Cryogenic refrigerator and method for operating the same

Abstract

This cryogenic freezer (10) comprises: an expander (14) that comprises an expansion motor (40), comprising a motor rotating shaft (40a), a displacer (18) that, by moving reciprocally in a linear manner due to rotation of the motor rotating shaft (40a), causes the volume of an expansion space of a working gas to vary, and a rotary valve (42) that controls ventilation of the working gas into the expansion space by rotating due to the rotation of the motor rotating shaft (40a); a pressure sensor that measures the pressure of the working gas and outputs a measurement signal indicating the measured pressure; and a controller (100) that receives the measurement signal, detects characteristic points that appear cyclically in the measured pressure during operation of the cryogenic freezer (10), and acquires a motor drive waveform indicating a command rotation speed for the motor rotating shaft (40a) that is determined so as to vary during a single rotation of the motor rotating shaft (40a).

Description

[Technical Field]

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

[0002] Some cryogenic refrigerators, such as the Gifford-McMahon (GM) refrigerator, have a reciprocating displacer to periodically change the volume of the expansion space for the working gas. A refrigeration cycle is achieved in a cryogenic refrigerator by varying the pressure in the expansion space in proper synchronization with the periodic volume fluctuations of the expansion space. One typical method for driving the reciprocating motion of the displacer is to mechanically connect a drive source such as an electric motor to the displacer, and reciprocate the displacer by the rotation output by the motor. One rotation of the motor corresponds to one reciprocation of the displacer, i.e., one refrigeration cycle. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-101917 Summary of the Invention [Problem to be solved by the invention]

[0004] To improve the refrigeration capacity of a cryogenic refrigerator, attempts have been made to optimally control the movement speed of the displacer according to its position by changing the rotational speed of the motor that drives the displacer within one rotation. To achieve this, a typical approach is to detect the position of the displacer, i.e., the rotational position of the motor, and then control the rotational speed of the motor and, ultimately, the movement speed of the displacer according to this detected position. However, this approach requires the addition of a position detector to the motor. Such a position detector is relatively expensive and can increase the manufacturing cost of the cryogenic refrigerator. Furthermore, the addition of a position detector can also cause problems, such as an increase in the size of the motor.

[0005] One exemplary objective of certain aspects of the present invention is to enable optimal operation of a cryogenic refrigerator without position sensing. [Means for solving the problem]

[0006] According to one aspect of the present invention, a cryogenic refrigerator includes an expander including: an expander motor having a motor rotating shaft; a displacer connected to the motor rotating shaft so as to move linearly back and forth with rotation of the motor rotating shaft, the displacer changing the volume of the expansion space for the working gas with the reciprocating movement; and a rotary valve connected to the motor rotating shaft so as to rotate with rotation of the motor rotating shaft, the rotary valve controlling the intake and exhaust of the working gas to the expansion space; a pressure sensor that measures the pressure of the working gas and outputs a measurement signal indicative of the measured pressure; and a controller that receives the measurement signal, detects characteristic points that periodically appear in the measured pressure during operation of the cryogenic refrigerator, acquires a motor drive waveform that indicates a command rotation speed of the motor rotating shaft that is set to change within one rotation of the motor rotating shaft, and outputs the motor drive waveform in synchronization with the characteristic points that periodically appear.

[0007] According to one aspect of the present invention, there is provided a method for operating a cryogenic refrigerator. The cryogenic refrigerator includes an expander motor having a motor rotating shaft, a displacer connected to the motor rotating shaft so as to move linearly back and forth with rotation of the motor rotating shaft, the displacer changing the volume of an expansion space for a working gas as the displacer moves back and forth, and a rotary valve connected to the motor rotating shaft so as to rotate with rotation of the motor rotating shaft, the rotary valve controlling intake and exhaust of the working gas to and from the expansion space. The method includes measuring the pressure of the working gas, detecting characteristic points that periodically appear in the measured pressure during operation of the cryogenic refrigerator, acquiring a motor drive waveform that indicates a command rotation speed of the motor rotating shaft, the command rotation speed being determined to change within one rotation of the motor rotating shaft, and outputting the motor drive waveform in synchronization with the characteristic points.

[0008] According to one aspect of the present invention, a cryogenic refrigerator includes an expander motor having a motor rotating shaft, a displacer connected to the motor rotating shaft so as to move linearly back and forth with rotation of the motor rotating shaft, and changing the volume of the expansion space of the working gas by the reciprocating motion, the displacer passing through top dead center, where the volume of the expansion space is maximum, within a first angle range in one rotation of the motor rotating shaft, and passing through the midpoint between top dead center and bottom dead center, where the volume of the expansion space is minimum, within a second angle range following the first angle range in one rotation of the motor rotating shaft, and a controller that operates the expander motor so as to reduce the rotational speed of the motor rotating shaft in the second angle range compared to the first angle range.

[0009] Any combination of the above components or mutual substitution of the components or expressions of the present invention between methods, devices, systems, etc. are also valid aspects of the present invention. [Effects of the Invention]

[0010] According to the present invention, it is possible to achieve optimal operation of a cryogenic refrigerator without position detection. [Brief explanation of the drawings]

[0011] [Figure 1]1 is a diagram schematically illustrating a cryogenic refrigerator according to an embodiment. [Figure 2] 1 is a diagram schematically illustrating a cryogenic refrigerator according to an embodiment. [Figure 3] FIG. 2 is an exploded perspective view schematically illustrating a drive mechanism for an expander of a cryogenic refrigerator according to an embodiment. [Figure 4] 5A and 5B are diagrams illustrating an example of changes in the command rotation speed of the expander motor indicated by the first motor drive waveform in the embodiment. [Figure 5] 6 is a diagram showing an example of a change in the command rotation speed of the expander motor indicated by the second motor drive waveform in the embodiment. FIG. [Figure 6] FIG. 10 is a diagram showing an example of characteristic points that periodically appear in the measured pressure of a cryogenic refrigerator according to the embodiment. [Figure 7] 4 is a flowchart illustrating a method for controlling a cryogenic refrigerator according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the description and drawings, identical or equivalent components, parts, and processes are designated by the same reference numerals, and redundant explanations will be omitted as appropriate. The scale and shape of each part shown in the drawings are set for convenience to facilitate explanation, and should not be interpreted as limiting unless otherwise specified. The embodiments are merely examples and do not limit the scope of the present invention in any way. All features and combinations thereof described in the embodiments are not necessarily essential to the invention.

[0013] 1 and 2 are diagrams that schematically show a cryogenic refrigerator 10 according to an embodiment. As an example, the cryogenic refrigerator 10 is a two-stage Gifford-McMahon (GM) refrigerator. FIG. 1 schematically shows a compressor 12 and an expander 14 that constitute the cryogenic refrigerator 10 together with a controller 100, and FIG. 2 shows the internal structure of the expander 14 of the cryogenic refrigerator 10. The controller 100 is provided to control the cryogenic refrigerator 10.

[0014] The compressor 12 is configured to recover the working gas of the cryogenic refrigerator 10 from the expander 14, increase the pressure of the recovered working gas, and supply the working gas to the expander 14 again. The compressor 12 and the expander 14 form the refrigeration cycle of the cryogenic refrigerator 10, thereby enabling the cryogenic refrigerator 10 to provide the desired cryogenic cooling. The expander 14 is also referred to as a cold head. The working gas, also referred to as a refrigerant gas, is typically helium gas, although other suitable gases may be used. For ease of understanding, the flow direction of the working gas is indicated by arrows in FIG. 1.

[0015] Generally, 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 both significantly higher than atmospheric pressure and can be referred to as the first high pressure and the second high pressure, respectively. For ease of explanation, the first high pressure and the second high pressure are also simply referred to as the high pressure and the 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, e.g., approximately 0.8 MPa. For ease of understanding, the flow direction of the working gas is indicated by an arrow.

[0016] The expander 14 includes a refrigerator cylinder 16, a displacer assembly (hereinafter sometimes simply referred to as a displacer) 18, and a refrigerator housing 20. The refrigerator cylinder 16 guides the linear reciprocating motion of the displacer 18, and forms expansion chambers (32, 34) between the refrigerator cylinder 16 and the displacer 18 as expansion spaces for the working gas. The refrigerator cylinder 16 and the refrigerator housing 20 are joined to each other, thereby forming the housing of the expander 14, i.e., an airtight container that houses the displacer 18.

[0017] In this document, for convenience in explaining the positional relationships between the components of the cryocooler 10, the side closer to the top dead center of the displacer's axial reciprocating motion will be referred to as "top" and the side closer to the bottom dead center as "bottom." 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 cryocooler 10, a temperature gradient occurs in which the temperature decreases from top to bottom in the axial direction, so the top side can also be referred to as the high-temperature side and the bottom side as the low-temperature side.

[0018] The refrigerator 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, and the second cylinder 16b has 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 includes a first displacer 18a and a second displacer 18b that are connected to each other and move together. The first displacer 18a and the second displacer 18b are, for example, cylindrical members, and the second displacer 18b has 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 accommodated in the first cylinder 16a, and the second displacer 18b is accommodated in the second cylinder 16b. The first displacer 18a is capable of reciprocating in the axial direction along the first cylinder 16a, and the second displacer 18b is capable of reciprocating in the axial direction along the second cylinder 16b.

[0021] 2, the first displacer 18a accommodates the first regenerator 26. The first regenerator 26 is formed by filling a cylindrical main body of the first displacer 18a with a wire mesh such as copper or other suitable first regenerator material. The upper and lower lids of the first displacer 18a may be provided as separate members from the main body of the first displacer 18a, and the upper and lower lids of the first displacer 18a may be fixed to the main body by suitable means such as fastening or welding, thereby accommodating the first regenerator material in the first displacer 18a.

[0022] Similarly, the second displacer 18b accommodates the second regenerator 28. The second regenerator 28 is formed by filling the cylindrical main body of the second displacer 18b with a non-magnetic regenerator material such as bismuth, a magnetic regenerator material such as HoCu2, or another suitable second regenerator material. The second regenerator material may be formed in a granular form. The upper and lower covers of the second displacer 18b may be provided as separate members from the main body of the second displacer 18b, and the upper and lower covers of the second displacer 18b may be fixed to the main body by suitable means such as fastening or welding, thereby accommodating the second regenerator material in the second displacer 18b.

[0023] The displacer 18 defines a room-temperature chamber 30, a first expansion chamber 32, and a second expansion chamber 34 inside the refrigerator cylinder 16. The expander 14 includes a first cooling stage 33 and a second cooling stage 35 for heat exchange with the desired object or medium to be cooled by the cryogenic refrigerator 10. The room-temperature chamber 30 is defined between the upper cover of the first displacer 18a and the top of the first cylinder 16a. The first expansion chamber 32 is defined between the lower cover of the first displacer 18a and the first cooling stage 33. The second expansion chamber 34 is defined between the lower cover 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 to surround the first expansion chamber 32, and the second cooling stage 35 is fixed to the lower part of the second cylinder 16b to surround the second expansion chamber 34.

[0024] The first regenerator 26 is connected to the room-temperature chamber 30 through a working gas passage 36a formed in the upper lid of the first displacer 18a, and is connected to the first expansion chamber 32 through a working 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 a working 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 a working 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 so that the flow of working gas between the first expansion chamber 32, the second expansion chamber 34 and the room temperature chamber 30 is guided to the first regenerator 26 and the second regenerator 28, rather than through the clearance between the refrigerator cylinder 16 and the displacer 18. The first seal 38a may be attached to an upper 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 attached to an upper cover of the second displacer 18b so as to be positioned between the second displacer 18b and the second cylinder 16b.

[0026] The expander 14 also includes an expander motor 40 and a rotary valve 42. The expander motor 40 is provided in the expander 14 as a drive source for the displacer 18 and the rotary valve 42. As shown in FIG. 3 , the expander motor 40 includes a motor shaft 40a that outputs the rotation of the expander motor 40. The expander motor 40 is an electric motor that can variably control the rotation speed of the motor shaft 40a, and may be, for example, a permanent magnet motor driven by three-phase AC or a stepping motor. The expander motor 40 is attached to the refrigerator housing 20. The rotary valve 42 is housed in the refrigerator housing 20.

[0027] The displacer 18 is connected to the motor shaft 40a so that it moves linearly back and forth as the motor shaft 40a rotates, and the reciprocating movement changes the volume of the expansion space for the working gas. One rotation of the motor shaft 40a causes the displacer 18 to move back and forth once.

[0028] If one rotation of the motor rotating shaft 40a is divided into four angular ranges, the displacer 18 passes through top dead center in the first angular range, passes the midpoint between top dead center and bottom dead center in the second angular range following the first angular range, passes bottom dead center in the third angular range following the second angular range, and passes the midpoint in the fourth angular range following the third angular range. Following the fourth angular range, the rotation of the motor rotating shaft 40a enters the first angular range. If the rotation angle of the motor rotating shaft 40a when the displacer 18 is at top dead center is represented as 0 degrees, the first angular range, second angular range, third angular range, and fourth angular range include 0 degrees, 90 degrees, 180 degrees, and 270 degrees, respectively.

[0029] As shown in FIG. 2, the rotary valve 42 functionally includes a high-pressure valve 42a and a low-pressure valve 42b and is configured to generate periodic pressure fluctuations within the refrigerator cylinder 16. The rotary valve 42 determines the start and end timings of the intake of working gas into the expansion space using the high-pressure valve 42a, and the start and end timings of the exhaust of working gas from the expansion space using the low-pressure valve 42b. The working gas discharge port of the compressor 12 is connected to the room-temperature chamber 30 via the high-pressure valve 42a, and the working gas inlet port of the compressor 12 is connected to the room-temperature chamber 30 via the low-pressure valve 42b. The high-pressure valve 42a and the low-pressure valve 42b are configured to selectively and alternately open and close (i.e., one is open when the other is closed). Various known configurations can be used for the working gas flow paths formed in the rotary valve 42 to form the high-pressure valve 42a and the low-pressure valve 42b, and will not be described in detail here.

[0030] The rotary valve 42 is connected to the motor rotary shaft 40a so as to rotate with the rotation of the motor rotary shaft 40a, and controls the intake and exhaust of working gas to the expansion space. One rotation of the motor rotary shaft 40a results in one rotation of the rotary valve 42. In designing the rotary valve 42, the intake start timing is determined relative to the bottom dead center of the displacer 18, and the exhaust start timing is determined relative to the top dead center of the displacer 18. Alternatively, the intake end timing and the exhaust end timing may be determined relative to the top dead center and bottom dead center of the displacer 18, respectively.

[0031] The intake start timing is set between the midpoint between the top dead center and the bottom dead center and the bottom dead center during the downward movement of the displacer 18, or near the bottom dead center. For example, the intake start timing may be set between 120 degrees (or 150 degrees) and 180 degrees in terms of the rotation angle of the motor rotary shaft 40a. The intake end timing is set prior to the exhaust start timing during the upward movement of the displacer 18.

[0032] The exhaust start timing is set between the midpoint between the top dead center and the bottom dead center and the top dead center during the upward movement of the displacer 18, or near the top dead center. For example, the exhaust start timing may be set between 300 degrees (or 330 degrees) and 360 degrees in terms of the rotation angle of the motor rotary shaft 40a. The exhaust end timing is set prior to the intake start timing during the downward movement of the displacer 18.

[0033] The phase of the refrigeration cycle is determined by the combination of the position of the displacer 18 (i.e., the volume of the expansion space) and the rotation angle of the rotary valve 42 (i.e., the pressure in the expansion space). One rotation of the expander motor 40 realizes one refrigeration cycle, and the rotation angle of the motor rotary shaft 40a can be associated with the phase of the refrigeration cycle.

[0034] The expander 14 may also include a temperature sensor 48 that measures the temperature of the second cooling stage 35 (and / or the first cooling stage 33) and outputs a measured temperature signal indicative of the measured temperature.

[0035] 3 is an exploded perspective view schematically illustrating the drive mechanism of the expander 14 of the cryogenic refrigerator 10 according to the embodiment. The motor shaft 40a is connected to the displacer 18 via a motion conversion mechanism 43 and a displacer drive shaft 44. In this embodiment, the motion conversion mechanism 43 is a Scotch yoke mechanism that converts the rotation of the motor shaft 40a into linear motion.

[0036] 3, the motion conversion mechanism 43 includes a crank 45 and a scotch yoke 46. The crank 45 is fixed to the motor rotary shaft 40a. The crank 45 has a crank pin 45a at a position eccentric to the position at which the motor rotary shaft 40a is fixed. The crank pin 45a extends parallel to the motor rotary shaft 40a on the opposite side of the crank 45 from the motor rotary shaft 40a.

[0037] The Scotch yoke 46 includes a yoke plate 46a and a roller bearing 46b. An upper rod 47 is fixed to the upper center of the yoke plate 46a so as to extend upward, and a displacer drive shaft 44 is fixed to the lower center of the yoke plate 46a so as to extend downward. A horizontally elongated window 46a1 is formed in the center of the yoke plate 46a, extending in a direction perpendicular to the direction in which the upper rod 47 and the displacer drive shaft 44 extend (i.e., the axial direction), and a roller bearing 46b is rotatably disposed within the horizontally elongated window 46a1. An engagement hole 46b1 that engages with the crank pin 45a is formed in the center of the roller bearing 46b, and the crank pin 45a passes through the engagement hole 46b1. The upper rod 47 and the displacer drive shaft 44 may each be slidably supported in the refrigerator housing 20 shown in FIG. 1.

[0038] The displacer drive shaft 44 connects the motion conversion mechanism 43 to the displacer 18 (specifically, the first displacer 18a as shown in FIG. 2). One end of the displacer drive shaft 44 is fixed to the yoke plate 46a, and the other end is fixed to the displacer 18. As shown in FIG. 1, the motion conversion mechanism 43 is housed in the refrigerator housing 20 and extends from the refrigerator housing 20 into the refrigerator cylinder 16. As shown in FIG. 2, the displacer drive shaft 44 passes through the room-temperature chamber 30 and is fixed to the top cover of the first displacer 18a.

[0039] The motor rotary shaft 40a is also connected to the rotary valve 42. The rotary valve 42 is disposed on the opposite side of the motion converting mechanism 43 from the expander motor 40, with its rotary shaft being coaxial with the motor rotary shaft 40a. The rotary valve 42 may include a valve body fixed to the refrigerator housing 20 and stationary, and a valve disc supported by the refrigerator housing 20 so as to be rotatable and slidable relative to the valve body, and may be configured so that the high-pressure valve 42a and the low-pressure valve 42b are alternately opened and closed by the rotation and sliding of the valve disc relative to the valve body. A crank pin 45a passing through the engagement hole 46b1 may be fixed to the valve disc, whereby the motor rotary shaft 40a rotates the valve disc relative to the valve body.

[0040] When the motor rotary shaft 40a rotates, the roller bearing 46b engaged with the crank pin 45a moves back and forth along the horizontally elongated window 46a1 while rotating in a circular motion, causing the Scotch yoke 46 and displacer drive shaft 44 to move back and forth in the axial direction. Therefore, the rotation of the expander motor 40 causes the displacer 18 to move back and forth in the axial direction within the refrigerator cylinder 16. The rotation of the expander motor 40 also rotates the rotary valve 42.

[0041] Referring again to FIG. 1 , the compressor 12 includes a high-pressure gas outlet 50, a low-pressure gas inlet 51, a high-pressure flow path 52, a low-pressure flow path 53, a first pressure sensor 54, a second pressure sensor 55, a compressor body 56, and a compressor housing 58. The high-pressure gas outlet 50 is installed in the compressor housing 58 as a working gas discharge port of the compressor 12, and the low-pressure gas inlet 51 is installed in the compressor housing 58 as a working gas suction port of the compressor 12. The high-pressure flow path 52 connects the discharge port of the compressor body 56 to the high-pressure gas outlet 50, and the low-pressure flow path 53 connects the low-pressure gas inlet 51 to the suction port of the compressor body 56. The compressor housing 58 houses the high-pressure flow path 52, the low-pressure flow path 53, the first pressure sensor 54, the second pressure sensor 55, and the compressor body 56. The compressor 12 is also referred to as a compressor unit.

[0042] The compressor body 56 is configured to compress the working gas drawn in through its intake port and discharge the compressed gas from its discharge port. The compressor body 56 may be, for example, a scroll type, rotary type, or other type of pump that pressurizes the working gas. In this embodiment, the compressor body 56 is configured to discharge a fixed, constant flow rate of the working gas. Alternatively, the compressor body 56 may be configured to vary the flow rate of the working gas that it discharges. The compressor body 56 may also be referred to as a compression capsule.

[0043] The first pressure sensor 54 is disposed in the high-pressure flow path 52 to measure the pressure of the working gas flowing through the high-pressure flow path 52. The first pressure sensor 54 is configured to output a first measured pressure signal P1 representing the measured pressure. The second pressure sensor 55 is disposed in the low-pressure flow path 53 to measure the pressure of the working gas flowing through the low-pressure flow path 53. The second pressure sensor 55 is configured to output a second measured pressure signal P2 representing the measured pressure. Therefore, the first pressure sensor 54 and the second pressure sensor 55 can also be referred to as the high-pressure sensor and the low-pressure sensor, respectively. In this specification, either the first pressure sensor 54 or the second pressure sensor 55, or both, may be collectively referred to as simply the "pressure sensor."

[0044] The compressor 12 may have various other components. For example, the high-pressure flow path 52 may be provided with an oil separator, adsorber, etc. The low-pressure flow path 53 may be provided with a storage tank or other components. The compressor 12 may also be provided with an oil circulation system that cools the compressor body 56 with oil, a cooling system that cools the oil, etc. To prevent excessive pressure in the high-pressure flow path 52, a bypass flow path may be provided to release pressure from the high-pressure flow path 52 to the low-pressure flow path 53.

[0045] The cryogenic refrigerator 10 also includes a gas line 62 that circulates working gas between the compressor 12 and the expander 14. The gas line 62 includes a high-pressure line 63 that connects the compressor 12 to the expander 14 so as to supply high-pressure working gas from the compressor 12 to the expander 14, and a low-pressure line 64 that connects the compressor 12 to the expander 14 so as to recover low-pressure working gas from the expander 14 to the compressor 12. The refrigerator housing 20 of the expander 14 is provided with a high-pressure gas inlet 22 and a low-pressure gas outlet 24. The high-pressure gas inlet 22 is connected to the high-pressure gas outlet 50 by a high-pressure pipe 65, and the low-pressure gas outlet 24 is connected to the low-pressure gas inlet 51 by a low-pressure pipe 66. The high-pressure line 63 consists of the high-pressure pipe 65 and the high-pressure flow path 52, and the low-pressure line 64 consists of the low-pressure pipe 66 and the low-pressure flow path 53. The rotary valve 42 operates to alternately connect the high pressure line 63 and the low pressure line 64 to the expansion space within the expander 14 .

[0046] It should be noted that pressure measurement units such as the first pressure sensor 54 and the second pressure sensor 55 do not necessarily need to be provided in the compressor 12, and may be provided at any location where pressure can be measured, such as the gas line 62 or the expander 14. For example, the first pressure sensor 54 may be provided at any location in the high-pressure line 63, and the second pressure sensor 55 may be provided at any location in the low-pressure line 64.

[0047] 1, the cryogenic refrigerator 10 is provided with a controller 100 that controls the expander motor 40. The controller 100 is electrically connected to a first pressure sensor 54 and a second pressure sensor 55 to acquire a first measured pressure signal P1 and a second measured pressure signal P2. The controller 100 is also electrically connected to a temperature sensor 48 to acquire a measured temperature signal from the temperature sensor 48.

[0048] As will be described in detail later, the controller 100 receives at least one of the first measured pressure signal P1 and the second measured pressure signal P2, detects characteristic points that periodically appear in the measured pressure while the cryogenic refrigerator 10 is operating, acquires a motor drive waveform S that indicates a command rotation speed of the motor rotating shaft 40a, and outputs the motor drive waveform S in synchronization with the periodically appearing characteristic points. The command rotation speed of the motor rotating shaft 40a is set to change during one rotation of the motor rotating shaft 40a.

[0049] As an exemplary configuration, controller 100 includes a processing unit (processor) 110, a storage unit (memory) 112, and a motor driving unit (motor driver) 120. Processing unit 110 receives at least one of first measured pressure signal P1 and second measured pressure signal P2, detects characteristic points that periodically appear in the measured pressure while cryogenic refrigerator 10 is operating, obtains motor driving waveform S from storage unit 112, and outputs motor driving waveform S to motor driving unit 120 in synchronization with the periodically appearing characteristic points. Storage unit 112 stores motor driving waveform S.

[0050] The motor drive unit 120 is supplied with power from an external power source 80 such as a commercial power source (three-phase AC power source). The expander motor 40 may be connected to the external power source 80 via the compressor 12, for example, and may be supplied with power from the external power source 80. In this case, the compressor 12 may be considered as the power source for the expander motor 40.

[0051] The motor drive unit 120 generates a motor drive current from the external power supply 80 in accordance with the received motor drive waveform S and supplies this to the expander motor 40. In this way, the expander motor 40 rotates the motor rotary shaft 40a at the command rotation speed indicated by the motor drive waveform S. The motor rotary shaft 40a rotates while increasing or decreasing the rotation speed within one rotation in accordance with the motor drive waveform S. The rotation of the expander motor 40 causes the cryogenic refrigerator 10 to generate a refrigeration cycle and provide cryogenic cooling.

[0052] The motor drive unit 120 may be equipped with an inverter that controls the operating frequency of the expander motor 40. The expander motor 40 can rotate the motor rotary shaft 40a at a rotation speed determined by the output frequency of the inverter. As an example, the output frequency of the inverter (i.e., the operating frequency of the expander motor 40) can vary within a range of 30 Hz to 100 Hz, or within a range of 40 Hz to 70 Hz. The cryogenic refrigerator 10 can change the frequency of the refrigeration cycle (number of cycles per unit time) by controlling the operating frequency of the expander motor 40.

[0053] In the illustrated example, the controller 100 is provided separately from the compressor 12 and the expander 14 and connected to them, but this is not limited thereto. The controller 100 may be mounted on the compressor 12. The controller 100 may be mounted on the expander 14, for example, by being mounted on the expander motor 40. Alternatively, the controller 100 may be divided into multiple parts and provided in the cryogenic refrigerator 10, for example, with part of the controller 100 (e.g., the processing unit 110 and the memory unit 112) mounted on the compressor 12 and another part of the controller 100 (e.g., the motor drive unit 120) mounted on the expander 14.

[0054] The controller 100 is realized as a hardware configuration by elements and circuits such as a computer CPU and memory, and as a software configuration by a computer program, etc., but is depicted as functional blocks realized by the cooperation of these elements in Figure 1. Those skilled in the art will understand that these functional blocks can be realized in various ways by combining hardware and software.

[0055] When the compressor 12 and the expander motor 40 are operating, the cryogenic refrigerator 10 generates periodic volume fluctuations and synchronized pressure fluctuations of the working gas in the first expansion chamber 32 and the second expansion chamber 34. Typically, during the intake stroke, the low-pressure valve 42b closes and the high-pressure valve 42a opens, causing high-pressure working gas to flow from the compressor 12 through the high-pressure valve 42a into the room-temperature chamber 30, be supplied to the first expansion chamber 32 through the first regenerator 26, and be supplied to the second expansion chamber 34 through the second regenerator 28. In this way, the pressures of the first expansion chamber 32 and the second expansion chamber 34 are increased from low to high. At this time, the displacer 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 stroke ends when the high-pressure valve 42a closes.

[0056] During the exhaust stroke, the high-pressure valve 42a closes and the low-pressure valve 42b opens, opening the high-pressure first and second expansion chambers 32 and 34 to the low-pressure working gas inlet of the compressor 12. This causes the working gas to expand in the first and second expansion chambers 32 and 34, resulting in the low-pressure working gas being discharged from the first and second expansion chambers 32 and 34 through the first and second regenerators 26 and 28 to the room-temperature chamber 30. At this time, the displacer 18 is moved downward from top dead center to bottom dead center, reducing the volumes 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 42b. When the low-pressure valve 42b closes, the exhaust stroke ends.

[0057] The working gas recovered from the expander 14 to the compressor 12 passes through the low-pressure line 64, i.e., from the low-pressure gas outlet 24 of the expander 14 through the low-pressure piping 66 to enter the low-pressure gas inlet 51 of the compressor 12, and then passes through the low-pressure flow path 53 to return to the compressor main body 56. The working gas is compressed and pressurized by the compressor main body 56. The working gas supplied from the compressor 12 to the expander 14 passes through the high-pressure line 63, i.e., from the compressor main body 56 through the high-pressure flow path 52 to exit the high-pressure gas outlet 50 of the compressor 12, and then passes through the high-pressure piping 65 and the high-pressure gas inlet 22 of the expander 14 to be supplied to the expander 14.

[0058] 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 in the range of, for example, about 20 K to about 40 K. The second cooling stage 35 can be cooled to a second cooling temperature (for example, about 1 K to about 4 K) that is lower than the first cooling temperature.

[0059] The cryogenic refrigerator 10 can perform initial cooling and steady-state operation following the initial cooling. Initial cooling is an operating mode of the expander 14 in which the cryogenic refrigerator 10 is rapidly cooled from an initial temperature to a cryogenic temperature upon startup. Steady-state operation is an operating mode of the expander 14 in which the expander 14 maintains the cryogenically cooled state achieved by the initial cooling. The initial temperature may be ambient temperature (e.g., room temperature). The expander 14 is cooled to a standard cooling temperature (e.g., a first cooling temperature or a second cooling temperature) during the initial cooling, and during steady-state operation, the expander 14 is maintained within an allowable cryogenic temperature range that includes the standard cooling temperature. The standard cooling temperature varies depending on the application and settings of the cryogenic refrigerator 10, but is typically approximately 4.2 K or less when used to cool superconducting devices. In other cooling applications, the standard cooling temperature may be, for example, approximately 10 K to 20 K, or even 10 K or less. As described above, the initial cooling can also be referred to as a cool-down.

[0060] The switch from initial cooling to steady operation may be controlled by the controller 100. For example, the controller 100 may compare the measured temperature of the second cooling stage 35 (and / or the first cooling stage 33) with a preset switching temperature based on the measured temperature signal from the temperature sensor 48, and perform initial cooling if the measured temperature is higher than the switching temperature, or may transition from initial cooling to steady operation if the measured temperature is equal to or lower than the switching temperature. The switching temperature may be the above-mentioned standard cooling temperature, or may be a temperature somewhat higher than the standard cooling temperature (for example, a temperature higher than the standard cooling temperature by within 5 K or within 10 K).

[0061] Generally, in steady-state cooling, the cryogenic refrigerator 10 only needs to provide a refrigeration capacity that balances with the heat load, and therefore does not often require a very high refrigeration capacity. On the other hand, since the initial cooling is merely a preparation for starting to cool the object by the cryogenic refrigerator 10, it is desirable that the required time be as short as possible. Therefore, the refrigeration capacity of the cryogenic refrigerator 10 during initial cooling may be increased by increasing the rotation speed of the expander motor 40 compared to steady-state operation.

[0062] For example, the controller 100 may determine the current operation mode of the cryogenic refrigerator 10, and when the cryogenic refrigerator 10 is in initial cooling, control the motor drive unit 120 so that the operation frequency of the expander motor 40 is higher than when the cryogenic refrigerator 10 is in steady operation. The operation frequency of the expander motor 40 in initial cooling may be higher than the input frequency (e.g., 50 Hz or 60 Hz) from the external power supply 80 to the motor drive unit 120, and the operation frequency of the expander motor 40 in steady operation may be equal to or lower than this input frequency.

[0063] However, while driving the expander motor 40 at high speed in this way can increase the refrigeration capacity, it also increases the load on the expander motor 40 due to driving the displacer 18 (and rotary valve 42). Therefore, in the initial cooling, it is desirable to achieve both high cooling capacity (i.e., shortened cooling time) and reduced load on the expander motor 40. On the other hand, from the perspective of improving energy conservation, in steady operation, it is desirable to maximize the PV work obtained in one refrigeration cycle to achieve efficient cooling. Thus, the optimal operating method for the cryogenic refrigerator 10 varies depending on the situation.

[0064] Therefore, in this embodiment, the processing unit 110 of the controller 100 may receive at least one of the first measured pressure signal P1 and the second measured pressure signal P2, detect characteristic points that periodically appear in the measured pressure during operation of the cryogenic refrigerator 10, select one motor drive waveform S from the plurality of motor drive waveforms, synchronize the selected motor drive waveform S with the periodically appearing characteristic points, and output the selected motor drive waveform S to the motor driver 120. The plurality of motor drive waveforms each indicate a command rotation speed of the motor rotating shaft 40a that is determined to change in a different manner from each other during one rotation of the motor rotating shaft 40a. The memory unit 112 stores these motor drive waveforms. The plurality of motor drive waveforms may include a first motor drive waveform and a second motor drive waveform, as described below. The processing unit 110 may determine the current operating mode of the cryogenic refrigerator 10, and select the first motor drive waveform if the cryogenic refrigerator 10 is in initial cooling mode, and select the second motor drive waveform if the cryogenic refrigerator 10 is in steady operation.

[0065] FIG. 4 is a diagram showing an example of changes in the command rotation speed of the expander motor 40 indicated by the first motor drive waveform according to the embodiment. FIG. 5 is a diagram showing an example of changes in the command rotation speed of the expander motor 40 indicated by the second motor drive waveform according to the embodiment. FIGS. 4 and 5 illustrate changes in the command rotation speed during one rotation of the motor rotating shaft 40a. The vertical axis indicates the value of the command rotation speed, and the horizontal axis indicates the rotation angle of the motor rotating shaft 40a. As described above, the rotation angle of the motor rotating shaft 40a when the displacer 18 is at top dead center is represented as 0 degrees.

[0066] The displacer 18 passes through top dead center in a first angle range A1, passes through the midpoint between top dead center and bottom dead center in a second angle range A2 that follows the first angle range A1, passes through bottom dead center in a third angle range A3 that follows the second angle range A2, and passes through the midpoint in a fourth angle range A4 that follows the third angle range A3. The first angle range A1, second angle range A2, third angle range A3, and fourth angle range A4 include 0 degrees, 90 degrees, 180 degrees, and 270 degrees, respectively. The intake start timing of the rotary valve 42 is set in the third angle range A3, and the exhaust start timing is set in the first angle range A1.

[0067] When the expander motor 40 is connected to the displacer 18 via a motion conversion mechanism 43, mechanical analysis has shown that the load on the expander motor 40 increases when the rotation angle of the motor rotating shaft 40a is around 90 degrees and 270 degrees.

[0068] 4, the first motor drive waveform is determined so that the command rotation speed of the motor rotating shaft 40a decreases in the second angle range A2 compared to the first angle range A1. Also, the command rotation speed of the motor rotating shaft 40a increases in the third angle range A3 compared to the second angle range A2. Similarly, the first motor drive waveform is determined so that the command rotation speed of the motor rotating shaft 40a decreases in the fourth angle range A4 compared to the third angle range A3, and increases in the first angle range A1 compared to the fourth angle range A4.

[0069] In this way, the command rotation speed of the motor rotating shaft 40a is reduced in the second angle range A2 including 90 degrees and the fourth angle range A4 including 270 degrees, so the rotation of the motor rotating shaft 40a is decelerated in these angle ranges. This reduces the load on the expander motor 40 in these angle ranges. At the same time, the motor rotating shaft 40a can be rotated at a relatively high speed in other rotation angles (i.e., the first angle range A1 and the third angle range A3). This increases the frequency of the refrigeration cycle and enhances the refrigeration capacity of the cryocooler 10 compared to when the motor rotating shaft 40a is rotated at a constant, low rotation speed. This achieves both a shorter cooling time due to high cooling capacity and a reduced load on the expander motor 40. Therefore, the first motor drive waveform is suitable for driving the expander motor 40 during initial cooling.

[0070] It has also been found that the PV work obtained in one refrigeration cycle can be increased by reducing the moving speed of the displacer 18 from the exhaust start timing to the top dead center of the displacer 18. This effect is more pronounced when the cryogenic refrigerator 10 is cooled to a cryogenic temperature, such as during steady-state operation.

[0071] Therefore, unlike the first motor drive waveform, the second motor drive waveform is determined so that the command rotation speed of the motor rotating shaft 40a increases in the second angle range A2 compared to the first angle range A1, as shown in Figure 5. The command rotation speed of the motor rotating shaft 40a increases further in the third angle range A3 compared to the second angle range A2. Furthermore, the second motor drive waveform is determined so that the command rotation speed of the motor rotating shaft 40a decreases in the fourth angle range A4 compared to the third angle range A3, and further decreases in the first angle range A1 compared to the fourth angle range A4.

[0072] In this way, the command rotation speed of the motor rotating shaft 40a is reduced in the first angle range A1 compared to other angle ranges. In the first angle range A1, the rotation speed of the motor rotating shaft 40a is suppressed, and the displacer 18 also rotates at a low speed. Since the first angle range A1 includes the exhaust start timing and the top dead center of the displacer 18, the PV work obtained in one refrigeration cycle can be increased. The second motor drive waveform is suitable for driving the expander motor 40 in steady operation.

[0073] The first and second motor drive waveforms described above are examples of possible motor drive waveforms, and various variations in the rotational speed of the motor shaft 40a during one rotation may be used in the embodiments. For example, in the first motor drive waveform of FIG. 4, the command rotational speeds are shown to be equal in the first angle range A1 and the third angle range A3, and equal in the second angle range A2 and the fourth angle range A4, but this is not limiting. The command rotational speeds may be different in the first angle range A1 and the third angle range A3, or may be different in the second angle range A2 and the fourth angle range A4. The command rotational speeds may be equal or different between the first and second motor drive waveforms.

[0074] In the examples of Figures 4 and 5, the widths of the first angle range and the third angle range are equal, and the widths of the second angle range and the fourth angle range are equal. The widths of the first angle range A1 and the third angle range A3 are greater than the widths of the second angle range A2 and the fourth angle range A4. Each angle range extends equally on both sides of a reference angle such as 0 degrees, 90 degrees, 180 degrees, or 270 degrees. However, setting the angle ranges in this manner is not required, and various other settings are also possible. For example, the widths of each angle range may all be equal or may differ from one another.

[0075] In the above example, one rotation of the motor rotating shaft 40a is divided into four angle ranges for convenience, but one rotation of the motor rotating shaft 40a may be divided into fewer or more angle ranges, and a command rotation speed may be determined for each of those angle ranges. The angle ranges may be set to the same or different values ​​for the first motor drive waveform and the second motor drive waveform.

[0076] The first motor drive waveform may be used in an operating condition other than initial cooling, and the second motor drive waveform may be used in an operating condition other than steady operation.

[0077] FIG. 6 is a diagram showing an example of characteristic points that periodically appear in the measured pressure of the cryogenic refrigerator 10 according to the embodiment. FIG. 6 illustrates the measured pressures of the high-pressure line 63 and the low-pressure line 64 in one refrigeration cycle. The vertical axis represents the measured pressure, and the horizontal axis represents the rotation angle of the motor rotating shaft 40a. In this example, the top dead center of the displacer 18 corresponds to the rotation angle B.

[0078] As described above, in this embodiment, a feature point that periodically appears in the measured pressure during operation of the cryocooler 10 is detected. This feature point periodically appears in the measured pressure of the pressure sensor as a fluctuation in the working gas pressure associated with an intake stroke (e.g., intake start timing) or an exhaust stroke (e.g., exhaust start timing) of the cryocooler 10. The periodically appearing feature point is a feature point that periodically appears in the measured pressure of the high-pressure line 63 due to the intake of working gas into the expansion space via the rotary valve 42, or a feature point that periodically appears in the measured pressure of the low-pressure line 64 due to the exhaust of working gas from the expansion space via the rotary valve 42. The feature point may be a sign change in the rate of change of the measured pressure. This sign change may be a change from a positive value to zero or a change from a negative value to zero.

[0079] Because the high-pressure line 63 is connected to the discharge port of the compressor main body 56, the pressure in the high-pressure line 63 is essentially equal to the discharge pressure of the compressor 12. However, when the high-pressure line 63 is connected to the expansion space of the expander 14 via the rotary valve 42 during the intake stroke of the cryogenic refrigerator 10, working gas flows from the high-pressure line 63 to the expander 14, causing a slight transient drop in the pressure in the high-pressure line 63. For example, characteristic point C1 shown in FIG. 6 indicates this pressure drop. Characteristic point C1 can be considered the timing when intake begins. Thereafter, the pressure in the high-pressure line 63 gradually recovers due to the supply of working gas from the compressor 12. Characteristic point C2 indicates the transition point from a decrease in the pressure in the high-pressure line 63 to an increase. Characteristic point C2 can be associated with the timing when intake begins. In this way, pressure fluctuations in the high-pressure line 63 can be detected as characteristic points.

[0080] Similarly, pressure fluctuations in the low-pressure line 64 can also be detected as a characteristic point. Because the low-pressure line 64 is connected to the suction port of the compressor body 56, the pressure in the low-pressure line 64 is essentially equal to the suction pressure of the compressor 12. However, when the low-pressure line 64 is connected to the expansion space of the expander 14 via the rotary valve 42 during the exhaust stroke of the cryogenic refrigerator 10, working gas flows from the expander 14 into the low-pressure line 64, causing a slight transient increase in the pressure in the low-pressure line 64. For example, characteristic point C3 shown in FIG. 6 indicates this pressure increase. Characteristic point C3 can be considered the timing when exhaust begins. Thereafter, the pressure in the low-pressure line 64 gradually decreases as the working gas is returned to the compressor 12. Characteristic point C4 indicates the transition point from an increase in the pressure in the low-pressure line 64 to a decrease. Characteristic point C4 can be associated with the timing when exhaust begins.

[0081] A pressure sensor may be provided in the expander 14, and the pressure in the expansion space may be measured by this pressure sensor. In this case, characteristic points that periodically appear in the measured pressure in the expansion space may be detected.

[0082] 7 is a flowchart illustrating a method for controlling the cryogenic refrigerator 10 according to the embodiment. This method is repeatedly executed by the controller 100 at predetermined intervals while the cryogenic refrigerator 10 is in operation.

[0083] 7, in this method, the pressure of the working gas is first measured (S10). For example, the pressure of the high-pressure line 63 is measured by the first pressure sensor 54. The first pressure sensor 54 outputs a first measured pressure signal P1 representing the measured pressure PH of the high-pressure line 63 to the controller 100. Alternatively, the pressure of the low-pressure line 64 may be measured by the second pressure sensor 55. The second pressure sensor 55 outputs a second measured pressure signal P2 representing the measured pressure PL of the low-pressure line 64 to the controller 100.

[0084] The processing unit 110 detects characteristic points that periodically appear in the measured pressure (S11). For example, the processing unit 110 receives the first measured pressure signal P1 and detects characteristic points that periodically appear in the measured pressure PH during operation of the cryogenic refrigerator 10. The detected characteristic points may represent the timing at which the rotary valve 42 starts suction. Alternatively, the processing unit 110 receives the second measured pressure signal P2 and detects characteristic points that periodically appear in the measured pressure PL during operation of the cryogenic refrigerator 10. In this case, the detected characteristic points may represent the timing at which the rotary valve 42 starts exhaust. The detected characteristic points represent the phases of the refrigeration cycle, and the phases of the refrigeration cycle correspond to the rotational angle of the expander motor 40, so the processing unit 110 can identify the motor rotational angle from the characteristic points.

[0085] The processing unit 110 acquires the motor drive waveform S from the storage unit 112 (S12). Here, the processing unit 110 may select one motor drive waveform S from a plurality of motor drive waveforms and acquire the selected motor drive waveform S from the storage unit 112. As described above, the plurality of motor drive waveforms may include a first motor drive waveform and a second motor drive waveform. The processing unit 110 may determine the current operation mode of the cryogenic refrigerator 10, and select the first motor drive waveform if the cryogenic refrigerator 10 is in initial cooling, or select the second motor drive waveform if the cryogenic refrigerator 10 is in steady operation.

[0086] The processing unit 110 synchronizes the acquired motor drive waveform S with the detected characteristic point and outputs it to the motor driving unit 120 (S13). The processing unit 110 outputs the motor drive waveform S to the motor driving unit 120 in a feedforward manner. The output motor drive waveform S corresponds to at least one refrigeration cycle starting from the point in time when the characteristic point is detected (for example, the detected point in time when intake or exhaust starts). Therefore, the motor driving unit 120 receives a command rotation speed for the motor rotating shaft 40a that drives the motor rotating shaft 40a to rotate at least one revolution starting from the point in time when the characteristic point is detected.

[0087] Processing unit 110 may detect a characteristic point in each refrigeration cycle, and each time a characteristic point is detected, output a motor drive waveform S corresponding to one refrigeration cycle to motor driving unit 120. Alternatively, detection every time is not essential, and processing unit 110 may detect a characteristic point each time a plurality of refrigeration cycles are performed, and output a motor drive waveform S corresponding to the plurality of refrigeration cycles to motor driving unit 120.

[0088] Even if a feature point is detected before the previously output motor drive waveform S ends, processing unit 110 may output a motor drive waveform S starting from the time point at which the feature point was detected to motor drive unit 120. Alternatively, processing unit 110 may regard a feature point detected before the motor drive waveform S ends as a false detection and ignore it.

[0089] In addition, if it is expected that a time delay will occur between the time when the characteristic point is detected and the time when the motor drive waveform is output, the processing unit 110 may output to the motor drive unit 120 a motor drive waveform S corresponding to at least one refrigeration cycle starting from a reference time point that takes this delay into account.

[0090] If the periodically appearing characteristic points are not detected due to a failure of the pressure sensor or the like, the controller 100 may acquire and output a (third) motor drive waveform determined to keep the command rotation speed of the motor rotating shaft 40a constant. In this case, the processing unit 110 may acquire this third motor drive waveform from the storage unit 112 and output it to the motor drive unit 120. In this way, even if the characteristic points are not detected, the supply of the command rotation speed is not interrupted, so that the expansion motor 40 can continue to rotate at a constant speed, and the cryogenic refrigerator 10 can continue to operate.

[0091] The motor drive unit 120 generates a motor drive current from the external power supply 80 in accordance with the received motor drive waveform S and supplies this to the expander motor 40. In this way, the expander motor 40 rotates the motor rotary shaft 40a at the command rotation speed indicated by the motor drive waveform S. In accordance with the motor drive waveform S, the motor rotary shaft 40a rotates while increasing or decreasing the rotation speed within one rotation (or at a constant rotation speed). The rotation of the expander motor 40 causes the cryogenic refrigerator 10 to generate a refrigeration cycle and provide cryogenic cooling.

[0092] According to the embodiment, the phase of the refrigeration cycle is identified based on the measured pressure, and a command rotation speed after the rotation angle of the expander motor 40 corresponding to the identified phase can be given to the expander motor 40 without impairing real-time performance.

[0093] Generally, a position detector such as an encoder is required to control the speed of the motor according to the rotation angle, but adding such a position detector to the cryogenic refrigerator 10 may cause inconveniences such as an increase in the manufacturing cost of the cryogenic refrigerator 10 and an increase in the size of the expander motor 40. However, since the cryogenic refrigerator 10 is often originally equipped with pressure sensors such as the first pressure sensor 54 and the second pressure sensor 55, such inconveniences do not arise.

[0094] Furthermore, in the embodiment, the expander motor 40 is controlled by feedforward control, not by real-time feedback control, which is advantageous in that the risk of occurrence of problems that may occur in control, such as oscillation, is reduced.

[0095] In the embodiment, the command rotation speed can be prepared in advance to realize optimal operation of the cryogenic refrigerator 10, so that the cryogenic refrigerator 10 can be optimally operated without position detection. For example, it is possible to provide optimal operation required for different operating conditions of the cryogenic refrigerator 10 (for example, initial cooling and steady operation) by switching according to the conditions.

[0096] Note that it is not essential to switch the command rotation speed of the expander motor 40 depending on the operating conditions. In one embodiment, the cryogenic refrigerator 10 may include an expander motor 40 having a motor rotating shaft 40a, a displacer 18 connected to the motor rotating shaft 40a so as to move linearly back and forth with rotation of the motor rotating shaft 40a, and changing the volume of the expansion space of the working gas by the reciprocating movement, the displacer 18 passing through top dead center, where the volume of the expansion space is maximum, in a first angular range during one rotation of the motor rotating shaft 40a, and passing through an intermediate point between the top dead center and bottom dead center, where the volume of the expansion space is minimum, in a second angular range following the first angular range during one rotation of the motor rotating shaft 40a, and a controller 100 that operates the expander motor 40 so as to reduce the rotation speed of the motor rotating shaft 40a in the second angular range compared to the first angular range. The controller 100 may operate the expander motor 40 so as to reduce the rotation speed of the motor rotary shaft 40a in the second angle range compared to the first angle range, at least during the initial cooling.

[0097] The controller 100 may operate the expander motor 40 based on the output of a detector that detects a parameter related to (or convertible into) the rotation angle of the motor rotary shaft 40a. Such a detector may be, for example, a pressure sensor provided in the cryogenic refrigerator 10, such as the first pressure sensor 54 or the second pressure sensor 55. Alternatively, the detector may be an encoder that detects the rotation angle of the expander motor 40. The detector may also be a position sensor that measures the position of the displacer 18. The pressure control mechanism of the cryogenic refrigerator 10 does not have to be a rotary valve, and the high-pressure valve 42a and the low-pressure valve 42b may each be a valve that can be controlled independently, and these valves do not have to be mechanically connected to the expander motor 40.

[0098] Although the above-described embodiment has been described with reference to an example in which the cryogenic refrigerator 10 is a two-stage GM refrigerator, the present invention is not limited to this. The cryogenic refrigerator 10 may be a single-stage or multi-stage GM refrigerator, or may be any other type of cryogenic refrigerator in which a displacer is driven by an expander motor.

[0099] The present invention has been described above based on examples. It will be understood by those skilled in the art that the present invention is not limited to the above-described embodiments, and that various design changes and modifications are possible, and that such modifications are also within the scope of the present invention. [Industrial Applicability]

[0100] The present invention can be used in the field of cryogenic refrigerators and methods for operating cryogenic refrigerators. [Explanation of symbols]

[0101] 10 cryogenic refrigerator, 12 compressor, 14 expander, 18 displacer, 40 expander motor, 40a motor rotating shaft, 42 rotary valve, 63 high-pressure line, 64 low-pressure line, 100 controller.

Claims

1. an expander including: an expander motor having a motor rotary shaft; a displacer connected to the motor rotary shaft so as to move linearly back and forth with rotation of the motor rotary shaft, the displacer changing the volume of an expansion space for a working gas with the reciprocating movement; and a rotary valve connected to the motor rotary shaft so as to rotate with rotation of the motor rotary shaft, the rotary valve controlling intake and exhaust of the working gas into the expansion space; a pressure sensor that measures the pressure of the working gas and outputs a measurement signal indicative of the measured pressure; receiving the measurement signal; detecting characteristic points that periodically appear in the measured pressure during operation of the cryogenic refrigerator; acquiring a motor drive waveform that indicates a command rotation speed of the motor rotation shaft that is determined to change during one rotation of the motor rotation shaft; a controller configured to output the motor drive waveform in synchronization with the periodically appearing characteristic points.

2. the controller is configured to select one motor drive waveform from a plurality of motor drive waveforms, and output the selected motor drive waveform in synchronization with the periodically occurring characteristic points; 2. The cryogenic refrigerator according to claim 1, wherein the plurality of motor drive waveforms each indicate a command rotation speed of the motor shaft that is determined to change in a different manner from one another within one rotation of the motor shaft.

3. the displacer is configured to pass through a top dead center, at which the volume of the expansion space is maximum, within a first angular range in one rotation of the motor rotary shaft, and to pass through an intermediate point between the top dead center and a bottom dead center, at which the volume of the expansion space is minimum, within a second angular range in one rotation of the motor rotary shaft, the second angular range being subsequent to the first angular range; 3. The cryogenic refrigerator of claim 2, wherein the plurality of motor drive waveforms include a first motor drive waveform and a second motor drive waveform, the first motor drive waveform being determined so that a command rotation speed of the motor rotating shaft decreases in the second angle range compared to the first angle range, and the second motor drive waveform being determined so that a command rotation speed of the motor rotating shaft increases in the second angle range compared to the first angle range.

4. 4. The cryogenic refrigerator of claim 3, wherein the controller is configured to select the first motor drive waveform during initial cooling, which cools the cryogenic refrigerator from an initial temperature, and to select the second motor drive waveform during steady operation, which maintains the cryogenic refrigerator after the initial cooling.

5. the displacer is configured to pass through a top dead center, at which the volume of the expansion space is maximum, within a first angular range in one rotation of the motor rotary shaft, and to pass through an intermediate point between the top dead center and a bottom dead center, at which the volume of the expansion space is minimum, within a second angular range in one rotation of the motor rotary shaft, the second angular range being subsequent to the first angular range; 2. The cryogenic refrigerator according to claim 1, wherein the motor drive waveform is determined so that a command rotation speed of the motor shaft is reduced in the second angle range compared to the first angle range.

6. 2. The cryogenic refrigerator according to claim 1, wherein the controller is configured to acquire and output a motor drive waveform determined to keep a command rotation speed of the motor rotation shaft constant when the periodically appearing characteristic points are not detected.

7. A compressor; a high-pressure line connecting the compressor to the expander so as to supply high-pressure working gas from the compressor to the expander; 7. The cryogenic refrigerator according to claim 1, wherein the pressure sensor measures the pressure of the working gas in the high-pressure line.

8. 8. The cryogenic refrigerator according to claim 7, wherein the periodically appearing characteristic point is a characteristic point that periodically appears in the measured pressure of the high-pressure line due to the intake of working gas into the expansion space via the rotary valve.

9. A compressor; a low-pressure line connecting the compressor to the expander so as to recover low-pressure working gas from the expander to the compressor; 7. The cryogenic refrigerator according to claim 1, wherein the pressure sensor measures the pressure of the working gas in the low-pressure line.

10. 10. The cryogenic refrigerator according to claim 9, wherein the periodically appearing characteristic point is a characteristic point that periodically appears in the measured pressure of the low-pressure line due to exhaust of the working gas from the expansion space through the rotary valve.

11. A method for operating a cryogenic refrigerator, the cryogenic refrigerator comprising an expander including: an expander motor having a motor rotating shaft; a displacer connected to the motor rotating shaft so as to move linearly back and forth with rotation of the motor rotating shaft, the displacer changing the volume of an expansion space for a working gas with the reciprocating movement; and a rotary valve connected to the motor rotating shaft so as to rotate with rotation of the motor rotating shaft, the rotary valve controlling intake and exhaust of the working gas into the expansion space, the method comprising: measuring the pressure of the working gas; detecting periodic characteristic points in the measured pressure during operation of the cryogenic refrigerator; acquiring a motor drive waveform that indicates a command rotation speed of the motor shaft, the command rotation speed being determined to change within one rotation of the motor shaft; outputting the motor drive waveform in synchronization with the periodically occurring feature points.

12. an expander motor having a motor rotating shaft; a displacer connected to the motor rotary shaft so as to move linearly back and forth with rotation of the motor rotary shaft, the displacer changing the volume of an expansion space of the working gas by the reciprocating movement, the displacer passing through top dead center, where the volume of the expansion space is maximum, within a first angular range in one rotation of the motor rotary shaft, and passing through an intermediate point between the top dead center and bottom dead center, where the volume of the expansion space is minimum, within a second angular range following the first angular range in one rotation of the motor rotary shaft; a controller that operates the expander motor so as to reduce the rotation speed of the motor rotary shaft in the second angle range compared to the first angle range.

Images