US3104112A

US3104112A - Stair climbing wheel chair

Info

Publication number: US3104112A
Application number: US206698A
Authority: US
Inventors: Jesse W Crail
Original assignee: Individual
Current assignee: Individual
Priority date: 1962-07-02
Filing date: 1962-07-02
Publication date: 1963-09-17
Anticipated expiration: 1980-09-17

Description

sept. 17, 1963 3,104,112

J. W. CRAIL STAIR CLIMBING WHEEL CHAIR Filed July 2, 1962 4@ Hb 44 INVENToR. 4 I3 JESSE W. CRA/L United States Patent 3,104,112 STAIR CLHVIBING WHEEL CHAR .lesse W. Crail, 38692 Edenhurst Ave., Los Angeles, Calif. Filed July 2, 1962, Ser. No. 296,693 4 Claims. (Cl. 28d- 5.2)

This invention relates generally to stair climbing wheel chairs, and more particularly to such a wheel chair in which auxiliary front wheels can be lowered land releasably locked into stair climbing position by a backward swinging linkage means, in combination with an adjustable pressure driving means which can be temporarily retracted for operation of said back-ward swinging linkage means.

A great variety of wheel chairs have been designed for the convenient transport of persons who suffer from some disability which prevents them from walking for an extended period of time, or from walking at all. A large and important category of wheel chair designs include a means of locomotion in which the use-r himself supplies the driving power. Many handicapped persons are handicapped only with respect to walking, Iand are equal to or superior to unhandicapped persons in the strength and dexterity of their arms and hands. Wheel chairs have, therefore, been ydesigned with manually operated crank means, reciprocating drive levers and the like. Usual-ly, such occupant-operated chairs are also provided with handles at the back so that they can be pushed by an attendant when the occupant does not wish to make the physical exertion required when he is supplying his own power of locomotion.

However, many healthy handicapped persons do not want to rely upon the presence of an attendant, and prefer to travel alone almost as freely 4as if they were able to walk as well as the average unhandicapped person. Many excellent wheel chairs heretofore known have provided the handicapped person with complete mobility as long as he has restricted himself to horizontal or nearly horizontal services. Up t the present time, no wheel chair capable of climbing stairs has come into widespread use.

Various stair climbing wheel chairs have been proposed, but all have suffered from some major limitation which made them unsuited or impractical for most wheel chair users. Thus, some stair climbing wheel chair designs have involved such extensive and massive mechanism that only the most athletic of wheel chair users could apply the muscle power needed to operate them `on stairs, or even on horizontal services. Other stair climbing wheel chairs have required electrical or gasoline power means.

Almost all widely used rwheel chairs can be folded into a collapsed posit-ion. Experience has proven that this feature is a very important one, not merely for convenience in storage when the chair is not in use, but also for transporting the chair when the occupant travels by automobile or by public transportation means, or when the occupant wishes to sit in a theater seat and tempor-arily store the chair in a space small enough to prevent it from blocking the passage of other people. Some previously proposed stair climbing Wheel chairs have involved a construction inconsistent with collapsibility; consequently, `such designs have never been accepted into general use.

It is an important object of the present invention to pro-vide a stair climbing Iwheel chair construction which can be used in folding wheel chairs.

It is another important object yof the present invention to provide a wheel chair in which the stair climbing mechanism is light, very strong, and readily operable on stairs by a person of average strength, without the aid of any auxiliary motor means.

,ice

It is important to note that in the achievement of these objects, it has been necessary to provide safety means to prevent any runaway of the wheel chair during the stair climbing operation. Also, the manual drive mechanism used during stair climbing has been made retractable so that ordinary hand rings can be used when traveling on the level.

Still another important feature of the present invention, which makes it substantially superior to previously known stair climbing designs, is that the wheel chair occupant :is able to convert his Wheel chair into stair climbing position, while at the same time lifting the weight of himself land his chair, by means of the linkage which enables him to apply the maximum strength of his arms.

The objects and `advantages of the invention are achieved by means of =a lconstruction which will best be understood from -a description of one preferred specific embodiment, which is illustrated in the accompanying drawings, in which:

FIGURE 1 is la right side elevational view of a Wheel chair constructed according to the invention, with the stair climbing mechanism retracted and out of use, so that the chair can be conveniently moved over a 'horizontal surface by the occupant;

.FIGURE 2 is a right side elevational view of the chair of FIGURE l, but with the stair climbing mechanism lowered into stair climbing position;

FIGURE 3 is a plan View of the wheel chair as viewed in FIGURE l, but showin-g the left manual driving wheel rotated into ia retracted position;

FIGURE 4 is a perspective view of a fragmentary portion of the wheel chair, yas seen from a point looking at the left rear vertical frame member, but with portions of the chair disassembled to reveal construction which would otherwise be concealed; and

FIGURE 5 is a detail perspective view of a latch employed for locking the stair climbing mechanism in retracted position'as illustrated in FIGURE l.

In the drawings, the wheel chair, indicated generally by the numeral 10, is seen to have `all its essential parts mounted on a folding metal frame indicated generally by the numeral r11, and comprised :of right and left

side frame members

12 and 13, respectively, best seen in the plan View of FIGURE 3, and folding

cross-bar members

14 and 15.

The `

side frame members

12 and 13 are substantially identical in construction. 'Ihe fra-mes may be of standard types used in wheel chairs Iwell known in presently used designs. For example, chrome plated steel tubing welded into the shape shown, `or any convenient equivalent shape may be employed. In the particular embodiment illustrated, right side frame 12 (and also left side frame 13) is comprised of front and rear

vertical members

20 and 21, an-d three

horizontal members

22, 23, and 24, all l welded together into an integral side frame structure. Upper horizontal member 22 serves as an arm rest; middle horizontal member 23- is a seat frame member; and the lower horizontal member 24 is a base member for the side frame 12.

As seen in FIGURE 3, the folding crossbar members '14 and 15 serve to hold the Iside

frame members

12 and 13 parallel to each other and spaced from each other a ldistance corresponding .to the width yof the wheel chair seat.

'Ifhe novelty of the present invention does not reside in the particular means by which folding is achieved, or in the particular construction yof folding cro-ssbars 14 and I15. The novelty resides in a combination which provides a stair climbing wheel chair, and in a stair climbing mechanism which, unlike many previously known stair are rotatably connected by

sleeves

33 and 34 on seat frame member 23 and base frame member 24, respectively, of the side frames `12 and 13. It will be understood, however, that any suitable folding mechanism may be used between the

side frames

12 and 13 for holding them in erected position for wheel chair use, or folded together for storage.

The plan view of FIGURE 3 reveals that a readily foldable fabric seat 4t) and fabric back 41 (shown partially broken `away to illustrate the

folding crossbars

14 and 15 in plan) are stretched between the

side frames

12 and 13. Also, as is conventional in most folding wheel chairs, each of the

side frames

12 and 13 is provided at the forward portion with

foot support brackets

42 and 43, which support folding foot rests 44 and 45, respectively. Push handles 46 and 47 are provided at the rear of the wheel chair 1t? on the upper ends of rear vertical members 21.

The main wheels provided for rolling of the wheel chair are not the twenty-five inch hard-tire wheels usually found in most of the folding lwheel chairs available on the market at the present time, but are larger, and use pneumatic tires. The main wheels, right and left

main wheels

50 and 51, respectively, lare rotatably mounted on right and left stub wheel shafts 52 land 53, respectively. Tlie main wheels are provided with hand-propulsion rings 50a and 51a seen in'pl-an in FIG. 3, and partially broken away in FIGS. l and 2 for purposes of illustration of the stair climbing mechanism. The

stub shafts

52 and 53 are integrally mounted on the rear verticals 21 of right and

left side frames

12 and 13, usually just a short space below the level of the seat frame members 23. Main wheels 50 yand 51 `are usually of a light spoke and rim construction with inflated rubber tires 54. Also, the main wheels are usually of relatively large diameter, being between thirty inches by two inches in the specific embodiment, so as to provide the wheel chair user with a smooth rolling transport despite irregularities in ground surface, and also, so that an attendant may push or pull the wheel chair up the average stairway, lwhich usually has treads and risers of about ten inches and seven inches, respectively.

The forward part of the wheel chair 10 is provided with rolling support by right yand left identical swiveling casters, typically illustrated by right caster 60. Preferably, the two swiveling casters 60 are mounted under the forward portions of

side frames

12 and 13, respectively.

It has been common in previously known wheel chairs to provide the occupant with crank-operated friction wheels with `which to achieve self-locomotion. Right and

left friction lwheels

65 and 66, and their associated cranks 67 and 63, are illustrated as mounted on arm rest member 22 of the side frames 12 'and 13. They are adapted, when in driving position as illustrated in FIG- URES 1 `and 2 for right `friction wheel 65, to bear against the tread of tires 54, 'and thereby enable an occupant to drive the `niain wheels G and 51 by manual rotation of

cranks

67 and 68. However, the

friction wheels

65 and 66 in the illustrated specic embodiment of the present invention are mounted in a novel manner in order to coact with other components of the inventive combination which makes it possible t0 use the wheel chair of the invention for self-locomotion Iup a stairway.

It is `a much preferred form of the present invention to make the

friction wheels

65 and 66 retractable from a driving position `as illustrated for right friction wheel in FIGURES l, 2, and 3, and for left friction wheel in FIGURE 4, on the one hand, and, on the other hand, a retracted position illustrated in FIGURE 3 for left friction wheel 66. Also, `as will be described hereinafter, it

l is much preferred to provide the right and left friction wheels with adjustable drive pressure means.

Before proceeding to a detailed description of the `preferred form of

retractable friction wheels

65 and 66, the principal stair climbing mechanism will be described. The wheel chair 10 provided with right and left

stair climbing wheels

70 and 71, which [are mounted at the forward ends of

arms

72 and 73, on stub shafts 74 `and 75, respectively.

Arms

72 and 73 are pivotally rmounted to side frames 12 and 13, preferably in a simple and convenient way by being mounted 'on main

wheel stub shafts

52 and 53, inboard of main wheels 5t) `and 51. Thus, the stair climbing wheels 7G and 71 may be selectively swung between 'a retracted position, as illustrated in FIGURE l, when not in use; and a stair climbing position, as illustrated in FIGURE 2, when lowered for stair climbing use.

The right and left arms 72 `and 73 may be braced to each other to form a rigid unitary frame structure by means of transverse brace 75, which is `preferably hinged at the ends and middle as indicated by hinges 76, so as to be foldable with the wheel chair 10. A standard type of bolt latch 77, or any convenient type of releasable locking means is provided on the transverse brace 75 to lock it into unfolded position.

Also, as illustrated in FIGURE 5, a retractable spring latch 78 is mounted on the forward side of side frame 12 so yas to provide releasable means for locking the

arms

72 and 73 in the raised position illustrated in FIGURE l.

The

4arms

72 and 73 are pulled downward into the stair climbing position of FIGURE 2 by means of right and left linkages, 8i) and 81, respectively, which are pivotally mounted at fulcrurns 82 vand 83, respectively, in relatively massive fulcrum support `bars 84 and S5, respectively, which are integral parts of right and left side frames, I12 and 13, respectively.

The linkages Si) and 81 lare identical, and are constructed as illustrated for linkage 8i) in FIGURES l and 2. A bell crank 86 is mounted in the fulcrum S2. At its lower end, it is connected by pivot connection 87 to an arm link 88, which is in turn pivotally connected at 89 to arm 72. A locking stop 90 is Welded to the `upper end of arm link 8S, so that it forms a rigid brace for arm 72 when the linkage 80 is pulled into the position illustrated in FIGURE 2.

Preferably, the upper end of valve crank 86 is provided with a folding lever ram 95, hinged to the bell crank at 96. This folding nature makes it possible to fold the lever downward and out of the way of the friction wheels 65 'and 66, when the wheel chair 10 is traveling horizontally, and the stair climbing apparatus is out of use, as illustrated in FIGURE l.

Although the operating levers 95 could be formed to by-pass the

cranks

67 and 68, while the latter are in their normal outboard position, it is much preferred to make

friction wheels

65 and 66 retractable, as illustrated for friction wheel 66 in FIGURE 3, by means to be described hereinafter, so that the seated occupant of rwheel chair 10 will have a maximum of leverage with a minimum of reach for converting from horizontal travel position of FIGURE 1 tto the stair climbing position of FIGURE 2.

In FIGURE 4, the arch of movement of the lever 95 is illustrated by the arrow 100. Also, it vwill ,be seen that a catch 101 is welded to the outboard side of the arm member 22 so as to catch lever arm 95 and retain the linkage v81 in stair climbing disposition. An identical construction is provided yfor the right side frame 12.

FIGURES 3 and 4 illustrate retraction and adjustment for the

friction wheels

65 and 66. It will be understood that the crank 68 has `been removed from the friction wheel 66 in FIGURE 4, in order `to better illustrate the vertical adjustment of friction wheel 66. As seen in FIG- URE 4, friction wheel 66 carries an integral crank shaft 110, which is journalled in an inverted adjustable yoke 1,11. Yoke 111 is vertically adjustable within an outer yoke 112, the sides of which are provided -with vertical slots 113 -to permit the vertical adjustment of friction Wheel shaft 110.

Outer yoke 112 is welded integrally to a sleeve 114,

lwhich is rotatable on arm member 22, between an outboard ldriving position (as illustrated for rig-ht friction wheel 65 in FIGURE 3) and an inboard retracted po- -sition (as illustratedl yfor left friction wheel 66 in F-IG- 'URE 3) to permit full swing of lever 95 .along the arc 'indicated in FIGURE 4 by double arrow 100, for purposes of lowering

arms

72 and 73 to stair climbing position illustrated in FIGURE 2. A latch 115 is provided for releasably locking the sleeve 114 in drive position.

Vertical adjustment of the

drive wheels

65 and 66 is accomplished by means illustrated for drive wheel 66 in FIGURE 4. A smallv adjustment crank 120, with la threaded vertical shaft 121, is received in a threaded bore 122 in the upper portion of outer yyoke 112, so that rop tation of adjustment crank 120 can be used to lforce its lower end against the upper portion of inner yoke 111,

thereby driving it downward into greater pressure of en- `position .for providing safety against accidental runaway.

As seen in FIGURE l, `a ratchet wheel 131 is rotatable integral with main Wheel 50 on right main wheel stub shaft 52, ratchet Wheel 131 being formed 'with teeth 131a beveled in a direction to prevent clockwise movement when travelling in :an upstairs direction, only, when engaged as shown in FIGURE 2. However, a `ratchet pawl 132, .at the lower end of pawl bar 133` is held out of engagement with the ratchet teeth 131a as illustrated in FIGURE 1, and lowered into engaging position during stair climbing, las illustrated in FIGURE 2. The pawl bar 133 is vertically reciprocable in

brackets

134, 135, and 136, being urged downwardly by a spring 137 engaging .a shoulder 138, integral with the bar 1313'. A catch 139, on the back of rear vertical member 21 is provided to hold bar 133 in its disengaged position. However, when bar 133 lowered into its engaged position for stair climbing, the spring 137 acts to urge the pawl 132 Adownwardly into engagement with ratchet teeth 131a.

It will be seen yfrom the foregoing description that I bave provided a simple but effective stair climbing means of light Weight, which can be varied to suit ya variety of forms of construction Without departing from the spirit of the invention. Also, it will be noted that my stair climbing mechanism not restricted to the heavy, nonfolding type of wheel chair, but may be used on wheel chairs both folding and non-folding. Indeed, in its preferred form, it is especially adapted because of its lightness in Weight Iand fol-ding features to be used in a light Weight folding wheel chair intended for self-propulsion by the user.

Although no brake means is illustrated or described, any suitable brake means would be a desirable accessory.

It will be understood that my invention is not restricted to the details of the specific embodiment illustrated but is intended to comprehend the variants obvious to those skilled in the art but falling within t-he scope of the following claims. For example, the simple catch d may be replaced by any suitable latch means. There is usually sufficient flexibility in lever 95 so that it can be released from catch 101 simply by a short backward pull, followed by a lateral deflection outward. However, more complex movable latch means, such as latch 78, illustrated in FIGURE 5, and used for holding np the arms 6 12 and 13, may be used on arm members 22 `for locking lever in the position shown in FIGURE 4.

Having thus described the invention, 'what is claimed Ias new in `support of Letters Patent is:

ll. In an occupant-propelled folding wheel chair of the type in which side frames are supported on folding crossbar means, each side frame having a front caster and a rear main wheel sufiiciently large in diameter to roll over normal stair steps, and in which the occupant can propel the chair by hand-operated means for driving said main wheels, a stair climbing mechanism which includes: a pair of arms, one carried on each of said side frames, each said arm being pivoted at its rearward end coaXially with one of said main Wheels to permit the forward end of said arm to swing between a raised and lowered position; a pair of stair-cli-mbing wheels, one rotatably mounted on the forward end of each of .said arms, said wheels having a diameter smaller than said main wheels but large enough to roll over normal stair steps; a transverse brace member between said arms, said brace member being disposed suliiciently forward to clear the side frames'of said wheel chair during swinging movement of said arms,

'and said brace member being foldable to cooperate with the folding of said wheel chair; a pair of linkage means, one on each of said side frames, each of said linkage means being pivotally mounted on one of said side frames and each said linkage means being adapted to be manually operated by an occupant of said wheel chair to move said arms from a raised position to a lowered position for stair climbing; a ratchet gear rotatable integrally with each of said main wheels; retractable pawl means for engaging said ratchet -gear during stair climbing operation; and releasable latch means for holding said stair climbing mechanism in stair climbing position.

2. A stair climbing, folding wheel chair, which includes: a pair of side frames, each of said side frames including an arm rest member; foldable seat and back means between said side frames; a foldable transverse structure between said side frames, for holding said side frames a seat-width apart, or alternatively, in a position folded together; a front wheel means on each of said side frames; a main wheel rotatably mounted on each of said side frames near the rear thereof, each of said main wheels having sufficient radius to bring its rim into the vicinity of said shaft portion of said arm rests member; a manually-operated drive means for driving said main wheel on each of said arm rests, and rotatable between a drive position adjacent the rim of said main wheel, and a retracted position inboard of said arm rest member; a pair of arms, one carried on each of said -side fra-mes, each said arm being pivoted at the rearward part of one of said side frames to permit the forward end of said arm to swing between a raised and lowered position; a wheel rotatably mounted on the forward end of each of said arms; a transverse brace member between said arms, said brace member being disposed sufficiently forward to clear the side frames of said wheel chair during swinging movement of said arms, and said brace member being foldable to cooperate with the folding of said wheel chair; a pair of linkage means, one on each of said side frames, each of said linkage means being pivotal-ly mounted on one of said side frames, and each said linkage means being adapted to move said arms from a raised position to a lowered position for stair climbing; lever means for operating each of said linkage means, said lever means being movable from a position forward of said drive means carrier to a position aft of said drive means carrier when said carrier is retracted to an unloaded position; ratchet means integral with said main wheel; and pawl means engageable with said ratchet means for stair climbing, and retractable for horizontal travel.

3. A stair climbing, folding wheel chair, which includes: a pair of side frames, each of said side frames including an arm rest member with a cylindrical shaft portion near the forward end; foldable seat and back means between said side frames; a foldable transverse structure between said side frames, for holding said side frames a seat-width apart, or alternatively, in a position folded together; a front wheel means on each of said frames; a main wheel shaft projecting laterally outward from each of said side frames, at the rear portion thereof; a main wheel rotatably mounted on each of said main wheel shafts, each of said main wheels having suflicient radius to -bring its rim into the vicinity of said shaft portion of said ar-m rests member; a drive means carrier yoke including a sleeve rotatably carried on said shaft portion of each of said arm rests; and rotatable between a drive position adjacent the rim of said main wheel, and a retracted position inboard of said arm rest mem-ber; a locking means for locking each of said drive means carrier in drive position; a manually operated friction drive wheel mounted in each of said carrier yokes for driving said main wheels; a pair of arms, one carried on each of said side frames, each said arm being pivoted at its rearward end on one of said main wheel shafts to permit the forward end of said arm to swing between a raised and lowered position; a wheel rotatably mounted on the forward end of each of said arms; a transverse Ibrace member between said arms, said brace member being disposed suciently forward to clear the side frames of said wheel chair during swinging movement of said arms, and said brace member being foldable to cooperate with the fold- -ing of said wheel chair; a pair of linkage means, one on each of said side frames, each of said linkage means being pivotally mounted on one of said side frames, and each said linkage means being adapted to move said arms from a raised position to a lowered position for stair climbing; lever Imeans for operating each of said linkage means, said lever means being movable from a position forward of said drive means carrier to a position aft of said drive means carrier when said carrier is retracted to an unloaded position; ratchet means for preventing runaway of said wheel chair movement during stair climbing; and a releasable latch means on at least one of said arm rest members for holding said stair climbing mechanism in stair climbing position.

4. A stair climbing, `folding wheel chair, which includes: a pair of side lframes, each of said side frames including an arm rest member with a cylindrical shaft portion near the forward end; foldable seat and back mea-ns between said side frames; a yfoldable transverse structure between said side frames, for holding said side frames a seatwvidt'n apart, or alternatively, in a position folded together; a front wheel means on each tof said side frames; a main wheel shaft projecting laterally outward from each of said side frames, at the rear portion thereof; a main wheel rotatably mounted on each of said main wheel shafts, each of said main wheels having suicient radius to bring its rim into the vicinity of said shaft portion of said arm rest members; a pair of drive means carriers, one of said carriers being rotatably carried on said shaft portion of each of said side frames, and rotatable between a drive position adjcent the rim of said main wheel, and a retracted position inboard of said arm rest member; a locking means for locking each of said drive means carriers in drive position; an inverted yoke member vertically adjustable within each of said drive means carriers; friction wheels rotatably mounted in said inverted yokes, and en gaging the rims 4of said main wheels; a pair of crank means `for rotating said friction wheels and thereby driving said main wheels; adjustment means between said drive carrier 4and said inverted yoke for adjusting the pressure of said friction wheel against the rim of said main wheel; a pair of arms, one carried on each of said side frames, each said arm being pivoted at its rearward end on one of said main wheel shafts -to permit the forward end of said arm to swing between a raised and lowered position; a wheel rotatably mounted on the forward end of each of said arms; a transverse brace member between said arms, said brace member being `disposed sufficient forward to clear the side frames of said wheel chair during swinging movement of said arms, and said brace member being tfoldable to cooperate with the folding of said wheel chair; a pair of linkage means, one on each of said side frames, each of said li-nkage means being pivotally mounted on one of said side frames, and each said linkage means being adapted to move said arms from a raised position to a lowered position for stair climbing; lever means for operating each of said linkage means, said lever means being movable from a position forward of said drive means carrier to a position aft of said drive means carrier when said carrier is retracted to an unloaded position; first releasable latch means for retaining said stair climbing mechanism in stair climbing position, and second releasable latch means for holding it in a raised inoperative position.

References Cited in the le of this patent UNITED STATES PATENTS 838,228 Williams Dec. 11, 1906 865,514 Mullenmeister Sept. 10, 1907 2,643,898 Everest et al June 10, 1953 FOREIGN PATENTS 215,765 Germany Nov. 2, 1909 717,241 Germany Feb. 9, 1942 137,096 Great Britain Jan. 8, 1920

Claims

1. IN AN OCCUPANT-PROPELLED FOLDING WHEEL CHAIR OF THE TYPE IN WHICH SIDE FRAMES ARE SUPPORTED ON FOLDING CROSSBAR MEANS, EACH SIDE FRAME HAVING A FRONT CASTER AND A REAR MAIN WHEEL SUFFICIENTLY LARGE IN DIAMETER TO ROLL OVER NORMAL STAIR STEPS, AND IN WHICH THE OCCUPANT CAN PROPEL THE CHAIR BY HAND-OPERATED MEANS FOR DRIVING SAID MAIN WHEELS, A STAIR CLIMBING MECHANISM WHICH INCLUDES: A PAIR OF ARMS, ONE CARRIED ON EACH OF SAID SIDE FRAMES, EACH SAID ARM BEING PIVOTED AT ITS REARWARD END COAXIALLY WITH ONE OF SAID MAIN WHEELS TO PERMIT THE FORWARD END OF SAID ARM TO SWING BETWEEN A RAISED AND LOWERED POSITION; A PAIR OF STAIR-CLIMBING WHEELS, ONE ROTATABLY MOUNTED ON THE FORWARD END OF EACH OF SAID ARMS, SAID WHEELS HAVING A DIAMETER SMALLER THAN SAID MAIN WHEELS BUT LARGE ENOUGH TO ROLL OVER NORMAL STAIR STEPS; A TRANSVERSE BRACE MEMBER BETWEEN SAID ARMS, SAID BRACE MEMBER BEING DISPOSED SUFFICIENTLY FORWARD TO CLEAR THE SIDE FRAMES OF SAID WHEEL CHAIR DURING SWINGING MOVEMENT OF SAID ARMS, AND SAID BRACE MEMBER BEING FOLDABLE TO COOPERATE WITH THE FOLDING OF SAID WHEEL CHAIR; A PAIR OF LINKAGE MEANS, ONE ON EACH OF SAID SIDE FRAMES, EACH OF SAID LINKAGE