You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a regular application of U.S. Provisional Patent application Serial No. 60/330,127 filed on Oct. 19, 2001, the entirety of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to elevation and alignment variable gangways which extend and bridge a gap such as between two misaligned platforms. 
     BACKGROUND OF THE INVENTION 
     There are often situations where one must bridge a gap between discontinuous surfaces or platforms using a structural surface, like a gangway, which is sufficient to support cartage or passenger traffic. Gangways are used particularly in cargo or passenger loading between a dock and a boat, a ramp and an aircraft, or a loading platform and a vehicle. 
     One example is a situation where an access ramp is placed adjacent an airplane cabin access doorway. In order to insert a gangway, the ramp will usually have an exit platform which is adjusted approximately to the same elevation as the sill of the aircraft doorway. Further, the surface must usually be carefully positioned so as to be aligned with the doorway. In many instances, it is only important that the gangway reach the sill of the doorway&#39;s platform. However, the alignment is particularly important when there are fixed hand rails projecting from the doorway&#39;s platform; these rails act to constrain access. In such a case, the gangway must be precisely aligned to pass between the hand rails and reach the doorway&#39;s platform recessed through the rails. 
     Again in an aircraft context, the boarding and deplaning of disabled persons must be addressed and can be particularly challenging because neither the aircraft nor the boarding device can be accurately positioned. Unlike large commercial aircraft, smaller regional aircraft have aircraft cabin doors which cannot be aligned with the usual boarding tunnels and motorized bridges. Instead, the cabin doors comprise a pivoting door the inside of which is fitted with stairs for boarding and deplaning. When the door is pivoted outwardly from the aircraft fuselage to open the aircraft doorway, the distal end of the door reaches downwardly to the tarmac. The inside of the aircraft door forms a staircase and side hand rails pivot into an upright and supporting position. Certainly, the stairs are difficult to navigate by the mobility-impaired and impossible for accommodating wheelchairs. Further, the cabin door and particularly the side handrails, tend to block many of the usual apparatus adapted to provide elevated access to the aircraft doorway, including wheelchair lifts and inclined ramps. It is difficult to successfully extend outwards to bridge between the platforms while still being able to pass between the narrow, constricting side handrails. It is also important to be able to secure the gangway from slipping from the platform during use. 
     SUMMARY OF THE INVENTION 
     The difficulties associated with alignment between two, often narrow, passageways are obviated using a fully floating gangway. In one embodiment, the floating gangway is supported in a mobile ramp and comprises a movable frame sandwiched movably in an operating plane between lower and upper parallel bearing surfaces. A bridging element or gangway extends from the frame&#39;s front end for extending to another platform such as an aircraft doorway. Manipulation of the frame forwards, rearwardly, and rotationally enables the gangway to be aligned with the doorway. Further, the gangway can be pivotally connected to the frame so as to enable vertical adjustment of the gangway so to adapt to differential elevations of the proximal and distal ends of the gangway. In the case of aircraft or watercraft, this elevation can also vary during the boarding process. The floating gangway is equally adaptable to structures such as mobile ramps, stationary jet bridges, warehouse loading docks and the like. 
     In one aspect of the invention, a method for aligning a gangway between a first platform and a second platform is provided comprising the steps of: 
     supporting a frame between two spaced and parallel bearing surfaces which are positioned below the first platform, the frame being movable in an operating plane parallel to the bearing surfaces; 
     supporting a proximal end of a gangway from the frame and extending a distal end of the gangway to the second platform; and 
     manipulating the frame in the operating plane so as to align the supported gangway with the second platform. 
     Preferably, alignment is further aided by pivoting the proximal end of the gangway from the frame so as to align the elevation of the distal end of the gangway with the second platform. Preferably, in applications associated with the damage critical components of aircraft, it is advantageous to hand manipulate the gangway to minimize risk to the aircraft from insensitive powered movements. To this end, counterbalancing of the gangway about its pivot aids in easing the hand manipulation. Powered assisted manipulation can also be applied. Further, to provide enhanced continuity, one can independently bridge between gangway and the platform using a flap so as to provide a contiguous surface therebetween as the frame is being manipulated. Once manipulated, it is advantageous to lock the gangway to avoid movement in use, such a locking capability being particularly desirable in situations where there is a risk of movement and safety is an issue. 
     In a broad apparatus aspect, a gangway is supported by a movable frame positioned below a first platform and substantially parallel thereto, the frame having a front end and a rear end and movable at least to translate and rotate in an operating plane, and preferably laterally as well. Preferably, said operating plane is defined by movably supporting and sandwiching the frame between upper and lower bearing surfaces, the lower bearing surface positioned below the frame and parallel to the operating plane and the upper bearing surface positioned spaced above and parallel to the operating plane. A bridge extends forward from the frame&#39;s front end for extending between the frame and the second platform and so that, as the frame moves, the bridge also translates and rotates with respect to the second platform. Preferably, the bridge is pivotally connected at a hinge to the frame and is counterbalanced to make the frame easier to manipulate. A flap between the bridge and first platform forms a contiguous gangway and ensures continuity in all platform traffic situations. 
     In one embodiment, the frame is movably supported between the upper and lower surfaces by one or more first bearings, preferably laterally spaced swiveling castors, for moveably supporting the front end and one or more second bearings, such as another swiveling castor, positioned rearwardly of the first bearings. Bridge weight loads the front end of the frame and causes the front castors to bear against the lower bearing surface and causes the rear end of the frame to rotate upwardly so that the rear castor bears upwardly against the upper bearing surface. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side schematic view of one embodiment of the invention and an exploded plan view of one embodiment of a locking mechanism utilizing a perforated indexing locking plate; and further illustrating the frame, the indexing lock mechanism and two positions of the pivoting bridge; 
     FIG. 2 is a side schematic view of a ramp embodiment of the invention illustrating forward and rearward movement of the frame and pivoting action of the flap and the bridge; 
     FIG. 3 is a side schematic view of a loading dock embodiment of the invention illustrating forward and rearward movement of the frame and pivoting action of the flap and the bridge; 
     FIGS. 4 a - 4   c  illustrate side schematic views accordingly to FIG.  2  and which show three stages of rearward movement of the frame with the gangway reaching three different extents on the target surface; 
     FIGS. 5 a  and  5   b  illustrate top schematic views accordingly to FIG. 2, FIG. 3 a  illustrating the lateral, forward and rearward extent of the lower bearing surface shown in hidden lines under the ramp and the gangway; 
     FIGS. 6 a  and  6   b  illustrate top schematic views accordingly to FIG. 2 wherein the frame is translated both laterally and fore and aft so as to successfully position the gangway onto the target surface despite the ramp being offset to one side and alternatively being close to or spaced from the target surface respectively; 
     FIGS. 7 a  and  7   b  illustrate top schematic views accordingly to FIG. 2 wherein the frame is rotated and translated so as to successfully position the gangway onto the target surface despite the ramp being angularly misaligned from the target surface one way or the other respectively; 
     FIG. 8 is a partial perspective view of an embodiment of the invention having a frame using front castors bearing against a lower bearing surface and a rear castor bearing against the underside of the ramp, and having both a flap and a bridge forming the gangway; 
     FIG. 9 illustrates one application in which the invention is useful for enabling a gangway to aligning between narrowly spaced handrails of an aircraft cabin door; and 
     FIG. 10 is an alternate embodiment of the locking mechanism which locks all movement of the frame and supported gangway. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Having reference to FIG. 1, a structure  10  such as a mobile ramp  11  comprises a surface which forms a first platform  12  having a front end  13  positioned adjacent and spaced from a second surface forming a second platform  15 . While not shown in great detail, the structure  10  can be an aircraft access ramp  11  which is equipped with wheels (FIG. 2) so as to enable it to be mobile for positioning adjacent the second platform  15 , such as an aircraft entry or doorway (See FIG.  9 ). 
     A space or gap results between the first and second platforms  12 , 15 . The objective is to move pedestrian or other traffic between the first and second platforms  12 , 15 . Typically, the platforms  12 , 15  are only approximately arranged at the same elevation and are often misaligned. 
     A gangway  16  is used to bridge the gap. The gangway  16  comprises a bridge  17  mounted at a proximal end  18  to the structure  10 . The bridge  17  extends outwardly from the first platform  12  so that a distal end  19  reaches towards the sill  15   a  of the second platform  15 . If there is some existing disparity or potential variation in elevations between the platforms  12 , 15 , the bridge  17  can be pivotally mounted to the first platform  15  at pivot point  20 . 
     For accommodating maximum flexibility in aligning the bridge  17  to the second platform  15 , the pivot point  20  is mounted to a movable frame  25  located beneath the first platform  12 . The frame  25  has a front end  26  and a rear end  27 . The frame  25  is movable relative to the first platform  12  and in an operational or operating plane  30  substantially parallel to the first platform  12 . The frame  25  can be translated and rotated within the operation plane in a least a forwards and rearwards direction. Lateral movement further adds alignment versatility to the gangway. 
     Due to the relative movement of the frame  25  and the first platform  12 , a small discontinuity can form between the bridge&#39;s pivot point  20  and the first platform  12 . This discontinuity can be bridged with an overlapping filler surface  31  including examples such as by using a forward extension of the first platform  12 , a rearward extension of the bridge  17  itself, a rearward extension from the front of the frame  26 , by a surface formed by the frame  25  itself if it is immediately adjacent beneath the first platform  12 , or preferably by a separate interfacing flap  32 . The filler surface  31  and first platform  12  form a contiguous surface but are moveable with respect to each other. The gangway  16  between platforms  12 , 15  therefore comprises the substantially continuous surfaces of the filler surface  31  and the bridge  17 . 
     As shown in FIG. 1 the filler surface  31  comprises an interfacing flap  32  extending rearwardly from the frame&#39;s front end  26  to the first platform  12 . The contiguous gangway  16  is completed by the portion of the bridge  17  which extends forwards from the frame&#39;s front end  26  at the pivot point  20 . The interfacing flap  32  can be a rearward extension which is cantilevered from the frame  25  and which is parallel to the first platform (FIGS.  1  and  3 ). Preferably, the interfacing flap  32  can be pivoted from the frame&#39;s front end  26  (FIG. 2) to improve maintenance access to the frame  25  or to provide a closer interface between the first platform  12  and the interfacing flap  32 . Note that a pivot point for each of the interfacing flap  32  and the bridge  17  may be the same pivot point  20  or independent and adjacent pivot points  33 , 20 . 
     The interfacing flap  32  and bridge&#39;s pivot point  20  are connected at the frame&#39;s front end  26  so that loads imposed on the gangway  16  are transferred into the frame&#39;s front end  26 . One or more first bearings  40 , preferably two bearings  40   a , 40   b , support the frame&#39;s front end  26  and act as a fulcrum, forcing the frame&#39;s rear end  27  to bear upwardly under load. At least one second bearing  41  restrains the reaction at the frame&#39;s rear end  27 , maintaining the frame substantially in its operating plane  30 . The first and second bearings  40 , 41  enable relatively frictionless freedom of movement of the frame  25  within the operating plane  30 . The first bearings  40  or  40   a , 40   b  bear against and are supported upon a planer lower surface  42  which is supported in the structure  10  and is maintained parallel to the first platform  12 . The second bearing  41  bears against and is supported by a planer upper surface  43  supported in the structure  10  and which is maintained parallel to the first platform  12 . While usual in all cases, depending upon the particular structure  10 , the underside of the first platform  12  may conveniently serve as the upper surface  43 . The upper and lower surfaces  43 , 42  are located beneath the first platform  12 . The first and second bearings  40 , 41  sandwich the frame  25  between the upper surface  43  and the lower surface  42  and may comprise: lubricated facing surfaces; ball bearings in races or as shown in this embodiment, preferably some form of swiveling castors. 
     An operator can manipulate the movement of the bridge  17  and frame  25  by grasping the bridge directly or via a handlebar  45  which is affixed to the bridge  17  and extending laterally and conveniently to the side (also see FIG.  8 ). It is also possible to add drive means to aid the operator in manipulating the bridge. 
     Once the bridge  17  is in position, it is preferably secured with some form of locking means or mechanism  50  to avoid movement and slippage of the bridge  17  from the sill  15   a  of second platform  15 . The frame  25  can be fitted with a first locking means  51   a  and the structure  10  with a complementary second locking means  51   b . When engaged the first and second locking means  51 , 52  lock the frame&#39;s movement relative to the structure  10  and thus arrest or lock the bridge  17  movement. As shown in FIG. 1, one form of locking mechanism  50  comprises a combination of an indexed perforated plate  52  as the second locking means  51   b  and one or more moveable pins  53  as the first locking means  51   a . If there is more than one pin  53 , the pins  53 , 53  . . . and perforations  54  in the plate  52  are cooperatively spaced so as to ensure engagement or one or more of the pins and perforations  53 , 54  regardless of the position of the frame  25 . Each pin  53  is actuable between a released position, free of the perforated plate  52 , and a locked position, engaged in one of the perforations  54  in the plate  52 . To further ensure safety in operation, a “deadman” or normally-locked system is employed. A spring  47  normally drives the pin  53  into the locked position which is only overcome and moved to the released position upon manual actuation by the operator manipulating the bridge  17 . A mechanism for releasing the pin  53  could include a sheathed cable  48  between a hand lever  46  and the pin or pins  53  as shown in the simplified schematic arrangement of FIG.  1 . The relative frame  25  or structure  10  mounting of the pins  53  and the perforated plate  52  could be reversed mounted. 
     As shown in FIG. 2, the first platform  12  is supported in a ramp  11  having means  14  for adjusting the elevation of the first platform&#39;s front end  13 . Accordingly, the angle of the ramp and first platform  12  can be varied. The interfacing flap  32  and bridge  17  rotate at their respective pivot points  33 , 20  so as to maintain continuity. The handle bars  45  and indexed locking system  50  are not shown in FIG. 2 so as to avoid obscuring additional of the embodiments of the invention. The bridge  17  may be fitted with handrails  71  (See FIG. 4 c .) which contributes to the bridge&#39;s weight. Accordingly and advantageously, some form of counterbalance means is provided for resisting the tendency of the bridge  17  to rotate abruptly under gravity when being lowered to the second platform  15 . A biasing means such as a form of spring  60  is shown at the juncture of the frame  25  and bridge  17  to counteract or balance the offset weight of the bridge  17  about its pivot pint  20 . A suitable spring  60  is a coil spring having its ends secured to the bridge  17  and the frame  25  respectively. 
     Another challenge posed by variable and increasing the angle of the first platform  12  is that the movable frame  25  inherently wishes to move down slope along its operating plane  30  under the increasing influence of gravity. As the angle of the first platform moves off horizontal and the angle increases, the operator must overcome increasing weight of the frame. 
     One approach is to use the handle bars  45  affixed to the bridge as shown in FIG.  1  and strongly manhandle the bridge  17 . While not essential, further assistance can be provided in manipulating or repositioning of the frame  25  by preferably providing a counterweight system  61  to counteracts the loads associated with the frame  25 . A planer counterweight supporting surface  62  is provided which is supported in the structure  10  and which is maintained parallel to the first platform  12 . A counterweight  63  is moveable on the counterweight support surface  62 , preferably on rollers  64 . A flexible tension member such as a cable  65  extends between the frame  25 , forwards around a turning bearing or pulley  66  and back for connection to the counterweight  63 . In operation, an increase in angle of the frame&#39;s operation plane  30  also increases the angle of the counterweight&#39;s supporting surface  62 , permitting the counterweight  63  to impose a frame-counterbalancing force, through the cable  65 . 
     Having reference to FIG. 3, as shown in an optional loading dock embodiment, where the first platform remains substantially horizontal, a frame counterweight system is of little assistance and is not provided. 
     In operation, and having reference now to FIGS. 4 a - 4   c , the bridge&#39;s pivot point  20  is a hinge  70  mounted to the frame&#39;s front end  26 . The hinge  70  is offset upwardly from the frame&#39;s operating plane  30 . Accordingly, in use, both the flap  32  and the bridge&#39;s hinge  70  lie substantially in the plane of the first platform  12 . 
     As shown in FIGS. 4 a - 4   c , due to a variety of constraints on the ground, the relative positioning of the platforms  12 , 15 , or merely the actions of the operator, the resulting relative end position of the first and second platforms  12 , 15  may be at any of a variety of locations, resulting in spacing or gaps of variable distance. Accordingly, for a large gap as shown in FIG. 4 a , the frame  25  is moved considerably forwards in its operating plane  30 , so as to translate the bridge  17  forwards to reach the second platform  15 . The bridge  17  is pivotally lowered to engage the second platform&#39;s sill  15   a . For medium and smaller gaps, the frame can be moved progressively forwards or rearwards so that the bridge engages the sill  15   a.    
     As is shown in FIG. 4 c , the ability to manipulate the bridge is particularly advantageous when there are lateral constraints as well. As illustrated, the bridge and any handrails  71  are manipulated to fit within a framed doorway  72  of the second platform  15 . 
     Having reference to FIGS. 5 a  and  5   b , the first and second platforms  12 , 15  are shown in plan view with the gangway  16  extending therebetween. In FIG. 5 a , the outline of the entire planer surface of the lower support  42  is shown in hidden lines as necessary where it is obscured by the first platform  12 . In FIG. 5 b , the frame  25  and the first and second bearings  40   a , 40   b , 41  are shown in hidden lines beneath the first platform  12  and gangway  16  respectively. The frame  25  is shown as a triangular structure having two first bearings  40   a , 40   b  at the frame&#39;s front end  26  and which are shown as being freely swiveling castors (see also FIG.  8 ). One freely swiveling castor is provided as the second bearing  41  at the frame&#39;s rear end. 
     Turning to FIGS. 6 a ,  6   b ,  7   a  and  7   b , the extent of movement and the capability of the gangway  16  to be manipulated in the operating plane  30  through a variety of translations and rotations are shown. Throughout, the frame  25  is illustrated in hidden lines beneath the first platform  12  and gangway  16 . 
     FIG. 6 a  illustrates translation of the gangway  16  and frame  25  forwards to reach a distant second platform  15 . FIG. 6 b  illustrates translation of the gangway where the second platform  15  is more closely spaced. Both FIGS. 6 a  and  6   b  illustrate the capability for lateral translation which accommodates side to side misalignment of the first platform  12  and a dimensionally constricted second platform  15  (such as a framed doorway  72 —see FIGS. 4 c  and  9 ). 
     FIGS. 7 a  and  7   b  illustrate angular misalignment of the first platform  12 , while permitting rotation of the frame  25  and gangway  16  to align properly with the second platform  15 . 
     Having reference now to FIG. 8, in one detailed embodiment of the invention, the frame&#39;s front end  26  is shown supported or bearing against the lower support on two laterally-spaced swiveling castors  40   a , 40   b . A form of the frame  25  having castors is illustrated, in a schematic form, in FIG. 5 b . The castors  40   a , 40   b  are mounted to the underside of a cross member  25   x  extending across the frame  25 . A single swiveling castor  41  is mounted to the top of the frame  25  adjacent its rear end  27 . The bridge  17  is pivoted outwardly from a first hinge  70  mounted to the top of a standoff  25   s  extending upwardly from the frame&#39;s front end  26 . The handlebars  45  are shown secured to a side edge  73  of the bridge  17 . A frame lock actuator lever  16  is partially represented on the right-hand end of the handlebars  45 . The flap  32  is shown pivoted from a second hinge  70   b  also mounted to the standoff  25   s.    
     As an example of a situation involving a constricted or constrained second platform, and referring to FIG. 9, one embodiment of the present invention enables access to the constricted doorway of a small commercial aircraft. The end of the bridge  17  is shown approaching the sill  15   a  of the doorway platform  15 , while also accurately negotiating between fixed and narrow handrails  73 . 
     Having reference to FIG. 10, an alternate locking mechanism  50  comprises two of more arrays of spring loaded pins  53 . The pins  53  can be gang-retracted from their normal position using a mechanism to release the pins  53  from the perforated plate  52  and thereby unlock the frame  25  for movement. A cable  55  extending from a hand release  46  can pull a yoke  56  so as to simultaneously to retract all the pins  53 . When the yoke and pins  53  are released, biasing springs  57  driven the pins  53  towards the plate  52  so that one or more of the pins will engage a cooperating perforation  54  and provide a secure, safe and trustworthy lock. Each pin  53  is illustrated having a small shank  58  forming range of motion shoulders or stops  59  which cooperate with the yoke  56 . 
     It is understood that there are a variety of structures and platforms to which the method and apparatus of the floating gangway can be applied, whether the structure is mobile or stationary. There are many forms of frame support, bearings and braking mechanism which can be drawn from the prior art which enable the movement and locking of the frame in its operating plane. A variety of known drive mechanisms can be added to assist the operator in manipulating the various masses of the structure, frame and gangway and automating the alignment of the gangway.

Summary:
A fully floating gangway comprises a movable frame sandwiched movably in an operating plane between lower and upper parallel bearing surfaces which are supported from and positioned below a first platform. A gangway extends from the frame&#39;s front end for extending to another platform such as an aircraft doorway so that the gangway can be aligned therewith by manipulating the frame in the operating plane. Preferably the frame and bearing surfaces are supported in a mobile structures such as passenger ramp. The gangway is preferably pivoted from the frame for adapting to differential elevations. The pivoting gangway can be counterbalanced for ease of manipulation. A braking system is provided to lock gangway against movement once positioned.