Adjustment method for a free-piston Stirling refrigerator

Abstract

The free-piston Stirling refrigerator is adjusted according to individual differences to ensure proper operation. [Solution] A method for adjusting a free-piston Stirling refrigerator 1, which has a linear motor 27, a piston 26, and a displacer 19 provided in a casing 4 having a tip 9 that serves as a heat-absorbing part, and a drive circuit 42 that supplies alternating current to an electromagnetic coil 36 of the linear motor 27, wherein the drive circuit 42 comprises a main control unit 43, an inverter circuit 45, and a storage unit 47, wherein the method involves deriving a drive frequency X that satisfies the condition that the cooling capacity is maximized when the tip 9 is at a predetermined temperature, storing this drive frequency X in the storage unit 47, and adjusting the main control unit 43 to output the alternating current of this stored drive frequency X to the inverter circuit 45, thereby driving the free-piston Stirling refrigerator 1 so that the cooling capacity is maximized when the tip 9 is at a predetermined temperature.

Description

Technical Field

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[0001] The present invention relates to a method for adjusting a free piston Stirling refrigerator.

Background Art

[0002] Conventionally, as this type of free piston Stirling refrigerator, there are known ones having a casing with a tip portion serving as a heat absorption portion, a linear motor provided in the casing, a piston provided in the casing and reciprocated by the linear motor, a displacer provided in the casing and reciprocating with a predetermined phase difference from the piston, and control means (corresponding to the drive circuit of the present invention) for supplying an alternating current to the electromagnetic coil of the linear motor. This control means is known to have a control circuit (corresponding to the main control unit of the present invention) and an inverter circuit (see Patent Document Ⅰ). Such a free piston Stirling refrigerator reciprocates the piston at a constant frequency by supplying an alternating current of a constant frequency to the electromagnetic coil of the linear motor, and vibrations are generated at a constant frequency due to the reciprocation of this piston and the displacer. In order to reduce this vibration, a vibration absorption unit for reducing vibrations of a specific frequency is provided in the casing of the free piston Stirling refrigerator.

Prior Art Documents

Patent Documents

[0003]

Patent Document Ⅰ

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention aims to solve the above problems and provide an adjustment method for a free-piston Stirling refrigerator that can be operated appropriately according to individual differences. [Means for solving the problem]

[0006] The adjustment method for a free-piston Stirling refrigerator according to claim 1 of the present invention comprises a casing having a heat-absorbing section, a linear motor provided in the casing, a piston provided in the casing and reciprocated by the linear motor, a displacer provided in the casing and reciprocating with the piston with a predetermined phase difference, and a drive circuit that supplies alternating current to the electromagnetic coil of the linear motor, wherein the drive circuit comprises a main control unit, an inverter circuit, and a memory unit, the adjustment method for a free-piston Stirling refrigerator comprises deriving a drive frequency that satisfies the condition for maximizing the cooling capacity when the heat-absorbing section is at a predetermined temperature, storing this drive frequency in the memory unit, and causing the main control unit to output power to the inverter circuit at this stored drive frequency.

[0007] Furthermore, the control method for a free-piston type Stirling refrigerator described in claim 2 of the present invention is as follows: In claim 1, the drive frequency output by the inverter circuit is changed while the heat absorption section is kept at a predetermined temperature, the drive frequency, voltage value and current value at that temperature are obtained, the relationship between the ratio of the current value and voltage value and the drive frequency is derived, the drive frequency at which the ratio of the current value and voltage value at the predetermined temperature of the heat absorption section is the ratio of the maximum current value and maximum voltage value obtained from the maximum voltage and maximum current that the inverter circuit can output is derived, and this drive frequency is stored in the memory unit.

[0008] Furthermore, the adjustment method for a free-piston type Stirling refrigerator described in claim 3 of the present invention is as follows: In claim 1, the drive frequency output by the inverter circuit is changed while the heat absorption section is kept at a first temperature, and the relationship between the temperature of the heat absorption section and the ratio of the current value and voltage value for each frequency is derived; the drive frequency output by the inverter circuit is changed while the heat absorption section is kept at a second temperature, and the relationship between the temperature of the heat absorption section and the ratio of the current value and voltage value for each frequency is derived; the ratio of the current value and voltage value at the first temperature and the ratio of the current value and voltage value at the second temperature are linearly interpolated for each frequency; the drive frequency at which the linearly interpolated ratio of the current value and voltage value at a desired temperature of the heat absorption section becomes the ratio of the maximum current value and maximum voltage value obtained from the maximum voltage value and maximum current value that the inverter circuit can output is derived; and this drive frequency is stored in the memory unit.

[0009] Furthermore, the adjustment method for a free-piston Stirling refrigerator described in claim 4 of the present invention is as follows: In claim 1, the free-piston Stirling refrigerator is first adjusted by changing the drive frequency output by the inverter circuit while maintaining the heat absorption section at a first temperature in a reference free-piston Stirling refrigerator, deriving the relationship between the temperature of the heat absorption section and the ratio of the current and voltage values ​​for each frequency, changing the drive frequency output by the inverter circuit while maintaining the heat absorption section at a second temperature, deriving the relationship between the temperature of the heat absorption section and the ratio of the current and voltage values ​​for each frequency, linearly interpolating the ratio of the current and voltage values ​​at the first temperature and the ratio of the current and voltage values ​​at the second temperature for each frequency, accumulating the obtained data of the temperature, current and voltage values ​​ratio, and adjusting the free-piston Stirling refrigerator. - In a piston-type Stirling refrigerator, the drive frequency output by the inverter circuit is changed while maintaining the heat absorption section at a first or second temperature. The relationship between the temperature of the heat absorption section and the ratio of current and voltage values ​​for each frequency is derived. Based on the accumulated data and the relationship between the temperature of the heat absorption section and the ratio of current and voltage values ​​for each frequency at the first or second temperature, the characteristics of the temperature of the heat absorption section and the ratio of current and voltage values ​​of the free-piston type Stirling refrigerator to be adjusted are estimated. The drive frequency at which the estimated ratio of current and voltage values ​​at the desired temperature of the heat absorption section corresponds to the ratio of the maximum current value to the maximum voltage value obtained from the maximum voltage value and maximum current value that the inverter circuit can output is derived, and this drive frequency is stored in the memory unit. [Effects of the Invention]

[0010] The control method for a free-piston type Stirling refrigerator described in claim 1 of the present invention allows the free-piston type Stirling refrigerator to be driven in such a way that the cooling capacity is maximized when the heat absorption section is at a predetermined temperature.

[0011] Furthermore, by changing the drive frequency output by the inverter circuit while maintaining the heat absorption section at a predetermined temperature, obtaining the drive frequency, voltage value, and current value at that temperature, deriving the relationship between the ratio of the current value and voltage value and the drive frequency, and deriving a drive frequency at which the ratio of the current value and voltage value at the predetermined temperature of the heat absorption section is equal to the ratio of the maximum current value and maximum voltage value obtained from the maximum voltage and maximum current that the inverter circuit can output, and storing this drive frequency in the memory unit, the free-piston type Stirling refrigerator can be driven so that the cooling capacity is maximized when the heat absorption section is at a predetermined temperature.

[0012] Furthermore, by changing the drive frequency output by the inverter circuit while maintaining the heat absorption section at a first temperature, deriving the relationship between the temperature of the heat absorption section and the ratio of current and voltage values ​​for each frequency; changing the drive frequency output by the inverter circuit while maintaining the heat absorption section at a second temperature, deriving the relationship between the temperature of the heat absorption section and the ratio of current and voltage values ​​for each frequency; linearly interpolating the ratio of current and voltage values ​​at the first temperature and the ratio of current and voltage values ​​at the second temperature for each frequency; deriving a drive frequency at which the linearly interpolated ratio of current and voltage values ​​at a desired temperature of the heat absorption section is equal to the ratio of maximum current and maximum voltage values ​​obtained from the maximum voltage and maximum current values ​​that the inverter circuit can output; and storing this drive frequency in the memory unit, the free-piston type Stirling refrigerator can be driven so that the cooling capacity is maximized at the desired temperature of the heat absorption section.

[0013] Furthermore, the following steps are performed in advance: In the free-piston Stirling refrigerator, which serves as a reference, the drive frequency output by the inverter circuit is changed while maintaining the heat absorption section at a first temperature, and the relationship between the temperature of the heat absorption section and the ratio of current and voltage values ​​for each frequency is derived; the drive frequency output by the inverter circuit is changed while maintaining the heat absorption section at a second temperature, and the relationship between the temperature of the heat absorption section and the ratio of current and voltage values ​​for each frequency is derived; the ratio of current and voltage values ​​at the first temperature and the ratio of current and voltage values ​​at the second temperature are linearly interpolated for each frequency, and the obtained data of the temperature, current and voltage ratios is stored and adjusted in the free-piston Stirling refrigerator, which is adjusted while maintaining the heat absorption section at a first or second temperature, and the drive frequency output by the inverter circuit is changed. By changing the temperature of the heat-absorbing section and deriving the relationship between the temperature, current value, and voltage value ratio for each frequency, and estimating the characteristics of the temperature, current value, and voltage value ratio of the heat-absorbing section of the free-piston Stirling refrigerator to be adjusted from the accumulated data and the relationship between the temperature, current value, and voltage value ratio of the heat-absorbing section for each frequency at the first or second temperature, a drive frequency is derived at which the estimated value of the current value and voltage value ratio at the desired temperature of the heat-absorbing section is equal to the value of the ratio of the maximum current value and maximum voltage value obtained from the maximum voltage value and maximum current value that the inverter circuit can output, and by storing this drive frequency in the memory unit, the measurement time for each unit can be shortened and the free-piston Stirling refrigerator can be driven so that the cooling capacity is maximized at the desired temperature of the heat-absorbing section. [Brief explanation of the drawing]

[0014] [Figure 1] This is a cross-sectional view of a free-piston Stirling refrigerator showing a first embodiment of the present invention. [Figure 2] This is a block diagram of the electrical system. [Figure 3] This graph shows the relationship between the driving frequency of the AC current supplied to the electromagnetic coil and the [current value / voltage value]. [Figure 4] This graph shows the relationship between the AC drive frequency supplied to the electromagnetic coil and the [current value / voltage value] for each aircraft model. [Figure 5]It is a graph showing the relationship between the temperature of the heat absorption part and the value of [current value / voltage value] of the alternating current supplied to the electromagnetic coil. [Figure 6] It is an explanatory diagram of the combination of the refrigerator main body and the vibration absorption unit. [Figure 7] It is an explanatory diagram showing the adjustment procedure of the vibration absorption unit. [Figure 8] It is a graph showing the relationship between the driving frequency of the alternating current supplied to the electromagnetic coil of the free piston Stirling refrigerator showing the second embodiment of the present invention and the value of [current value / voltage value]. [Figure 9] It is a graph showing the relationship between the temperature of the heat absorption part and the value of [current value / voltage value] of the alternating current supplied to the electromagnetic coil.

Mode for Carrying Out the Invention

[0015] Hereinafter, the first embodiment of the present invention will be described based on FIGS. 1 and 7. First, the configuration will be described. 1 is a free piston type Stirling refrigerator of the present invention. This Stirling refrigerator 1 is configured to include a refrigerator main body 2 and a vibration absorption unit 3.

[0016] The refrigerator main body 2 has a metal casing 4. And this casing 4 has a first casing body 5 and a second casing body 6. The first casing body 5 is integrally formed with a cylindrical portion 7 formed in a small-diameter cylindrical shape and a large-diameter portion 8 with an open base end. And the cylindrical portion 7 has a closed tip portion 9, an intermediate portion 10, and a base portion 11. Further, the large-diameter portion 8 has an end face portion 12 formed in a substantially circular protruding curved surface shape and a short cylindrical side face portion 13. Similarly, the second casing body 6 has a cylindrical side face portion 14 and another end face portion 15 formed in a substantially circular protruding curved surface shape. And the large-diameter portion 8 and the second casing body 6 form a cylindrical body portion 16. Further, an attachment portion 17 for attaching the vibration absorption unit 3 is integrally provided on the other end face portion 15 of the second casing body 6.

[0017] A cylinder 18, which extends into the body portion 16, is coaxially inserted into the cylindrical portion 7. That is, the central axis A of the cylinder 18 coincides with the central axis A of the cylindrical portion 7. The cylinder 18 is formed from metal. A displacer 19 is slidably housed inside the tip of the cylinder 18. An expansion chamber E is formed between the tip of the displacer 19 and the tip portion 9 of the cylindrical portion 7, and the inside and outside of the cylinder 18 are connected by a gap 20. In the intermediate portion 10, a regenerator 21 is provided between the inner circumference of the cylindrical portion 7 and the outer circumference of the cylinder 18, and in the base portion 11, a communication hole 22 is formed in the cylinder 18 itself, connecting the inside and outside of the cylinder 18. Furthermore, a heat-absorbing fin 23 is provided between the inner circumference of the tip 9 of the cylindrical portion 7 and the outer circumference of the tip of the cylinder 18, and a heat-dissipating fin 24 is provided between the inner circumference of the cylindrical portion 7 and the outer circumference of the cylinder 18 between the regenerator 21 and the communication hole 22. A path 25 is formed from the inner tip of the cylinder 18, passing through the gap 20, the heat-absorbing fin 23, the regenerator 21, the heat-dissipating fin 24, and the communication hole 22 to the compression chamber C inside the cylinder 18. In addition, a piston 26 is housed inside the base side of the cylinder 18 within the body portion 16 so as to be slidable in the direction of the central axis A. The base end of this piston 26 is coaxially connected to the linear motor 27. The linear motor 27 is configured to include a movable element 29 that is connected to the base end of the piston 26 by a connecting body 28 and extends coaxially around the outer circumference of the base end of the cylinder 18, and an annular stator 30 provided close to the outer circumference of the movable element 29.

[0018] Also, a first leaf spring 31 for controlling the operation of the piston 26 is connected to the connecting body 28 that connects the mover 29 to the piston 26. Further, one end of a rod 32 that operates together with the displacer 19 is connected to the proximal end side of the displacer 19, and a second leaf spring 33 is connected to the other end of the rod 32. The rod 32 passes through the center of the piston 26 and extends in the direction of the central axis A. The first and second leaf springs 31 and 33 are disposed outside the proximal end side of the cylinder 18 within the body 16, and the second leaf spring 33 is disposed at a position farther from the proximal end side of the cylinder 18 than the first leaf spring 31.

[0019] The mover 29 includes a frame 34 and a cylindrical permanent magnet 35 fixed to one end side of the frame 34. The stator 30 includes an electromagnetic coil 36, an outer core 37 provided to surround the electromagnetic coil 36, and an inner core 38. The outer core 37 is disposed outside the permanent magnet 35, and the inner core 38 is disposed inside the permanent magnet 35.

[0020] The vibration absorption unit 3 is attached to the attachment portion 17. The attachment portion 17 is provided coaxially with the central axis A. The vibration absorption unit 3 includes a connection portion 39 connected to the attachment portion 17, a leaf spring 40 attached to the connection portion 39, and a balance weight 41 attached to the leaf spring 40. The vibration absorption unit 3 is configured to be axially symmetric and is coaxial with the central axis A when attached to the attachment portion 17.

[0021] The electrical system for operating the Stirling refrigerator 1 will now be described. 42 is a drive circuit. This drive circuit 42 is composed of a main control unit 43, a power supply circuit 44, an inverter circuit 45, a galvanometer circuit 46, and a storage unit 47. A DC power supply 48, an operation unit 49, a temperature sensor 50, an anomaly detector 51, and the electromagnetic coil 36 are connected to the drive circuit 42. The DC power supply 48 is connected to the power supply circuit 44. The power supply circuit 44 is connected to the main control unit 43 and the inverter circuit 45. The electromagnetic coil 36 is connected to the inverter circuit 45 via the galvanometer circuit 46. The storage unit 47, inverter circuit 45, galvanometer circuit 46, operation unit 49, temperature sensor 50, and anomaly detector 51 are connected to the main control unit 43. The storage unit 47 stores a PWM data table. Based on this PWM data table and signals from the temperature sensor 50 and the anomaly detector 51, the main control unit 43 outputs a command to the inverter circuit 45 to output alternating current at a predetermined drive frequency and voltage value. Based on the command input from the main control unit 43, the inverter circuit 45 uses the DC supplied from the power supply circuit 44 to create alternating current at a predetermined drive frequency and voltage value and supplies it to the electromagnetic coil 36. The galvanometer circuit 46 measures the current value of the alternating current supplied from the inverter circuit 45 to the electromagnetic coil 36 and inputs it to the main control unit 43. The operation unit 49 is operated for starting / stopping the Stirling refrigerator 1, adjusting the set temperature, etc. The temperature sensor 50 measures the temperature of the tip 9, which is the heat-absorbing part of the Stirling refrigerator 1. Furthermore, the anomaly detector 51 is for detecting, for example, hitting (collision between the displacer 19 and the piston 26 or collision between the displacer 19 and the tip 9).

[0022] Next, the control of the Stirling refrigerator 1 will be described. A heat-absorbing element (e.g., a heater) is thermally connected to the tip 9 for adjustment purposes. When the operation unit 49 is operated to activate the Stirling refrigerator 1, the main control unit 43 of the drive circuit 42 outputs a command to the inverter circuit 45 to output AC at a reference frequency fcHz based on the PWM table stored in the memory unit 47. The inverter circuit 45 then generates AC at a predetermined frequency and voltage from the DC supplied from the DC power supply 48 and supplies it to the electromagnetic coil 36. When AC is supplied to the electromagnetic coil 36 in this way, the piston 26 and the displacer 19 reciprocate with a predetermined phase difference, and due to the action of the reverse Stirling cycle, heat is absorbed at the tip 9, which is the heat-absorbing part, and dissipated at the base 11, which is the heat-dissipating part. At the same time, heat is supplied to the tip 9 by energizing the heat-absorbing element. The temperature of the tip portion 9 is detected by the temperature sensor 50 and input to the main control unit 43.

[0023] When the tip portion 9 reaches a first temperature, the output of the electric heat conversion element is controlled to maintain this first temperature. That is, when the tip portion 9 falls below the first temperature, the amount of current supplied to the electric heat conversion element is increased to increase the amount of heat generated, and when the tip portion 9 rises above the first temperature, the amount of current supplied to the electric heat conversion element is decreased to decrease the amount of heat generated. In this example, the first temperature is -23.3°C (249.85K), which is a temperature commonly used in evaluation tests of refrigerators. With the tip portion 9 maintaining the first temperature, the main control unit 43 outputs a command to the inverter circuit 45 to change the drive frequency. The change in drive frequency may be performed automatically by the main control unit 43, or it may be performed by an operator manually operating the control unit 49. The inverter circuit 45 then generates alternating current with the changed drive frequency and voltage value from the DC supplied from the DC power supply 48 and supplies it to the electromagnetic coil 36. In this example, the drive frequency is varied in 0.2Hz increments within the range of fc ± 1Hz. This drive frequency and voltage value are obtained from a PWM table. The AC current value is measured by the galvanometer circuit 46 and input to the main control unit 43. In this way, the relationship between the drive frequency and the ratio of the current value to the voltage value (in this embodiment, [current value / voltage value]) is derived. In this embodiment, [current value / voltage value] is the ratio of the current value to the voltage value, but [voltage value / current value] may also be used as the ratio of the current value to the voltage value.

[0024] Next, the drive circuit 42 controls the inverter circuit 45 so that the tip portion 9 reaches a second temperature, either automatically or manually by the operator. Once the tip portion 9 reaches the second temperature, the output of the thermoelectric conversion element is controlled to maintain this second temperature. In this example, the second temperature is -80°C (193.15K). With the tip portion 9 maintaining the second temperature, the main control unit 43 outputs a command to the inverter circuit 45 to change the drive frequency. The change in drive frequency may be performed automatically by the main control unit 43, or by the operator manually operating the control unit 49. The inverter circuit 45 then generates alternating current with the changed drive frequency and voltage value from the DC supplied from the DC power supply 48 and supplies it to the electromagnetic coil 36. The current value of this alternating current is measured by the galvanometer circuit 46 and input to the main control unit 43.

[0025] Figure 3 is a graph showing the relationship between the AC drive frequency, voltage value, and current value obtained in this manner. Note that both the AC current value and voltage value are variables and fluctuate with the drive frequency. Therefore, a low [current value / voltage value] in Figure 3 does not necessarily indicate low power consumption.

[0026] In the graph of Figure 3, Y is the value of [maximum current value / maximum voltage value] obtained from the maximum voltage value and maximum current value that the inverter circuit 45 can output. The inventors have found that when the tip portion 9, which is the heat-absorbing part, is at a predetermined temperature, the driving frequency at which the AC [current value / voltage value] at that temperature equals the [maximum current value / maximum voltage value] is the condition under which the maximum capacity at that temperature can be achieved, based on the relationship between the driving frequency and [current value / voltage value]. Therefore, in this embodiment, it can be seen that the maximum capacity can be achieved when the tip portion 9 is at -80℃ at X = fc + 0.34 Hz. However, in this embodiment, the driving frequency is adjusted in increments of 0.2 Hz, so the driving frequency is adjusted to fc + 0.4 Hz.

[0027] As mentioned above, the Stirling refrigerator 1 may exhibit significant individual differences in cooling and electrical characteristics due to the accumulation of tolerances in several components. For example, Figure 4 is a graph showing the relationship between the drive frequency and [current value / voltage value] for each unit when the tip 9 is at -80°C. As shown in this graph, the relationship between the drive frequency and [current value / voltage value] may differ for each unit. In this case, the maximum capacity at -80°C is achieved at X1=fc+0.34Hz for unit 1, X2=fc-0.16Hz for unit 2, and X3=fc+0.68Hz for unit 3. As mentioned above, in this embodiment, the drive frequency is adjusted in 0.2Hz increments, so the drive frequency is adjusted to fc+0.4Hz for unit 1, fc-0.2Hz for unit 2, and fc+0.6Hz for unit 3.

[0028] Furthermore, there are cases where it is desired that the tip portion 9 achieves maximum performance at any temperature between the first and second temperatures. In this case, as shown in Figure 5, the value of [current value / voltage value] when the tip portion 9 is at the first temperature and the value of [current value / voltage value] when the tip portion 9 is at the second temperature are linearly interpolated and determined for each drive frequency. That is, the relationship between the temperature of the tip portion 9 and the [current value / voltage value] is determined for each drive frequency. Then, the frequency at which the line closest to the intersection of the desired temperature of the tip portion 9 and the [maximum current value / maximum voltage value] is determined is found. For example, in Figure 5, it can be seen that if the tip portion 9 is to achieve maximum performance at -50°C, the drive frequency should be fc-0.8Hz, and if the tip portion 9 is to achieve maximum performance at -70°C, the drive frequency should be fcHz. In this way, by using the value obtained by linearly interpolating the two temperatures and the [current value / voltage value] at those temperatures, the drive frequency that achieves maximum performance when the tip portion 9 is at any temperature can be determined with minimal measurement data. The inventors have also found that there are no practical problems even when using values ​​obtained by linearly interpolating the two temperatures of the tip portion 9 and the [current value / voltage value] at those temperatures.

[0029] In this way, when an alternating current of the adjusted drive frequency is supplied to the electromagnetic coil 36, the refrigerator body 2 generates vibrations of the same frequency as the adjusted drive frequency. The vibrations generated by the refrigerator body 2 are then reduced by the vibration absorption unit 3 attached to the refrigerator body 2. As is well known, the vibration absorption unit 3 for reducing the vibrations of the refrigerator body 2 can reduce vibrations of a natural frequency f determined by the spring constant k of the leaf spring 40 and the mass m of the balance weight 41. If the frequency of the vibrations generated by the refrigerator body 2 matches the natural frequency f, the vibrations generated by the refrigerator body 2 are reduced by the vibration absorption unit 3. The natural frequency f = ((k / m)^0.5) / 2π.

[0030] In conventional Stirling refrigerators, the driving frequency of the AC current supplied to the electromagnetic coil of the linear motor was fixed, so the frequency of the generated vibrations was also fixed, and the natural frequency f of the vibration absorption unit was also fixed. However, because there are tolerances in the spring constant of the leaf spring and the mass of the balance weight, it was necessary to fine-tune the natural frequency f of the vibration absorption unit. This fine-tuning can be done by adjusting the spring constant of the leaf spring, adjusting the mass of the balance weight, or both, but in practice, adjusting the mass of the balance weight is easier than adjusting the spring constant of the leaf spring, so the natural frequency f was often fine-tuned by adjusting the mass of the balance weight. Also, it was easier to add weight to the balance weight than to reduce its mass. From the above formula, it can be seen that if the spring constant of the leaf spring is the same, increasing the mass of the balance weight will decrease the natural frequency f. Therefore, the mass of the balance weight was set to a value slightly higher than the target natural frequency f, taking into account the tolerance of the spring constant of the leaf spring. By adding an additional weight to the balance weight, the natural frequency f was reduced to the target value.

[0031] In this embodiment, since the drive frequency of the AC supplied to the electromagnetic coil 36 is adjusted, the frequency of vibrations generated by the refrigerator body 2 also fluctuates. Therefore, when the drive frequency of the AC supplied to the electromagnetic coil 36 is adjusted, it becomes necessary to adjust the natural frequency f of the vibration absorption unit 3 beyond the range of fine adjustment possible with conventional vibration absorption units.

[0032] However, in this embodiment, since the adjustment range of the drive frequency is fc ± 1 Hz, vibrations of the refrigerator body 2 also occur in the range of fc ± 1 Hz. Therefore, the natural frequency f of the vibration absorption unit 3 needs to be adjustable within a range of up to 2 Hz. If the natural frequency of the vibration absorption unit 3 before adjustment is f0, then, as mentioned above, if the mass m of the balance weight 41 is set so that f0 is slightly higher than fc + 1 Hz, then when the frequency of the AC current is set to fc - 1 Hz, many additional weights 52 must be added to the balance weight 41. Furthermore, depending on the size of the balance weight 41, there is a risk that there will be no place to attach the additional weights 52. Therefore, in this embodiment, several types of vibration absorption units 3a, 3b, 3c... are prepared by combining several types of balance weights 41a, 41b, 41c... with masses ma, mb, mc... and leaf springs 40, and fine adjustments are made by adding the additional weights 52 to the balance weights 41a, 41b, 41c... of these vibration absorption units 3a, 3b, 3c.... By doing so, the number of additional weights 52 can be reduced, making it easy to adjust the vibration absorption units 3a, 3b, 3c.... Then, by selecting one of the vibration absorption units 3a, 3b, 3c... according to the adjusted drive frequency and attaching it to the refrigerator body 2, the Stirling refrigerator 1 can be easily assembled.

[0033] The additional weight 52 can be a magnet (provided the balance weight 41 is made of a magnetic material such as steel) or a screw. When the additional weight 52 is a magnet, it is more expensive than when it is a screw, but it can be added even when the balance weight 41 is vibrating, making it easy to adjust the mass. When the additional weight 52 is a screw, it cannot be added unless the vibration of the balance weight 41 is stopped, but it is cheaper than when it is a magnet.

[0034] Furthermore, the vibration absorption unit 3 does not need to be actually attached to the refrigerator body 2 for fine adjustment. As shown in Figure 7, it may be attached to a regulator 53 that vibrates at a predetermined frequency in the range including fc ± 1 Hz, and the natural frequency f may be adjusted. In this case, first (a) the vibration absorption unit 3 before adjustment is attached to the regulator 53, and (b) vibration is applied while changing the frequency. At this time, the frequency at which the vibration is reduced the most is the natural frequency f0 of the vibration absorption unit 3 before adjustment. Once this natural frequency f0 before adjustment is determined, (c) several additional weights 52 are attached to the balance weight 41. The approximate change in the natural frequency f for each additional weight 52 added can be calculated from the design spring constant of the leaf spring 40, the design mass of the balance weight 41, and the unit mass of the additional weights 52. Therefore, the approximate number of additional weights 52 to be added can be calculated from the difference between the natural frequency f0 before adjustment and the target natural frequency f. The number of additional weights 52 calculated in this way are attached to the balance weight 41, and (b) the vibration is excited again at the frequency to be adjusted. That is, if the desired frequency is f=fcHz, the vibration is excited at fcHz. Similarly, if the desired frequency is f=fc+1Hz, the vibration is excited at fc+1Hz. The vibration reduction capacity at this time is then measured, and (c) the additional weights 52 are added or removed for fine adjustment. In this way, when the natural frequency f is adjusted so that the vibration reduction capacity is maximized at the desired frequency, (d) the adjusted vibration absorption unit 3 is removed from the adjuster 53.

[0035] By preparing the vibration absorption units 3a, 3b, 3c… adjusted in this manner in advance for each settable drive frequency (in 0.2 Hz increments in this embodiment), the Stirling refrigerator 1 can be assembled more easily by determining the drive frequency of the AC supplied to the electromagnetic coil 36 and then attaching the vibration absorption units 3a, 3b, 3c… that match that frequency to the mounting section 17.

[0036] As described above, the present invention provides a method for adjusting a free-piston Stirling refrigerator 1, which comprises a casing 4 having a tip portion 9 that serves as a heat-absorbing portion, a linear motor 27 provided inside the casing 4, a piston 26 provided inside the casing 4 and reciprocated by the linear motor 27, a displacer 19 provided inside the casing 4 and reciprocating with the piston 26 with a predetermined phase difference, and a drive circuit 42 that supplies alternating current to an electromagnetic coil 36 of the linear motor 27, wherein the drive circuit 42 comprises a main control unit 43, an inverter circuit 45, and a storage unit 47. The method involves deriving a drive frequency X that satisfies the condition for maximizing the cooling capacity when the tip portion 9 is at a predetermined temperature, storing this frequency X in the storage unit 47, and adjusting the main control unit 43 to output the alternating current of this stored frequency X to the inverter circuit 45, thereby driving the free-piston Stirling refrigerator 1 so that the cooling capacity is maximized when the tip portion 9 is at a predetermined temperature.

[0037] Furthermore, the present invention allows the free-piston type Stirling refrigerator 1 to be driven so that the cooling capacity is maximized when the tip portion 9 is at a predetermined temperature. This is achieved by changing the drive frequency output by the inverter circuit 45 while maintaining the tip portion 9 at a predetermined temperature, obtaining the drive frequency, voltage value, and current value at that temperature, deriving the relationship between [current value / voltage value] and drive frequency, deriving a drive frequency X such that the [current value / voltage value] at a predetermined temperature of the tip portion 9 is equal to the [maximum current value / maximum voltage value] obtained from the maximum voltage value and maximum current value that the inverter circuit 45 can output, and adjusting the system to store this drive frequency X in the storage unit 47.

[0038] Furthermore, the present invention allows the free-piston Stirling refrigerator 1 to be driven so that the cooling capacity is maximized at the desired temperature of the tip 9 by adjusting the drive frequency output by the inverter circuit 45 while maintaining the tip 9 at a first temperature of -23.3°C, deriving the relationship between the temperature of the tip 9 and the [current value / voltage value] for each drive frequency, changing the drive frequency output by the inverter circuit 45 while maintaining the tip 9 at a second temperature of -80°C, deriving the relationship between the temperature of the tip 9 and the [current value / voltage value] for each drive frequency, linearly interpolating the [current value / voltage value] at -23.3°C and the [current value / voltage value] at -80°C for each drive frequency, deriving a drive frequency X such that the linearly interpolated [current value / voltage value] at the desired temperature of the tip 9 is the [maximum current value / maximum voltage value] obtained from the maximum voltage value and maximum current value that the inverter circuit 45 can output, and storing this drive frequency X in the storage unit 47.

[0039] Next, a second embodiment of the present invention will be described with reference to Figures 8 and 9. Note that the refrigerator body 2, vibration absorption unit 3, and drive circuit 42 to be adjusted are the same as those in the first embodiment described above, so their description will be omitted. Furthermore, it is assumed that, as shown in Figures 3 and 5 of the first embodiment, the relationship between the AC drive frequency and [current value / voltage value] at the first and second heat absorption section temperatures has been derived and stored for multiple units.

[0040] In this embodiment, with the tip portion 9 of the casing 4, which is the heat-absorbing portion, maintaining a temperature of -80°C (the second temperature in the first embodiment), the main control unit 43 of the drive circuit 42 outputs a command to the inverter circuit 45 to change the drive frequency supplied to the electromagnetic coil 36 of the linear motor 27. The change in drive frequency may be performed automatically by the main control unit 43, or it may be performed by an operator manually operating the control unit 49. The inverter circuit 45 then generates AC with the changed drive frequency and voltage value from the DC supplied from the DC power supply 48 and supplies it to the electromagnetic coil 36. The current value of this AC is measured by the galvanometer circuit 46 and input to the main control unit 43.

[0041] Figure 8 is a graph showing the relationship between the drive frequency, voltage value, and current value obtained in this way. In the graph of Figure 8, Y is the value of [maximum current value / maximum voltage value] obtained from the maximum voltage value and maximum current value that the inverter circuit 45 can output. The inventors have found that when the tip portion 9, which is the heat-absorbing part, is at a predetermined temperature, the drive frequency at which the AC [current value / voltage value] at that temperature equals [maximum current value / maximum voltage value] is the condition under which the maximum capacity at that temperature can be achieved, based on the relationship between the drive frequency and [current value / voltage value]. Therefore, in this embodiment, it can be seen that the maximum capacity can be achieved when the tip portion 9 is at -80℃ at X = fc + 0.34 Hz. However, in this embodiment, since the frequency of the AC current is adjusted in 0.2 Hz increments, the frequency of the AC current is adjusted to fc + 0.4 Hz.

[0042] Furthermore, there are cases where it is desired that the tip portion 9 achieves its maximum performance at any temperature higher than -80°C. In this case, as shown in Figure 9, the value of [current value / voltage value] when the tip portion 9 is -80°C and the value of [current value / voltage value] when the tip portion 9 is -23.3°C (the first temperature in the first embodiment) are linearly interpolated and estimated from the accumulated data, and determined for each drive frequency. That is, the relationship between the temperature of the tip portion 9 and the [current value / voltage value] is estimated from the accumulated data for each drive frequency. Then, the value of the line closest to the intersection of the temperature of the tip portion 9 at which maximum performance is desired and the [maximum current value / maximum voltage value] is determined. For example, in Figure 9, it can be seen that if the tip portion 9 is to achieve its maximum performance at -50°C, the drive frequency should be fc-0.8Hz, and if the tip portion 9 is to achieve its maximum performance at -70°C, the drive frequency should be fcHz. In this way, by linearly interpolating two temperatures and the [current value / voltage value] at those temperatures, and then estimating and using the resulting value from accumulated data, it is possible to determine the drive frequency that allows the tip portion 9 to perform at its maximum capacity when it is at any given temperature, using a minimum amount of measurement data.

[0043] In this embodiment, the relationship between the temperature of the tip 9 and the [current value / voltage value] at that temperature is merely an estimate, and therefore its accuracy is lower than that of the first embodiment. However, as more data is accumulated, the relationship between the temperature of the tip 9 and the [current value / voltage value] at that temperature can be estimated with practically acceptable accuracy. Furthermore, compared to the first embodiment, half the amount of measurement data is required, thus reducing the time needed for adjustment.

[0044] As described above, the present invention provides a method for adjusting a free-piston type Stirling refrigerator 1, which comprises a casing 4 having a tip portion 9 that serves as a heat-absorbing portion, a linear motor 27 provided inside the casing 4, a piston 26 provided inside the casing 4 and reciprocated by the linear motor 27, a displacer 19 provided inside the casing 4 and reciprocating with the piston 26 with a predetermined phase difference, and a drive circuit 42 that supplies alternating current to an electromagnetic coil 36 of the linear motor 27, wherein the drive circuit 42 comprises a main control unit 43, an inverter circuit 45, and a storage unit 47. The method involves deriving a drive frequency X that satisfies the condition for maximizing the cooling capacity when the tip portion 9 is at a predetermined temperature, storing this drive frequency X in the storage unit 47, and adjusting the main control unit 43 to output the alternating current of the stored drive frequency X to the inverter circuit 45, thereby driving the free-piston type Stirling refrigerator 1 so that the cooling capacity is maximized when the tip portion 9 is at a predetermined temperature.

[0045] Furthermore, the present invention allows the free-piston type Stirling refrigerator 1 to be driven so that the cooling capacity is maximized when the tip portion 9 is at a predetermined temperature. This is achieved by changing the drive frequency output by the inverter circuit 45 while maintaining the tip portion 9 at a predetermined temperature, obtaining the drive frequency, voltage value, and current value at that temperature, deriving the relationship between [current value / voltage value] and drive frequency, deriving a drive frequency X such that the [current value / voltage value] at a predetermined temperature of the tip portion 9 is equal to the [maximum current value / maximum voltage value] obtained from the maximum voltage value and maximum current value that the inverter circuit 45 can output, and adjusting the system to store this drive frequency X in the storage unit 47.

[0046] Furthermore, the present invention involves first maintaining the tip 9 at a first temperature of -23.3°C in the reference free-piston Stirling refrigerator 1 while changing the drive frequency output by the inverter circuit 45, deriving the relationship between the temperature of the tip 9 and the [current value / voltage value] for each drive frequency, maintaining the tip 9 at a second temperature of -80°C while changing the drive frequency output by the inverter circuit 45, deriving the relationship between the temperature of the tip 9 and the [current value / voltage value] for each drive frequency, linearly interpolating the [current value / voltage value] at -23.3°C and the [current value / voltage value] at -80°C for each drive frequency, accumulating the obtained temperature and [current value / voltage value] data, and adjusting the free-piston Stirling refrigerator 1 while maintaining the tip 9 at a second temperature of -80°C while changing the drive frequency output by the inverter circuit 45 By changing the drive frequency output by the inverter, the relationship between the temperature of the tip 9 and the [current value / voltage value] for each drive frequency is derived, and the characteristics of the temperature of the tip 9 and the [current value / voltage value] of the free-piston type Stirling refrigerator 1 to be adjusted are estimated from the accumulated data and the relationship between the temperature of the tip 9 and the [current value / voltage value] for each drive frequency at -80℃, and the drive frequency at which the estimated [current value / voltage value] at the desired temperature of the tip 9 becomes the [maximum current value / maximum voltage value] obtained from the maximum voltage value and maximum current value that the inverter circuit 45 can output is derived, and by adjusting to store this drive frequency in the memory unit 47, the measurement time for each unit can be shortened and the free-piston type Stirling refrigerator 1 can be driven so that the cooling capacity is maximized at the desired temperature of the tip 9.

[0047] It should be noted that the present invention is not limited to the embodiments described above, and various modifications can be implemented within the scope of the gist of the invention. For example, in each of the above embodiments, the first temperature of the heat absorption section was set to -23.3°C and the second temperature to -80°C, but these temperatures can be set arbitrarily. Also, in the second embodiment, the characteristics of the temperature of the heat absorption section and the [current value / voltage value] were estimated from the relationship between the drive frequency and the [current value / voltage value] when the heat absorption section is at the second temperature, but the characteristics of the temperature of the heat absorption section and the [current value / voltage value] may be estimated from the relationship between the drive frequency and the [current value / voltage value] when the heat absorption section is at the first temperature. Furthermore, in each of the above embodiments, the [current value / voltage value] was used as the ratio of current value to voltage value, but the [voltage value / current value] may be used for adjustment. Moreover, in each of the above embodiments, the adjustment range of the drive frequency was set to fc ± 1 Hz, but the adjustable range of the drive frequency can be set arbitrarily. [Explanation of symbols]

[0048] 1. Free-piston Stirling refrigerator 4. Casing 9 Tip (heat absorption part) 19 Displacer 26 pistons 27 Linear motor 36 Electromagnetic coil 42 Drive Circuit 43 Main Control Unit 45 Inverter Circuit 47 Memory section The frequency at which X,X1,X2,X3 [current value / voltage value] equals [maximum current value / maximum voltage value]. Y [Maximum current value / Maximum voltage value]

Claims

1. A method for adjusting a free-piston Stirling refrigerator, comprising a casing having a heat-absorbing section, a linear motor provided within the casing, a piston provided within the casing and reciprocated by the linear motor, a displacer provided within the casing and reciprocating with the piston with a predetermined phase difference, and a drive circuit that supplies alternating current to the electromagnetic coil of the linear motor, wherein the drive circuit comprises a main control unit, an inverter circuit, and a memory unit, A method for adjusting a free-piston type Stirling refrigerator, characterized by deriving a drive frequency that satisfies the condition for maximizing the cooling capacity when the heat absorption section is at a predetermined temperature, storing this drive frequency in the memory unit, and having the main control unit output power to the inverter circuit at this stored drive frequency.

2. While maintaining the heat-absorbing section at a predetermined temperature, the drive frequency output by the inverter circuit is changed, and the drive frequency, voltage value, and current value at that temperature are obtained. The relationship between the ratio of the current value to the voltage value and the drive frequency is then derived. A method for adjusting a free-piston type Stirling refrigerator according to claim 1, characterized in that the ratio of the current value to the voltage value at a predetermined temperature of the heat-absorbing section is the ratio of the maximum current value to the maximum voltage value obtained from the maximum voltage and maximum current that the inverter circuit can output, and this drive frequency is stored in the memory unit.

3. While maintaining the heat-absorbing section at a first temperature, the drive frequency output by the inverter circuit is changed, and the relationship between the temperature of the heat-absorbing section and the ratio of the current value and voltage value for each frequency is derived. While maintaining the heat-absorbing section at a second temperature, the drive frequency output by the inverter circuit is changed, and the relationship between the temperature of the heat-absorbing section and the ratio of the current value and voltage value for each frequency is derived. The ratio of current to voltage at the first temperature and the ratio of current to voltage at the second temperature are linearly interpolated for each frequency. A method for adjusting a free-piston type Stirling refrigerator according to claim 1, characterized in that the ratio of linearly interpolated current and voltage values ​​at a desired temperature of the heat-absorbing section is derived as the ratio of the maximum current and maximum voltage values ​​obtained from the maximum voltage and maximum current values ​​that the inverter circuit can output, and this drive frequency is stored in the memory unit.

4. Prior to this, using the standard free-piston type Stirling refrigerator, While maintaining the heat-absorbing section at a first temperature, the drive frequency output by the inverter circuit is changed, and the relationship between the temperature of the heat-absorbing section and the ratio of the current value and voltage value for each frequency is derived. While maintaining the heat-absorbing section at a second temperature, the drive frequency output by the inverter circuit is changed, and the relationship between the temperature of the heat-absorbing section and the ratio of the current value and voltage value for each frequency is derived. The ratio of current to voltage at the first temperature and the ratio of current to voltage at the second temperature are linearly interpolated for each frequency. The obtained data of the ratio of temperature, current value, and voltage value is stored, In the free-piston Stirling refrigerator being adjusted, the drive frequency output by the inverter circuit is changed while maintaining the heat absorption section at the first or second temperature, and the relationship between the temperature of the heat absorption section and the ratio of the current value and voltage value for each frequency is derived. Based on the accumulated data and the relationship between the temperature of the heat-absorbing section and the ratio of current and voltage values ​​for each frequency at the first or second temperature, the characteristics of the temperature of the heat-absorbing section and the ratio of current and voltage values ​​of the free-piston type Stirling refrigerator to be adjusted are estimated. A method for adjusting a free-piston type Stirling refrigerator according to claim 1, characterized in that the ratio of the current value to the voltage value estimated at a desired temperature of the heat-absorbing section is the ratio of the maximum current value to the maximum voltage value obtained from the maximum voltage value and maximum current value that the inverter circuit can output, and this drive frequency is stored in the memory unit.

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