A method is disclosed of installing a barrier device at a passageway. The method includes attaching a barrier housing containing a retractable barrier to a structural element on one side of the passageway, extending the barrier a desired distance from the barrier housing, with the barrier so extended, setting an extension limit of the barrier to prevent subsequent extension of the barrier beyond the desired distance from the barrier housing and, with the extension limit set, retracting the barrier into the housing. The set extension limit can permit subsequent retraction and re-extension of the barrier up to the set extension limit.

BACKGROUND 
     The invention relates to child safety barriers, such as are placed across doorways to protect children. 
     Safety gates are found in interior doorways in the homes of many people with infants or small children. Some such gates are rigidly mounted to one side of a passage and can swing open. Others, for example, are secured by pressure against a doorframe, and removed entirely to allow passage. Still others, for example Sandsborg, U.S. Pat. No. 5,690,317, have suggested expanding a flexible barrier across a doorway to act as a safety gate for children. Improvements in manufacturability and ease of use are desired for such gates. 
     SUMMARY OF THE INVENTION 
     The invention features a flexible barrier-type safety gate that can be readily adjusted to set a maximum extension width when mounting the gate in position. 
     In one broad aspect a method of installing a barrier device at a passageway is disclosed that includes attaching a barrier housing to a structural element on one side of the passageway, the barrier housing containing a retractable barrier that is extendable across the passageway, extending the barrier a desired distance from the barrier housing, with the barrier so extended, setting an extension limit of the barrier to prevent subsequent extension of the barrier beyond the desired distance from the barrier housing, the extension limit permitting subsequent retraction and re-extension of the barrier up to the set extension limit, and with the extension limit set, retracting the barrier into the housing. The method may also include attaching a receptacle housing with a receptacle capable of mating to a latching device on the barrier and re-extending the barrier to engage the latching device with the receptacle to prevent the barrier from inadvertently retracting. Setting the extension limit of the barrier can include positioning an adjustable stop so that it contacts a stop member coupled to the barrier to impede subsequent movement of the barrier stop member beyond that position. The barrier can be coupled at one edge to a shaft, and the barrier stop member can include a shaft gear secured to the shaft and coupled to a stop gear. The stop gear can be configured to rotate less than 360 degrees when the barrier is extended from a fully retracted position to a fully extended position and can be configured to rotate less than 360 degrees for each full rotation of the shaft. The stop gear may be coupled to the shaft gear through an intermediate gear, with the shaft gear and the intermediate gear defining a first reduction ratio that is between about 1:1 and 20:1, that is more preferably between about 2:1 and 7:1 and that is most preferably about 3.25:1, and the intermediate gear and the stop gear defining a second reduction ratio that is between about 1:1 and 20:1, that is more preferably between about 2:1 and 7:1 and that is most preferably about 3.25:1. The first and second reduction ratios can be combined to define a total reduction ratio that is between about 5:1 and 20:1 and that is more preferably about 10.25:1. The adjustable stop position may be adjusted by positioning might adjustment knob that is exposed for manual manipulation by an operator. The adjustment knob can be rotatable about an axis to a selectable position thereby setting a desired position of the adjustable stop. 
     In a second broad aspect, an adjustable width child safety device is disclosed that includes a housing mountable to a surface on one side of a passageway, a main shaft coupled to the housing for rotation about an axis, a flexible barrier secured to the main shaft at an inner edge of the barrier, the barrier being extendable across the passageway to inhibit passage by a child and an extension limiter coupling a first end of the main shaft to the housing. The extension limiter includes an adjustable stop configured to be secured to the housing in any of a multiplicity of selectable positions, and a barrier stop member coupled to the main shaft to rotate as the shaft turns. The barrier stop member is positioned to engage the adjustable stop as the barrier is extended with the adjustable stop secured in a selected position, thereby limiting further extension of the barrier from the housing, while permitting subsequent retraction and re-extension of the barrier up to an extension limit set by the selected position of the adjustable stop. The barrier stop member can include a shaft gear secured to the main shaft, and a stop gear coupled to the shaft gear. The stop gear can include a discrete stop surface defining a rotational limit of the shaft, the stop surface being positioned to engage the adjustable stop thereby impeding rotation of the stop gear with respect to the housing. The stop gear can be constructed to rotate less than 360 degrees for each full rotation of the shaft. The stop gear can be coupled to the shaft gear through an intermediate gear, the shaft gear and the intermediate gear defining a first reduction ratio, and the intermediate gear and the stop gear defining a second reduction ratio. The first and second reduction ratios combine to define a total reduction ratio that is between about 5:1 and 20:1 but is more preferably about 10.25:1. The total reduction ratio can be such that the stop gear rotates less than 360 degrees as the barrier is extended from a fully retracted position to a fully extended position. Each of the first and second reduction ratios can be between about 1:1 and 20:1 but is more preferably between about 2:1 and 7:1 and is most preferably about 3.25:1. 
     The adjustable stop can include an adjustment knob exposed for manual manipulation by an operator to set the adjustable stop in a desired position. The adjustment knob can be rotatable about an axis to a multiplicity of selectable positions, each selectable position corresponding to a selectable position of the adjustable stop. The adjustable width child safety device can further include a lock positioned to engage the adjustable stop and to prevent adjustment of a selected position of the adjustable stop until the lock is released. 
     The adjustable width child safety device can also include a spring load assembly coupling the barrier to the housing and biasing the barrier position toward a retracted position. The spring loading assembly can include a stationary shaft at least partially contained within the main shaft and securely attached to the housing. A torsion spring can be disposed between the stationary shaft and the rotatable main shaft, and can have a first end that is securely attached to the stationary shaft and a second end securely attached to the main shaft. The width of the flexible barrier, perpendicular to its direction of extension, can range from about 1 to 4 feet. 
     The adjustable width child safety device also can include a latch housing mountable to a surface on an opposite side of the passageway and defining a latch receptacle for receiving and releasably securing a latch assembly that is secured to an outer edge of the barrier. The latch assembly can include a latch release trigger operable to withdraw a locking tab from a slot in the latch housing and a trigger lock having an adjustable position to either enable or prevent the latch release trigger from withdrawing the locking tab from the slot in the latch housing. The latch release trigger and the trigger lock may be simultaneously operated using a single hand. Typically the barrier can extend from the housing to a distance between about 12 inches and 72 inches or more preferably between about 24 and 51 inches. The barrier can be a flexible sheet void of holes there through larger than 1 square inch in area or a mesh sheet. 
     In yet another broad aspect, an adjustable width child safety device is disclosed that includes a housing mountable to a surface on one side of a passageway, a main shaft having a first end and a second end, each end being coupled to the housing and allowing rotation of the main shaft about an axis, a flexible barrier secured to the main shaft at one edge of the barrier, and extendable across the passageway to inhibit passage by a child, an extension limiter coupling the first end of the main shaft to the housing, the extension limiter including a movable member with a shaft gear secured to the main shaft, an intermediate gear coupled to the shaft gear, and a stop gear coupled to the intermediate gear, the stop gear comprising a rotation limiting flag and configured to rotate less than 360° for each rotation that the main shaft makes, and a fixed member with a rotation limiting flag stop having an adjustable position, positionable to impede the motion of the stop gear, thereby, setting a rotational limit of the main shaft with respect to the housing while permitting subsequent retraction and re-extension of the barrier up to the set rotational limit. The child safety barrier also includes a rotational limit adjustment knob securely coupled to the fixed member, the rotational limit adjustment knob being rotatable about an axis to enable adjusting the position of the fixed member, the rotational limit adjustment knob being matable with a locking member. The shaft gear and the intermediate gear define a first reduction ratio and the intermediate gear and the stop gear define a second reduction ratio, the first and second reduction ratios combine to define a total reduction ratio. The total reduction ratio can be such that the stop gear rotates less than 360 degrees as the barrier is extended from a fully retracted position to a fully extended position. Each of the first and the second reduction ratios can be between approximately 1:1 and 20:1. The total reduction ratio can be between about 5:1 and 20:1. 
     The adjustable width child safety device also can include a stationary shaft at least partially contained within the main shaft and securely attached to the housing. A torsion spring can be disposed between the stationary shaft and the main shaft, the torsion spring having a first end securely attached to the stationary shaft and a second end securely attached to the main shaft. The adjustable width child safety device can be configured to block access through the passageway over a height that is between about 1 and 4 feet. 
     The adjustable width child safety device also can include a latch receptacle housing mounted to a surface on an opposite side of the passageway and defining a latch receptacle for receiving and releasably securing a latch assembly secured to an outer edge of the barrier. 
     Implementation of the techniques and apparatus described herein may provide one or more of the following advantages. A barrier with a set extension limit can be simply erected to prevent children from traversing a passageway. At the same time, the barrier can allow an adult to simply unlatch the barrier, retract the barrier, traverse the passageway, re-extend and relatch the barrier to the original extended position. The barrier extension limit need not be set each time the passageway is traversed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B are frontal views of a child safety barrier installed at a passageway. 
     FIG. 2 is an exploded view of the housing end of the barrier. 
     FIG. 3 is a top view of the housing end of the barrier, as mounted in a passageway. 
     FIG. 4A is a cross-sectional view taken along line  4 A— 4 A of FIG.  3 . 
     FIG. 4B is a cross-sectional view taken along line  4 B— 4 B of FIG.  3 . 
     FIG. 5 is a partial cutaway view illustrating a spring load assembly. 
     FIG. 6A is a partial cutaway view of the latching assembly. 
     FIG. 6B is a top view of the upper latch receptacle assembly of FIG.  6 A. 
    
    
     DETAILED DESCRIPTION 
     FIGS. 1A & 1B illustrate an adjustable width child safety barrier assembly  100  installed at a passageway  102 . The barrier assembly  100  includes a flexible barrier  112  that can be extended across the passageway  102  to prevent the passage of a child. The barrier  112  can be, for example, a polyester mesh cloth, typically not including holes larger than approximately 1 square inch. One or more reinforcement rods  122  can be attached, for example by using heat sealing techniques, to the cloth barrier  112  thereby enhancing the structural integrity of the barrier  112 . These rods  122  could be manufactured, for example, from fiberglass. The height of the barrier  112 , measured in a direction perpendicular to the direction of barrier extension, can range from approximately one to four feet but is typically about 28 inches. The fully extended width of the barrier can be between approximately 12 and 72 inches or, more preferably, between approximately 24 and 51 inches. 
     The barrier assembly  100  includes a roller side housing  104  mounted to a structural element  106  on one side of the passageway  102 . A rotatable main shaft  108  is secured to the housing  104  for rotation about an axis  110 . The barrier  112  is securely attached at one edge to the main shaft  108  so that the main shaft  108  rotates as the barrier  112  is either extended or retracted. The barrier  112  includes a latching assembly  114  attached to an edge of the barrier  112  opposite the barrier's attachment to the main shaft  108 . The latching assembly  114  includes an upper latching element  124 , a lower latching element  128 , and a rod  126  that connects the upper and lower latching elements together. With the barrier  112  extended across the width of the passageway  102 , as depicted in FIG. 1B, the latching assembly  114  can be positioned to mate with an upper receptacle assembly  116  and a lower receptacle assembly  120 . The upper receptacle assembly  116  and the lower receptacle assembly  120  can be connected to each other and are mounted to a structural element  118  on a side of the passageway  102  opposite the rollerside housing  104 . 
     The barrier assembly  100  can be spring loaded so that the barrier  112  tends to automatically retract toward the housing  104  in the absence of any opposing forces. 
     The roller side housing  104  includes provisions that enable an operator to set a maximum extension limit for the barrier  112 , thereby defining a position, beyond which the barrier  112  is prevented from extending. Typically, such an extension limit would be set with the barrier  112  initially extended to a desired position, for example, across the width of a passageway  102 . The barrier assembly  100  can then be set to prevent subsequent extension of the barrier  112  beyond that set limit position, while allowing subsequent retraction and re-extension of the barrier  112  up to that limit position without requiring any further adjustments to the maximum extension limit. Alternatively, an extension limit can be set with the barrier  112  initially in a fully retracted position. In that case, when extended, the barrier  112  would be prevented from extending beyond a position defined by the set extension limit. 
     FIG. 2 illustrates a partial exploded view of detailing particular implementation of a child safety barrier assembly  100 . The components illustrated include structural elements, extension limiting elements, and retractor elements. The flexible barrier  112  also is illustrated and is connected to the main shaft  108 . 
     The structural elements include two wall mount brackets  206  that can be securely mounted, for example, to a structural element  106  on one side of a passageway  102 . A mounting rail  208  can be secured to the wall mount brackets  206  and can provide structural support for the various components coupled to it. Clips can be provided in the wall mount brackets  206  that can easily snap into apertures in the mounting rail  208  and also can easily snap out of those apertures. Such an arrangement can facilitate connecting and disconnecting the mounting rail  208  from wall mount brackets  206 . 
     A housing  210 ,  212  includes an upper housing member  210  and a lower housing member  212  that can be securely attached together. The housing  210 ,  212  can be mounted to a horizontal portion of the mounting rail  208 . 
     Extension limiting elements couple the upper end of the rotatable main shaft  108  to the stationary housing  210 ,  212  and include components that enable an operator to define an extension limit position, beyond which the barrier  112  cannot be extended, while permitting subsequent retraction and re-extension of the barrier to any position up to the set extension limit. 
     A rotatable stop gear  214  includes a position indicating flag that projects upward from the upper surface of the stop gear  214 . The stop gear  214  is coupled to the main shaft  108  and is typically configured to rotate fewer than 360 degrees for each full rotation of the main shaft  108 . The stop gear  214  also may be configured to rotate fewer than 360 degrees when the barrier  112  is extended from a fully retracted position to a fully extended position. A fixed member  216  also is illustrated and has a rotatably adjustable and lockable position. The fixed member  216  includes a limit tab projecting radially outward from its perimeter surface that is positionable to set a limit of extension for the barrier  112  with respect to the main shaft  108 . The limit tab is positioned to intersect the projected path of the position indicating flag on the stop gear  214 . That point of intersection defines a rotational limit position for the stop gear  214  and by extension a limit of extension for the barrier  112 . 
     A portion of the main shaft  108  passes through the lower housing member  212  and is securely attached to a shaft gear  218 . As such, the shaft gear  218  rotates about the same axis  110  as the main shaft  108 , and maintains the same relative angular position as the main shaft  108 . As the main shaft  108  rotates, so too does the shaft gear  218 . 
     The shaft gear  218  includes multiple sections, and each section typically has a different outside diameter. The section of the shaft gear  218  that passes into the opening at the top of the main shaft  108  has a reduced diameter, which may be tapered or keyed to affect a secure connection between the two components. The section immediately adjacent includes a larger diameter. This step to a larger diameter prevents the shaft gear  218  from slipping into the opening in the main shaft  108 . The shaft gear  218  includes a second reduced diameter section that includes gear teeth arranged around its perimeter surface. These gear teeth mesh with and can drive a complimentary set of gear teeth on an adjacent intermediate gear  220 . 
     The intermediate gear  220  is rotatable about an axis that is parallel to the axis  110  of the main shaft  108 . The intermediate gear  220  includes an upper reduced diameter section with gear teeth arranged around its perimeter surface. A boss in the lower housing member  212  passes through a bore in the intermediate gear  220  and supports the intermediate gear  220 . The intermediate gear  220  typically rotates fewer degrees than the main shaft  108  does and rotates in an opposite direction from the direction that the main shaft  108  rotates. The shaft gear  218  and the intermediate gear  220  define a first reduction ratio that is typically between about 1:1 and 20:1, is more preferably between about 2:1 and 7:1 and is most preferably about 3.25:1. The gear teeth of the upper, reduced diameter section of the intermediate gear  220  mesh with and can drive a complimentary set of gear teeth on a perimeter surface of an adjacent stop gear  214 . This complementary set of gear teeth on the stop gear  214  is located on a perimeter surface of a first section of the stop gear  214 . Above that section, the stop gear  214  has a larger diameter section. The intermediate gear  220  and the stop gear  214  define a second reduction ratio that is typically between about 1:1 and 20:1, is more preferably between about 2:1 and 7:1 and is most preferably about 3.25:1. 
     The first reduction ratio and the second reduction ratio combine to define a total reduction ratio that is between about 5:1 and 20:1, but is preferably about 10.25:1. The stop gear  214  typically rotates in the same direction as the main shaft  108 , but at a reduced speed. The stop gear  214  also typically rotates fewer than 360 degrees for each full rotation of the main shaft  108 , and is typically configured to rotate fewer than 360 degrees as the barrier  112  is extended from a fully retracted position to a fully extended position. 
     A shoulder washer  222  is positioned above the stop gear  214  and can be secured, for example, by a screw to threads machined into a bore in the shaft gear  218 . The shoulder washer  222  includes a first portion having a reduced outer diameter and a second portion having a larger diameter portion. The shoulder washer  222  passes through holes in the stop gear  214  and the mounting rail  208 , thereby providing structural support, minimizing vertical play at the stop gear  214 , and helping to maintain axial alignment at the stop gear  214  to keep it centered about its axis of rotation. 
     A fixed member  216  is positioned above the shoulder washer  222  so that the stop tab that extends outward from its perimeter intersects the path of travel for the stop gear  214  flag. The fixed member  216  is securely coupled to an externally accessible, adjustably positionable adjustment knob  224  that is exposed for manual manipulation by an operator to set the fixed member  216  in a desired position. 
     A position locking assembly  240 ,  242  can lock the set position of the adjustment knob  224  and the fixed member  216 . The locking assembly  240 ,  242  includes an upper locking element  240  and a lower locking element  242 . The lower locking element  242  is coupled to the housing  210 ,  212  and can be mated with a notch on the adjustment knob  224  to inhibit subsequent rotational movement of the adjustment knob  224  and the fixed element  216  relative to the housing  210 ,  212 . The upper locking element  240  is externally accessible and has an adjustable position. The upper locking element  240  can be positioned relative to the lower locking element  242  in such a manner, that, adjustment of its position can impose a force on the lower locking element  242 , thereby withdrawing it from the notch on the adjustment knob  224 . Such a withdrawal can permit an operator to subsequently adjust the position of the adjustment knob  224  and the fixed member  216 . 
     The retracting assembly includes a stationary shaft  226  securely coupled to the lower housing  246  through a tab bushing  244  pressed into an opening at the bottom of the stationary shaft  226 , a press fit tab washer  232 , a friction tab disc  234 , and a spring tab  236 . The spring tab  236  securely mates with both the tab bushing  244  and a recessed area of the lower housing  228 , and prevents the stationary shaft from rotating relative to the lower housing  246 . 
     The main shaft  108  is securely coupled to a shaft adapter  238  that is positioned above a bushing washer  248  within a recessed portion of the lower housing  228 . The main shaft  108 , shaft adapter  238  and bushing washer  248  can rotate about the same axis. The inner diameter of the bushing washer  248  is positioned to contact an outer surface of the stationary friction tab disc  234 . 
     A spring  228  is disposed to at least partially surround the stationary shaft  226  and to pass at least partially inside the main shaft  108 . The spring  228  is captured at an upper end by a plug  230 , which is securely attached, for example, by press fitting to an opening at the upper end of the stationary shaft  226 . The spring  228  is coupled at the opposite end to a threaded portion of the rotatable shaft adapter  238 . As the barrier  112  is extended, the main shaft  108  rotates and the spring  228  tension increases, thereby biasing the barrier  112  toward a retracted position. 
     FIG. 3 illustrates a top view of the housing end of the barrier, as mounted to a structural element  106  of a passageway  102 . 
     FIG. 4A illustrates a cross sectional side view detailing an extension limiting assembly. As discussed above, the main shaft  108  passes through an opening in the lower housing member  212  and is securely coupled to the shaft gear  218 . The upper portion of the shaft gear  218  includes gear teeth around its perimeter that mate with and drive a complimentary set of gear teeth located on the perimeter of intermediate gear  220 . Intermediate gear  220  also includes an upper reduced diameter section with gear teeth around its perimeter. This second set of gear teeth on the intermediate gear  220  meshes with and drives a complimentary set of gear teeth located on a perimeter surface of stop gear  214 . The stop gear  214  includes a flag (not shown) projecting upward from its upper surface. 
     The fixed member  216  includes a tab (not shown) projecting radially outward from its perimeter surface, positioned to intersect the path of the stop gear  214  flag. The fixed member  216  is securely coupled to the adjustment knob  224 . These two components can be rotated as a single unit about an axis. By rotating these two components, an operator can adjust the position of a rotational limit of the stop gear  214  and consequently adjust the position of a rotational limit of the main shaft  108 . 
     The assembled locking member  240 ,  242  is also illustrated. The lower locking element  242  is positioned to mate with a recessed portion of the adjustment knob  224  thereby preventing any rotational movement of either the adjustment knob  224  or the fixed member  216 . The locking member can be removed from the recessed portion of the adjustment knob  224  by moving the upper locking element  240  in a direction identified by the arrow  300 . Withdrawing the lower locking element  242  from the recessed portion of the adjustment knob  224  frees the adjustment knob  224  and the fixed member  216  to be subsequently rotated to a desired position. The bottom portion of the adjustment knob  224  may include gear teeth around its perimeter surface. These gear teeth can mesh with a complimentary set of gear teeth on the upper housing  210 , effectively preventing an operator from rotating the adjustment knob  224  without lifting it thereby disengaging the mating gear teeth from each other. 
     FIG. 4B illustrates an alternate cut away view of the extension limiting assembly discussed above. 
     FIG. 5 illustrates a partial sectional cutaway view of a particular implementation of a child safety barrier including a spring loaded retraction assembly. A stationary shaft  226  is positioned within the rotatable main shaft  108 . The stationary shaft  226  is securely coupled to the lower housing  246 . A tab bushing  244  is securely attached to the stationary shaft  226  by a press fit connection into an opening at the bottom of the stationary shaft  226 . The tab bushing  244  includes an internal passage oriented axially. A spring tab  236  fits snugly into the internal passage of the tab bushing  244  and is securely attached to a recess in the lower housing  246 . This spring tab  236 /tab bushing  244  arrangement prevents the stationary shaft  226  from rotating with respect to the lower housing  246 . 
     The main shaft  108  is securely coupled to a shaft adapter  238  and these two components can rotate together. A spring  228  surrounds at least a portion of the stationary shaft  226 . The spring  228  is securely coupled to the upper end of the stationary shaft  226  by a plug  230  that is pressed into an opening at the upper end of the stationary shaft  226 . The plug  230  remains stationary with respect to the stationary shaft  226 . A first end of the spring passes through a notch at the top of the plug  230 . A second end of the spring is wound onto threads around the perimeter of the shaft adapter  238 . As the main shaft  108  rotates, the shaft adapter  238  also rotates. Such rotation winds the spring  228 , thereby increasing the resultant spring tension. In this manner, the spring  228  can bias the barrier  112  toward a fully retracted position. 
     The tab bushing  244  is positioned above a stationary tab washer  232 . The stationary tab washer  232  is positioned above a stationary friction tab disc  234 . The outer perimeter of the stationary friction tab disc  234  provides a journal surface that the rotatable bushing washer  248  can rub against. The rotatable bushing washer  248  is press fit into the rotatable shaft adapter  238 . 
     FIG. 6A illustrates a particular embodiment of an upper latching element  124  and a wall mounted receptacle assembly  116 . The upper latching element  124  includes a latch housing  500  with an externally accessible trigger lock handle  502  and an externally accessible latch release trigger  504 . 
     The trigger lock handle  502  is securely coupled to an internal trigger lock  506 . The trigger lock  506  is arranged to pivot around a pivot point  508  that is coupled to the latch housing  500 . In the absence of any external forces, the trigger lock  506  is maintained in a locked position by a positioning force imposed by a trigger lock spring  510 . Alternatively, a flexure, that is, an elastic plastic tab may be used to provide the positioning force in lieu of the trigger lock spring  510 . 
     The upper latching element  124  can be prevented from disengaging from the receptacle assembly  116  by a spring-loaded latch  512  that is positionable to pass through an opening in the latch housing  500  and to be captured in a notch  514  of the receptacle assembly  116 . The mating of the latch  512  and the notch  514  prevents the upper latching element  124  from being moved upward relative to the receptacle assembly  116 , thereby ensuring that the upper latching element  124  cannot be inadvertently dislodged from the receptacle assembly  116 . The latch  512  is biased toward a locked position, that is, a position wherein it is extended through the opening in the latch housing  500 , by the latch spring  516 . 
     The latch release trigger  504  extends into the latch housing  500  and is positionable to contact the latch  512 . When the trigger lock handle  502  is moved in a direction indicated by arrow  518 , the latch release trigger  504  can be then moved in a direction indicated by arrow  520  to counteract the force applied by the latch spring  516  on the latch  512 . The latch  512  can be withdrawn from the notch  514  and toward the latch housing  500  eventually clearing the notch  514  and allowing the upper latch element  124  to be disengaged from the receptacle assembly  116 . 
     The upper latching element  124  is desirably configured to enable an operator to engage and disengage it from the receptacle assembly  116  using only a single hand. 
     To engage the upper latching element  124  with the receptacle assembly  116 , an operator would typically first position the lower latching element  128  to mate with the lower receptacle assembly  120 . The operator can then position the rod  126  inside the upper receptacle assembly  116  and lower the upper latching element  124  into place. The beveled edge  520  at the bottom of the latch  512  can facilitate coupling the upper latching element  124  to the upper receptacle assembly  116 . 
     Two sequential motions are required to disengage the upper latching element  124  from the receptacle assembly  116  as illustrated in the figure. The first motion includes moving the trigger lock handle  502  in a direction indicated by the arrow  518 , thereby causing the right edge of the trigger lock  506  to move away from the latch release trigger  504 . Such a motion will enable the latch release trigger  504  to be moved freely in a direction indicated by the arrow  520 . The second motion includes actually moving the latch release trigger  504  in a direction indicated by the arrow  520 , thereby disengaging the latch  512  from the notch  514  in the receptacle assembly  116 . The upper latching element  124  can then be lifted to a position so that the rod  126  can be slipped out of the c-shaped receptacles  518  of the receptacle assembly  116 . 
     An alternative arrangement might not include the illustrated trigger lock  506  and its associated components. Such an arrangement might allow an operator to unlatch the barrier  112  from the receptacle assembly  116  using only a single hand motion. In such a case, the force required to perform such an operation would be generally large enough to prevent an infant or small child from performing the operation. Typically such a force might be between about 12 and 15 pounds and might be implemented, for example, by an arrangement of springs or elastic members. 
     FIG. 6B illustrates a plan view of the upper receptacle assembly  116  having a c-shaped receptacle  518 . The orientation of the c-shaped receptacle may be varied. 
     Various modifications to the apparatus and techniques described herein are possible. For example, the reduction ratio defined by the shaft gear, the intermediate gear, and the stop gear as specifically described herein may be implemented using an alternate gearing arrangement with either more or less reduction stages. The barrier assembly may be hand retractable and may not include provisions for spring loading the retraction feature of the barrier. The upper latching element may not include a two-step operation for disengaging it from the receptacle. Generally, if the latching mechanism is capable of being disengaged using only a single operation, the required force required to perform such an operation will be at least approximately 13 pounds to prevent a young child from being able to perform the operation. 
     Different techniques may be used for connecting various components to each other, such as welding, molding, using adhesives, keying or press fitting. Additionally, the general shapes and relative sizes of the different components can vary. Specific materials used also might differ depending on specific requirements of a particular application. 
     The apparatus and techniques described herein could be adapted for use in barriers directed to limit passage of dogs, cats, or other animals in addition to children. 
     Accordingly other implementations are within the scope of the following claims.