CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. Provisional Patent Application No. 63/007,883 filed April 9, 2020 and entitled “ANNULAR CRYOCOOLER COMPRESSOR SYSTEMS AND METHODS,” which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

One or more embodiments of the invention relate generally to cryogenic refrigeration devices and more particularly, for example, to motorized compressors for refrigeration systems and methods.

BACKGROUND

Cryogenic refrigeration systems, or cryocoolers, are typically used to cool other devices to temperatures approaching or below approximately 120 Kelvin, and, more generally, can be used to cool devices to between 200 and 60 Kelvin, for example, depending on the overall heat load presented by a particular device. Such cooled devices are often one of a variety of different types of sensor systems that operate better (e.g., produce measurements with less noise, higher sensitivity, higher accuracy, higher responsiveness, and/or with other generally more desirable performance metrics) when cooled and/or otherwise unable to operate without being cooled. For example, one such category of sensor systems that can benefit from being cooled includes infrared cameras (e.g., including a focal plane array (FPA) of individual infrared sensors), which measure or capture infrared (e.g., thermal) emissions from objects as infrared/thermal images and/or video. Cooling such infrared cameras generally increases detector sensitivity (e.g., by decreasing thermal noise intrinsic to the individual infrared sensors), which can result in overall more accurate and reliable infrared imagery.

Cryocoolers for use with infrared cameras can be quite small (e.g., designed to fit within a volume of approximately 3 x 3 x 2 inches, or less), yet be able to provide sufficient cooling power (e.g., a measure, typically in Watts, of a refrigerator’s ability to extract heat from a coupled device) to cool at least portions of an infrared camera to the range of temperatures desired for, for example, relatively low noise thermal imagery, while experiencing the thermal load typical of an operating infrared camera. Vibrations generated by motors driving such cryocoolers, and conventional vibration mitigation techniques, can under some circumstances have substantial negative impact on the weight, cost, and overall performance of the cryocooler and/or sensor system. Moreover, reductions in system size and weight can be helpful to facilitate various compact system applications, including integration with a flight platform, an unmanned aerial vehicle (UAVs), as a handheld weapon sight, and as a handheld camera, for example.

Thus, there is a need in the art for a relatively compact cryocooler that is able to maintain or increase overall system performance, at least with respect to vibrations and system size, relative to conventional systems.

SUMMARY

Techniques are disclosed for systems and methods to reduce the overall physical size of and mechanical vibrations within a cryocooler/refrigeration system configured to provide cryogenic and/or general cooling of a device or sensor system. In one embodiment, a system may include an annular linear compressor configured to generate a compression wave of working gas for the system. The annular linear compressor may include an annular cylinder head with a pressure plate and a neck protruding from one side of the annular cylinder head; a compressor housing configured to mate with the pressure plate and the neck of the annular cylinder head and form a sealed cavity therebetween; and an annular cylinder assembly disposed within the sealed cavity and about the neck of the annular cylinder head, where the annular cylinder assembly includes an annular piston assembly disposed within an annular cylinder of the annular cylinder assembly.

In another embodiment, a method may include receiving operational parameters corresponding to operation of a cryocooler controlled by a cryocooler controller; generating motor driver control signals based, at least in part, on the received operational parameters; and generating, by a motor driver of the cryocooler controller, drive signals based, at least in part, on the motor driver control signals, to drive an annular linear compressor of the cryocooler. The annular linear compressor may include an annular cylinder head with a pressure plate and a neck protruding from one side of the annular cylinder head; a compressor housing configured to mate with the pressure plate and the neck of the annular cylinder head and form a sealed cavity therebetween; and an annular cylinder assembly disposed within the sealed cavity and about the neck of the annular cylinder head, where the annular cylinder assembly includes an annular piston assembly disposed within an annular cylinder of the annular cylinder assembly.

The scope of the invention is defined by the claims, which are incorporated into this section by reference. A more complete understanding of embodiments of the invention will be afforded to those skilled in the art, as well as a realization of additional advantages thereof, by a consideration of the following detailed description of one or more embodiments. Reference will be made to the appended sheets of drawings that will first be described briefly.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 illustrates a block diagram of a refrigeration system including an annular linear compressor in accordance with an embodiment of the disclosure.

Fig. 2 A illustrates a block diagram of a split-pair Stirling refrigerator/cryocooler including a non-integrated cylindrical linear compressor in accordance with an embodiment of the disclosure. Fig. 2B illustrates an image of a split-pair Stirling refrigerator/cryocooler including a non-integrated cylindrical linear compressor in accordance with an embodiment of the disclosure.

Fig. 3 A illustrates a block diagram of a split-pair Stirling refrigerator/cryocooler including an annular linear compressor in accordance with an embodiment of the disclosure. Fig. 3B illustrates a block diagram of a refrigeration system including an annular linear compressor in accordance with an embodiment of the disclosure.

Fig. 3C illustrates a cross section of a refrigeration system including an annular linear compressor in accordance with an embodiment of the disclosure.

Fig. 4A illustrates an annular cylinder head for an annular linear compressor of a refrigeration system in accordance with an embodiment of the disclosure.

Fig. 4B illustrates a gas transfer plate for a refrigeration system including an annular linear compressor in accordance with an embodiment of the disclosure. Fig. 5A illustrates a cross section of an annular piston assembly for an annular linear compressor of a refrigeration system in accordance with an embodiment of the disclosure.

Fig. 5B illustrates an annular piston assembly for an annular linear compressor of a refrigeration system in accordance with an embodiment of the disclosure.

Fig. 6 illustrates a flow diagram of operation of an annular linear compressor for a refrigeration system in accordance with an embodiment of the disclosure.

Fig. 7 is a flowchart illustrating a method for operating a refrigerator/cryocooler in accordance with an embodiment of the disclosure.

Embodiments of the invention and their advantages are best understood by referring to the detailed description that follows. It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures.

DETAILED DESCRIPTION

In accordance with various embodiments of the present disclosure, compact and powerful refrigeration systems and methods may advantageously employ an annular linear compressor.

For example, linear coolers are increasingly used for compact and lightweight applications because of their improved downward size scalability over, for example, rotary coolers. Virtually all integrated dewar cooler assemblies (IDCAs) using linear coolers do not utilize the space around the dewar enclosure in an efficient way due to the conventional cooler compressor being physically located adjacent to the Dewar body (e.g., similar to that shown in Fig. 2B). Dewar enclosures are usually cylindrical and include a relatively narrow neck concentric with a relatively wide head. The head or main body is typically relatively wide because it must fit and thermally isolate a focal plane array (FP A), motherboard, and/or other electronic device or element to be cooled and have room for external electrical connections (e.g., wire-bonding connections to feed-through pins). The neck is typically relatively narrow because it generally only needs to house and thermally isolate the expander of the cooler, which is typically a relatively narrow component, as described herein. The distance a conventional cooler compressor is spaced from the dewar enclosure is often determined by the widest part of the dewar enclosure, which is typically the head region. Therefore, the radial volume around the dewar enclosure neck region is mostly unoccupied in most conventional IDCA designs, and so it is essentially wasted space. Embodiments provide a linear cryocooler compressor that employs an annular piston assembly rather than a solid cylindrical piston typical of conventional linear cooler compressors. Such annular linear compressors efficiently occupy the space around the dewar enclosure because they are annular in shape, with an annular gap in the center that the dewar enclosure occupies, thereby allowing the volume of the overall envelope of the IDCAto be smaller. Moreover, because the center of mass of the annular piston assembly in such an annular linear compressor can be oriented to oscillate in line with an optical path of a coupled imaging device, embodiments provide relatively high performance with a single piston despite the increased vibration relative to conventional dual opposed piston compressors (e.g., similar to that shown in Fig. 2B). Such reduction of moving parts can significantly reduce cost compared to dual opposed piston compressor designs.

By more fully integrating the annular linear compressor with the rest of the refrigeration/sensor system, embodiments of the annular linear compressor can be configured to reduce radial vibrations transmitted to a coupled electronic device (e.g., a cooled infrared camera) while substantially maintaining the compactness and cooling power of the refrigeration system. The increased performance and flexibility of the constituent refrigeration systems, relative to systems employing relatively large vibration mitigation techniques, allows coupled cooled sensor systems to operate according to higher performance characteristics than achievable with conventional refrigeration systems, particularly where compactness is at a premium, such as in applications involving spaceflight, unmanned aircraft systems, handheld systems, relatively large and/or high power-dissipating sensor systems, and/or battery or solar powered systems.

For example, infrared cameras may be used for nighttime or other applications when ambient lighting is poor or when environmental conditions are otherwise non-conducive to visible spectrum imaging, and they may also be used for applications in which additional non- visible-spectrum information about a scene is desired, such as for gas leak detection. In each application, it is typically desirable to reduce noise and variability in images captured by the infrared camera by cooling at least a focal plane array (FP A) of the infrared camera to a cryogenic and/or relatively stable temperature while the images are captured. It is also typically desirable to minimize system vibrations that can cause heating, blurring, and/or interference with operation of the infrared camera. The reduced radial vibrations provided by embodiments of the present disclosure result in lower noise and/or blur in resulting infrared imagery and more reliable and accurate infrared images (e.g., in particular, thermal images). Fig. 1 illustrates a block diagram of a refrigeration system 100 including an annular linear compressor 172 in accordance with an embodiment of the disclosure. As shown in Fig. 1, refrigeration system 100 includes power supply 112 providing an input power signal over power leads 113 to cooler controller 120, which then provides motor drive signals and/or other system drive signals over power leads 123 to drive annular linear compressor/motor 172 and/or other elements of cryocooler 170. In general, cryocooler 170 operates to cool cold finger 176, which is thermally coupled to and configured to cool/extract heat from at least a portion (e.g., FPA 182) of electronic device/sensor/camera 180 through thermal interface 177. As shown in Fig. 1, cryocooler controller 120 may be configured to receive various sensor signals (e.g., corresponding to an input voltage of the input power signal provided by power supply 112, an output voltage of motor drive signals generated by motor driver 140/cryocooler controller 120, temperatures of various components of refrigeration system 100 measured by temperature sensors 134, and/or other sensor signals corresponding to operation of cryocooler 170, annular linear compressor 172, and/or other elements of refrigeration system 100) as feedback of operation of cryocooler 170 and/or other elements of refrigeration system 100, and to adjust drive signals provided to annular linear compressor 172 and/or other elements of cryocooler 170 accordingly (e.g., so as provide a stable and/or desired temperature and/or cooling power with relatively little mechanical vibration at cold finger 176).

Also shown in Fig. 1 is user interface 110. User interface 110 may be implemented as a personal computer, a tablet, a smart phone, a mobile computing device and/or vehicle interface, and/or one or more of a display, a touch screen, a keyboard, a mouse, a joystick, a knob, button, or switch, and/or any other device capable of accepting user input and/or providing feedback to a user. More generally, user interface 110 may be configured to provide user-level control of refrigeration system 100 and to provide operational feedback to a user of system 100.

User interface 110 may be integrated with any appropriate logic device (e.g., processing device, microcontroller, processor, application specific integrated circuit (ASIC), field programmable gate array (FPGA), memory storage device, memory reader, or other device or combinations of devices) that may be adapted to execute, store, and/or receive appropriate instructions, such as software instructions implementing a control loop for controlling various operations of system 100. In addition, user interface 110 may include a machine readable medium provided for storing non-transitory instructions for loading into and execution by user interface 110. In these and other embodiments, user interface 110 may be implemented with other components where appropriate, such as volatile memory, non-volatile memory, and/or various analog and/or digital components for interfacing with devices of system 100.

In various embodiments, user interface 110 may be configured to provide an initialization signal to cryocooler controller 120 to begin operation of cryocooler 170, for example, or to provide a temperature set point and/or other operational parameters (e.g., corresponding to a desired operational state of cryocooler 170) to cryocooler controller 120. In specific embodiments, user interface 110 may be configured to provide and/or update configuration data, including logic-level configuration data, to cryocooler controller 120 to facilitate control of operation of cryocooler 170, as described herein. User interface 110 may also be configured to receive an operating temperature, power draw, efficiency, and/or other operating characteristic and/or measured feedback of operation of cryocooler 170 and/or other elements of refrigeration system 100 (e.g., from cryocooler controller 120 and/or other elements of system 100) and provide such information for display or indication to a user. In some embodiments, user interface 110 may be configured to receive infrared images captured by camera 180 (e.g., over data leads 111) and provide the infrared images for display to a user.

Power supply 112 may be implemented as a battery, solar cell, mechanical generator, and/or other power generating and/or delivery device, which may be provided specifically to power refrigeration system 100, for example, and/or be coupled to, integrated with, or generated as part of the operation of a separate platform, such as a sensor, vehicle, aircraft, watercraft, or other fixed or mobile platform. In some embodiments, power supply 112 may be configured to provide an input DC power signal over power leads 113, such as a 12V, 40V, 48V, or other voltage level DC power signal. More generally, power supply 112 may be configured to provide any type of input power signal over power leads 113 that can be converted by cryocooler controller 120 into motor drive signals and/or other drive signals appropriate to drive annular linear compressor 172 and/or other elements of cryocooler 170.

As shown in Fig. 1, cryocooler controller 120 includes motor driver controller 130, feedback interface 132, motor driver 140, and optional other modules 122. In additional embodiments, such as where cryocooler 170 includes multiple motors and/or compressors, cryocooler controller 120 may be implemented with multiple motor drivers, for example, that may each be controlled independently by motor driver control signals generated by motor driver controller 130. Motor driver controller 130 may be implemented as any appropriate logic device (e.g., processing device, microcontroller, processor, ASIC, FPGA, memory storage device, memory reader, or other device or combinations of devices) that may be adapted to execute, store, and/or receive appropriate instructions, such as software instructions implementing a control loop for controlling various operations of cryocooler 170 and/or other components of system 100. For example, motor driver controller 130 may be configured to receive operational parameters corresponding to operation of cryocooler 170 and generate motor driver control signals configured to control operation of motor driver 140 based, at least in part, on the received operational parameters.

In addition, motor driver controller 130 may include a machine readable medium provided for storing data and/or non-transitory instructions for loading into and execution by motor driver controller 130. In these and other embodiments, motor driver controller 130 may be implemented with other components where appropriate, such as volatile memory, non-volatile memory, and/or various analog and/or digital components for interfacing with devices of system 100. In a particular embodiment, motor driver controller 130 may be implemented substantially entirely by a programmable logic device (PLD), such as an FPGA, which may be configured to implement (e.g., using programmable resources) and perform any of the methods described herein. In such embodiments, user interface 110 may be configured to provide/update configuration data over data leads 111 to motor driver controller 130 that is configured to implement/update/ modify such methods in programmable resources and/or other elements of motor driver controller 130.

Motor driver 140 may be implemented by one or more electrical components, such as various electrically controllable switches/transistors, an inductor, and a capacitor, that are configured to receive motor driver control signals and/or other drive signals from motor driver controller 130 and to generate drive signals based, at least in part, on the motor driver control signals and/or the other drive signals, to drive annular linear compressor 172 and/or other elements of cryocooler 170.

Feedback interface 132 may be implemented by one or more of a multichannel analog to digital converter, a reference signal source, a temperature sensor, a digital communication interface, and/or other electrical or electronic components configured to receive and/or measure sensor signals corresponding to operation of cryocooler 170 and/or other elements of system 100 (e.g., over sensor leads 124) and convert such sensor signals into corresponding feedback data indicative of an operational state of cryocooler 170 and/or other elements of system 100. Feedback interface 132 may be configured to provide such feedback data to motor driver controller 130 to help adjust operation of cryocooler 170 and/or other elements of system 100 according to various desired operational characteristics or states of cryocooler 170 and/or other elements of system 100.

For example, feedback interface 132 may be configured to receive one or more sensor signals (e.g., from temperature sensor 134) and generate feedback data corresponding to operation of cryocooler 170, and motor driver controller 120 may be configured to receive the feedback data from feedback interface 132 and generate motor driver control signals and/or other drive signals based, at least in part, on the feedback data. In some embodiments, one or more of temperature sensors 134 may be implemented as diodes with characteristic voltage/temperature responses. Feedback interface 132 may be configured to provide a reference current to a diode and to measure/digitize the resulting voltage developed across the diode, which is proportional to the temperature of the temperature sensor 134. Advantageously, such diodes may be integrated with FPA 182 of camera 180, for example, allowing direct and precise measurement and feedback of a temperature of FPA 182.

In some embodiments, the one or more sensor signals received by feedback interface 132 may include a measured temperature of cold finger 176 of cryocooler 170 and/or electronic device 180 thermally coupled to cryocooler 170 (e.g., via thermal interface 177). Corresponding feedback data may be provided to motor driver controller 120, which may be configured to determine a feedback error based, at least in part, on a setpoint corresponding to a desired temperature for cold finger 176 and/or electronic device 180 and the received feedback data. In such embodiments, motor driver controller 120 may be configured to generate motor driver control signals based, at least in part, on the determined feedback error.

In other embodiments, the one or more sensor signals received by feedback interface 132 may include a measured vibration amplitude of cold finger 176 of cryocooler 170 and/or electronic device 180 thermally coupled to cryocooler 170 (e.g., via thermal interface 177). Corresponding feedback data may be provided to motor driver controller 120, which may be configured to determine a constant or time varying amplitude, phase, and/or other drive signal characteristic based, at least in part, on a desired maximum vibration amplitude for cold finger 176 and/or electronic device 180 and the received feedback data. In such embodiments, motor driver controller 120 may be configured to generate driver control signals based, at least in part, on the determined feedback error.

More generally, motor driver controller 120 may be configured to determine the feedback error, a ramp enable state corresponding to an operational state of cryocooler 170, and/or a ramp error based, at least in part, on feedback data (e.g., generated by feedback interface 132) corresponding to a measured temperature of cold finger 176 and/or electronic device 180, a measured input voltage of a power signal received by motor driver 140, a measured output voltage of drive signals generated by motor driver 140, and/or a measured temperature of cryocooler controller 120 (e.g., measured by feedback interface 132). In such embodiments, motor driver controller 120 may be configured to generate motor driver control signals based, at least in part, on the determined feedback error, ramp enable state, and/or ramp error. Optional other modules 122 may include various power, digital, and/or analog signal interfaces, sensors, and/or additional circuitry configured to facilitate operation of any element of cryocooler controller 120.

Cryocooler 170 may be implemented as any cooler or refrigeration system configured to convert electrical power delivered over power leads 123 to annular linear compressor 172 into cooling power generated by expander/refrigerator 174 at cold finger 176. In some embodiments, cryocooler 170 may be implemented as a Stirling refrigerator, for example, and in particular embodiments, as a miniature split-pair Stirling refrigerator including annular linear compressor 172, as described in more detail with reference to Figs. 3A-C. As shown in Fig. 1, cryocooler 170 may include one or more temperature sensors 134 configured to provide sensor signals indicative of a measured temperature of a corresponding element of cryocooler 170 (e.g., of annular linear compressor 172, for fault detection, or of cold finger 176, for operating temperature feedback) to feedback interface 132 of cryocooler controller 120. Optional other modules 178 may include additional temperature or electrical signal sensors, vibration sensors, various mechanical or thermal linkages, dewar cavities, working gas reservoirs, and/or other mechanical or electrical components or sensors configured to facilitate operation of any element of cryocooler 170 and/or provide additional operational feedback to cryocooler controller 120.

As shown in Fig. 1, cryocooler 170 may be thermally coupled to electronic device/sensor/camera 180 via thermal interface 177. For example, thermal interface 177 may be implemented by thermal grease, thermal tape, copper or aluminum plate or film, and/or other materials and/or structures configured to provide a reliable and highly thermally conductive link between cryocooler 170 and at least a portion of electronic device/sensor/camera 180. Electronic device/sensor/camera 180 may be any device, sensor, or imaging device that operates better (e.g., with higher signal to noise operational characteristics and/or with higher performance according to other performance metrics) when cooled, for example, or that is otherwise unable to operate without cooling.

For example, electronic device/camera 180 may include an infrared imaging sensor implemented as FPA 182, which may be coupled to optics 184 and be configured to image infrared radiation (e.g., including thermal radiation) emitted from a scene in view of optics 184. In some embodiments, cryocooler 170 may be directly coupled (e.g., via thermal interface 177) to a sensor (e.g., /FPA 182) of electronic device/camera 180 and primarily be configured to cool such sensor. In other embodiments, cryocooler 170 may be coupled to various elements of electronic device/camera 180 (e.g., optics 184, camera body 181, and/or other modules 186) and be configured to cool such various elements to help increase performance of electronic device/camera 180.

As shown in Fig. 1, electronic device/camera 180 may include one or more temperature sensors 134 configured to provide sensor signals indicative of a measured temperature of a corresponding element of electronic device/camera 180 (e.g., of FPA 182, for operating temperature feedback) to feedback interface 132 of cryocooler controller 120. Optional other modules 186 may include additional temperature or electrical signal sensors, FPAs of sensors sensitive to different spectrums (e.g., visible light), other optical elements, and/or other mechanical or electrical components or sensors configured to facilitate operation of any element of electronic device/camera 180 and/or provide additional operational feedback to cryocooler controller 120.

Also shown in Fig. 1 is optional other modules 190 of system 100 coupled to user interface 120 over data leads 111 and to other elements of system 100 over leads 192. Other modules 190 may include additional sensors, additional temperature or electrical signal sensors, an actuated gimbal and associated control subsystem to aim electronic device/camera 180 according to a desired direction, an accelerometer, a gyroscope, a global navigation satellite system receiver, a compass, other orientation and/or position sensors, vibration sensors, thermal management subsystems, structural support, thermal and/or electrical shielding, and/or other mechanical or electrical components or sensors configured to facilitate operation of any element of refrigeration system 100 and/or provide additional operational feedback to cryocooler controller 120.

Fig. 2 A illustrates a block diagram of a split-pair Stirling refrigerator/cryocooler 270 including a non-integrated cylindrical linear compressor 172B in accordance with an embodiment of the disclosure. In the embodiment shown in Fig. 2A, cryocooler 270 includes non-integrated cylindrical linear compressor/motor 172B adjacent to and in fluid communication with refrigerator/expander 174 via gas transfer line/tube 277. In general operation, motor/compressor 172B may be energized by motor driver 140 to compress working gas within the compression space (e.g., between pistons 271) and deliver a compression wave/mass flow of working gas through gas transfer line 277 to expander/refrigerator 174. Heat in the working gas generated at least in part by the compression is extracted at motor/compressor 172B and dissipated into the environment, rather than injected into expander 174.

The compression wave/mass flow causes regenerator/displacer 274 to move towards cold finger 176 and through inductive windings 278 within expander cylinder head 279, and at least a portion of the working gas travels through porous regenerator/displacer 274 and into expansion space 276. A restoring force provided by transducer/balancer system 280 and inductive windings 278, and the draw-back of pistons 271 (as controlled by drive signals provided by motor driver 140, for example) in between compression strokes draws regenerator/ displacer 274 back towards expander cylinder head 279 and expands the working gas within expansion space 276, thereby extracting heat from the environment through cold finger 176 and embedding it within the expanded working gas. Repeated operation of such cycle moves heat extracted from cold finger 176 (e.g., and anything thermally coupled to cold finger 176) to motor/compressor 172B, and the transferred heat is dissipated into the environment (e.g., using various heat exchangers and thermal management coupled to motor/compressor 172B), as is common with various Stirling cycle refrigeration systems.

As shown in Fig. 2A, motor/compressor 172B may be implemented with inductive windings 272 configured to cause pistons 271 to move towards each other to compress gas within the compression space therebetween. In some embodiments, motor driver 140 of cryocooler controller 120 may be electrically coupled to windings 272 of motor/compressor 172B (e.g., over power leads 123) and the motor drive signals generated by motor driver 140 may be used to drive pistons 271 to generate the compression wave/mass flow, as in a linear motor/compressor arrangement, as described herein. Other motor/compressor arrangements are contemplated, including various linear motor arrangements, other compressor arrangements, and/or cyclical motor and/or motor/compressor arrangements.

As also shown in Fig. 2A, expander 174 may be implemented with inductive windings 278 configured to limit the stroke of displacer 274 (e.g., so as not to impact cold finger 176 or expander cylinder head 279) and to help balance motion of displacer 274 and/or compensate for the mechanical vibrations caused by reciprocation of displacer 274 within expander 174. In some embodiments, motor driver 140 of cryocooler controller 120 (e.g., or an additional motor driver of cryocooler controller 120) may be electrically coupled to windings/coil 278 of expander 174 (e.g., over power leads 123) and balancer system drive signals generated by motor driver 140 may be used to drive displacer 274 and/or motion of windings/coil 278 as in a linear motor arrangement, similar in some aspects to operation of motor/compressor 172B described herein.

In alternative embodiments, transducer/balancer system 280 and/or inductive windings 278 may be replaced and/or supplemented with a mechanical spring or spring system coupled to displacer 274 within expander cylinder head 279 and configured to provide such restoring forces, as described herein.

Fig. 2B illustrates an image of a split-pair Stirling refrigerator/cryocooler 270 including a non-integrated cylindrical linear compressor 172B that may be controlled by cryocooler controller 120 of Fig. 1 in accordance with an embodiment of the disclosure. Fig. 2B illustrates the general size of a miniaturized cryocooler 270 that is analogous to cryocooler 270 of Fig. 2A and that may be used to cool FPA 182 of camera 180 in Fig. 1. For example, motor/compressor 172B may be approximately 2.6” in length, gas transfer line 277 may be approximately the same length (e.g., or shorter or longer, depending on application needs), and displacer 174 may be approximately 2” in length with a cold finger diameter of approximately 0.5”. In general, a cryocooler of a size and type similar to cryocooler 270 of Fig. 2B may be controlled by cryocooler controller 120 to reach stable operating temperatures, under typical heat loads, of approximately 77K to 120K, or higher temperatures depending on the application needs. More generally, various cryocooler arrangements (e.g., including cryocooler arrangements including and/or different from a split-pair Stirling refrigerator arrangement) may be controlled by cryocooler controller 120 to reach a wide range of stable operating temperatures, cooling powers, and/or subject to a wide variety of different size, power, and weight constraints.

Embodiments described herein replace the split-pair Stirling refrigerator/cryocooler 270 including non-integrated cylindrical linear compressor 172B with a refrigeration system including an annular linear compressor configured to occupy the space about expander 174 (e.g., and any interposing dewar enclosure) and provide various dual use elements to reduce size, weight, and cost.

For example, Fig. 3 A illustrates a block diagram of a split-pair Stirling refrigerator/cryocooler 370 including an annular linear compressor 372 in accordance with an embodiment of the disclosure. In various embodiments, cryocooler 370 and annular linear compressor 372 may be interchangeable with cryocooler 170 and annular linear compressor 172 of Fig. 1. As shown in Fig. 3 A, cryocooler 370 includes annular linear compressor 372 configured to deliver or generate a compression wave/mass flow of working gas from annular cylinder assembly 310 through gas transferline 277 to expander/refrigerator 174 in order to facilitate cooling of cold finger 176, as described herein. As shown in the embodiment illustrated in Fig. 3 A, gas transfer line 277 may be at least partially formed within gas transfer plate 377, which may also be configured to provide mechanical support and/or coupling between annular linear compressor 372 and expander 174, as shown. In various embodiments, annular linear compressor 372 may be sized to form an annular gap 373 between an inner surface of annular linear compressor 372 and an outer surface of expander 174, so as to leave room for a dewar enclosure to protect and/or thermally isolate expander 174 from the environment and/or annular linear compressor 372, for example, and to help mechanically isolate expander 174 from at least radial vibrations generated by annular linear compressor 372.

Fig. 3B illustrates a block diagram of a refrigeration system 300 including annular linear compressor 372 in accordance with an embodiment of the disclosure. In the embodiment shown in Fig. 3B, refrigeration system 300 includes annular linear compressor 372 of Fig. 3 A coupled to expander 174 and dewar enclosure 382. For example, dewar enclosure 382 may be configured to couple mechanically to gas transfer plate 377 at seal 386 and within annular gap 373 to form a thermally insulating vacuum space 384 between expander 174 and the environment and to leave a portion of annular gap 373 between dewar enclosure 382 to help mechanically isolate expander 174 and/or electronic device 380 (e.g., camera 180) from mechanical vibrations generated by annular linear compressor 372. In some embodiments, where electronic device 380 is implemented as a camera coupled to and cooled by cold finger 176, dewar enclosure 382 may be implemented with various additional elements to facilitate imaging/sensing by electronic device 380 through dewar enclosure 382, such as optical sight/aperture 388, as shown. In alternative embodiments, dewar enclosure 382 may be configured to couple mechanically to a housing for expander 174 (e.g., expander housing 374 shown in Fig. 3C) at a corresponding seal and within annular gap 373 to form at least a portion of thermally insulating vacuum space 384 between expander 174 and the environment.

Fig. 3C illustrates a cross section of refrigeration system 300 including annular linear compressor 372 in accordance with an embodiment of the disclosure. As shown in detail in Fig. 3, refrigeration system 300 includes annular linear compressor 372 with annular cylinder assembly 310 of Fig. 3A coupled to expander 174 and dewar enclosure 382. In various embodiments, annular cylinder assembly 310 may include outer yoke 316 disposed substantially about annular inductive windings/coil 312, annular piston assembly 320 disposed within annular cylinder/bore 314, and inner yoke 318, all disposed within a cavity formed by annular cylinder head 371-1 and compressor housing 371-2 (e.g., which may be welded together to form a sealed cavity), as shown. In some embodiments, such sealed cavity may provide a bounce space for annular piston assembly 320. Advantageously, the annular shape of annular linear compressor 372 provides an annular hollow (e.g., similar to annular gap 373) in which expander 174 and dewar enclosure 382 may be placed to form a relatively compact refrigeration system 300, as described herein.

Working gas compressed by annular piston assembly 320 travels through gas transfer line 277 and gas transfer plate 377 into expander 174, and reciprocating motion of annular piston assembly 320, coupled with sympathetic reciprocating motion of elements of expander 174 (e.g., enabled by mechanical spring system 379-2 disposed within expander cylinder head 379-1) generates cooling at cold finger 176 to extract heat from electronic device 380. Neck 383 of dewar enclosure 382 is disposed about expander 174 and within annular gap 373 and may engage and/or seal against gas transfer plate 377 and/or expander housing 374, which may itself couple mechanically to gas transfer plate 377 and help thermally and mechanically isolate at least cold finger 176 from the environment and/or mechanical vibrations generated by annular linear compressor 372.

In some embodiments, annular piston assembly 320 may be implemented as a split-piston assembly with a magnetic core. For example, as shown in the embodiment illustrated by Fig.

3C, annular piston assembly 320 may include inner split piston head 322 configured to form a seal with inner annular cylinder surface 315-1 of annular cylinder 314, outer split piston head 326 configured to form a seal with outer annular cylinder surface 315-2 of annular cylinder 314, and piston magnet ring 324 disposed within a cavity formed by split piston heads 322 and 326, as shown. In such embodiments, reciprocating motion of annular piston assembly 320 may be driven by drive signals provided to annular inductive windings 312 (e.g., by motor driver 140), which generate a varying magnetic field originating at annular inductive windings 312 (e.g., and shaped, at least in part, by inner and outer yokes 316 and 318) that couples inductively with piston magnet ring 324 and mechanically drives motion of annular piston assembly 320.

In various embodiments, annular cylinder/bore 314 may include inner annular cylinder surface 315-1 and outer annular cylinder surface 315-2 configured to seal against annular piston assembly 320 and ground (e.g., simultaneously for increased concentricity accuracy, to simplify alignment) to form a selected clearance gap about annular piston assembly 320 and to provide a desired surface finish, so as to reduce operational wear. Annular cylinder/bore 314 may be formed with relatively thin walls to reduce any detrimental magnetic shielding effect on the indicative coupling between annular inductive windings 312 and annular piston assembly 320. Outer yoke 316 may be implemented as a substantially annular sheath formed around annular inductive windings 312 from soft magnetic material and be configured to help carry and/or shape magnetic flux generated by annular inductive windings 312 and/or motion of annular piston assembly 320. Inner yoke 318 may be implemented as a substantially annular ring formed interior to annular cylinder 314 from soft magnetic material and be configured to help carry and/or shape magnetic flux generated by annular inductive windings 312 and/or motion of annular piston assembly 320. In some embodiments, outer yoke 316 and/or inductive windings 312 may be integrated with outer annular cylinder surface/wall 315-2, for example, and inner yoke 318 may be at least partially integrated with annular piston assembly 320 and/or inner annular cylinder surface 315-1. More generally, outer yoke 316 and inner yoke 318 may be implemented according to any desired shapes and/or materials disposed within compressor housing 371-2 and configured to help carry and/or shape magnetic flux generated by annular inductive windings 312 and/or motion of annular piston assembly 320 and inductively couple inductive windings 312 to annular piston assembly 320 across the full range of motion of annular piston assembly 320.

In various embodiments, annular linear compressor 372 may provide benefits over conventional compressor arrangements by eliminating the space required for such elements to be spaced from expander 174 and dewar enclosure 382 and, often, mounted separately and requiring separate mounting systems. Advantageously, embodiments of refrigeration system 200 may be relatively compact due to the annular stacking of expander 174, dewar enclosure 382, and annular linear compressor 372. Moreover, embodiments of refrigeration system 300 including annular linear compressor 372 may generate and/or couple relatively little radial mechanical vibration (e.g., mechanical vibrations orthogonal to the direction of linear reciprocal motion of expander 174) through to electronic device 380, which reduces risk of detrimental blurring typically caused by such radial mechanical vibration modes in embodiments where electronic device 380 is implemented as a visual, thermal, and/or multispectral camera with an FPAthat is oriented substantially perpendicular to motion of expander 174 and/or with an optical axis that is oriented substantially parallel to motion of expander 174. Advantageously, the annular stacking of expander 174, dewar enclosure 382, and annular linear compressor 372 primarily generates axial mechanical vibrations (e.g., parallel to the direction of linear reciprocal motion of expander 174) that typically do not cause such detrimental blurring.

As can be seen from Fig. 3C, in some embodiments, annular inductive windings 312 and annular piston assembly 320 may be implemented according to a moving magnet design, for example, which can provide increased motor efficiency and eliminate a need for moving electrical connections within annular linear compressor 372. Since the diameter of annular piston assembly 320 is large relative to the diameter of expander 174, annular piston assembly 320 can have a relatively large surface area (e.g., used to move or compress working gas, or used to seal or form bearing surfaces against annular cylinder 314) while occupying a relatively small radial volume (e.g., the radial thickness and/or axial length of annular piston assembly 320 may be relatively small). Moreover, larger diameters generate lower contact stresses (e.g., shorter or slower piston strokes, less curvature per unit circumference of annular piston assembly 320), which provides embodiments with the potential for relatively long wear life.

While a single piston design can mean more pronounced mechanical vibrations than with dual piston designs, such mechanical vibrations generated by embodiments described herein are generally axial and parallel to the motion of expander 174 and/or an optical path of electronic device/camera 380 and do not significantly detrimentally affect the performance of electronic device/camera 380, unlike radial mechanical vibrations. Embodiments of refrigeration system 300 effectively damp or eliminate substantially all radial mechanical vibrations generated by operation of annular linear compressor 372 and/or other elements of refrigeration system 300.

Fig. 4 A illustrates annular cylinder head 371-1 for annular linear compressor 372 of refrigeration system 300 in accordance with an embodiment of the disclosure. In Fig. 4A, diagram 400 is shaded or hatched to identify annular cylinder head 371-1 within refrigeration system 300 of Fig. 3C. As shown in Fig. 4A, annular cylinder head 371-1 includes pressure plate 471 configured to support and mechanically couple annular cylinder assembly 310 to gas transfer plate 377. Annular cylinder head 371-1 may also include neck 473 (e.g., a hollow cylindrical shaft) protruding from one side of pressure plate 471 and configured to support and position inner yoke 318 of annular cylinder assembly 310 within annular linear compressor 372 and to help define annular gap 373, in which portions of expander 174 and dewar enclosure 382 may be disposed to facilitate annular stacking of expander 174, dewar enclosure 382, and annular linear compressor 372, as described herein. In various embodiments, annular cylinder head 371-1 may also form a portion of gas transferline 277 between annular cylinder 314/annular piston assembly 320 and expander 174. In various embodiments, annular cylinder head 371-1 may be configured to form a mount for elements of annular cylinder assembly 310, to support and/or form a mount for various electrical and/or working gas (e.g., sealed) feedthroughs, and/or to provide a working gas fill port, as described herein.

Fig. 4B illustrates gas transfer plate 377 for refrigeration system 300 including annular linear compressor 372 in accordance with an embodiment of the disclosure. In Fig. 4B, diagram 401 is shaded or hatched to identify gas transfer plate 377 within refrigeration system 300 of Fig. 3C. As shown in Fig. 4B, gas transfer plate 377 includes pressure plate 477 configured to support, align, and mechanically couple annular cylinder head 371-1 and expander 174 (e.g., expander housing 374) to each other. Gas transfer plate 377 may also form or include expander cylinder head 379-1 configured to seal expander housing 374 and allow for reciprocating motion of elements of expander 174 (e.g., enabled by mechanical spring system 379-2 disposed within expander cylinder head 379-1). In various embodiments, gas transfer plate 377 may also form a portion of gas transfer line 277 (e.g., gas transfer line orifice 277-1 linking to annular cylinder head 371-1 and gas transfer line orifice 277-2 linking to expander 174) between annular cylinder 314/annular piston assembly 320 and expander 174. By integrating both a gas transfer line and an expander cylinder head (e.g., and its associated bounce space for expander 174) within gas transfer plate 377, embodiments of refrigeration system 300 may be formed relatively compactly, for example, and provide minimal coupling of radial mechanical vibrations between elements of refrigeration system 300.

Fig. 5A illustrates a cross section of annular piston assembly 320 for annular linear compressor 372 of refrigeration system 300 in accordance with an embodiment of the disclosure. As shown in Fig. 5A, annular piston assembly 320 may include inner split piston head 322 configured to form a moving seal with inner annular cylinder/bore surface 315-1, outer split piston head 326 configured to form a moving seal with outer annular cylinder/bore surface 315- 2, and piston magnet ring 324 disposed in a piston cavity formed by inner and outer split piston heads 322 and 326. In some embodiments, the seals between annular piston assembly 320 and inner/outer annular cylinder surfaces 315-1 and 315-2 may include one or more liners 515 and/or 526 formed on exterior surfaces of annular piston assembly 320 and/or inner/outer annular cylinder surfaces 315-1 and 315-2 to help reduce friction between annular piston assembly 320 and inner/outer annular cylinder surfaces 315-1 and 315-2 and seal annular piston assembly 320 within inner/outer annular cylinder surfaces 315-1 and 315-2 so as to now allow blow by of working gas during operation of refrigeration system 300.

In some embodiments, annular piston assembly 320 may be formed by grinding split piston heads 322 and 326 from bulk material (e.g., to match their respective bore surfaces), and press fitting and/or adhesively affixing or otherwise bonding inner split piston head 322, piston magnet ring 324, and outer split piston head 326 to each other, as shown. Liners 515 and/or 526 may be formed from PTFE or other liner material that is deposited, adhesively affixed, or otherwise formed on the various surfaces before annular piston assembly 320 is inserted into annular cylinder cavity 514 and used to move working gas through gas transfer line 277 through motion along the noted direction of piston travel. In various embodiments, annular piston assembly 320 may be configured to create pressure waves within annular cylinder 314 that drive the overall thermodynamic cycle, when driven by drive signals provided to inductive wiring 312.

Fig. 5B illustrates annular piston assembly 320 for annular linear compressor 372 of refrigeration system 300 in accordance with an embodiment of the disclosure. In the embodiment shown in Fig. 5B, annular piston assembly 320 includes an inner liner 522 formed on inner split piston head 322, outer liner 526 formed on outer split piston head 326, and a multielement piston magnet ring 524. In some embodiments, piston magnet ring 524 may be formed from multiple arcuate permanent magnet segments of a full ring to facilitate manufacture and/or assembly. Although shown in Fig. 5B as a full 360 degree magnet ring, in alternative embodiments piston magnet ring 524 may be formed from multiple spaced magnet segments (e.g., to form a partial or spaced magnet ring) with various shapes, for example, to facilitate a particular application or desired weight and/or inductive coupling to annular inductive windings 312. Moreover, annular inductive windings 312 (e.g., and inner and outer yokes 318 and 316) may be formed as a full 360 degree inductive winding ring, multiple arcuate inductive winding segments, and/or multiple spaced inductive winding segments, for example, to match a particular magnet and/or inductive coupling arrangement of piston magnet ring 524.

Fig. 6 illustrates a flow diagram 600 of operation of annular linear compressor 372 for refrigeration system 300 in accordance with an embodiment of the disclosure. In state 601, annular inductive windings 312 are driving piston magnet ring 524 of annular piston assembly 320 to the left within annular cylinder cavity 514, thus forcing working gas through gas transfer line 277 in annular cylinder head 371-1 and eventually into expander 174 (e.g., normally residing within annular gap 373 of annular linear compressor 372). In various embodiments, inductive coupling between inductive windings 312 and piston magnet ring 524 of annular piston assembly 320 may be configured to apply a damping force to motion of annular piston assembly 320, increasingly as it approaches annular cylinder head 371-1 adjacent to annular cylinder cavity 514, to reduce risk of impact with annular cylinder head 371-1 or sudden deceleration of annular piston assembly 320 that might cause increased mechanical vibrations within annular linear compressor 372.

In state 602, annular inductive windings 312 are driving piston magnet ring 524 of annular piston assembly 320 to the right within annular cylinder cavity 514, thus drawing working gas through gas transfer line 277 into annular cylinder cavity 514. In various embodiments, inductive coupling between inductive windings 312 and piston magnet ring 524 of annular piston assembly 320 may be configured to apply a damping force to motion of annular piston assembly 320, increasingly as it approaches an end of annular cylinder cavity 514 (e.g., adjacent to a cavity formed by compressor housing 371-2), to reduce risk of impact with compressor housing 371-2, sudden deceleration of annular piston assembly 320 that might cause increased mechanical vibrations within annular linear compressor 372, and/or of annular piston assembly 320 partially and/or fully exiting or misaligning with annular cylinder cavity 514.

While the various embodiments illustrated in Fig. 3C and Figs. 5A through 6 include a drive coil implemented as inductive windings 312 driving a moving magnet implemented as piston magnet ring 524, in alternative embodiments, annular linear compressor 372 may be implemented according to a moving coil motor, for example, where inductive windings 312 are replaced with a cylinder magnet ring, which may be similar in size and/or placement to inductive windings 312 and/or similar in general construction to piston magnet ring 324 and/or 524, and where piston magnet ring 324 is replaced with piston inductive windings, which may be similar in size and/or placement to piston magnet ring 324 and/or 524 and/or similar in general construction to inductive windings 312. In such embodiments, electrical leads from such piston inductive windings may be routed from annular piston assembly 320 (e.g., from a non- compressing face of annular piston assembly 320 opposite gas transfer line 277 through annular cylinder cavity 514) into the cavity formed by compressor housing 371-2.

In such moving coil embodiments, reciprocating motion of annular piston assembly 320 may be driven by drive signals provided to such piston inductive windings (e.g., by motor driver 140), which generate a varying magnetic field originating at such piston inductive windings (e.g., and shaped, at least in part, by inner and outer yokes 316 and 318) that couples inductively with such cylinder magnet ring and mechanically drives motion of annular piston assembly 320. Moreover, in such moving coil embodiments, outer yoke 316 and inner yoke 318 may be implemented according to any desired shapes and/or materials disposed within compressor housing 371-2 and configured to help carry and/or shape magnetic flux generated by such piston inductive windings and/or motion of annular piston assembly 320 and inductively couple such piston inductive windings to such cylinder magnet ring across the full range of motion of annular piston assembly 320.

Fig. 7 is a flowchart illustrating a method 700 for operating a refrigerator/cryocooler with an annular linear compressor in accordance with an embodiment of the disclosure. One or more portions of process 700 may be performed by cryocooler controller 120 and utilizing any elements of systems, components, logic, or methods described with reference to Figs. 1-6. It should be appreciated that any step, sub-step, sub-process, or block of process 700 may be performed in an order or arrangement different from the embodiment illustrated by Fig. 7. In some embodiments, any portion of process 700 may be implemented in a loop so as to continuously operate, such as in a control loop, for example.

At block 702, operational parameters for a cryocooler are received. For example, motor driver controller 130 of cryocooler controller 120 may be configured to receive operational parameters from user interface 110 and/or a memory (other modules 122), such as a temperature setpoint corresponding to a desired temperature for cold finger 176 and/or electronic device 180/FPA 182. In some embodiments, motor driver controller 130 may also be configured to receive feedback data corresponding to operation of cryocooler 170 from feedback interface 132. Feedback interface 132 may be configured to receive one or more sensor signals (e.g., from temperature sensors 134 and/or other sources) and generate corresponding feedback data to be delivered to motor driver controller 130, as described herein. At block 704, motor driver control signals based, at least in part, on operational parameters for a cryocooler are generated. For example, motor driver controller 130 of cryocooler controller 120 may be configured to generate motor driver control signals for cryocooler 170 based, at least in part, on operational parameters received in block 702. In some embodiments, motor driver controller 130 may be configured to generate motor driver control signals based, at least in part, on feedback data and/or operational parameters received in block 702. For example, motor driver controller 130 may be configured to determine feedback errors based, at least in part, on a setpoint corresponding to a desired temperature for cold finger 176 and/or electronic device 180 and feedback data corresponding to a measured temperature of cold finger 176 and/or electronic device 180. Motor driver controller 130 may then generate motor driver control signals based, at least in part, on the determined feedback error.

In further embodiments, motor driver controller 130 may be configured to generate motor driver control signals and/or other control signals based, at least in part, on operational parameters received in block 702. For example, motor driver controller 130 may be configured to determine feedback errors based, at least in part, on a set point corresponding to a desired temperature for cold finger 176 and/or electronic device 180 and feedback data corresponding to a measured temperature of cold finger 176 and/or electronic device 180. Motor driver controller 130 may then generate motor driver control signals and/or other control signals based, at least in part, on the determined feedback error.

At block 706, motor drive signals based on motor driver control signals are generated.

For example, motor driver controller 130 of cryocooler controller 120 may be configured to provide motor driver control signals generated in block 704 to motor driver 140. In further embodiments, motor driver controller 130 of cryocooler controller 120 may be configured to provide motor driver control signals and any other control signals generated in block 704 to motor driver 140. Motor driver 140 may then provide corresponding motor drive signals and/or other drive signals to annular linear compressor 172, indictive windings 312, and/or other elements of refrigeration system 100 or 300 to control operation of cryocooler 170 or 370, as described herein.

Although embodiments described herein are primarily directed to annular linear compressors for refrigeration systems, similar techniques may be used to reduce the size and radial mechanical vibrations generated by a linear compressor for other types of gas handling systems. For example, annular linear compressor 372 in Fig. 3C may be modified with check and/or actuated valves along gas transfer line 277 to provide one way working gas flow, for example, and/or increased pressures generated by multiple cycles of motion of annular piston assembly 310 within annular cylinder 312. Moreover, embodiments of annular linear compressor 372 may be implemented with an active balancer (e.g., a separate annular weight driven by separate inductive windings within compressor housing 371-2 and configured to counteract linear momentum changes of annular piston assembly 310) to help reduce axial mechanical vibrations, as described herein.

Where applicable, various embodiments provided by the present disclosure can be implemented using hardware, software, or combinations of hardware and software. Also, where applicable, the various hardware components and/or software components set forth herein can be combined into composite components comprising software, hardware, and/or both without departing from the spirit of the present disclosure. Where applicable, the various hardware components and/or software components set forth herein can be separated into sub-components comprising software, hardware, or both without departing from the spirit of the present disclosure. In addition, where applicable, it is contemplated that software components can be implemented as hardware components, and vice-versa.

Software in accordance with the present disclosure, such as non-transitory instructions, program code, and/or data, can be stored on one or more non-transitory machine readable mediums. It is also contemplated that software identified herein can be implemented using one or more general purpose or specific purpose computers and/or computer systems, networked and/or otherwise. Where applicable, the ordering of various steps described herein can be changed, combined into composite steps, and/or separated into sub-steps to provide features described herein.

Embodiments described above illustrate but do not limit the invention. It should also be understood that numerous modifications and variations are possible in accordance with the principles of the invention. Accordingly, the scope of the invention is defined only by the following claims.