Cryocooler and method for operating a cryocooler

Abstract

An ultra-low temperature refrigerator (10) is provided with an expander (14), a pressure sensor, and a controller (100). The expander (14) is provided with an expander motor (40) having a motor rotating shaft (40a), a displacer (18) that performs linear reciprocating movement by rotation of the motor rotating shaft (40a) to change the volume of an expansion space of working gas, and a rotary valve (42) that performs rotation by rotation of the motor rotating shaft (40a) to control intake and exhaust of the working gas with respect to the expansion space. The pressure sensor measures the pressure of the working gas and outputs a measurement signal indicating the measured pressure. The controller (100) is configured to receive the measurement signal, detect a characteristic point periodically appearing on the measured pressure during operation of the ultra-low temperature refrigerator (10), acquire a motor drive waveform indicating a command rotational speed of the motor rotating shaft (40a) set to change in one rotation of the motor rotating shaft (40a), and output the motor drive waveform after synchronization with the periodically appearing characteristic point.

Description

Technical Field

[0001] This invention relates to an ultra-low temperature refrigerator and its operating method. Background Technology

[0002] In cryogenic refrigerators, such as the Gifford-McMahon (GM) refrigerator, a displacement device reciprocates to periodically change the volume of the expansion space of the working gas. A refrigeration cycle is formed in the cryogenic refrigerator by appropriately synchronizing the pressure in the expansion space with the periodic volume changes of the expansion space. One representative method of driving the reciprocating movement of the displacement device is to mechanically connect a drive source such as a motor to the displacement device and use the rotation output by the motor to cause the displacement device to reciprocate. One rotation of the motor corresponds to one reciprocation of the displacement device (i.e., one refrigeration cycle).

[0003] Previous technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 6-101917 Summary of the Invention

[0006] The technical problem to be solved by the invention

[0007] Previously, from the perspective of improving the cooling capacity of cryogenic refrigerators, attempts were made to change the rotational speed of the motor driving the displacement device during a single rotation, thereby achieving optimal control of the displacement device's movement speed based on its position. To achieve this, a typical approach is to detect the displacement device's position (i.e., the motor's rotational position) and control the motor's rotational speed based on this detected position, thus controlling the displacement device's movement speed. However, this method requires adding a position detector to the motor. Such position detectors are relatively expensive, potentially increasing the manufacturing cost of the cryogenic refrigerator. Furthermore, the addition of a position detector may lead to a larger motor.

[0008] One of the exemplary objectives of one embodiment of the present invention is to achieve optimal operation of the cryogenic refrigerator without position detection.

[0009] means for solving technical problems

[0010] According to one embodiment of the present invention, a cryogenic refrigerator includes an expander, a pressure sensor, and a controller. The expander includes: an expander motor with a motor rotating shaft; a displacement device connected to the motor rotating shaft in a linear reciprocating manner via the rotation of the motor rotating shaft, and changing the volume of the expansion space of the working gas by reciprocating movement; and a rotary valve connected to the motor rotating shaft in a rotatable manner via the rotation of the motor rotating shaft, and controlling the intake and exhaust of the working gas relative to the expansion space. The pressure sensor measures the pressure of the working gas and outputs a measurement signal representing the measured pressure. The controller is configured to receive the measurement signal, detect characteristic points that periodically appear on the measured pressure during the operation of the cryogenic refrigerator, acquire a motor drive waveform representing the command speed of the motor rotating shaft, which is set to change in one rotation of the motor rotating shaft, and output the motor drive waveform after synchronizing it with the periodically appearing characteristic points.

[0011] According to one embodiment of the present invention, a method for operating a cryogenic refrigerator is provided. The cryogenic refrigerator includes an expander, which comprises: an expander motor with a motor rotating shaft; a displacement device connected to the motor rotating shaft for linear reciprocating movement via rotation, and for changing the volume of the expansion space of the working gas through reciprocating movement; and a rotary valve connected to the motor rotating shaft for rotation via rotation, and for controlling the intake and exhaust of the working gas relative to the expansion space. The method includes the following steps: measuring the pressure of the working gas; detecting characteristic points that periodically appear on the measured pressure during the operation of the cryogenic refrigerator; acquiring a motor drive waveform representing the commanded rotational speed of the motor rotating shaft, the commanded rotational speed of the motor rotating shaft being set to vary in one rotation of the motor rotating shaft; and outputting the motor drive waveform synchronized with the periodically appearing characteristic points.

[0012] According to one embodiment of the present invention, a cryogenic refrigerator includes: an expander motor having a motor rotating shaft; a displacement device connected to the motor rotating shaft in a linear reciprocating manner by rotating the motor rotating shaft, and changing the volume of the expansion space of the working gas by reciprocating movement, passing through the top dead center where the volume of the expansion space is largest in a first angular range during one rotation of the motor rotating shaft, and passing through the midpoint between the top dead center and the bottom dead center where the volume of the expansion space is smallest in a subsequent second angular range during one rotation of the motor rotating shaft; and a controller that causes the expander motor to operate such that the rotational speed of the motor rotating shaft is reduced in the second angular range compared to the first angular range.

[0013] Furthermore, any combination of the above-mentioned constituent elements, or the substitution of the constituent elements or expressions of the present invention among methods, apparatuses, systems, etc., are also valid embodiments of the present invention.

[0014] Invention Effects

[0015] According to the present invention, the optimal operation of the cryogenic refrigerator can be achieved without position detection. Attached Figure Description

[0016] Figure 1 This is a diagram that roughly illustrates the cryogenic refrigerator involved in the implementation method.

[0017] Figure 2 This is a diagram that roughly illustrates the cryogenic refrigerator involved in the implementation method.

[0018] Figure 3 This is a perspective exploded view that schematically represents the drive mechanism of the expander of the cryogenic refrigerator involved in the embodiment.

[0019] Figure 4 This is a diagram illustrating an example of the change in the commanded rotational speed of the expander motor as represented by the first motor drive waveform according to the embodiment.

[0020] Figure 5 This is a diagram illustrating an example of the change in the commanded rotational speed of the expander motor as represented by the second motor drive waveform according to the embodiment.

[0021] Figure 6 This is a diagram illustrating an example of characteristic points that periodically appear on the measured pressure of the cryogenic refrigerator according to the embodiment.

[0022] Figure 7 This is a flowchart illustrating the control method of the cryogenic refrigerator involved in the implementation method. Detailed Implementation

[0023] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description and drawings, the same or equivalent constituent elements, components, and processes are labeled with the same symbols, and repeated descriptions are omitted where appropriate. For ease of explanation, scales or shapes of various parts are appropriately shown in the drawings, which are not intended to be limiting unless otherwise specified. The embodiments are illustrative and do not limit the scope of the invention in any way. All features or combinations thereof described in the embodiments are not necessarily essential to the invention.

[0024] Figure 1 and Figure 2 This is a schematic diagram illustrating the cryogenic refrigerator 10 involved in the embodiment. As an example, the cryogenic refrigerator 10 is a two-stage Gifford-McMahon (GM) refrigerator. Figure 1 The controller 100 and the compressor 12 and expander 14 constituting the cryogenic refrigerator 10 are schematically shown in the figure. Figure 2The internal structure of the expander 14 of the cryogenic refrigerator 10 is shown. The controller 100 is provided for controlling the cryogenic refrigerator 10.

[0025] The compressor 12 is configured to recover the working gas of the cryogenic refrigerator 10 from the expander 14, pressurize the recovered working gas, and then supply it back to the expander 14. The compressor 12 and the expander 14 constitute 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 the cold head. The working gas is also referred to as the refrigerant gas, typically helium, but other suitable gases may also be used. For ease of understanding, in Figure 1 The arrows in the diagram indicate the direction of the working gas flow.

[0026] Furthermore, the pressure of the working gas supplied from compressor 12 to expander 14 and the pressure of the working gas returned from expander 14 to compressor 12 are typically much 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 will also be 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, for example, about 0.8 MPa. For ease of understanding, arrows are used to indicate the flow direction of the working gas.

[0027] The expander 14 includes a refrigerator cylinder 16, a displacement assembly (hereinafter sometimes simply referred to as the displacement) 18, and a refrigerator housing 20. The refrigerator cylinder 16 guides the displacement 18 in linear reciprocating motion, and expansion chambers 32 and 34, which serve as expansion spaces for the working gas, are formed between the refrigerator cylinder 16 and the displacement 18. The refrigerator cylinder 16 and the refrigerator housing 20 are joined together to form the frame of the expander 14 (i.e., an airtight container housing the displacement 18).

[0028] In this specification, to illustrate the positional relationships between the components of the cryogenic refrigerator 10, for convenience, the side closer to the top dead center of the axial reciprocating movement of the displacement device is labeled "upper," and the side closer to the bottom dead center is labeled "lower." The top dead center is the position of the displacement device with the largest expansion space volume, and the bottom dead center is the position of the displacement device with the smallest expansion space volume. During operation of the cryogenic refrigerator 10, a temperature gradient is generated from the upper axial direction downwards; therefore, the upper side can also be referred to as the high-temperature side, and the lower side as the low-temperature side.

[0029] The refrigeration unit cylinder block 16 includes a first cylinder block 16a and a second cylinder block 16b. As an example, the first cylinder block 16a and the second cylinder block 16b are cylindrical components, with the diameter of the second cylinder block 16b being smaller than the diameter of the first cylinder block 16a. The first cylinder block 16a and the second cylinder block 16b are coaxially arranged, and the lower end of the first cylinder block 16a is rigidly connected to the upper end of the second cylinder block 16b.

[0030] The displacement assembly 18 includes a first displacement 18a and a second displacement 18b connected together, which move integrally. As an example, the first displacement 18a and the second displacement 18b are cylindrical components, with the diameter of the second displacement 18b being smaller than the diameter of the first displacement 18a. The first displacement 18a and the second displacement 18b are coaxially arranged.

[0031] The first displacement device 18a is housed in the first cylinder block 16a, and the second displacement device 18b is housed in the second cylinder block 16b. The first displacement device 18a is capable of axial reciprocating along the first cylinder block 16a, and the second displacement device 18b is capable of axial reciprocating along the second cylinder block 16b.

[0032] like Figure 2 As shown, the first displacement device 18a houses the first cold storage device 26. The first cold storage device 26 is formed by filling the cylindrical main body of the first displacement device 18a with a metal wire mesh, such as copper, or other suitable first cold storage material. The upper and lower cover portions of the first displacement device 18a can be components different from the main body of the first displacement device 18a. The upper and lower cover portions of the first displacement device 18a can be fixed to the main body by appropriate methods such as fastening or welding, thereby accommodating the first cold storage material within the first displacement device 18a.

[0033] Similarly, the second displacement device 18b houses the second cold storage device 28. The second cold storage device 28 is formed by filling the cylindrical main body of the second displacement device 18b with, for example, a non-magnetic cold storage material such as bismuth, a magnetic cold storage material such as HoCu2, or other suitable second cold storage material. The second cold storage material can be formed in granular form. The upper and lower cover portions of the second displacement device 18b can be components different from the main body of the second displacement device 18b. The upper and lower cover portions of the second displacement device 18b can be fixed to the main body by appropriate methods such as fastening or welding, thereby accommodating the second cold storage material within the second displacement device 18b.

[0034] The displacement chamber 18 forms a chamber 30, a first expansion chamber 32, and a second expansion chamber 34 inside the cryogenic refrigerator 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 platform 33 and a second cooling platform 35. The chamber 30 is formed between the upper cover of the first displacement chamber 18a and the upper part of the first cylinder 16a. The first expansion chamber 32 is formed between the lower cover of the first displacement chamber 18a and the first cooling platform 33. The second expansion chamber 34 is formed between the lower cover of the second displacement chamber 18b and the second cooling platform 35. The first cooling platform 33 is fixed to the lower part of the first cylinder 16a in a manner surrounding the first expansion chamber 32, and the second cooling platform 35 is fixed to the lower part of the second cylinder 16b in a manner surrounding the second expansion chamber 34.

[0035] The first cold accumulator 26 is connected to the chamber 30 via a working gas flow path 36a formed on the upper cover of the first displacement device 18a, and is connected to the first expansion chamber 32 via a working gas flow path 36b formed on the lower cover of the first displacement device 18a. The second cold accumulator 28 is connected to the first cold accumulator 26 via a working gas flow path 36c formed from the lower cover of the first displacement device 18a to the upper cover of the second displacement device 18b. Furthermore, the second cold accumulator 28 is connected to the second expansion chamber 34 via a working gas flow path 36d formed on the lower cover of the second displacement device 18b.

[0036] To prevent the working airflow between the first expansion chamber 32, the second expansion chamber 34, and the chamber temperature 30 from entering the gap between the refrigeration cylinder 16 and the displacement device 18 and thus into the first accumulator 26 and the second accumulator 28, a first seal 38a and a second seal 38b can be provided. The first seal 38a can be installed on the upper cover of the first displacement device 18a, positioned between the first displacement device 18a and the first cylinder 16a. The second seal 38b can be installed on the upper cover of the second displacement device 18b, positioned between the second displacement device 18b and the second cylinder 16b.

[0037] Furthermore, the expander 14 includes an expander motor 40 and a rotary valve 42. The expander motor 40 is provided in the expander 14 as the drive source for the displacement device 18 and the rotary valve 42. Figure 3 As shown, the expander motor 40 includes a motor rotating shaft 40a that outputs the rotation of the expander motor 40. The expander motor 40 is an electric motor capable of controlling the variable speed of the motor rotating shaft 40a, such as a permanent magnet motor or a stepper motor driven by three-phase AC power. The expander motor 40 is mounted in the refrigerator housing 20. The rotary valve 42 is housed in the refrigerator housing 20.

[0038] The displacement device 18 is connected to the motor rotating shaft 40a in a linear reciprocating motion via the rotation of the motor rotating shaft 40a, and changes the volume of the expansion space of the working gas by reciprocating motion. One rotation of the motor rotating shaft 40a results in one reciprocation of the displacement device 18.

[0039] Here, when dividing one rotation of the motor shaft 40a into four angular ranges, it can be said that the displacement device 18 passes the top dead center in the first angular range, passes the midpoint between the top dead center and the bottom dead center in the second angular range following the first angular range, passes the 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. After the fourth angular range, the rotation of the motor shaft 40a enters the first angular range. If the rotation angle of the motor shaft 40a when the displacement device 18 is at the top dead center is represented as 0 degrees, then the first, second, third, and fourth angular ranges respectively contain 0 degrees, 90 degrees, 180 degrees, and 270 degrees.

[0040] like Figure 2 As shown, the rotary valve 42 is configured to functionally include a high-pressure valve 42a and a low-pressure valve 42b, and to generate periodic pressure fluctuations within the refrigeration unit cylinder 16. The rotary valve 42 is configured to set the start and end times for supplying working gas to the expansion space via the high-pressure valve 42a, and the start and end times for discharging working gas from the expansion space via the low-pressure valve 42b. The working gas outlet of the compressor 12 is connected to the chamber temperature 30 via the high-pressure valve 42a, and the working gas inlet of the compressor 12 is connected to the chamber temperature 30 via the low-pressure valve 42b. The high-pressure valve 42a and the low-pressure valve 42b are configured to selectively alternate opening and closing (i.e., while one valve is open, the other is closed). The working gas flow path formed in the rotary valve 42 in the manner of configuring the high-pressure valve 42a and the low-pressure valve 42b can be implemented in various known ways, which will not be described in detail here.

[0041] Rotary valve 42 is connected to motor shaft 40a by rotating via the motor shaft 40a, and controls the intake and exhaust of working gas relative to the expansion space. One rotation of motor shaft 40a causes rotary valve 42 to rotate one revolution. In the design of rotary valve 42, the intake start time is set to be associated with the bottom dead center of displacer 18, and the exhaust start time is set to be associated with the top dead center of displacer 18. Furthermore, the intake end time and exhaust end time can also be set to be associated with the top dead center and bottom dead center of displacer 18, respectively.

[0042] The intake start time is set during the period from when the displacementr 18 moves downward, from the midpoint between the top dead center and the bottom dead center until it reaches the bottom dead center, or near the bottom dead center. For example, the intake start time can be set between 120 degrees (or 150 degrees) and 180 degrees of the rotation angle of the motor shaft 40a. Furthermore, the intake end time is set before the exhaust start time during the upward movement of the displacementr 18.

[0043] The exhaust start time is set during the period from when the displacementr 18 moves upward, from the midpoint between the top dead center and the bottom dead center until it reaches the top dead center, or near the top dead center. For example, the exhaust start time can be set between 300 degrees (or 330 degrees) and 360 degrees of the rotation angle of the motor shaft 40a. Furthermore, the exhaust end time is set before the intake start time during the downward movement of the displacementr 18.

[0044] The phase of the refrigeration cycle is determined by the combination of the position of the displacement device 18 (i.e., the volume of the expansion space) and the rotation angle of the rotary valve 42 (i.e., the pressure of the expansion space). One rotation of the expander motor 40 completes one refrigeration cycle, and the rotation angle of the motor shaft 40a can be correlated with the phase of the refrigeration cycle.

[0045] Furthermore, the expander 14 may also be equipped with a temperature sensor 48, which measures the temperature of the second cooling stage 35 (and / or the first cooling stage 33) and outputs a measured temperature signal representing the measured temperature.

[0046] Figure 3 This is a schematic exploded perspective view showing the drive mechanism of the expander 14 of the cryogenic refrigerator 10 according to the embodiment. The motor rotation shaft 40a is connected to the displacement device 18 via a motion conversion mechanism 43 and a displacement device drive shaft 44. In this embodiment, the motion conversion mechanism 43 is an anti-rotation yoke mechanism that converts the rotation of the motor rotation shaft 40a into linear motion.

[0047] like Figure 3 As shown, the motion conversion mechanism 43 includes a crank 45 and an anti-rotation yoke 46. The crank 45 is fixed to the motor rotating shaft 40a. A crank pin 45a is located at an eccentric position from the fixed position of the motor rotating shaft 40a on the crank 45. The crank pin 45a extends parallel to the motor rotating shaft 40a on the side of the crank 45 opposite to the motor rotating shaft 40a.

[0048] The anti-rotation 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, extending upwards, and a displacement drive shaft 44 is fixed to the lower center, extending downwards. A transverse window 46a1 is formed in the center of the yoke plate 46a, extending in a direction orthogonal to the extending direction (i.e., axial direction) of the upper rod 47 and the displacement drive shaft 44. The roller bearing 46b is rotatably disposed within the transverse window 46a1. A locking hole 46b1 is formed in the center of the roller bearing 46b, engaging with a crank pin 45a, which passes through the locking hole 46b1. The upper rod 47 and the displacement drive shaft 44 are slidably supported on the yoke plate 46a. Figure 1 The refrigeration unit housing 20 shown.

[0049] The displacement drive shaft 44 connects the motion conversion mechanism 43 to the displacement device 18 (specifically, such as...). Figure 2 The first displacement device 18a is shown. One end of the displacement device drive shaft 44 is fixed to the yoke plate 46a, and the other end is fixed to the displacement device 18. Figure 1 As shown, the motion conversion mechanism 43 is housed within the refrigerator housing 20 and extends from the refrigerator housing 20 toward the refrigerator cylinder 16. Figure 2 As shown, the displacement drive shaft 44 is fixed to the upper cover of the first displacement device 18a via the chamber 30.

[0050] The motor rotating shaft 40a is also connected to the rotary valve 42. The rotary valve 42 is positioned opposite the expander motor 40 to the motion conversion mechanism 43, and the rotating shaft of the rotary valve 42 is coaxial with the motor rotating shaft 40a. The rotary valve 42 may have a valve body fixed to the refrigerator housing 20 and thus stationary, and a valve disc supported on the refrigerator housing 20 in a manner rotatable relative to the valve body. It may be configured to alternately open and close the high-pressure valve 42a and the low-pressure valve 42b by rotating and sliding the valve disc relative to the valve body. A crank pin 45a passing through the engagement hole 46b1 is fixed to the valve disc, thereby allowing the motor rotating shaft 40a to rotate the valve disc relative to the valve body.

[0051] When the motor shaft 40a rotates, the roller bearing 46b, engaged with the crank pin 45a, rotates in a circular motion while reciprocating along the transverse window 46a1. This causes the anti-rotation yoke 46 and the displacement drive shaft 44 to reciprocate axially. Therefore, by rotating the expander motor 40, the displacement device 18 reciprocates axially within the refrigerator cylinder 16. Furthermore, by rotating the expander motor 40, the rotary valve 42 also rotates.

[0052] Refer again Figure 1The 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 frame 58. The high-pressure gas outlet 50 is located in the compressor frame 58 as the working gas discharge port of the compressor 12, and the low-pressure gas inlet 51 is located in the compressor frame 58 as the working gas intake 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 intake port of the compressor body 56. The compressor frame 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.

[0053] The compressor body 56 is configured to internally compress the working gas drawn in from its inlet and discharge it from its outlet. The compressor body 56 can be, for example, a scroll pump, a rotary pump, or other pump that pressurizes the working gas. In this embodiment, the compressor body 56 is configured to discharge a constant flow rate of working gas. Alternatively, the compressor body 56 may be configured to allow a variable flow rate of discharged working gas. The compressor body 56 is sometimes also referred to as a compression chamber.

[0054] The first pressure sensor 54 is disposed on 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 indicating the measured pressure. The second pressure sensor 55 is disposed on 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 indicating the measured pressure. Therefore, the first pressure sensor 54 and the second pressure sensor 55 can also be referred to as a high-pressure sensor and a low-pressure sensor, respectively. Furthermore, in this specification, either the first pressure sensor 54 or the second pressure sensor 55, or both, are sometimes referred to as "pressure sensors".

[0055] In addition, the compressor 12 may have various other components. For example, an oil separator, an adsorber, etc., may be provided on the high-pressure flow path 52. A storage tank and other components may be provided on the low-pressure flow path 53. Furthermore, an oil circulation system that uses oil to cool the compressor body 56 and a cooling system for cooling the oil may be provided on the compressor 12. To prevent the pressure in the high-pressure flow path 52 from becoming too high, a bypass flow path may also be provided to release the pressure from the high-pressure flow path 52 to the low-pressure flow path 53.

[0056] Furthermore, the cryogenic refrigerator 10 includes a gas pipeline 62 that circulates the working gas between the compressor 12 and the expander 14. The gas pipeline 62 includes a high-pressure pipeline 63 connecting the compressor 12 and the expander 14 to supply high-pressure working gas from the compressor 12 to the expander 14, and a low-pressure pipeline 64 connecting the compressor 12 and the expander 14 to recover low-pressure working gas from the expander 14 back to the compressor 12. A high-pressure gas inlet 22 and a low-pressure gas outlet 24 are provided on the refrigerator housing 20 of the expander 14. The high-pressure gas inlet 22 is connected to the high-pressure gas outlet 50 via a high-pressure piping 65, and the low-pressure gas outlet 24 is connected to the low-pressure gas inlet 51 via a low-pressure piping 66. The high-pressure pipeline 63 consists of the high-pressure piping 65 and the high-pressure flow path 52, and the low-pressure pipeline 64 consists of the low-pressure piping 66 and the low-pressure flow path 53. The rotary valve 42 operates in such a way that the high-pressure line 63 and the low-pressure line 64 are alternately connected to the expansion space within the expander 14.

[0057] Furthermore, the pressure measuring units, such as the first pressure sensor 54 and the second pressure sensor 55, do not necessarily have to be installed on the compressor 12. They can also be installed at any location capable of measuring pressure, such as the gas pipeline 62 or the expander 14. For example, the first pressure sensor 54 can be installed at any location on the high-pressure pipeline 63, and the second pressure sensor 55 can be installed at any location on the low-pressure pipeline 64.

[0058] like Figure 1 As shown, the cryogenic refrigerator 10 is equipped with a controller 100 for controlling the expander motor 40. The controller 100 is electrically connected to a first pressure sensor 54 and a second pressure sensor 55 to obtain a first measured pressure signal P1 and a second measured pressure signal P2. Furthermore, the controller 100 is electrically connected to a temperature sensor 48 to obtain a measured temperature signal from the temperature sensor 48.

[0059] 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 on the measured pressure during the operation of the cryogenic refrigerator 10, acquires the motor drive waveform S representing the commanded rotational speed of the motor shaft 40a, and outputs the motor drive waveform S after synchronizing it with the periodically appearing characteristic points (details are provided below). The commanded rotational speed of the motor shaft 40a is set to vary during one rotation of the motor shaft 40a.

[0060] As an exemplary structure, the controller 100 includes a processing unit (processor) 110, a storage unit (memory) 112, and a motor drive unit (motor driver) 120. The processing unit 110 receives at least one of a first measured pressure signal P1 and a second measured pressure signal P2, detects characteristic points that periodically appear on the measured pressure during the operation of the cryogenic refrigerator 10, acquires a motor drive waveform S from the storage unit 112, synchronizes the motor drive waveform S with the periodically appearing characteristic points, and then outputs it to the motor drive unit 120. The storage unit 112 stores the motor drive waveform S.

[0061] An external power source 80, such as a commercial power supply (three-phase AC power), supplies power to the motor drive unit 120. Alternatively, the expander motor 40 can also receive power by connecting to the external power source 80 via the compressor 12, in which case the compressor 12 can be considered as the power source for the expander motor 40.

[0062] The motor drive unit 120 generates a motor drive current from the external power supply 80 according to the received motor drive waveform S and supplies it to the expander motor 40. Thus, the expander motor 40 causes the motor shaft 40a to rotate at the commanded speed shown in the motor drive waveform S. The motor shaft 40a rotates by increasing or decreasing its speed in one rotation according to the motor drive waveform S. Through the rotation of the expander motor 40, the cryogenic refrigerator 10 generates a refrigeration cycle and provides cryogenic cooling.

[0063] The motor drive unit 120 can be equipped with a frequency converter, which controls the operating frequency of the expander motor 40. The expander motor 40 enables the motor shaft 40a to rotate at a speed determined by the output frequency of the frequency converter. For example, the output frequency of the frequency converter (i.e., the operating frequency of the expander motor 40) can vary in the range of 30Hz to 100Hz or in the range of 40Hz to 70Hz. The cryogenic refrigerator 10 controls the operating frequency of the expander motor 40, thereby changing the frequency of the refrigeration cycle (number of cycles per unit time).

[0064] In the illustrated example, the controller 100 is separately installed and connected to the compressor 12 and expander 14, but this is not a limitation. The controller 100 may also be mounted on the compressor 12. The controller 100 may also be mounted on the expander 14 (i.e., it may be mounted on the expander motor 40, etc.). Alternatively, the controller 100 may be divided into multiple parts and installed on the cryogenic refrigerator 10. For example, one part of the controller 100 (e.g., the processing unit 110 and the storage unit 112) may be mounted on the compressor 12, and another part of the controller 100 (e.g., the motor drive unit 120) may be mounted on the expander 14, etc.

[0065] The controller 100 is implemented in terms of hardware structure through components or circuits, such as a computer's CPU or memory, and in terms of software structure through computer programs, etc. Figure 1 The functional blocks that are realized through their cooperation are appropriately depicted. Those skilled in the art will understand that these functional blocks can be implemented in various forms through a combination of hardware and software.

[0066] During the operation of the compressor 12 and expander motor 40, the cryogenic refrigerator 10 generates periodic volume changes and synchronous pressure changes of the working gas in the first expansion chamber 32 and the second expansion chamber 34. Typically, in the intake process, by closing the low-pressure valve 42b and opening the high-pressure valve 42a, high-pressure working gas flows from the compressor 12 through the high-pressure valve 42a into the chamber 30, and is supplied to the first expansion chamber 32 via the first accumulator 26, and then to the second expansion chamber 34 via the second accumulator 28. As a result, the first expansion chamber 32 and the second expansion chamber 34 are pressurized from low pressure to high pressure. At this time, the displacement device 18 moves from the bottom dead center to the top dead center, and the volume of the first expansion chamber 32 and the second expansion chamber 34 increases. If the high-pressure valve 42a is closed, the intake process ends.

[0067] During the exhaust process, by closing the high-pressure valve 42a and opening the low-pressure valve 42b, the high-pressure first expansion chamber 32 and second expansion chamber 34 are connected to the low-pressure working gas inlet of the compressor 12. Therefore, the working gas expands in the first expansion chamber 32 and second expansion chamber 34, resulting in the low-pressure working gas being discharged from the first expansion chamber 32 and second expansion chamber 34 through the first accumulator 26 and second accumulator 28 towards the chamber temperature 30. At this time, the displacement device 18 moves from top dead center to bottom dead center, and the volume of the first expansion chamber 32 and second expansion chamber 34 decreases. The working gas is recovered from the expander 14 to the compressor 12 after passing through the low-pressure valve 42b. If the low-pressure valve 42b is closed, the exhaust process ends.

[0068] The working gas recovered from expander 14 to compressor 12 returns to compressor body 56 via low-pressure line 64 (i.e., from low-pressure gas outlet 24 of expander 14 through low-pressure piping 66 into low-pressure gas inlet 51 of compressor 12, and further through low-pressure flow path 53). The working gas is compressed and pressurized by compressor body 56. The working gas supplied from compressor 12 to expander 14 is supplied to expander 14 via high-pressure line 63 (i.e., from compressor body 56 through high-pressure flow path 52, discharged from high-pressure gas outlet 50 of compressor 12, and then through high-pressure piping 65) and high-pressure gas inlet 22 of expander 14.

[0069] This forms a refrigeration cycle (e.g., a GM cycle), whereby the first cooling stage 33 and the second cooling stage 35 are cooled to the desired ultra-low temperature. The first cooling stage 33 can be cooled to a first cooling temperature (e.g., in the range of about 20K to about 40K). The second cooling stage 35 can be cooled to a second cooling temperature lower than the first cooling temperature (e.g., about 1K to about 4K).

[0070] The cryogenic refrigerator 10 is capable of performing initial cooling and steady-state operation following initial cooling. Initial cooling is the operating mode of the expander 14, which rapidly cools from an initial temperature to a cryogenic state when the cryogenic refrigerator 10 is started. Steady-state operation is the operating mode of the expander 14, which maintains the cryogenic state achieved through initial cooling. The initial temperature can be the ambient temperature (e.g., room temperature). The expander 14 is cooled to a standard cooling temperature (e.g., a first cooling temperature, a second cooling temperature) based on the initial cooling and is maintained within the permissible temperature range of the cryogenic state, including the standard cooling temperature, during steady-state operation. The standard cooling temperature varies depending on the application and settings of the cryogenic refrigerator 10. For example, in applications involving cooling superconducting devices, a typical standard cooling temperature is below approximately 4.2 K. In other cooling applications, the standard cooling temperature may be, for example, approximately 10 K to 20 K, or below 10 K. As mentioned above, initial cooling can also be referred to as temperature reduction.

[0071] The switching from initial cooling to steady-state operation can be controlled by controller 100. For example, controller 100 can 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 temperature sensor 48, and perform initial cooling when the measured temperature is higher than the switching temperature, and switch from initial cooling to steady-state operation when the measured temperature is lower than the switching temperature. The switching temperature can be the standard cooling temperature mentioned above, or a temperature slightly higher than the standard cooling temperature (e.g., a temperature only 5K or 10K higher than the standard cooling temperature).

[0072] Typically, during steady-state operation, the cryogenic refrigerator 10 only needs to provide cooling capacity matching the heat load, and therefore usually does not require a very high cooling capacity. On the other hand, initial cooling is merely a preparation for using the cryogenic refrigerator 10 to begin cooling the object, so the expected time is as short as possible. Therefore, during initial cooling, the speed of the expander motor 40 can be increased compared to steady-state operation, thereby increasing the cooling capacity of the cryogenic refrigerator 10 during initial cooling.

[0073] For example, the controller 100 can determine the current operating mode of the cryogenic refrigerator 10 and control the motor drive unit 120 so that the operating frequency of the expander motor 40 is higher when the cryogenic refrigerator 10 is in the initial cooling phase than when it is in steady-state operation. The operating frequency of the expander motor 40 in the initial cooling phase can be higher than the input frequency (e.g., 50Hz or 60Hz) from the external power supply 80 to the motor drive unit 120, while the operating frequency of the expander motor 40 in steady-state operation can be the same as or lower than the input frequency.

[0074] However, while driving the expander motor 40 at such a high speed can increase the cooling capacity, it also increases the load applied to the expander motor 40 to drive the displacement valve 18 (and the rotary valve 42). Therefore, it is desirable to balance high cooling capacity (i.e., shortening the cooling time) and reduced load on the expander motor 40 during initial cooling. On the other hand, from the viewpoint of improving energy efficiency, it is desirable to maximize the PV work obtained in one refrigeration cycle during steady-state operation to achieve efficient cooling. Thus, the most suitable operating method for the cryogenic refrigerator 10 varies depending on the circumstances.

[0075] Therefore, in this embodiment, the processing unit 110 of the controller 100 can receive at least one of the first measured pressure signal P1 and the second measured pressure signal P2, detect characteristic points that periodically appear on the measured pressure during the operation of the cryogenic refrigerator 10, select a motor drive waveform S from a plurality of motor drive waveforms, synchronize the selected motor drive waveform S with the periodically appearing characteristic points, and output it to the motor drive unit 120. The plurality of motor drive waveforms respectively represent the command speed of the motor rotating shaft 40a, which is set to change in different ways during one rotation of the motor rotating shaft 40a. The storage unit 112 stores these motor drive waveforms. As described later, the plurality of motor drive waveforms may include a first motor drive waveform and a second motor drive waveform. The processing unit 110 can determine the current operating mode of the cryogenic refrigerator 10, and select the first motor drive waveform when in the initial cooling stage, and select the second motor drive waveform when in steady-state operation.

[0076] Figure 4 This is a diagram illustrating an example of the change in the commanded rotational speed of the expander motor 40, as represented by the first motor drive waveform according to the embodiment. Figure 5 This is a diagram illustrating an example of the change in the commanded rotational speed of the expander motor 40, as represented by the second motor drive waveform according to the embodiment. Figure 4 and Figure 5The diagram illustrates the change in the commanded rotational speed during one rotation of the motor shaft 40a. The vertical axis represents the value of the commanded rotational speed, and the horizontal axis represents the rotation angle of the motor shaft 40a. As described above, the rotation angle of the motor shaft 40a when the displacement device 18 is at top dead center is represented as 0 degrees.

[0077] The displacement valve 18 passes through the top dead center in the first angular range A1, then passes through the midpoint between the top dead center and the bottom dead center in the second angular range A2 within the first angular range A1, then passes through the bottom dead center in the third angular range A3 within the second angular range A2, and finally passes through the midpoint in the fourth angular range A4 within the third angular range A3. The first angular range A1, the second angular range A2, the third angular range A3, and the fourth angular range A4 respectively encompass 0 degrees, 90 degrees, 180 degrees, and 270 degrees. The intake start time of the rotary valve 42 is set in the third angular range A3, and the exhaust start time is set in the first angular range A1.

[0078] When the expander motor 40 is connected to the displacement device 18 via the motion conversion mechanism 43, it is known from mechanical analysis that when the rotation angle of the motor rotating shaft 40a is around 90 degrees and around 270 degrees, the load applied to the expander motor 40 becomes higher.

[0079] Therefore, as Figure 4 As shown, the first motor drive waveform is set such that the commanded rotational speed of the motor shaft 40a decreases in the second angular range A2 compared to the first angular range A1. Furthermore, the commanded rotational speed of the motor shaft 40a increases in the third angular range A3 compared to the second angular range A2. Similarly, the first motor drive waveform is set such that the commanded rotational speed of the motor shaft 40a decreases in the fourth angular range A4 compared to the third angular range A3, and increases in the first angular range A1 compared to the fourth angular range A4.

[0080] In this way, since the commanded rotational speed of the motor shaft 40a decreases in the second angular range A2 (containing 90 degrees) and the fourth angular range A4 (containing 270 degrees), the rotation of the motor shaft 40a slows down in these angular ranges. Therefore, the load applied to the expander motor 40 in these angular ranges can be reduced. At the same time, in other rotational angles (i.e., the first angular range A1 and the third angular range A3), the motor shaft 40a can rotate at a relatively high speed. Therefore, compared to the case where the motor shaft 40a rotates at a constant low speed, the frequency of the refrigeration cycle can be increased, thereby increasing the cooling capacity of the cryogenic refrigerator 10. Therefore, it is possible to balance the reduction of cooling time based on high cooling capacity with the reduction of the load applied to the expander motor 40. Therefore, the first motor drive waveform is suitable for driving the expander motor 40 during initial cooling.

[0081] Furthermore, it is known that by suppressing the moving speed of the displacement device 18 from the start of exhaust to the top dead center of the displacement device 18, the PV work obtained in one refrigeration cycle can be increased. This effect is more pronounced when the cryogenic refrigerator 10 is cooled to a cryogenic temperature, such as during steady-state operation.

[0082] Therefore, as Figure 5 As shown, unlike the first motor drive waveform, the second motor drive waveform is set such that the commanded rotational speed of the motor shaft 40a increases in the second angular range A2 compared to the first angular range A1. The commanded rotational speed of the motor shaft 40a further increases in the third angular range A3 compared to the second angular range A2. Furthermore, the second motor drive waveform is set such that the commanded rotational speed of the motor shaft 40a decreases in the fourth angular range A4 compared to the third angular range A3, and further decreases in the first angular range A1 compared to the fourth angular range A4.

[0083] In this way, the commanded rotational speed of the motor shaft 40a is reduced in the first angular range A1 compared to other angular ranges. The rotational speed of the motor shaft 40a is suppressed in the first angular range A1, and the displacement device 18 also operates at low speed. The first angular range A1 includes the exhaust start moment and the top dead center of the displacement device 18, thus increasing the PV work obtained in one refrigeration cycle. The second motor drive waveform is suitable for driving the expander motor 40 in steady-state operation.

[0084] Furthermore, the first and second motor drive waveforms described above are examples of possible motor drive waveforms. In this embodiment, the change in rotational speed of the motor shaft 40a during one rotation can take various forms. For example, for convenience, in... Figure 4 The first motor drive waveform shows a case where the commanded speed is the same in the first angle range A1 and the third angle range A3, and the same in the second angle range A2 and the fourth angle range A4, but it is not limited to this. The commanded speed can be different in the first angle range A1 and the third angle range A3, or it can be different in the second angle range A2 and the fourth angle range A4. Furthermore, the commanded speed can use the same value in the first motor drive waveform and the second motor drive waveform, or it can use different values.

[0085] exist Figure 4 and Figure 5In the example, the widths of the first and third angle ranges are the same, as are the widths of the second and fourth angle ranges. 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 expands equally to both sides from reference angles of 0 degrees, 90 degrees, 180 degrees, and 270 degrees. However, this setting of angle ranges is not mandatory, and various other settings are possible. For example, the widths of all angle ranges can be the same, or they can be different.

[0086] Furthermore, for convenience, in the above example, one rotation of the motor shaft 40a is divided into four angular ranges. However, one rotation of the motor shaft 40a can also be divided into fewer or more angular ranges, and a command speed can be set for each of these angular ranges. The angular ranges can be set to be the same or different in the first motor drive waveform and the second motor drive waveform.

[0087] The first motor drive waveform can also be used in operating conditions other than initial cooling. The second motor drive waveform can also be used in operating conditions other than steady-state operation.

[0088] Figure 6 This is a diagram illustrating an example of characteristic points that periodically appear on the measured pressure of the cryogenic refrigerator 10 according to the embodiment. Figure 6 The diagram illustrates the measured pressures of the high-pressure line 63 and the low-pressure line 64 during one cycle of the refrigeration cycle. The vertical axis represents the measured pressure, and the horizontal axis represents the rotation angle of the motor shaft 40a. In this example, the top dead center of the displacement device 18 corresponds to the rotation angle B.

[0089] As shown above, in this embodiment, characteristic points that periodically appear on the measured pressure during the operation of the cryogenic refrigerator 10 are detected. These characteristic points appear periodically on the measured pressure of the pressure sensor as variations in the working gas pressure associated with the intake process (e.g., the start of intake) or exhaust process (e.g., the start of exhaust) of the cryogenic refrigerator 10. The periodically appearing characteristic points are those that periodically appear on 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 those that periodically appear on the measured pressure of the low-pressure line 64 due to the discharge of working gas from the expansion space via the rotary valve 42. The characteristic points can also be changes in the sign of the rate of change of the measured pressure. This change in sign can be from a positive value to zero or from a negative value to zero.

[0090] High-pressure line 63 is connected to the discharge port of compressor body 56, therefore the pressure of high-pressure line 63 is basically the same as the discharge pressure of compressor 12. However, during the intake process of cryogenic refrigerator 10, when high-pressure line 63 is connected to the expansion space of expander 14 via rotary valve 42, the working gas flows from high-pressure line 63 to expander 14, and the pressure of high-pressure line 63 will decrease slightly and transiently. For example, Figure 6 Feature point C1 indicates the pressure drop. Feature point C1 can be considered the start of the intake. Afterwards, the pressure in high-pressure line 63 gradually recovers through the supply of working gas from compressor 12. Feature point C2 indicates the transition point where the pressure in high-pressure line 63 changes from decreasing to increasing. Feature point C2 can be correlated with the start of the intake. In this way, pressure changes in high-pressure line 63 can be detected as feature points.

[0091] Similarly, pressure fluctuations in the low-pressure line 64 can also be detected as characteristic points. The low-pressure line 64 is connected to the suction port of the compressor body 56, therefore the pressure in the low-pressure line 64 is essentially the same as the suction pressure of the compressor 12. However, during the exhaust process of the cryogenic refrigerator 10, when the low-pressure line 64 is connected to the expansion space of the expander 14 via the rotary valve 42, the working gas flows from the expander 14 into the low-pressure line 64, causing a slight, transient increase in pressure in the low-pressure line 64. For example, Figure 6 Feature point C3 indicates the pressure increase. Feature point C3 can be considered the start of exhaust. Afterwards, the pressure in low-pressure line 64 gradually decreases as the compressor 12 recovers the working gas. Feature point C4 represents the transition point where the pressure in low-pressure line 64 changes from increasing to decreasing. Feature point C4 can be correlated with the start of exhaust.

[0092] Alternatively, a pressure sensor can be installed inside the expander 14 to measure the pressure in the expansion space. In this case, characteristic points that periodically appear on the measured pressure in the expansion space can also be detected.

[0093] Figure 7 This is a flowchart illustrating the control method of the cryogenic refrigerator 10 according to the embodiment. During the operation of the cryogenic refrigerator 10, the controller 100 repeatedly executes this method at a predetermined cycle.

[0094] like Figure 7As shown, 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 a first pressure sensor 54. The first pressure sensor 54 outputs a first measurement 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 can be measured by a second pressure sensor 55. The second pressure sensor 55 outputs a second measurement pressure signal P2, representing the measured pressure PL of the low-pressure line 64, to the controller 100.

[0095] The processing unit 110 detects characteristic points that periodically appear on the measured pressure (S11). For example, after receiving the first measured pressure signal P1, the processing unit 110 detects characteristic points that periodically appear on the measured pressure PH during the operation of the cryogenic refrigerator 10. The detected characteristic points can indicate the start time of the intake of the rotary valve 42. Alternatively, the processing unit 110 can also detect characteristic points that periodically appear on the measured pressure PL during the operation of the cryogenic refrigerator 10 after receiving the second measured pressure signal P2. In this case, the detected characteristic points can indicate the start time of the exhaust of the rotary valve 42. The characteristic points detected in this way indicate the phase of the refrigeration cycle, and the phase of the refrigeration cycle is correlated with the rotation angle of the expander motor 40. Therefore, the processing unit 110 can determine the motor rotation angle based on the characteristic points.

[0096] The processing unit 110 acquires the motor drive waveform S from the storage unit 112 (S12). Here, the processing unit 110 can select one motor drive waveform S from multiple motor drive waveforms and acquire the selected motor drive waveform S from the storage unit 112. As described above, the multiple motor drive waveforms may include a first motor drive waveform and a second motor drive waveform. The processing unit 110 can determine the current operating mode of the cryogenic refrigerator 10, selecting the first motor drive waveform when in the initial cooling phase and selecting the second motor drive waveform when in steady-state operation.

[0097] The processing unit 110 synchronizes the acquired motor drive waveform S with the detected feature point and outputs it to the motor drive unit 120 (S13). The processing unit 110 outputs the motor drive waveform S to the motor drive unit 120 in a feedforward manner. The output motor drive waveform S corresponds to at least one cycle of the refrigeration cycle starting from the detection time of the feature point (e.g., the detection time of the start of intake or exhaust). Therefore, the motor drive unit 120 receives the command speed of the motor rotating shaft 40a, which rotates at least one revolution from the detection time of the feature point.

[0098] The processing unit 110 may also detect feature points in each cooling cycle and output a motor drive waveform S equivalent to one cooling cycle to the motor drive unit 120 each time a feature point is detected. Alternatively, without performing detection every time, the processing unit 110 may detect feature points every few cycles of the cooling cycle and output a motor drive waveform S equivalent to several cooling cycles to the motor drive unit 120.

[0099] Even if a feature point is detected before the end of the previously output motor drive waveform S, the processing unit 110 can still output the motor drive waveform S, starting from the detection time of the feature point, to the motor drive unit 120. Alternatively, the processing unit 110 can ignore the feature point detected before the end of the motor drive waveform S as a false detection.

[0100] In addition, when there is a time delay from the detection time of the feature point to the output of the motor drive waveform, the processing unit 110 can output the motor drive waveform S of at least one cycle of the cooling cycle, which is equivalent to the reference time that takes into account the delay, to the motor drive unit 120.

[0101] When periodically occurring feature points cannot be detected due to a malfunction of the pressure sensor, the controller 100 can acquire and output a (third) motor drive waveform set in a manner that keeps the commanded rotational speed of the motor shaft 40a constant. At this time, the processing unit 110 can acquire this third motor drive waveform from the storage unit 112 and output it to the motor drive unit 120. In this way, even when feature points cannot be detected, the supply of the commanded rotational speed will not be interrupted, thus enabling the expander motor 40 to continue rotating at a constant speed, thereby enabling the cryogenic refrigerator 10 to continue operating.

[0102] The motor drive unit 120 generates a motor drive current from the external power supply 80 according to the received motor drive waveform S and supplies it to the expander motor 40. Thus, the expander motor 40 causes the motor shaft 40a to rotate at the commanded speed indicated by the motor drive waveform S. According to the motor drive waveform S, the motor shaft 40a rotates while increasing or decreasing its speed (or at a constant speed) in one rotation. Through the rotation of the expander motor 40, the cryogenic refrigerator 10 generates a refrigeration cycle and provides cryogenic cooling.

[0103] According to the implementation method, the phase of the refrigeration cycle can be determined based on the measured pressure, and a command speed of the expander motor 40 after the rotation angle of the expander motor 40 corresponding to the determined phase can be given without compromising real-time performance.

[0104] Typically, speed control of a motor corresponding to its rotation angle requires position detectors such as encoders. However, adding such position detectors to the cryogenic refrigerator 10 could increase the manufacturing cost of the cryogenic refrigerator 10 or lead to a larger expansion motor 40. In contrast, most cryogenic refrigerators 10 already have pressure sensors such as a first pressure sensor 54 and a second pressure sensor 55, so such problems do not occur.

[0105] Furthermore, in this implementation, the expander motor 40 is controlled in a feedforward manner instead of real-time feedback control, which reduces the risk of adverse control conditions such as oscillations, and is therefore advantageous.

[0106] In this implementation, a pre-set command speed is used to achieve optimal operation of the cryogenic refrigerator 10, thus enabling optimal operation of the cryogenic refrigerator 10 without position detection. For example, it is possible to switch and provide the optimal operation required for different operating states of the cryogenic refrigerator 10 (e.g., initial cooling and steady-state operation) as needed.

[0107] Furthermore, switching the command speed of the expander motor 40 according to the operating state is not necessary. In one embodiment, the cryogenic refrigerator 10 may include: an expander motor 40 having a motor rotating shaft 40a; a displacement device 18 connected to the motor rotating shaft 40a in a linear reciprocating motion via the rotation of the motor rotating shaft 40a, and changing the volume of the expansion space of the working gas by reciprocating motion, passing through the top dead center where the expansion space volume is largest in a first angular range during one rotation of the motor rotating shaft 40a, and passing through the midpoint between the top dead center and the bottom dead center where the expansion space volume is smallest in a subsequent second angular range during one rotation of the motor rotating shaft 40a; and a controller 100 that causes the expander motor 40 to operate with the rotation speed of the motor rotating shaft 40a decreasing in the second angular range compared to the first angular range. The controller 100 can cause the expander motor 40 to operate with the rotation speed of the motor rotating shaft 40a decreasing in the second angular range compared to the first angular range, at least during initial cooling.

[0108] The controller 100 can actuate the expander motor 40 based on the output of a detector that detects a (calculable) parameter related to the rotation angle of the motor shaft 40a. Such a detector could be, for example, a pressure sensor such as a first pressure sensor 54 and a second pressure sensor 55 mounted on the cryogenic refrigerator 10. Alternatively, the detector could be an encoder that detects the rotation angle of the expander motor 40. The detector could also be a position sensor that measures the position of the displacement device 18. The pressure control mechanism of the cryogenic refrigerator 10 may not be a rotary valve; the high-pressure valve 42a and the low-pressure valve 42b can be valves that can be controlled separately, and these valves may not be mechanically connected to the expander motor 40.

[0109] In the above embodiments, the case where the cryogenic refrigerator 10 is a two-stage GM refrigerator is illustrated, but it is not limited to this. The cryogenic refrigerator 10 can also be a single-stage or multi-stage GM refrigerator, and it can also be other types of cryogenic refrigerators that utilize an expander motor to drive a displacement device.

[0110] The present invention has been described above with reference to the embodiments. Those skilled in the art should understand that the present invention is not limited to the above-described embodiments, and various design changes and modifications are possible, and such modifications are also within the scope of the present invention.

[0111] Industrial availability

[0112] This invention can be applied to the field of cryogenic refrigerators and methods for operating cryogenic refrigerators.

[0113] Symbol Explanation

[0114] 10-Cryogenic refrigerator, 12-Compressor, 14-Expander, 18-Displacement device, 40-Expander motor, 40a-Motor rotating shaft, 42-Rotary valve, 63-High-pressure pipeline, 64-Low-pressure pipeline, 100-Controller.

Claims

1. An ultra-low temperature refrigerator, characterized in that, Equipped with an expander, pressure sensor, and controller. The expander includes: an expander motor with a motor rotating shaft; a displacement device connected to the motor rotating shaft for linear reciprocating movement via rotation, and for changing the volume of the expansion space of the working gas through reciprocating movement; and a rotary valve connected to the motor rotating shaft for rotation via rotation, and for controlling the intake and exhaust of the working gas relative to the expansion space. The pressure sensor measures the pressure of the working gas and outputs a measurement signal representing the measured pressure. The controller is configured as follows: Receive the measurement signal, The characteristic points that periodically appear on the measured pressure during the operation of the cryogenic refrigerator are detected. Acquire a motor drive waveform representing the commanded rotational speed of the motor shaft, which is set to vary during one rotation of the motor shaft. The motor drive waveform is output after being synchronized with the periodically appearing feature points.

2. The cryogenic refrigerator according to claim 1, characterized in that, The controller is configured to select one motor drive waveform from multiple motor drive waveforms, synchronize the selected motor drive waveform with the periodically occurring feature points, and then output the selected waveform. The plurality of motor drive waveforms respectively represent the commanded rotational speed of the motor rotating shaft, which is set to vary in different ways during one rotation of the motor rotating shaft.

3. The cryogenic refrigerator according to claim 2, characterized in that, The displacement device is configured such that, during one rotation of the motor shaft, a first angular range passes through the top dead center where the expansion space has the largest volume, and a subsequent second angular range during one rotation of the motor shaft, following the first angular range, passes through the midpoint between the top dead center and the bottom dead center where the expansion space has the smallest volume. The plurality of motor drive waveforms include a first motor drive waveform and a second motor drive waveform. The first motor drive waveform is set such that the commanded rotational speed of the motor shaft is smaller in the second angular range than in the first angular range, and the second motor drive waveform is set such that the commanded rotational speed of the motor shaft is larger in the second angular range than in the first angular range.

4. The cryogenic refrigerator according to claim 3, characterized in that, The controller is configured to select the first motor drive waveform during the initial cooling process from the initial temperature to the ultra-low temperature, and to select the second motor drive waveform during the steady-state operation that maintains the ultra-low temperature following the initial cooling.

5. The cryogenic refrigerator according to claim 1, characterized in that, The displacement device is configured such that, during one rotation of the motor shaft, a first angular range passes through the top dead center where the expansion space has the largest volume, and a subsequent second angular range during one rotation of the motor shaft, following the first angular range, passes through the midpoint between the top dead center and the bottom dead center where the expansion space has the smallest volume. The motor drive waveform is set such that the commanded rotational speed of the motor shaft is reduced in the second angular range compared to the first angular range.

6. The cryogenic refrigerator according to any one of claims 1 to 5, characterized in that, The controller is configured to acquire and output a motor drive waveform that sets the command rotation speed of the motor shaft to be constant when the periodically occurring feature points cannot be detected.

7. The cryogenic refrigerator according to any one of claims 1 to 6, characterized in that, It also has: Compressor; and A high-pressure pipeline connects the compressor and the expander in a manner that supplies high-pressure working gas from the compressor to the expander. The pressure sensor measures the pressure of the working gas on the high-pressure pipeline.

8. The cryogenic refrigerator according to claim 7, characterized in that, The periodically occurring feature points are characteristic points that appear periodically on the measured pressure of the high-pressure pipeline by the intake of working gas into the expansion space via the rotary valve.

9. The cryogenic refrigerator according to any one of claims 1 to 6, characterized in that, It also has: Compressor; and A low-pressure line connects the compressor and the expander to recover low-pressure working gas from the expander to the compressor. The pressure sensor measures the pressure of the working gas on the low-pressure pipeline.

10. The cryogenic refrigerator according to claim 9, characterized in that, The periodically occurring feature points are those that periodically appear on the measured pressure of the low-pressure pipeline by the discharge of working gas from the expansion space via the rotary valve.

11. A method for operating an ultra-low temperature refrigerator, characterized in that, The cryogenic refrigerator includes an expander, which comprises: an expander motor with a motor rotating shaft; a displacement device connected to the motor rotating shaft for linear reciprocating movement via rotation, and for changing the volume of the expansion space of the working gas through reciprocating movement; and a rotary valve connected to the motor rotating shaft for rotation via rotation, and for controlling the intake and exhaust of the working gas relative to the expansion space. The method includes the following steps: Measure the pressure of the working gas; The characteristic points that periodically appear on the measured pressure during the operation of the cryogenic refrigerator are detected. Acquire a motor drive waveform representing the commanded rotational speed of the motor shaft, wherein the commanded rotational speed of the motor shaft is set to vary during one rotation of the motor shaft; and The motor drive waveform is output after being synchronized with the periodically appearing feature points.

12. An ultra-low temperature refrigerator, characterized in that, have: Expander motor, equipped with a motor rotating shaft; The displacement device is connected to the motor rotating shaft in a linear reciprocating manner by the rotation of the motor rotating shaft, and changes the volume of the expansion space of the working gas by reciprocating movement. In one rotation of the motor rotating shaft, the first angular range passes through the top dead center where the volume of the expansion space is the largest, and in a subsequent rotation of the motor rotating shaft, the second angular range following the first angular range passes through the midpoint between the top dead center and the bottom dead center where the volume of the expansion space is the smallest. and The controller causes the expander motor to operate in such a way that the rotational speed of the motor shaft is reduced in the second angular range compared to the first angular range.

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