Hydraulic stretcher device

~<~576 The invention relates to a trauma strotchar or cot for dlsabled, lnJured, or 8~ ck lndlvlduals. More particularly, thls lnventlon relate~ to stretchers for disabled lndivlduals which can be deslrably adJusted to facll~tate thelr handllng ~nd treatment.

Speclflcally thls ~nvention r~lats~ to a hydraul~c 2tretcher devlc~ whlch can be posltloned by me~nn of hydraullc cyllnder~, and ~hlch also lnclude~ lmproved ~eans for securlng certaln of tha ~tretcher's sdJustable features ln desired 1~ posltions, as well as a pat~ent-supportlng top sultable for X-ray examlnatlons.

BAC~GROUND ART Many o~ the patlents ln hospltals and other treatment centers are lnambulatory and requlre movable cot~ or Qtretchers for their movement ln and about th~ oenters, and to and ro~ dlagnostlc or other treatment areas. It ls neces~ary that ~tretchers employed for thls purpose be capable of belng ralsed or lowered, horlzontally and other~lse, for ease o sccQss by ~edlcal perJonnol, or for other rea~on~. In ~any ca~es, the patlQnt 19 phyJlcally unable to mov~, elther becausQ of unconsclousness or lnflrmlty:

oonJequently, the stretcher ~u~t be extremely Jtable to avoid the po~sibil~ty of t~pping or other misadventurQ durlng patlent transportatlon or 3~ 129~S ~ 6 treatment. The stretcher is often sub~ected to unbalanced loads during u~e, increaslng the rlsk of lateral tilting, therefore, addlng to the importanoe of structural ~tability. In addition, certain medical procedure~ require that one end of the patient be rai~ed or lowered relatlve to the other end. Such ad~u~tment, known as the Trendelenberg po~ition, i9 employed, for example, in the case of cardlac arre~t, where the head of the patient i9 lowered to allow concentration of blood in the patlant's head. It 19 also very desirable that certaln features of stretcher devices such as re~tralning, or safety rails, lntravenous support poles, etc., be securable ln ~everal positions. In additlon, in order for such features to be practical, they must be capable of being easlly and rellably secured in the particular posltlon selected.

In the past, many different types of stretchers have been devlsed, both of the mechanical variety, as well as some hydraullcally operated devlces. As mlght be expected, stretchers of the mechanical type are not as convenient as hydraullc ~tretchers, slnce they requlre hand manlpulatlon of the apparatus assoclated therewlth to ral~le, lower, and otherwise posltlon the stretcher devlces. On the other hand, hydraullc strQtchers heretofore proposed have generally been unstably ~upported by the hydraullc cyllnders employed. In ~dditlon, their hydraullc controls have not been conveniently located, and oftentlmes they have been of a type dlfficult to operate.

Furthermore, when a hydraullc stretcher i~ being raised, lt occa~lonally encounter~ an ob~tructing 576 --3-obstacle. In previous hydraullc stretchers, operating pressures withln their hydraullc ~y~tems normally continue to rise ln such cases untll component breakage results, due to the fact that the obstructlon ~ 9 unobserved, and because the mechanical advantage of the pre~sure lnducing mechanism prevent~ the lack of stretcher movement ~rom belng notlced until component breaklng pressures have been reached. Other disadvantages of the prior art devices include the fact that where multlple posltionable features such as restraining rails, I.V. poles and the llke are associated with the ~tretcher, the devices used to look such features into thelr deslred posltions are relatively dlfficult to operate, ~ubJect to wear, and otherwise less than satisfactory. Also, when the X-ray of pat~entq transported on stretchers is requlred, lt nece~sitates tran~fer of the patient to a specially conatructed X-ray table, an operatlon lnvolvlng the possiblllty of patient lnJury.

D~SCLOSURE OF THE INVENTION In llght of the foregolng, lt is a flrst aspect of thls inventlon to provlde a stable, hydraullcally adJustable trauma stretcher or cot for supportlng dlsabled lndlvlduals;

- lt 19 a second aspect o the lnventlon to furnlqh a hydraullc stretcher devlce, elther end of whlch ~ay be ralsed or lowered lndependently of the other end, ln a Trendelenberg posltlon;

lt 19 a further aspect of the herein descrlbed lnvention to teach a hydraullc stretcher device, the hydraulic system of which lncludes a ~5 .

.

~ Z~L~ 5 ~ --4-feature to protect the hydraulic syste~ agalnst destructively high pressures;

yet another a~pect of this lnventlon ls to provlde a hydraulic qtretcher with eaQlly acce~sible, simply operated hydraulic controls, de~lgned to po~ltlon the stretcher in lts desired orlentation;

an additional a~pect of the lnvention ls to allow a stretcher device to be fitted with ad~ustable features which are capable of being secured in their selected positlon by reliable, long wearing, and easy^to-operate adjustment locks;

another aspect of the lnvention described is to furnlsh a hydraullc stretcher device which 19 sultable for taklng X-rays of patlent3 supported thereon;

the foregoing and other aspects of the lnvention are provided by a hydraul1c stretcher devlce comprlsing:

a rectangular top support assembly:

a rectangular botto~ frame assembly:

two, lndependently oparable, pairs of hydraullc positlonlng cyllnders, and positlon ~tablllzlng bars, sald posltlonlng cyllnders ad~ustably connectlng ~aid bottom ~rame and top ~upport assemblles, and ~ald piston stablllzing bars connectlng the plston rods o~ paired cyllnders together, wherein one palr of ~sld cyllnders 19 located adJacent the head end of the stretcher, one cyllnder on each slde thereof, whlle another palr of said cylinders lq located adJacent the foot end o the ~tretcher, one cyllnder on each slde thereof, the cylinders ln each sald palr being hydraullcally lnterconnected 3S and operating ln tandem wlth each other:

S~6 other aspects of the lnvention are provlded by a hydraulic ~tretcher devlce comprislng:

a rectangular top support a~sembly:

a wheel mounted, rectangular bottom frame assembly;

two, independently operable pair~ of hydraulic positloninq cylinders having floating plston rod~ associated therewlth, and plston stablllzing bars, said posltionlng cylinder3 adJustably connecting said bottom rame and top support assemblies, and ~ald plston stabllizing bars connectlng the piston rods of palred cyllnders together, wherein one pair of sald cylinders i9 located sd~acent to the-head of the stretcher, one cylinder on each side thereof, the cylinders in each said palr being hydraullcally interconnected and operated ln tandem with each other, and wherein each pair of said paired cylinder~ is connected to a separate pump-powered hydraulic system that includes a two-way valve that can be operated to dlrect hydraullc fluld to said pair, or to release said.

fluld therefrom, said system al~o lncludlng a pressure relief valve that prevents the pressure of sald fluld wlthln sald system from exceedlng a . predetermlned amount, the pump~ powerlng the two systems belng powered by a single foot pumplng lever, and whereln further, said two-way valves can be operated by controls mounted on sald stre~cher remote from sald valves;

stlll other aspects of the lnventlon are provlded by an X-ray permeable patlent support structure comprlsing a lamlnated .~heet that 12~4~576 lncludes as components thereof an inner core, and covering outer surface skin adhered to the hori20ntal surface~ and longltudinal ~ide edge~ of sald core, whereln sald core i9 formed by a materlal selected from the group consi~tlng of a foamed plastlc materlal, and balsawood, and wherein a fir~t skin covering one of said horizontal surfaces i9 selected from the group conslsting of a mat layer comprising carbon graphite filamentary material encapsulated in a plastic re~in, and a matrix of filamentary high molecular welght polyethylene enoap3ulated in a plastic re~in, and a second ~kin coverlng the other of ~aid horizontal surface~ comprises a layer of riberglass.

~RIEF DESCRIPTION OF THE DRAWINGS Flg. 1 is an isometrlc vlew of a hydraulic stretcher devlce of the lnvention;

Flg. 2 is a side elevation of the stretcher device disposed ln a Trendelenberg posltio~:

Fig. 3 is an lsometric view of a slmplifled frame structure of the stretcher showlng some of the conceptual detallq of the hydraulic and mechanical llnkage~;

Flg. 4 19 8 front elevation vlew of a tapered lock assembly of the type u~ed to secure adJustable features of the ~tretcher ln selected posltlons: .

30Flg. 5 1~ a right side elevation of the sprlng-loaded tapered lock assembly of Fig. 4;

Flg. 6 shows a partial section of the lamlnatlon comprising the X-ray stretcher top;

~2~ 6 Fig. 7 is a schematic diagram of the hydraulic system of the inventlon.

Flg. 8 showq a croqs sectlon of a free-floating hydraullc cyllnder employed with the stretcher device of the invention.

BEST MODE FOR CARRYING OUT T~E INVENTION Fig. 1 shows an lqometric vlew of the hydraullc stretcher device, generally 10, of the invention comprislng a top support assembly, generally 12, wh~ch is connected to a bottom frame assembly, generally 14, by means o~ hydraulic cyllnders 16 located near each corner of the stretcher, the two cyllnders at each end of the stretcher belng interconnected and operated together a-~ a palr. The hydraullc cyllnders are powered by pump3 operated by pump lever 18, the pump~, together with associated valvlng and the like being, for example, located in hydraullc system houslng 20.

The stretcher 10, whlch i9 mounted on caster wheels 15, ls provlded with a stretcher top 23 whlch includes a hinged back rest 24, fastened to back rest support yoke 26.

The support yoke 26 i8 adapted to flt into notches provided ln top support assembly 12, not shown, so that the angle of the back re~t 24 can be ad~usted to whatQver angle 19 deqlred by placing the support yoke ln the approprlate notch.

Stretcher 10 is also equipped wlth plvotal restralning rails 28 which plvot ln tapered lock assemblle~ 32.

Also attached to stretcher 10 19 a foldlng, tele~coping intravenou~ support pole 30.

Both the lntravenous pole 30, and restralnlng ralls 28, are ad~ustable in the dlrectlon of the arrows ~hown ad~acent such lZ~fix~;76 --8-component~. Al~o to be seen in Flg. 1 are hydraullc controls 21, the posltion of which determlne~ whlch palr of the cyllnders 16 ls to be sctlvated by the hydraullc pump~. X-ray fllm support access 25 lllustrates the area in whlch X-ray fllm can be posltloned when a patient on the stretcher 1~ to be subJected to X-ray examlnatlon.

Whlle variou-q materlalq may be used for con~tructing the stretcher, quch aq steel, magne~lum, or aluminum, the uqe of a hard, anodized alumlnum frame 1~ not only essy to clean, but avolds the posslblllty of rust or corroslon under normal clrcumstances. Dimenslons of the stretcher may vary wlthln a falrly broad range and stlll be maneuverable ln a treatment center; however, a stretcher havlng a length of about 75 to 85 inches, and a wldth of about 26 to 32 lnches 19 sultable for mo~t purpo3es. The ad~ustable helght of the Atretcher may also be selected to accommodate the particular use to whlch the stretcher ls to be put. Commonly, however, the ~tretcher wlll be designed to have an ad~ustable helght, variable between about 20 lnche~ to 40 lnches.

Optlonally, the hydraullc stretcher devlce of the lnventlon may be fitted with various other features such a~ electrlcally conductlve caster wheels, four wheel brake locks operable at elther end of the stretcher for convenlence of ho3pltal personnel, an open stora~e tray as~oclated wlth the bottom frame assembly 14 for personal effects of the patlent, an equipment tray mounted above stretcher top 23 at the foot of the qtretcher, a foot board which includes a patlent chart holder mounted on the foot end of the stretcher, pu3h bars 1:Z9~5~ at both tha head and foot ends of the stretcher for ease in movlng the stretcher, and simllar aonv~anlences~ Fig. 2 lllustrates a slde elevatlon of the stretcher device 10, dlsposed ln a Trendelenberg position. In the Figure, which ~how~ bottom frame a~sembly 14 connected by hydraullc cyllnders 16 to top support assembly 12, pre~sure ha- been generated in the hydraulic ~ystem~ by mean~ of pump lever 18. However, hydraulic control~ 21, connected to hydraulic valving by means control cable 22 have been set to provide pressurized hydraullc fluld to only one pair of hydraulic cyllnders 16, in the Flgure, the cyllnders adJacent to hydraulic system housing 20, on each side of the stretcher. As a re~ult, tha top support assembly 12 of stretcher 10 19 disposed at an angle relative to the horizontal, termed a ~Trendelenberg~ positlon. The Figure shows restraining rails 28 in their raised, or safety positlon, secured therein by tapered lock assemblle~ 32. The backrest support yoke 26 ha~ been disengaged from the backrest adJustment notches, 30 that the backrest lq ln its lowered, lnoperative mode. In addition, lntrav~nous support pole 30 has been folded down toits storage positlon, ln whlch it is secured by adJacent tapered lock as~embly 32'.

The Flgure lllustrates a Trandelenberg positlon ln whlch the foot end of the stretcher 10 has been elevated. Hydraullc controls 21 can be set, however, 80 that hydraulic pressurs is furnlshed only to the palr of hydraullc cylinders 16 located at the head end of the stretcher, in the Flgure, the end at whlch the intravenous support .

~.2~457t~ -10pole 30 19 located, resultlng ln the head of the patlent belng elevated, whlle the patient's feet are lowered. When the hydraulic controls 21 are set so that hydraullc pressure 13 furnl~hed to each palr o~ hydraullc cyllnders 16, l.e., at both the head and foot of tha stretcher, the stretcher can be elevated in a horlzontal posltion. By suitable -u~e of the controls, it is posslble to adjust the hydraullc pressure ln each pair of cyllnder~ 90 a9 to tllt the top o~ the stretcher at whatever angle ls required, and/or to lower or elevate the stretcher to ~hatever heiqht ls required. Whlle the hydraulic control~ 21 are -~hown ln Fiq. 2 at the foot end of the stretcher, they can, lS optlonally, be located elsewhere lf de~ired.

Flg. 3 shows an lsometrlc vlew of the framework of a stretcher 10, slmpllfled for purposes of lllustratlon, and detalllng 90mQ ltg hydraulic and mechanlcal linkages.

The Flgure shows one pair of hydraullc cyllnders 16 attached to the top support assembly by means of plston rods 17, attached at pivot polnts 41, whlle another palr of hydraullc cyllnders 1~ attached by pl3ton rods ln plston rbd slots 39.

As top support assembly 12, 19 ad~usted ln the Trendelenberg posltlon, the plston rods 17 attached to plston rod ~lots 39 are free to move ln the ~lot~, thus accommodatlng the requlred change in length of that part o~ the top support assembly posltloned between the palr~ of hydraullc cylinders 16, ~ald change ln length beinq necessary to accomodate the angle of the top support assembly lmposed by lts positloning ln the Trendelenberg conflguratlon.

In Flg. 3, piston rod slot 39 19 .

--ll- shown dlsposed at the right end of the stretcher, uhile piston rod pivot polnt 41 is loc~ted at the other end, adjacent to the hydraulic system housing. If desired, however, the positlons of the plston rod plvot point 41 and the piston rod slot 39 can be rever~ed, lt simply belng neces~ary to provlde a method of piston rod 17 attachment to accommodate the requlred lncreased length of the top support assembly 12 positioned between the pairs of hydraullc cylinders 16, as previously explalned. The hydraullc fluid llnes 49 show the lnterconnectlon between palrs of hydraullc cyllnders 16, and exempllfy how hydraulic fluld may be dlverted to each palr of cyllnders separately, lS from the hydraullc pump located ln hydraullc system houslng 20, thus allowing hydraulic fluld to be dlrected to the two pairs of cyllnders, separately. While the lnterconnection of each palr of cyllnders allows the end of the stretcher ~upported by the palr of cylinders to be raised or lowered by the cyllnders opsratlng simultaneously, lt 19 necessary to connect the piston rods 17 of each pair wlth a stablllzer bar 33. The stabilizer bar 33, whlch 19 permanently attached to plston rod9 17 uhlch lt connects, 19 necessary to prevent lateral tlltlng of the top support assembly 12 ln those lnstances ln whlch an unbalanced force 19 applled to one slde of the table.

Were lt not for stablllzer bar 33, the lnnerconnectlon between the cyllnders would cause hydraullc fluld to be forced from the cyllnder over whlch the unbalanced force is applied, resultlng in lowerlng of the s~de of the stretcher to which the force is applied, and producing a corre~pondlng elevatlon of the opposite 57~;

-12side, due to the dl~placed hydraullc fluld being forced into the opposlte cyllnder.

The result would be an undesirable lateral tilting of the table.

Fig. 4 i9 a front elevation of a tapered lock assembly, generally 32, lllu-~trating the mechanls~ employed to secure side rail~ 28 and intravenous qupport pole 30 in a selected positlon.

In the Flgure, whlch lllu~trates locking of a restrainlng rail 2a ~ a bolt houslng 40 iq shown supported by members forming part of top support assembly 12.

Contained ln bolt housing 40 are locking bolt 34, which 1~ urged by spring 38 lnto a locklng hole 42 in the receiver 44 fixed to restralnlng rall 28.

The lock as~embly 32 19 operated by applying a manual force to bolt handle 36, whlch ls attached to locking bolt 34, in a dlrection which opposes the force exerted by spring 38.

Thls cau~es bolt 34 to sllde downward in passageway 37, dlsengaging the conlcal top of the locklng bolt from a locklng hole 42.

The restralnlng rall 2~ can thereupon be rotated to lts deslred posltlon, a posltion ln whlch a locklng hole 42 ls ln allgnment wlth locklng bolt 34.

When restralnlng rall 28 is ln such an aligned posltlon, and no force 19 applied to bolt handle 36, sprlng 38 wlll urge locklng bolt 34 lnto the allgned locking hole 42, thus flrmly securing and locklng the restralning rall ln positlon, due to the actlon of the sprlng.

The tapered lock assembly 32 19 not only easy to operate, but the conlcal, or tapered end of locklng bolt 34 is rugged, long-wearlng, and tends to be self-allgning.

While three locktng holeq 42 are shown ln the Flgure, more or fewer ~2~4S76 -13such holes may be provlded, dependlng upon the positions in which lt is deslred to secure the feature to be locked.

Fig. S illustrates a right side elevation o~ the ~pring-loaded tapered lock a3sembly 32 o~ Fig. 4. Included in bolt hou~lng 40 may be ~een clarifylng details of locking bolt 34, bolt handle 36, and sprlng 3~. Also shown 19 adjustment ~lot 35 down which bol~ handle 36 is forced, when adJustlng restraining rail 29. The Figure ~how~ the fastening of recelver 44 to re~tralnlng rail 28, by means of a key 43. The po~itioning of bolt housing 40 ad~acent member~ of top support assembly 12 ls also ~hown.

Fig. 6 ls a partlal cross-sectlon of an X-ray top whlch may be employed ln fabricating stretcher top 23. The Figure shows a laminatlon comprislng an lnner core 46 sandwlched between two outer surface skln~ 4~ in a ~box~ configurat$on, the surface ~kins belng overlapped on the side edges..

In the cour~e of conducting X-ray examinations of patients, the patient is normally supported on a table between a source of X-radiation, and the film on which an X-ray picture wlll be recelved. The materlal from whlah the table 19 made must pos~e~s several characterlstlcs. FlrYt of all, lt must be strong enough to support the patlent, and at the same tlme lt must be permeable to X-rays, or X-ray blockage will result ln 80 much data 1099 that lt wlll be lmposs1ble to produce a meanlngful lmage on the fllm, The materlal must also exhlblt mlnlmal -~scatter~, or dlffraction of X-rays pas~ing through it, to obtain good resolution, and a sharp lmage.

It has been found, for example, that when more than about 14X data loss is experlenced, the X-ray plctures obtained are frequently too cloudy to be useful for dlagnostlc purposes. As u3ed herein, the term ~data 109~ deflned as the amount of gamma rays produced by a radloactlve lsotope source which are dlffracted from a straight line path by a material lnterposed between the sour¢e and a detector, such a9 a scintillatlon camera detector.

In the past, materlal~ containing carbon graphlte mats have been employed because of thelr excellent X-ray permeability characteristlcs, rlgid~ty, and high strength. Such, mats are produced from carbon graphlte filamentary material, partlcularly flber~ woven lnto fabric, surrounded by an encapsulatlng plastlc rqsin 80 to ~orm a substantially rigid ~heet. Unfortunately, however, the material i9 expenslve, partlcularly when used ln a thlcknes~ sufficient to support the patient.

Flberglas~, onthe other hand, while being much less expensive, has the di~advantage of produclng ob~ectionable scatter to X-rays passlng through it, making sharp lmages dlfflcult or lmposslble to obtaln when the flberglass 18 used ln thlcknesses sultable for supportlng patients undergoing the X-ray dlagnosls. It ha~ now been dlscovered, however, that when the lamlnate ~tructure described ln connectlon wlth the Flgure 19 fabricated 90 that the periphery of the lnner core 46 transverse to the longltudlnal axis of the stretcher 10 1~ completely covered with adherent surface ~kln, the equivalent of a ~box~ structural member 19 achieved, i.e., a type of structural member which --15-exhiblts great strength. The ~ignlflcance of forming such lamlnate in a box configuration ln whlch the outer skins of the lamination are folded over each other at the edges of the X-ray top, or are otherwise configured in the course of the top's construction so that the core 19 entirely ~urrounded by the outar ~kins, i9 that the amount of carbon graphlte needed to obtain sufficient strength in the stretcher top can be ~igniicantly and advantageously reduced. Furthermore, due to the great ~trength of the surface skin~core box type construction, not only can the thickneqs of tha carbon graphite surface be reduced, bu~ the slgnlflcantly less expenslve fiberglass can be used for one ~urface skin, ~lnce it can be made thin enough to reduce X-ray scatter and data loss to an acceptable point~ that ls below about 14%. In other words, the combination of a box-type, lamlnate structure, ln combinatlon with two outer surface skins, only one of which 19 of the carbon graphite type, the other being of fiberglass, a materlal prevlou~ly belleved to be unacceptable for X-ray purposes, provldes a high ~trength, relatlvely low cost lamlnate, ldeally ~uited for an X-ray dlagnostlc patlent support surface. In addltlon, lt ha~ been found that such a surface i8 ldeally sulted for use in stretcher devlces for reasons lncludlng lts rlgldlty, hlgh strength, llghtwelght, and relatlvely low cost.

Refarrlng agaln to the Flgure, one outer surface skln 48 wlll be made from a mat of carbon graphite fllamentary materlal encap~ulated ln a pla~tlc re-~ln, typically the mat ltself compri~ing about 1/3 of the weight of the surface skln, the 57~ -16balance being other components, including particularly the encapsulating plastlc reqin. The other ~urface skln 4~ is comprised of fiberglass contalnlng from about 20X to 35% by welght of flberglass filamentary materlal, for example, chopped qtrand fiberglass, the balance being resin, B ~uch as for example, ~opper~ 6604-T resin.

Frequently, the outer surface sklns lnclude a layer of gel coat for cosmetic reasons. It iq necessary that the fiberglass surface skln thickness be in the range of about 0.01 to 0.12 lnches lf an undesirable level of data 109~ and scatter is to be avolded, and a skln thickness of about 0.01 to 0.08 provldes particularly good X-ray results. Although the carbon graphite surface skln layer is more transparent to the passage of X-ray~, the ~urface skin 28 made from it will have a similar thickness for a number of reasons including cost, structural con~lderation~, and the llke. Inner core 46 may be made from a varlety of materlals, however, the use of clo~ed-cell rlgld foams i~ especially useful.

It has been found, however, that when foams with cell~ having a diameter greater than about 8 to 10 mils are employed, the cells themselves have a tendency to form obJectlonable patterns in the resulting X-ray plctures: conseguently, foams with celln no greater than the slze are strongly preferr~d. Of the3e, foam~ made from PVC or polymethylacryllmlde have been found to be partlcularly advantageous, wlth the polymethylacrylimlde foam belng especlally preferred for a variety of rea~ons lncluding particularly, lts lightweight and great strength.

~hile inner cores made from foams of the type ~RP~ $7~ -17de~cribed provide a number of advantageq, lncluding ea~q of fabrlcation, bal~awood cores may also be employed.

Inner core 46 wlll usually have a thickne~s of from about O.la to 2 inches, however, in a preferred embodiment, an inner core o~ from about 0.12 to 2.00 inche~ thick i-~ used.

The components of the lamination, ~.e., the outer surace ~kin~ 48 and inner core 46 are laid up in any of the way~ well known in the art, and ean be secured together by the adhesion obtained from a coating of resin, for example, the re3in used to form the fibergla~ or carbon graphite surface skins.

Laminatlon~ of the type described have been found to be capable of passlng up to about 94X of the X-rays dlrected through them, whlle producing negllgible scatter, well below the 14X level prevlously referred to.

Although either of the outer aurace sklns 48 may be in contact with the patlent, that 19, constltute the upper horlzontal surface skln, ordinarlly, the upper surface skin will be that containlng the carbon graphlte mat.

In a further embodlment, lt ha~ been found that a ~urface ~kln comprlsing a matrlx of flbers, preferably ln the form of a woven mat, formed from hlgh molecular welght polyethylene, generally from about 1 to 5 mllllon, and possesslng a very high degree of crystalline orlentatlon, for example, from about 95X to 99%, encap~ulated ln a plastlc resln, for ln~tance a polye~ter resin, may be substltuted for the fiberglass skin, or for both it and the carbon graphlte skln.

lZ~ 7~;

-18Such flbers, produced by a procesa called ~gel-splnnlng~ ln which the polyethylene polymer 19 dlssolved for the purpoqe of dlsentangllng the poly~er chains, and then spun, include tho~e produced by the Allied Signal Company of Peter~burg, Vlrginia, marketed under the Trademark ~SPECTRA~ fibers. The thickne~ of the re~in encapsulated polyethylene fiber surfacQ skins sub~tituted for the flberglass surface skins prevlously referred to, or for both those and the carbon graphite surface ~klns, will normally have a thlckness withln the same range descrlbed ln connectlon wlth the sub~tltuted, surface sklns.

When 80 substltuted, the encapsulated polyethylene flber ~urface ~klns make po~lble constructlon of box-type lamlnated structures of the type descrlbed, whlch have great physlcal ~trength, as well as the ablllty to pass up to about 96% to 97X of the X-ray~ directed through such structures, and with only negllgible scatter.

Flg. 7 ls a schematic dlagram of the hydraullc system of the stretcher devlce. Flg. 7 shows top support assembly 12 attached to the plston rod~ of hydraullc cyllnders 16, the plston rods of each palr of hydraullc cyllnders being connected by stablllzer bars 33. The hydraullc cyllnder~ 15 are connected by the hydraullc lines 49 to hydraullc pump~ 50, whlch sre operated by pump lever 1~. Pump lever 18 19 normally actuated by the foot of the user, although a hand operated lever could also be employed. If desired, separate actlvatlng pump levers 18 could be supplied for each of the pump~ 40, or the pump~ could ba actlvated electrlcally, for example, wlth 129457ti electriaity supplied by a battery. Also shown are the hydraullc fluld reservolr 53, check valves 56 and 58, 2-way valve~ 54, and pressure rellef valves 52. Operatlon of the syqtem begin~ by actlvating the pumps 50 wlth pump lever 18. Thl~ draw~ hydraullc fluld from hydraullc 1uld reservoir 53 past check valveq 56 whlch allow the fluld to pass through them to the pumps, but prevent flow in the reverse direction. The pump forces the hydraulic ~luld through check valves S~, the latter preventlng reverse flow, and on to hydraullc cyllnders 16 causlng the piston rods, and therefore the top -qupport assembly 12 of the stretcher device to rlse. The operatlon de~cribed 19 that which lS occurs when two-way valve~ 54 are posltloned in thelr closed, ~luld blocklng mode, lllu-~trated.

When the two-way valves are posltloned ln thelr open ~ode, hydraulic fluid is allowed to escape from hydraullc cyllnders 16 and return through the two-way valves ln the direction of the arrows to the hydraullc fluld reservolr 53, resulting ln a lowerlng of the piston rods. A~ will be appreclated, it 19 pos3ible to have one of the two-way valves 54 open, whlle the other remalns closed, a sQttlng whlch results in only one end of the stretcher devlce rlslng, posltionlng the stretcher dev~ce ln the Trendelenberg conflguratlon. Al~o, when the plston rods are ln an extended positlon, a two-way valve 54 may be opened, releaslng hydraullc therefrom, untll the top ~upport assembly 12 of the stretcher devlce drops to a deslred lower poqltlon, at whlch point the two-way valve is agaln closed, maintalning the top support of the stretcher ln the deslred lZ~457G -20po3itlon. Pressure relief valves 52 are adJusted to open at a pressure ~ust below that at which hydraullc system component damage would occur.

~hen ~uch pressure 19 reached, the pre~sure rellef valve 52 opens, causing hydraulic fluid to recycle from the pumps 50 back to the hydraulic fluid reservolr S3.

Fig. 8 is a cro~ sectlon of a hydraulic cyllnder 16 employed with the stretcher device of 10 the lnvention, illu~trating the ~free-floating~ relatlonship between the plston rod 17 and the hydraullc cylinder 16.

As explalned in connection with Fig. 3, lt 19 necessary to connect the piston rod 17 of each lS pair of hydraulic cylinders 16 with a stabllizer bar 33 in order to prevent lateral tiltinq of the top Rupport a~embly 12 when unbalanced forces are applled to only one side of the table. When pairs of the hydraullc cylinder~ are thus lnflexibly interconnected, the plstons 60 frequently have a tendency to become stuck withln the cyllnder, due to misalignment rslated to the tolerance~ involved ln the manufacturing process. Thls tendency is overco~e in the hydraulic stretcher devlce of the invention through provl~lon of a ~free-floating~ cyllnder-plston rod relatlonshlp. As shown in the Flgure, the plston rod 17 19 fastened to the piston by mean~ of a wrlst pln 66, anchored ln the walls of the piston, whlch pa~ses through a wrist pin bore hole 64 in the pi~ton rod 17. The diameter of wriRt pln 66 1~ sufflciently smaller than the wrlst pin bore hole 64 through which it extends to allow the plston rod a relatively high degree of freedom to move or ~float~ about the wrist pin. This ~'~5'457ti freedom allows the plston rod to accommodate itself to the sllght misalignments whlch result from applled loads, manuacturlng tolerance~, or otherwise, avoldlng bindlng between the pi~ton and the cylinder wall of the type whlch would render the cylinder lnoperable.

The required difference in diameter between the wrlst p1n and the wrist pin bore hole wlll depend upon the relatlve dimensions of the plston rod and plston: however, in the casa of a piston about 1 inch in dlameter, fixed to a piston rod havlng a diameter of about 3/4 lnch, the dlfference in the dlameter of the wrlst pin and the wrlst pln bore hole wlll commonly be about 1/16 inch.

In other words, in the case of a wrlst pin approximately 1/8 lnch in diameter, a typical size, the wrist pln bore hole will have a dlameter of about 3/16 lnch.

While the Figures lllustrated and the descriptlon provlded, are ln some instances directed to configurations of a hydraulic stretcher device havlng particular structural features, lt wlll be understood that certaln of the structural and configuratlonal details may be varied withln the skllls available in the art wlthout departlng from the spirit of the lnvention.

Therefore, wile in accordance wlth the Patent Statutes, a preferred embodlment and best mode ha~ been presented, the scope of ths invention is not llmlted thereto, but rather ls measured by the scope of the attached claims.