Cryogenic refrigeration apparatus and table for controller of cryogenic refrigeration apparatus

Abstract

A cryogenic refrigeration apparatus (10) comprises: an expander (14) that is provided with an expander motor (42), a first cooling stage (33), and a second cooling stage (35), and that is configured to cool the first cooling stage (33) and the second cooling stage (35) by operating the expander motor (42); a first temperature sensor (52) that measures a first temperature of the first cooling stage (33); a second temperature sensor (54) that measures a second temperature of the second cooling stage (35); and a controller (110) that is configured to acquire the measured first temperature from the first temperature sensor (52), acquire the measured second temperature from the second temperature sensor (54), determine the rotation speed of the expander motor (42) from the measured first temperature and the measured second temperature in accordance with a predetermined relationship among the first temperature, the second temperature, and the rotation speed of the expander motor (42), and operate the expander motor (42) on the basis of the determined rotation speed.

Description

Table for cryogenic refrigerator and cryogenic refrigerator controller

[0001] The present invention relates to a cryogenic refrigerator and a table for a controller of a cryogenic refrigerator.

[0002] Cryogenic refrigerators are used to cool various objects, such as superconducting equipment, measuring instruments, and samples, that are used in cryogenic environments.

[0003] Japanese Patent Publication No. 2004-3792

[0004] To cool an object using a cryogenic refrigerator, the refrigerator must first be started and cooled from its initial temperature (such as room temperature) to the desired cryogenic temperature. This is also known as the cryogenic refrigerator's cool-down. Since the cool-down is merely preparation for starting the cooling of the object, it is desirable that the time required is as short as possible.

[0005] One exemplary objective of a certain aspect of the present invention is to shorten the cool-down time of a cryogenic refrigerator.

[0006] According to one aspect of the present invention, the cryogenic refrigerator comprises an expander motor, a first cooling stage, and a second cooling stage, and an expander configured to cool the first and second cooling stages by operating the expander motor; a first temperature sensor for measuring the first temperature of the first cooling stage, a second temperature sensor for measuring the second temperature of the second cooling stage; and a controller configured to acquire the measured first temperature from the first temperature sensor, acquire the measured second temperature from the second temperature sensor, determine the rotation speed of the expander motor from the measured first and second temperatures according to a predetermined relationship between the first temperature, the second temperature, and the rotation speed of the expander motor, and operate the expander motor based on the determined rotation speed.

[0007] According to an aspect of the present invention, a table is provided for causing a controller of a cryogenic refrigerator to function so as to determine the rotational speed of an expander motor from a measured first temperature of a first cooling stage and a measured second temperature of a second cooling stage. The table is configured to associate a first temperature condition with a first rotational speed of the expander motor and a second temperature condition with a second rotational speed of the expander motor. The first temperature condition indicates that the measured first temperature is in a first temperature range and the measured second temperature is in a first temperature band. The second temperature condition indicates that the measured first temperature is in a second temperature range lower than the first temperature range and the measured second temperature is in a second temperature band lower than the first temperature band. The second rotational speed is lower than the first rotational speed.

[0008] In addition, any combination of the above components or components and expressions of the present invention that are mutually replaced between a method, an apparatus, a system, etc. are also effective as aspects of the present invention.

[0009] According to the present invention, the cool-down time of a cryogenic refrigerator can be shortened.

[0010] It is a diagram schematically showing a cryogenic refrigerator according to an embodiment. It is a diagram schematically showing a cryogenic refrigerator according to an embodiment. It is a flowchart for explaining a control method of a cryogenic refrigerator according to an embodiment. It is a diagram schematically showing an example of a temperature rate table according to an embodiment. It is a flowchart for explaining a control method of a cryogenic refrigerator according to an embodiment.

[0011] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. The same or equivalent components, members, and processes in the description and drawings are denoted by the same reference numerals, and duplicate descriptions are omitted as appropriate. The scales and shapes of the respective parts shown are set for convenience in order to facilitate the explanation, and are not to be construed in a limited manner unless otherwise specified. The embodiments are examples and do not limit the scope of the present invention in any way. Not all features and combinations thereof described in the embodiments are necessarily essential to the invention.

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

[0013] The cryogenic refrigerator 10 includes a compressor 12 and an expander 14. The compressor 12 and the expander 14 constitute a refrigeration cycle of the cryogenic refrigerator 10, whereby the cryogenic refrigerator 10 can provide desired cryogenic cooling. The expander 14 is also referred to as a cold head. Further, the cryogenic refrigerator 10 includes a control device 100 that controls the cryogenic refrigerator 10.

[0014] The compressor 12 is configured to recover the working gas of the cryogenic refrigerator 10 from the expander 14, boost the recovered working gas, and supply the working gas to the expander 14 again. The working gas is also referred to as a refrigerant gas and is typically helium gas, but other suitable gases may be used.

[0015] In general, both the pressure of the working gas supplied from the compressor 12 to the expander 14 and the pressure of the working gas recovered from the expander 14 to the compressor 12 are much higher than the atmospheric pressure, and can be referred to as the first high pressure and the second high pressure, respectively. For convenience of explanation, the first high pressure and the second high pressure are also simply referred to as high pressure and low pressure, respectively. Typically, the high pressure is, for example, 2 to 3 MPa. The low pressure is, for example, 0.5 to 1.5 MPa, and is, for example, about 0.8 MPa.

[0016] The expander 14 includes an expander cylinder 16 and a displacer assembly 18. The expander cylinder 16 guides the linear reciprocating motion of the displacer assembly 18 and forms an expansion chamber (32, 34) of the working gas between the expander cylinder 16 and the displacer assembly 18. Further, the expander 14 includes a pressure switching valve 40 that determines the intake start timing of the working gas into the expansion chamber and the exhaust start timing of the working gas from the expansion chamber.

[0017] In this book, for convenience, in order to explain the positional relationships between the components of the cryogenic refrigerator 10, the side of the displacer closer to the top dead center in its axial reciprocating motion will be referred to as "upper," and the side closer to the bottom dead center 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 operation of the cryogenic refrigerator 10, a temperature gradient occurs in which the temperature decreases from the upper axial direction downwards, so the upper side can also be called the high-temperature side and the lower side the low-temperature side.

[0018] The expander 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.

[0019] The displacer assembly 18 comprises a first displacer 18a and a second displacer 18b connected to each other, which move together as a single unit. 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.

[0020] 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.

[0021] As shown in Figure 2, the first displacer 18a houses the first cooler 26. The first cooler 26 is formed by filling the cylindrical body of the first displacer 18a with a wire mesh, such as copper, or other suitable first coolant. The upper and lower lids of the first displacer 18a may be provided as separate components from the body of the first displacer 18a, and the upper and lower lids of the first displacer 18a may be fixed to the body by appropriate means such as fastening or welding, thereby housing the first coolant in the first displacer 18a.

[0022] Similarly, the second displacer 18b houses the second regenerator 28. The second regenerator 28 contains a non-magnetic regenerative material such as bismuth, HoCu, etc. inside the cylindrical body of the second displacer 18b. ２ It is formed by filling it with a magnetic thermal storage material such as, or other suitable second thermal storage material. The second thermal storage material may be formed into granules. The upper and lower lids of the second displacer 18b may be provided as separate components from the main body of the second displacer 18b, and the upper and lower lids of the second displacer 18b may be fixed to the main body by suitable means such as fastening or welding, thereby housing the second thermal storage material in the second displacer 18b.

[0023] The displacer assembly 18 has an upper chamber 30, a first expansion chamber 32, and a second expansion chamber 34 formed inside the expander cylinder 16. For heat exchange with the desired object or medium to be cooled by the cryogenic refrigerator 10, the expander 14 includes a first cooling stage 33 and a second cooling stage 35. The upper chamber 30 is formed between the upper lid of the first displacer 18a and the upper part of the first cylinder 16a. The first expansion chamber 32 is formed between the lower lid of the first displacer 18a and the first cooling stage 33. The second expansion chamber 34 is formed between the lower lid of the second displacer 18b and the second cooling stage 35. The first cooling stage 33 is fixed to the lower part 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 part of the second cylinder 16b so as to surround the second expansion chamber 34.

[0024] The first regenerator 26 is connected to the upper chamber 30 through an operating gas passage 36a formed in the upper lid of the first displacer 18a, and to the first expansion chamber 32 through an operating gas passage 36b formed in the lower lid of the first displacer 18a. The second regenerator 28 is connected to the first regenerator 26 through an operating gas passage 36c formed from the lower lid of the first displacer 18a to the upper lid of the second displacer 18b. The second regenerator 28 is also connected to the second expansion chamber 34 through an operating gas passage 36d formed in the lower lid of the second displacer 18b.

[0025] A first seal 38a and a second seal 38b may be provided to ensure that the working gas flow between the first expansion chamber 32, the second expansion chamber 34 and the upper chamber 30 is directed to the first regenerator 26 and the second regenerator 28, rather than to the clearance between the expander cylinder 16 and the displacer assembly 18. The first seal 38a may be mounted on the top cover of the first displacer 18a so as to be positioned between the first displacer 18a and the first cylinder 16a. The second seal 38b may be mounted on the top cover of the second displacer 18b so as to be positioned between the second displacer 18b and the second cylinder 16b.

[0026] As shown in Figure 1, the expander 14 includes an expander housing 20 that houses a pressure switching valve 40. The expander housing 20 is coupled to the expander cylinder 16, thereby forming an airtight container that houses the pressure switching valve 40 and the displacer assembly 18. The expander 14 also includes an expander motor 42 and a motion conversion mechanism 43. The expander motor 42 is mounted on the expander housing 20. The motion conversion mechanism 43, like the pressure switching valve 40, is housed in the expander housing 20.

[0027] 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 expander cylinder 16. The working gas discharge port of the compressor 12 is connected to the upper chamber 30 via the high-pressure valve 40a, and the working gas intake port 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).

[0028] The pressure switching valve 40 may take the form of a rotary valve. That is, the pressure switching valve 40 may be configured such that the high-pressure valve 40a and the low-pressure valve 40b are alternately opened and closed by the rotational sliding of the valve disc relative to the stationary valve body. In that case, the expander motor 42 may be connected to the pressure switching valve 40 so as to rotate the valve disc of the pressure switching valve 40. For example, the pressure switching valve 40 may be positioned such that the valve rotation axis is coaxial with the rotation axis of the expander motor 42.

[0029] Alternatively, the high-pressure valve 40a and the low-pressure valve 40b may each be individually controllable valves, in which case the pressure switching valve 40 does not need to be connected to the expander motor 42.

[0030] The expander 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 converts the rotational motion output by the expander motor 42 into linear reciprocating motion of the displacer drive shaft 44. The displacer drive shaft 44 extends from the motion conversion mechanism 43 into the upper chamber 30 and is fixed to the upper cover of the first displacer 18a. The rotation of the expander motor 42 is converted into axial reciprocating motion of the displacer drive shaft 44 by the motion conversion mechanism 43, and the displacer assembly 18 reciprocates linearly in the axial direction within the expander cylinder 16.

[0031] Incidentally, the cryogenic refrigerator 10 is powered by a power source 46 such as a commercial power source (three-phase AC power source). The power source 46 is connected to the compressor 12 and the inverter 48. The expander motor 42 is connected to the power source 46 via the inverter 48. The inverter 48 may be mounted on the control device 100, or it may constitute part of the control device 100. In the illustrated example, the compressor 12 and the inverter 48 are each connected to the power source 46 individually. Note that the expander motor 42 and the inverter 48 may also be connected to the power source 46 via the compressor 12, in which case the compressor 12 can be considered as the power source for the expander motor 42.

[0032] The expander motor 42 is, for example, a permanent magnet motor driven by three-phase alternating current. The operating frequency of the expander motor 42 (i.e., the rotational speed of the expander motor 42) is controlled by the inverter 48. As an example, the operating frequency of the expander motor 42 can vary in the range of 30 Hz to 150 Hz, preferably in the range of 40 Hz to 70 Hz. That is, the rotational speed of the expander motor 42 can vary in the range of 36 rpm to 180 rpm, preferably in the range of 48 rpm to 84 rpm.

[0033] Furthermore, the cryogenic refrigerator 10 may also be equipped with a current sensor 50, a first temperature sensor 52, and a second temperature sensor 54.

[0034] The current sensor 50 is configured to measure the current supplied from the inverter 48 to the expander motor 42. The current sensor 50 may also be configured to output a motor current signal S1 indicating the measured current to the control device 100. The current sensor 50 may be a contact-type or non-contact-type current sensor provided on the power supply wiring connecting the inverter 48 to the expander motor 42.

[0035] The first temperature sensor 52 is configured to measure the temperature of the first cooling stage 33 (hereinafter also referred to as the first temperature). The first temperature sensor 52 may be configured to output a first temperature signal T1 indicating the measured temperature of the first cooling stage 33 to the control device 100. The first temperature sensor 52 may be attached to the first cooling stage 33.

[0036] The second temperature sensor 54 is configured to measure the temperature of the second cooling stage 35 (hereinafter also referred to as the second temperature). The second temperature sensor 54 may be configured to output a second temperature signal T2 indicating the measured temperature of the second cooling stage 35 to the control device 100. The second temperature sensor 54 may be attached to the second cooling stage 35.

[0037] The control device 100 includes a controller 110 that controls the expander motor 42. As will be described in detail later, the controller 110 may be configured to acquire outputs from sensors provided in the cryogenic refrigerator 10 (for example, a motor current signal S1, a first temperature signal T1, and / or a second temperature signal T2), determine the rotational speed (for example, the operating frequency) of the expander motor 42 based on the acquired sensor outputs, and operate the expander motor 42 based on the determined rotational speed.

[0038] The controller 110 may be configured to generate a motor control command S2 representing the determined rotational speed of the expander motor 42 and output it to the inverter 48. The inverter 48 may be configured to operate the expander motor 42 at the determined rotational speed according to the motor control command S2.

[0039] In the illustrated example, the control device 100 is provided separately from the compressor 12 and the expander 14 and connected to them, but this is not limited to the case. The control device 100 may be mounted on the compressor 12. Alternatively, the control device 100 may be provided on the expander 14, such as by being mounted on the expander motor 42. Alternatively, the controller 110 may be mounted on the compressor 12 and the inverter 48 may be mounted on the expander 14, with the controller 110 and inverter 48 being installed separately.

[0040] The control device 100 is implemented in hardware form by components and circuits such as a computer's CPU and memory, and in software form by computer programs, etc., but in Figure 1, it is depicted as a functional block realized through the coordination of these components as appropriate. Those skilled in the art will understand that these functional blocks can be realized in various forms by combinations of hardware and software.

[0041] For example, the controller 110 can be implemented as a combination of a processor (hardware) such as a CPU (Central Processing Unit) or microcontroller, and a software program executed by the processor (hardware). Such a hardware processor may consist of a programmable logic device such as an FPGA (Field Programmable Gate Array), or a control circuit such as a programmable logic controller (PLC). The software program may be a computer program that causes the controller 110 to execute the control of the expander motor 42 according to the embodiment.

[0042] When the compressor 12 and expander motor 42 of the cryogenic refrigerator 10 are in operation, periodic volume fluctuations and synchronized pressure fluctuations of the working gas occur in the first expansion chamber 32 and the second expansion chamber 34. Typically, during the intake process, the low-pressure valve 40b closes and the high-pressure valve 40a opens, causing high-pressure working gas to flow from the compressor 12 through the high-pressure valve 40a into the upper chamber 30, where it is supplied to the first expansion chamber 32 through the first regenerator 26 and to the second expansion chamber 34 through the second regenerator 28. In this way, the first expansion chamber 32 and the second expansion chamber 34 are pressurized from low to high. At this time, the displacer assembly 18 is moved upward from bottom dead center to top dead center, increasing the volumes of the first expansion chamber 32 and the second expansion chamber 34. The intake process ends when the high-pressure valve 40a closes.

[0043] In the exhaust process, the high-pressure valve 40a closes and the low-pressure valve 40b opens, opening the high-pressure first expansion chamber 32 and second expansion chamber 34 to the low-pressure working gas inlet of the compressor 12. At this time, the working gas expands in the first and second expansion chambers 32 and 34, and as a result the working gas, which has become low-pressure, is discharged from the first and second expansion chambers 32 and 34 through the first and second regenerators 26 and 28 to the upper chamber 30. At this time, the displacer assembly 18 moves downward from top dead center to bottom dead center, reducing the volume of the first and second expansion chambers 32 and 34. The working gas is recovered from the expander 14 to the compressor 12 through the low-pressure valve 40b. When the low-pressure valve 40b closes, the exhaust process ends.

[0044] In this way, a refrigeration cycle such as a GM cycle is configured, and the first cooling stage 33 and the second cooling stage 35 are cooled to a desired cryogenic temperature. The first cooling stage 33 can be cooled to a first cooling temperature. The second cooling stage 35 can be cooled to a second cooling temperature lower than the first cooling temperature.

[0045] The cryogenic refrigerator 10 is capable of both steady-state operation and a cool-down operation that precedes the steady-state operation. Cool-down operation is an operating mode in which the cryogenic refrigerator 10 is rapidly cooled from ambient temperature (e.g., room temperature) to a cryogenic temperature when it is started up, while steady-state operation is an operating mode in which the cryogenic refrigerator 10 maintains the cryogenic temperature achieved by the cool-down operation. Cool-down operation is also called the initial cooling of the cryogenic refrigerator 10.

[0046] The cryogenic refrigerator 10 is cooled to a target cooling temperature by a cool-down operation, and in steady-state operation, it is maintained within the allowable cryogenic temperature range, including this target cooling temperature. The target cooling temperature varies depending on the application and settings of the cryogenic refrigerator 10. The target cooling temperature of the first cooling stage 33 may be selected from a range of approximately 20K to approximately 100K, for example, and the target cooling temperature of the second cooling stage 35 may be selected from a range of approximately 1K to approximately 20K. Typically, in cooling applications for superconducting devices, the target cooling temperature of the second cooling stage 35 is approximately 4.2K or less.

[0047] As mentioned at the beginning of this book, the cool-down operation is merely preparation for starting the cryogenic cooling of the object by the cryogenic refrigerator 10, so it is desirable that the time required for this operation be as short as possible. The cooling capacity of the cryogenic refrigerator 10 is proportional to the number of refrigeration cycles per unit time, which is typically equal to the rotational speed of the expander motor 42. Therefore, by increasing the rotational speed of the expander motor 42 during the cool-down operation, the cooling capacity of the cryogenic refrigerator 10 can be increased, and the time required for the cool-down operation can be shortened. The faster the expander motor 42 is operated, the shorter the time required for the cool-down operation can be.

[0048] Therefore, the controller 110 may be configured to increase the rotational speed of the expander motor 42 during cool-down operation compared to during steady-state operation. Increasing the rotational speed of the expander motor 42 in this way compared to steady-state operation, thereby increasing the cooling capacity of the cryogenic refrigerator 10, is also called accelerated cooling of the cryogenic refrigerator 10.

[0049] The density of the working gas in the cryogenic refrigerator 10, typically helium gas, increases as the temperature of the first cooling stage 33 and the second cooling stage 35 of the expander 14 decreases. As the density increases, the pressure loss caused by the driving of the displacer assembly 18 within the expander 14 increases, and as a result, the drive load torque of the expander motor 42 tends to increase. During cool-down operation, the first cooling stage 33 and the second cooling stage 35 are cooled from ambient temperature (e.g., room temperature) to the target cooling temperature, and the working gas density within the expander 14 also increases, which can lead to a significant increase in the drive load torque of the expander motor 42. High-speed operation of the expander motor 42 due to accelerated cooling can further increase the drive load torque of the expander motor 42. If the drive load torque increases and exceeds the rated torque of the expander motor 42, the expander motor 42 may malfunction. For example, the expander motor 42 may malfunction or stop.

[0050] Therefore, in this embodiment, the controller 110 is configured to acquire the measured first temperature from the first temperature sensor 52 and the measured second temperature from the second temperature sensor 54. Furthermore, the controller 110 is configured to determine the rotation speed of the expander motor 42 from the measured first temperature and the measured second temperature according to a predetermined relationship between the first temperature, the second temperature and the rotation speed of the expander motor 42, and to operate the expander motor 42 based on the determined rotation speed. This predetermined relationship may include a table (hereinafter also referred to as a temperature-speed table) 112 that causes the controller 110 to function in order to determine the rotation speed of the expander motor 42 from the measured first temperature and the measured second temperature.

[0051] The predetermined relationship between the first temperature, the second temperature, and the rotational speed of the expander motor 42 can be set to increase the rotational speed of the expander motor 42 during cool-down operation compared to steady-state operation. Furthermore, this predetermined relationship can be set to avoid an excessive increase in the drive load torque of the expander motor 42 due to the decrease in the temperature of the expander 14. The relationship can be set appropriately based on the designer's empirical knowledge or experiments and simulations conducted by the designer. In this way, the rotational speed of the expander motor 42 during cool-down operation is increased compared to steady-state operation, thereby increasing the cooling capacity of the cryogenic refrigerator 10 and shortening the time required for cool-down operation. In addition, an excessive increase in the drive load torque of the expander motor 42 during accelerated cooling during cool-down can be suppressed, reducing the risk of malfunction of the expander motor 42.

[0052] The temperature history during the cool-down operation of the first cooling stage 33 and the second cooling stage 35 varies depending on the operating environment of the cryogenic refrigerator 10. For example, the heavier the weight of the object to be cooled by the first cooling stage 33 (for example, in the cooling of a superconducting device, this could be a radiation shield surrounding a superconducting coil), the longer it takes to cool the first cooling stage 33. Similarly, the heavier the weight of the object to be cooled by the second cooling stage 35 (for example, in the cooling of a superconducting device, this could be a superconducting coil), the longer it takes to cool the second cooling stage 35. Furthermore, the temperature history during the cool-down operation is also affected by the weight ratio of the object to be cooled by the first cooling stage 33 and the object to be cooled by the second cooling stage 35. For example, if the weight of the object to be cooled by the second cooling stage 35 is greater than the weight of the object to be cooled by the first cooling stage 33, the first cooling stage 33 may be cooled to a lower temperature faster and at least temporarily during the cool-down operation than the second cooling stage 35.

[0053] According to the embodiment, the rotation speed of the expander motor 42 is determined from the measured first temperature and the measured second temperature according to a predetermined relationship between the first temperature, the second temperature, and the rotation speed of the expander motor 42. Therefore, the rotation speed of the expander motor 42 can be determined according to the temperature of the first cooling stage 33 and the second cooling stage 35 that changes during the cool-down operation. Thus, the time required for the cool-down operation can be shortened according to various operating environments of the cryogenic refrigerator 10, and the risk of malfunction of the expander motor 42 can be reduced.

[0054] The relationship may be predetermined such that the rotational speed of the expander motor 42 decreases as the first temperature decreases, and the rotational speed of the expander motor 42 decreases as the second temperature decreases. In this way, the rotational speed of the expander motor 42 can be reduced in response to the increase in the density of the working gas in the expander 14 due to the decrease in the temperature of the first cooling stage 33. Also, the rotational speed of the expander motor 42 can be reduced in response to the increase in the density of the working gas in the expander 14 due to the decrease in the temperature of the second cooling stage 35. This reduces the pressure loss in the expander 14 due to the increase in the density of the working gas, and maintains or suppresses the decrease in the cooling capacity of the cryogenic refrigerator 10. Therefore, the time required for the cool-down operation can be shortened. In addition, it is possible to suppress an excessive increase in the drive load torque of the expander motor 42 during accelerated cooling during cool-down, and reduce the risk of malfunction of the expander motor 42.

[0055] The relationship may be predetermined such that the rate of decrease in the rotational speed of the expander motor 42 increases as the first temperature decreases, and the rate of decrease in the rotational speed of the expander motor 42 increases as the second temperature decreases.

[0056] The density of the working gas in the cryogenic refrigerator 10, typically the density of helium gas, tends to increase more significantly as the temperature of the first cooling stage 33 and the second cooling stage 35 of the expander 14 decreases. That is, the rate of increase in the density of the working gas can be greater as the cooling temperature of the expander 14 decreases. For example, the density of helium gas increases significantly in the temperature range below 100K compared to the temperature range above 100K.

[0057] Therefore, by increasing the rate of decrease in the rotational speed of the expander motor 42 in accordance with the temperature decrease of the first cooling stage 33, it is possible to cope with the large increase in working gas density corresponding to the temperature decrease of the first cooling stage 33. Similarly, by increasing the rate of decrease in the rotational speed of the expander motor 42 in accordance with the temperature decrease of the second cooling stage 35, it is possible to cope with the large increase in working gas density corresponding to the temperature decrease of the second cooling stage 35. This shortens the time required for cool-down operation and reduces the risk of malfunction of the expander motor 42.

[0058] The relationship may be predetermined so that a safety margin is ensured in the load factor of the expander motor 42 when the first cooling stage 33 is at a measured first temperature, the second cooling stage 35 is at a measured second temperature, and the expander motor 42 is operated at a determined rotational speed. The load factor of the expander motor 42 refers to the ratio of the actual load of the expander motor 42 (e.g., drive load torque) to the rated load of the expander motor 42 (e.g., rated torque). The actual load of the expander motor 42 may be the maximum load in a single refrigeration cycle. The maximum load typically occurs during the exhaust process of the cryogenic refrigerator 10.

[0059] The relationship may be predetermined, for example, so that the load factor of the expander motor 42 is 70% or less. In this case, a safety margin of at least 30% will be ensured for the load factor of the expander motor 42. Alternatively, the relationship may be predetermined so that the load factor of the expander motor 42 is 60% or less (with a safety margin of at least 40%), or 80% or less (with a safety margin of at least 20%).

[0060] The relationship can be set as appropriate based on the designer's empirical knowledge or experiments and simulations conducted by the designer. For example, by operating the expander motor 42 at a certain rotational speed under specific temperature conditions in which the first cooling stage 33 is cooled to a first temperature and the second cooling stage 35 is cooled to a second temperature, the load factor of the expander motor 42 at that rotational speed can be obtained. By performing such experiments or simulations for various rotational speeds, the rotational speed of the expander motor 42 that achieves a predetermined load factor under those specific temperature conditions can be determined. By performing this for various temperature conditions, the rotational speed of the expander motor 42 that achieves a predetermined load factor under those temperature conditions can be determined.

[0061] Figure 3 is a flowchart illustrating a control method for the cryogenic refrigerator 10 according to an embodiment. This method is repeatedly executed at predetermined intervals by the controller 110 during the operation of the cryogenic refrigerator 10 in order to accelerate the cooling of the cryogenic refrigerator 10. The accelerated cooling of the cryogenic refrigerator 10 is performed at least during the cool-down operation.

[0062] In this method, first, the temperatures of the first cooling stage 33 and the second cooling stage 35 are measured (S10). The first temperature of the first cooling stage 33 is measured by the first temperature sensor 52, and the second temperature of the second cooling stage 35 is measured by the second temperature sensor 54. The controller 110 receives the first temperature signal T1 from the first temperature sensor 52 and obtains the first temperature of the first cooling stage 33 measured from the first temperature signal T1. The controller 110 receives the second temperature signal T2 from the second temperature sensor 54 and obtains the second temperature of the second cooling stage 35 measured from the second temperature signal T2.

[0063] Next, the rotational speed of the expander motor 42 is determined (S11). The controller 110 determines the rotational speed of the expander motor 42 from the measured first temperature and the measured second temperature, according to a predetermined relationship (for example, table 112) between the first temperature, the second temperature, and the rotational speed of the expander motor 42.

[0064] Then, the expander motor 42 is operated based on the determined rotational speed (S12). The controller 110 generates a motor control command S2 representing the determined rotational speed of the expander motor 42 and outputs it to the inverter 48. The inverter 48 operates the expander motor 42 at the determined rotational speed according to the motor control command S2. In this way, the expander motor 42 can be operated at an appropriate rotational speed according to the temperatures of the first cooling stage 33 and the second cooling stage 35.

[0065] In conjunction with the temperature measurement (S10), the controller 110 may compare the measured first temperature with the target cooling temperature of the first cooling stage 33, compare the measured second temperature with the target cooling temperature of the second cooling stage 35, and continue or terminate accelerated cooling based on the temperature comparison.

[0066] For example, if the measured first temperature is below the target cooling temperature of the first cooling stage 33, and the measured second temperature is below the target cooling temperature of the second cooling stage 35, the controller 110 may terminate accelerated cooling. In this case, the controller 110 may transition from cool-down operation to steady-state operation. In steady-state operation, the controller 110 may control the rotation speed of the expander motor 42 (for example, by feedback control such as PID control) based on the first temperature signal T1 (or second temperature signal T2) to minimize the deviation of the measured temperature from the target cooling temperature.

[0067] Otherwise, that is, if the measured first temperature exceeds the target cooling temperature of the first cooling stage 33, or if the measured second temperature exceeds the target cooling temperature of the second cooling stage 35, the controller 110 may continue accelerated cooling. In this case, the controller 110 may determine the rotational speed of the expander motor 42 as described above (S11), and operate the expander motor 42 based on the determined rotational speed (S12).

[0068] Alternatively, the method shown in Figure 3 may be carried out continuously not only during the cool-down operation but also during steady-state operation.

[0069] Figure 4 is a schematic diagram showing an example of a temperature rate table according to an embodiment. As shown in the figure, the table 112 can be represented by a coordinate plane with the first temperature of the first cooling stage 33 on the horizontal axis and the second temperature of the second cooling stage 35 on the vertical axis.

[0070] Both the first and second temperatures are the initial temperature T. ＩＮ It begins from there. The initial temperature may be, for example, the ambient temperature of the cryogenic refrigerator 10 (for example, room temperature). The first temperature is the lowest temperature T that the first cooling stage 33 can reach. １Ｌ And that's the end; the second temperature is the lowest temperature T that the second cooling stage 35 can reach. ２Ｌ And that's it. The lowest temperature T of the first cooling stage 33. １Ｌ The target cooling temperature of the first cooling stage 33 may be or a temperature somewhat lower than that. The minimum temperature T of the second cooling stage 35. ２ＬIt may be the target cooling temperature of the second cooling stage 35 or a temperature slightly lower than that.

[0071] In Table 112, the first temperature is divided into a plurality of temperature ranges. Also, the second temperature is divided into a plurality of temperature zones. The temperature conditions are determined by the combination of the temperature range and the temperature zone.

[0072] In this example, the first temperature is divided into five temperature ranges 114_1 to 5. The upper limit of the first temperature range 114_1 is the initial temperature T ＩＮ It is the temperature range with that as the upper limit. The second temperature range 114_2 is a temperature range lower than the first temperature range 114_1 adjacent to the first temperature range 114_1. Therefore, the lower limit of the first temperature range 114_1 corresponds to the upper limit of the second temperature range 114_2. Similarly, the third temperature range 114_3 is a temperature range lower than the second temperature range 114_2 adjacent to the second temperature range 114_2. The fourth temperature range 114_4 is a temperature range lower than the third temperature range 114_3 adjacent to the third temperature range 114_3. The fifth temperature range 114_5 is a temperature range lower than the fourth temperature range 114_4 adjacent to the fourth temperature range 114_4. The lower limit of the fifth temperature range 114_5 is the lowest temperature T of the first cooling stage 33 １Ｌ of it.

[0073] Also, the second temperature is divided into five temperature zones 116_1 to 5. The upper limit of the first temperature zone 116_1 is the initial temperature T ＩＮ It is the temperature range with that as the upper limit. The second temperature zone 116_2 is a temperature range lower than the first temperature zone 116_1 adjacent to the first temperature zone 116_1. Therefore, the lower limit of the first temperature zone 116_1 corresponds to the upper limit of the second temperature zone 116_2. Similarly, the third temperature zone 116_3 is a temperature range lower than the second temperature zone 116_2 adjacent to the second temperature zone 116_2. The fourth temperature zone 116_4 is a temperature range lower than the third temperature zone 116_3 adjacent to the third temperature zone 116_3. The fifth temperature zone 116_5 is a temperature range lower than the fourth temperature zone 116_4 adjacent to the fourth temperature zone 116_4. The lower limit of the fifth temperature zone 116_5 is the lowest temperature T of the second cooling stage 35 ２Ｌ of it.

[0074] The first temperature condition indicates that the measured first temperature is in the first temperature range 114_1 and the measured second temperature is in the first temperature zone 116_1. Similarly, the second temperature condition indicates that the measured first temperature is in the second temperature range 114_2 and the measured second temperature is in the second temperature zone 116_2. The third temperature condition indicates that the measured first temperature is in the third temperature range 114_3 and the measured second temperature is in the third temperature zone 116_3. The fourth temperature condition indicates that the measured first temperature is in the fourth temperature range 114_4 and the measured second temperature is in the fourth temperature zone 116_4. The fifth temperature condition indicates that the measured first temperature is in the fifth temperature range 114_5 and the measured second temperature is in the fifth temperature zone 116_5.

[0075] Table 112 is configured to associate multiple temperature conditions with the rotational speed of the expander motor 42. In this example, Table 112 associates the first temperature condition with the first value f of the rotational speed of the expander motor 42. １ Similarly, Table 112 corresponds to the second value f of the rotational speed of the expander motor 42 for the second, third, fourth, and fifth temperature conditions, respectively. ２ , the third value f ３ , the fourth value f ４ , the 5th action ５ Correspond to the value of the rotational speed f of the expander motor 42. １ ~f ５ For example, the rpm may be selected from a range of 60 rpm to 180 rpm.

[0076] In this example, the second value f represents the rotational speed of the expander motor 42. ２ The first value is f １ Lower than (f ２ <f １ Similarly, the third value f ３ The second value is f ２ Lower than (f ３ <f ２ ). The fourth value f ４ The third value is f ３ Lower than (f ４ <f ３ ). The fifth value f ５ The fourth value is f ４ Lower than (f ５<f ４ ). In this way, the table 112 may be predetermined to reduce the rotational speed of the expander motor 42 as the first temperature decreases. Alternatively, the table 112 may be predetermined to reduce the rotational speed of the expander motor 42 as the second temperature decreases.

[0077] Furthermore, the second value f of the rotational speed of the expander motor 42 ２ From the third value f ３ The rate of decrease in rotational speed is the first value f １ From the second value f ２ It may be greater than the rate of decrease in rotational speed. Similarly, the third value f ３ From the fourth value f ４ The rate of decrease in rotational speed is the second value f ２ From the third value f ３ The fourth value f may be greater than the rate of rotational speed reduction. ４ The fifth value f ５ The rate of decrease in rotational speed is the third value f ３ From the fourth value f ４ The rate of decrease in rotational speed may be greater than that of the first temperature. In this way, the table 112 may be predetermined to increase the rate of decrease in rotational speed of the expander motor 42 as the first temperature decreases. Alternatively, the table 112 may be predetermined to increase the rate of decrease in rotational speed of the expander motor 42 as the second temperature decreases.

[0078] Therefore, the controller 110 can identify the temperature conditions that include the measured first and second temperatures by referring to the table 112, and determine the rotational speed value of the expander motor 42 corresponding to the identified temperature conditions.

[0079] In the example of Table 112 shown in Figure 4, the determined rotational speed values ​​for the expander motor 42 are discrete. In this example, there are five temperature conditions and five corresponding rotational speed values ​​f １ ~f ５ This is because it is merely defined in Table 112.

[0080] If it is desirable to make the determined rotational speed of the expander motor 42 continuous, that is, to smoothly adjust the rotational speed of the expander motor 42 in accordance with the temperature change of the expander 14, then the temperature ranges for the first temperature and the temperature ranges for the second temperature may be narrowed to set more temperature conditions, and a rotational speed value may be associated with each of these temperature conditions.

[0081] Alternatively, the predetermined relationship between the first temperature, the second temperature, and the rotational speed of the expander motor 42 may include an equation relating temperature and rotational speed. In this way, the value of the rotational speed of the expander motor 42 that is determined can be made continuous.

[0082] For example, the rotational speed f is equal to the first temperature T. １ and the second temperature T ２ It may include a linear combination of, for example, f = f ＩＮ - (A / T １ +B / T ２ ) may also be the case. Here, f ＩＮ This is the initial value of the rotation speed (for example, the first value f in the table 112 above). １ ) and A and B are constants. In this way, the first temperature T １ As the temperature decreases, the rotational speed f of the expander motor 42 is reduced, and the second temperature T ２ As the temperature decreases, the rotational speed f of the expander motor 42 can be reduced.

[0083] Instead of using the rotational speed value of the expander motor 42, the rotational speed value f at the reference temperature (e.g., initial temperature) is used. ０ The rotational speed f at a certain temperature T. Ｔ ratio f Ｔ / f ０ This may be used. For example, Table 112 compares multiple temperature conditions f Ｔ / f ０ It may be configured to correspond to a specific value.

[0084] Figure 5 is a flowchart illustrating a control method for the cryogenic refrigerator 10 according to an embodiment. Figure 5 shows a modified version of the control method shown in Figure 3. In the control method shown in Figure 5, similar to the method in Figure 3, the temperatures of the first cooling stage 33 and the second cooling stage 35 are measured (S10), the rotational speed of the expander motor 42 is determined (S11), and the expander motor 42 is operated based on the determined rotational speed (S12). In S11, as described above, the rotational speed of the expander motor 42 is determined from the measured first temperature and the measured second temperature according to a predetermined relationship (for example, table 112) between the first temperature, the second temperature, and the rotational speed of the expander motor 42.

[0085] However, in the control method shown in Figure 5, the rotational speed of the expander motor 42, which is determined based on the temperatures of the first cooling stage 33 and the second cooling stage 35, may be corrected as needed. Therefore, the controller 110 may be configured to acquire parameters associated with the load torque of the expander motor 42, correct the rotational speed determined based on the acquired parameters, and operate the expander motor 42 based on the corrected rotational speed.

[0086] As shown in Figure 5, the rotational speed correction of the expander motor 42 is performed between S11 and S12. First, a parameter associated with the load torque of the expander motor 42 is acquired (S20). This parameter may be, for example, the current supplied from the inverter 48 to the expander motor 42 (hereinafter also referred to as the motor current). Therefore, the controller 110 may receive the motor current signal S1 from the current sensor 50 and acquire the motor current based on the motor current signal S1. Alternatively, the inverter 48 may be configured to measure the motor current, and the controller 110 may acquire the motor current from the inverter 48. Since the motor current has a known relationship with the load torque of the expander motor 42, the drive load torque of the expander motor 42 can be determined by monitoring the motor current.

[0087] The tolerance range for the parameters is set (S21). The controller 110 may set the tolerance range for the parameters based on the rotational speed of the expander motor 42 determined in S11. In other words, the tolerance range may be set to different ranges depending on the determined rotational speed of the expander motor 42. The tolerance range may be predetermined so as to ensure a safety margin in the load factor of the expander motor 42 when the expander motor 42 is operated so that the parameters fall within the tolerance range.

[0088] The tolerance range may have an upper limit and a lower limit, and the upper and lower limits may be set to different values ​​depending on the determined rotational speed of the expander motor 42. For example, when motor current is used as a parameter, the load torque of the expander motor 42 tends to increase as the rotational speed of the expander motor 42 increases. Therefore, the upper and lower limits of the tolerance range of the parameter may be larger as the rotational speed of the expander motor 42 increases. For example, if the rotational speed of the expander motor 42 is a first value f １ The upper and lower limits of the allowable range in this case are, respectively, the rotational speed of the expander motor 42, which is the second value f. ２ The upper and lower limits of the allowable range may be greater than the upper and lower limits when this is the case. Similarly, the rotational speed of the expander motor 42 may be greater than the second value f ２ The upper and lower limits of the allowable range in this case are the rotational speed of the expander motor 42, which is the third value f. ３ It may be greater than the upper and lower limits of the acceptable range when this is the case.

[0089] In this embodiment, since the rotational speed of the expander motor 42 is related to the temperature conditions (for example, by table 112), the allowable range of the parameters may be set according to the temperature conditions.

[0090] The acquired parameter is compared with the set tolerance range (S22). The controller 110 may determine whether the acquired parameter falls within the set tolerance range. If the acquired parameter is less than or equal to the upper limit of the tolerance range and greater than or equal to the lower limit, the controller 110 determines that the parameter is within the tolerance range. If the acquired parameter is greater than the upper limit of the tolerance range, the controller 110 determines that the parameter is outside the tolerance range. If the acquired parameter is less than the lower limit of the tolerance range, the controller 110 determines that the parameter is outside the tolerance range.

[0091] Based on the comparison in S22, it is determined whether or not to correct the rotational speed of the inflator motor 42 that was determined in S11 (S23). If the parameter is outside the allowable range, the controller 110 corrects the rotational speed of the inflator motor 42 determined in S11 by a predetermined amount if the parameter is greater than the upper limit of the allowable range. If the parameter is less than the lower limit of the allowable range, the controller 110 corrects the rotational speed of the inflator motor 42 determined in S11 by a predetermined amount if the parameter is less than the lower limit of the allowable range. On the other hand, if the parameter is within the allowable range, the controller 110 does not correct the rotational speed of the inflator motor 42 determined in S11. That is, the controller 110 uses the rotational speed of the inflator motor 42 determined in S11 as is.

[0092] Then, the inflator motor 42 is operated (S12). If the rotational speed of the inflator motor 42 is corrected in S23, the controller 110 generates a motor control command S2 representing the corrected rotational speed of the inflator motor 42 and outputs it to the inverter 48. If the rotational speed of the inflator motor 42 is not corrected in S23, the controller 110 generates a motor control command S2 representing the rotational speed of the inflator motor 42 determined in S11 and outputs it to the inverter 48. The inverter 48 operates the inflator motor 42 at the determined rotational speed according to the motor control command S2.

[0093] If the parameter is greater than the upper limit of the allowable range, the drive load torque of the expander motor 42 may be too high. In this case, the rotational speed of the expander motor 42 is reduced, and therefore the drive load torque of the expander motor 42 is also reduced. Consequently, the risk of the drive load torque exceeding the rated torque of the expander motor 42 and causing malfunction of the expander motor 42 is also reduced. Conversely, if the parameter is smaller than the lower limit of the allowable range, the rotational speed of the expander motor 42 is increased. In this way, the cooling capacity of the cryogenic refrigerator 10 can be increased, thereby shortening the time required for cool-down operation.

[0094] The drive load torque of the expander motor 42 may be used as a parameter associated with the load torque of the expander motor 42. In this case, the controller 110 may calculate the drive load torque of the expander motor 42 from the motor current. Alternatively, the expander motor 42 may be equipped with a torque sensor, and the controller 110 may obtain the drive load torque of the expander motor 42 based on the output from the torque sensor.

[0095] 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.

[0096] In the above-described embodiment, the case in which the cryogenic refrigerator 10 is a two-stage GM refrigerator is described as an example. However, the cryogenic refrigerator 10 according to the embodiment may be any other type of two-stage or multi-stage cryogenic refrigerator equipped with an expander motor 42 for operating the expander 14 (for example, for driving the displacer assembly 18 in the expander 14).

[0097] The present invention can be used in the field of cryogenic refrigerators and tables for cryogenic refrigerator controllers.

[0098] 10 Cryogenic refrigerator, 14 Expander, 33 First cooling stage, 35 Second cooling stage, 42 Expander motor, 52 First temperature sensor, 54 Second temperature sensor, 110 Controller, 112 Table.

Claims

1. A cryogenic refrigerator comprising: an expander motor, a first cooling stage, and a second cooling stage, configured to cool the first and second cooling stages by operating the expander motor; a first temperature sensor for measuring the first temperature of the first cooling stage; a second temperature sensor for measuring the second temperature of the second cooling stage; and a controller configured to acquire the measured first temperature from the first temperature sensor, acquire the measured second temperature from the second temperature sensor, determine the rotation speed of the expander motor from the measured first and second temperatures according to a predetermined relationship between the first temperature, the second temperature, and the rotation speed of the expander motor, and operate the expander motor based on the determined rotation speed.

2. The cryogenic refrigerator according to claim 1, characterized in that the relationship is predetermined such that the rotational speed of the expander motor decreases as the first temperature decreases, and the rotational speed of the expander motor decreases as the second temperature decreases.

3. The cryogenic refrigerator according to claim 2, characterized in that the relationship is predetermined such that the rate of decrease in the rotational speed of the expander motor increases as the first temperature decreases, and the rate of decrease in the rotational speed of the expander motor increases as the second temperature decreases.

4. The cryogenic refrigerator according to any one of claims 1 to 3, wherein the relationship includes a table for causing the controller to function to determine the rotational speed of the expander motor from the measured first temperature and the measured second temperature, the table is configured to associate the first temperature condition with the first rotational speed of the expander motor and the second temperature condition with the second rotational speed of the expander motor, the first temperature condition represents that the measured first temperature is in a first temperature range and the measured second temperature is in a first temperature zone, the second temperature condition represents that the measured first temperature is in a second temperature range lower than the first temperature range and the measured second temperature is in a second temperature zone lower than the first temperature zone, and the second rotational speed is lower than the first rotational speed.

5. The cryogenic refrigerator according to claim 4, wherein the table is further configured to associate a third temperature condition with a third rotational speed of the expander motor, the third temperature condition represents that the measured first temperature is in a third temperature range lower than the second temperature range, the measured second temperature is in a third temperature range lower than the second temperature range, the third rotational speed is lower than the second rotational speed, and the rate of decrease in rotational speed from the second rotational speed to the third rotational speed is greater than the rate of decrease in rotational speed from the first rotational speed to the second rotational speed.

6. The cryogenic refrigerator according to any one of claims 1 to 3, characterized in that the relationship is predetermined such that a safety margin is ensured in the load factor of the expander motor when the first cooling stage is at the measured first temperature, the second cooling stage is at the measured second temperature, and the expander motor is operated at the determined rotational speed.

7. The cryogenic refrigerator according to any one of claims 1 to 3, characterized in that the controller is configured to acquire parameters associated with the load torque of the expander motor, correct the determined rotational speed based on the acquired parameters, and operate the expander motor based on the corrected rotational speed.

8. The cryogenic refrigerator according to claim 7, characterized in that the controller is configured to set an allowable range for the parameters based on the determined rotational speed, compare the acquired parameters with the set allowable range, and decide whether or not to correct the determined rotational speed based on the comparison.

9. A table for causing a controller of a cryogenic refrigerator to function in such a way that it determines the rotational speed of an expander motor from a first temperature measured in a first cooling stage and a second temperature measured in a second cooling stage, wherein the table is configured to associate a first temperature condition with a first rotational speed of the expander motor and a second temperature condition with a second rotational speed of the expander motor, wherein the first temperature condition represents that the measured first temperature is in a first temperature range and the measured second temperature is in a first temperature zone, wherein the second temperature condition represents that the measured first temperature is in a second temperature range lower than the first temperature range and the measured second temperature is in a second temperature zone lower than the first temperature zone, and the second rotational speed is lower than the first rotational speed.

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