Patent Publication Number: US-11662594-B2

Title: Head-mounted display assemblies and related methods for interpupillary distance adjustments

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/075,028, titled “HEAD-MOUNTED DISPLAY ASSEMBLIES AND RELATED METHODS FOR INTERPUPILLARY DISTANCE ADJUSTMENTS,” filed 20 Oct. 2020, which claims the benefit of U.S. Provisional Patent Application Ser. No. 63/007,586, titled “HEAD-MOUNTED DISPLAY ASSEMBLIES AND RELATED METHODS FOR INTERPUPILLARY DISTANCE ADJUSTMENTS,” filed 9 Apr. 2020, and U.S. Provisional Patent Application Ser. No. 62/929,932, titled “HEAD-MOUNTED DISPLAY ASSEMBLIES AND RELATED METHODS FOR INTERPUPILLARY DISTANCE ADJUSTMENTS,” filed 3 Nov. 2019, the entire disclosure of each of which is incorporated herein by reference. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings illustrate a number of example embodiments and are a part of the specification. Together with the following description, these drawings demonstrate and explain various principles of the present disclosure. 
       FIG.  1 A  is a perspective view and  FIG.  1 B  is a cross-sectional side view of a head-mounted display assembly, according to at least one embodiment of the present disclosure. 
       FIG.  2    is a detailed cross-sectional side view of the head-mounted display assembly of  FIG.  1    with optical lenses at a first IPD setting, according to at least one additional embodiment of the present disclosure. 
       FIG.  3    is a detailed cross-sectional side view of the head-mounted display assembly of  FIG.  1    with the optical lenses at a second IPD setting, according to at least one embodiment of the present disclosure. 
       FIGS.  4 A and  4 B  are detailed cross-sectional views of portions of head-mounted display assemblies, according to at least some embodiments of the present disclosure. 
       FIG.  5    is a perspective view of a head-mounted display assembly, according to at least one embodiment of the present disclosure. 
       FIG.  6    is a front view of a head-mounted display assembly, according to at least one additional embodiment of the present disclosure. 
       FIG.  7    is a back view of a detent mechanism of the head-mounted display assembly of  FIG.  6   , according to at least one embodiment of the present disclosure. 
       FIG.  8    is a side view of the detent mechanism of  FIG.  7   . 
       FIG.  9    is a perspective view of a portion of a head-mounted display assembly including a position sensor, according to at least one embodiment of the present disclosure. 
       FIG.  10    is a flow diagram illustrating a method of fabricating a head-mounted display assembly, according to at least one embodiment of the present disclosure. 
       FIG.  11    is a flow diagram illustrating a method of adjusting an interpupillary distance of a head-mounted display assembly, according to at least one embodiment of the present disclosure. 
       FIG.  12    is an illustration of an example virtual-reality headset that may be used in connection with embodiments of this disclosure. 
       FIG.  13    is an illustration of an example virtual-reality environment according to embodiments of this disclosure. 
    
    
     Throughout the drawings, identical reference characters and descriptions indicate similar, but not necessarily identical, elements. While the example embodiments described herein are susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, the example embodiments described herein are not intended to be limited to the particular forms disclosed. Rather, the present disclosure covers all modifications, equivalents, and alternatives falling within the scope of the appended claims. 
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Artificial-reality systems, such as virtual-reality systems or augmented-reality systems, typically display computer-generated content to users in order to create immersive experiences. The content may be displayed on a head-mounted display (“HMD”) screen. For example, a virtual-reality system may create three-dimensional renderings to simulate an environment or a virtual space. Alternatively, augmented-reality systems may merge computer-generated content with a user&#39;s view of a real-world environment to enhance interactions with the real-world environment. These systems may provide users with the ability to navigate and alter digital content that may provide helpful information about real-world objects. HMD systems sometimes include two optical lenses—one for each eye—positioned in front of the screen. The lenses may magnify and/or provide an appropriate focus to images displayed on the screen. Contamination (e.g., dust particles, fingerprints, etc.) on the lenses or the screen can undesirably block or otherwise obscure portions of a displayed image. Moving parts in HMD systems can sometimes produce or move contamination in front of the displayed image. 
     Different users have different head and face shapes and sizes. For example, a particular user&#39;s eyes may be located closer or farther apart from each other, compared to other users. The distance between the center of an HMD user&#39;s pupils is commonly referred to as “interpupillary distance” or “IPD.” Positioning the lenses to match a particular user&#39;s IPD improves picture quality for that user. To accommodate different IPDs, some HMDs include a mechanism to adjust an IPD setting and, therefore, a relative position between the optical lenses. Some HMDs include two separate screens coupled to the two respective lenses. Each lens and screen pair may be movable relative to the other lens and screen pair to adjust for IPD. Each lens and screen pair may include a sealed interior to inhibit the introduction of contamination, to improve or maintain picture quality. However, two such screens are generally more expensive to integrate into HMDs compared to a single screen. However, conventional HMD systems with one screen and IPD adjustment capability generally have a configuration that may allow contamination to be introduced onto the screen and/or onto a screen side of the lenses. 
     The present disclosure is generally directed to HMD assemblies that may include a single near-eye display (“NED”) screen and two eyecups that are movable relative to each other to adjust for IPDs of different users. An enclosure may be disposed over the single NED screen. The enclosure may include a first transparent component positioned between the first lens and the single NED screen and a second transparent component positioned between the second lens and the single NED screen. 
     The enclosure, including the first and second transparent components, may provide a clean volume over the single NED screen to reduce contamination on the screen while also allowing for interpupillary adjustments. As will be explained in greater detail below, embodiments of the present disclosure may enable IPD adjustments over a single, sealed display screen. The single display screen may reduce a cost of HMD assemblies with IPD adjustability, compared to conventional HMD assemblies with two separate display screens. Additionally, the enclosure over the single NED screen may facilitate keeping the screen clean and substantially free from contamination, which might otherwise obstruct a user&#39;s view of blocked pixels of the display screen. Contamination (e.g., dust, particles, other debris) that may be present between the first and second lenses and the respective first and second transparent components may be substantially out-of-focus. The out-of-focus contamination, if sufficiently small, may be essentially invisible to the user. Even larger contamination may be less visible than if the contamination were positioned at the NED screen surface. 
     In some examples, the term “substantially” in reference to a given parameter, property, or condition may mean and include to a degree that one of ordinary skill in the art would understand that the given parameter, property, or condition is met with a small degree of variance, such as within acceptable manufacturing tolerances. By way of example, depending on the particular parameter, property, or condition that is substantially met, the parameter, property, or condition may be at least 90% met, at least 95% met, or even at least 99% met. 
     Features from any of the embodiments described herein may be used in combination with one another in accordance with the general principles described herein. These and other embodiments, features, and advantages will be more fully understood upon reading the following detailed description in conjunction with the accompanying drawings and claims. 
     The following will provide, with reference to  FIGS.  1 A- 3   , detailed descriptions of various example HMD assemblies according to the present disclosure. With reference to  FIGS.  4 A and  4 B , the following will provide detailed descriptions of example sliding interfaces for IPD adjustability of HMD assemblies of the present disclosure. With reference to  FIG.  5   , the following will provide detailed descriptions of example HMD assemblies according to additional embodiments of the present disclosure. With reference to  FIGS.  10  and  11   , the following will provide detailed descriptions of example methods of fabricating HMD assemblies and of adjusting an IPD of HMD assemblies, respectively. With reference to  FIGS.  8  and  9   , the following will provide detailed descriptions of example artificial-reality systems and environments that may be used in conjunction with HMD assemblies of the present disclosure. 
       FIGS.  1 A and  1 B  illustrate an HMD assembly  100  that may include a first eyecup  102  and a second eyecup  104  positioned over a single NED screen  106 , with an enclosure  108  positioned between the eyecups  102 ,  104  and the single NED screen  106 .  FIG.  2    illustrates a detailed view of certain components of the HMD assembly  100 . Referring to  FIGS.  1 A- 2   , the eyecups  102 ,  104 , single NED screen  106 , and enclosure  108  may be mounted on an HMD support frame  110 , which may also support an eye bracket  112  that may be shaped and positioned for resting against the user&#39;s face when the HMD assembly  100  is donned by the user. In some examples, a flexible shroud  109  may be positioned over at least portions (e.g., peripheral portions) of the eyecups  102 ,  104 , such as to provide an aesthetic cover and/or a dust cover over underlying components of the HMD assembly  100 . 
     In some examples, relational terms, such as “first,” “second,” “upper,” “lower,” “over,” “underlying,” etc., may be used for clarity and convenience in understanding the disclosure and accompanying drawings and may not necessarily connote or depend on any specific preference, orientation, or order, except where the context clearly indicates otherwise. 
     The eyecups  102 ,  104  may be configured for positioning in front of intended locations of a user&#39;s eyes when the HMD assembly  100  is donned by the user. For example, the first eyecup  102  may be configured for viewing the single NED screen  106  with the user&#39;s left eye and the second eyecup  104  may be configured for viewing the single NED screen  106  with the user&#39;s right eye. The first eyecup  102  may support a first optical lens  114  and the second eyecup  104  may support a second optical lens  116 . For example, each of the optical lenses  114 ,  116  may be a corrective ophthalmic lens (e.g., a positive-optical power (i.e., magnifying) lens, a negative-optical power (i.e., diminishing) lens, a lens for correction of an aberration, etc.), a zero-power optical lens, an adjustable (e.g., deformable) optical lens, a Fresnel lens, or another optical lens element. Optionally, an anti-reflective coating may be applied to the optical lenses  114 ,  116 . 
     The first eyecup  102  may include a first rigid housing  118  at least partially defining a first interior volume  120 . Similarly, the second eyecup  104  may include a second rigid housing  122  at least partially defining a second interior volume  124 . A base of the first rigid housing  118  may include a first flange  126 , which may extend radially outward from a sidewall of the first rigid housing  118 . Similarly, a base of the second rigid housing  122  may include a second flange  128 , which may extend radially outward from a sidewall of the second rigid housing  122 . 
     The optical lenses  114 ,  116  may be sealed (e.g., hermetically sealed) against and supported by the rigid housings  118 ,  122 . The optical lenses  114 ,  116  may be positioned to focus images displayed by the single NED screen  106  to the user&#39;s eyes when the HMD assembly  100  is donned by the user. 
     The enclosure  108  may include a first transparent component  130  positioned between the first optical lens  114  and the single NED screen  106  and a second transparent component  132  positioned between the second optical lens  116  and the single NED screen  106 . An outer region of the first and second transparent components  130 ,  132  may be coupled to the eye-facing surface of the single NED screen  106  via a sealing structure  134  of the HMD support frame  110 . Thus, the enclosure  108  may be defined by the first and second transparent components  130 ,  132 , the single NED screen  106 , and the sealing structure  134 . In some examples, the enclosure  108  may be a hermetically sealed enclosure to inhibit the introduction of contaminants (e.g., particles) on the eye-facing surface of the single NED screen  106 . Contamination that may be present over the first and second transparent components  130  (e.g., outside of the enclosure  108 ) may be substantially out-of-focus to a user viewing the single NED screen  106  through the optical lenses  114 ,  116 . 
     By way of example and not limitation, the first and second transparent components  130 ,  132  may be or include the same material or two respective different materials. The first and second transparent components  130 ,  132  may include a glass material, a transparent polymeric material (e.g., polycarbonate, polymethylmethacrylate, polyethylene terephthalate, cyclic olefin copolymer, polypropylene, styrene methyl methacrylate, styrene acrylonitrile resin, polystyrene, etc.), and/or a crystalline material, etc. In some examples, the first and second transparent components  130 ,  132  may be substantially planar and may exhibit substantially zero optical power. The first and second transparent components  130 ,  132  may be stationary relative to the single NED screen  106 , the eye bracket  112 , and the sealing structure  134 . By configuring the first and second transparent components  130 ,  132  as stationary relative to the single NED screen  106 , the number of moving parts adjacent to the single NED screen  106  that might otherwise generate or move contaminants (e.g., particles) may be reduced. 
     A first sealing element  136  may be disposed between the first flange  126  and the first transparent component  130 . A second sealing element  138  may be disposed between the second flange  128  and the second transparent component  130 . The first and second sealing elements  136 ,  138  may be configured for allowing the first eyecup  102  and the second eyecup  104  to move (e.g., slide) relative to the first and second transparent components  130 ,  132 , such as to adjust an IPD setting of the HMD assembly  100 . The first and second sealing elements  136 ,  138  may be configured to inhibit particles from entering the first and second interior volumes  120 ,  124 . 
     By way of example and not limitation, the first and second sealing elements  136 ,  138  may each be an O-ring, a foam (e.g., closed-cell foam) ring, a foam ring bonded to a structural base (e.g., a foam ring bonded to a polyethylene terephthalate base), a V-ring, an X-ring, a gasket, etc. The material of the first and second sealing elements  136 ,  138  may be or include a polymer material, such as an elastomeric material, a foam material, a combination thereof, etc. 
     As noted above, the first eyecup  102  and the second eyecup  104  may be movable (e.g., in a direction that is parallel to a surface of the single NED screen  106 , such as in a left-and-right direction from the perspective of  FIGS.  1 A and  1 B ) relative to each other to adjust for an IPD of the user&#39;s eyes. At least one of the eyecups  102 ,  104  may also be movable relative to the single NED screen  106 . In some embodiments, the first eyecup  102  and the second eyecup  104  may be movable relative to each other over a distance of up to about 10 mm. The eyecups  102 ,  104  may be independently movable relative to the HMD support frame  110 , or the eyecups  102 ,  104  may be configured to simultaneously move inward (e.g., toward each other) or outward (e.g., away from each other) at substantially equal distances and rates relative to the single NED screen  106 . 
     As shown in  FIG.  1    by way of example, one or more IPD input mechanisms  140  (e.g., switches, sliders, knobs, buttons, etc.) may be integrated into the HMD support frame  110  and configured to allow the user of the HMD assembly  100  to adjust the IPD of the eyecups  102 ,  104  according to preference. Alternatively or additionally, IPD adjustments may be made by one or more electromechanical actuators (e.g., linear actuators, rotational motors, etc.), which may be controlled by a computing system associated with the HMD assembly  100  or by the user&#39;s manipulation of the IPD input mechanism(s)  140 . 
     A first IPD setting IPD 1  may correspond to a distance between a first optical axis A 1  of the first optical lens  114  and a second optical axis A 2  of the second optical lens  116  when the first and second optical lenses  114  are in a first position, as shown in  FIG.  2   . A second IPD setting IPD 2  may correspond to the distance between the first and second optical axes A 1 , A 2  when the first and second optical lenses  114  are in a second position, as shown in  FIG.  3   . In the example shown, the first eyecup  102  and the second eyecup  104  are closer to each other at the second IPD setting IPD 2  comparted to the first IPD setting IPD 1 . Thus, the first IPD setting IPD 1  may be useful for a user that has a generally wide IPD, and the second IPD setting IPD 2  may be useful for a different user that has a generally narrow IPD. 
     Referring  FIGS.  2  and  3   , the first transparent component  130  may be positioned a first distance D 1  from the single NED screen  106  and the second transparent component  132  may be positioned a second distance D 2  from the single NED screen  106 . By way of example and not limitation, each of the first distance D 1  and the second distance D 2  may be in the range of about 10 mm to about 20 mm. 
     In some embodiments, the first distance D 1  may be different from the second distance D 2 . For example, the first distance D 1  may be at least about 2 mm greater than the second distance D 2 . This difference between the first and second distances D 1 , D 2  may enable a portion of the first and second flanges  126 ,  128  between the first and second eyecups  102 ,  104  to overlap when the first and second eyecups  102 ,  104  are close together (e.g., at the second IPD setting IPD 2 ), as shown in  FIG.  3   . Thus, the difference between the first and second distances D 1 , D 2  may facilitate the positioning of the first and second eyecups  102 ,  104  closer together than would otherwise be possible without the difference, since the first and second flanges  126 ,  128  are at different levels and thus do not physically interfere with each other at the second IPD setting IPD 2 . 
     The single NED screen  106  may include an electronic display screen for presenting visual content to the user. For example, the single NED screen  106  may include a liquid crystal display (LCD), light-emitting diode (LED) display, organic LED (OLED) display, a waveguide for directing light from a projector to the user, and/or any other suitable type of display screen. In some embodiments, the single NED screen  106  may be configured for displaying respective stereoscopic images to the user through the first eyecup  102  and the second eyecup  104  to create an impression of a three-dimensional image. 
       FIG.  4 A  illustrates a detailed cross-sectional view of a portion of an HMD assembly  400 A. Like the HMD assembly  100  described above with reference to  FIGS.  1 A- 3   , the HMD assembly  400 A of  FIG.  4 A  may include a first eyecup  402  and a second eyecup  404  respectively disposed over a first transparent component  420  and a second transparent component  432 . The first eyecup  402  may include a first rigid housing  418  and the second eyecup  404  may include a second rigid housing  422 . A first flange  426  may extend radially outward from a sidewall of the first rigid housing  418 , and a second flange  428  may extend radially outward from a sidewall of the second rigid housing  422 . A first sealing element  436  may be positioned between the first flange  426  and the first transparent component  430  to form a seal (e.g., a hermetic seal) between the first eyecup  402  and the first transparent component  430 . Likewise, a second sealing element  438  may be positioned between the second flange  428  and the second transparent component  432  to form a seal (e.g., a hermetic seal) between the second eyecup  404  and the second transparent component  432 . 
     By way of example and not limitation, the first flange  426  may include a first groove  442  in which a portion of the first sealing element  436  may be positioned. Thus, the first sealing element  436  may be coupled to the first flange  426  and may be movable along with the first flange  426  relative to the first transparent component  430 . A first sliding interface  444  may be between the first sealing element  436  and the first transparent component  430 . Similarly, the second flange  428  may include a second groove  446  in which a portion of the second sealing element  438  may be positioned. The second sealing element  438  may be coupled to the second flange  428  and may be movable along with the second flange  428  relative to the second transparent component  432 . A second sliding interface  448  may be between the second sealing element  438  and the second transparent component  432 . In this case, to adjust for a user&#39;s IPD, the first and second eyecups  402 ,  404  and the first and second sealing elements  436 ,  438  may be movable relative to the first and second transparent components  430 ,  432 . 
       FIG.  4 B  illustrates a detailed cross-sectional view of a portion of an HMD assembly  400 B having a different configuration than the HMD assembly  400 A of  FIG.  4 A . In this example, the first groove  442  may be located in the first transparent component  430  and a portion of the first sealing element  436  may be positioned in the first groove  442 . Thus, the first sliding interface  444  may be between the first sealing element  436  and the first flange  426 . Similarly, the second groove  446  may be located in the second transparent component  432  and a portion of the second sealing element  438  may be positioned in the second groove  446 . Thus, the second sliding interface  448  may be between the second sealing element  438  and the second flange  428 . In this case, to adjust for a user&#39;s IPD, the first and second eyecups  402 ,  404  may be movable relative to the first and second transparent components  430 ,  432  and relative to the first and second sealing elements  436 ,  438 . 
       FIG.  5    is a perspective view of a portion of an HMD assembly  500 , according to additional embodiments of the present disclosure. Some components of the HMD assembly  500  are removed in  FIG.  5    to better view underlying portions of the HMD assembly  500 . The HMD assembly  500  of  FIG.  5    may be similar to the HMD assembly  100  described above with reference to  FIGS.  1 A- 3   . For example, the HMD assembly  500  may include a first eyecup  502  and a second eyecup  504  positioned over a single NED screen  506 . The eyecups  502 ,  504  and the single NED screen  506  may be coupled to and supported by an HMD support frame  510 . The first eyecup  502  may include a first rigid housing  518  to which a first optical lens  514  may be coupled. The second eyecup  504  may include a second rigid housing  522  to which a second optical lens (not shown in the view of  FIG.  5    for clarity) may be coupled. The first rigid housing  518  may at least partially define a first interior volume  520  of the first eyecup  502 . Similarly, the second rigid housing  522  may at least partially define a second interior volume  524  of the second eyecup  504 . 
     The first and second eyecups  502 ,  504  may be positioned over and movable relative to an enclosure  508  (shown in dashed lines in  FIG.  5   ) that may be positioned over the single NED screen  506 . The enclosure  508  may be hermetically sealed to inhibit the introduction of contamination on a user-facing surface of the single NED screen  506 . 
     The eyecups  502 ,  504  may be movable relative to each other and/or relative to the single NED screen  506 , such as to adjust for the user&#39;s IPD. The HMD assembly  500  of  FIG.  5    may also include an IPD adjustment mechanism  550 , which may include a track  552  (e.g., a rod, a slide, etc.), a first IPD adjustment bracket  554  slidably coupling the first rigid housing  518  to the track  552 , and a second IPD adjustment bracket  556  slidably coupling the second rigid housing  522  to the track  552 . The IPD adjustment mechanism  550  may, in some examples, also include one or more IPD input mechanisms (not shown in the view of  FIG.  5   , but similar to the IPD input mechanism  140  described above) with which the user may interact to control the movement of the eyecups  502 ,  504  for IPD adjustments. In addition or alternatively, a cam, pusher, electromechanical actuator (e.g., a motor, a linear actuator, etc.), or other suitable component may be included to move the IPD adjustment brackets  554 ,  556  and eyecups  502 ,  504  along the track  552 . 
     As illustrated in  FIG.  5   , the IPD adjustment brackets  554 ,  556  may, in some embodiments, each include two spaced apart slider elements  558  engaged with and movable along the track  552 , such as to provide sufficient stability to the respective eyecups  502 ,  504 . The slider elements  558  may be engaged with the track  552  in a manner that maintains the eyecups  502 ,  504  in position after an IPD adjustment is made. In some examples, a detent mechanism  560  (shown in  FIG.  5    in dashed lines) may be employed to maintain the eyecups  502 ,  504  in their relative position after an IPD adjustment is made. For example, the detent mechanism  560  may include a ratchet, a frictional interface, a pin and rack, or another suitable mechanism for maintaining the relative positions of the eyecups  502 ,  504 . In some examples, the HMD assembly  500  may optionally include another set of a track and IPD adjustment brackets positioned on an opposite side of the eyecups  502 ,  504  from the track  552  and IPD adjustment brackets  554 ,  556  shown in  FIG.  5   , such as for additional mechanical stability. 
       FIG.  6    is a front view of an HMD assembly  600  that may include a first eyecup  602  (e.g., a left eyecup for positioning a first optical lens over a left eye of an intended user) and a second eyecup  604  (e.g., a right eyecup for positioning a second optical lens over a right eye of the intended user) positioned over a single NED screen  605 . As discussed above, an enclosure may be positioned between the eyecups  602 ,  604  and the single NED screen  605 . The eyecups  602 ,  604 , and single NED screen may be mounted on an HMD support frame  608 . 
     The eyecups  602 ,  604  may be movable relative to the HMD support frame  608  and/or relative to each other to adjust for a user&#39;s IPD. For example, each of the eyecups  602 ,  604  may be slidably coupled to and movable along an upper track  606  (e.g., a rod, a slide, etc.) that may be mounted on the HMD support frame  608 . The eyecups  602 ,  604  may also be respectively slidably coupled to and movable along a first lower track  610  and a second lower track  612  that may be mounted on the HMD support frame  608 . The first lower track  610  and second lower track  612  may be positioned on opposite sides of the eyecups  602 ,  604  from the upper track  606 . As illustrated in  FIG.  6   , in some examples the first lower track  610  and second lower track  612  may be separated from each other, such as to accommodate an intended user&#39;s nose. In additional examples, the first lower track  610  and second lower track  612  may be portions of a single, integral, unitary track. 
     The HMD assembly  600  may also include a detent mechanism  614  to maintain the eyecups  602 ,  604  in position relative to each other and relative to the HMD support frame  608 . In some embodiments, the detent mechanism  614  may also be configured to keep each of the eyecups  602 ,  604  substantially equidistant from a lateral centerline of the HMD assembly  600 . As illustrated in  FIG.  6   , the detent mechanism  614  may include a first rack  616  extending inward from the first eyecup  602 , a second rack  618  extending inward from the second eyecup  604 , and a pinion  620  engaged with the first rack  616  and second rack  618 . The pinion  620  may be rotatably coupled to the HMD support frame  608 . Teeth of the pinion  620  may be engaged with teeth of the first rack  616  on a first side of the pinion  620  and with teeth of the second rack  618  on a second, opposite side of the pinion  620 . Thus, when the first eyecup  602  moves inward (e.g., to the right from the perspective of  FIG.  6   ), the second eyecup  604  may also move inward (e.g., to the left from the perspective of  FIG.  6   ) due to rotation of the pinion  620 . Similarly, when the first eyecup  602  moves outward (e.g., to the left from the perspective of  FIG.  6   ), the second eyecup  604  may also move outward (e.g., to the right from the perspective of  FIG.  6   ) due to rotation of the pinion  620  in an opposite direction. 
     The detent mechanism  614  may include a feature that enables the eyecups  602 ,  604  to be maintained in position once moved. For example, the eyecups  602 ,  604  may be maintained in two, three, four, or five distinct positions by the detent mechanism  614 . An example embodiment of the detent mechanism  614  capable of maintaining the eyecups  602 ,  604  in position is illustrated in  FIGS.  7  and  8   . 
       FIG.  7    is a back view of the detent mechanism  614 , and  FIG.  8    is a side view of the detent mechanism  614 . As shown in  FIG.  8   , the pinion  620  may be mounted on a detent base  622 . As shown in  FIGS.  7  and  8   , the detent base  622  may include grooves  624  in a back face thereof that is opposite the pinion  620 . One or more detent extensions  626  may be mounted to the HMD support frame  608  ( FIG.  6   ). In the embodiment shown, there are two detent extensions  626 , although a single detent extensions  626  or more than two detent extensions  626  may be used in additional embodiments. The detent extensions  626  may be biased (e.g., spring-loaded) toward the detent base  622  and positioned relative to at least one of the grooves  624  to protrude into the respective grooves  624  when the detent extensions  626  and the grooves  624  are aligned with each other. 
     For example, as shown in  FIGS.  7  and  8   , the detent extensions  626  may include a ball that is biased toward the detent base  622  by a coil spring  628 . However, the detent extensions  626  of the present disclosure are not limited to this configuration. In additional embodiments, the detent extensions  626  may have a cylindrical shape, a hemispherical shape, a pin shape, a shaft with a rounded end, a shaft with an angled end (e.g., having a triangular or trapezoidal longitudinal cross section), or any other suitable shape. In addition, the detent extension  626  may be biased toward the detent base  622  with a biasing element that is not a coil spring, such as a leaf spring, an elastomer, or another suitable biasing element. 
     The detent mechanism  614  may be configured to position the eyecups  602  at predetermined IPD settings. For example, the eyecups  602 ,  604  may be moved inward or outward by a user applying an inward or outward physical force directly on one or both of the eyecups  602 ,  604 . In additional embodiments, an IPD adjustment mechanism may be used, such as the IPD adjustment mechanism  140  described above with reference to  FIG.  1 A  or an electromechanical actuator. When the eyecups  602 ,  604  ( FIG.  6   ) are moved inward or outward, the first rack  616  and/or the second rack  618  may interact with the pinion  620  to rotate the pinion  620 . Rotation of the pinion  620  may in turn rotate the detent base  622 . As the detent base  622  rotates, the detent extensions  626  may be forced out of the respective grooves  624  against the biasing force applied by the coil spring  628 . As the detent base  622  continues to rotate, the detent extensions  626  may be biased into other adjacent grooves  624 , providing a tactile indication (e.g., a snap or click) to the user that the eyecups  602 ,  604  are at a predetermined IPD setting. The grooves  624  may be sized and spaced to correspond to a certain number of predetermined IPD settings, such as two (e.g., large and small), three (e.g., large, medium, and small), four, or five predetermined IPD settings. In one example, the grooves  624  may be sized and spaced to correspond to a first small IPD setting of about 58 mm measured between optical axes of the eyecups  602 ,  604 , a second medium IPD setting of about 63 mm, and a third large IPD setting of about 68 mm. 
     Referring again to  FIG.  6   , in some examples, the HMD assembly  600  may also include an IPD indicator  630  to provide an indication of the current IPD setting. For example, the IPD indicator  630  may include an aperture through a structure coupled to either the first eyecup  602  or the second eyecup  604 . Beneath the aperture, there may be a visual indication of the IPD setting. For example, the visual indication may include the letters S, M, and L corresponding to a small, medium, and large IPD setting. Other example visual indications may include numbers (e.g., 1 through 5 corresponding to five IPD settings, or 58, 63, and 68 corresponding to the IPD setting in millimeters, etc.), other letters (e.g., A through D corresponding to four IPD settings, “min,” “med,” and “max” corresponding to minimum, medium, and maximum IPD settings, etc.), colors (e.g., green, yellow, and red corresponding to three IPD settings, etc.), a diagram (e.g., showing eyes at different distances from each other, etc.), or combinations thereof. When the detent mechanism  614  is used to set the eyecups  602 ,  604  to one of the predetermined IPD settings, the aperture of the IPD indicator  630  may be aligned with one of the visual indications of the IPD settings, such that a user can view the visual indication through the aperture to determine the current IPD setting. 
     Even with the detent mechanism  614 , the HMD assembly  600  may benefit from a position sensor to accurately measure and/or verify the current IPD setting of the HMD assembly  600 .  FIG.  9    illustrates a portion of an HMD assembly  900  with an IPD position sensor  942 . In some respects, the HMD assembly  900  may be similar to the HMD assembly  600  of  FIG.  6   . For example, the HMD assembly  900  may include a first eyecup  902 , a second eyecup  904 , a single NED screen  905 , a track  906  along which the eyecups  902 ,  904  may be movable for adjusting an IPD setting, an HMD support frame  908 , a detent mechanism  914 , and an IPD indicator  930 . 
     The IPD position sensor  942  may be configured to sense a lateral position of one or both of the eyecups  902 ,  904  relative to each other and/or relative to the HMD support frame  908 . For example, the IPD position sensor  942  may include a Hall effect sensor, a rotary encoder, a linear encoder, or another suitable position sensor. In the example shown in  FIG.  9   , the IPD position sensor  942  is illustrated as a Hall effect sensor configured to sense a magnitude of a magnetic field of a moving magnet. The IPD position sensor  942  may include a probe  944  mounted to the HMD support frame  908  and a permanent magnet  946  mounted to one of the eyecups  902 ,  904 . When the eyecups  902 ,  904  are laterally moved, the permanent magnet  946  may move relative to the probe  944 . The movement of the permanent magnet  946  may result in a change in magnitude of a magnetic field sensed by the probe  944 . This change in magnitude sensed by the probe  944  may be correlated to a relative position between the probe  944  and the permanent magnet  946 , and ultimately to a relative position between the eyecups  902 ,  904 . The data from the IPD position sensor  942  may be used to determine the actual IPD setting of the eyecups  902 ,  904 , such as for use by software to adjust an image displayed on the single NED screen  905 , to provide an indication to the user of the IPD setting, etc. 
     In the embodiment illustrated in  FIG.  9   , the probe  944  is mounted on the HMD support frame  908  and the permanent magnet  946  is mounted on one of the eyecups  902 ,  904 . However, the present disclosure is not limited to this configuration. In additional embodiments, the probe  944  may be mounted on one of the eyecups  902 ,  904  and the permanent magnet  946  may be mounted on the HMD support frame  908 , or the probe may be mounted on one of the eyecups  902 ,  904  and the permanent magnet  946  may be mounted on the other of the eyecups  902 ,  904 . In yet further embodiments, the permanent magnet  946  may be replaced by a non-permanent magnet, such as an electromagnet. In additional embodiments, as noted above, the IPD position sensor  942  may be another type of position sensor other than a Hall effect sensor. 
       FIG.  10    is a flow diagram illustrating a method  1000  of fabricating an HMD assembly, according to at least one embodiment of the present disclosure. At operation  1010 , a first transparent component and a second transparent component may be positioned and hermetically sealed over a single NED screen to form an enclosure. Operation  1010  may be performed in a variety of ways. For example, the first transparent component may be positioned a first distance from the single NED screen and the second transparent component may be positioned a second, different distance from the single NED screen. In some embodiments, the hermetic seal may be accomplished with sealing structure that may couple the transparent components to the single NED screen. 
     At operation  1020 , a first eyecup supporting a first lens may be slidably positioned over the first transparent component. Operation  1020  may be performed in a variety of ways. For example, a first sealing element may be positioned between the first eyecup and the first transparent component. A first sliding interface may be between the first eyecup and the first sealing element or, alternatively, may be between the first transparent component and the first sealing element. 
     At operation  1030 , a second eyecup supporting a second lens may be slidably positioned over the second transparent component. Operation  1030  may be performed in a variety of ways. For example, a second sealing element may be positioned between the second eyecup and the second transparent component. A second sliding interface may be between the second eyecup and the second sealing element or, alternatively, may be between the second transparent component and the second sealing element. The first eyecup and the second eyecup may be movable relative to each other, such as to adjust for an IPD of a user of the HMD assembly. In some embodiments, the respective distances between the single NED screen and the first and second transparent components may be different, such as to allow flanges extending radially outward from the eyecups to at least partially overlap each other when an IPD setting of the eyecups is at its minimum operating position. 
     In some examples, the method  1000  may also include additional operations. For example, an IPD adjustment mechanism may be assembled to the first eyecup and to the second eyecup in a position to move the first eyecup and the second eyecup relative to each other, such as to adjust for an IPD. 
       FIG.  11    is a flow diagram illustrating a method  1100  of adjusting an interpupillary distance of an HMD assembly, according to at least one embodiment of the present disclosure. At operation  1110 , a first eyecup may be moved over a first transparent component that is positioned over a single NED screen. At operation  1120 , a second may be moved over a second transparent component that is positioned over the single NED screen. Operations  1110  and  1120  may be performed in a variety of ways. For example, the eyecups may be moved toward or away from each other to adjust for a user&#39;s IPD. The single NED screen, the first transparent component, and the second transparent component may define a hermetically sealed enclosure. 
     Accordingly, the present disclosure includes HMD assemblies and related methods that may enable IPD adjustments that inhibit (e.g., reduce or eliminate) the introduction of contamination onto a display screen. At the same time, the disclosed HMD assemblies may include a single NED screen, which may reduce a cost of fabricating and operating the HMD assemblies. Various configurations and materials are disclosed, each of which may be advantageously employed for a variety of uses and applications. 
     As noted above, embodiments of the present disclosure may include or be implemented in conjunction with various types of artificial-reality systems. Artificial-reality content may include video, audio, haptic feedback, or some combination thereof, any of which may be presented in a single channel or in multiple channels (such as stereo video that produces a three-dimensional (3D) effect to the viewer). Additionally, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof, that are used to, e.g., create content in an artificial reality and/or are otherwise used in (e.g., to perform activities in) an artificial reality. 
     Artificial-reality systems may be implemented in a variety of different form factors and configurations. Artificial-reality systems may include an NED that provides visibility into the real world (e.g., an augmented-reality system) or that visually immerses a user in an artificial reality (e.g., virtual-reality system  1200  in  FIG.  12   ). While some artificial-reality devices may be self-contained systems, other artificial-reality devices may communicate and/or coordinate with external devices to provide an artificial-reality experience to a user. Examples of such external devices include handheld controllers, mobile devices, desktop computers, devices worn by a user, devices worn by one or more other users, and/or any other suitable external system. 
     As noted, some artificial-reality systems may substantially replace one or more of a user&#39;s sensory perceptions of the real world with a virtual experience. One example of this type of system is a head-worn display system, such as the virtual-reality system  1200  in  FIG.  12   , that mostly or completely covers a user&#39;s field of view. The virtual-reality system  1200  may include a front rigid body  1202  and a band  1204  shaped to fit around a user&#39;s head. The virtual-reality system  1200  may also include output audio transducers  1206 (A) and  1206 (B). Furthermore, while not shown in  FIG.  12   , the front rigid body  1202  may include one or more electronic elements, including one or more electronic displays, one or more inertial measurement units (IMUS), one or more tracking emitters or detectors, and/or any other suitable device or system for creating an artificial reality experience. 
     Artificial-reality systems may include a variety of types of visual feedback mechanisms. For example, display devices in the virtual-reality system  1200  may include one or more liquid crystal displays (LCDs), light-emitting diode (LED) displays, organic LED (OLED) displays, and/or any other suitable type of display screen. As discussed above artificial-reality systems may include a single display screen for both eyes. Some artificial-reality systems may also include optical subsystems having one or more lenses (e.g., conventional concave or convex lenses, Fresnel lenses, adjustable liquid lenses, etc.) through which a user may view a display screen. 
     In addition to or instead of using display screens, some artificial-reality systems may include one or more projection systems. For example, display devices in the virtual-reality system  1200  may include micro-LED projectors that project light (using, e.g., a waveguide) into display devices, such as clear combiner lenses that allow ambient light to pass through. The display devices may refract the projected light toward a user&#39;s pupil and may enable a user to simultaneously view both artificial-reality content and the real world. Artificial-reality systems may also be configured with any other suitable type or form of image projection system. 
     Artificial-reality systems may also include various types of computer vision components and subsystems. For example, the virtual-reality system  1200  may include one or more optical sensors, such as two-dimensional (2D) or 3D cameras, time-of-flight depth sensors, single-beam or sweeping laser rangefinders, 3D LiDAR sensors, and/or any other suitable type or form of optical sensor. An artificial-reality system may process data from one or more of these sensors to identify a location of a user, to map the real world, to provide a user with context about real-world surroundings, and/or to perform a variety of other functions. 
     Artificial-reality systems may also include one or more input and/or output audio transducers. In the example shown in  FIG.  12   , the output audio transducers  1206 (A), and  1206 (B) may include voice coil speakers, ribbon speakers, electrostatic speakers, piezoelectric speakers, bone conduction transducers, cartilage conduction transducers, and/or any other suitable type or form of audio transducer. Similarly, input audio transducers may include condenser microphones, dynamic microphones, ribbon microphones, and/or any other type or form of input transducer. In some embodiments, a single transducer may be used for both audio input and audio output. 
     While not shown in  FIG.  12   , artificial-reality systems may include tactile (i.e., haptic) feedback systems, which may be incorporated into headwear, gloves, body suits, handheld controllers, environmental devices (e.g., chairs, floormats, etc.), and/or any other type of device or system. Haptic feedback systems may provide various types of cutaneous feedback, including vibration, force, traction, texture, and/or temperature. Haptic feedback systems may also provide various types of kinesthetic feedback, such as motion and compliance. Haptic feedback may be implemented using motors, piezoelectric actuators, fluidic systems, and/or a variety of other types of feedback mechanisms. Haptic feedback systems may be implemented independent of other artificial-reality devices, within other artificial-reality devices, and/or in conjunction with other artificial-reality devices. 
     By providing haptic sensations, audible content, and/or visual content, artificial-reality systems may create an entire virtual experience or enhance a user&#39;s real-world experience in a variety of contexts and environments. For instance, artificial-reality systems may assist or extend a user&#39;s perception, memory, or cognition within a particular environment. Some systems may enhance a user&#39;s interactions with other people in the real world or may enable more immersive interactions with other people in a virtual world. Artificial-reality systems may also be used for educational purposes (e.g., for teaching or training in schools, hospitals, government organizations, military organizations, business enterprises, etc.), entertainment purposes (e.g., for playing video games, listening to music, watching video content, etc.), and/or for accessibility purposes (e.g., as hearing aids, visuals aids, etc.). The embodiments disclosed herein may enable or enhance a user&#39;s artificial-reality experience in one or more of these contexts and environments and/or in other contexts and environments. 
     As noted, the artificial-reality system  1200  may be used with a variety of other types of devices to provide a more compelling artificial-reality experience. These devices may include haptic interfaces with transducers that provide haptic feedback and/or that collect haptic information about a user&#39;s interaction with an environment. The artificial-reality systems disclosed herein may include various types of haptic interfaces that detect or convey various types of haptic information, including tactile feedback (e.g., feedback that a user detects via nerves in the skin, which may also be referred to as cutaneous feedback) and/or kinesthetic feedback (e.g., feedback that a user detects via receptors located in muscles, joints, and/or tendons). 
     Haptic feedback may be provided by interfaces positioned within a user&#39;s environment (e.g., chairs, tables, floors, etc.) and/or interfaces on articles that may be worn or carried by a user (e.g., gloves, wristbands, etc.). As an example, a vibrotactile system may be in the form of a wearable glove and/or wristband. The haptic device may include a flexible, wearable textile material that is shaped and configured for positioning against a user&#39;s hand and wrist, respectively. This disclosure also includes vibrotactile systems that may be shaped and configured for positioning against other human body parts, such as a finger, an arm, a head, a torso, a foot, or a leg. By way of example and not limitation, vibrotactile systems according to various embodiments of the present disclosure may also be in the form of a glove, a headband, an armband, a sleeve, a head covering, a sock, a shirt, or pants, among other possibilities. In some examples, the term “textile” may include any flexible, wearable material, including woven fabric, non-woven fabric, leather, cloth, a flexible polymer material, composite materials, etc. 
     Haptic wearables may be implemented in a variety of types of artificial-reality systems and environments.  FIG.  13    shows an example artificial-reality environment  1300  including one head-mounted virtual-reality display and two haptic devices (i.e., gloves), and in other embodiments any number and/or combination of these components and other components may be included in an artificial-reality system. For example, in some embodiments there may be multiple head-mounted displays each having an associated haptic device, with each head-mounted display and each haptic device communicating with the same console, portable computing device, or other computing system. 
     Head-mounted display  1302  generally represents any type or form of virtual-reality system, such as the virtual-reality system  1200  in  FIG.  12   . Haptic device  1304  generally represents any type or form of wearable device, worn by a use of an artificial-reality system, that provides haptic feedback to the user to give the user the perception that he or she is physically engaging with a virtual object. In some embodiments, the haptic device  1304  may provide haptic feedback by applying vibration, motion, and/or force to the user. For example, the haptic device  1304  may limit or augment a user&#39;s movement. To give a specific example, the haptic device  1304  may limit a user&#39;s hand from moving forward so that the user has the perception that his or her hand has come in physical contact with a virtual wall. In this specific example, one or more actuators within the haptic advice may achieve the physical-movement restriction by pumping fluid into an inflatable bladder of the haptic device. In some examples, a user may also use the haptic device  1304  to send action requests to a console. Examples of action requests include, without limitation, requests to start an application and/or end the application and/or requests to perform a particular action within the application. 
     The haptic devices  1304  may include any suitable number and/or type of haptic transducer, sensor, and/or feedback mechanism. For example, the haptic devices  1304  may include one or more mechanical transducers, piezoelectric transducers, and/or fluidic transducers. The haptic devices  1304  may also include various combinations of different types and forms of transducers that work together or independently to enhance a user&#39;s artificial-reality experience. 
     By way of non-limiting examples, the following embodiments are included in the present disclosure. 
     Example 1: A head-mounted display assembly, which may include: a first eyecup and a second eyecup configured for respectively positioning a first lens and a second lens in front of intended locations of a user&#39;s eyes when the head-mounted display assembly is donned by the user; a single near-eye display screen configured for displaying an image to the user through the first eyecup and the second eyecup; and an enclosure over the single near-eye display screen, the enclosure including: a first transparent component positioned between the first lens and the single near-eye display screen; and a second transparent component positioned between the second lens and the single near-eye display screen, wherein the first eyecup and the second eyecup are movable relative to each other and relative to the first transparent component and the second transparent component to adjust for an interpupillary distance of the user&#39;s eyes. 
     Example 2: The head-mounted display assembly of Example 1, wherein at least one of the first eyecup or the second eyecup is movable relative to the single near-eye display screen. 
     Example 3: The head-mounted display assembly of Example 1 or Example 2, wherein the first transparent component is positioned a first distance from the single near-eye display screen and the second transparent component is positioned a second distance from the single near-eye display screen, wherein the second distance is less than the first distance. 
     Example 4: The head-mounted display assembly of Example 3, wherein each of the first distance and the second distance is in a range of about 10 mm to about 20 mm. 
     Example 5: The head-mounted display assembly of Example 3 or 4, wherein a difference between the first distance and the second distance is at least about 2 mm. 
     Example 6: The head-mounted display assembly of any of Examples 1 through 5, wherein the first transparent component and the second transparent component may include at least one of: a polymer material; a glass material; or a crystalline material. 
     Example 7: The head-mounted display assembly of any of Examples 1 through 6, wherein the enclosure may include a hermetically sealed enclosure defined over the single near-eye display screen and under the first transparent component and the second transparent component. 
     Example 8: The head-mounted display assembly of any of Examples 1 through 7, wherein the first transparent component and the second transparent component are positioned a distance from the single near-eye display screen such that contaminants disposed on the first transparent component and the second transparent component are substantially out-of-focus to a user viewing the single near-eye display screen through the first lens and the second lens. 
     Example 9: The head-mounted display assembly of any of Examples 1 through 8, which may further include a first sealing element positioned between the first eyecup and the first transparent component and a second sealing element positioned between the second eyecup and the second transparent component. 
     Example 10: The head-mounted display assembly of Example 9, wherein a first sliding interface is between the first sealing element and the first transparent component and a second sliding interface is between the second sealing element and the second transparent component. 
     Example 11: The head-mounted display assembly of Example 9, wherein a first sliding interface is between the first sealing element and the first eyecup and a second sliding interface is between the second sealing element and the second eyecup. 
     Example 12: The head-mounted display assembly of any of Examples 9 through 11, wherein each of the first sealing element and the second sealing element may include at least one of: an elastomeric material; or a closed-cell foam material. 
     Example 13: The head-mounted display assembly of any of Examples 1 through 12, wherein: the first eyecup may include a first sidewall and a first flange extending radially outward from the first sidewall adjacent to the first transparent component; and the second eyecup may include a second sidewall and a second flange extending radially outward from the second sidewall adjacent to the second transparent component. 
     Example 14: The head-mounted display assembly of any of Examples 1 through 13, which may further include an interpupillary distance adjustment mechanism coupled to the first eyecup and to the second eyecup for adjusting a distance between the first eyecup and the second eyecup. 
     Example 15: The head-mounted display assembly of Example 14, which may further include a detent mechanism configured to maintain a relative position of the first eyecup and the second eyecup after an adjustment is made for the interpupillary distance of the user&#39;s eyes. 
     Example 16: The head-mounted display assembly of any of Examples 1 through 15, wherein the first eyecup and the second eyecup are movable relative to each other over a distance of up to about 10 mm. 
     Example 17: A method of fabricating a head-mounted display assembly, which may include: hermetically sealing a first transparent component and a second transparent component over a single near-eye display screen to form an enclosure; slidably positioning a first eyecup supporting a first lens over the first transparent component; and slidably positioning a second eyecup supporting a second lens over the second transparent component, wherein the first eyecup and the second eyecup are positioned to move relative to each other and relative to the first transparent component and the second transparent component to adjust for an interpupillary distance of a user&#39;s eyes when the head-mounted display assembly is donned by the user. 
     Example 18: The method of Example 17, which may further include: positioning a first sealing element between the first eyecup and the first transparent component; and positioning a second sealing element between the second eyecup and the second transparent component. 
     Example 19: The method of Example 17 or 18, which may further include positioning the first transparent component at a first distance from the single near-eye display screen and positioning the second transparent component at a second distance from the single near-eye display screen, wherein the second distance is less than the first distance. 
     Example 20: An artificial-reality device, which may include: a first eyecup including a first lens; a second eyecup including a second lens, wherein the first eyecup and the second eyecup are movable relative to each other to adjust for an interpupillary distance of a user&#39;s eyes; a single near-eye display screen configured for displaying an image to the user through the first eyecup and the second eyecup; at least one processor configured for rendering the image for display on the single near-eye display screen; and an enclosure over the single near-eye display screen, the enclosure including: a first transparent component positioned between the first lens and the single near-eye display screen; and a second transparent component positioned between the second lens and the single near-eye display screen, wherein the first transparent component and the second transparent component are stationary relative to the single near-eye display screen. 
     Example 21: A method of adjusting an interpupillary distance of a head-mounted display assembly, which may include: moving a first eyecup over a first transparent component that is positioned over a single near-eye display screen; and moving a second eyecup over a second transparent component that is positioned over the single near-eye display screen, wherein the single near-eye display screen, the first transparent component, and the second transparent component define a hermetically sealed enclosure. 
     The process parameters and sequence of the steps described and/or illustrated herein are given by way of example only and can be varied as desired. For example, while the steps illustrated and/or described herein may be shown or discussed in a particular order, these steps do not necessarily need to be performed in the order illustrated or discussed. The various example methods described and/or illustrated herein may also omit one or more of the steps described or illustrated herein or include additional steps in addition to those disclosed. 
     The preceding description has been provided to enable others skilled in the art to best utilize various aspects of the example embodiments disclosed herein. This example description is not intended to be exhaustive or to be limited to any precise form disclosed. Many modifications and variations are possible without departing from the spirit and scope of the present disclosure. The embodiments disclosed herein should be considered in all respects illustrative and not restrictive. Reference should be made to the appended claims and their equivalents in determining the scope of the present disclosure. 
     Unless otherwise noted, the terms “connected to” and “coupled to” (and their derivatives), as used in the specification and claims, are to be construed as permitting both direct and indirect (i.e., via other elements or components) connection. In addition, the terms “a” or “an,” as used in the specification and claims, are to be construed as meaning “at least one of.” Finally, for ease of use, the terms “including” and “having” (and their derivatives), as used in the specification and claims, are interchangeable with and have the same meaning as the word “comprising.”