Patent Publication Number: US-2023160513-A1

Title: Compact portable oxygen concentrator

Description:
INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS 
     Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet as filed with the present application are hereby incorporated by reference under 37 CFR 1.57. The present application is a divisional of U.S. application Ser. No. 16/837,813, entitled COMPACT PORTABLE OXYGEN CONCENTRATOR, filed Apr. 1, 2020, which claims priority benefit of U.S. Provisional Application No. 62/827,689, entitled “COMPACT PORTABLE OXYGEN CONCENTRATOR,” filed Apr. 1, 2019, each of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Field 
     The present disclosure relates to oxygen concentrators for personal use and in particular to portable oxygen concentrators. 
     Description of the Related Art 
     Personal oxygen concentrators are devices that convert ambient air to an oxygen enriched gas for therapeutic use. They are becoming increasingly popular as alternatives to liquid oxygen vessels and compressed gas cylinders. Such personal oxygen concentrators exist in both portable form for ambulatory use and stationary form for use inside the home. To be practical for everyday use by patients needing therapeutic oxygen, portable oxygen concentrators are generally preferred over stationary ones. It is desirable that such portable oxygen concentrators be small, lightweight, efficient, reliable, and relatively inexpensive. Efforts to design an oxygen concentrator having all of these desirable attributes may be inherently limited by the size and weight of the individual components. Further reductions in size and weight of portable oxygen concentrators without sacrificing performance may require new approaches to concentrator design. 
     SUMMARY 
     Portable oxygen concentrator elements may be provided that include improved compressor control features, high density gas tight interconnects, integrated sensor blocks, space efficient adsorber designs, improved airflow, and improved battery retention. The result of the elements is an extremely compact, light reliable portable oxygen concentrator that is easy to assemble and relatively inexpensive. 
     In one aspect, a battery retaining system for a portable oxygen concentrator is provided. The battery retaining system includes a first rail configured to receive a first slide of a battery, a second rail configured to receive a second slide of the battery, the second rail being spaced apart from the first rail so as to form a channel configured to receive the battery, and a flexible stiffening mechanism configured to impart a biasing force on a surface of the battery when the battery is received within the channel. The flexible stiffening mechanism includes a protrusion projecting from the first rail at least partially towards the second rail and a slit positioned behind the protrusion and configured to facilitate travel of the protrusion fore and aft. 
     In some embodiments, the system further includes one or more protrusions projecting from the second rail at least partially towards the first rail, the one or more protrusions being configured to contact the battery when the battery is positioned within the channel. In some embodiments, the channel extends between an open proximal end and a closed distal end, wherein at least one of the one or more protrusions projecting from the second rail are positioned proximally relative to the protrusion of the first rail. In some embodiments, the channel extends between an open proximal end and a closed distal end, wherein at least one of the one or more protrusions projecting from the second rail are positioned distally relative to the protrusion of the first rail. In some embodiments, the one or more protrusions projecting from the second rail comprise a first protrusion positioned proximally relative to the protrusion of the first rail and a second protrusion positioned distally relative to the protrusion of the first rail. In some embodiments, the flexible stiffening mechanism maintains contact between the first rail and the battery to stabilize the battery within the channel, the battery having a battery size that is smaller than an upper tolerance level. In some embodiments, the flexible stiffening is configured to impart the biasing force on the surface of the battery so as to align an electrical connector of the battery with an electrical connector of the portable oxygen concentrator. In some embodiments, the flexible stiffening mechanism is configured to impart the biasing force on the surface of the battery to impart stability to the installation of the battery. In some embodiments, the biasing force of the flexible stiffening mechanism is sufficiently flexible to permit translation of the battery within the channel past the protrusion. 
     In another aspect, a portable oxygen concentrator is provided. The portable oxygen concentrator includes a chassis base, a printed circuit board mounted at a superior end of the chassis base, the printed circuit board including a first electrical connector, and an outer housing configured to removably couple to the chassis base. The outer housing includes one or more controls of a user interface and a second electrical connector in electrical communication with the controls of the user interface, the second electrical connector being positioned to align with and mate with the first electrical connector when the outer housing is coupled to the chassis base. 
     In some embodiments, the printed circuit board comprises a user interface display. In some embodiments, the outer housing is configured to define an enclosed volume around the printed circuit board when coupled to the chassis base. In some embodiments, the outer housing is configured to seal the enclosed printed circuit board from external moisture when coupled to the chassis base. In some embodiments, the first electrical connector is oriented on the printed circuit board so as to face in a generally superior direction and the second electrical connector is oriented on the outer housing so as to face in a generally inferior direction. 
     In another aspect, a gas concentrator is provided. The gas concentrator includes a chassis base, a compressor assembly, an outer housing coupled to the chassis base so as to define an internal volume enclosing the compressor assembly, and a shell structure positioned within the internal volume, the shell structure including one or more insulating panels disposed about the compressor assembly. 
     In some embodiments, the shell structure separates the compressor assembly from one or more elements positioned within the internal volume of the concentrator, the one or more elements comprising one or more adsorbers coupled to the chassis base, one or more pneumatic modules, one or more electronic modules, or one or more sensor modules. In some embodiments, the shell structure forms at least a portion of an at least partially sealed chamber around the compressor assembly. In some embodiments, the gas concentrator further includes a printed circuit board, the printed circuit board forming at least a portion of the at least partially sealed chamber. In some embodiments, an interior surface of the outer housing forms at least a portion of the at least partially sealed chamber. 
     In another aspect, a gas concentrator is provided. The gas concentrator includes a chassis base, a compressor assembly, an airflow generator, one or more exhaust ports, and an outer housing coupled to the chassis base so as to define an internal volume enclosing the compressor assembly and the airflow generator, the outer housing including one or more air inlets, wherein the one or more air inlets are recessed within the outer housing or extend along a curved or angled surface of the outer housing, wherein the airflow generator is configured to direct airflow along an airflow path between the one or more air inlets and the one or more exhaust ports. 
     In some embodiments, the one or more air inlets include a first air inlet and a second air inlet, wherein the first air inlet and the second air inlet are positioned on opposite surfaces of the housing. In some embodiments, the one or more exhaust ports comprise a first exhaust port and a second exhaust port, wherein the first exhaust port and the second exhaust port are formed within opposite side surfaces of the chassis base. In some embodiments, the gas concentrator further includes a battery coupled to the chassis base, wherein the one or more exhaust ports are formed in a portion of the chassis base extending laterally beyond a lateral edge of the battery. In some embodiments, the exhaust ports are directed at a downward angle over a recess formed in the portion of the chassis base extending laterally beyond a lateral edge of the battery, thereby preventing obstruction of the exhaust ports if the concentrator is placed adjacent a flat surface. 
     In another aspect, an adsorber for a gas concentrator is provided. The adsorber includes an adsorbent material including adsorbent particles and a vessel housing the adsorbent material. The vessel includes a vessel wall having a non-circular cross section and at least one stiffening support, wherein a combination of a thickness of the vessel wall and a stiffness of the stiffening support is sufficient to limit deformation of the vessel wall to at least one of less than 0.1 mm and less than 25% of an average diameter of the adsorbent particles under a pressure swing of at least 30 psi within the vessel. 
     In some embodiments, the deformation of the vessel wall is less than 0.05 mm under a pressure swing of at least 30 psi within the vessel. In some embodiments, a cross section of the adsorber is at least 90% filled with the adsorbent material. In some embodiments, the vessel wall has an oblong cross section. In some embodiments, the at least one stiffening support includes a stiffening rib extending at least one of across an interior of the vessel and along an interior wall of the vessel. In some embodiments, the at least one stiffening support includes a stiffening rib positioned on an exterior surface of the vessel. In some embodiments, the adsorber further includes a filter positioned within a cavity formed by a protrusion extending from a superior end of the vessel, the protrusion having a cross section different than the cross section of the vessel wall. In some embodiments, the protrusion is cylindrical. In some embodiments, the protrusion is integrally formed with the vessel wall. 
     In another aspect, an adsorber for a gas concentrator is provided. The adsorber includes an adsorbent material including adsorbent particles and a vessel housing the adsorbent material. The vessel includes a vessel wall having a non-circular cross section and at least one stiffening support, wherein a cross section of the adsorber is at least 90% filled with the adsorbent material. 
     In some embodiments, the vessel wall has an oblong cross section. In some embodiments, the at least one stiffening support including a stiffening rib extending at least one of across an interior of the vessel and along an interior wall of the vessel. In some embodiments, the at least one stiffening support includes a stiffening rib positioned on an exterior surface of the vessel. In some embodiments, the adsorber further includes a filter positioned within a cavity formed by a protrusion extending from a superior end of the vessel, the protrusion having a cross section different than the cross section of the vessel wall. In some embodiments, the protrusion is cylindrical. In some embodiments, the protrusion is integrally formed with the vessel wall. 
     In another aspect, an adsorber system is provided. The adsorber system includes a first adsorber including an adsorbent material including adsorbent particles and a vessel housing the adsorbent material. The vessel includes a vessel wall having a non-circular cross section and at least one stiffening support. The adsorber system includes a second adsorber including an adsorbent material comprising adsorbent particles and a vessel housing the adsorbent material. The vessel includes a vessel wall having a non-circular cross section and at least one stiffening support. The vessel wall of the first adsorber is joined to the vessel wall of the second adsorber. 
     In some embodiments, the vessel wall of the first adsorber is integrally formed with the vessel wall of the second adsorber. In some embodiments, the stiffening support of the first adsorber is aligned with the stiffening support of the second adsorber. In some embodiments, the vessel wall of the first adsorber and the vessel wall of the second adsorber each comprise an oblong cross section. 
     In another aspect, a compressor assembly for a portable oxygen concentrator is provided. The compressor assembly incudes a first compressor chamber including a first connector, a second compressor chamber including a connector, and a tube including a first end including a first connection interface configured to connect to the first connector and a second end including a second connection interface configured to connect to the second connector, wherein the first connection interface is shaped to maintain the connection between the first connector and the first connection interface in a fixed orientation and the second connection interface is shaped to maintain the connection between the second connector and the second connection interface in a fixed orientation, wherein one or more of the first connector, the second connector, and the tube are compliant. 
     In some embodiments, the first connector has a shape and the first connection interface of the tube has a shape that matches the shape of the first connector. In some embodiments, the second connector has a shape and the second connection interface has a shape that matches the shape of the second connector. In some embodiments, the shapes of the first connection interface, the second connection interface, the first connector, and the second connector are square. 
     In another aspect, a compressor assembly for a portable oxygen concentrator is provided. The compressor assembly includes a compliant mount including at least one connector. The at least one connector includes a compliant member and a pair of protruding tabs extending from the compliant member. The compressor assembly further includes a compressor including a first compressor chamber, a second compressor chamber, and at least one pair of slots, the at least one pair of slots configured to receive the pair of protruding tabs of the at least one connector. 
     In some embodiments, the protruding tabs are spaced 180° apart from one another around a circumference of the compliant member. In some embodiments, the pair of protruding tabs are formed of a different material than the compliant member. In some embodiments, the compliant mount is coupled to the compressor by a hollow screw. In some embodiments, intake air is drawn through the hollow screw. In some embodiments, the at least one connector comprises two connectors. 
     In another aspect, a sensor assembly is provided. The sensor assembly includes an oxygen sensor, the oxygen sensor including at least one emitter including an active surface configured to emit an acoustic signal, at least one receiver including an active surface configured to receive the acoustic signal, and a body forming a chamber. The body includes a first opening configured to receive the at least one emitter such that the active surface of the at least one emitter is exposed to the chamber, a second opening configured to receive the at least one receiver such that the active surface of the at least one receiver is exposed to the chamber, and at least two reflectors configured to reflect the acoustic signal so as to establish an acoustic path between the active surface of the emitter and the active surface of the receiver. 
     In some embodiments, the first opening and the second opening are coplanar. In some embodiments, the active surface of the emitter and the active surface of the receiver are coplanar. In some embodiments, the active surface of the emitter and the active surface of the receiver are oriented to face in parallel directions. In some embodiments, the oxygen sensor further includes one or more sealing rings configured to provide a seal between the first opening and the emitter and the second opening and the receiver. In some embodiments, the sensor assembly further includes a printed circuit board, wherein the emitter and receiver are mounted to the printed circuit board, and wherein the printed circuit board is mounted to the body. In some embodiments, the oxygen sensor includes a temperature sensor configured to measure a temperature of oxygen gas within the chamber. In some embodiments, the oxygen sensor includes a temperature sensor configured to measure a temperature of air outside the chamber. In some embodiments, the oxygen sensor includes a pressure sensor configured to measure a pressure of oxygen gas within the chamber. In some embodiments, the oxygen sensor includes a pressure sensor configured to measure a pressure of air outside the chamber. In some embodiments, the sensor assembly further includes a breath detection sensor. 
     In another aspect, a method of operating a compressor system is provided. The method includes determining an efficiency of a compressor configured to operate at a plurality of output flow settings. The compressor system includes a motor, a power source providing a DC power source voltage, a voltage controller configured to selectively modify the power source voltage to provide a plurality of supply voltages, and a pulse width modulation controller configured to selectively apply pulse width modulation to the supply voltages at a plurality of pulse width modulation duty cycles, thereby providing a plurality of motor control signals. Determining an efficiency of the compressor includes one or more of measuring, calibrating, calculating, or modeling motor efficiency over a range of supply voltage and pulse width modulation duty cycle combinations, each combination comprising a supply voltage of the plurality of supply voltages and a pulse width modulation duty cycle of the plurality of pulse width modulation duty cycles. The method further includes selecting a supply voltage of the plurality of supply voltages and a pulse width modulation duty cycle of the plurality of pulse width modulation duty cycles for use at at least one output flow setting of the plurality of output flow settings based on the determined efficiency of the compressor, generating the selected supply voltage by maintaining, reducing, or increasing a nominal supply voltage, and applying the selected pulse width modulation duty cycle. 
     In some embodiments, the nominal supply voltage is a desired supply voltage for one of the plurality of output flow settings. In some embodiments, the nominal supply voltage is a desired supply voltage for a maximum output flow setting of the plurality of output flow settings. In some embodiments, the power source is one of a battery, a fixed power source comprising car DC power ports, or an AC to DC power supply. In some embodiments, the power source is a battery, and the method further includes dynamically monitoring the power source voltage and adjusting one or both of the supply voltage and the pulse width modulation duty cycle to accommodate power source voltage changes to achieve a desired efficiency of the compressor. In some embodiments. the compressor system is part of a swing adsorption system and the method further include monitoring a pressure profile over the course of a pressure swing adsorption cycle, a pressure-vacuum swing adsorption cycle, or a vacuum swing adsorption cycle and dynamically adjusting the supply voltage and pulse width modulation duty cycle to improve efficiency over the course of the pressure swing adsorption cycle, the pressure-vacuum swing adsorption cycle, or the vacuum swing adsorption cycle. In some embodiments, monitoring the head profile and adjusting the supply voltage and pulse width modulation duty cycle are performed during the pressure swing adsorption cycle, the pressure-vacuum swing adsorption cycle, or the vacuum swing adsorption cycle. In some embodiments, monitoring the head profile includes monitoring one or more of current measurements, power measurements, and pressure measurements through a feed forward process. In some embodiments, the nominal supply voltage is used without pulse width modulation as the motor control signal for a highest output flow setting of the plurality of outflow settings of the compressor. In some embodiments, a combination of supply voltage regulation and pulse width modulation are applied to the nominal supply voltage to provide motor control signals for one or more output flow settings lower than the highest output flow setting of the compressor. In some embodiments, the selected supply voltage and the selected pulse width modulation duty cycle are selected to optimize efficiency at a most commonly used output flow setting of the plurality of output flow settings while maintaining the ability to operate at each of the plurality of output flow settings. In some embodiments, the selected supply voltage and the selected pulse width modulation duty cycle are selected to reduce switching losses at at least one output flow setting of the plurality of output flow settings. In some embodiments, the voltage controller is configured to modify the power source voltage to provide one or more supply voltages higher than the power source voltage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects and advantages of the embodiments provided herein are described with reference to the following detailed description in conjunction with the accompanying drawings. Throughout the drawings, reference numbers may be re-used to indicate correspondence between referenced elements. The drawings are provided to illustrate example embodiments described herein and are not intended to limit the scope of the disclosure. 
         FIG.  1 A  shows a simplified system block diagram of an exemplary portable oxygen concentrator; 
         FIG.  1 B  shows an isometric view of internal components of one embodiment of an exemplary portable oxygen concentrator; 
         FIG.  1 C  shows a cutaway isometric view of the internal components of one embodiment of an exemplary portable oxygen concentrator illustrating internal air flow; 
         FIG.  1 D  shows one embodiment of an exemplary portable oxygen concentrator with a battery; 
         FIG.  1 E  shows one embodiment of the portable oxygen concentrator of  FIG.  1 D  resting on a side against a flat surface; 
         FIG.  2    shows an isometric view of one embodiment of an exemplary portable oxygen concentrator with a removable external housing; 
         FIGS.  3 A and  3 B  show an illustrative embodiment of an interconnect system between the outer housing and the concentrator chassis of one embodiment of an exemplary portable oxygen concentrator; 
         FIGS.  4 A through  4 D,  5 A, and  5 B  show an illustrative embodiment of gas separation adsorber assembly of an exemplary portable oxygen concentrator; 
         FIGS.  6 A through  6 D  show an illustrative embodiment of a battery retention and alignment assembly of an exemplary portable oxygen concentrator; 
         FIGS.  7 A through  7 K  show illustrative embodiments of gas interconnection elements of an exemplary portable oxygen concentrator; 
         FIGS.  8 A through  8 D  show various illustrative embodiments of compressor mounting elements of an exemplary portable oxygen concentrator; 
         FIGS.  9 A through  9 F  show various illustrative embodiments of elements of oxygen and other sensor block arrangements of an exemplary portable oxygen concentrator; 
         FIGS.  10 A through  10 F  show various illustrative elements of compressor motor control of an exemplary portable oxygen concentrator. 
     
    
    
     DETAILED DESCRIPTION 
     Personal use therapeutic oxygen concentrators that convert ambient air into oxygen enriched gas are increasing in popularity, both in portable and stationary forms. They are generally much smaller in size and different in design as compared to industrial gas concentrators. An example portable oxygen concentrator, including its use and operation, is described in co-pending U.S. application Ser. No. 15/427,948, entitled “GAS CONCENTRATOR WITH REMOVABLE CARTRIDGE ADSORBENT BEDS,” which is incorporated herein by reference in its entirety. Another example of such a portable oxygen concentrator is described in U.S. application Ser. No. 15/608,775, entitled “COMPACT PORTABLE OXYGEN CONCENTRATOR,” which is incorporated by reference in its entirety. Another example of such a portable oxygen concentrator is described in U.S. application Ser. No. 15/608,788, entitled “GAS CONCENTRATOR WITH REMOVABLE CARTRIDGE ADSORBENT BEDS,” which is incorporated herein by reference in its entirety. Such oxygen concentrators, because of their small size and intended personal use, have differing design considerations from large industrial concentrators intended to produce large quantities of concentrated gas. For example, in an illustrative embodiment, the portable concentrator according to the present disclosure may be between 25 and 200 cubic inches in size, between 2 and 7 pounds in weight, and may produce between 300 and 3000 ml/min of concentrated oxygen. 
       FIG.  1 A  is a schematic illustration of an exemplary oxygen concentrator system  100  in accordance with an embodiment of the present disclosure. As shown in  FIG.  1 A , the system  100  generally includes an air inlet  1  through which ambient air is drawn into the system, a compressor assembly  2  for pressurizing the ambient air to provide a feed gas, a gas separation unit or system  3  which receives and processes the feed gas to produce a product gas having a higher oxygen content than the ambient air, a gas delivery system  7 , such as a conserver, for delivering the oxygen-rich product gas to a patient, and an exhaust outlet or port  6  for releasing nitrogen-rich waste gas and spent cooling airflow gas. As used herein, spent cooling airflow gas can refer to airflow gas that has been used to cool portions of the concentrator system  100 . The system  100  further includes a feed/waste manifold  9 , a product valve manifold  10 , a product gas storage  4 , a user/data interface  8 , and a programmable controller  5  for controlling the operation of the system. 
     In some embodiments, ambient air drawn into the system through air inlet  1  can be used to supply the gas separation system  3  with pressurized gas to flush out nitrogen-rich waste gas. Ambient air drawn into the system through the air inlet  1  can also be used to cool the internal components of the system. This air movement may be provided by an airflow generator, such as a fan or blower, located at the air inlet  1 , at the exhaust outlet  6 , or along an air flow path between the air inlet  1  and the exhaust outlet  6 . To achieve proper air flow, an airflow generator may be employed in some embodiments. In some embodiments, airflow may be generated, for example, by a cooling fan or blower. In some embodiments, the cooling fan or blower can have dimensions in the range of 40 mm×40 mm to 100 mm×100 mm in diameter and 20 mm to 60 mm in depth. One or more fans in varying sizes and locations may also be employed in some embodiments to optimize air flow and minimize noise. As indicated schematically in  FIG.  1 A , the air flow may be directed to pass over the internal components of the oxygen concentrator system  100 . In some embodiments, the waste gas from the gas separation system  3  and the spent cooling gas both exit the system  100  via the exhaust outlet  6 . In some embodiments, the exhaust outlet  6  is positioned adjacent or immediately adjacent the compressor assembly  2 . In some embodiments, the air flow path directs cool air to pass over the other components of the system before reaching the compressor assembly  2 . The compressor assembly  2  can generate significant heat during operation. In some embodiments, the compressor assembly  2  is placed adjacent to the exhaust outlet  6  to achieve improved cooling effectiveness. In some embodiments, an airflow generator, such as a fan, blower, or other means, may be positioned along the air flow path to push and/or pull air through the system  100  interior from the air inlet  1  to the exhaust outlet  6  or between the air inlet  1  and the exhaust outlet  6 . In some embodiments, a plurality of air inlets and/or a plurality of exhaust outlets may be employed to achieve appropriate cooling. In some embodiments, the concentrator  100  can include a plurality of airflow generators to achieve appropriate cooling. 
     In some embodiments, the gas separation system  3  is a pressure swing adsorption (PSA) gas separation system. In some embodiments, the gas separation system  3  is a vacuum swing adsorption (VSA) system. In some embodiments, the gas separation system  3  is a vacuum pressure swing adsorption (VPSA) system. The gas separation system  3  may include one or more adsorbers. The adsorbers can employ pressure, vacuum, or a combination thereof to separate the components of ambient air to produce an oxygen-rich product gas. Ambient air is drawn in by the compressor assembly  2  through a filter and through an elongated and/or tortuous air path designed to minimize the escape of noise caused by the compressor assembly  2 . In some embodiments, the compressor assembly  2  may include a single cylinder or multi-cylinder reciprocating piston compressor employing pressure or a combination of pressure and vacuum cylinders. In some embodiments, the compressor assembly  2  may alternatively or additionally include other compressors types such as scroll, linear free piston, rotary vane, rotary screw, conical screw, or diaphragm type compressors. 
     Pressurized air may be discharged from the compressor assembly  2  at a rate of 5 SLPM to 15 SLPM per LPM or approximately 5 SLPM to 15 SLPM per LPM of oxygen-rich gas produced at a pressure up to 3 bar. The pressurized air is directed to one of two or more adsorbers of the gas separation system  3  by one or more feed/waste valves that may be housed in a feed/waste manifold  9 . The feed/waste valve configuration in the feed/waste manifold  9  can vary by embodiment and may include one or more solenoid valves, piezoelectric valves, air piloted valves, rotary valves, cam actuated valves, and/or diaphragm valves. In some embodiments, the feed/waste valves may be decoupled from the compressor assembly  2 , adsorbers of the gas separation system  3 , and other structural components to reduce transmission of noise from the valves to other system components or the exterior of the oxygen concentrator system  100 . A valve fluid path may be connected with compliant members to achieve an appropriate level of mechanical isolation, and the feed/waste manifold  9  or valve mounting can be additionally isolated from other components. Alternatively, in some embodiments, the valves may be directly mounted to relatively high-mass, high density components, such as a compressor head of the compressor assembly  2  or the adsorbers of the gas separation system  3  to reduce noise transmission. These components may also then be isolated from other components in the system, particularly large plastic bodies such as housings or chassis components. The feed/waste valves contained in feed/waste manifold  9  can additionally direct exhaust nitrogen-rich gas from the adsorbers of the gas separation unit  3  to a muffler in a pressure swing adsorption (PSA) system or to a vacuum pump in a vacuum swing adsorption (VSA) or vacuum pressure swing adsorption (VPSA) system. 
     In some embodiments, the adsorbers of the gas separation system  3  are designed to be removable and replaceable as described in the above incorporated references. Each adsorber can include an adsorbent material and a vessel housing the adsorbent material. The adsorbent material can be in the form of an adsorbent bed. The adsorbent bed may contain at least one pretreatment adsorbent layer that is directed to water and carbon dioxide removal to prevent contamination of a main layer adsorbent. In some embodiments, this material may be a desiccant such as activated alumina or silica gel. In alternate embodiments, the pretreatment layer may contain a sodium or lithium exchanged zeolite. The adsorbent bed can also include a main layer adsorbent that is directed to separate oxygen from nitrogen in ambient air. The main layer adsorbent may be a lithium exchanged zeolite material. Nitrogen is retained in the adsorber, while oxygen-rich gas is allowed to pass through the adsorber into the product valves or product valve manifold  10 . 
     The product valve manifold  10  may include one or more of solenoid valves, piezoelectric valves, air piloted valves, rotary valves, cam actuated valves, or diaphragm valves, check valves, and orifices to control gas flow. The product valve manifold  10  connects to the adsorbers of the PSA gas separation system  3  and may be decoupled from the adsorbers and other structural components to reduce noise transmission and vibration between valves and other components in the system. The product valve manifold  10  may also be part of a common assembly with the feed/waste valve manifold  9  with appropriate portions of the valve directing gas into and out of the adsorbers. 
     In some embodiments, oxygen-rich gas flows from the product valve manifold  10  to an integrated assembly that is directed to product gas storage  4 , oxygen gas concentration measurement, oxygen gas pressure and temperature sensing, as well oxygen gas filtration, and oxygen gas delivery, e.g. a gas delivery system  7 . In some embodiments, the gas delivery system  7  can be a conserver. In some embodiments, the integrated assembly contains multiple sensors  11  for various functions including ambient pressure sensing, oxygen gas pressure measurement, breath pressure or cannula pressure measurement, and temperature measurement. 
     The control of the oxygen concentrator system  100  can be achieved by a programmable controller  5 . The oxygen concentrator system  100  also may contain a user/data interface  8 . The user/data interface  8  can include one or more buttons or other inputs to control various features or functions of the concentrator system  100  such as, for example, power state, oxygen flow rate, and or any other concentrator system function. Other embodiments additionally contain an LCD display, at least one removable and rechargeable battery, and an integrated oxygen conserving device to deliver oxygen gas synchronously with a patient&#39;s onset of inhalation to maintain clinical efficacy while reducing the amount of oxygen-rich gas delivered to the patient by a factor of about 2:1 to 9:1. 
       FIGS.  1 B- 1 E  and  FIG.  2    illustrate an embodiment of the oxygen concentrator system disclosed herein in the form of a portable oxygen concentrator  100   a . The concentrator system  100   a  can include any of the same or similar features and functions as the concentrator system  100 .  FIGS.  1 B and  1 C  are interior isometric views taken from two opposing sides of the oxygen concentrator  100   a.  As shown in  FIG.  1 B , the portable oxygen concentrator  100   a  includes a dual function chassis base  111 . The chassis base  111  can serve as a support for the internal components of the oxygen concentrator  100   a.  The chassis base  111  can also serve as a mount for a power source, such as a battery. 
     As shown in  FIGS.  1 B and  1 C , the portable oxygen concentrator  100   a  further includes one or more adsorbers  140  positioned on one end of the chassis base  111 , a compressor assembly  190 , and a shell structure  195 . In some embodiments, the adsorbers  140  are non-cylindrical adsorbers. The vessels forming the adsorbers  140  can be generally non-cylindrical in shape. 
     As shown in  FIG.  1 C , the oxygen concentrator  100   a  includes an outer housing  115  coupled to the chassis base  111  so as to define an internal volume enclosing elements of the concentrator system  100   a,  such as the adsorbers  140 , an airflow generator  165 , the compressor assembly  190 , and the shell structure  195 . In some embodiments, the shell structure  195  can include one or more insulating panels  195   a - c  disposed about the compressor assembly  190 . In some embodiments, the shell structure  195  can surround the compressor assembly  190 . In some embodiments, the shell structure  195  is configured to separate the cooling airflow in the oxygen concentrator system  100   a  from the higher temperature, spent airflow adjacent the compressor assembly  190  that is ready to be expelled from one or more exhaust outlets or ports  161 . In some embodiments, the shell structure  195  forms at least a portion of an enclosure or at least partially sealed chamber around the compressor assembly  190 . In some embodiments, insulating panels  195   a - c  can be disposed adjacent the compressor assembly  190 , for example, in an angled arrangement, which together with the other components surrounding the compressor assembly  190  (e.g., printed circuit board) form an enclosure or at least partially sealed chamber that impedes or prevents heat transfer from the higher temperature, spent airflow to the cooling airflow. In some embodiments, a printed circuit board, such as printed circuit board  150  as shown in  FIG.  2   , can form at least a portion of an enclosure or at least partially sealed chamber around the compressor assembly  190 . In some embodiments, an interior surface of the housing  115  can form at least a portion of an enclosure or at least partially sealed chamber around the compressor assembly. In some embodiments, the shell structure  195  can separate the compressor assembly  190  from one or more other elements positioned within the internal volume defined by the housing  115 , such as the adsorbers  140 . 
     The portable oxygen concentrator  100   a  further includes one or more pneumatics modules, sensor modules, and display modules. As shown in  FIGS.  1 B-C , in some embodiments, the one or more pneumatics modules, sensor modules, and display modules can be formed as a combined upper pneumatics, sensor, and display module  145  that can be detachably removed as a unit. In some embodiments, the shell structure  195  can separate the compressor assembly  190  from one or more pneumatics modules, one or more sensor modules, one or more electronic modules, or other elements of the concentrator system. 
     The oxygen concentrator  100   a  further includes one or more user interface controls  175 , a control electronics printed circuit board (PCB) (not shown), one or more electrical connectors  120  adapted to mate with connectors coupled to the housing  115 , and a printed circuit board (PCB)  170 . The printed circuit board  170  can be a user interface display/sensor PCB or sensor block PCB, or include both. The printed circuit board (PCB)  170  can include various control sensors such as oxygen purity, pressure, and temperature sensors. In some embodiments, the printed circuit board  170  can include or be coupled to a user interface display  171 . In some embodiments, the upper pneumatics, sensor, and display module  145  includes an interface manifold  147  that can be removably attached to an end of the adsorbers  140  and the product manifold. In some embodiments, the control sensors can be electrically connected to the interface. In some embodiments, the shell structure  195  in combination with the PCB  150  and a top portion of the housing  115  can enclose the compressor assembly  190  in a chamber or “hot box” in which hot air is retained, for example, by creating an enclosure or at least partially sealed chamber around the compressor assembly  190 . This chamber or hot box can separate airflow from an airflow generator, such as a fan or blower, into hotter air adjacent the compressor and cooler air outside the hot box. 
       FIG.  1 C  shows an implementation of the cool to hotter airflow control as described above. In this airflow implementation, an airflow generator  165  is mounted directly over the compressor assembly  190 . The airflow generator  165  can be a blower or fan. The outer housing  115  can include one or more air inlets  160   a - b . The air inlets  160   a - b  can be recessed within the outer housing  115  or extend along a curved or angled surface of the outer housing  115 . In some embodiments, the air inlet  160   a  and the air inlet  160   b  can be positioned on different faces or surfaces of the outer housing  115 . In some embodiments the air inlet  160   a  and the air inlet  160   b  can be positioned on opposite surfaces of the outer housing  115 . Air can be drawn in from two sides of the oxygen concentrator  100   a  through the air inlets  160   a  and  160   b  disposed on opposing sides of the oxygen concentrator  100   a.  In alternative embodiments, the air inlet  160   a  and the air inlet  160   b  can be positioned on the same face or surface of the outer housing  115 . In some embodiments, internal components can be positioned such that cooler outside air flows over most of the internal components before being directed to the vicinity of the compressor assembly  190 . 
     The airflow generator  165  is configured to direct airflow along an airflow path between the one or more air inlets  160   a - b  and one or more exhaust outlets or ports  161 . In some embodiments, one or more exhaust ports  161  can be positioned within the chassis base  111 . In some embodiments, the chassis base  111  can include exhaust ports  161  on opposite side surfaces of the chassis base  111 . Both exhaust gas from the PSA gas separation unit and the fully downstream spent cooling gas are exhausted through exhaust ports  161  on each side of chassis base  111 . In alternative embodiments, the exhaust ports  161  can be positioned on the same side of the chassis base  111 . In some embodiments, higher temperature, spent cooling airflow is confined to the area surrounding the compressor assembly  190  and exhausted immediately adjacent the bottom of the compressor assembly  190 . This is an example of a push/pull airflow in which the compressor assembly  190  is positioned at a downstream end of the airflow path immediately before the exhaust ports  161 . Such an arrangement can accomplish the delivery of cool air to many of or most of the internal components before exhausting hot air from the higher temperature components in the vicinity of the compressor assembly  190 . In some embodiments, it is desirable to exhaust hot air in the vicinity of the compressor assembly as soon as possible, for example, to reduce backflow of the higher temperature air from the vicinity of the compressor assembly  190  to other internal regions of the concentrator  100   a.  The positioning of the exhaust ports  161  adjacent to the compressor assembly  190  can reduce such a backflow. Advantageously, the cooling air flow path of the oxygen concentrator system  100   a  ends at an area adjacent the component that generates the most heat, for example, the compressor assembly  190 , so that the spent cooling air can be expelled before affecting other components. 
     The oxygen concentrator  100   a  is configured to minimize the likelihood of impeding the airflow through the device in as many use situations as possible such as, for example, placing the oxygen concentrator  100   a  against a flat vertical surface or laying the concentrator  100   a  on its side (other than the intended bottom side). The air inlets  160   a  and  160   b  are designed and arranged to substantially reduce the risk of inlet vent obstruction. The exhaust ports  161  are contoured such that they cannot be blocked by any single plane. In one embodiment, the exhaust ports  161  are disposed on only one side of the chassis base  111  such that the ports  161  directs hot exhaust gas away from the patient&#39;s body when the oxygen concentrator  100   a  is being carried adjacent to the patient body such as in a shoulder bag or hip bag. In some embodiments, the design of the air inlets  160   a - b  and/or exhaust ports  161  can include additional geometrical details such as curvature of a face of the air inlets  160   a - b  and/or exhaust ports  161 , recessing of the air inlets  160   a - b  and/or exhaust ports  161  below the surface of the concentrator housing  115 , and/or angling of the exhaust ports  161  to direct both air flow and noise in a desirable direction as it exits the concentrator system  100   a.  In some embodiments, the exhaust ports  161  are angled away from a removable battery  110  coupled to the chassis base  111  to prevent heating of the battery  110 . In some embodiments, the exhaust ports  161  can be formed in a portion of the chassis base  111  extending laterally beyond a lateral edge of the battery  110 . In some embodiments, the exhaust ports  161  are directed at a downward angle over a recess formed in the portion of the chassis base  111  extending laterally beyond a lateral edge of the battery  110 . The angling and positioning of the exhaust ports  161  can prevent obstruction of the exhausts ports  161  if the concentrator is placed against or adjacent a flat surface. 
     In one embodiment, each air inlet  160   a - b  includes an opening defined by an exterior border  162   a - b  that is recessed from a portion of the exterior surface of the housing  115 , which may have a planar or convex contour. In some embodiments, the recessed exterior borders  162   a - b  of the air inlets  160   a - b  in combination with the convex contour of the exterior surface of the housing  115  form an air gap that permits at least some air to flow through even when the exterior surface of the housing is resting against a planar surface such as a table top. In some embodiments, a middle section of each exterior border  162   a - b  is not coplanar with the opposing end sections such that the middle section slightly protrudes from the opposing end sections. In some embodiments, the air inlets  160   a - b  comprise louvers having a curved configuration adapted to increase intake of airflow from multiple directions. 
       FIG.  1 D  shows the oxygen concentrator  100   a  having the battery  110  slidably mounted to a lower surface  166  of the chassis base  111 . As also shown in  FIG.  1 D , a plurality of the exhaust ports  161  are disposed horizontally along a lower edge  164  of the chassis base  111 . Each exhaust port  161  comprises a recessed opening  163  defined by an exterior border that is disposed on the sidewall  168  and lower surface  166  of the chassis base  111 . The recessed opening  163  extends into the sidewall  168  and partially into the lower surface of the chassis base  111  so as to form an opening that allows for at least two airflow paths  169   a - b  from the oxygen concentrator. In some embodiments, the airflow paths  169   a  and  169   b  can be offset. In some embodiments, the airflow paths  169   a  and  169   b  can be perpendicular or generally perpendicular. As  FIG.  1 D  further shows, at least a portion of a lateral side  112  of the battery  110  is recessed such that when the battery  110  is mounted to the chassis base  111 , the sidewall  168  of the chassis base  111  protrudes outwardly from the recessed portion of the lateral side  112  of the battery  110  thereby exposing the recessed opening  163  of each exhaust port  161 . Additionally, the battery recess near the exhaust ports  161  provides additional space for the exhaust gas heat to dissipate with minimal contact to the battery housing, which minimizes the amount of exhaust gas heat which may be transferred to the battery  110 . Minimizing battery heating is advantageous to battery performance and life, particularly if the heat is specific to a portion of the battery such as the small region surrounding the exhaust outlets.  FIG.  1 E  shows the oxygen concentrator  100   a  resting against a flat surface  200  on the side where the exhaust ports  161  are located. As shown in  FIG.  1 E , the recessed openings  163  of the exhaust ports  161  are not obstructed even though the side with the exhaust ports  161  is resting against a planar surface. The configuration of the exhaust ports  161  in combination with the battery design enable air  169   b  to still flow out of the exhaust ports  161 . In one embodiment, the exhaust ports  161  comprise louvers having a configuration adapted to direct air to flow in an angled direction. Combined, these features increase the likelihood of full or partial air flow helping to prevent overheating even if the oxygen concentrator  100   a  is improperly positioned during use. 
     As described in co-pending application Ser. No. 15/608,775, one way to implement a portable oxygen concentrator package is to mount the internal workings, e.g., the adsorbers, valves, compressor and controller elements to a chassis and cover the chassis and internal elements with a removable outer housing. Such an arrangement is shown in  FIG.  2   . The outer housing  115  is configured to removably couple to the chassis base  111 . As shown in  FIG.  2   , the outer housing  115  contains user interface elements including one or more user interface controls  175 . The user interface controls  175  can be electrically connected to the PCB  170 . The PCB  170  can be mounted to a superior end of the chassis base  111 . In addition, as shown in  FIG.  2   , the interior components of the oxygen concentrator  100   a  are designed and arranged in a manner such that the overall exterior contour created by the interior components substantially conforms to the rectangular shaped outer housing  115  so as to reduce waste of space inside the housing  115 . For example, the two adsorbers  140  positioned on one end of the chassis form an exterior contour containing somewhat flattened sides with rounded corners to mirror the configuration of the outer housing  115 . The PCB  150  is positioned in a vertical orientation along a lateral side of the chassis to mirror the flat lateral side of the outer housing  115 . 
       FIGS.  3 A and  3 B  show an improved design for making the electrical connection between the outer housing  115  and the interior components of the oxygen concentrator  100   a.  As shown in  FIG.  3 A , the outer housing  115  can include one or more electrical connectors  125  in electrical communication with the electrical components of the outer housing  115 , such as the user interface controls  175 . The electrical connectors  120  can reside on the PCB  170 . The electrical connectors  125  can be positioned to align with and mate with the electoral connectors  120  when the outer housing  115  is coupled to the chassis base  111 . 
     The outer housing  115  can be configured to define an enclosed volume around the printed circuit board  170  when coupled to the chassis base  111 . The outer housing  115  can be configured to seal the printed circuit board from external moisture when coupled to the chassis base  111 . 
     The connectors  120  can be oriented on the PCB  170  so as to face in a generally superior direction. The connectors  125  can be positioned on an interior surface of a top wall of the housing  115 , and may be oriented to face in a generally inferior direction. During assembly of the oxygen concentrator  100 , the outer housing  115  can be traversed generally inferiorly over the internal components of the oxygen concentrator  100  and mated with the chassis  111 . These connectors are disposed such that when the outer housing  115  is mated to chassis  111 , connectors  120  and  125  mate. This arrangement can facilitate ease of manufacture and improved sealing of the housing  115  and chassis  111 . This arrangement allows for establishment of an electrical connection and a mechanical connection without requiring additional external openings in the outer housing that could provide access to moisture. 
     One of the drivers in making a portable oxygen concentrator as small and light as possible is to optimize the operation of the adsorbers  140  of the PSA gas separation unit  3 . In general, each adsorber  140  contains an adsorbent material  141  that filters at a molecular level. In some embodiments, the adsorbent material  141  is in the form of an adsorbent bed. In some embodiments, the adsorbent material  141  can filter between nitrogen and oxygen molecules in a manner described above and otherwise employed in gas separation devices including portable oxygen concentrators. In some embodiments, the adsorbent material  141  can include adsorbent particles. Many conventional portable oxygen concentrators utilize zeolite beads for this molecular filter material. These adsorbent particles are densely packed into an adsorbent bed vessel or pressure vessel  144 . The vessel  144  and the adsorbent material  141 , possibly in combination with other components, can form the adsorber  140 . To work effectively and achieve reasonable operational lifetimes, it is important that the adsorbent particles are packed closely and are constrained from movement during PSA cycles when the adsorbers  140  may be subject to zero to 10&#39;s of PSI over the course of a few seconds. Portable oxygen concentrators typically utilize adsorbers  140  having vessels  144  with circular cross-sections, such as those shown in  FIG.  4 A , for example, because a circular cross section allows for thin vessel walls  148  with no or little deformation, keeping the adsorber designs light while ensuring rigidity. However, many oxygen concentrator housing  115  shapes are rectangular solids, typically with some curvature. As shown in  FIGS.  4 A,  4 B, and  4 C , a circular cross section vessel  144  is not an efficient way to maximize capacity if the circular columns have to fit into a more or less rectangular shape. 
     In some embodiments, vessels  144  having non-circular cross sections are used. However, once a vessel  144  design deviates from a circular cross-section, the surfaces, particularly any resulting flat surfaces are more prone to deformation under pressure. One way to counteract potential deformation is to utilize thicker vessel walls  148  as shown in  FIG.  4 B . However, thicker vessel walls  148  may diminish the advantage in space gained by using the non-circular cross-section shape and add weight rather than performance to the oxygen generating system. 
       FIG.  4 D  shows a vessel shape tailored to utilize most of the space at one end of the outer housing  115  in the oxygen concentrator  100   a  shown above. The shape of the vessel  144  shown in  FIG.  4 D  is non-circular in cross section. In some embodiments, such a shape can include flat deformation prone surface areas. 
     As shown in  FIG.  5 A , in some embodiments, the adsorbers  140  can include stiffening supports  146  to stiffen the vessel  144  in a direction of likely deformation. In some embodiments, the stiffing supports  146  can be stiffening ribs. In some embodiments, the stiffening supports  146  can extend across an interior of the vessel  144 . In some embodiments, the stiffening supports  146  can extend along an interior wall of the vessel  144 . In some embodiments, each adsorber  140  can include a single stiffening support  146 . In some embodiments, each adsorber  140  can include a plurality of stiffening supports  146 . In some embodiments, each adsorber  140  can include one or more stiffening supports  146  extending across an interior of the vessel  144  and/or one or more stiffening supports  146  extending along an interior wall of the vessel  144 . 
     In some embodiments, one or more stiffening supports  146  may alternatively or additionally be added on an exterior portion of the vessel  144 . In some embodiments, one or more stiffening supports  146  can be positioned on an exterior surface of the vessel  144 . 
     Adding features to stiffen the structure at the point of deflection can substantially mitigate the deformation with minimum added weight relative to changing the overall wall thickness. In one embodiment, the adsorber system comprises two adsorbers  140  having vessels  144  with oblong, obround, semicircular, or generally semicircular cross-sections joined together. In addition, the non-circular vessels  144  allow more adsorbent material to be placed in the same internal concentrator volume, which in turn increases the oxygen delivery capacity of the oxygen concentrator without increasing the size. In some embodiments, a cross-section of the adsorber  140  can be at least 90% filled with adsorbent material  141 . In some embodiments, a cross-section of a portion of the adsorber  140  housing adsorbent material  141  can be at least 90% filled with adsorbent material  141 . In some embodiments, the portion of the adsorber  140  filled with adsorbent material  141  can be filled such that at any cross-section of the portion the adsorber  140  is at least 90% filled with adsorbent material  141 . 
     In some embodiments, a combination of a thickness of the vessel wall  148  and a stiffness of the stiffening support  146  is sufficient to limit deformation of the vessel wall  148  to at least one of less than 0.1 mm and less than 25% of an average diameter of the adsorbent particles under a pressure swing of at least 30 psi within the vessel  144 . In some embodiments, a combination of a thickness of the vessel wall  148  and a stiffness of the stiffening support  146  is sufficient to limit deformation of the vessel wall  148  to less than 0.05 mm under a pressure swing of at least 30 psi within the vessel  144 . 
     For suitable vessel materials, e.g. materials with suitable stiffness/weight, such as aluminum, magnesium, or plastics materials, it has been found that a combination of wall thickness/support rib stiffness equivalent to achieving maximum deformation of 25% of the adsorbent material particle size under a pressure swing of 30 psi makes possible a shape such as shown in  FIG.  4 D , an optimized non-circular cross section for a particular shaped volume, with a wall thickness as small as 0.030 inches in a cast magnesium or aluminum material along with strengthening ribs. Other materials and volume shapes may be addressed using similar constraints. 
     As shown in  FIG.  4 D- 5 B , in some embodiments, an adsorber system can include a plurality of adsorbers  140 . In some embodiments, the adsorber system can include a first adsorber  140  and a second adsorber  140 . In some embodiments, the vessel wall  148  of the first adsorber  140  is joined to the vessel wall  148  of the second adsorber  140 . In some embodiments, the vessel wall  148  of the first adsorber  140  is integrally formed with the vessel wall  148  of the second adsorber  140 . In some embodiments, the stiffening support  146  of the first adsorber  140  is integrally formed with the stiffening support  146  of the second adsorber  140 . As shown in  FIG.  5 B , in certain embodiments, filters  147  can be recessed within cavities  152  at a superior end of the adsorber  140 . In some embodiments, the cavities are defined by the wall  148 . In some embodiments, the cavities  152  have a cross-section with a different size and/or shape relative to the inferior portions of the adsorber  140 . For example, the cavities can be formed by generally disc-shaped protrusions  153 . In some embodiments, the cavities  152  can be formed within protrusions  153  extending from a superior end of the vessel  144 . The protrusions  153  can have a cross section different than a cross section of the vessel wall  148 . In some embodiments, the protrusion  153  is cylindrical. In some embodiments, the protrusions  153  are integrally formed with the vessel walls  148 . 
     Recession of the filters  147  within the cavities can allow for use of filters or flites having a different shape and/or size relative to the vessel wall  148  of the adsorber  140 . For example, recessing the filters  147  within the cavities can allow for use of a round filter or frit with a vessel  144  having a non-circular cross-section. 
     As shown in  FIG.  5 B , the adsorber  140  can be sealed at its bottom end via a plate  149  having O-rings  151 . 
     In some embodiments, the walls  148  may have a uniform or variable wall thickness. 
     As shown in  FIG.  2   , and shown in co-pending U.S. application Ser. No. 15/608,775, in some embodiments, the battery  110  may act as a suitable base for the portable oxygen concentrator  100  due to its ability to create a low center of gravity for the oxygen concentrator itself. 
     In previous oxygen concentrator designs produced by the Applicant, a battery has two raised slides in the form of shaped bars extending along part of the length of each side of the battery. The slides can fit into rails on a concentrator chassis base. The slides are placed in the rails, and the battery is slid onto the chassis until electrical connectors from the battery and chassis base are mated and a retainer mating piece contacts a hand actuated retainer. The combination of the mated electrical connector, the relatively long slide/rail connection, and the retainer serves to hold the battery in place within the chassis base. Removal consists of releasing the retainer and sliding the battery out. 
       FIGS.  6 A-D  show an embodiment of an arrangement for securing a battery  110  to a chassis base  111 .  FIG.  6 A  shows the battery  110  separated from the chassis base  111 .  FIG.  6 C  shows the battery  110  coupled to the chassis base  111 . 
     As shown in  FIGS.  6 A-D , the oxygen concentrator  100  includes rails  113   a - b . The first rail  113   a  is configured to receive a first slide  114   a  of a battery  110 . The second rail  113   b  is configured to receive a second slide  114   b  of the battery  110 . The second rail  113   b  can be spaced apart from the first rail  113   a  so as to form a channel  116  for receiving the battery  110 . The channel  116  can include an open proximal end  117   a  and a closed distal end  117   b.    
     As shown in  FIG.  6 A , the rails  113   a - b  include a flexible stiffening mechanism  129 . The flexible stiffening mechanism  129  is configured to impart a biasing force on a surface  127  of the battery  110  when the battery  110  is received in the channel  116 . 
     In certain embodiments, the flexible stiffening mechanism  129  includes a bump or protrusion  133   a.  The protrusion  133   a  projects from the first rail  113   a  towards the second rail  113   b.  The flexible stiffening mechanism also includes a slit  130  positioned behind the protrusion. The slit  130  can be configured to facilitate or allow for travel of the protrusion  133   a  fore and aft (i.e., towards the second rail  113   b  or away from the second rail  113   b ). In some embodiments, the slit  130  can facilitate or allow for flexion of the section of the rail from which the protrusion  133   a  projections. For example, in some embodiments, the slit  130  can be positioned, shaped, dimensioned, or otherwise configured to allow for movement of the section of the rail from which the protrusion  133   a  projects. In certain embodiments, the protrusion  133   a  may alternatively or additionally be deformable so as to facilitate flexion of the protrusion  133   a.  In certain embodiments, the stiffening mechanism  129  can maintain contact between the first rail  113   a  and the battery  110  to stabilize the battery  110  within the channel  116 , for example, while the battery  110  is inserted into the channel  116  and while the battery  110  is fully seated within the channel  116 .  FIGS.  6 B and  6 D  depict the flexible stiffening mechanism before and after, respectively, a portion of the battery  110  contacts the flexible stiffening mechanism  129 , for example, during an insertion of the battery  110  into the channel  116 . 
     In certain embodiments, the biasing force  110  of the flexible stiffening mechanism  129  is sufficiently flexible to permit translation of the battery  110  within the channel  116  past the protrusion  133   a.    
     Incorporating a flexible stiffening mechanism  129  to the battery attachment of a portable oxygen concentrator  100  can facilitate alignments of smaller and more tightly spaced electrical connections, such as an electrical connector  126  of the battery  110  and an electrical connector  128  of the concentrator  100 . In the absence of a flexible stiffening mechanism, at one end of manufacturing tolerances of a battery and a concentrator, some combinations may bind or be difficult for the customer to install. Conversely, at the other end of the manufacturing tolerances, the battery may rattle or cause intermittent or undependable electrical connections between the battery and the concentrator. Use of the flexible stiffening mechanism  129  can facilitate increased stability when using a battery  110  that has a size smaller than an upper tolerance level to reduce installation difficulty. In some embodiments, the flexibility of the stiffening mechanism  129  can facilitate contact between a batteries  110  having different sizes. For example, in some embodiments, the stiffening mechanism  129  can facilitate contact between the first rail  113   a  and a battery  110  having a size that is smaller than an upper tolerance level of battery sizes capable of being received within the channel  116 . As described herein, the increased stability can reduce rattle of the battery  110 , for example lateral movement of the battery orthogonal to an axis along which the battery  110  is inserted, and loss of the electrical connections between the battery and concentrator. 
     In some embodiments, the flexible stiffening mechanism  129  is configured to impart the biasing force on the surface  127  of the battery  110  so as to align the electrical connector  126  of the battery  110  with the electrical connector  128  of the concentrator  100   a . By improving alignment of the electrical connections, wear and tear resulting from battery attachment can be reduced. 
     In some embodiments, one or more protrusions can project from the second rail  113   b  at least partially towards the first rail  113   a.  The one or more protrusions projecting from the second rail  113   b  can be configured to contact the battery  110  when the battery  110  is positioned within the channel  116 . In some embodiments, at least one protrusion  133   b  projection from the second rail  113   b  is positioned proximally relative to the protrusion  133   a.  In at least some embodiments, at least one protrusion  133   c  projecting from the second rail  113   b  is positioned distally relative to the protrusion  133   a.  In certain embodiments, the flexible stiffening mechanism  129  is configured to impart the biasing force on the surface  127  of the battery  110  to impart stability to the installation of the battery  110 . 
     In some embodiments, the protrusions  133   a - c  can form a three point stiffening hold. The protrusions  133   a - c  can be positioned on the rails  113   a - b  so that they lightly contact the battery  110  structure when the battery  110  is received within the channel  116 . The protrusions  133   a - c  can be sized to contact the battery  110  when inserted into the channel  116 , but also allow the battery  110  to be slid along the rails  113   a - b  from the open proximal end to the closed distal end, e.g., by providing one or more forces, such as the biasing force of the flexible stiffening mechanism and/or one or more frictional forces, upon the battery  110  of a sufficient magnitude to allow movement of the battery when an external force above a threshold magnitude is applied thereto, but restrict movement of the battery  110  when an external force below a threshold magnitude is applied thereto. 
     The flexible stiffening mechanism  129  and the protrusions  133   b - c  can provide an improved coupling of the battery  110  onto the rails  113   a - b . This flexion of the stiffening mechanism  129  can achieve better battery engagement and alignment than previous designs without adding space, weight, or cost. 
     While a single flexible stiffening member  129  on a first rail  113   a  is described, it is contemplated that a plurality of flexible stiffening members  129  can be employed on one or both of the rails  113   a - b . While the flexible stiffening mechanism is described as having a protrusion  133   a  and a slit  130 , other suitable flexible stiffening mechanisms or spring mechanisms may be employed. While two protrusions, protrusions  133   b  and  133   c,  on the second rail  113   b  are described, it is contemplated that one protrusion or more than two protrusion  133   b - c  can be employed on one or both of the rails  113   a - b.    
     As described herein, portable oxygen concentrators can benefit from designs that are compact in size and internally simple. Due to the flow of gas through a portable oxygen concentration, multiple gas tight interconnections can be required within the interior of the portable oxygen concentrators. Barbed connections are commonly used in portable oxygen concentrators, in which a compliant tube is stretched over a barb on the end of a mating piece. Barbed connections can be limited to small numbers of in line connections both in terms of manufacturability of a two-dimensional arrangement of barbed fittings and in difficulty of installation and removal of tubes from such a two-dimensional arrangement. 
     An improved approach to multiple gas connections in one-piece parts is shown in  FIGS.  7 A-C . A multi-port interconnection  181  is shown in several views with tubes  180  mated thereto. In some embodiments, the interconnection  181  can be compliant or elastomeric. In some embodiments, the interconnection  181  can be formed of a single piece. The interconnection  181  can include a plurality of ports  184 , each port configured to receive a tube  180 . Each port can include one or more sealing rings  182 . In some embodiments, each sealing ring  182  can be in the form of a raised bump on the inside wall of one of the ports  184  of the multi-port connector  181 , is employed. Tubes  180  are pressed into the ports  184  of the interconnect  181  until they pass the sealing ring  182 . The compression of both the compliant interconnect piece  181  as well as the tubes  180  around the sealing ring  182  provides sealing and/or positioning functions. The raised bump can be circular in some embodiments, but may be any other suitable shape, such as rectangular or triangular. Such an arrangement lends itself to manufacturability and usability for multiple two-dimensional port arrangements such as shown in  FIG.  7 C . 
     In some embodiments, compression around the sealing ring  182  of one port  184  can extend into adjacent ports  184  if not addressed. To reduce the spacing required between the ports  184  to achieve a higher density multi-port interconnect  181 , in some embodiments, the sealing rings  182  can be positioned at offset locations in adjacent ports  184  as shown in  FIG.  7 B . Given that the tube sizes in portable oxygen concentrators tend to be on the order of 1 cm in diameter or less, it can be important to keep the density of ports  184  in multi-port interconnect  181  high, for example, so that a multi-port interconnect  181  in the form of a block such as shown in  FIG.  7 C  can make multiple connections between ports  184  and tubes  180  in a space just a few cm in dimension. 
     Alternatively, in some embodiments, as shown in  FIGS.  7 D and  7 E , the same or a similar effect can be achieved by use of a non-elastomeric member  183 . In some embodiments, a non-elastomeric member  183  can uniformly compress the seal of multiple ports  184  in a single body in the elastomeric element  181 . By utilizing a non-compliant or non-elastomeric member  183  that is assembled onto or manufactured into the elastomer  181 , uniform compression can be achieved on multiple interconnect ports  184 . The addition of the non-compliant member  183  can also allow the use of secondary mounting features such as snap fits, screw bosses, hooks, or simple bosses to maintain the position of the mating parts under pressure. This allows the single member  183  to provide both a pneumatic connection and mechanical position connection in a single component. In some embodiments, the combination elastomeric/non-elastomeric arrangement shown in  FIG.  7 E  can also incorporate sealing ring structures, such as sealing rings  182 . The integrally formed multi-port block designs shown in  FIGS.  7 A-E  can provide the sealing and mechanical retention required in a portable oxygen concentrator, but still allow for removal, for repair, or service. In contrast, barb designs employed in other oxygen concentrators can prevent removal of tubes without damage to the tube, barb, or both. In some embodiments, the interconnects  181  shown in  FIGS.  7 A-E  can form a secure connection without requiring secondary retainers such as zip ties or clamps on each individual tube  180 . The interconnects  181  can retain many tubes  180  and connections with greatly fewer secondary mounting features than in single port interconnects. 
       FIGS.  7 F and  7 G  depict an embodiment of an elastomeric multi-port interconnection implementation  181  with four ports and sealing rings  182 . As shown in  FIGS.  7 H and  7 I , in some embodiments, two non-elastomeric pieces are molded as described above to form an interconnection element have a compliant interconnect  181  and non-elastomeric pieces  183 . In some embodiments, adding non-elastomeric pieces  183  to a compliant interconnect  181  to form an assembly can allow for the use of mounting elements, such as fastener holes, in a more rigid medium than an elastomeric interconnect alone, thus forming an interconnection assembly offering both elastomeric isolation along with secure mechanical mounting. Interconnection assembly elements  181  and  183  may be joined in a variety of ways, including over molding the elastomeric piece to the hard plastic pieces when the elastomeric piece is formed, assembling the components together with mechanical mating features, or bonding the elastomeric piece to the hard plastic pieces. 
       FIGS.  7 J and  7 K  show interconnection assemblies have elements  181  and  183  mating with two sets of tubes—tubes  180   a  from a valve assembly and tubes  180   b  from a manifold assembly. When assembled together, the multi-port interconnect assembly having element  181  and  183  provides compact multiple gas connections in a small footprint, allows for elastomeric isolation between the two assemblies, and is easy to assemble. 
     As has been described in co-pending U.S. patent application Ser. Nos. 15/608,775 and 15/027,948, the mounting of a compressor or compressor assembly in a portable oxygen concentrator can requires the use of mate-able gas transport compliant members to accommodate the vibration levels of the compressors, as well as to dampen sound and vibration. In the case of mounts on the intake of the compressor, these members typically include circular tube connections and can be by necessity thin and flexible to maintain vibration isolation at low frequency rates of 150 Hz or below. Such connections are reliable and functional and may be fastened through the interior of the mount utilizing a screw or retainer with a hole through it for air intake into the compressor. However, during assembly, these round tube connections can allow for the connections to rotate due to the torque of the fastener, complicating the assembly process and introducing variability into the final assembled configuration. In the case of output of the compressor, compliant members may also twist or be incorrectly aligned during installation, also introducing assembly variation. 
     An improved arrangement is shown in  FIGS.  8 A-C . Compressor assembly  190  includes a first compressor chamber  172   a  having a first connector  191   a  and a second compressor chamber  172   b  having a connector  191   b . The compressor assembly  190  further includes tube  192 . The tube  192  includes a first end having a first connection interface  173   a  configured to couple to the first connector  191   a  to form a first interconnect. The compliant member  192  includes a second end having a second connection interface  173   b  configured to couple to the second connector  191   b  to form a second interconnect. A connection between the first connection interface  173   a  to the first connector  191   a  and the second connection interface  173   b  to the second connector  191   b  forms a gas connection between the first compressor chamber  172   a  and the second compressor chamber  172   b.    
     In some embodiments, one or more of the first connector  191   a,  the second connector  191   b,  and the tube  192  can be compliant. Utilization of at least one compliant component can facilitate ease of connection between the tube  192  and both the first connector  191   a  and  191   b.    
     The first connection interface  173   a  can be shaped, dimensioned, and/or otherwise configured to maintain the first interconnect in a fixed orientation. The second connection interface  173   b  can be shaped, dimensioned, and/or otherwise configured to maintain the second interconnect in a fixed orientation. 
     In some embodiments, the first connector  191   a  can have a shape that matches the shape of the first connection interface  173   a.  In some embodiments, the first connection interface  173   a  and the first connector  191   a  can be shaped such that the first connection interface  173   a  and the first connector  191   a  can mate in only one possible orientation. In some embodiments, the first connection interface  173   a  and the first connector  191   a  can be shaped such that the first connection interface  173   a  and the first connector  191   a  are prevented from rotating when mated. In some embodiments, the first connection interface  173   a  and the first connector  19   a  can be square, generally square, or any other suitable shape. In some embodiments, the second connector  191   b  can have a shape that matches the shape of the second connection interface  173   b.  In some embodiments, the second connection interface  173   b  and the second connector  191   b  can be shaped such that the second connection interface  173   b  and the second connector  191   b  can mate in only one possible orientation. In some embodiments, the second connection interface  173   b  and the second connector  191   b  can be shaped such that the second connection interface  173   b  and the second connector  191   b  are prevented from rotating when mated. In some embodiments, the second connection interface  173   b  and the second connector  191   b  can be square, generally square, or any other suitable shape. 
     In some embodiments, one or both of the first connector  191   a  and the second connector  191   b  can be in the form of protrusions. In some embodiments, one or both of the first connection interface  173   a  and the second connection interface  173   b  can be in the form of receptacles. Alternatively, in some embodiments, one or both of the first connector  191   a  and the second connector  191   b  can be in the form of receptacles, and one or both of the first connection interface  173   a  and the second connection interface  173   b  can be in the form of protrusions. 
     In some embodiments, a sealing element  189  can extend from each of the connectors  191   a  and  191   b  and into the tube  192  when the connectors  191   a  and  191   b  are coupled thereto. Each of the sealing elements  189  can be configured to form a seal with a complementary sealing element  194  positioned within an interior of the tube  192 . Alternatively, in some embodiments, sealing elements  194  can extend from the tube  192  into the first connectors  191   a  and  191   b  to mate with complementary sealing elements  189  within the connectors  191   a  and  191   b.    
     Mount  193  illustrates another type of clocking. The mount  193  includes a base  193   a  and one or more connectors  193   b.  Each of the connectors  193   b  can include a compliant member  174 . Each of the connectors  193   b  can further include one or more protruding tabs  176  extending from the compliant member  174 . In some embodiments, each of the connectors  193   b  can include a pair of protruding tabs  176 . In some embodiments, the pair of protruding tabs  176  can be spaced 180 degrees apart from one another about a circumference of the compliant member  174 . In some embodiments, the one or more protruding tabs  176  can be configured to couple with one or more complementary slots  177  on the compressor  190  configured to receive the pair of protruding tabs  176 . In some embodiments, the coupling between the protruding tabs  176  and the slots  177  can clock the interconnect in a fixed orientation. Other tab/slot or post/hole arrangements may also be used. For example, in some embodiments, the mount  193  includes slots configured to receive protruding tabs from the compressor assembly  190 . 
     In some embodiments, the protruding tabs  176  can be formed of a different material than the compliant member  174 . In some embodiments, as shown in  FIG.  8 C , the protruding tabs  176  can be part of a separate clocking member or insert  195 , which can be formed of a rigid material, such as metal or plastic. The insert  195  can adds rigidity to the clocking connection. In some embodiments, the compliant member  174  and the clocking member  195  may be attached during a molding process, joined with adhesives, or clamped together. In some embodiments, the base  193   a  may also be separately manufactured. In some embodiments, the base  193   a  can be formed of a rigid material such as metal or plastic. The base  193   a  can add rigidity to the clocking connection. 
     In some embodiments, the mount  193  can be coupled to the compressor assembly  190  by a hollow screw. In some embodiments, intake air can be drawn through the hollow screw. 
     In some embodiments, the inclusion of clocking arrangements for compliant member interconnects improves the manufacturing of the portable oxygen concentrator. In the absence of clocking members, compliant member  193  may twist during installation, which can lead to tearing of the material or the compressor assembly being held out of place by the twisting of the mount. 
     Portable oxygen concentrators can require compact O 2  sensors to monitor the oxygen content of the gas delivered to patients. Such sensors can be difficult to find commercially in the size range and price points required for portable oxygen concentrators. Accordingly, many commercial portable concentrators have custom designed oxygen sensors. These sensors generally rely on the fact that the speed of sound in a gas is dependent on the gas composition and therefore oxygen concentration can be inferred from the speed of sound. 
     Examples of oxygen sensor designs for the oxygen concentrators are shown in  FIGS.  9 A and  9 B . A sound emitter  201  is mounted to one end of tube  200 , and a sound receiver  202  is mounted to the other end of the tube  100 . In principle, a measurement can be performed based on the speed of sound (approximately 350 m/s), a length of the tube, and a transit time between the emitter  201  and the receiver  202 . In practice, pressure and temperature variations affect signal reception rise time, and standing wave propagation may induce distortions that make the actual use of such a sensor problematic, and significant design and implementation issues affect this type of design. In addition, commercially available transducers are available in limited packaging options, potentially making the inclusion of such a sensor into the concentrator labor intensive. 
     An alternative embodiment of an oxygen sensor  210  is shown in  FIGS.  9 C and  9 D . The oxygen sensor  210  includes an emitter  201  comprising an active surface  211  configured to emit an acoustic signal. The oxygen sensor  210  includes a receiver  202  having an active surface  212  configured to receive an acoustic signal. The oxygen sensor  210  further includes a body  215  forming a chamber  205 . The body  215  includes a first opening  216  configured to receive the emitter  201  such that the active surface  211  of the emitter  201  is exposed to the chamber  205 . The body  215  includes a second opening  217  configured to receive the receiver  202  such that the active surface  212  of the receiver  202  is exposed to the chamber  205 . 
     In some embodiments, body  215  can include one or more reflectors  218  configured to reflect an acoustic signal so as to establish an acoustic path between the active surface  211  of the emitter  201  and the active surface  212  of the receiver  202 . In some embodiments, the body  215  can include at least two reflectors  218 . In some embodiments, the reflectors  218  can be formed by or positioned on two angled opposing faces within the body  215 . An example of an acoustic path  206  is shown in  FIG.  9 D . Alternative arrangements may include an acoustic path with one reflection or multiple reflections. 
     In some embodiments, the first opening  216  and the second opening  217  can be coplanar. In some embodiments, the first opening  216  and the second opening  217  can be positioned in parallel to one another. In some embodiments, the active surface  211  of the emitter  201  and the active surface  212  of the receiver  202  can be coplanar. In some embodiments, the emitter  201  and receiver  202  are mounted with their active surfaces  211  and  212  in the same orientation, for example, parallel with one another. In some embodiments, the active surface  211  of the emitter  201  and the active surface  212  of the receiver  202  are oriented to face in parallel directions. 
     In some embodiments, the oxygen sensor  210  further includes one or more seals  204 . The seals  204  can be in the form of sealing rings. In some embodiments, the seals  204  can include a first seal  204  configured to provide a seal between the first opening  216  and the emitter  201  and a second seal  204  configured to provide a seal between the second opening  217  and the receiver  202 . 
     In some embodiments, the sensor  210  can include a printed circuit board  203 . In some embodiments, the emitter  201  and receiver and  202  can be co-mounted to the printed circuit board  203 . In some embodiments, one or more additional sensors, such as a temperature sensor  219   a  and/or a pressure sensor  219   b  as shown in  FIGS.  9 D,  9 E, and  9 F , may be co-mounted to the PCB  203 . In some embodiments, the body  215  may mount directly to the PCB  203 . In some embodiments the body  215  and seals  204  can mount directly to the PCB. 
     In some embodiments, the temperature sensor  219   a  can be configured to measure a temperature of oxygen gas within the chamber  205 . In some embodiments, the temperature sensor  219   a  can be configured to measure a temperature of air outside the chamber  205 . 
     In some embodiments, the pressure sensor  219   b  can be configured to measure a pressure of oxygen gas within the chamber  205 . In some embodiments, the pressure sensor  219   b  can be configured to measure the pressure of air outside the chamber  205 . 
     In some embodiments, the sound path  206  within the chamber  205  may be configured to reduce standing wave propagation, eliminating or at least reducing one of the difficult to characterize behaviors of the tube type sensors shown in  FIGS.  9 A-B . 
     Many portable oxygen concentrators provide two or more output flow settings, thereby allowing a single model concentrator to address a range of patient oxygen needs. In some embodiments, it may be desirable for the compressor for such concentrators to be designed with a maximum flow setting driving the intended compressor capacity. However, it is often the case that most users will operate a given concentrator model at a flow setting lower than maximum flow during use of the oxygen concentrator. In some instances, a user will operate the oxygen concentrator at a number of different settings during use. In some instances, a user will operate the oxygen concentrator at a setting lower than the maximum flow setting during a majority of the duration of use of the concentrator. Thus, even though a compressor motor must be capable of operating at the maximum flow setting, the highest flow setting may not be used often. Accordingly, it may be advantageous to tune the motor and motor control function to improve efficiency at the most commonly used flow settings while maintaining the ability to operate across the full range of flow settings. 
     Referring to  FIG.  10 A , a simplified illustration of a control system  188  for controlling a motor  199  of the compressor  190  is shown. The control system  188  includes a power source  198 , a voltage controller  196 , and a pulse width modulation (PWM) controller  197 . In some embodiments, the voltage controller  196  and PWM controller  197  can be combined into a single motor controller or, alternatively, may be separate elements. 
     In some embodiments, the power source  198  provides a power source voltage. In some embodiments, the power source  188  provides a DC power source voltage. In some embodiments, the power source is a battery, an AC to DC power supply, a fixed power source having car DC power ports, or any other suitable power source. 
     In some embodiments, one or both of the voltage controller  196  and the PWM controller  197  can drive operation of the compressor  190 , for example, by providing compressor motor control signals. In some embodiments, the voltage controller  196  is configured to selectively modify the power source voltage to provide a plurality of supply voltages. In some embodiments, the voltage controller  196  is configured to modify the power source voltage to provide one or more supply voltages higher than the power source voltage. 
     In some embodiments, the pulse width modulation controller  197  is configured to selectively apply pulse width modulation to supply voltages at plurality of pulse width modulation duty cycles. In some embodiments, one or both of the voltage controller  196  and PWM controller  197  can be used to provide a plurality of motor control signals to the motor  199 . 
     In some embodiments, for example, when the power source  188  is a battery, the method for operating the compressor  190  further includes dynamically monitoring the power source voltage and adjusting one or both of the supply voltage and the pulse width modulation duty cycle to accommodate power source voltage changes to achieve a desired efficiency of the compressor. 
       FIGS.  10 B-C  show examples of oxygen concentrator voltages over time. Many oxygen concentrators operate in a manner illustrated in  FIG.  10 C . A nominal voltage is supplied from a power source, and the motor speed and therefore compressor output is controlled by applying PWM control to the nominal voltage, varying the motor speed by changing the duty cycle of the PWM supply signal. Thus, a low duty cycle is applied for the lowest settings varying up to a very high duty cycle or even a non-modulated DC signal for the highest settings. 
     However, the voltage level of the nominal voltage also has an effect of compressor efficiency. For example, switching losses when PWM is applied may be lower if the voltage level is lower. Losses may be minimized by modulating the nominal voltage, for example, using a voltage controller  196 , and keeping the PWM duty cycle near 100%, or, alternatively at or near a certain target threshold. Additionally, the efficiency curve of a given compressor motor can roll off at higher torques at a given speed for a certain supply voltage. In general, the efficiency of a compressor motor and controller operation has been found to be a function of both PWM duty cycle and voltage supply level. It is possible to measure, e.g. calibrate, motor efficiency over a range of supply voltage/PWM duty cycle combinations to optimize battery lifetime for each combination. 
     Battery lifetime naturally varies significantly with concentrator output flow. For one concentrator design produced by the applicant of the current disclosure, with six settings, the most common setting used by patients is the second from the lowest setting. At this setting, the concentrator may have several hours of battery life, for example 10 hours. At the highest flow setting, the concentrator may have one hour of use time. Therefore, an adjustment of efficiency that say adds 10% to the most used setting will add a full hour of use time. If the improvement in efficiency at the most common setting results in a 10% loss at the high setting, that penalty is only six minutes. It is therefore advantageous to tune the compressor motor control to achieve higher efficiency at the commonly used lower settings, and this tuning can be improved by varying the supply voltage as well as the PWM duty cycle, for example, by the voltage controller  196  and PWM controller  197  as described above. 
     Accordingly, a method of operating an oxygen concentrator can include modifying the power source voltage using the voltage controller  196  and the PWM controller  197 . A concentrator design can be calibrated over a range of supply voltages and PWM duty cycles, possibly with the maximum setting representing a very high duty cycle and/or the highest achievable voltage. 
     For some concentrator designs, efficiencies as a function of supply voltage/PWM duty cycle may be calculated, modeled, or measured. Some combination of techniques may be used. In some embodiments, a nominal voltage may be supplied which may be increased or decreased concurrently, for example, by the voltage controller  196 , with PWM control, for example, by the PWM controller  197 , to achieve efficiency targets at each flow setting. The use of a supply voltage controller  196  in addition to the PWM controller  197  may result in a decreased compressor-motor-controller efficiency at certain operational points due to the operation of these electronics, but an optimum configuration can be found that results in minimal losses at a desired design point. These losses may then be less than losses encountered from a PWM only control based system, resulting in a higher overall system efficiency. For example, in some embodiments, switching losses may be reduced. In  FIGS.  10 B-D , a nominal voltage and a PWM rate that is selected from calibration data that achieves desirable efficiency at a most common setting is supplied.  FIGS.  10 C and  10 D  show similar amounts of effective voltage being applied to the motor for different amounts of applied voltage and PWM duty cycle applied. For the less common settings, a combination of increasing or decreasing supply voltage and changing PWM duty cycle is applied. Of course, other combinations may be used as well, such as providing a DC voltage configured for the highest setting, and lowering the voltage and changing PWM for each lower setting. However, when the nominal settings are picked, the result is that both supply voltage and PWM duty cycle are varied to selectively increase efficiency at desired flow settings. This can be illustrated in the surface plot in  FIGS.  10 E and  10 F , which show how the effective motor voltage is a function of a combination of both applied voltage and the PWM duty cycle. The intersection of a given horizontal plane with the surface plot exemplifies the available combination of PWM and applied voltage that results in the same effective motor voltage along the intersecting line. Along this line is a maximum efficiency point that can be measured or calculated. 
     Battery-operated devices can have various supply voltages, such as from a car or an AC to DC power supply, as well as various voltages depending upon the state of charge or depletion of the battery. It is possible to monitor the dynamically changing battery voltage and accordingly modify the PWM duty cycle and voltage to the controller dynamically to maximize system efficiency. It is also possible to increase the supply voltage relative to battery voltage on some higher flow settings to achieve desired motor performance while letting the voltage available from the battery to pass through and utilize only PWM control on other flow settings. 
     In some embodiments, a method for operating a compressor assembly  190  includes determining an efficiency of the compressor assembly  190 . Determining the efficiency of the compressor assembly  190  can include measuring, calibrating, calculating, or modeling motor efficiency of the motor  199  over a range of supply voltage and pulse width modulation duty cycle combinations. Each combination can include a supply voltage from the voltage controller  196  and a pulse width modulation duty cycle from the pulse width modulation controller  197 . 
     In some embodiments, the method for operating the compressor assembly  190  can include selecting a supply voltage and a pulse width modulation duty cycle for use at at least one output flow setting based on the determined efficiency of the compressor assembly  190 . 
     In some embodiments, the method for operating the compressor  190  assembly  190  can include generating the selected supply voltage by maintaining, reducing, or increasing a nominal supply voltage, for example, using the voltage controller  196 . In some embodiments, the nominal supply voltage is a desired voltage for one of the plurality of output flow settings. In some embodiments, the nominal supply voltage is a desired supply voltage for a maximum output flow setting. In some embodiments, the nominal supply voltage is used without pulse width modulation as the motor control signal for a highest output flow setting of the plurality of outflow settings of the compressor assembly  190 . In some embodiments, a combination of supply voltage regulation, for example, using the voltage controller  196 , and pulse width modulation, for example, using the PWM controller  197 , are applied to the nominal supply voltage to provide motor control signals to the motor  199  for one or more output flow settings lower than the highest output flow setting of the compressor assembly  190 . 
     In some embodiments, the selected supply voltage and the selected pulse width modulation duty cycle are selected to optimize efficiency at a most commonly used output flow setting of the plurality of output flow settings while maintaining the ability to operate at each of the plurality of output flow settings. 
     In some embodiments, the selected supply voltage and the selected pulse width modulation duty cycle are selected to reduce switching losses at at least one output flow setting of the plurality of output flow settings. 
     In some embodiments, the method for operating the compressor  190  can include applying the selected pulse width modulating duty cycle. 
     In addition to having multiple flow settings, the nature of a swing adsorption system results in a head profile that changes dynamically over the course of a pressure, pressure-vacuum, or vacuum swing cycle. The amount that the load on the compressor motor and control electronics varies over the course of a cycle depends on the number of valves utilized, number of beds used, product gas tank used, and sequencing and timing (e.g. specific PSA cycle employed) and can thus vary from ˜0-30 psi. It is therefore advantageous to modulate the controller voltage and PWM duty cycle dynamically to optimize efficiency over the course of a PSA cycle. This can be performed in real-time using current, power, or pressure measurements, a feed-forward method using any of the aforementioned, any combination of them, or other techniques. 
     In some embodiments, in which the compressor is part of a swing adsorption system, the method for operating the compressor  190  can include monitoring a pressure profile over the course of a pressure swing adsorption cycle, a pressure-vacuum swing adsorption cycle, or a vacuum swing adsorption cycle. In some embodiments, the method can include dynamically adjusting the supply voltage and pulse width modulation duty cycle to improve efficiency over the course of the pressure swing adsorption cycle, the pressure-vacuum swing adsorption cycle, or the vacuum swing adsorption cycle. In some embodiments, monitoring the head profile and adjusting the supply voltage and pulse width modulation duty cycle are performed during the pressure swing adsorption cycle, the pressure-vacuum swing adsorption cycle, or the vacuum swing adsorption cycle. In some embodiments, monitoring the head profile includes monitoring one or more of current measurements, power measurements, and pressure measurements through a feed forward process. 
     The embodiments described herein are exemplary. Modifications, rearrangements, substitute processes, alternative elements, etc. may be made to these embodiments and still be encompassed within the teachings set forth herein. One or more of the processes described herein may be carried out by one or more processing and/or digital devices, suitably programmed. 
     The various illustrative processing, data display, and user interfaces described in connection with the embodiments disclosed herein can be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, and modules have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. The described functionality can be implemented in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the disclosure. 
     The various illustrative logical blocks and modules described in connection with the embodiments disclosed herein can be implemented or performed by a machine, such as a processor configured with specific instructions, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A processor can be a microprocessor, but in the alternative, the processor can be a controller, microcontroller, or state machine, combinations of the same, or the like. A processor can also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
     The elements of the embodiments disclosed herein can be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module can reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of computer-readable storage medium known in the art. An exemplary storage medium can be coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium can be integral to the processor. The processor and the storage medium can reside in an ASIC. A software module can comprise computer-executable instructions which cause a hardware processor to execute the computer-executable instructions. 
     Conditional language used herein, such as, among others, “can,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements, and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment. The terms “comprising,” “including,” “having,” “involving,” and the like are synonymous and are used inclusively, in an open-ended fashion, and do not exclude additional elements, features, acts, operations, and so forth. Also, the term “or” is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term “or” means one, some, or all of the elements in the list. 
     Disjunctive language such as the phrase “at least one of X, Y or Z,” unless specifically stated otherwise, is otherwise understood with the context as used in general to present that an item, term, etc., may be either X, Y or Z, or any combination thereof (e.g., X, Y and/or Z). Thus, such disjunctive language is not generally intended to, and should not, imply that certain embodiments require at least one of X, at least one of Y or at least one of Z to each be present. 
     Unless otherwise explicitly stated, articles such as “a” or “an” should generally be interpreted to include one or more described items. Accordingly, phrases such as “a device configured to” are intended to include one or more recited devices. Such one or more recited devices can also be collectively configured to carry out the stated recitations. For example, “a processor configured to carry out recitations A, B and C” can include a first processor configured to carry out recitation A working in conjunction with a second processor configured to carry out recitations B and C. 
     While the above detailed description has shown, described, and pointed out novel features as applied to illustrative embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the devices illustrated can be made without departing from the spirit of the disclosure. As will be recognized, certain embodiments described herein can be embodied within a form that does not provide all of the features and benefits set forth herein, as some features can be used or practiced separately from others. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.