3 MPa) working gas is supplied from the compressor 12 to the cold head 14 through the high-pressure valve 40a, and low-pressure (e.g., 0.5-1.5 MPa) working gas is recovered from the cold head 14 to the compressor 12 through the low-pressure valve 40b. For understanding, the direction of the working gas flow is indicated by arrows in Figure 2.

[0026] A drive motor 42 is provided to drive the reciprocating motion of the displacer assembly 18. The drive motor 42 is connected to the displacer drive shaft 44 via a motion conversion mechanism 43, such as a Scotch yoke mechanism. The motion conversion mechanism 43, as well as the pressure switching valve 40, is housed in the refrigerator housing 20. The displacer drive shaft 44 extends from the motion conversion mechanism 43 through the refrigerator housing 20 into the upper chamber 30 and is fixed to the top cover of the first displacer 18a. A third seal 38c is provided to prevent leakage of working gas from the upper chamber 30 to the refrigerator housing 20 (which may be maintained at a low pressure as described above). The third seal 38c may be mounted on the refrigerator housing 20 so as to be positioned between the refrigerator housing 20 and the displacer drive shaft 44.

[0027] When the drive motor 42 is driven, the rotational output of the drive motor 42 is converted by the motion conversion mechanism 43 into axial reciprocating motion of the displacer drive shaft 44, causing the displacer assembly 18 to reciprocate axially within the refrigerator cylinder 16. The drive motor 42 is also connected to a pressure switching valve 40 to selectively and alternately open and close the high-pressure valve 40a and the low-pressure valve 40b.

[0028] Furthermore, the cryogenic refrigerator 10 includes an operating gas line 46 connecting the compressor 12 to a plurality of cold heads 14. The operating gas line 46 includes a high-pressure line 46a for supplying high-pressure operating gas from the compressor 12 to the plurality of cold heads 14, and a low-pressure line 46b for recovering low-pressure operating gas from the plurality of cold heads 14 to the compressor 12. The high-pressure line 46a extends from the operating gas outlet of the compressor 12, branches off along the way, and is connected to the pressure switching valve 40 of each cold head 14. The low-pressure line 46b extends from the operating gas inlet of the compressor 12, branches off along the way, and is connected to the pressure switching valve 40 of each cold head 14. In this way, as described above, the operating gas outlet of the compressor 12 is connected to the high-pressure valve 40a of each cold head 14, and the operating gas inlet of the compressor 12 is connected to the low-pressure valve 40b of each cold head 14.

[0029] With the above configuration, when the compressor 12 and drive motor 42 are driven and the displacer assembly 18 and pressure switching valve 40 are operated, the cryogenic refrigerator 10 generates periodic volume fluctuations in the first expansion chamber 32 and the second expansion chamber 34 and synchronized pressure fluctuations of the working gas, thereby forming a refrigeration cycle and cooling the first cooling stage 33 and the second cooling stage 35 to the desired cryogenic temperature. The first cooling stage 33 can be cooled to a first cooling temperature, for example, in the range of about 20K to about 40K. The second cooling stage 35 can be cooled to a second cooling temperature lower than the first cooling temperature (for example, about 1K to about 4K).

[0030] The cryogenic refrigerator 10 also includes a first pressure sensor 48a, a second pressure sensor 48b, and a controller 50. The first pressure sensor 48a measures the pressure of the working gas on the supply side from the compressor 12 to the multiple cold heads 14, i.e., the high-pressure line 46a. The second pressure sensor 48b measures the pressure of the working gas on the recovery side from the multiple cold heads 14 to the compressor 12, i.e., the low-pressure line 46b. For convenience of explanation, the first pressure sensor 48a and the second pressure sensor 48b may be collectively referred to as the pressure sensor 48 below. The pressure sensor 48 is communicably connected to the controller 50 by wire or wireless means and can transmit the measured pressure waveform data to the controller 50.

[0031] The first pressure sensor 48a may be installed at any location on the high-pressure line 46a. For example, the first pressure sensor 48a may be located inside the housing of the compressor 12 and measure the pressure of the high-pressure line 46a within the compressor 12. Alternatively, the first pressure sensor 48a may be installed in the working gas piping connecting the compressor 12 and the cold head 14 as the high-pressure line 46a. Similarly, the second pressure sensor 48b may be installed at any location on the low-pressure line 46b.

[0032] The periodic operation of the pressure switching valve 40 (i.e., the periodic alternating opening and closing of the high-pressure valve 40a and the low-pressure valve 40b) can cause periodic pressure fluctuations (pulsations) in the working gas line 46. For example, in the high-pressure line 46a, when the high-pressure valve 40a opens, working gas flows from the high-pressure line 46a into the cold head 14, causing a slight decrease in the pressure in the high-pressure line 46a. This pressure drop is then recovered when the high-pressure valve 40a closes, due to the supply of working gas from the compressor 12 to the high-pressure line 46a. Such pressure fluctuations in the high-pressure line 46a can be detected by the first pressure sensor 48a. That is, periodic pressure fluctuations may appear in the pressure waveform data measured by the first pressure sensor 48a. Similarly, periodic pressure fluctuations that may occur in the low-pressure line 46b due to the periodic opening and closing of the low-pressure valve 40b may appear in the pressure waveform data measured by the second pressure sensor 48b.

[0033] These periodic pressure fluctuations reflect the valve timing of the pressure switching valve 40, and consequently, the phase of the refrigeration cycle of the cold head 14. Therefore, by monitoring the pressure waveform of the working gas line 46 (at least one of the high-pressure line 46a and the low-pressure line 46b) using the pressure sensor 48 (at least one of the first pressure sensor 48a and the second pressure sensor 48b), the valve timing of the pressure switching valve 40 can be determined. By acquiring the valve timing of the pressure switching valve 40 for each cold head 14 and starting each cold head 14 so that these valve timings are not synchronized, it becomes possible to operate multiple cold heads 14 simultaneously and asynchronously.

[0034] Therefore, in this embodiment, the controller 50 is configured to acquire individual pressure waveform data measured by the pressure sensor 48 when each of the multiple cold heads 14 is operated individually, and to operate the multiple cold heads 14 simultaneously and asynchronously based on the individual pressure waveform data.

[0035] The controller 50 is implemented in hardware form by components and circuits such as the CPU (Central Processing Unit) and memory of a computer, and in software form by computer programs, etc., but in the diagram it is depicted as a functional block realized through the coordination of these components as appropriate. It will be understood by those skilled in the art that these functional blocks can be realized in various forms by combinations of hardware and software.

[0036] Figure 3 is a flowchart illustrating an example of an operating method for the cryogenic refrigerator 10 according to the embodiment. The process illustrated in Figure 3 is performed by the controller 50 as preparation for the normal operation of the cryogenic refrigerator 10, in which multiple cold heads 14 are operated simultaneously. As described below, the controller 50 may be configured to operate the multiple cold heads 14 simultaneously and asynchronously based on a comparison of individual pressure waveform data.

[0037] As shown in Figure 3, the first cold head 14a is started (S10). The controller 50 starts operating the first cold head 14a by turning on the drive motor 42 of the first cold head 14a. At this time, the first cold head 14a is operated individually. That is, only the first cold head 14a is operated, and the other cold heads 14, including the second cold head 14b, are stopped.

[0038] The controller 50 acquires individual pressure waveform data measured by the pressure sensor 48 for the first cold head 14a during individual operation of the first cold head 14a (S11). The individual pressure waveform data is acquired over at least one or more refrigeration cycles of the cold head 14. The individual pressure waveform data may be pressure waveform data of the high-pressure line 46a measured by the first pressure sensor 48a, or pressure waveform data of the low-pressure line 46b measured by the second pressure sensor 48b.

[0039] When individual pressure waveform data is acquired for the first cold head 14a, the first cold head 14a is stopped (S12). The controller 50 terminates the operation of the first cold head 14a by turning off the drive motor 42 for the first cold head 14a.

[0040] Next, the second cold head 14b is started in the same manner (S13), individual pressure waveform data is acquired for the second cold head 14b during its individual operation (S14), and then the second cold head 14b is stopped (S15).

[0041] Next, the acquired individual pressure waveform data are compared (S16). The controller 50 compares the individual pressure waveform data of the first cold head 14a with the individual pressure waveform data of the second cold head 14b and determines the phase difference between these two pressure waveforms. The controller 50 determines the timing of pressure fluctuations caused by the same specific valve timing from the individual pressure waveform data of the first cold head 14a and the second cold head 14b, and determines the phase difference between the two pressure waveforms from these time differences. For example, if the individual pressure waveform data is measured by the first pressure sensor 48a, the controller 50 can detect the timing of pressure drops in the high-pressure line 46a corresponding to the opening timing of the high-pressure valve 40a from the individual pressure waveform data of the first cold head 14a and the second cold head 14b, and determine the phase difference between the two pressure waveforms from these.

[0042] Then, the cryogenic refrigerator 10 starts normal operation (S17). The controller 50 operates multiple cold heads 14 simultaneously and asynchronously based on a comparison of individual pressure waveform data.

[0043] For example, the controller 50 determines whether the phase difference of the determined pressure waveforms is non-zero. If the determined phase difference is non-zero, the controller 50 starts the first cold head 14a and the second cold head 14b simultaneously. In this way, the phase difference of the pressure waveforms of the first cold head 14a and the second cold head 14b is maintained while these cold heads start operation. Therefore, the valve timing of the two cold heads can be made asynchronous.

[0044] On the other hand, if the determined phase difference is zero, the controller 50 starts the first cold head 14a and the second cold head 14b with a time difference. That is, one cold head is started first, and the other cold head is started later. This delay time can be a non-integer multiple of one cycle of the refrigeration cycle of the cold head 14 (i.e., one period of the pressure waveform). In this way, the two cold heads start operating with a phase difference corresponding to the delay time. Therefore, the valve timing of the two cold heads can be made asynchronous.

[0045] If the cryogenic refrigerator 10 has three or more cold heads 14, the controller 50 can repeat the same process to acquire individual pressure waveform data measured by the pressure sensor 48 when each of the cold heads 14 is operated individually, and operate the multiple cold heads 14 simultaneously and asynchronously based on a comparison of the individual pressure waveform data.

[0046] Therefore, according to the embodiment, a cryogenic refrigerator 10 can be provided by operating multiple cold heads 14 simultaneously in asynchronous manner. In particular, even in a cryogenic refrigerator 10 in which each cold head 14 is not equipped with an inverter and the drive motor 42 is operated at a fixed operating frequency, multiple cold heads 14 can be operated simultaneously in asynchronous manner.

[0047] Figure 4 is a flowchart showing another example of the operation method of the cryogenic refrigerator 10 according to the embodiment. The process illustrated in Figure 4 is performed by the controller 50 as preparation for the normal operation of the cryogenic refrigerator 10, in which multiple cold heads 14 are operated simultaneously, prior to the normal operation of the cryogenic refrigerator 10, similar to the process in Figure 3.

[0048] As described below, the controller 50 may be configured to acquire overall pressure waveform data measured by the pressure sensor 48 when multiple cold heads 14 are operated simultaneously, acquire overall pressure amplitude from the overall pressure waveform data, acquire the sum of individual pressure amplitudes from the individual pressure waveform data of the multiple cold heads 14, and operate the multiple cold heads 14 asynchronously and simultaneously based on a comparison between the overall pressure amplitude and the sum of the individual pressure amplitudes.

[0049] As shown in Figure 4, the first cold head 14a is started (S10), individual pressure waveform data is acquired for the first cold head 14a during its individual operation (S11), and then the first cold head 14a is stopped (S12). Then, the second cold head 14b is started (S13), and individual pressure waveform data is acquired for the second cold head 14b during its individual operation (S14). If the cryogenic refrigerator 10 has three or more cold heads 14, individual pressure waveform data is acquired for each of these cold heads 14 in a similar manner. This acquisition of individual pressure waveform data can be performed in the same manner as the process shown in Figure 3.

[0050] Next, multiple cold heads 14 are operated simultaneously (S20). For example, if the cryogenic refrigerator 10 has two cold heads 14, the first cold head 14a is restarted after acquiring individual pressure waveform data for the second cold head 14b. The first cold head 14a and the second cold head 14b are then operated simultaneously. If the cryogenic refrigerator 10 has three or more cold heads 14, any stopped cold heads 14 are restarted, and all cold heads 14 are operated simultaneously.

[0051] The controller 50 acquires the integrated pressure waveform data measured by the pressure sensor 48 during the simultaneous operation of the plurality of cold heads 14 (S21). The integrated pressure waveform data is acquired over at least one or a plurality of refrigeration cycles of the cold heads 14. The integrated pressure waveform data may be the pressure waveform data of the high-pressure line 46a measured by the first pressure sensor 48a, or may be the pressure waveform data of the low-pressure line 46b measured by the second pressure sensor 48b.

[0052] The controller 50 acquires the pressure amplitude (referred to herein as the integrated pressure amplitude) from the acquired integrated pressure waveform data (S22). Further, the controller 50 acquires the pressure amplitude (referred to herein as the individual pressure amplitude) from the individual pressure waveform data of the plurality of cold heads 14, and calculates the sum of the individual pressure amplitudes (S23).

[0053] Next, the integrated pressure amplitude and the sum of the individual pressure amplitudes are compared (S24). The controller 50 compares the integrated pressure amplitude with the sum of the individual pressure amplitudes, and determines the magnitude relationship between the two. When the valve timings of the plurality of cold heads 14 are synchronized, the integrated pressure amplitude becomes equal to the sum of the individual pressure amplitudes. Conversely, when the valve timings of the plurality of cold heads 14 are asynchronous, it is considered that the integrated pressure amplitude becomes smaller than the sum of the individual pressure amplitudes.

[0054] For example, consider the case where the cryogenic refrigerator 10 has two cold heads 14. Let the individual pressure amplitude of the first cold head 14a be A, the individual pressure amplitude of the second cold head 14b be B, and the integrated pressure amplitude when these two cold heads 14 are operated simultaneously be C. When the valve timings of the two cold heads 14 are synchronized, C = A + B holds. On the other hand, when the valve timings of the two cold heads 14 are asynchronous, C < A + B should hold.

[0055] In addition, when it is assumed that multiple cold heads 14 have the same individual pressure amplitude (for example, when the multiple cold heads 14 are cold heads of the same specification), since the individual pressure amplitude for a certain cold head can also be used for other cold heads, it is not essential to obtain the individual pressure amplitude for each cold head. For example, considering the case where the individual pressure amplitudes of two cold heads 14 are equal, if the valve timings of the two cold heads 14 are synchronized, C = 2A holds, and if the valve timings of the two cold heads 14 are asynchronous, C < 2A should hold.

[0056] Therefore, when the overall pressure amplitude is smaller than the sum of the individual pressure amplitudes (for example, C < A + B, or C < 2A), the controller 50 continues the simultaneous operation of the multiple cold heads 14 (S25). In this case, the valve timings of the multiple cold heads 14 are asynchronous.

[0057] On the other hand, when the overall pressure amplitude is equal to the sum of the individual pressure amplitudes (for example, C = A + B, or C = 2A), the controller 50 stops one of the cold heads 14 (for example, the second cold head 14b) once, and restarts it again after the elapse of the waiting time (S26). This waiting time may be a non-integer multiple of one cycle of the refrigeration cycle of the cold head 14 (that is, one cycle of the pressure waveform). By doing so, the two cold heads are operated with a phase difference corresponding to the waiting time. Therefore, the valve timings of the two cold heads can be made asynchronous.

[0058] When the cryogenic refrigerator 10 has three or more cold heads 14, the controller 50 can simultaneously operate the multiple cold heads 14 asynchronously based on the comparison between the overall pressure amplitude and the sum of the individual pressure amplitudes by the same process.

[0059] According to this embodiment, a cryogenic refrigerator 10 can be provided by operating multiple cold heads 14 simultaneously in asynchronous manner. In particular, even in a cryogenic refrigerator 10 in which each cold head 14 is not equipped with an inverter and the drive motor 42 operates at a fixed operating frequency, multiple cold heads 14 can be operated simultaneously in asynchronous manner.

[0060] The present invention has been described above based on examples. Those skilled in the art will understand that the present invention is not limited to the above embodiments, that various design changes are possible, and that various modifications are possible, and that such modifications also fall within the scope of the present invention. Various features described in relation to one embodiment are applicable to other embodiments. New embodiments resulting from combinations will possess the combined effects of each of the embodiments combined.

[0061] In the above-described embodiment, the case in which the cryogenic refrigerator 10 has one compressor 12 is explained as an example, but the cryogenic refrigerator 10 may have multiple (for example, two) compressors 12.

[0062] In the above-described embodiment, the case in which the cryogenic refrigerator 10 is a two-stage GM refrigerator is explained as an example, but it is not limited to this. The cryogenic refrigerator 10 may be a single-stage or multi-stage GM refrigerator, or even another type of cryogenic refrigerator such as a pulse tube refrigerator.

[0063] The present invention has been described above based on examples. Those skilled in the art will understand that the present invention is not limited to the above embodiments, that various design changes are possible, and that various modifications are possible, and that such modifications also fall within the scope of the present invention. [Explanation of symbols]

[0064] 10 Cryogenic refrigerator, 12 Compressor, 14 Cold head, 14a First cold head, 14b Second cold head, 46 Working gas line, 46a High pressure line, 46b Low pressure line, 48 Pressure sensor, 48a First pressure sensor, 48b Second pressure sensor, 50 Controller.

Claims

1. Compressor and, Multiple cold heads connected in parallel to the compressor, A pressure sensor that measures the pressure of the working gas on the supply side from the compressor to the plurality of cold heads or on the recovery side from the plurality of cold heads to the compressor, A cryogenic refrigerator comprising: a controller configured to acquire individual pressure waveform data measured by the pressure sensor when each of the plurality of cold heads is operated individually, and to operate the plurality of cold heads simultaneously and asynchronously based on the individual pressure waveform data.

2. The cryogenic refrigerator according to claim 1, characterized in that the controller is configured to operate the plurality of cold heads simultaneously and asynchronously based on a comparison of the individual pressure waveform data.

3. The aforementioned controller, When the multiple cold heads are operating simultaneously, the combined pressure waveform data measured by the pressure sensor is acquired. The total pressure amplitude is obtained from the aforementioned total pressure waveform data. The sum of the individual pressure amplitudes is obtained from the individual pressure waveform data of the plurality of cold heads. The cryogenic refrigerator according to claim 1, characterized in that the plurality of cold heads are configured to be operated asynchronously and simultaneously based on a comparison of the total pressure amplitude and the sum of the individual pressure amplitudes.

4. A method for operating a cryogenic refrigerator, wherein the cryogenic refrigerator comprises a compressor and a plurality of cold heads connected in parallel to the compressor, and the method is: For each of the aforementioned multiple cold heads, during the individual operation of the cold head, the pressure of the working gas is measured on the supply side from the compressor to the multiple cold heads or on the recovery side from the multiple cold heads to the compressor. A method characterized by comprising simultaneously operating the plurality of cold heads asynchronously based on pressure waveforms obtained by measurement.

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