Patent Description:
In a multi-system cryocooler including a plurality of cryocoolers, when the opening and closing timings of the pressure switching valves of the respective cryocoolers coincide with each other when the cryocoolers are operated at the same time, the refrigerating performance may deteriorate. In the related art, in order to avoid this, it is known that an inverter provided in each cryocooler is used to make the operating frequencies of the cryocoolers different and make the valve timing asynchronous (for example, <CIT>). <CIT> discloses a cryocooler according to the preamble of claim <NUM>.

The above-mentioned method cannot be applied to a cryocooler without an inverter.

It is desirable to provide a new technology which can operate a plurality of cold heads at the same time asynchronously.

According to an aspect of the present invention, there is provided a cryocooler as defined in claim <NUM>. includes: a compressor; a plurality of cold heads connected in parallel to the compressor; a pressure sensor that measures a pressure of a working gas on a supply side from the compressor to the plurality of cold heads or on a collection side from the plurality of cold heads to the compressor; and a controller that acquires individual pressure waveform data measured by the pressure sensor when the cold heads are individually operated for each of the plurality of cold heads, and operates the plurality of cold heads at the same time asynchronously based on the individual pressure waveform data.

According to another aspect of the present invention, there is provided a method for operating a cryocooler as defined in claim <NUM>. The cryocooler includes a compressor and a plurality of cold heads connected in parallel to the compressor. The method includes measuring a pressure of a working gas on a supply side from the compressor to the plurality of cold heads or on a collection side from the plurality of cold heads to the compressor during individual operation of the cold heads for each of the plurality of cold heads; and operating the plurality of cold heads at the same time asynchronously based on a pressure waveform obtained by measurement.

According to the present invention, a plurality of cold heads can be operated at the same time asynchronously.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the description and drawings, the same or equivalent components, members, and processes will be assigned with the same reference symbols, and redundant description thereof will be omitted as appropriate. The scales and shapes of each illustrated part are set for convenience in order to make the description easy to understand, and are not to be understood as limiting unless stated otherwise. The embodiments are merely examples and do not limit the scope of the present invention. All characteristics and combinations to be described in the embodiment are not necessarily essential to the invention.

<FIG> and <FIG> are views schematically illustrating a cryocooler <NUM> according to an embodiment of the present invention. As an example, the cryocooler <NUM> is a two-stage Gifford-McMahon (GM) cryocooler. <FIG> illustrates the appearance of the cryocooler <NUM>, and <FIG> illustrates the internal structure of the cryocooler <NUM>.

The cryocooler <NUM> includes a compressor <NUM> and a plurality of cold heads <NUM> connected in parallel to the compressor <NUM>. The compressor <NUM> is configured to collect the working gas of the cryocooler <NUM> from the cold head <NUM>, pressurize the collected working gas, and supply the working gas to the cold head <NUM> again. The plurality of cold heads <NUM> may include at least two cold heads <NUM>, that is, a first cold head 14a and a second cold head 14b. The cold head <NUM> is also called an expander. The working gas is also referred to as a refrigerant gas and is usually a helium gas, but other suitable gas may be used.

The cold head <NUM> includes a cryocooler cylinder <NUM>, a displacer assembly <NUM>, and a cryocooler housing <NUM>. The cryocooler housing <NUM> is coupled to the cryocooler cylinder <NUM>, thereby forming a hermetic container that accommodates the displacer assembly <NUM>. The internal volume of the cryocooler housing <NUM> may be connected to the low pressure side of the compressor <NUM> and maintained at a low pressure.

The cryocooler cylinder <NUM> has a first cylinder 16a and a second cylinder 16b. As an example, the first cylinder 16a and the second cylinder 16b are members having a cylindrical shape, and the second cylinder 16b has a diameter smaller than that of the first cylinder 16a. The first cylinder 16a and the second cylinder 16b are coaxially disposed, and a lower end of the first cylinder 16a is rigidly connected to an upper end of the second cylinder 16b.

The displacer assembly <NUM> has a first displacer 18a and a second displacer 18b. As an example, the first displacer 18a and the second displacer 18b are members having a cylindrical shape, and the second displacer 18b has a diameter smaller than that of the first displacer 18a. The first displacer 18a and the second displacer 18b are disposed coaxially with each other.

The first displacer 18a is accommodated in the first cylinder 16a, and the second displacer 18b is accommodated in the second cylinder 16b. The first displacer 18a can reciprocate in the axial direction along the first cylinder 16a, and the second displacer 18b can reciprocate 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 integrally.

In this specification, in order to describe the positional relationship between the components of the cryocooler <NUM>, for convenience, the side close to the top dead center of the axial reciprocation of the displacer is "upper", and the side close to the bottom dead center is "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 the minimum. Since a temperature gradient is generated in which the temperature drops from the upper side to the lower side in the axial direction during the operation of the cryocooler <NUM>, the upper side can be referred to as a high temperature side and the lower side can be referred to as a low temperature side.

The first displacer 18a accommodates a first regenerator <NUM>. The first regenerator <NUM> is formed by filling a tubular main body portion of the first displacer 18a with a wire mesh such as copper or other appropriate first regenerator material. The upper lid portion and the lower lid portion of the first displacer 18a may be provided as members separate from the main body portion of the first displacer 18a, the upper lid portion and the lower lid portion of the first displacer 18a may be fixed to the main body by appropriate means such as fastening or welding, and accordingly, the first regenerator material may be accommodated in the first displacer 18a.

Similarly, the second displacer 18b accommodates a second regenerator <NUM>. The second regenerator <NUM> is formed by filling a tubular main body portion of the second displacer 18b with a non-magnetic regenerator material such as bismuth, a magnetic regenerator material such as HoCu<NUM>, or other appropriate second regenerator material. The second regenerator material may be formed in a granular shape. The upper lid portion and the lower lid portion of the second displacer 18b may be provided as members separate from the main body portion of the second displacer 18b, the upper lid portion and the lower lid portion of the second displacer 18b may be fixed to the main body by appropriate means such as fastening or welding, and accordingly, the second regenerator material may be accommodated in the second displacer 18b.

The displacer assembly <NUM> forms an upper portion chamber <NUM>, a first expansion chamber <NUM>, and a second expansion chamber <NUM> inside the cryocooler cylinder <NUM>. The cold head <NUM> includes a first cooling stage <NUM> and a second cooling stage <NUM> for heat exchange with a desired object or medium to be cooled by the cryocooler <NUM>. The upper portion chamber <NUM> 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 <NUM> is formed between the lower lid portion of the first displacer 18a and the first cooling stage <NUM>. The second expansion chamber <NUM> is formed between the lower lid portion of the second displacer 18b and the second cooling stage <NUM>. The first cooling stage <NUM> is fixed to the lower portion of the first cylinder 16a to surround the first expansion chamber <NUM>, and the second cooling stage <NUM> is fixed to the lower portion of the second cylinder 16b to surround the second expansion chamber <NUM>.

The first regenerator <NUM> is connected to the upper portion chamber <NUM> through a working gas flow path 36a formed in the upper lid portion of the first displacer 18a, and is connected to the first expansion chamber <NUM> through a working gas flow path 36b formed in the lower lid portion of the first displacer 18a. The second regenerator <NUM> is connected to the first regenerator <NUM> through a working 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. In addition, the second regenerator <NUM> is connected to the second expansion chamber <NUM> through a working gas flow path 36d formed in the lower lid portion of the second displacer 18b.

The working gas flow between the first expansion chamber <NUM>, the second expansion chamber <NUM>, and the upper portion chamber <NUM> is not the clearance between the cryocooler cylinder <NUM> and the displacer assembly <NUM>, but a first seal 38a and a second seal 38b may be provided to be guided to the first regenerator <NUM> and the second regenerator <NUM>. The first seal 38a may be mounted to the upper lid portion of the first displacer 18a to be disposed between the first displacer 18a and the first cylinder 16a. The second seal 38b may be mounted to the upper lid portion of the second displacer 18b to be disposed between the second displacer 18b and the second cylinder 16b.

Further, the cold head <NUM> includes a pressure switching valve <NUM> and a driving motor <NUM>. The pressure switching valve <NUM> is accommodated in the cryocooler housing <NUM>, and the driving motor <NUM> is attached to the cryocooler housing <NUM>.

As illustrated in <FIG>, the pressure switching valve <NUM> includes the high pressure valve 40a and the low pressure valve 40b, and is configured to generate periodic pressure fluctuation in the cryocooler cylinder <NUM>. The working gas discharge port of the compressor <NUM> is connected to the upper portion chamber <NUM> via the high pressure valve 40a, and the working gas suction port of the compressor <NUM> is connected to the upper portion chamber <NUM> via the low pressure valve 40b. The high pressure valve 40a and the low pressure valve 40b are configured to selectively and alternately open and close (that is, when one is open, the other is closed). A high pressure (for example, <NUM> to <NUM> MPa) working gas is supplied from the compressor <NUM> to the cold head <NUM> through the high pressure valve 40a, and a low pressure (for example, <NUM> to <NUM> MPa) working gas is collected from the cold head <NUM> to the compressor <NUM> through the low pressure valve 40b. For the sake of understanding, the flow direction of the working gas is indicated by an arrow in <FIG>.

The driving motor <NUM> is provided to drive the reciprocating motion of the displacer assembly <NUM>. The driving motor <NUM> is connected to a displacer drive shaft <NUM> via a motion conversion mechanism <NUM> such as a Scotch yoke mechanism. The motion conversion mechanism <NUM> is accommodated in the cryocooler housing <NUM> similar to the pressure switching valve <NUM>. The displacer drive shaft <NUM> extends from the motion conversion mechanism <NUM> into the upper portion chamber <NUM> through the cryocooler housing <NUM>, and is fixed to the upper lid portion of the first displacer 18a. A third seal 38c is provided in order to prevent leakage of the working gas from the upper portion chamber <NUM> to the cryocooler housing <NUM> (which may be maintained at a low pressure as described above). The third seal 38c may be mounted to the cryocooler housing <NUM> to be disposed between the cryocooler housing <NUM> and the displacer drive shaft <NUM>.

When the driving motor <NUM> is driven, the rotational output of the driving motor <NUM> is converted into axial reciprocation of the displacer drive shaft <NUM> by the motion conversion mechanism <NUM>, and the displacer assembly <NUM> reciprocates in the cryocooler cylinder <NUM> in the axial direction. Further, the driving motor <NUM> is connected to the pressure switching valve <NUM> to selectively and alternately open and close the high pressure valve 40a and the low pressure valve 40b.

In addition, the cryocooler <NUM> includes a working gas line <NUM> that connects the compressor <NUM> and the plurality of cold heads <NUM>. The working gas line <NUM> includes a high pressure line 46a for supplying the high pressure working gas from the compressor <NUM> to the plurality of cold heads <NUM>, and a low pressure line 46b for collecting the low pressure working gas from the plurality of cold heads <NUM> to the compressor <NUM>. The high pressure line 46a extends from a working gas discharge port of the compressor <NUM>, branches in the middle, and is connected to a pressure switching valve <NUM> of each cold head <NUM>. The low pressure line 46b extends from a working gas suction port of the compressor <NUM>, branches in the middle, and is connected to a pressure switching valve <NUM> of each cold head <NUM>. In this manner, as described above, the working gas discharge port of the compressor <NUM> is connected to the high pressure valve 40a of each cold head <NUM>, and the working gas suction port of the compressor <NUM> is connected to the low pressure valve 40b of each cold head <NUM>.

According to the above-described configuration, the cryocooler <NUM> generates periodic volume fluctuations in the first expansion chamber <NUM> and the second expansion chamber <NUM> and pressure fluctuations of the working gas synchronized therewith when the compressor <NUM> and the driving motor <NUM> are driven to operate the displacer assembly <NUM> and the pressure switching valve <NUM>, and accordingly, the refrigeration cycle is configured, and the first cooling stage <NUM> and the second cooling stage <NUM> are cooled to a desired cryogenic temperature. The first cooling stage <NUM> can be cooled to a first cooling temperature in the range of, for example, approximately <NUM> to approximately <NUM>. The second cooling stage <NUM> can be cooled to a second cooling temperature (for example, approximately <NUM> to approximately <NUM>) lower than the first cooling temperature.

In addition, the cryocooler <NUM> includes a first pressure sensor 48a, a second pressure sensor 48b, and a controller <NUM>. The first pressure sensor 48a measures the pressure of the working gas on the supply side from the compressor <NUM> to the plurality of cold heads <NUM>, that is, on the high pressure line 46a. The second pressure sensor 48b measures the pressure of the working gas on the collection side from the plurality of cold heads <NUM> to the compressor <NUM>, that is, on the low pressure line 46b. Hereinafter, for convenience of description, the first pressure sensor 48a and the second pressure sensor 48b may be collectively referred to as a pressure sensor <NUM>. The pressure sensor <NUM> is connected to be capable of communicating with the controller <NUM> by wire or wirelessly, and can transmit the measured pressure waveform data to the controller <NUM>.

The first pressure sensor 48a can be installed at any place on the high pressure line 46a. For example, the first pressure sensor 48a may be disposed inside the housing of the compressor <NUM> and may measure the pressure of the high pressure line 46a inside the compressor <NUM>. Alternatively, the first pressure sensor 48a may be installed in the working gas pipe connecting the compressor <NUM> and the cold head <NUM> as the high pressure line 46a. Similarly, the second pressure sensor 48b can be installed at any place on the low pressure line 46b.

The periodic operation of the pressure switching valve <NUM> (that is, the periodic alternating opening and closing of the high pressure valve 40a and the low pressure valve 40b) may cause a periodic pressure fluctuation (pulsation) in the working gas line <NUM>. For example, in the high pressure line 46a, when the high pressure valve 40a is opened, the working gas flows from the high pressure line 46a into the cold head <NUM>, and thus the pressure of the high pressure line 46a may decrease to some extent. When the high pressure valve 40a is subsequently closed, this pressure drop is restored by supplying a working gas from the compressor <NUM> to the high pressure line 46a. Such a pressure fluctuation 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, in the pressure waveform data measured by the second pressure sensor 48b, a periodic pressure fluctuation that may occur in the low pressure line 46b due to the periodic opening and closing of the low pressure valve 40b may appear.

Such a periodic pressure fluctuation reflects the valve timing of the pressure switching valve <NUM>, and thus the phase of the refrigeration cycle of the cold head <NUM>. Therefore, by monitoring the pressure waveform of the working gas line <NUM> (at least one of the high pressure line 46a and the low pressure line 46b) by using the pressure sensor <NUM> (at least one of the first pressure sensor 48a and the second pressure sensor 48b), the valve timing of the pressure switching valve <NUM> can be identified. By acquiring the valve timings of the pressure switching valves <NUM> for each cold head <NUM> and starting each cold head <NUM> such that the valve timings are not synchronized with each other, a plurality of cold heads <NUM> can be operated at the same time asynchronously.

Therefore, in the present embodiment, the controller <NUM> is configured to acquire individual pressure waveform data measured by the pressure sensor <NUM> when the cold heads <NUM> are individually operated for each of the plurality of cold heads <NUM>, and operate the plurality of cold heads <NUM> at the same time asynchronously based on the individual pressure waveform data.

The controller <NUM> is realized as a hardware configuration by elements or circuits such as a central processing unit (CPU) or memory of a computer, and is realized by a computer program or the like as a software configuration. In the drawing, these are drawn as functional blocks realized by their cooperation as appropriate. It is understood by those skilled in the art that the functional blocks can be realized in various forms by combining hardware and software.

<FIG> is a flowchart illustrating an example of the method for operating the cryocooler <NUM> according to the embodiment. The processing illustrated in <FIG> is executed by the controller <NUM> in preparation for the normal operation prior to the normal operation of the cryocooler <NUM> in which the plurality of cold heads <NUM> are operated at the same time. As will be described below, the controller <NUM> may operate the plurality of cold heads <NUM> at the same time asynchronously based on the comparison between the individual pressure waveform data.

As illustrated in <FIG>, the first cold head 14a is started (S10). The controller <NUM> starts the operation of the first cold head 14a by turning on the driving motor <NUM> of the first cold head 14a. At this time, the first cold heads 14a are individually operated. That is, only the first cold head 14a is operated, and the operation of the other cold heads <NUM> including the second cold head 14b is stopped.

The controller <NUM> acquires individual pressure waveform data measured by the pressure sensor <NUM> for the first cold head 14a during the individual operation of the first cold head 14a (S11). The individual pressure waveform data is acquired over the refrigeration cycle of at least one or a plurality of cold head <NUM>. The individual 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.

When the individual pressure waveform data is acquired for the first cold head 14a, the first cold head 14a is stopped (S12). The controller <NUM> ends the operation of the first cold head 14a by turning on the driving motor <NUM> of the first cold head 14a.

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

Next, the acquired individual pressure waveform data are compared with each other (S16). The controller <NUM> 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 the two pressure waveforms. The controller <NUM> determines the generation timing of the pressure fluctuation 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 the time difference thereof. For example, when the individual pressure waveform data is measured by the first pressure sensor 48a, the controller <NUM> can detect the generation timing of pressure drop of the high pressure line 46a corresponding to the opening timing of the high pressure valve 40a from each of 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.

Then, the normal operation of the cryocooler <NUM> is started (S17). The controller <NUM> operates the plurality of cold heads <NUM> at the same time asynchronously based on the comparison between the individual pressure waveform data.

For example, the controller <NUM> determines whether or not the phase difference of the determined pressure waveform is non-zero. When the determined phase difference is non-zero, the controller <NUM> starts the first cold head 14a and the second cold head 14b at the same time. In this manner, the cold heads are started to operate while the phase difference between the pressure waveforms of the first cold head 14a and the second cold head 14b is kept. Therefore, the valve timings of the two cold heads can be made asynchronous.

On the other hand, when the determined phase difference is zero, the controller <NUM> 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. The delay time may be a non-integer multiple of one refrigeration cycle of the cold head <NUM> (that is, one cycle of the pressure waveform). In this manner, the operation of the two cold heads is started with a phase difference corresponding to the delay time. Therefore, the valve timings of the two cold heads can be made asynchronous.

In a case where the cryocooler <NUM> has three or more cold heads <NUM>, by repeating the same processing, the controller <NUM> can acquire individual pressure waveform data measured by the pressure sensor <NUM> when the cold heads <NUM> are individually operated for each of the plurality of cold heads <NUM>, and operate the plurality of cold heads <NUM> at the same time asynchronously based on the comparison between the individual pressure waveform data.

Therefore, according to the embodiment, the cryocooler <NUM> can be provided by operating the plurality of cold heads <NUM> at the same time asynchronously. In particular, even in the cryocooler <NUM> in which each cold head <NUM> is not equipped with an inverter and the driving motor <NUM> is operated at a fixed operating frequency, the plurality of cold heads <NUM> can be operated at the same time asynchronously.

<FIG> is a flowchart illustrating another example of the method for operating the cryocooler <NUM> according to the embodiment. Similar to the processing of <FIG>, the processing illustrated in <FIG> is executed by the controller <NUM> in preparation for the normal operation prior to the normal operation of the cryocooler <NUM> in which the plurality of cold heads <NUM> are operated at the same time.

As will be described below, the controller <NUM> acquires total pressure waveform data measured by the pressure sensor <NUM> when the plurality of cold heads <NUM> are operated at the same time, acquires a total pressure amplitude from the total pressure waveform data, acquires a total sum of individual pressure amplitudes from the individual pressure waveform data of the plurality of cold heads <NUM>, and operates the plurality of cold heads <NUM> at the same time asynchronously based on comparison between the total pressure amplitude and the total sum of the individual pressure amplitudes.

As illustrated in <FIG>, the first cold head 14a is started (S10), individual pressure waveform data is acquired for the first cold head 14a during the individual operation of the first cold head 14a (S11), and then the first cold head 14a is stopped (S12). In addition, the second cold head 14b is started (S13), and individual pressure waveform data is acquired for the second cold head 14b during the individual operation of the second cold head 14b (S14). When the cryocooler <NUM> has three or more cold heads <NUM>, individual pressure waveform data is acquired for each of the cold heads <NUM> in the same manner. The acquisition of the individual pressure waveform data can be executed in the same manner as in the processing of <FIG>.

Subsequently, the plurality of cold heads <NUM> are operated at the same time (S20). For example, when the cryocooler <NUM> has two cold heads <NUM>, the first cold head 14a is started again after the individual pressure waveform data of the second cold head 14b is acquired. The first cold head 14a and the second cold head 14b are operated at the same time. When the cryocooler <NUM> has three or more cold heads <NUM>, the stopped cold heads <NUM> are started again, and all the cold heads <NUM> are operated at the same time.

The controller <NUM> acquires the total pressure waveform data measured by the pressure sensor <NUM> during the simultaneous operation of the plurality of cold heads <NUM> (S21). The total pressure waveform data is acquired over the refrigeration cycle of at least one or a plurality of cold head <NUM>. The total 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.

The controller <NUM> acquires a pressure amplitude from the acquired total pressure waveform data (also referred to as a total pressure amplitude in this specification) (S22). In addition, the controller <NUM> acquires the pressure amplitude from the individual pressure waveform data of the plurality of cold heads <NUM> (also referred to as the individual pressure amplitude in this specification), and calculates the total sum of the individual pressure amplitudes (S23).

Next, the total pressure amplitude and total sum of the individual pressure amplitudes are compared (S24). The controller <NUM> compares the total pressure amplitude and the total sum of the individual pressure amplitudes, and determines the magnitude relationship between the two. It is considered that, when the valve timings of the plurality of cold heads <NUM> are synchronized, the total pressure amplitude becomes equal to the total sum of the individual pressure amplitudes, and conversely, when the valve timings of the plurality of cold heads <NUM> are asynchronous, the total pressure amplitude is smaller than the total sum of the individual pressure amplitudes.

For example, a case where the cryocooler <NUM> has two cold heads <NUM> is considered. The individual pressure amplitudes of the first cold head 14a are represented by A, the individual pressure amplitudes of the second cold head 14b are represented by B, and the total pressure amplitude when these two cold heads <NUM> are operated at the same time is represented by C. While C = A + B is established when the valve timings of the two cold heads <NUM> are synchronized, C < A + B should be established when the valve timings of the two cold heads <NUM> are asynchronous.

When it is assumed that the plurality of cold heads <NUM> have the same individual pressure amplitude (for example, when the plurality of cold heads <NUM> are cold heads having the same specifications), since the individual pressure amplitudes of a certain cold head can also be used for another cold head, it is not essential to acquire an individual pressure amplitude for each cold head. For example, considering a case where the individual pressure amplitudes of the two cold heads <NUM> are equal, when the valve timings of the two cold heads <NUM> are synchronized, C = 2A should be established and when the valve timings of the two cold heads <NUM> are asynchronous, C < 2A should be established.

Therefore, when the total pressure amplitude is smaller than the total sum of the individual pressure amplitudes (for example, C < A + B or C < 2A), the controller <NUM> continues the operation of the plurality of cold heads <NUM> at the same time (S25). In this case, the valve timings of the cold heads of the plurality of cold heads <NUM> are asynchronous.

On the other hand, when the total pressure amplitude is equal to the total sum of the individual pressure amplitudes (for example, C = A + B or C = 2A), the controller <NUM> stops one cold head <NUM> (for example, the second cold head 14b) once and is started again after a lapse of waiting time (S26). The waiting time may be a non-integer multiple of one refrigeration cycle of the cold head <NUM> (that is, one cycle of the pressure waveform). In this manner, the operation of the two cold heads is operated with a phase difference corresponding to the waiting time. Therefore, the valve timings of the two cold heads can be made asynchronous.

When the cryocooler <NUM> has three or more cold heads <NUM>, the controller <NUM> can operate the plurality of cold heads <NUM> at the same time asynchronously based on the comparison between the total pressure amplitude and the total sum of the individual pressure amplitudes by the same processing.

According to the embodiment, the cryocooler <NUM> can be provided by operating the plurality of cold heads <NUM> at the same time asynchronously. In particular, even in the cryocooler <NUM> in which each cold head <NUM> is not equipped with an inverter and the driving motor <NUM> is operated at a fixed operating frequency, the plurality of cold heads <NUM> can be operated at the same time asynchronously.

Above, the present invention was described based on examples. It will be understood by those skilled in the art that the present invention is not limited to the above-described embodiment, various design changes are possible, various modification examples are possible, and such modification examples are also within the scope of the present invention. Various characteristics described in relation to one embodiment are also applicable to other embodiments. A new embodiment generated through combination also has the effects of each of the combined embodiments.

In the above-described embodiment, a case where the cryocooler <NUM> has one compressor <NUM> is described as an example. However, the cryocooler <NUM> may include a plurality of (for example, two) compressors <NUM>.

In the above-described embodiment, a case where the cryocooler <NUM> is a two-stage GM cryocooler was described as an example, but the present invention is not limited thereto. The cryocooler <NUM> may be a single-stage or multistage GM cryocooler, and may be another type of cryocooler such as a pulse tube cryocooler.

Claim 1:
A cryocooler (<NUM>) comprising:
a compressor (<NUM>);
a plurality of cold heads (<NUM>) connected in parallel to the compressor (<NUM>); characterized by further comprising:
a pressure sensor (<NUM>) that measures a pressure of a working gas on a supply side from the compressor (<NUM>) to the plurality of cold heads (<NUM>) or on a collection side from the plurality of cold heads (<NUM>) to the compressor (<NUM>); and
a controller (<NUM>) that acquires individual pressure waveform data measured by the pressure sensor (<NUM>) when the cold heads (<NUM>) are individually operated for each of the plurality of cold heads (<NUM>), and operates the plurality of cold heads (<NUM>) at the same time asynchronously based on the individual pressure waveform data.