Patent Publication Number: US-2021170694-A1

Title: High frequency welding for headgear

Description:
INCORPORATION BY REFERENCE OF PRIORITY APPLICATIONS 
     The entireties of any and all priority applications are hereby incorporated by reference herein and made a part of the present disclosure. 
     BACKGROUND 
     Technical Field 
     The present disclosure generally relates to headgear for patient interfaces. 
     Description of the Related Art 
     In patients suffering from obstructive sleep apnea (OSA), muscles that normally keep the upper airway open relax during slumber to the extent that the airway is constrained or completely closed off, a phenomenon often manifesting itself in the form of snoring. When this occurs for a period of time, the patient&#39;s brain typically recognizes a threat of hypoxia and partially wakes the patient in order to open the airway so that normal breathing may resume. The patient may be unaware of these waking episodes, which may occur as many as several hundred times per session of sleep. This partial awakening may significantly reduce the quality of the patient&#39;s sleep, over time potentially leading to a variety of symptoms, including excessive daytime sleepiness, chronic fatigue, elevated heart rate, elevated blood pressure, weight gain, headaches, irritability, depression and anxiety. 
     Obstructive sleep apnea is commonly treated with the application of positive airway pressure (PAP) therapy. PAP therapy involves delivering a flow of gas to a patient at a therapeutic pressure above atmospheric pressure that will reduce the frequency and/or duration of apneas, hypopneas, and/or flow limitations. The therapy is often implemented by using a positive airway pressure device to deliver a pressurized stream of air through a conduit to a patient through a patient interface or mask positioned on the face of the patient. 
     SUMMARY 
     A patient interface for use with PAP therapy or other respiratory therapies involving the administration of gas can comprise headgear that helps to retain the patient interface on the face of a patient. The headgear generally interfaces with a frame that serves as a channel through which gas is delivered to the patient and the headgear comprises one or more straps that pass around the patient&#39;s head. To reduce the material waste and cost of producing headgear, instead of producing the entire headgear from a single blank of material, it is desirable to cut headgear straps from the material and join them via stitching, adhesives, or welding processes, e.g., high-frequency welding processes. In high-frequency welding, the straps can be overlapped to define an overlap weld region. The straps can be forced together (e.g., placed under pressure) through the use of a weld tool adapted to deliver high-frequency energy to the weld region. High-frequency welding is useful for joining straps quickly and in a sterile manner. However, in some cases, the welded joints can have visible markings, burns or bulges that reduce the aesthetic appeal and/or comfort of the headgear. 
     Certain features, aspects and advantages of at least one of the configurations disclosed herein include the realization that overlapping headgear straps or other materials can be joined through the use of a weld tool adapted to deliver high-frequency energy, wherein the weld tool comprises pins extending from a contact surface of the weld tool that at least partially penetrate each of the overlapping headgear straps. To diffuse the heat and/or energy generated at the contact surface of the weld tool near the pins, portions of the surface of the weld tool surrounding the pins can be inwardly chamfered. The contact surface of the weld tool can have beveled or rounded edges to further reduce the undesired concentration of energy along parts of the surfaces of headgear straps. One or both of the headgear straps can be specially formed to reduce potential distortions in shape encountered in the welding process. More aesthetically pleasing and/or comfortable headgear may thus be formed. 
     Thus, in accordance with certain features, aspects and advantages of at least one of the embodiments disclosed herein, a method of producing headgear for a patient interface is disclosed. The method comprises using a weld tool to apply high-frequency energy to a weld region defined by overlapping top and bottom straps. The weld tool comprises pins that at least partially penetrate both the top and bottom straps. In some configurations, the pins may extend from a contact surface of the weld tool. In some configurations, the material comprised in at least one of the straps may be at least in part polar or may comprise polar molecules, moieties or sections. 
     In some configurations, the top and bottom headgear straps are positioned on a weld base and the weld tool is forced against the weld region to apply pressure to the headgear straps. 
     In some configurations, the pins fully penetrate the top headgear strap and partially penetrate the bottom headgear strap. In some such configurations, the pins penetrate 20% or about 20% of the depth of the bottom headgear strap. In other configurations, the pins penetrate 1% to 99% or about 1% to about 99% of the depth of the bottom headgear strap, or about 10% to about 90%, or about 20% to about 80%, or about 30% to about 70%, or about 40% to about 60%, or about 50% of the depth of the bottom headgear strap. 
     In some configurations, the surface of the weld tool that faces the weld region (e.g., the contact surface of the weld tool) comprises beveled or rounded edges. 
     In some configurations, portions of the surface of the weld tool surrounding the pins are inwardly chamfered. In some such configurations, the chamfered portions are substantially arcuate or rounded. In some such configurations, the substantially arcuate chamfered portions are defined by crater-like recesses present in the surface of the weld tool. In some such configurations, the curvatures of the sides of the crater-like recesses are defined by substantially circular cross-sections of the weld tool having radii x that are proportional to the average distance between pins y according to the range of ratios x:y=0.3 to 0.4 or about 0.3 to about 0.4. 
     In some configurations, the pins are arranged in a plurality of rows. In some such configurations, the rows are offset such that pins are present in a honeycomb arrangement. 
     In some configurations, the pins are arranged such that each pin is substantially equidistant from adjacent pins. 
     In some configurations, either of top or bottom headgear straps comprises an edge section and a body section, the edge section having a smaller width than the body section. In some such configurations, the width of the edge section is in the range of 80% to 90% or about 80% to about 90% of the width of the body section. A substantially curved transition region can lie between the body section and the edge section. 
     In some configurations, the average distance between adjacent pins is in the range of about 1.5 mm to about 2.0 mm. 
     In some configurations, the average distance between adjacent pins is in the range of about 3 to about 4 times the average width of the pins. 
     Additionally, in accordance with certain features, aspects and advantages of at least one of the embodiments disclosed herein, a method of welding two straps of material together is disclosed. The method comprises using a weld tool to apply high-frequency energy to a weld region defined by overlapping top and bottom straps. The weld tool comprises pins that fully penetrate the top strap and penetrate 20% or about 20% of the depth of the bottom strap. In other configurations, the pins penetrate 1%-99% or about 1%-about 99% of the depth of the bottom strap, or about 10% to about 90%, or about 20% to about 80%, or about 30% to about 70%, or about 40% to about 60%, or about 50% of the depth of the bottom strap. The material comprised in at least one of the straps is at least in part polar or comprises polar molecules, moieties or sections. 
     In some configurations, the top and bottom straps are positioned on a weld base and the weld tool is forced against the weld region to apply pressure to the straps. 
     In some configurations, the surface of the weld tool that faces the weld region (e.g., the contact surface of the weld tool) comprises beveled or rounded edges. 
     In some configurations, portions of the surface of the weld tool surrounding the pins are inwardly chamfered. In some such configurations, the chamfered portions are substantially arcuate. In some such configurations, the substantially arcuate chamfered portions are defined by crater-like recesses present in the surface of the weld tool. In some such configurations, the curvatures of the sides of the crater-like recesses are defined by substantially circular cross-sections of the weld tool having radii x that are proportional to the average distance between pins y according to the range of ratios x:y=0.3 to 0.4 or about 0.3 to about 0.4. 
     In some configurations, the pins are arranged in a plurality of rows. In some such configurations, the rows are offset such that the pins are present in a honeycomb arrangement. 
     In some configurations, the pins are arranged such that each pin is substantially equidistant from adjacent pins. 
     In some configurations, either the top or bottom straps comprises an edge section and a body section, the edge section having a smaller width than the body section. In some such configurations, the width of the edge section is in the range of 80% to 90% or about 80% to about 90% of the width of the body section. A substantially curved transition region can lie between the body section and the edge section. 
     In some configurations, the average distance between adjacent pins is in the range of 1.5 mm to 2.0 mm or about 1.5 mm to about 2.0 mm. 
     In some configurations, the average distance between adjacent pins is in the range of 3 to 4 or about 3 to about 4 times the average width of the pins. 
     Additionally, in accordance with certain features, aspects and advantages of at least one of the embodiments disclosed herein, a method of welding two straps of material together is disclosed. The method comprises using a weld tool to apply high-frequency energy to a weld region defined by overlapping top and bottom straps, wherein either the top or bottom straps comprises an edge section and a body section, the edge section having a smaller width than the body section. The material comprised in at least one of the straps is at least in part polar or comprises polar molecules, moieties or sections. 
     In some configurations, the weld tool comprises pins that at least partially penetrate both the top and bottom straps. In some such configurations, pins fully penetrate the top strap and partially penetrate the bottom strap. The pins can be arranged in a plurality of rows. In some such configurations, the rows are offset such that the pins are present in a honeycomb arrangement. The pins can be arranged such that each pin is substantially equidistant from adjacent pins. 
     In some configurations, portions of the surface of the weld tool surrounding the pins are inwardly chamfered. In some such configurations, the chamfered portions are substantially arcuate. In some such configurations, the substantially arcuate chamfered portions are defined by crater-like recesses present in the surface of the weld tool. In some such configurations, the curvatures of the sides of the crater-like recesses are defined by substantially circular cross-sections of the weld tool having radii x that are proportional to the average distance between pins y according to the ratio x:y=about 0.3 to about 0.4. 
     In some configurations, the top and bottom straps are positioned on a weld base and the weld tool is forced against the weld region to apply pressure to the straps. 
     In some configurations, the surface of the weld tool that faces the weld region (e.g., the contact surface of the weld tool) comprises beveled or rounded edges. 
     Additionally, in accordance with certain features, aspects and advantages of at least one of the embodiments disclosed herein, a method of welding two straps of material together is disclosed. The method comprises using a weld tool to apply high-frequency energy to a weld region defined by overlapping top and bottom straps, the weld tool comprising pins that at least partially penetrate both the top and bottom straps, wherein the portions of the surface of the weld tool surrounding the pins are inwardly chamfered. The material is at least in part polar or comprises polar molecules. 
     In some configurations, the chamfered portions are substantially arcuate. In some such configurations, the substantially arcuate chamfered portions are defined by crater-like recesses present in the surface of the weld tool. In some such configurations, the curvatures of the sides of the crater-like recesses are defined by substantially circular cross-sections of the weld tool having radii x that are proportional to the average distance between pins y according to the ratio x:y=about 0.3 to about 0.4. 
     Additionally, in accordance with certain features, aspects and advantages of at least one of the embodiments disclosed herein, a method of welding two straps of material together is disclosed. The method comprises forcing a weld tool against a weld region defined by overlapping top and bottom straps positioned on a weld base and applying high-frequency energy using the weld tool, the weld tool comprising pins that at least partially penetrate both the top and bottom straps, wherein a surface of the weld tool that contacts the weld region comprises beveled or rounded edges. 
     Additionally, in accordance with certain features, aspects and advantages of at least one of the embodiments disclosed herein, headgear is disclosed. The headgear is produced at least in part using one or more of the methods described above or elsewhere in this disclosure. 
     Additionally, in accordance with certain features, aspects and advantages of at least one of the embodiments disclosed herein, a patient interface is disclosed. The patient interface comprises headgear produced at least in part using one or more of the methods described above or elsewhere in this disclosure. In some configurations, the patient interface further comprises a cushion module adapted to be positioned over the face of a patient and a frame removably secured to the cushion module, the frame adapted to receive a gases flow from a flow generator. 
     Additionally, in accordance with certain features, aspects and advantages of at least one of the embodiments disclosed herein, a respiratory therapy system is disclosed. The respiratory therapy system comprises a flow generator (e.g. PAP device), a patient interface and a conduit extending between the flow generator and the patient interface. In some configurations, the respiratory therapy system also comprises a humidifier in-line between the flow generator and the patient interface. The patient interface comprises headgear produced at least in part using one or more of the methods described above or elsewhere in this disclosure. 
     Additionally, in accordance with certain features, aspects and advantages of at least one of the embodiments disclosed herein, a weld tool is disclosed. The weld tool is adapted to be used in a high-frequency welding process. The weld tool comprises a plurality of pins extending from a contact surface of the weld tool, wherein portions of the contact surface surrounding the pins are inwardly chamfered. 
     In some configurations, the chamfered portions are substantially arcuate. In some such configurations, the substantially arcuate chamfered portions are defined by crater-like recesses present in the surface of the weld tool. In some such configurations, the curvatures of the sides of the crater-like recesses are defined by substantially circular cross-sections of the weld tool having radii x that are proportional to the average distance between pins y according to the ratio x:y=about 0.3 to about 0.4. 
     In some configurations, the pins are arranged in a plurality of rows. In some configurations, the rows are offset such that the pins are present in a honeycomb arrangement. The pins can be arranged such that each pin is substantially equidistant from adjacent pins. 
     Additionally, in accordance with certain features, aspects and advantages of at least one of the embodiments disclosed herein, a weld tool is disclosed. The weld tool is adapted to be used in a high-frequency welding process. The weld tool comprises a plurality of pins extending from a contact surface of the weld tool. The contact surface comprises beveled or rounded edges. 
     In some configurations, the pins are arranged in a plurality of rows. In some such configurations, the rows are offset such that the pins are present in a honeycomb arrangement. The pins can be arranged such that each pin is substantially equidistant from adjacent pins. 
     Additionally, in accordance with certain features, aspects and advantages of at least one of the embodiments disclosed herein, a welding system is disclosed. The welding system comprises a weld tool adapted to the used in a high-frequency welding process. The weld tool comprises a plurality of pins extending from a contact surface of the weld tool. At least portions of the contact surface of the weld tool surrounding the pins are inwardly chamfered. The welding system additionally comprises a weld base. The weld base is adapted to support material to be welded. In use, the weld tool is forced against the material supported by the base. 
     In some configurations, the welding system additionally comprises a stop adapted to limit the range of axial motion between the weld tool and the weld base. In some such configurations, the stop extends outwardly from the weld tool and rests upon a raised portion of the weld base. 
     In some configurations, the chamfered portions are substantially arcuate. In some such configurations, the substantially arcuate chamfered portions are defined by crater-like recesses present in the surface of the weld tool. In some such configurations, the curvatures of the sides of the crater-like recesses are defined by substantially circular cross-sections of the weld tool having radii x that are proportional to the average distance between pins y according to the ratio x:y=about 0.3 to about 0.4. 
     In some configurations, the pins are arranged in a plurality of rows. In some such configurations, the rows are offset such that the pins are present in a honeycomb arrangement. The pins can be arranged such that each pin is substantially equidistant from adjacent pins. 
     Additionally, in accordance with certain features, aspects and advantages of at least one of the embodiments disclosed herein, a welding system is disclosed. The welding system comprises a weld tool adapted to be used in a high-frequency welding process. The weld tool comprises a plurality of pins extending from a contact surface of the weld tool. The contact surface comprises beveled or rounded edges. The welding system additionally comprises a weld base. The weld base is adapted to support material to be welded. In use, the weld tool is forced against the material supported by the base. 
     In some configurations, the welding system further comprises a stop adapted to limit the range of axial motion between the weld tool and the weld base. In some such configurations, the stop extends outwardly from the weld tool and rests upon a raised portion of the weld base. 
     Additionally, in accordance with certain features, aspects and advantages of at least one of the embodiments disclosed herein, a welding system for welding together top and bottom sheets of fabric is disclosed. The welding system comprises a weld tool adapted to be used in a high-frequency welding process. The weld tool comprises a plurality of pins extending from a contact surface of the weld tool. The welding system additionally comprises a weld base. The weld base has a cavity to support the top and bottom sheets in an overlapping relationship. The weld tool and the cavity have a corresponding shape such that the weld tool engages the cavity and the contact surface applies pressure to the top and bottom sheets. 
     In some configurations, the pins are arranged in a single-file row along an outer edge of the weld tool. 
     In some configurations, the pins are arranged in a double-file row along an outer edge of the weld tool. 
     In some configurations, the pins are arranged in a staggered row along an outer edge of the weld tool. 
     In some configurations, the pins have a diameter within a range of 0.3 mm to 1.0 mm. 
     In some configurations, centers of the pins are spaced apart a distance of 2.5 mm to 6.0 mm. 
     In some configurations, the weld tool is formed from a thermally insulating material. 
     In some configurations, the contact surface of the weld tool has a thermally insulating coating. 
     In some configurations, the pins are arranged in a plurality of rows. In some such configurations, the rows are offset such that the pins are present in a honeycomb arrangement. The pins can be arranged such that each pin is substantially equidistant from adjacent pins. 
     In some configurations, the pins in the honeycomb arrangement are arranged in a hexagonal shape around a center pin. 
     In some configurations, the pins arranged in the hexagonal shape are enclosed within a hexagonal-shaped area that surrounds the pins. Outer segments that define the hexagonal-shaped area are tangent to outer edges of outermost adjacent pins. A pin density ratio is defined as a ratio between a total area of the pins versus an area of the hexagonal-shaped area. 
     In some configurations, the pin density ratio is equal to 33.85%. 
     In some configurations, each pin has a diameter of 0.5 mm, and wherein a distance between each pin is 1.0 mm. 
     In some configurations, the pins in the honeycomb arrangement are arranged in concentric hexagons around a center pin. 
     In some configurations, the pins arranged in concentric hexagons are enclosed within a hexagonal-shaped area that surrounds the pins. Outer segments that define the hexagonal-shaped area are tangent to outer edges of outermost adjacent pins. A pin density ratio is defined as a ratio between a total area of the pins versus an area of the hexagonal-shaped area. 
     In some configurations, the pin density ratio is equal to 28.37%. 
     In some configurations, each pin has a diameter of 0.5 mm and a distance between each pin is 1.0 mm. The honeycomb arrangement can have two concentric hexagons, and a radial distance between centers of adjacent pins is 1.0 mm. 
     In some configurations, the pins are arranged in a concentric circular arrangement having pins arranged in at least one concentric circle around a center pin. 
     In some configurations, the pins arranged in at least one concentric circle are enclosed within a circular-shaped area that surrounds the pins. An outermost circle that defines the circular area is defined by radially outermost points of the outermost pins. A pin density ratio is defined as a ratio between a total area of the pins versus an area of the circular-shaped area. 
     In some configurations, the pin density ratio is equal to 18.34%. 
     In some configurations, each pin has a diameter of 0.5 mm. The concentric circular arrangement includes three concentric circles, and a radial distance between centers of adjacent pins is 1.0 mm. 
     In some configurations, the pins are arranged in a square grid arrangement having each row squarely aligned with an adjacent row and each row having a quantity of pins that is equal to a quantity of rows. 
     In some configurations, the pins are arranged such that each pin is spaced equidistant to an adjacent pin. 
     In some configurations, an orthogonal distance between an outer edge of each pin is equal a diameter of each pin. The pins arranged in the square grid arrangement are enclosed within a square-shaped area that surrounds the pins. Outer segments that define the square-shaped area are tangent to outer edges of outermost adjacent pins. A pin density ratio is defined as a ratio between a total area of the pins versus an area of the square-shaped area. 
     In some configurations, the pin density ratio is equal to 21.71%. 
     In some configurations, the diameter of each pin is equal to 0.5 mm. 
     In some configurations, the pins have either a first diameter or a second diameter, and the pins alternate between the first diameter and the second diameter along a length of each row. 
     In some configurations, the pins arranged in the square grid arrangement are enclosed within a square-shaped area that surrounds the pins. Outer segments that define the square-shaped area are tangent to outer edges of outermost alternating pins. A pin density ratio is defined as a ratio between a total area of the pins versus an area of the square-shaped area. 
     In some configurations, the pin density ratio is equal to 13.59% 
     In some configurations, the first diameter is equal to 0.5 mm and the second diameter is equal to 0.25 mm. An orthogonal distance between an outer edge of each pin is equal 0.625 mm. 
     In some configurations, the pins are arranged such that each pin is spaced equidistant to an adjacent pin along a length of the row. 
     In some configurations, the pins are enclosed within a square-shaped area that surrounds the pins. Outer segments that define the square-shaped area are tangent to outer edges of outermost pins. A pin density ratio is defined as a ratio between a total area of the pins versus an area of the square-shaped area. 
     In some configurations, the pin density ratio is equal to 19.63%. 
     In some configurations, the diameter of each pin is equal to 0.5 mm and a distance between centers of pins of adjacent rows in a direction perpendicular to a length of the row is 1.0 mm. 
     In some configurations, the pins have identical diameters along a length of the row and the pins in each row alternate between a first diameter and a second diameter. 
     In some configurations, the pins are enclosed within a square-shaped area that surrounds the pins. Outer segments that define the square-shaped area are tangent to outer edges of outermost pins. A pin density ratio is defined as a ratio between a total area of the pins versus an area of the square-shaped area. 
     In some configurations, the pin density ratio is equal to 14.09%. 
     In some configurations, the first diameter is equal to 0.5 mm and the second diameter is equal to 0.25 mm. A distance between centers of adjacent pins along a length of the row is equal to 1.0 mm, and a distance between centers of pins of adjacent rows in a direction perpendicular to a length of the row is 1.0 mm. 
     In some configurations, the pin densities are within a range of 10-50%. 
     In some configurations, the pin densities are within a range of 15-35%. 
     In some configurations, the pin densities are within a range of 15-25%. 
     In some configurations, the pins have a pointed tip. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Specific embodiments and modifications thereof will become apparent to those skilled in the art from the detailed description herein having reference to the figures that follow, of which: 
         FIG. 1  shows a schematic diagram of a respiratory therapy system. 
         FIGS. 2A and 2B  show rear perspective and front views, respectively, of a patient wearing a patient interface. 
         FIG. 3  shows a view of respiratory headgear that is shown in  FIGS. 2A and 2B . 
         FIG. 4  shows a high-frequency welding system. 
         FIG. 5  shows a weld tool for use in high-frequency welding. 
         FIGS. 6A-6D  show a top-down diagram detailing the positioning of various components during a high-frequency welding process. 
         FIGS. 7A-7D  show a side view of a process of high-frequency welding a pair of overlapping straps together. 
         FIGS. 8A-8L  show various views of weld tools for use in high-frequency welding. 
         FIGS. 9A and 9B  show a cross-section of a diagram of a high-frequency welding system and a close-up view of the cross-section of the diagram, respectively. 
         FIG. 10  shows a cross-section of a diagram of a high-frequency welding system. 
         FIG. 11  shows a close-up cross-sectional view of a pair of welded straps. 
         FIG. 12  shows a close-up view of a cross-section of straps and a pin having pointed tip. 
         FIG. 13  shows a plan view of a high-frequency welding system. 
         FIG. 14  shows a side view illustrating the weld tool inserted into the weld base of the high-frequency welding system. 
         FIG. 15  shows a side view illustrating the weld tool partially inserted into the weld base of the high-frequency welding system. 
         FIGS. 16A-16D  show a headgear strap welded by the high-frequency welding system. 
         FIGS. 17A and 17B  show alternative pin arrangements for the high-frequency welding system. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to the non-limiting exemplary embodiment illustrated in  FIG. 1 , a respiratory therapy system  100  is shown. The respiratory therapy system  100  comprises a flow generator  102 . The flow generator  102  comprises a PAP device. The flow generator  102  receives gases from a gases inlet  104  and propels them to a humidifier  106 . The flow generator  102  and the humidifier  106  may be part of an integrated flow delivery system or may share a housing  108 . The humidifier  106  heats and humidifies the gases. Heated and humidified gases are passed from a humidifier outlet to a gases conduit  112 . The gases conduit  112  comprises a heater  114 . The heater  114  reduces or prevents the condensation of moisture along the walls of the gases conduit  112 . Gases are passed from the gases conduit  112  to a patient interface  200  through which they are delivered to a patient. The respiratory therapy system  100  comprises a controller  111  that controls the operation of the flow generator  102 . The controller  111  also controls the operation of the humidifier  106 . The respiratory therapy system  100  comprises an input/output (I/O) module  110 . The I/O module  110  comprises a way for a user to interact with and set parameters for the flow generator  102  and/or humidifier  106  as well as receive information regarding the operation of the respiratory therapy system  100  and/or its components. The I/O module  110  may comprise, for example, buttons, knobs, dials, switches, levers, touch screens, speakers, displays and/or other input or output elements. In some configurations, the humidifier  106  may not be present. In some configurations, the gas conduit  112  may not have a heater  114 . In some configurations, the flow generator  102  may comprise elements other than PAP devices, including but not limited to high flow therapy devices or ventilation devices. 
       FIGS. 2A and 2B  demonstrate a non-limiting patient interface  200  that can be used with the respiratory therapy system  100  shown in  FIG. 1 . As illustrated, the patient interface  200  comprises a nasal mask. In some configurations, the patient interface  200  may comprise a sealing or non-sealing interface. For example, the patient interface  200  may comprise an oral mask, an oro-nasal mask, a full face mask, a nasal pillows mask, an endotracheal tube, a combination of the above, or some other gas conveying system or apparatus. 
     The patient interface  200  shown comprises a frame  202  adapted to receive gases from a gases source (for example, the flow generator  102  described elsewhere in this disclosure with reference to  FIG. 1 ) and channel them to the patient. An aperture  204  in the frame  202  is adapted to receive an elbow component  206  configured to interface with a gases delivery conduit (for example, the gases conduit  112  described elsewhere in this disclosure with reference to  FIG. 1 ). The elbow component  206  may be adapted to swivel or rotate (through, for example, a ball-joint connection). The elbow component  206  comprises vent holes  207  that permit a leak flow to escape the patient interface  200 . The vent holes  207  can help to mitigate the build-up of carbon dioxide in the patient interface  200  and/or gas delivery conduit. The frame  202  interfaces with a cushion module  220 . The cushion module  220  comprises a relatively rigid or hard cushion housing adapted to interface with the frame  202  and a relatively flexible or soft cushion adapted to sealingly engage with the patient&#39;s face to provide a substantially sealed gas passageway between the patient and the gases delivery conduit. The frame  202  comprises a neck  208  that substantially extends along the head of the patient across, for example, the nasalis muscles and the procerus muscles. The neck  208  ends in a forehead support  210  comprising first and second hooked legs  212 ,  213 . Openings  214 ,  215  are defined between the hooked legs  212 ,  213  and the forehead support  210 . The frame  202  also comprises apertures  216 ,  218 . 
     Headgear  300  interfaces with the frame  202  to provide a way for retaining the patient interface  200  on the face. A four-point connection with the frame  202  is made available using the openings  214 ,  215  present near the forehead support  210  and using the apertures  216 ,  218  present on the frame  202 . The headgear  300  comprises left and right top straps  304 ,  302  and left and right bottom straps  308 ,  306 . The top and bottom straps  302 ,  304 ,  306 ,  308  join at a back section  316 . The back section  316  comprises a top back strap  318  and a bottom back strap  320 . The headgear  300  additionally comprises a crown strap  314  that extends between the left and right top straps  304 ,  302 . To interface with the frame  202 , the left and right bottom straps  308 ,  306  are looped through openings  223 ,  221  present in hook connectors  217 ,  219  that are retained in the apertures  216 ,  218  present on the frame  202 . The left and right bottom straps  308 ,  306  comprise loop patches  316 ,  314  that allow the straps  308 ,  306  to be loosened or tightened and fixed into place (for example, using corresponding hooked regions on the straps  308 ,  306  to facilitate a hook-and-loop fastening arrangement) after they are looped through the openings  223 ,  221 . The left and right top straps  304 ,  302  are looped at the ends. The looped ends are placed over the hooked legs  212 ,  213  such that they are retained between the forehead support  210  and the hooked legs  212 ,  213 . Similarly, the left and right top straps  304 ,  302  comprise loop patches  312 ,  310  that allow straps  304 ,  302  to be loosened or tightened and fixed into place (for example, using corresponding hooked regions on the straps  304 ,  302  to facilitate a hook-and-loop fastening arrangement) after they are positioned on the hooked legs  212 ,  213 . 
       FIG. 3  shows another view of the headgear  300  illustrated in  FIGS. 2A and 2B . As shown, the headgear  300  comprises a plurality of strap sections S joined at joints J. In particular, the left and right top straps  304 ,  302  form strap sections S 1 , S 2  and are joined at J 5  to form the top back strap  318  of the back section  316 . The left and right top straps  304 ,  302  are also joined at joints J 7 , J 6  via the crown strap  314 , which forms strap section S 3 . The bottom back strap  320 , which forms strap section S 4  is joined to the top back strap  318  through joints J 4 , J 3 , and interfaces with left and right bottom straps  308 ,  306  (sections S 5 , S 6 ) through joints J 2 , J 1 . In the illustrated configuration, the joints J are formed through the use of high-frequency welding. The strap sections S can be formed from any material appropriate for use with respiratory headgear, including but not limited to fabrics, fabric/foam composites or Breath-O-Prene™. 
       FIG. 4  illustrates a high-frequency welding system  400  adapted to manufacture headgear from sections (e.g. strap sections) S of headgear (for example, but not limited to, the headgear described elsewhere in this disclosure with reference to  FIG. 3 ). High-frequency welding as described in this disclosure refers to a method of joining sections of material (e.g., straps, sheets, films, etc.) (the material comprised in at least one of the sections at least in part being polar or comprising polar molecules, moieties or sections) together using a rapidly alternating electric field (including, but not necessarily limited to, electric fields having alternation frequencies in the range of 13 to 100 or about 13 to about 100 megahertz, or, for example, 27.12 or about 27.12 megahertz). The welding system  400  comprises a weld base (e.g., anvil)  402  comprising a relatively elevated section  403  and a relatively depressed section  404  adapted to hold overlapping straps of headgear. A stop plate  406  rests on the relatively elevated section  403  of the weld base  402 . The stop plate  406  comprises apertures through which weld tools (e.g. horn)  408  protrude. In use, the weld tools  408  may be energized with electromagnetic energy (using an energy source, not shown), causing the weld tools  408  to generate alternating electric fields that cause polar molecules in the straps of material to oscillate and orient themselves with respect to the field. This movement of the polar molecules generates heat, causing a temperature increase that results in the melting of the sheets. The weld tools  408  are forced (using a press, not shown) against weld regions defined by overlapping top and bottom sheets to apply pressure to the sheets. It should be understood that ‘top’ and ‘bottom’ as used in this disclosure can be interpreted as referring to positioning with respect to a weld tool  408  rather than with respect to gravity. The top sheet can refer to the sheet closest to the weld tool  408  and the bottom sheet can refer to the sheet furthest from the weld tool  408 . The combination of melting and pressure promotes the formation of a welded joint between the sheets. The weld tools  408  further comprise rows of pin heads  410  that are further described below with reference to the accompanying figures. Although the weld tools  408  shown are rectangular or hexagonal, it should be understood that the weld tools  408  could have other shapes, including, but not limited to, triangular or circular shapes. In some configurations, the stop plate  406  could be integrally formed with or be in the form of a single piece with one or more of the weld tools  408 . 
       FIG. 5  illustrates a weld tool  408  configured to be used with the high frequency welding system  400 . The weld tool  408  comprises a top section  412  that rests on the stop plate  406  (see  FIG. 4 ) in use and cooperates with the stop plate  406  to limit the range of axial motion between the weld tool  408  and the weld base  402 . The weld tool  408  comprises a bottom section  414 . The bottom section  414  comprises a lower average cross-sectional area than the cross-sectional area of the top section  412 . The bottom section  414  is adapted to protrude through apertures in the stop plate  406  as described elsewhere in this disclosure with reference to  FIG. 4 . The bottom section  414  comprises a contact surface  416  that is forced against straps of material to apply pressure. The weld tool  408  comprises a plurality of pins  413  (see also  FIGS. 7A-7D  and the accompanying disclosure), the pins comprising pin heads  410  and ends  418 . The pins  413  enter the weld tool  408  through apertures in the top section  412 , extend through the body of the weld tool  408  and protrude (e.g., via ends  418 ) through the bottom section  414 . In alternative configurations, the weld tool  408  could comprise only a single pin. In some configurations, the pins  413  could be permanently positioned in the weld tool  408  (for example, via the use of adhesives or frictional fits or couplings). In some configurations, and particularly if the weld tool  408  is integrally formed with the stop plate  406 , the weld tool may only comprise a single section. Usage of the weld tool  408  is further described below with reference to the accompanying figures. 
       FIGS. 6A-6D  show non-limiting exemplary diagrams for the positioning of various components during a high-frequency welding method. The illustrated straps are headgear straps. However, straps of materials for forming other articles (including, but not limited to, articles of clothing) could be used.  FIG. 6A  shows a bottom strap  500 . As used above or elsewhere in this disclosure, it should be understood that the words ‘top’ and ‘bottom’ do not refer to the relative positions of the straps with respect to the force of gravity but, instead, refer to the relative positions of the straps with respect to the weld tool  408 . The bottom strap  500  comprises a body section  500 A of a first width and an edge section  500 B of a second width. The edge section  500 B is inwardly stepped relative to the body region  500 A. In other words, the edge section  500 B is of a smaller width than the body section  500 A. In the illustrated configuration, the body section  500 A has a width L 1  of 17 mm or about 17 mm. The edge section  500 B has a width L 2  of 15 mm or about 15 mm with insteps L 3 , L 4  of 1 mm on either side of the edge section  500 B. In some configurations, the width of the edge section  500 B may be in the range of about 60% to about 97% of the width of the body section  500 A, or about 65% to about 95%, or about 70% to about 93%, or about 80% to about 90% of the width of the body section  500 A. Maintaining the desired width of the body section  500 A relative to the width of the edge section  500 B helps to mitigate the tendency of molten material to flow too far outwardly from the weld region  504  (see  FIG. 6B ), which can cause undesired bulging at the sides of the finished weld joint formed at the weld region  504 . If two rectangular straps are welded together, a weld joint with bulging edges along the sides of the joint is more likely to be formed. Using a strap with inset portions can create cavities in which excess molten material can reside. A substantially curved transition region TR lies between the body section  500 A and the edge section  500 B. The transition region TR promotes adequate distribution of energy during welding, allowing for the formation of an aesthetically acceptable weld joint. In alternative configurations, the transition region TR may not be present. In  FIG. 6B , a portion of a substantially rectangular top strap  502  is laid over the bottom strap  500 . A weld region  504  is defined by the overlapping top and bottom straps  502 ,  504 . However, in other configurations, both of the straps  502 ,  500  could have substantially rectangular shapes. In still other configurations, either or both of the straps could have other shapes, including, but not limited to, circular or triangular shapes. 
       FIG. 6C  shows the position of the bottom section  414  of the weld tool  408  over the weld region  504 . As shown, at least the contact surface  416  of the bottom section  414  (i.e., on the underside of the bottom section  414 ) comprises a stepped shape similar to shape of the bottom strap  500 . Using a contact surface  416  with a stepped shape promotes the distribution of energy along the contact surface  416 , further mitigating undesired bulging at the sides of the weld joint formed at the weld region  504 . However, in other configurations the contact surface  416  could have other shapes, including, but not limited to, rectangular, circular or triangular shapes. Additionally, as shown, the bottom section  414  extends outwardly past the weld region  504  and/or contact surface  416 . In some configurations, the edges of the bottom section  414  may extend, for example, 1 mm or about 1 mm past the edges of the weld region  504 . The larger footprint of the bottom section  414  helps to improve the tolerance of errors in proper placement of the weld tool  408 .  FIG. 6D  shows the position of the top section  412 . As shown, the top section  412  is substantially rectangular with rounded edges. However, in other configurations, the top section  412  may have other shapes, including, but not limited to, triangular or circular shapes. 
       FIGS. 7A-7D  illustrate a non-limiting exemplary high-frequency welding method.  FIG. 7A  demonstrates again a weld region  504  defined by overlapping top and bottom straps  502 ,  500 . The straps  502 ,  500  can lie in the depressed section  404  of the base plate  402 . As described elsewhere in this disclosure, the weld tool  408  comprises a top section  412  and a bottom section  414  comprising a contact surface  416 . The weld tool  408  comprises pins  413  that pass through the weld tool  408 , extending from pin heads  410  positioned on the top section  412  to ends  418  projecting from the contact surface  416  of the bottom section  414 . The top section  412  can cooperate with the stop plate  406  and the elevated section  403  of the weld base  402  to limit axial movement of the weld tool  408  relative to the weld base  402  (see  FIG. 7B ). As the weld tool  408  is moved into the weld region  504 , the contact surface  416  is forced against the weld region  504 . The urging of the contact surface  416  against the weld region  504  provides pressure to the straps  502 ,  500 . The ends  418  of the pins  413  that project outwardly from the contact surface  416  penetrate the entire depth of the top strap  502  and partially penetrate the bottom strap  500 . 
     In the illustrated configuration, the stop plate  406  and the elevated portion  403  of the weld base  402  are positioned such that a clearance L 2  of 2.5 mm or about 2.5 mm is present between the contact surface  416  and the recessed portion  404  of the weld base  402 . The ends  418  of the pins  413  project a length L 3  of about 1.5 mm from the contact surface  416 . About 1 mm of clearance L 1  is present between the ends  418  of the pins  413  and the recessed portion  404 . The ratio L 2 :L 1  in the illustrated configuration, then, is about 2.5:1. In other configurations, the ratio L 2 :L 1  can comprise other values. For example, the ratio L 2 :L 1  can be in the range of 2:1 to 3:1 or about 2:1 to about 3:1. In other configurations, the straps  502 ,  500  are each 1.25 mm or about 1.25 mm thick when compressed by the weld tool  408 . The ends  418 , then, penetrate the full 1.25 mm thickness of the top strap  502  and 0.25 mm or about 0.25 mm of the depth of the bottom strap  500 . In other words, the pins  413  penetrate 20% or about 20% of the depth of the bottom strap  500 . In other configurations, the pins  413  can penetrate about 5% to about 50% of the depth of the bottom strap  500 , or about 10% to about 40%, or about 15% to about 30%. In still other configurations, the pins  413  can penetrate 1% to 99% or about 1% to about 99% of the depth of the bottom strap  500 , or about 10% to about 90%, or about 20% to about 80%, or about 30% to about 70%, or about 40% to about 60%, or about 50% of the depth of the bottom strap  500 . 
     It has been discovered that the depth of penetration of the bottom strap  500  can factor into the weld strength and aesthetic appeal of the weld joint formed at the weld region  504 . If the penetration depth is too high, in some cases the ends  418  may not deliver enough energy to the interface between the top and bottom straps  502 ,  500 . Additionally, too much energy may be delivered to the bottom strap  500 , which can promote excessive melting or burning of the bottom strap  500 . If the penetration depth is too low, in some cases the ends  418  may not project far enough into the bottom strap  500 , or the ends  418  may not project at all into the bottom strap  500 . Too much energy may be delivered to the top strap  502 , which can promote excessive melting or burning of the top strap  502 . 
     Additionally, it has been discovered that it is desirable to minimize the clearance L 1  to decrease the chance of electrical arcing from the contact surface  416  and/or ends  418  to the weld base  404 . Undesired electrical arcing can cause excessive melting and/or burns in one or both of the straps  502 ,  500 , which can lead to aesthetically unappealing welded joints. In some configurations, the clearance L 1  can be about 80% of the pin length L 3  (ratio L 1 :L 3 =about 0.8). In other configurations, the ratio L 1 :L 3  can be in the range of, for example, about 0.7 to about 0.9. 
     As shown in  FIG. 7C , electromagnetic energy applied to the weld tool  408  is concentrated at the ends  418  of the pins  413 , resulting in the generation of high-frequency alternating electric fields (represented using arcs W on either side of the contact surface  416 ). The electric fields cause polar molecules in the straps  502 ,  500  to oscillate and orient themselves with respect to the fields, which generates heat in the straps  502 ,  500  causing them to melt and fuse. Pressure applied using the contact surface  416  of the weld tool  408  (together with the press described elsewhere in this disclosure with reference to  FIG. 4 ) promotes the formation of a weld joint J at the weld region  504 . The weld tool  408  is then pulled away from the finished weld joint J (see  FIG. 7D ). 
       FIGS. 8A-8C  show bottom, side, and bottom close-up views of a non-limiting exemplary weld tool  408 . As shown in  FIG. 8C , the contact surface  416  comprises apertures  420  adapted to hold the pins  413 . The apertures  420  are defined by recesses  422  present in the contact surface  416 . The recesses  422  can be crater-like, or can have substantially hemi-spherical or frustoconical geometry. The recesses  422  lie on portions of the contact surface  416  surrounding the pins  413  (particularly near the ends  418 ) in use. In the illustrated contact surface  416 , the apertures  420  (and pins  413  in use) are arranged in rows such that consecutive or touching recesses  422  are present. The rows may be offset by about half of the distance between the centers of two adjacent apertures  420  of a given row. The offset is such that the rows are arranged in a honeycomb-like shape. 
       FIG. 8D  illustrates a weld tool  408  having a similar aperture arrangement (recesses  422  not illustrated) as  FIG. 8C . The apertures  420 , which hold the pins  413  (not shown), are offset and spaced apart such that each aperture  420  is substantially equidistant from each adjacent aperture  420 . As illustrated, six apertures  420  are arranged around a center aperture  420  in a hexagonal arrangement or honeycomb-like shape and spaced apart from each adjacent aperture  420  by a distance X. Each aperture  420  has a diameter D. Maintaining proper spacing of the apertures  420  (and ends  418  in use) can promote an even or balanced weld joint. Further, the hexagonal arrangement of the apertures  420  provides uniform weld strength and flex characteristics across the weld joint. Preferably, the distance X may be 1.0 mm and the diameter D may be 0.5 mm. However, the distance X and diameter D can, for example, be larger or smaller than shown and described with reference to the illustrated embodiment. In the illustrated configuration, the hexagonal arrangement has an overall height H of 2.232 mm and an overall width W of 2.5 mm. The apertures  420  are enclosed within a hexagonal-shaped area that surrounds the apertures  420 . That is, the welding area of the weld tool  408  may be defined as a hexagonal-shaped area that surrounds the apertures  420 . As illustrated, outer segments S that define the hexagonal-shaped area are tangent to outer edges of outermost adjacent pins  420 . The segments S may have a length of 1.25 mm such that the total area of the hexagonal-shaped area is 4.06 mm 2 . As such, seven apertures  420  having a diameter D of 0.5 mm provide a total aperture area of 1.374 mm 2 . As each aperture  420  accommodates a pin  413  having a substantially identical diameter and area, a pin density percentage may be defined as a ratio percentage of pin area versus total welding area (i.e., hexagonal-shaped area). Therefore, a weld tool  408  having seven apertures  420  with diameters D of 0.5 mm, spaced apart by a distance X of 1.0 mm and arranged in a hexagonal arrangement having a total area of 4.06 mm 2 , has a pin density percentage of 33.8%. Accordingly, a strap or material welded by the weld tool  408  with the illustrated hexagonal arrangement can have a weld joint that approximates the pin density. In the instant example, the pin density is 33.8%, which may result in the weld joint having approximately 33.8% melted welded material within the weld area or pin area. The actual portion of melted material within the weld or pin area can vary based on relevant factors of the welding process (e.g., weld power, weld time, materials being welded, etc.). Thus, the actual portion of melted material may differ from the pin density, but will likely fall within a range the approximates the pin density (e.g., within 5%, 10%, 20% or 25% of the pin density). A weld joint having a higher pin density percentage provides a less flexible weld joint than a weld joint having a lower pin density percentage. This is because more of the weld joint will include melted welded material which is relatively rigid and inflexible. As a result, there will be less fabric between each of the weld points that has not been melted and is still able to be flexed or stretched, thereby, allowing the strap or material to stretch. In alternative configurations, the apertures  420  may have a diameter D between 0.1 to 1.0 mm. As such, decreasing the diameter D of the aperture  420  (and the pin  413 ) will decrease the pin density percentage and result in a weld joint with more flexibility and/or stretch while larger diameters will provide less flexibility and/or stretch. Accordingly, the diameter D and/or distance X may be varied according to the amount of flex or stretch desired by the weld joint. 
       FIG. 8E  illustrates a similar hexagonal arrangement as  FIG. 8D  with identical aperture diameters D and distance X between apertures  420 .  FIG. 8E  differs by having nineteen total apertures  420  with the apertures  420  arranged in two concentric hexagons around a center aperture  420 . As such, due to the increased number of apertures  420 , the hexagonal arrangement has segments S with a length of 2.25 mm such that the total area of the hexagonal-shaped area 13.15 mm 2 . Therefore, a weld tool  408  having nineteen apertures  420  with diameters D of 0.5 mm and that are arranged in a hexagonal arrangement, has a pin density percentage of 28%. Thus, compared to the pin density percentage of 33.8% provided by the seven apertures  420  in the hexagonal arrangement in  FIG. 8D , the pin density percentage decreases as the number of apertures  420  and the overall hexagonal-shaped area increases. 
       FIG. 8F  illustrates a weld tool  408  having a radial arrangement with thirty-one apertures  420  arranged in three concentric circles around a center aperture  420 . Each aperture  420  has a diameter D of 0.5 mm. The distance X between each aperture  420  in the radial direction is 0.5 mm. The total radial distance R from the center aperture  420  to a radially-outermost point of the outermost apertures  420  is 3.25 mm, which defines a circular-shaped area with a total area of 33.18 mm 2 . Therefore, a weld tool  408  having thirty-one apertures  420  arranged in three concentric circles, spaced apart a distance X of 0.5 mm and having a diameter D of 0.5 mm, has a pin density percentage of 18%. Further, as illustrated, the circumferential distance between adjacent apertures  420  increases as the distance from the center of the weld joint increases. Accordingly, the flexibility of the weld joint will be greater in regions further away from the center of the weld joint. Therefore, the radial aperture arrangement in  FIG. 8F  provides different strength and flexibility characteristics compared to the hexagonal aperture arrangements in  FIG. 8A-8E . In other configurations, the outermost apertures  420  may have an ovular or elongated shape to reduce the circumferential distance between adjacent apertures  420  and provide additional strength to the regions further from the center of the weld joint. 
       FIG. 8G  illustrates a weld tool  408  having a square grid aperture arrangement with one hundred apertures  420  aligned in ten rows having ten apertures  420  per row. Each aperture  420  is spaced apart from each adjacent aperture  420  by distances X, Y of 0.5 mm. Each aperture  420  has a diameter D of 0.5 mm. As such, the diameter D and distances X, Y of the apertures  420  have a  1 : 1  relationship. The square grid arrangement has a height H and width W of 9.5 mm. Therefore, a weld tool  408  having one hundred apertures  420  with a diameter D of 0.5 mm and arranged in the square grid arrangement illustrated in  FIG. 8G , has a pin density percentage of 21.71%. In alternative configurations, the diameter D may have a value of 0.1 to 1.0 mm and distance X may have a value different than the distance Y with values between 0.1 to 5.0 mm. 
       FIG. 8H  also illustrates a weld tool  408  having a square grid arrangement with one hundred apertures  420 A,  420 B aligned in ten rows having ten apertures  420 A,  420 B per row. However, in contrast to  FIG. 8G , the square grid arrangement includes large apertures  420 A and small apertures  420 B which are alternatingly disposed along the length of each row. The large apertures  420 A have a diameter D 1  of 0.5 mm and the small apertures  420 B have a diameter D 2  of 0.25 mm. Each aperture  420 A,  420 B is spaced apart from each adjacent aperture  420 A,  420 B by distances X, Y of 0.625 mm. The square grid arrangement has a height H and width W of 9.5 mm. Therefore, a weld tool  408  having fifty large apertures  420 A and fifty small apertures  420 B arranged in a square grid arrangement as illustrated in  FIG. 8H , has a pin density percentage of 13.59%. Thus, compared to the pin density percentage of 21.71% provided by the square grid aperture arrangement in  FIG. 8G , the square grid arrangement having apertures  420 A,  420 B with large and small diameters D 1 , D 2  may provide a weld joint with greater flexibility. In alternative configurations, the diameter D may have a value of 0.1 to 1.0 mm and the distance X may have a value different than the distance Y with values between 0.2 to 5.0 mm. 
       FIG. 8I  also illustrates a weld tool  408  having a grid arrangement with apertures  420  arranged in rows having five apertures  420  per row. However, in contrast to  FIGS. 8G and 8H , each row is offset by a distance O from each adjacent row. Preferably, the offset distance O is 0.5 mm. Each aperture  420  is spaced apart from each adjacent aperture  420  by distances X, Y of 0.5 mm and each aperture  420  has a diameter D of 0.5 mm. 
     As such, the diameter D and the distances X, Y of the apertures  420  have a  1 : 1  relationship. The square grid arrangement has a height H and width W of 5.0 mm. Therefore, a weld tool  408  having twenty-five apertures  420  with a diameter D of 0.5 mm and arranged in a grid arrangement with offset rows, has a pin density percentage of 20%. Put another way, the grid arrangement has one aperture  420  for every 1 mm 2 . In alternative configurations, the diameter D may have a value of 0.1 to 1.0 mm and the distance X may have a different value than the distance Y with values ranging between 0.2 to 5.0 mm. Further, in some configurations, the offset distance O may be determined by the following equation: O=(X+D)/2. 
       FIG. 8J  also illustrates a weld tool  408  having a grid arrangement with offset rows. However, in contrast to  FIG. 8I  but similar to  FIG. 8H , the grid arrangement includes large apertures  420 A and small apertures  420 B which are disposed in alternating rows. The large apertures  420 A have a diameter D 1  of 0.5 mm and the small apertures have a diameter D 2  of 0.25 mm. Each large apertures  420 A is spaced apart a distance X 1  of 0.5 mm from each adjacent large apertures  420 A. Each small aperture  420 B is spaced apart a distance X 2  of 0.75 mm from each adjacent small aperture  420 B. Each row is offset by a distance O of 0.5 mm from each adjacent row. The grid arrangement has a height H of 5.0 mm and a width W of 4.875 mm. Therefore, a weld tool  408  having a bottom section  414  with twenty-five apertures  420  with diameters D 1 , D 2  and arranged in a grid arrangement with offset rows, has a pin density percentage of 14%. Thus, compared to the pin density percentage of 20% provided by the aperture arrangement in  FIG. 8I , the aperture arrangement having apertures  420 A,  420 B with large and small diameters D 1 , D 2  may provide a weld joint with greater flexibility. 
     For the aperture arrangements disclosed, the pin density percentage can be within a range of 10-50%. The pin density percentage may depend upon the region of the headgear where straps are joined since consideration must be given to the desired strength and flexibility for that region of the headgear. In some configurations, the pin density percentage can be within the range of 15-35%. Preferably, the pin density percentage is between 15-25%. 
     In other configurations, the apertures  420  (and pins  413  in use) may be arranged according to other shapes or patterns, including, but not limited to, sine wave, square wave, or zig-zag shapes. In other configurations, the distance of each aperture  420  from adjacent apertures  420  can be irregular or inconsistent over the contact surface  416 . For example, and as illustrated in  FIG. 8K , the apertures  420  may be randomly scattered over the contact surface  416 . In other configurations, the apertures  420  can be arranged in rows. For example, and as illustrated in  FIG. 8L , the apertures  420  may be arranged in vertical rows along the contact surface  416 . Arranging the apertures  420  in rows can allow for a relatively strong weld at the finished weld joint while allowing for flexing or bending at the weld joint in one or more axes (e.g. preferential bending). 
     As shown in  FIG. 8C , the contact surface  416  comprises beveled edges  424 . In some configurations, the edges  424  could be rounded or arcuate. Beveling or rounding the edges of the contact surface  416  lessens concentrations of energy on the edges of the weld region  504 . This can promote a more even or balanced weld joint and lessen chances of excessive melting or burning in undesired places. In other configurations, the contact surface  416  may comprise straight edges. 
       FIGS. 9A-9B  show a cross-section of a non-limiting exemplary recess  422  in more detail. The recess  422  is inwardly chamfered (in contrast with the straight edge  421  shown in  FIG. 10 ). The inwardly chamfered recess  422  is curved or substantially arcuate. The arcuate recess  422  can help prevent undesired concentrations of electromagnetic energy along portions of the contact surface  416 , which can minimize the chance of excessive melting or burning of the top strap  502  in use. In other configurations, the recess  422  can have straight edges. In other configurations, and as described elsewhere in this disclosure, beveled recesses  422  may also be used. The illustrated recess  422  is substantially crater-like. The curvatures of the sides of the crater-like recess  422  are defined by substantially circular cross-sections of the weld tool  408  (as shown by circle c in the close-up shown in  FIG. 9B ). In the illustrated configuration, the circle c comprises a radius r=0.6 mm or about 0.6 mm. In other configurations, the radius may, for example, be in the range of about 0.2 mm to about 1.0 mm, or about 0.3 mm to about 0.9 mm, or about 0.4 mm to about 0.8 mm, or about 0.5 mm or about 0.7 mm. In some configurations, the circle c has a radius r selected to give the contact surface  416  of the weld tool  408  a shape that allows for energy to be efficiently transferred to the weld region  504 . In some configurations, the curvatures of the sides of the crater-like recesses are defined by substantially circular cross-sections of the weld tool having radii x that are proportional to the average distance between pins y according to the ratio x:y. In some such configurations, the ratio x:y can be in the range of 0.3 to 0.4, or about 0.3 to about 0.4. In other configurations, the ratio x:y can be in the range of about 0.2 to about 0.5, or about 0.25 to about 0.45. 
       FIG. 11  shows a close up cross-sectional view of straps welded at a pair of weld points W 1 , W 2  using a pin  413  as a reference. The pin  413  has a width of 0.5 mm or about 0.5 mm. As can be seen, the illustrated non-limiting exemplary top and bottom straps  502 ,  500  each comprise several layers. The top strap  502  comprises cloth or fabric layers  502 A,  502 C (hereinafter generally referred to as cloth layers) comprising hairs  502 D that project outwardly from the layers  502 A,  502 C. The hairs  502 D may act as a hooked surface that can engage with, for example, the loop patches  316 ,  314 ,  312 ,  310  described elsewhere in this disclosure with reference to  FIGS. 2A-2B . The cloth layers  502 A,  502 C sandwich a foam layer  502 B. Similarly, the bottom strap  500  comprises cloth layers  500 A,  500 C sandwiching a foam layer  500 B. Hairs extending from the bottom fabric layer  502 C of the top strap  502  and hairs extending from the top fabric layer  500 A of the bottom strap  500  to at least some extent interweave and compress against one another when the straps are overlaid to form the weld region  504 , facilitating the formation of a weld joint. As can be seen, use of the disclosed welding methods, tools, apparatus and systems can promote a weld while mitigating the presence of visible bulges or burns. Additionally, the use of a weld tool  408  comprising pins  413  that protrude into the straps  502 ,  500  can reduce or eliminate the formation of witness marks (e.g., marks created by detailing on the contact surface  416  of the weld tool  408 , including, but not limited to, ridges or recesses) on the finished weld joints. Witness marks may be caused when the fabric is melted and the straps  502 ,  500  are fused together to become a solid plastic region that includes a portion of a visible surface of the fabric. It may be undesirable in some headgear for there to be regions of reduced flexibility and/or elasticity on or near a visible surface of the fabric (e.g., aesthetic appeal, user comfort, etc.). 
     Although the illustrated embodiments show that the weld tool  408  comprises pins  413  that are positioned over the weld base  402 , in some configurations, the weld base  402  may comprise the pins  413  and the weld tool  408  may primarily serve to exert pressure against the weld region  504 . In some configurations, both the weld tool  408  and the weld base  402  may comprise pins  413 . For example, pins extending from the weld tool  408  may penetrate the straps  502 ,  500  on one half of the weld region  504  and pins extending from the weld base  402  may penetrate the straps  502 ,  500  on the other half of the weld region  504 . In some configurations, the weld tool  408  can be secured to the weld base  402  and the weld press alone (described elsewhere in this disclosure with reference to  FIG. 4 ) can be used to apply pressure to the straps  502 ,  500 . 
     Although the illustrated embodiments show that two overlapping sections of material (e.g. straps) can be welded, in some configurations, a greater number of sections can be welded. For example, in some configurations  3 ,  4  or  5  straps can be welded together using the methods, apparatus, tools and systems disclosed. In some configurations, the weld tool  408  can comprise pins  413  that penetrate all of the sections of material. For example, three overlapping headgear straps (being called top, middle and bottom straps) may be welded using a weld tool  408  having pins  413  that penetrate the entire depth of the top and middle straps and a portion of the bottom strap. In other configurations, the pins  413  may be of variable length to promote adequate weld strength between straps along each strap interface. For example, if three overlapping headgear straps are used, a weld tool  408  having pins  413 , a portion of which penetrate the full depth of the top strap and a portion of the middle strap, another portion of which penetrate the full depth of the top and middle straps and a portion of the bottom strap, may be used. 
       FIG. 12  is a close-up cross-sectional view of a pin configuration which reduces or eliminates the formation of witness marks on the finished weld joints. The pin  413  has an elongate portion  417  that extends in a direction away from the weld tool (not shown) toward a pin end  418  that is opposite the weld tool (not shown). As illustrated, the elongate portion  417  narrows at the pin end  418  to form a pointed tip  419 . To weld the straps  502 ,  500  together, the pointed tip  419  pierces an outer surface  512 A and penetrates entirely through the top strap  502 . As opposed to applying pressure directly to the outer surface  512 A, piercing the outer surface  512 A causes the outer surface  512 A to remain substantially undeflected (i.e., the outer surface  512 A is not pressed closer to the inner surfaces  512 B,  510 B). As illustrated, while penetrating through the top strap  502 , the pin  413  presses the inner surface  512 B of the top strap  502  against the inner surface  510 B of the bottom strap  500 . While the inner surfaces  510 B,  512 B are compressed, electromagnetic energy is applied to the pin  413  which generates heat that causes the straps  502 ,  500  to melt around the weld point  506 , thereby, fusing the straps  502 ,  500  together. However, since the outer surface  512 A remains undeflected, the outer surface  512 A will not be joined in the weld. Accordingly, a visible witness mark will not be formed on the outer surface  512 A. In other configurations, it is possible that a portion of the pointed tip  419  may exit and extend through the inner surface  512 B of the top strap  502 . However, despite the pin end  418  penetrating through the inner surface  512 B, the pointed tip  419  may still press the inner surface  512 B of the top strap  502  against the inner surface  510 B of the bottom strap  500 . It should be understood that the shape and geometry of the elongate portion  417  and pointed tip  419  may vary according to the thickness and type of strap material, quantity and geometry of the pins, desired weld strength, etc. 
       FIGS. 13-15  illustrate a high frequency welding system  600  that may further reduce or eliminate the formation of a witness mark and form a weld joint that does not significantly effect or that preserves a substantial amount of the flexibility and/or elasticity of the fabric. The welding system  600  comprises a weld base (e.g., anvil)  610  and a weld tool  620 . The weld base  610  includes a top surface  612  and a positioning cavity  614  that is recessed below the top surface  612  and adapted to hold the top and bottom sheets of material  702 ,  704  in overlapping alignment prior to forming the strap  700  of the headgear. The weld tool  620  includes a top plate  622 , pins  624  and an insert portion  626 . The pins  624  are positioned within and extend through both the top plate  622  and the insert portion  626  such that the top plate  622  is connected to the insert portion  626  via the pins  624 . The weld tool  620  may also have bosses  638  positioned between the top plate  622  and the insert portion  626  to connect the top plate  622  to the insert portion  626 . In some configurations, the insert portion  626  may slide axially along the lengths of the pins  624  and the bosses  638 . 
     The pins  624  are substantially straight and include a head portion  632 , an elongate portion  634  and a tip portion  636 . The head portion  632  is positioned within the top plate  622  and extends entirely through the top plate  622 . An upper region of the head portion  632  may protrude from the top plate  622  to provide a connection with an energy source (not shown). The elongate portion  634  is connected to the head portion  632  and extends perpendicularly outward from the top plate  622  in a direction that is parallel to the insertion direction of the insert portion  626  into the positioning cavity  614 , as will be discussed in greater detail below. The elongate portion  634  extends entirely through the insert portion  626  such that elongate portion  634  protrudes outward from a surface  628  of the insert portion  626  that is opposite the top plate  622  and that faces the positioning cavity  614 . The tip portion  636  is positioned at the end of the elongate portion  634  that protrudes outwardly from the insert portion  626 . The elongate portion  634  and the tip portion  636  may protrude a distance from the surface  628  of the insert portion  626  according to the desired depth of penetration of the bottom sheet  704  (if any) and clearance, as previously disclosed. The elongate portion  634  of the pins  624  may have a diameter of 0.3 mm to 1 mm and the tip portion  636  may narrow to a point. The pins  624  may be spaced apart by a distance of 2.5 mm to 6 mm (i.e., between the centers of the pins  624 ) arranged in a single-file row along an outer edge of the surface  628  of the insert portion  626 . The pins  624  may be arranged in single-file rows that are aligned according to the direction of stretch of the finished product, which will be discussed in greater detail below. It should be noted that the welding system  600  is not limited to pins  624  arranged in single file rows and may be arranged according to any of the aperture/pin arrangements previously disclosed. 
     As illustrated in  FIGS. 14 and 15 , the top plate  622  may be joined with the weld base  602  such that the top plate  622  rests on top of the weld base  602  and the insert portion  626  is able to be inserted into the positioning cavity  614 . The insert portion  626  has a size and shape that corresponds with the shape of the positioning cavity  614 . Spacers  616  may be attached to the weld base  610  and/or the weld tool  620  to limit axial motion (i.e., the direction parallel to the insertion direction) between the weld base  610  and the weld tool  620  when the insert portion  626  is inserted into the positioning cavity  614 . The spacers  616  may be arranged to provide the desired clearance and depth of penetration (if any) into the bottom sheet  704 , as previously disclosed. 
     The weld base  610 , the top plate  622  and/or the insert portion  626  may be a non-conductive tool and/or formed from an insulating material, such as plastic, to reduce or minimize heat or energy transferred from the surface  628  of the insert portion  626  to the top and bottom sheets of material  702 ,  704 , thereby, further reducing or preventing the formation of a witness mark. Preferably, at least the weld base  610  and insert portion  626  (or other portions that contact the sheets  702 ,  704 ) are constructed from or comprise an insulating material. Therefore, the only heat or energy transferred to the top and bottom sheets  702 ,  704  are substantially provided by the pins  624 . In some configurations, any one or all of the top plate  622 , the pins  624  or the insert portion  626  may be formed from a non-insulating material, such as metal. However, with such a configuration, a thermally insulating material or coating may be applied to the surface  628  to reduce or minimize heat transferred from the surface  628  of the insert portion  626  to the top and bottom sheets  702 ,  704 . The non-conductive or insulating material can be selected in view of the type or particulars of the weld process. For example, the tool can be configured to reduce thermal conductivity or reduce electrical or electromagnetic conduction. The tool may be formed from a material that prevents or reduces thermal conductivity, electrical conductivity, or electromagnetic conductivity. 
     In operation, the strap  700  may be formed by inserting the top and bottom sheets  702 ,  704  into the positioning cavity  614 . The top and bottom sheets of material  702 ,  704  may be inserted and arranged in an overlapping relationship. It should be understood that ‘top’ and ‘bottom’ as used in this disclosure can be interpreted as referring to positioning with respect to the high frequency welding system  600  rather than with respect to gravity. The weld tool  620  is positioned onto the weld base  610  such that the insert portion  626  is inserted into the position cavity  614 . A compressive force is applied to the top plate  622  of the weld tool  620 . Accordingly, the pins  624  and the insert portion  626  contact and apply pressure to the top and bottom sheets  702 ,  704 . The tip portion  626  of the pins  624  penetrate the entire depth of the top sheet  702  and partially penetrate the bottom sheet  704 . The weld tool  620  is energized with electromagnetic energy (using an energy source, not shown), causing the pins  624  to generate alternating electric fields that cause polar molecules in the straps of material to oscillate and orient themselves with respect to the field. This movement of the polar molecules generates heat, causing a temperature increase that result in the melting of the sheets. Although the positioning cavity  614  and the insert portion  626  shown are rectangular, it should be understood that the positioning cavity  614  and the insert portion  626  could be formed in other shapes, for example, shapes which correspond to geometries of the straps to be welded. Further, the pins  624  are illustrated as having an elongate cylindrical shape. However, it should be understood that the pins could be formed in shapes (e.g., rectangular, ovular, etc. in cross-section) according to the desired strength and flexibility provided by the strap. 
       FIGS. 16A-16D  illustrate the strap  700  after the sheets  702 ,  704  have been welded together by the high frequency welding system  600 . As shown in  FIG. 16A , the strap  700  has linearly spaced weld points  710  that are equidistantly spaced apart along the length of the strap  700 . In contrast to a strap having a continuous seam weld, the weld points  710  are spaced apart such that the weld region formed by a single pin does not merge with a weld region from another pin. The weld points  710  provide a discontinuous weld such that the strap  700  can be stretched in a direction parallel to the direction of the linearly spaced weld points  710 . Each of the weld points  710  may be spaced apart from an adjacent weld point  710  by a distance of 3.5 mm (i.e., in a neutral un-stretched position of the strap  700 ), which also corresponds to the spacing between the pins  624 . Depending upon the amount of desired stretch and flexibility by the strap  700 , the distance between weld points  710  (i.e., distance between the centers of each weld points  710 ) may be within a range of 2.5 mm to 6.0 mm. Accordingly, a greater distance between weld points  710  will provide a greater amount of stretch and flexibility. However, significantly larger distances between weld points  710  may be undesirable because the edges of the strap  700  may split or bow outward (i.e., the sheets  702 ,  704  may separate) between the weld points  710  when the strap  700  is either bent or turned inside out. 
     As shown in  FIG. 16B , the weld points  710  may be visible when viewing the top sheet  702  of the strap  700  from a top-down view. However, as shown in  FIG. 16C , the weld points  710  are concealed within the strap  700  and not visible when viewing the bottom sheet  704  of the strap  700  from a top-down view.  FIG. 16D  illustrates a cross-sectional view of the strap  700 . As the pins  624  are arranged in single file rows along the outer edges of the top and bottom sheets  702 ,  704 , the weld points  710  are positioned along the outer edges of the top and bottom sheets  702 ,  704  such that a central opening  706  is provided at a center of the strap  700 . As illustrated in  FIG. 16D , the top sheet  702  and the outer edges of the top sheet  702  may be slightly more curved and deformed relative to the bottom sheet  704 . The downward pressure provided by the pins  624  may press and hold the outer edges of the top sheet  702  to the outer edges of the bottom sheet  704 . When the weld points  710  are formed, the top sheet  702  may retain a slight curvature due to the downward pressure provided by the pins  624 . The existence or amount of curvature may depend on the width and flexibility of the top and bottom sheets, the depth, geometry and position of the weld points, etc. In some configurations, the welding system  600  may be configured such that the top sheet is not more curved or deformed than the bottom sheet such that both the top and bottom straps are substantially identical. 
       FIGS. 17A and 17B  illustrate straps  800  welded together using alternative pin arrangements provided by the welding system  600 .  FIGS. 17A-B  illustrate welded straps  800  having equidistantly spaced weld points  810  that are located along the outer edges of the strap  800 . In contrast to the strap  700  in  FIGS. 16A-D , the strap  800  in  FIG. 17A  has double-file rows of linearly spaced weld points  810  along the length of the strap  800 . In  FIG. 17B , the strap  800  has weld points  810  arranged in a staggered row (i.e., each aperture  810  is offset from an adjacent aperture  810 ) along the length of the strap  800 . The alternative pin arrangements in  FIG. 17A-B  provide different strength and flexibility characteristics than the single-file pin arrangement of the strap  700  in  FIGS. 16A-D . For example, the double-file row of weld points  810  may provide greater weld strength but lower flexibility compared to the single-file row of weld points  710  in  FIGS. 16A-D . Conversely, the staggered row of weld points  810  may provide lower weld strength but greater flexibility compared to the single-file row of weld points  710  in  FIGS. 16A-D . However, similar to the single-file row of weld points  710  of strap  700 , both the double-file and staggered rows of weld points  810  may allow the strap  800  to stretch in a direction parallel to the lengthwise of the strap  800 , as indicated by the arrow in  FIGS. 17A and 17B . It should be understood that the welding system  600  is not limited to single-file, double-file or staggered pin arrangements and may utilize the pin arrangements disclosed herein according to the desired strength and flexibility characteristics of the strap. Further, although the illustrated embodiments show the top and bottom sheets in a fully overlapping relationship, the top and bottom sheets may still be welded despite only a portion of the top and bottom sheets overlapping. 
     Certain features, aspects and advantages of some configurations of the present disclosure have been described with reference to high-frequency welding of overlapping headgear straps. However, certain features, aspects and advantages of the methods, apparatus, tools and systems described may be advantageously used on other materials, including but not limited to sheets, plates and films, for the purpose of producing other products, including but not limited to articles of clothing. In addition, certain features, aspects and advantages of the use of methods, apparatus, tools and systems may be equally applied to other welding technologies, including but not limited to ultrasonic welding. 
     Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like, are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, that is to say, in the sense of “including, but not limited to.” 
     Where, in the foregoing description reference has been made to integers or components having known equivalents thereof, those integers or components are herein incorporated as if individually set forth. 
     The disclosed methods, apparatus and systems may also be said broadly to comprise the parts, elements and features referred to or indicated in the disclosure, individually or collectively, in any or all combinations of two or more of said parts, elements or features. 
     Recitation of ranges herein is merely intended to serve as a shorthand method of referring individually to each separate sub-range or value falling within the range, unless otherwise indicated herein, and each separate sub-range or value is incorporated into the specification as if it were individually recited herein. Moreover, the term “about,” when used in combination with a number or a range of numbers, shall be inclusive of standard manufacturing tolerances of the number recited as well as a rounding to the next significant figure represented by the number under standard rounding rules. Moreover, any dimensions or other values provided herein, including the number of decimal places or significant figures provided in such dimensions or values, are merely exemplary, unless otherwise indicated, and include the dimensions or values as rounded to any desired decimal place. 
     Reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that that prior art forms part of the common general knowledge in the field of endeavour in any country in the world. 
     Although the present disclosure has been described in terms of certain embodiments, other embodiments apparent to those of ordinary skill in the art also are within the scope of this disclosure. Thus, various changes and modifications may be made without departing from the spirit and scope of the disclosure. For instance, various components may be repositioned as desired. Moreover, not all of the features, aspects and advantages are necessarily required to practice the present disclosure. Accordingly, the scope of the present disclosure is intended to be defined only by the claims that follow.