Abstract:
A collapsible upright wheeled walker with adjustable armrests that support sufficient user upper-body weight to facilitate a natural upright gait and provide unassisted mobility for a wide range of mobility-impaired individuals. The apparatus may be easily and quickly folded (and unfolded) and may include bilateral stabilizing wheel suspensions to facilitate navigation over uneven terrain. The apparatus includes a frame-stiffening folder assembly and may also include mechanical brakes, an adjustable upper armrest assembly with removable padded forearm supports and two pairs of handles, at least one of which is disposed sufficiently forward to place the user within the polygonal footprint defined by the front and rear wheels to provide support without leaning, stooping, or risking falls.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is filed under 35 U.S.C. 111(a) pursuant to 37 CFR. 1.53(b) claiming the benefit under 35 U.S.C. §119(e) of U.S. Patent Application No. 62/162,706 filed on May 16, 2015 and entirely incorporated herein by reference and also claiming the benefit under 35 U.S.C. §119(e) of U.S. Patent Application No. 62/215,656 filed on Sep. 8, 2015 and entirely incorporated herein by reference. 
         [0002]    This application is related by common inventorship and subject matter to the commonly-assigned U.S. patent application Ser. No. 15/012,784 filed on Feb. 1, 2016, which is entirely incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    This invention relates generally to assistive mobility devices and more particularly to a collapsible upright wheeled weight-bearing walker. 
         [0005]    2. Description of the Related Art 
         [0006]    Assistive mobility devices, including walkers, are well-known in the art as useful means for reducing the disadvantages of mobility impairment suffered for many different reasons by many people, permitting more efficient ambulation over distance and thereby increased independence. Data from the National Long Term Care Survey suggests that increased use of assistive technology may have helped reduce disability at older ages [Manton, et al., “Changes in the Use of Personal Assistance and Special Equipment from 1982 to 1989: Results from the 1982 and 1989 NLTCS,”  Gerontologist  33(2):168-76 (April 1993)]. Although mobility device users represent a relatively small minority of the population with disabilities, their importance transcends their numbers because mobility devices are visible signs of disability and have become symbols of the very idea of disability. And the mobility-impaired population is increasing much faster than the general population [LaPlante et al., “Demographics and Trends in Wheeled Mobility Equipment Use and Accessibility in the Community,”  Assistive Technology,  22, 3-17, (2010)]. Accordingly, there has long been a growing demand for improved mobility assistance devices adaptable for improving ambulation for mobility-limited persons. 
         [0007]    Martins et al. [Martins et al., Assistive Mobility Devices focusing on Smart Walkers: Classification and Review,  Robotics and Autonomous Systems  60 (4), April 2012, pp. 548-562] classifies mobility assistance devices into the alternative devices intended for those with total loss of independent mobility (wheelchairs or autonomous powered vehicles) and assistive or augmentative devices for those with residual mobility capacity (prostheses, crutches, canes and walkers). For several reasons, most impaired individuals prefer to avoid association with the alternative devices associated with total incapacity. Similarly, the rehabilitation profession strongly prefers the assistive devices, which can be used for physical therapy and as mobility-training devices. Accordingly, there has long been a growing demand for improved assistive devices adapted for use by the less disabled among those who otherwise cannot move independently with existing assistive devices and rely on alternative devices such as wheelchairs and powered scooters. 
         [0008]    Mobility and manipulation are critical to living independently and are often strongly associated with the ability to continue to live safely in one&#39;s home. Simple assistive devices such as crutches, canes, walkers, and rollators (rolling walkers) can assist a person who has the endurance and strength to walk distances, but these devices must also provide some support or feedback to keep the person from losing their balance or enable the person to rest, when necessary. Although an impaired individual may eventually need an alternative device like a wheelchair or powered scooter, most strongly desire to retain the independence of the simpler assistive device for as long as possible. For this reason, there is a well-known and long-felt need for assistive device improvements that facilitate independent ambulation for the progressively more impaired individuals. 
         [0009]    Although popular, the most common assistive devices known in the art (canes, walkers and rollators) have many well-known disadvantages; even for the relatively mobile individual. 
         [0010]    The typical wheeled walker known in the art has many well-known disadvantages; such as requiring a stooping or a forward leaning posture to avoid a hobbled gait, difficulty in smooth transition over irregular terrain, little or no upper body and arm support, and requiring significant hand and arm strength to maneuver and to operate any available hand brake, for example. A stooping posture stresses the user&#39;s back and arms and risks tipping forward when encountering terrain obstacles. And most devices known in the art have no wheels or wheels too small to negotiate even small surface irregularities safely. Some devices are too heavy and awkward for an unassisted user to lift into a car trunk or van, which limits independent unassisted use. Walker brakes are often either nonexistent or ineffective for the unassisted impaired user, which adds risk of falls and injury and limits independence. 
         [0011]    The typical wheeled walker known in the art is neither designed nor intended to support significant user weight during use. As with a cane, the accepted purpose of a wheeled walker is simply to provide assistance in balance and gait, like an elaborate cane system. So the user engages the walker with hands and wrists alone, often with a stooping or leaning posture. The impaired user generally lacks the hand and wrist strength needed to continuously support significant upper body weight while walking in a stooped or forward-leaning position. Some wheeled walkers eliminate the seat to afford a more open walking footprint for the user. While this permits an improved and more natural walking position but offers no improved weight bearing capability and many users need an included seat to facilitate independent use over longer distances. 
         [0012]    The mobility assistance art is replete with suggestions for improving wheeled walkers. 
         [0013]    For example, in U.S. Pat. No. 8,100,415, Kindberg et al. disclose a wheel suspension that facilitates curb climbing when used with large wheels in, for example, a rollator. But Kindberg et al. limit their teachings to negotiating uneven terrain such as curbs. In U.S. Pat. No. D561,065, Kindberg et al. also disclose a walker frame design. 
         [0014]    And, for example, in U.S. Pat. No. 8,840,124, Serhan et al. disclose a safety brake in a rollator that improves the safety of seated users by using a braking system that locks the rollator wheels when the user sits down on the rollator seat, and releases the wheels when the user stands up. As another example, in U.S. Pat. No. 7,052,030, Serhan discloses a wheeled walker with cross-member supports adapted to permit both seat and basket with wheel sizes greater than seven to eight inches. In U.S. Pat. No. 6,886,575, Diamond discloses a locking assembly for use with a walker having foldable side members. And, for example, in U.S. Pat. No. 8,678,425, Schaaper et al. disclose a wheelchair having a moveable seat element facilitating use as a rollator. 
         [0015]    In U.S. Pat. No. 8,740,242, Slomp discloses a posterior walker configured to encourage a neutral spine during use. And, for example, in U.S. Pat. No. 7,559,560, Li et al. discloses a rollator having a foldable seat element. 
         [0016]    Some practitioners propose improving the walker mobility aid by adding upper support means for supporting the user&#39;s forearms, hands or shoulders to improve user comfort and posture. For example, in U.S. Pat. No. 5,657,783, Sisko et al. disclose accessory forearm rests that may be mounted to any conventional invalid walker, preferably disposed above the normal hand-grips to provide support for the user&#39;s arms. 
         [0017]    Such an upright wheeled walker may permit the user to walk upright but the wheeled walker known in the art is not adapted to support any user body weight beyond the relatively small portion in the forearms and hands. For example, in U.S. Pat. No. 8,540,256, Simpson discloses a walker with a forearm support frame to permit an upright user to step forward with the walker footprint but little weight bearing capacity. Similarly, in U.S. Pat. No. 8,740,242, Slomp discloses a foldable posterior walker with an anteriorly open frame that permits an upright user to step forward within the walker footprint but having little or no weight bearing capability. 
         [0018]    Improving a the wheeled walker by adding an upper-body support is advantageous because it facilitates an upright walking and standing posture, improved gait and comfort. But adding significant user body weight to the wheeled walker is also disadvantageous for stability. The increased weight borne on each wheel affects walker stability, braking, and terrain handling. For example, adding significant upright weight support to the wheeled walker introduces new disadvantages of increased lateral and longitudinal instability, risking falls and affecting user safety. Adding more weight support at a higher point on the walker increases the tipping torque at the wheels because of the increased force and distance. Any wheeled walker has longitudinal stability problems when rolling on slopes and over irregular terrain, which may imperil user safety by causing falls during use. This longitudinal instability problem is exacerbated by the fluctuating wheel loads imposed by the applied user weight during stepping, introducing a new lateral instability. 
         [0019]    Several practitioners suggest improvements to mitigate the wheeled walker longitudinal stability problem with braking system improvements. For example, in U.S. Pat. No. 8,998,223. Chang discloses a wheel braking system for a rollator with a “dead-man brake” whereby the wheels are halted upon the release of the user&#39;s hands from the handles, improving user safety on slopes. Similarly, in U.S. Pat. No. 9,221,433, Dunlap discloses a safety braking system for a rollator that includes a park mode, a walk mode and a brake mode with a handlebar control mechanism. 
         [0020]    Recognizing these new instability problems, practitioners have suggested turning to a powered vehicle to permit some user weight support in assistive devices. For example, in U.S. Pat. No. 8,794,252, Alghazi discloses a mobility apparatus with an integrated power source and four wheels so a user can stand on it and drive it as an electric mobility device, or disable it and use it as a passive walker. His device is collapsible and includes a pair of supporting beams disposed to support the user under the armpits, but such support does little to improve user posture or stability while walking with the passive device. And, in U.S. Pat. No. 8,234,009, Kitahama discloses an autonomous mobile apparatus that moves autonomously along near a specified person (user) while detecting and evaluating the surroundings to assess the danger level to the user, moving as necessary to avoid danger to the user based on the danger level detected. 
         [0021]    Others have proposed elaborate powered control systems to address these stability and other user safety problems. For example, in U.S. Pat. No. 7,708,120, Einbinder discloses an improvement to user safety consisting of a walker braking system using a controller and electrically actuated wheel brakes to provide push-button user control over braking and processor-controlled braking responsive to, for example, user hand position and the terrain slope. 
         [0022]    But such devices may be generally perceived by users as alternative devices (such as powered wheel chairs, stair climbers and vehicles) and do not represent the improved assistive device sought by most users. 
         [0023]    These and other examples of the mobility assistance art demonstrate that there is a continuing long-felt need for improved solutions to the walking posture, seating, weight support and portability problems discussed above. 
         [0024]    These unresolved problems and deficiencies are clearly felt in the art and are solved by this invention in the manner described below. 
       SUMMARY OF THE INVENTION 
       [0025]    This invention solves the well-known walking posture, instability and portability problems described above in a single apparatus by integrating for the first time folding improvements that stabilize the walker frame during use, adjustable forearm rests (for upper body support), an open rigidized frame permitting the user to stand and step within a polygonal footprint defined by the front and rear wheels, and adjustable handles elevated to permit the upright walking posture necessary for better health. The following description and drawing disclose for the first time how these advantageous features may be implemented in a single collapsible wheeled walker. 
         [0026]    It is a purpose of this invention to provide many adjustable features to facilitate unassisted mobility for a wide range of mobility-impaired individuals. 
         [0027]    It is an advantage of the apparatus of this invention that lightweight construction materials such as aluminum may be employed to reduce weight, thereby facilitating unassisted handling by a mobility-impaired person. 
         [0028]    It is an advantage of the apparatus of this invention that the upper arm support elements are each disposed at an ergonometric angle to facilitate a completely upright walking position with substantial upper body and arm support while walking within the polygonal footprint defined by the front and rear wheels. 
         [0029]    It is an advantage of the apparatus of this invention that facilitating an upright walking posture reduces heart and lung compression, improves circulation, thereby promoting the therapeutic effects of longer walking times after surgery and may ease recovery from injury. 
         [0030]    It is a feature of the apparatus of this invention that it may include two pairs of adjustable grips to provide a lower lateral pair for unsupported handling and an upper vertical pair with small short-throw brake levers disposed to facilitate easy braking operation by a user with arthritic hands. 
         [0031]    It is an advantage of the apparatus of this invention that the average-sized user, when gripping the upper pair of handles, is standing such that their hips are disposed substantially entirely forward of the line defined by the rear wheel axles. 
         [0032]    It is a feature of the apparatus of this invention that it may include dual-shoe adjustable cable-operated wheel brakes to reduce the grip strength required for the unassisted user to safely brake the apparatus. 
         [0033]    In an exemplary embodiment, the apparatus of this invention is a collapsible upright wheeled walker apparatus for augmenting an upright partially-supported walking gait on a walking surface for an unassisted user having one or more hands and forearms, comprising: a frame having two frame sides each having a top and a bottom and each frame side being disposed between a front frame portion and a rear frame portion; a plurality of wheel assemblies coupled to the frame for supporting the frame above the walking surface and disposed at the vertices of a polygonal footprint on the walking surface within which the user walks during use; an X-folder apparatus including an anterior element having two ends and a posterior element having two ends, wherein the anterior element is rotatably coupled to the posterior element, a first anterior element end is coupled to a first frame side and the second anterior element end is rotatably coupled to an anterior arm having a distal end that is coupled to the second frame side such that rotation of the anterior element in one direction with respect to the anterior arm is limited to an anterior over-center angle; and a first posterior element end is coupled to the second frame side and the second posterior element end is rotatably coupled to a posterior arm having a distal end that is coupled to the first frame side such that rotation of the posterior element in one direction with respect to the posterior arm is limited to a posterior over-center angle; two upper supports each coupled to and disposed at an adjustable height above a respective frame side; two forearm gutters each coupled to a respective upper support for engaging and supporting one user forearm during use, wherein each forearm gutter has a centerline disposed at a first gutter angle with respect to the walking surface and at a second gutter angle with respect to the other forearm gutter centerline; and two upper handles each coupled to a respective upper support anterior to the respective armrest gutter for gripping by one user hand, wherein each upper handle has a centerline disposed at a forward handle angle with respect to the respective forearm gutter centerline. 
         [0034]    The foregoing, together with other objects, features and advantages of this invention can be better appreciated with reference to the following specification, claims and the accompanying drawing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0035]    For a more complete understanding of this invention, reference is now made to the following detailed description of the embodiments as illustrated in the accompanying drawing, in which like reference designations represent like features throughout the several views and wherein: 
           [0036]      FIG. 1  is an oblique upper left front view of an exemplary embodiment of the upright wheeled walker of this invention; 
           [0037]      FIG. 2  is a front view of the upright wheeled walker embodiment of  FIG. 1 ; 
           [0038]      FIG. 3  is a top view of the upright wheeled walker embodiment of  FIG. 1  illustrating the plan views of the polygonal footprint defined by the front and rear wheels and the upper support elements of this invention; 
           [0039]      FIG. 4  is a right side view of the upright wheeled walker embodiment of  FIG. 1 ; 
           [0040]      FIG. 5  is a close-up oblique view of the left front wheel assembly element of the upright wheeled walker embodiment of  FIG. 1 ; 
           [0041]      FIG. 6  is a front view of both the open and collapsed dispositions of the upright wheeled walker embodiment of  FIG. 1  illustrating the operation of the X-Folder and bridge elements of this invention; 
           [0042]      FIG. 7  is a close-up oblique upper tight rear view of the forearm gutter and upper handle elements of the upright wheeled walker embodiment of  FIG. 1 ; 
           [0043]      FIGS. 8A-C  are diagrams illustrating the preferred orientation of the forearm gutter and upper handle elements of this invention; 
           [0044]      FIGS. 9A-D  are detail views illustrating the several frame rigidizing X-folder and bridge elements of the upright wheeled walker embodiment of  FIG. 1 ; and 
           [0045]      FIG. 10  is an oblique view of a user standing in a partially supported position within the polygonal footprint of the upright wheeled walker embodiment of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0046]      FIG. 1  shows a collapsible upright wheeled walker apparatus  100  with a frame  102  supported above a walking surface  104  on four wheel assemblies  106 A-D, including wheel assemblies  106 A-B under a front frame portion and wheel assemblies  106 C-D under a rear frame portion. Frame  102  includes the two frame sides  108 A-B, each having three connected frame side support elements, including the respective elements  110 A-B at the frame side bottoms and the respective element pairs each coupled to a respective upper support channel  112 A-B at the top of the respective frame sides  108 A-B. Wheel assemblies  106 A-D each includes a respective wheel  114 A-D and a respective wheel suspension assembly  116 A-D that is fixed to frame  102  at the vertices of a polygonal footprint  118  on walking surface  104  and are described in connection with  FIG. 5  below. Each of the two upper supports  120 A-B is inserted into and slidably engaged with a respective upper support channel  112 A-B. Each of two locking pins  122 A-B are engaged in a respective upper support channel  112 A-B and operate to lock the respective slidably engaged upper support  120 A-B at a selectable elevation above walking surface  104  for a particular user height 
         [0047]    Each upper support  120 A-B includes a respective forearm gutter  124 A-B and a respective upper handle  126 A-B, which are described in connection with  FIGS. 7 and 8A -C below.  FIG. 1  also shows the X-folder apparatus  127 , which includes an anterior element  128  rotatably-coupled to a posterior element  130  and the anterior arm  132  and the posterior arm  134 . The foldable frame bridge  136  is shown coupled between frame sides  108 A-B at an exemplary elevation above walking surface  104  and the foldable support bridge  138  is shown coupled between upper supports  120 A-B. X-Folder apparatus  127 , foldable frame bridge  136  and foldable support bridge  138  are all useful for collapsing upright wheeled walker  100  for convenient storage and transportation ( FIG. 6 ) and are all described in connection with  FIGS. 9A-D  below. 
         [0048]    Referring to  FIG. 10 , during use, after adjusting both upper supports  120 A-B to a desired elevation above surface  104 , a user  300  stands and steps within footprint  118  on walking surface  104  between frame sides  108 A-B and grasps a respective upper handle  126 A-B with each hand  302 A-B while resting each forearm  304 A-B in a respective armrest gutter  124 A-B, thereby resting at least some upper-body weight on walker apparatus  100  while standing on walking surface  104 . User  300  may then walk forward in the direction shown by the arrow  140  as walker apparatus  100  rolls over surface  104  while supporting at least some weight with armrest gutters  124 A-B, reducing user leg effort and improving user stability and thereby augmenting the user&#39;s ability to step along surface  104  without the assistance of another person. Each of the lower handles  142 A-B is disposed on a respective frame side  108 A-B to permit user  300  to grasp lower handles  142 A-B and move forward, using walker apparatus  100  only for stability without forearm support in the customary manner when desired. 
         [0049]    While the inventors prefer an embodiment with four wheel assemblies, with adjustments to the folder and suspension elements, the apparatus of this invention may also be embodied with three wheels, by using a single front wheel assembly, or with five wheels, by adding a central front wheel assembly, for example, without affecting the other advantages and features described herein. 
         [0050]      FIG. 2  shows a front view of walker apparatus  100  to better illustrate several components of the apparatus of this invention. Like numerals represent like features to those discussed above in connection with  FIG. 1 . In particular,  FIG. 2  better shows the frame bridge offset hinge  144  in foldable frame bridge  136 , the support bridge offset hinge  146  in foldable support bridge  138 , and the X-folder hinge  148  in X-folder apparatus  127  that rotatably couples anterior element  128  to posterior element  130 . Note that a first end of anterior element  128  is coupled to frame side  108 A by the hinge  150  and the opposite end of anterior element  128  is rotatably coupled to anterior arm  132  at the anterior bias hinge  152 . The distal end of anterior arm  132  is rotatably coupled to frame side  108 B by the two hinges  154  and  155  (see  FIG. 3 ) so the distance between hinges  150  and  154 - 155  can be adjusted over a small range by means of the anterior stop screw  156 , which may be better appreciated with reference to the discussion of  FIGS. 9A-D  below. Similarly, a first end of posterior element  130  is coupled to frame side  108 B by the hinge  160  and the opposite end of posterior element  130  is rotatably coupled to posterior arm  134  at the posterior bias hinge  162 . The distal end of posterior arm  134  is rotatably coupled to frame side  108 A by the two hinges  164  and  165  (see  FIG. 3 ) such that the distance between hinges  160  and  164 - 165  can be adjusted over a small range by means of the posterior stop screw  166 , which may be better appreciated with reference to the discussion of  FIGS. 9A-D  below.  FIG. 2  also shows the upper handle centerlines  170 A-B for upper handles  126 A-B respectively, disposition of which may be better appreciated with reference to the description of  FIGS. 7 and 8A -C below. And  FIG. 2  shows the two support bridge ends  172 A-B each rotatably coupled to a respective upper support  120 A-B and the two frame bridge ends  174 A-B each rotatably coupled to a respective upper support  120 A-B. 
         [0051]      FIG. 3  shows a top view of walker apparatus  100  to better illustrate several components of the apparatus of this invention. Like numerals represent like features to those discussed above in connection with  FIGS. 1-2 . in particular,  FIG. 3  shows the forearm gutter centerlines  176 A-B for forearm gutters  124 A-B respectively, the preferred disposition of which may be better appreciated with reference to the description of  FIGS. 7 and 8A -C below.  FIG. 3  better illustrates the coupling of anterior arm  132  to frame side  108 B and the coupling and disposition of posterior arm  134  to frame side  108 A, for example. 
         [0052]      FIG. 4  shows a right side view of walker apparatus  100  to better illustrate several components of the apparatus of this invention. Like numerals represent like features to those discussed above in connection with  FIGS. 1-3 .  FIG. 4  better illustrates the exemplary embodiment of posterior arm  134  and the adjustable engagement of upper support  120 A to upper support channel  112 A at the top of frame side  108 A, for example. 
         [0053]      FIG. 5  shows wheel assembly  106 B in more detail. A wheel fork assembly  178  is rotatably coupled to wheel  11413  at an axle  180  and to wheel suspension assembly  116 B at a hinge  182  thereby permitting displacement of frame element  110 B with respect to surface  104  responsive to any rotation of wheel fork assembly  178  about hinge  182 . Rotation of wheel fork assembly  134  about hinge  182  changes the elevation of frame element  110 B above axle  180 . A shock absorber assembly  184  is coupled between frame element  110 B and wheel fork  178  to moderate the transmission of wheel motion to the frame during use. Shock absorber assembly  184  includes a shock absorber (not shown) preloaded to a predetermined load limit and described in the commonly-assigned U.S. patent application Ser. No. 15/012,784 filed on Feb. 1, 2016 and entirely incorporated herein by reference. 
         [0054]      FIG. 6  illustrates the front view of  FIG. 2  of walker apparatus  100  in the open configuration (dotted lines) overlaid with the same walker apparatus  100  in a collapsed configuration (solid lines) useful for transportation and storage. Walker apparatus  100  may be folded from the open configuration to the collapsed configuration by (a) rotating both upper handles  126 A-B into the downward position shown, (b) releasing the locking pins  122 A-B ( FIGS. 1 and 4 ) and dropping the two upper supports  120 A-B down to their lowest elevation, (c) releasing frame bridge offset hinge  144  and support bridge offset hinge  146  and initiating the folding of frame bridge  136  and support bridge  138  respectively, and (d) collapsing frame bridge  136 , support bridge  138  and X-folder apparatus  127  while forcing the two frame sides  108 A-B together. It may be readily appreciated from  FIG. 6  that walker apparatus  100  may be returned to the open configuration for use by reversing these steps while forcing frame sides  108 A-B apart and locking frame bridge offset hinge  144  and support bridge offset hinge  146  before returning upper supports  120 A-B to their desired elevation and fixing them with locking pins  122 A-B before returning upper handles  126 A-B to their upright position shown in  FIG. 2 . 
         [0055]    When folding X-folder apparatus  127 , anterior element  128  rotates about X-folder hinge  148  with respect to posterior element  130  and rotation of each respective component also occurs at each of the six hinges  150 ,  154 - 155 ,  160  and  164 - 165  as may be appreciated from  FIG. 6 . Moreover, during such rotation, anterior arm  132  rotates about anterior bias hinge  152  at the distal end of anterior element  128  and posterior arm  134  rotates about posterior bias hinge  162  at distal end of posterior element  128 . The purpose and function of anterior and posterior bias hinges  152  and  162  are described below in connection with  FIGS. 9A-D . 
         [0056]      FIG. 7  provides a closer oblique view of the upper support structure of walker apparatus  100  to better illustrate the relative disposition and orientation of forearm gutters  124 A-B and upper handles  126 A- 13 , which features are now described in detail with reference to  FIGS. 8A-C . 
         [0057]      FIGS. 8A-C  are diagrams illustrating the preferred disposition and orientation of forearm gutters  124 A-B and upper handles  126 A-B.  FIG. 8A  illustrates the top view of  FIG. 3  with upper supports  120 A-B and support bridge  138  isolated for clarity. The inventors have found that forearm gutter centerlines  176 A-B are preferably aligned as shown, with the two angles  204 A-B fixed at about 14 degrees and being substantially equal, which provides the optimal ergonomic support for the widest range of user sizes when fixing the gutter spacing  205  to about 18.5±1 inches between the geometric midpoints  206 A-B of forearm gutters  124 A-B. Angles  204 A-B may be varied over a range of [0-18] degrees, but many orientations within that range would require changes to gutter spacing  205  to facilitate use by many users, who would find the reoriented forearm gutters  124 A-B either too closely spaced or too widely spaced for feasible use. The inventors have discovered that a 14 degree setting for angles  204 A-B is comfortable for the most users because it provides a “self-compensating” support system. This self-compensating feature may be appreciated by considering that a shorter user with shorter forearms must move her arms forward to grip upper handles  126 A-B. This places her elbows forward in the “V” defined by centerlines  176 A-B and places her (narrower) shoulders above a narrower position in the “V.” Alternatively, consider that a taller user with broader shoulders must move his arms back to grip upper handles  126 A-B. This places his elbows rearward in the “V” defined by centerlines  176 A-B and places his broader shoulders above a wider position in the “V.” The inventors found that this “self-compensation” permits using forearm gutters and upper handles with fixed spacing and orientation to support the majority of prospective users in comfort. 
         [0058]      FIG. 8B  is an isolated right-side view better illustrating the disposition and orientation of armrest gutter  124 A and upper handle  126 A with respect to walking surface  104  ( FIGS. 1 and 10 ). Although not seen in  FIG. 8B , the relative dispositions of armrest gutter  124 B and upper handle  126 B with respect to walking surface  104  are substantially the same as shown in  FIG. 8B . The horizontal line  208 A and the vertical line  210 A are respectively parallel and perpendicular to walking surface  104 . The inventors have discovered through testing that fixing the angle  212 A between horizontal line  208 A and the gutter axis  214 A to a value within the range [ 10 ,  20 ] degrees in an upward direction from rear to front as shown is preferred. The optimal ergonomic benefits are gained with angle  212 A fixed at about 14 degrees, which satisfies most people under most conditions. 
         [0059]    Similarly, the inventors discovered through testing that the forward handle angle  216 A between the gutter axis perpendicular  217 A and handle centerline  170 A is preferably fixed somewhere in the range of [10, 40] degrees (preferably at about 30 degrees) forward of gutter axis perpendicular  217 A or equivalently at about 120 degrees (30+90) forward from the plane defined by gutter axis  214 A and about 16 degrees (30−14) forward of true vertical. As seen below in connection with  FIG. 8C , each forward handle angle  216 A-B ( 216 B not shown) is fixed with respect to the plane defined by a respective gutter axis  214 A-B ( 214 B not shown) but each handle  126 A-B ( 1269  not shown) may be rotated about an axis co parallel with a respective forearm gutter centerline  176 A-B. The disposition and orientation of forearm gutter  1249  and upper handle  1269  may be appreciated by analogy when referring to this discussion of  FIG. 8B . 
         [0060]      FIG. 8C  is an isolated upper front oblique view better illustrating the disposition and orientation of armrest gutters  124 A-B and upper handles  126 A-B. Although similar to the front view of  FIG. 2 ,  FIG. 8C  is a view of a plane disposed perpendicularly to the plane defined by armrest gutter axes  176 A-B ( FIG. 8A ) and axes  214 A-B ( FIG. 8B ). This may be appreciated by recognizing that the viewpoint of  FIG. 8C  is elevated above the true horizontal viewpoint of  FIG. 2  by an angle equal to angle  212 A ( FIG. 8B ). Both the vertical line  210 B and vertical line  210 A are perpendicular to walking surface  104  ( FIGS. 1 and 10 ). The transverse handle angles  218 A-B may be varied independently and locked in any of several orientations between vertical (zero degrees) and horizontal (90 degrees) by releasing upper handle latches  186 A-B ( FIG. 8A ) and reorienting respective upper handles  126 A-B. The inventors have found that most users preferred fixing transverse handle angles  218 A-B at some value in a range of [0, 45] degrees with more preferring the larger value. 
         [0061]      FIG. 9A  illustrates the various frame-rigidizing folder elements of the apparatus of this invention.  FIG. 2  shows anterior and posterior stop screws  156  and  166  in a larger context. When walker apparatus  100  is in the open configuration shown in  FIGS. 2 and 9A , frame sides  108 A-B are substantially parallel to one another, which permits upper supports  120 A-B to rise or fall through their entire adjustment range without binding with the respective upper support channels  112 A-B. When frame bridge offset hinge  144  is latched, frame bridge  136  is under longitudinal compression and urges frame sides  108 A-B apart at hinges  174 A-B by applying an upper spreading force represented by the arrows  188 A-B to hinges  174 A-B respectively. Upper spreading force  188 A-B induces a lower spreading force represented by the arrows  190 A-B at hinges  150  and  160  respectively. Upper and lower spreading forces  188 A-B and  190 A-B induce a counterclockwise torque in frame side  108 A, represented by the arrow  192 A and an opposing clockwise torque in frame side  108 B, represented by the arrow  192 , urging frame sides  108 A-B (respectively) about hinges  150  and  160  and against hinges  164 - 165  and hinges  154 - 155  with a closing force represented by the arrows  194 A-B. This also may be appreciated by understanding that pulling hinge  150  outward (arrow  190 A) applies an inward force (arrow  194 B) on the opposite hinges  154 - 155 , because hinges  150  and hinges  154 - 155  are linked together by the coupled anterior element  128  and anterior arm  132 . Similarly, pulling hinge  160  outward (arrow  190 B) applies an inward force (arrow  194 A) on the opposite hinges  164 - 165 , because hinges  160  and  164 - 165  are linked together by the coupled posterior element  130  and posterior arm  134 . The frame-stiffening operation of anterior and posterior stop screws  156  and  166  is now described. 
         [0062]      FIG. 9B  is a top view that illustrates from above the upper spreading force at arrows  188 A-B from frame bridge  136  and the resulting lower spreading force at the arrows  190 A-B. Because frame bridge  136  is disposed behind X-folder apparatus  127  and posterior arm  134  is coupled at hinges  164  and  165 , closing force  194 A ( FIG. 9A ) is split into a rear closing force represented by the arrow  196 A and a front closing force represented by the arrow  198 A. Similarly, because anterior arm  132  is coupled at hinges  154  and  155 , closing force  194 B ( FIG. 9A ) is split into a rear closing force represented by the arrow  196 B and a front closing force represented by the arrow  198 B. It may be appreciated that front closing forces  198 A-B exceed rear closing forces  196 A-B because of the disposition of the upper spreading force at arrows  188 A-B. 
         [0063]    It is an important aspect of the apparatus of this invention that the upper spreading force at arrows  188 A-B across the latched frame bridge  136  eliminates all play or slack at hinges  150 ,  160 ,  154 - 155  and  164 - 165  and urges frame sides  108 A-B into torsion (torques  192 A-B in  FIG. 9A ). Another important aspect is that torques  192 A-B are each adjustable by means of the anterior and posterior tension adjusters, respectively, shown here embodied as adjustable stop screws  156  and  166 . The inventors have discovered that imposing such an adjustable torque on each of frame sides  108 A-B stiffens them against any new or transient forces applied through any one of upper supports  120 A-B or wheel assemblies  106 A-D that may otherwise push one of frame sides  108 A-B into rotation or translation with respect to the other or into shear. 
         [0064]    It may be appreciated from this description of  FIGS. 9A-B , for example, that frame bridge  136 , while nominally in compression, may be urged into tension by additional spreading forces transferred from the user weight supported by upper supports  120 A-B but, in this embodiment, such loading has little effect on frame stability because posterior and anterior arms  132  and  134  are both locked over center by upper spreading forces  188 A-B at frame bridge  136 . Support bridge  138  has a stiffening effect similar to that discussed above for frame bridge  136 , which stabilizes upper supports  120 A-B with respect to one another by linking them together and taking up any play between the interior surfaces of upper support channels  112 A-B and the respective upper support  120 A-B. 
         [0065]      FIG. 9C  provides a cross-sectional view of offset hinge  144  ( FIG. 9B ) showing the U-shaped member. Both frame bridge  136  and support bridge  138  are foldable at a respective offset hinge  144  and  146  that locks over center in compression, both functioning in the same manner. U-shaped member  200  functions to limit travel and thereby reduce loading of the bridge hinge latch  202 . 
         [0066]      FIG. 9D  provides an X-ray view of the detailed orientation and disposition of the several elements of X-folder apparatus  127  illustrating the function of the tension adjuster elements of this invention. When frame sides  108 A-B are disposed substantially parallel to one another, anterior and posterior arms  132 - 134  are each restrained at a substantially 5.55 degree angle (the arrows  220 A-B) over the center defined by the respective anterior and posterior elements  128  and  130 . Increasing the inward forces  194 A-B ( FIG. 9A ) at hinges  154  and  164  urges the over-center angles  220 A-B above 5.55 degrees. 
         [0067]    The anterior and posterior tension adjusters are embodied as stop screws  156  and  166 , respectively, abutting the lower ends of the anterior and posterior elements  128  and  130  to limit travel and control the tensions imposed to stabilize frame  102  ( FIG. 1 ). Frame tension is adjusted by screwing in stop screws  156  and  166  until contacting anterior and posterior elements  128  and  130  respectively, with frame bridge offset hinge  144  ( FIG. 9A ) unlatched. Stop screws  156  and  166  are each then turned inward by about ¾ turn to impose a tension that urges a reduction in the respective over-center angle  220 A-B to less than the nominal 5.55 degrees. Urging such reduction attempts to increase the effective length of the anterior element-arm combination ( 128  plus  132 ) and/or the posterior element-arm combination ( 130  plus  134 ), thereby pre-loading frame sides  108 A-B to stabilize and stiffen frame  102  in the open configuration ( FIGS. 1-4, 6 and 10 ). 
         [0068]    These elements are useful for pre-tensioning the walker frame of this invention. Once adjusted for adequate frame stabilization tension, and verified by forcing frame sides  108 A-B together and apart by means of lower handles  142 A-B, a thread locking agent (Loctite® 290 or equivalent) may be applied to stop screws  156  and  166 . This frame pre-tensioning feature of the walker apparatus of this invention also allow a wider tolerance for component length variation, which reduces fabrication costs. 
         [0069]    Clearly, other embodiments and modifications of this invention may occur readily to those of ordinary skill in the art in view of these teachings. Therefore, this invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawing.