Abstract:
An alignment tool for fitting a helmet to a wearer&#39;s hear and aligning helmet mounted visual display systems to the wearer&#39;s eyes in a reproducible manner. The alignment tool includes latch points that are connected to corresponding connection points on the helmet. These connection points are also the connection points for the helmet mounted visual display systems. The alignment tool allows for accurate measurement, alignment and fitting of the helmet to the wearers head based on the special relationship between the connection points and the wearer&#39;s eye. Once the helmet is fitted using the alignment tool, the helmet mounted visual display systems are connected to the helmet connection points and the wearer&#39;s eyes are substantially aligned for use with the visual display system.

Description:
RELATED APPLICATION 
     This application is a Divisional of U.S. patent application Ser. No. 09/640,442 now U.S. Pat. No. 6,292,953 B1 filed Aug. 17, 2000. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to helmet mounted visual display systems, and more particularly, to an alignment tool and method for fitting a helmet to a user for accurate alignment with the helmet mounted visual display systems. 
     BACKGROUND OF THE INVENTION 
     Various forms of military helmets are known according to the prior art. These helmets are constructed to protect the wearer&#39;s head against injury while providing communication and life support. In addition modern combat requires military personnel to utilize certain helmet-mounted electronic systems, for example night vision systems and helmet mounted displays. 
     A problem arises when military personnel need to train with different electronic systems, for example, outer helmet mounted displays for several types of aircraft. These displays have exacting requirements for positioning relative to the wearer&#39;s eyes. It has been determined that custom fitted inner helmets are necessary to meet such requirements. However, the outer helmets are too costly to custom fit every crewmember which will maintain or fly the aircraft. 
     Ideally, a custom fit inner helmet is provided to each individual. For example, an Inner Helmet Assembly pursuant to U.S. Pat. No. 5,584,073. 
     In order to properly position the inner helmet during custom fitting, a positioning fixture, as disclosed herein, may be utilized. The positioning fixture utilizes the latch assembly of the invention to attach to the inner helmet in the same manner as the ultimate outer helmet. The positioning fixture custom aligns the latch points on the inner helmet for each individual. The custom fittings are then secured to maintain the alignment in a reproducible manner. Accordingly, every custom fitted inner helmet provides a standard platform. 
     The outer helmets are then equipped with a uniform capture configuration to attach onto this standard platform via the latch assembly of the invention. 
     SUMMARY OF THE INVENTION 
     It is therefore a primary object of the present invention to provide a uniform capture assembly disposed on an outer device to latch onto a standard platform of an inner helmet. 
     It is another object of the present invention to provide a mounting surface on the outer device that assumes a predetermined orientation with respect to the inner helmet platform. 
     It is a further object of the invention to define a path for the outer device to follow during installation onto the inner helmet. 
     It is a further object of the invention to provide latch clearances that facilitate engagement and disengagement of the latch components. 
     It is another object of the invention to provide locking means for releasably securing an outer helmet onto the inner helmet. 
     These and other related objects are achieved according to an embodiment of the invention by providing a pair of strikers on flat temple panels of an inner helmet. An outer device or helmet includes a pair of inwardly-facing mounting surfaces that face the temple panels in the installed position. Ideally, the temple panels and mounting surfaces are all substantially parallel to each other. An arcuate channel assembly or track is disposed on each mounting surface for capturing a striker. The arc of the channel assembly corresponds to the curve generated by pivoting the outer device from front-to-back over a crown portion of the inner helmet into an installed position. For locking, quarter-turn fasteners located on the outer helmet may extend through holes in the lower, rear portion of the inner helmet to engage an interiorly-secured retention bar. 
     The channel assembly includes a base portion disposed adjacent the mounting surface, a central spacer portion and an upper portion. The tip end of the striker slidingly contacts the base portion during mounting of the outer helmet. The central spacer portion comprises a pair of arms spaced from the striker head by a distance D. The upper portion comprises a pair of rails spaced from the striker neck by a distance d that is less than D. The rails guide the neck portion along the length of the channel assembly and keep the head out of contact with the central spacer portion. The head and neck portions of the striker have a generally T-shaped cross-sectional profile. A concavity on the head or neck portion slidingly contacts facing regions of the upper portion. 
     The interchangeable latch system according to the invention is fitted for an outer helmet mounted display as follows. The inner helmet is placed onto the user and the internal fittings, straps, pads and/or cushions are adjusted to an approximate fit. The fitting fixture is installed onto the strikers. The fitting fixture includes fixed alignment guides that are used to view the user&#39;s eyes along an eye line E L  that is tangent to both of the front eyeball surfaces. Once aligned the connection line C L  of the strikers is parallel to and separated from the eye line E L  by a known and preset first vector V 1  that is the same for all users. 
     An outer helmet display has a desired viewing distance V D  from the users eyes. The outer helmet possesses a latch line L L  that will be coincident with the inner helmet connection line C L . The distance between the outer helmet latch line L L  and the display is defined by a second vector V 2 . The viewing distance V D  is equal to V 2  minus V 1 . Once V 1  is established, the second vector V 2  can be adjusted to obtain any desired viewing distance V D . 
     The inner helmet connection line C L  is located in the quadrant above and rearwardly of the viewer&#39;s eyeballs. In the vertical direction, C L  is generally between the viewer&#39;s eyes and the top of the head. The connection points comprise left and right connection points which are disposed in corresponding left and right vertical planes which are outwardly spaced from the viewer&#39;s head. The latch points comprise left and right latch points which pivot within corresponding left and right vertical planes which are outwardly spaced from the viewer&#39;s head. The viewing distance V D  may extend along a horizontal line of sight wherein E L  is perpendicular to V D . Where the first and second vectors V 1  and V 2  are in a common plane with the line of sight, V 1  and V 2  are perpendicular to E L . 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings to which reference is made in the instant specification and which are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views: 
     FIG. 1A is a left-front-top side perspective view of an inner and outer helmet equipped with a latch assembly according to the invention; 
     FIG. 1B is a left-front-top side perspective view of the outer helmet initially engaging the inner helmet latch component; 
     FIG. 1C is a left-front-top side perspective view of the outer helmet fully installed on the inner helmet; 
     FIG. 2A is a front-lower-left side perspective view of an embodiment of a striker adapted for mounting to the inner helmet; 
     FIG. 2B is an exploded view of an embodiment of an arcuate channel assembly that is adapted for mounting to an outer device; 
     FIG. 3 is a cross-sectional view of the engaged latch taken along the line III—III from FIG. 1C; and 
     FIG. 4 is a left-front-top side perspective view of an embodiment of a positioning fixture adapted for mounting on to the striker of the inner helmet. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now in detail to the drawings, and in particular FIGS. 1A,  1 B and  1 C, there is shown a series of views illustrating mounting of an outer helmet  30  onto an inner helmet  10 . The inner helmet may be of any type designed for a two-part helmet, for example, a custom-fitted inner helmet assembly. Once properly fitted, the inner helmet operates as a standard platform for mounting various types of outer helmets. The mechanism for obtaining this standard platform on the inner helmet is the interchangeable latch assembly and fitting fixture of the invention. Thus, a highly specialized or very expensive outer helmet can be mounted onto many different custom-fitted inner helmets. 
     Inner helmet  10  includes a front forehead dome  11  that generally overlies the wearer&#39;s forehead. On each side of front forehead dome  11  there is one temple panel  12 . The left side temple panel  12 , as viewed from the wearer&#39;s perspective, is shown in FIG.  1 A. The temple panels are generally located above, forwardly and outwardly from the wearer&#39;s temples. The temple panels are flat surfaces, generally parallel to each other. A striker  14  is mounted onto each flat temple panel  12 . 
     A crown portion  16  is disposed behind front forehead dome  11 . Inner helmet  10  also includes a rear portion  18  which has an aperture  20  formed therein for exposing a section of an internally secured retention bar  22 . Crown portion  16  and other internal fittings, pads, straps and/or cushions may be adjusted to alter the position at which inner helmet  10  sits on the wearer&#39;s head. Fitting is facilitated by the use of an alignment fixture  60  illustrated in FIG. 4, which will be discussed in greater detail below. More particularly, fitting consists of aligning strikers  14  to a predetermined location and orientation with respect to the wearer&#39;s eyes. 
     As can be seen in FIG. 2A, striker  14  includes a dome-shaped base  14   a  provided with three threaded bores, for example. Machine screws with suitable sized heads extend from the inside of inner helmet  10  through correspondingly sized holes in temple panel  12  and are screwed into the bores on base  14   a.  In the embodiment shown the central part of the striker base  14   a  extends upwardly into a neck  14   b  that terminates in a head  14   e.    
     The interior of outer helmet  30  is provided with a mounting surface  32  in the forward part of outer helmet  30 . One mounting surface is provided on either side. The mounting surfaces generally face each other and are generally parallel to each other. An arcuate track or channel assembly  34  is secured onto each mounting surface  32 . As can be seen in FIG. 2B, arcuate channel assembly  34  consists generally of a base portion  34   a,  a central spacer portion  34   e  and an upper portion  34   i.  Components  34   a,    34   e  and  34   i  include apertures in registration with each other. In the embodiment shown, each component has three apertures in a triangular configuration to accommodate screws. The screws pass through the components and are secured into mounting surface  32 . 
     Base portion  34   a  includes a rear-side  34   b  that is in contact with mounting surface  32 . The front side  34   c  faces central spacer portion  34   e  and includes a contact region  34   d.  The central spacer portion  34   e  includes a pair of arms  34   f ( 1 ) and  34   f ( 2 ) distanced from each other by a nominal arm spacing  34   g.  Upper portion  34   i  includes a pair of rails  34   m ( 1 ) and  34   m ( 2 ) separated by a slot  34   j  which overlies the gap between rails  34   f ( 1 ) and  34   f ( 2 ). The width of slot  34   j  is designated as the nominal rail spacing  34   k.    
     As can be seen in FIGS. 1A,  1 B and  1 C, the arcuate channel assembly is oriented on mounting surface  32  so that striker  14  is able to enter the open end of slot  34   j  in the position illustrated in FIG.  1 B. Rail  34   m ( 1 ) is the shorter rail and is provided with a smooth rounded end to allow neck  14   b  to easily slide past it as outer helmet  30  is moved downwardly over inner helmet  10 . Rail  34   m ( 2 ) is the longer rail and is designed to engage neck  14   b  and guide it in the direction of the arrow for reference numeral  34   j.  Slot  34   j  has the shape of an arc  36  that conforms to the shape of a curve  38 . Outer helmet  30  follows curve  38  during mounting as the outer helmet pivots into the fully installed position illustrated in FIG.  1 C. During the movement between FIGS. 1B and 1C, striker  14  is guided through slot  34   j  into the terminal position at the base of slot  34   j.    
     FIG. 3 illustrates the spacing between various portions of striker  14  and arcuate channel assembly  34 . Striker  14  includes a neck  14   b  having a neck diameter  14   c  and a head  14   e  having a head diameter  14   f.  Between neck  14   b  and upper portion  34   i  there is provided a radial neck clearance  14   d  on the order of magnitude of several thousandths of an inch. Radial neck clearance  14   d  is also referred to as d. These distances relate to nominal rail spacing  34   k  from FIG. 2B as follows: 
     
       
           34   k = 14   c +(2× 14   d ) 
       
     
     or 
     
       
           34   k = 14   c +(2 ×d ) 
       
     
     In contrast, a radial head clearance  14   g  is significantly larger, on the order of magnitude of several hundredths of an inch. Radial head clearance  14   g  is also referred to as D. These distances relate to nominal are spacing  34   g  as follows: 
     
       
           34   g = 14   f +(2× 14   g ) 
       
     
     or 
     
       
           34   g = 14   f +(2 ×D ) 
       
     
     The relative difference in clearances  14   d  (aka d) and  14   g  (aka D) insures that head  14   e  will avoid radial contact with arms  34   f  of central spacer portion  34   e  during mounting and removing of outer helmet  30 . This relationship may be represented as follows: 
     
       
           14   g &gt; 14   d   
       
     
     or 
     
       
         
           D&gt;d 
         
       
     
     Accordingly, contact and frictional resistance in the radial direction will only occur between neck  14   b  and upper portion  34   i.  In order to minimize the aforementioned friction, striker  14  is made from a different metallic material than upper portion  34   i  or one of the components is provided with a metallic coating different than the other component. In addition neck  14   b  may be provided with a concave chamfer, as shown in dotted line, to reduce the radial contact area from a line to two points. 
     In the left-right direction of the drawing three clearances are specified between striker  14  and upper portion  34 i and contact region  34   d  of arcuate channel assembly  34 . Clearances  13   b  and  13   c  may be of the same distance, on the order of magnitude of several thousandths of an inch. These distances relate to the overall head height as follows: 
     
       
         Height of Head  14   e  (measured left-to right)= 34   h − 13   b − 13   c   
       
     
     Clearance  13   a  is approximately twice that of either  13   b  or  13   c,  on the order of magnitude of hundredths of an inch. All three clearances  13   a,    13   b  and  13   c  are measured with striker  14  centrally positioned in the left-right direction, as illustrated. As a result, the relatively large surface area of base dome  14   a  is restricted from contacting the facing surface of upper portion  34   i.  Rather, any left-right movement of striker  14  would result in head  14   e  contacting either upper portion  34   i  or base portion  34   a.  To minimize the contact areas, the left side of head  14   e  that faces upper portion  34   i  is provided with a concave chamfer, as illustrated in the drawing in dotted line. The top of head  14   e  that faces base portion  34   a  is provided with a convex or dome shaped profile, also illustrated in the drawing in dotted line. Accordingly, upon leftward movement of striker  14 , head  14   e  would contact upper portion  34   i  along an arc shaped line. Upon displacement of striker  14  to the right, a small circular patch of head  14   e  would slide along contact region  34   d  of base portion  34   a.    
     Initially the degree of frictional contact between striker  14  and arcuate channel assembly  34  depends upon the proper spacing of the striker and arcuate channel mounting surfaces on inner helmet  10  and outer helmet  30 , respectively. In addition, the mounting surfaces must be parallel to each other so that the clearances are maintained during pivoting of the outer helmet during installation. 
     FIG. 4 shows a perspective view of an alignment tool  60  for assisting in the helmet fitting process for mounting and aligning helmet visual display systems according to an embodiment of the invention. Alignment tool  60  includes side arms  62  and an inter pupilary distance (IPD) scale  66  that connects the two side arms in a U-shape configuration. Each side arm  62  includes at least one latch point  64 ,  34  on an internal side thereof, and a sighting reticle  70 . The IPD scale  66  includes two slidably mounted front sighting/alignment guides  68   r  and  68   l  and an eye relief adjuster  72 . IPD scale  66  ordinarily includes measurement markings (not shown) that allow the exact measurement of the helmet wearer&#39;s IPD when sighting reticles  68   r  and  68   l  are aligned with the user&#39;s pupils. 
     The latch points  64  enable tool  60  to attach to respective connection points on a helmet. These connection points are also the connection points for the helmet mounted visual display system. Thus, the connection points on which latch points  64  connect, operate to fix a frame of reference for the alignment of the visual system with the respective helmet wearers eyes. Those of ordinary skill will recognize that the configuration of latch points  64  can change to accommodate various helmet connection points for different applications without departing from the spirit of the invention. 
     When alignment tool  60  is mounted on a helmet using latch points  64 , the left and right side sighting reticles  70  are used to align the helmet with respect to the user&#39;s eyeballs Eye relief adjuster  72  can be used to move the helmet fore and aft with respect to the user&#39;s head in order to obtain the required tangential alignment with the front surface of the user&#39;s eyeballs. The eye line E L  (described later) further describes this alignment. Once the fore/aft alignment has been made, the IPD measurement can be taken using front sighting reticles  68   r  and  68   l  and IPD scale  66 . Once the helmet has been aligned using the alignment tool  60 , the helmet is sized to that wearer so that the obtained alignment with the wearer&#39;s eye is replicated every time they don their helmet. 
     The interchangeable latch system according to the invention is installed and used as follows. To begin the custom fitting procedure, the user dons inner helmet  10  equipped with strikers  14 . Alignment fixture  60  is mounted onto the strikers in the exact same manner as an outer helmet. The internal fittings, strap, pads, and/or cushions on inner helmet  10  are adjusted until the eye alignment line E L  becomes tangentially aligned with to the front portion of the user&#39;s eyeballs. The left/right eye alignment guides  68   r  and  68   l  are used to insure that alignment line E L  is centered on the eyeball in the vertical direction. This establishes a first vector V 1  between a connection line C L  extending through the strikers and alignment line E L . The internal fittings, straps, pads, and/or cushions of inner helmet  10  are then tightened or secured to insure that this alignment is always reproduced whenever the inner helmet is donned. 
     By this fitting procedure, the inner helmets are custom fitted to their respective users. If necessary, several sizes of inner helmets may be provided to accommodate a large anthropometric range of users. The strikers on the various custom fitted helmets, then provide a standard platform onto which an outer helmet can be mounted. The standardization consists of vector V 1  being the same for all users. 
     Both arcuate channel assemblies  34  are installed onto outer helmet  30  so that slots  34   j  are oriented approximately horizontally when the helmet is upright. As outer helmet  30  is dropped down on to inner helmet  10 , both strikers  14  pass beyond lower rails  34   f.  Necks  14   b  of the strikers then contact upper rails  34   m ( 2 ) of upper portion  34   i.  Outer helmet  30  is rotated rearwardly over a crown portion of the inner helmet. When the outer helmet reaches the terminal position shown in FIG. IC, fasteners  40  are actuated to prevent inadvertent forward pivoting of outer helmet  30 . 
     Once installed the latch line L L  of arcuate channel assembly  34  becomes aligned with the connection line C L  of striker  14 . A second vector V 2  extends from the latch line L L  to a viewing surface or display S. The user&#39;s viewing distance V D  is the difference in magnitude of the two vectors (V 2 −V 1 ). If the display is oriented horizontally outward from the viewer&#39;s eyeballs, then the difference between the vectors V D  would only possess a horizontal component. Accordingly, if V 1  is known from alignment fixture  60 , then arcuate channel assemblies  34  can be mounted onto outer helmets at a distance V 2  from display surfaces S to achieve a desired viewing distance V D . 
     It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of our claims. For example, the appended method claims include configurations wherein an arcuate channel assembly or other structure is mounted on the inner helmet and/or a striker or other structure is mounted on the outer device. It is further obvious that various changes may be made in details within the scope of our claims without departing from the spirit of our invention. It is, therefore, to be understood that our invention is not to be limited to the specific details shown and described.