CA1195670A - Suspension system - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The invention relates to a counterbalancing apparatus which employs a piston-cylinder assembly wherein one end of the piston is under atmospheric pressure and the other end is under zero pressure so that the net force on the piston is always atmos-pheric pressure irrespective of the relative position of the piston and cylinder. This ensures a constant counterbalancing force for all positions of the object being counterbalanced.

Description

FIELD OF THE INVENTION
This invention relates to a device that has a piston-cylinder assembly for counterbalancing an object from an elevated support.
BACKGROUND OF THE INVENTION
Suspension systems for suspending an object wherein the weight of the object is counterbalanced so that -the objec-t can be moved in the gravitational field with apparent weightlessness are wel.L known. They are used extensively for mounting tools, photo-graphic e~uipment and measuring instruments~ The counterbalancing force is provided by many different means. A simple weight suspend-ed from a shieve is the mos-t elementary means of counterbalancing but due to spacial and other limitations it is not always acceptable.
Springs have been used and piston cylinder assemblies have been used. These latter expedients overcome obvious difficulties to the weigh-t, but they have the disadvantage that the counterbalanc-ing force :Ls not constan-t over the extent of -their travel. A
spring, for example, does not usually give a constant spring force Eor thc various degrees oE extension over i-ts range. Simi:larly, a pi,t:oll cyl:inder arrangeme}lt oE the type used in -the pas-t does not ~I:ive a constarlt counterbalancing force as the pis-ton and cylinder a~e moved re:Lative to each o-ther.
It is important in well designed counterbalancing systems that the coun-terbalancing force be constant. O-therwise, the object being counterbalanced will take on the characteristics of having more or less weight depending upon its position in -the gravitational field. Various means for adjus-ting for differences in counter-

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balancing devices as the counterbalancing device changes have be-en clevi.sed. They are, however, cumbersome and costly to manufacture and maintain.
This invention overcomes these disadvantages and provides a piston-cylinder counterbalancing device wherein the counterbalanc-ing force is the same for all relative positions of the piston with respect to the cylinder.
It is an object of the present invention to provide an :L1nproved apparatus for counterbalancing a force by using atmospher:ic :10 prccsure in such a way that the counterbalancing force does not vary with the position of the object being counterbalanced.
It is a further object of the invention to provide an i.mproved device for suspending an object in an easily manoeuvrable manller .
:1.5 It is a further object of the invention to provide a cour1t.c~rb.l].~r)c:Ln~3 devlce that. i.s effective and inexpensive to make.
SUMMARY OF TEII' INVI' TION
~ collnterbalallcing device according -to this inventior1 .10r colmtcIba:l.ancing tht? weigh-t of an object in the gravit.ati.ona:L
1`i.(`:1.d co11~1)r:ists a p:ist.on-cylinder counterbalancing asse1nbly having a l?iston an(l ..1 cylindtr reciprocabl.e wi.th respect -to each other;
:;r1-~.)t1lsior) b:r.acket for s~1spendin(~ an object o:E predetermined ~ei.cJht to be counterba]anced and for following the objec-t as it i.s moved in the gravitatlonal field; the object suspension bracket and the piston and eylinder assembly being interconnected to recip-rocate the piston and eylinder relatively to each other in response to movement of the suspension bracket in the gravitational field;
said eylinder at one end of said piston being at atmospheric pres-sure, and said cylin~er at the o-ther end of said piston having no pressure therein whereby the resultant force from cylinder pressures on the piston as the piston and cylinder reciprocate with respect -to each other is the force of atmospheric pressure for all positions 5 OL the plston with respect to the cylinder; the object suspension bracke-t and the piston and cylinder being interconnected as afore-said to counterbalance said resultant force from cylinder pressures on -the piston against the gravitational force of an object suspended fxom said object suspensi,on bracket in use.
1,0 _RIEF DESCRIPTION OF THE DRAWINGS
Example embodimen-ts of the invention are shown in the accompanying drawings in which:
Figure l is a perspective view of a suspension system;
E'igure 2 is a cross-sec-tional view in elevation of the counterbalancing assembly of Figure l, in an unloaded position;
F;gure 3 is a view similar to Figure 2 showing a position ol tl~e axselllb1y when carrying a weight;
Figure 4 is an exploded perspec-tive view of the follower atlCI its rno~lnt associated with the assembly of Figure 2;
'igure 5 (on the sarne sheet of Figllre :L) hot:t:om plan vi,ew Or t~lle courlterba1allcillc3 asselllbly of the system of Figure l showiny l:lle IllO~ ti,llc~ shaft and brake assembly;
]'`:igUL`~? 6 i5 a side view ;n elevation of an alternative eml~odilllellt of a suspension system;
~5 Figure 7 is a cross--sectional view of the counterbalancing assel~ly of Figure 6; and Figure 8 is a view similar to Figure 7 showing a position of the assembly when carrying a welght.

D~TAILED DESCP~IPTION
The example embodiment shown in ~igures 1 to 5 consists of a cylindrical ho~lsing 10 mounted on a support 12 w~lich is fixable to a ceiling or similar eleva-ted support. As seen in Flgure 2, housing 10 comprises two cylinder portions 14, 16 fixed together at flanges 18 to clamp a rolling diaphragm 20 which c~ vides the housing into a vented chamber 22 and a vacuum chamber 24. A piston 26 sli.des freely in vacuum chamber 24 and is fixed, by a bolt 28 passing through diaphragm 20, -to a forked cam frame 30 which carries .l0 a carn plate 32 spaced from diaphragm 20 in chamber 22, Support 12 comprises a U-shaped tubular member 34 having one upright sleeve 36 receiviny telescopically a rod 38 downwardly projecting frorn a base plate 40 attachable to a ceiling. A clamp 39 adjustab~y secures sleeve 36 on rod 38 in any selected position both vertically and horizonta~Lly (i.e~ slidably and rotationally) and a head 41 at the lower ~nd o~ the rod prevents t~e sleeve from s~i.pping off the end of the rod. The other upright sleeve 42 of mc~mber 3A telescopically receives a post 44 which projects upwardly ~hrollgh a slot 46 also acting to vent the chamber. Post 44 carries ~0 a~ its f.-.ree end a spherical follower 48 freely rotatabl.e l.n a S()C`]Cet: 50 . I~l.terllat.i.vely, a roller bearinct could be~ substituted .f-or sp]ler:iccll bearing 48. ~'ollower 48 bears actainst cam plate 32.
Ilout.i.inct :l.0 is pivotab:Ly mounted on post 4~ (see Figure 5~ by a pc~lr of bosses 52 which are integral with the housing, and a pivot ~5 pin 54 which carxies a knur~ed knob 55 into whi.ch the pivot pin is threaded. A rol]er pin 51 passes through a slot in the free end portion of pivot pin 54 and through a bore ln boss 52. A bel~.ville wàsher 53 is mounted on pivot pin 54 and functions as a variable '7~3 friction brake ~hen pulled ac3ainst post ~4 by rota-tlng knob 55.
An ape:r.ure 56 in end 58 of housinc~ 10 opens into vacuum charnber 24 and receives the threaded end 60 of a tubular seetion 61 of an arm 62. The otner end 64 of tubular arm section 61 is threaded 5 to receive a rod 66 which carries a yoke 68 pivotably mounted on the rod by a pin 70 and a collar 72. Rod 66 terminates at its free end in a knurled knob 74~ Within aperture 60 of housing 10 is a spring loadecl valve 76 which provides a one way passage for the release of air from vacuum chamber 24 into arm 62. Valve 76 acts to expel any :L0 l;r whieh may leak into vacuum chamber 24 by an imperfect seal or by breathirlg through the seal or through the wall of the housing.
In the operation of the example embodiment of Figures 1 to 5, the normal positic~n of rest of housing 10, i.e. with no object suspended from arm 62 is horizontal as séen in Figure 2 with piston 26 abutting end 58 of the housing. In this position of piston 26 th( alr in vacuum chamber 24 is expelled throuyh valve 76 into arm 62 alld the ambient air. When an object, such as an oscilloscope 80, is su-pended from the free end of arm 62, the arm 62 and piston-cylincier asselnbly 10 tends to turn c]ockwise about pivot pin 54 ~() in l)ost ~ of^ the basc. Fo:llower 48 on -the base abuts ean~ plate

3~ on pi.ston 30 wllile rolling downwardly a:Lon~ t:he carn plate.
';ince calll p:lat~ 32 is ~ttached to pis-ton 26 the end of cylincler s:licles dowrl and away from piston 26.
The suspension arm 62 upon which the oscilloscope 80 is suspended extends from the cylinder of the piston-cylinder assembly and the piston cylinder assernbly is pivotably mounted on the base at 54n When the arm 62 and its piston cylinder asser~ly is swung about axis 54 the piston and eylinder of the asser~ly move relative ~ 3S ~ ~

to each other as a result of their interconnection -through the cam 48 on base post ~4 and cam plate 32 on cam frame 30. Thus, movement of arm 64 in a vertical plane is transferred -to relative movement of the piston and cylinder of the pis-ton cyllnder assembly.
The thing that is required is to provide a constant balanc-ing force for the gravitatlonal force oE the weight of the oscilloscope.
Atmospheric pressure acts on the atmospheric end of the piston 26. The other end of the piston with respect to the housing is in a vacuum chamber of the cylinder and it has no pressure acting ~0 on it. Thus, -the net pressure on the ends of the piston is atmospher-ic pressure. It is constant and tends -to urge the piston with respect to the housing to the right in Figure 2. The force -that turns -the arm 62 in a clockwise direction about axis 54 tends to urge the pis-ton in the opposite direction. Thus, they oppose each other. If they are made equal they counterbalance each other and the effects of the force of gravity on the oscilloscope as it is moved in the gravitational field are eliminated.
The magnitude of the counterbalancing force on the atmos-pheric end of the piston depend on its area. Atmospheric pressure ~0 :is about 14 p.s.i. Thus, a piston with an area oE three square inche~ would provide a coun-terbalanclng force o~ about 42 pounds.
Variations in atmospheric pressure available for counter-b~ancincJ will vary from time to time with changes in atmospheric pressllre. I'he weight to be counterbalanced will remain constant.
.5 I'he weight of the oscilloscope is transferred to the piston-cylinder assembly through the arm 62, post 44 mechanical advantage configura-tion. By decreasing or lengthening arm 62 one can decrease or in-crease the reaction of the weight at the piston. Thus, by minor ~djustmen-t of the length or the arm one can match t~-le reaction of the weight at the piston to the counterbalanciny force supplied by the piston at -the time o~ use. The change in atmospheric pressure hereln referred to is one that takes place over an interval of time not one that could take place during a slngle use of the apparatus.
Of importance is that during operation, the counterbalanc-ing force does not change because it depends only on atmospheric pressure. The other end of the piston is subject to a vacuum ir~
respective of the position of the piston in -the cylinder. Hereto-fore, piston-cylinder assemblies used as balancing devices have had a pressure on at least one end of the pis-ton that varied with the position of the piston in the cylinder. This necessarily results ln a counterbalancing force that varies depending on the location of the object being counterbalanced, Some of these devices had apparatus for adjusting the pressure differential on the ends of the cylinder. This is cumber-~:om~, ~Y.pensive and difficult to maintain. By providing for atmos-pherlc pressure on one end of the cylinder and a Vacuu~ on the other end o:E the cylinder one can have a simple counterbalancinc3 ~() as.scltlh~y that provides a constant counterbalanc;lllcJ force irrespec-tive o~ l]le~ pos;t~i.on o~ t:he p,iston in the cylinder.
'I'here is fxiction in the moving par-ts of the device and 'i.ll t:h(? OpC'r.ll'i.OIl of t.ile de~vice this rnust be overcome as one movcs the coun-terbalanced object on the gravitational field. This is 7r~ a well known concept in counterbalancing devices and the effects o friction are not dealt with in -this specification.
Moreover, when the term "vacuum" is referred to herein, it is vacuum to give the practical result indicated. The device 5~

illustrated has been ~uilt and tested and is workable as explained.
l-t will be apparent that if -there was an~r subs-tan-tial amount of air in what has been described as the vacuum end of the piston that the pressure in that end would decrease as the volume expanded due to, say, outward pis-ton movement. This would result in a reduction in pressure on that side as a result of the piston movement. The reduetion in pressure would result in a net difference of counter-ba].ancing force. This invention depends on substantial vacuum on the vacuum side of the piston so that wi~h outward piston movement :l~ t~le p~essu:re does not reduce but rather stays a-t substantially zero c):~ substantial vacuum, ~ slight angle of tilt of cam plate 32, say 5 from the vertical, allows housing 10 to tilt upwardly from the horizontal and also allows the travel of piston 26 to be less, i.e. it minimizes ]5 ~the travel of the piston within housing 10.
It will be appreciated that any sui-table object may be stl.~E~ended f.rom the support by any suitable means, yoke 68 and oscil-~.oscore ~ being merely illustrative examples. It will also be app:re--c.iclted that the lengthening of post 44 will give a larc3er we~ic3h-t 20 ~eal^inc3 capac.ity to the uni.t~ Further, by increasi.ng -the diallleter i.stol~ 2~ a ~ .rcJcr eourl-terbalarlcing force and herlce we:ight bear~
l.rl~J c~apaei.t:y is obtained.
rrlle alternate ~mbod;.ment shown in Fic3ures 6 to 8 oE the c~raw.incJs CollSists of a cylindrical housing 110 mountecl on a support 112 whlch is fixable to a ceiling 113. As seen in Fiyure 7, housing 110 comprises two cylinder portions 114, 116 fixed together at flanges 118 to elamp a diaphragm 120 which divides the housing into a vented chamber 122 and a vacuum chamber 124. A piston 126 slides 5~'7~
freely in vacuum chamber 12'l and is fi~d, ~y a tubular boll 128 passins through a d:iaphragm 120 and piston 126, to a forked cam frame 130 which carries a cam plate 132 spaced from diaphragm 120 i.n chamber 122.
Support 112 comprises an angled tubular member 134 having an upright sleeve 136 recei-~ing -telescopically a further tubular rod 138 downwardly projecting from a base plate 140 fixed to ceiling 113. A c].amp 141 adjustably secures sleeve 136 on rod 138 in any select,ed position both slidably and rotationally and suitable means '1.. () I~)r~vents the sl.eeve from sliding off the rod. In -the example embodi-merlt a further face plate 142 attached to -the upper end of sleeve 136 hears against: an aperature 144 in a false ceiling 146 through which rod 138 passes. A downwardly projecting post 148 integral wi.th housi.ng 110 is carried by the free end of the horizon-tal por-tion of member 13~ in a bushing 150 (see Fi.gure 7~. A pin 149 passes through the free end portion of post 148 and bears agains-t a washer 151 whlch in turn bears against bushing 150 fixed in member ].3~. '' ~ pair of bosses 152 integra:l with housiny 110 project below the housing and carry a pin 154 on which a crarlk 156 is p.i.vQtLIlly mountecl at i.ts elbow. One arm 158 of crank 156 extends u~warcll.y -through slots 160 in housing 110 opening in-to ch~mber 122, tllc? .c;'l.ots acting to vent the chamber. ~rm 158 carr:ies at its free e~ld a spherical follower 162 freely rotatable in a socket 164.
Follower 162 bears against cam plate 132. Again, follower 162 coul.d be replaced by a roller in a suitable recess in arm 158.
The other arm 159 of crank 156 is tubular and is adjustable in length in the same manner as arm 62 in the previous embodiment --10~

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(see Fiyures 1 and 2).
.A suc-tion tube 170 leads into rod 138 of support 112, passes out through member 134 adjacent post 148, and enters housing 110 -through slot 160 (the tube ].ying in a recess 155 in arm 158) to connect with tubular bolt 128 at cam f:rame 130.
In the operation of the alternate example embodiment of Figures 6 to 8~ a vacuum is maintained in vacuum charnber 124 through suction tube 170 which is connected beyond rod 138 to.a vacuum source. When an object is attaehed to the free end (not showrl) of crank 156 the cran]{ pivots about pin 154 and follower .162 bears ayainst eam plate 132 and forees the eam plate to the righ-t :in chamber 122 of housing 110 as seen in Figure 8. I'hus, povotal movement of the arm is transferred into reciprocal movement of -the piston and eylinder. A weight suspended from the free end of arm 156 is in use eounterbalaneed by the eonstant pressure of the atmosphere on the atmospheriCend of the piston. In Figure 8 ~j,t; ton :1.2h moves to the right and in that Figure earn plate 132 has reaclled ~he end of the chamber 122.
Cam p].ate 132 may ex-tend upwardly out of housing 110 as ~() s}lown ln Fi.gures 7 and 8 (but not in Fi.gure 6) to i.ncrease the are l:hrollclll wl-:ieh er.ll-lk :l56 may pivot about pin 154. ~lso, arm 158 o~- c.~rallk 156 mcly he mac3e adjustable in length in the same manner as ar-n~ :l59 i.n or(ler to vary the eounterbalanced earryin~ capacity of the deviee. These modifieations are also applieable to the previous embodiment of Figures 1 to 5. Again, a larger diameter of piston 126 will inerease the counterbalancing force available.
Diaphragm 20 or 120 is a rolling diaphragm sueh as that sold by the Bellofram Corporation under the trade mark BELLOFRAM.

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'l~h~ BELLOFR~ ~olling diaphragm is a long stro~e, deep convolutioll, cons-tant area ~iaphragm which is ~'ree positioniny with complete rela~ation at any point in its stroke. Moreover, this diayhragm i,s responci,ve to e~tremely small pressure changes and has no mechanical spring gr~dient. Consequently when used with a vacuum in the present invention a constant coun-ter~alancing force over a wider range is provided.
It will be appreciated that the piston and diaphragm cc)mbination prov:ides a convenient movable wall of a vacuum charnber :l,0 bul, other means might be used such as a piston and an O--ring houc3h a vacuum seal would be more difficult to maintain.
In thls embodiment the objec-t suspension bracket is not a rnere e~tension of the piston-cylinder assembly as it was in the embGdiment of Figure 1 to 5. Rather, the piston-cylinder assembly 1.'~ relnains horizontal and the suspension bracket turns about an axis 15~ on the frame to permit vertical movement of an object suspended.
'I.'}le reclu:i.rement i.s tha-t the object suspension bracket 156 and the p~;ton and cy:l.inder be :i.nterconnected to reciprocate the'piston and cylinder re:Latively to each ot~er in response to movement of 0 ~}~e~ su.spension brc~cket in the gravitational f:ie:Ld.
st~ urther arrangement would be to suspelld the pist..on-c~y~..in~lcnL assell~bl.y in a vertical position and suspend the welght t'lil'('Ci:l.y l'XOlll thl~ }:)ottOm o.t~ the p:iston.
In evexy case, however, one end of the piston is in a vacuum chamber and the other end is subject to atmospheric pres-sure so that as they chanye position relatively to each o-ther there is no change of pressure acting on either end of the piston. This ensures a constant counterbalancing force equal to atmospheric pres-sure for all positions of the objec-t being counterbalanced.

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TTRll SUPPLEMENTARY DIS~LOSURE
It is ~irst desired to summarize certain prior ar~
which has come to light since the filing of the principal disclosure.
It is known to utilize piston and cylinder assemblies to counteract the weight of an object being suspended. An exemplary prior patent is U.S. Patent

4,000,873, Wallace, issued January 4, 1977. In this patent, a telescoping piston and cylinder arrangement counterbalances the weight of the object~
Another exemplary patent is U.S. 3,917,200, Johnson, issued November 4, 1975. In this device, pneumatic pressure is applied to a cylinder which acts in extension to counterbalance the weigh-t of an object suspended on an arm.
A patent more relevant to the present invention is U.S. 2,225,515, Wood, issued December 17, 1940. In this patent, the patentee suspends a weight directly from the bottom end of the piston within a vertical cylinderr the lower end of the piston being exposed to the atmosphere, the upper end o:E the piston being exposed to a constant pressure l.ower -than the a-tmosphere. Wood also provides a speci:Ei.c source of constant fluid pressure below atmospheric utilizing automatic pressure controls. A difficul.ty with th~
Wood pat~nt relates to the considerable comp].exity of thc apparatus which mai.ntains the upper chaT~er of t:he cy1.in~ler at a constant pressure below atmosphe:ric.
Tllis apparatus invo].ves pressure-responsive valves, a vacuum pump, var.ious l.ines, and automat:i.c pressure 3() controls. In view o:E this considerable compl.exity, it is clear -that it woul.d be of advantage to have a self-contained system capable of providing a relatively constant pressure drop across the piston, regardless of piston position rela-tive to the cylinder and without having to provide an external power source or a pressure-regulati.ng apparatus of the kind uti].ized by Wood or similar thereto.

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As pointed out in the principal diselosure, the provision of such a simplified but effective system is an object o~ one aspect of this invention.
The device diselosed herein has a further inventive aspeet, relating to the way in whieh the substantially constant pressure drop across the piston ean be transformed into a counterbalancing moment applied to a suspension arm supporting an object at a distance from a horizontal axis, in such a way that the counterbalancing moment diminishes or inereases in the same ratio as the moment required to maintain equilibrium thereby keeping the objeet in place at any angle of the arm, It will be appreeiated that, for example, as a suspension arm earrying an objeet at one end and pivoted at the other end swings down from the horizontal position (representing three o'elock on a clock face) to a downwardly extending position (for example equating to five o'clock on a clock face), the counterbalancing torque necessary to keep the objeet in plaee wil]. diminish by a factor which can be expressed in terms of the eosine of the angle through whieh the swing arm has swung.
It is an objeet o:E a further aspeet of this i.nvention to provide for this automatic adjustment of the counterbalancing mornent arm.
~RIEF DESCRIPTION OF DRAWI GS ADDED BY SUPPI.E.~ENTARY
D rSCLOSURE
In the drawinc3s added as part of this Suppl~-.?mentary Disclosure:
Figures 9 and 10 are vector diagrams illus-trating 3() }lOW the counterba.l.ancinc3 moment adjusts it.self to the mc~rnent e~erted by -the ohject being suspended;
Figure 11 is a vertical sectional view through a ~urther embodiment of a suspension system incorporating this invention; and Figure 12 is a sectional view taken at the line 12-12 in Figure 11.

5~jt~
DET~ILED DESCRIPTION OF T~IE DRA~:INGS
The principal disclosure points out that what is required is to provide a constant balancing force for the yravitational force of the weiyht of the oseilloscope. There are two factors which contribute to the provision of a constant or substantially eonstant counterbalancing force for the weight of an object suspended from the end of the arm 62~
The first factor relates to the ne-t force which is experienced between the piston 26 and -the housing l0 due to the difference in the pressures which are in effect at the two ends of the piston.
The prinei.pal diselosure explains that atmospherie pressure acts on -the leftward or atmospherie side of t:he piston 26, since the chamber 22 is open to the :1.5 atmosphere through the slot 46. The rightward side of the piston 26 in Figure 2 is subjected to a substantially complete vacuum, and therefore no pressure is exerted leftwardly against the rightward end of piston 26. As a result, the net pressure experienced by the piston is atmospherie pressure, and the foree applied to the piston will be determined by the atmospherie pressure and the piStOIl head cross-sectional area over which the atmospheric pressure acts. Of course, an equal and opposite force will be appli.ed to the housing 1.0, wheKeby to urge the piston 26 and housing l0 toward the posit:ion i.n which th~ vo1a.1me of the vacu1lm chamber 2~1 is the least.
~ec.1uC;e there is no or substantial].y no pressure in the vacuum chamber 2~ at the ri.yht of the piston 26, :~0 I^ecJ.~ ss o~ the position of the pi.ston 26, the net force attemptincJ to move the piston 26 to the right with respect to the cvl.indri.cal housiny l0 will remain constant.
The second factor contributing to a constant counterbalanciny of an object suspended at the rightward end of -the arm 62 is the georr.etric relationship of various por-tions of the apparatus shown in Figure 2. In Fi.gure 2, it will be appreciated that the actual force -.er-d.i.--~g to r.ctc~^^ t.,e _r.~ 62 to the horizontal position (after it has rotated clockwise under the in~luence of a weight suspended at its rightward end~ is the ~orce exerted between the cam follower 48 and the cam plate 32, which is identical to -the force exerted by atmospheric pressure against the leftward end of the piston 26 and equal to the force of atmospheric pressure on housing 16. This force is constant, and is the same regardless of the angle of rotation through which the arm 62 has moved. With arm 62 horizontal, this same force acts through a rnoment arm which is equal to the distance be-tween the centre of the cam follower 48 and the axis of the pivot pin 54. For perfect balance, the moment which is the product of the said force times the centre-to-centre distance be-tween the cam follower 48 and the pivot pin 54 must be the same as the moment defined as the weight of the object suspended a-t the rightward end of the arm 62 times the distance between -the axis of the pivot pin 54 and a vertical line passing through the centre of gravity of that object. This is a simplified equation which ignores the weight of the arm 62 itself. It is assurned for the purposes of this discussion that the arm is weightless, or is itself in balance about the pivot pin 54, in the absence of any objec-t be:i.ng suspended from the rightward end of the arm 62.
Loolcing at Figure 9, -the force E` represents the force exerted between -the cam foll.ower 48 and the cam pl.ate 32, and the distance a rep:resents -the moment arm whi.ch is the centre--to-centre distance be-tweell the cam foll..ower 48 allcl the pi.vot pin 54. Also in Fi.(3ure 9, ~ln ~.he weiyht W represents the weiyht of an object suspended at the righthand end of the arm 62, and the distance b represents the distance between -the axis of the pivot pin 54 and a ver-tical line passing through the centre of gravity of the object. As indicated in Figure 9, ignoring friction, perfect balance is achieved when Fa = Wb. The axis of the pivot pin 54 is represented in Figure 9 by the letter X.

~3567~3 Figure 10 shows the condition after ro~ation of the arm 62 through approximately 30O This brings the vertical line passing through the weight W closer to the axis X of the pivot pin 5~, reducing it to b cos~, where C~ is the angle through which the arm has rotated from the horizontal.
The force F acting between the cam following 48 and the cam plate 32 remains the same, however this force is now acting over a shorter moment arm, defined as a cos ~, where C~ is the angle through which the arm 62 has rotated.
Thlls it will be seen that, if perfect balance is achieved in the horizontal position, wherein Fa = W_, then perfect balance will be maintained at any angle ~ , since Fa cos 0~ will continue to be equal to Wb cos4-While it has been stated that one of the factorscontributing to perfect balance of the mechanism shown in Figure 2 is the constant force exerted between the piston 26 and the housing 10, it is to be emphasized that this constant force does not necessarily require a total vacuum at the rightward end of the piston 26.
What is essent.ial is that the pressure drop across the piston 26 be and remain substan-tially constant regardless of i.ts pos.ition wi-thin the housing 10, and of course the provis.ion of a complete vacuum at the r.ightward end is very convenient because it does not .re~uire an elaborate pressure monitoring system of the ]~ind contemplated by t~-te aforemer.ttioned Wood U.S.
Patent 2,225,515. Nonetheless, such a pressure maintaini.ng arrangement could be uti.lized successfully with the apparatus shown in Figure 2~ since it would combine with the equalization of moment arms explained with respect to Figures 9 and 10, to produce a restoring moment exactly matching the moment exerted by the weight W with respect to the axis X of the pivot pin 54.

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It is further to be pointed out that some residual pressure within the chamber to the right of the piston 26 could be allowed~ without in-terfering with the practical use of the device ill.ustrated in Figure 2.
If it were imagined that a small volume remained to the right of the piston 26 when the arm 62 was horizontal, and if it were imagined that a small pressure of perhaps 100 mm Hg were provided in that chamber~ then it will be appreciated that, as the piston 26 moved to the left with respect to -the housing 10, the pressure to the ri.ght of the piston would drop to proc~ressi.vely lower values, thus gradually increasing the net pressure across the pis-ton, and increasing the force exerted between the cam follower 48 and the cam plate 32. This would lead to an out--of-balance between the moment arms discussed with respect -to Figures 9 and 10, however by utilizing the frictional provision explained in connection with Figure 5 (the bellville washer 53 acting as a friction brake), the arm 62 could still be maintained in any position o:E angulati.on.
~ s an extension of -this concept, if the small vol.ume to the right of the piston 26 were in communication with a larger volume, for example with -the ccnt:le charnber of the arm 62 itself, and if the ~5 va].ve 76 werf? absent, then the variation in tl-e E)re-;sur-? .'elt at the ri.ght of the piston 26 during i-ts movelTlent wit:h r-spect to t}-e housing 10 would be .le(.:recl~.sf.!d, thus l.ea(lillcl to a more constan-t force l,t~t:weell tht.? calm :iollower 48 ancl the cam plate 32.
3() In surmmary, it wi:ll be appreciated that although a near perfect vacuum located at the right of the piston 26 (in Fi.gure 2) represents a preferred embodiment of this .invention~ the apparatus described would stil.l be quite workabl.e and functional with either a constant, low but nOn-zerG pressure to the right of the piston 26, or a non-zero pressure which underwent variation during movement of the piston 26, the variation being small enough to be cornpensated by the frictional effect 7 ~:3 of the bellville washer 53 (as well as the lriction of cam follower 48 and the inherent friction between other moving parts).
It is well understood that the atmosphere itself changes in pressure from day to day. These pressure changes will bring about corresponding changes ln the net force exerted across the piston 26, even -though the weight of the object to be counterbalanced will remain constant. These minor variations in atmospheric pressure may be compensated by changing the length of the arm 62 by rotatably -threading the rod 66 further in-to or further Ollt of the tubular arm section 61.
Because changes in atmospheric pressure are very yradual, it is unlikely that adjustment of the length of the arm 62 would have to be undertaken during a sinyle use of the apparatus.
While several embodiments of this invention have been illustrated in the accompany drawings, and described in the above disclosure, it will be evident to those skilled in the art that changes and modifications may be made therein, without departing frorn the essence of this invention as set forth in the appended claims.

Claims (19)

1. THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
   PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS
   FOLLOWS:
   l. Apparatus for counterbalancing the weight of an object in the gravitational field comprising:
   a piston-cylinder counterbalancing assembly having a piston and a cylinder reciprocable with respect to each other;
   a suspension bracket for suspending an object of predetermined weight to be counterbalanced and for following the object as it is moved in the gravitational field;
   the object suspension bracket and the piston and cylinder assembly being interconnected to reciprocate the piston and cylinder relatively to each other in response to movement of the suspension bracket in the gravitational field;
   said cylinder at one end of said piston being at atmospheric pressure, and said cylinder at the other end of said piston having no pressure therein whereby the resultant force from cylinder pressures on the piston as the piston and cylinder reciprocate with respect to each other is the force of atmospheric pressure for all positions of the piston with respect to the cylinder;
   the object suspension bracket and the piston and cylinder being interconnected as aforesaid to counterbalance said resultant force from cylinder pressures on the piston against the gravitational force of an object suspended from said object suspension bracket in use.
2. 2. Apparatus for counterbalancing the weight of an object in the gravitational field as claimed in claim 1 having:
   a base;
   said object suspension bracket being connected to said cylinder and comprising an arm extending from the cylinder from the free end of which an object of predetermined weight can be suspended as claimed in claim l;
   
   said piston and cylinder assembly being pivotally mounted on said base to permit vertical movement of said arm;
   means on said base in cooperative relation with the piston whereby the piston and cylinder are interconnected to reciprocate the piston and cylinder relatively to each other in response to movement of the suspension bracket in the gravitational field as claimed in claim 1.
3. 3. Apparatus for counterbalancing the weight of an object in the gravitational field as claimed in claim 1 wherein said piston is reciprocable in said cylinder to cause the end thereof to abut an end of said cylinder for one position of said suspension bracket;
   a passage from said latter mentioned end wall of said cylinder to atmosphere;
   a check valve in said passage biased to permit escape of air from said cylinder whereby all air can be evacuated from one end of said cylinder as said piston abuts the end of said cylinder.
4. 4. Apparatus for counterbalancing the weight of an object in the gravitational field as claimed in claim 2 wherein said piston is reciprocable in said cylinder to cause the end thereof to abut an end of said cylinder for one position of said suspension bracket;
   a passage from said latter mentioned end wall of said cylinder to atmosphere;
   a check valve in said passage biased to permit escape of air from said cylinder whereby all air can be evacuated from one end of said cylinder as said piston abuts the end of said cylinder.
5. 5. Apparatus for counterbalancing the weight of an object in the gravitational field comprising:
   a cylinder having first and second opposed ends, a piston slidably mounted within said cylinder, the piston defining with the first end a chamber exposed to atmospheric pressure, the piston defining with the second end a chamber in which the pressure is below atmospheric, the pressure drop across the piston from said first to said second chamber being substantially unchanged as the piston moves between two spaced-apart positions within the cylinder, whereby the piston is subjected to a substantially unchanging force, a swingable member pivoted about a substantially horizontal axis, the member being adapted to support the object at a location spaced from said axis, and a mechanism which applies the said substantially unchanging force against the swingable member through a moment arm of which the length varies in proportion to the horizontal distance between said horizontal axis and a vertical line through the object.
6. 6. The apparatus claimed in claim 5, in which the pressure in the second chamber is substantially a complete vacuum.
7. 7. The apparatus claimed in claim 5, including a fixed frame portion, and in which the cylinder is fixed with respect to the swingable member, said frame portion defining the horizontal axis and defining a fixed projection extending upwardly from the horizontal axis to support a bearing location, the piston having means for pressing against the bearing location in the direction of said second chamber.
8. 8. The apparatus claimed in claim 5, including a fixed frame portion, the cylinder being fixed with respect to the frame portion, the swingable member having a bracket moving therewith, the bracket supporting remote from the horizontal axis a bearing location positioned such that a line joining the bearing location to the axis is substantially perpendicular to a line joining the axis the the place on the member where the object is suspended, the piston having means for pressing against the bearing location in the direction of the second member.
9. 9. The apparatus claimed in claim 7, in which the pressure in the second chamber is substantially a complete vacuum.
10. 10. The apparatus claimed in claim 8, in which the pressure in the second chamber is substantially a complete vacuum.
11. 11. Apparatus for counterbalancing the weight of an object in the gravitational field comprising:
    suspension means for universally suspending the object to be counterbalanced and for following the object as it is moved universally in the gravitational field;
    said suspension means including a piston-cylinder counterbalancing assembly having a piston and a cylinder reciprocable with respect to each other; a first element with a horizontal axis and a swingable arm swingable about the horizontal axis of said first element; said piston being connected to one of said first element and swingable arm and said cylinder being connected to the other thereof whereby to reciprocate the piston and cylinder relatively to each other in response to swinging movement of the swingable arm about the horizontal axis of the first element;
    said cylinder having a first chamber at one end of said piston, said first chamber being at atmospheric pressure, and said cylinder having a second chamber at the other end of the said piston, said second chamber having a substantially complete vacuum therein, whereby the net force on the piston as the piston and cylinder reciprocate with respect to each other is substantially the force of atmospheric pressure for all position of the piston with respect to the cylinder;
    said suspension means and the piston and cylinder being interconnected as aforesaid so that the resultant force on the piston counterbalances the object as the piston and cylinder reciprocate with respect to each other.
12. 12. Apparatus for counterbalancing the weight of an object in the gravitational field as claimed in claim 11, wherein the said piston is reciprocable in said cylinder to cause said other end thereof to abut an end wall of said cylinder for one position of said swingable arm;
    a passage from said latter mentioned end wall of said cylinder to atmosphere;
    a check valve in said passage biased to permit escape of air from said cylinder whereby all air can be expelled from between said cylinder and said end wall as said other end of said piston abuts said end wall of said cylinder.
13. 13. A piston cylinder assembly for use as a counterbalance for an object suspended in the gravitational field comprising:
    a cylinder;
    a piston reciprocable in said cylinder;
    said cylinder being open to atmosphere at one end of said piston;
    said cylinder being substantially completely evacuated at the other end of said piston whereby the net pressure acting on said piston for all positions of said piston in said cylinder is substantially equal to atmospheric pressure.
14. 14. The apparatus claimed in claim 5, in which said mechanism includes a cam plate fixed with respect to the piston, and a cam follower which bears against said cam plate, and which moves with respect to the cam plate as the swingable member pivots about the said horizontal axis, the cam plate being angulated with respect to the cylinder axis, whereby to minimize piston movement with respect to the cylinder as the swingable arm pivots about the said horizontal axis.
15. 15. The apparatus claimed in claim 11, in which the suspension means includes a cam plate fixed with respect to the piston, and a cam follower bearing against the cam plate and moving along the cam plate as the piston reciprocates with respect to the cylinder, the cam plate being angulated with respect to the piston axis whereby to minimize piston movement with respect to the cylinder as the swingable arm swings about the said horizontal axis.
16. 16. The apparatus claimed in claim 5, in which the piston has an evacuating pump within it.
17. 17. The apparatus claimed in claim 11, in which the piston has an evacuating pump within it.
18. 18. The apparatus claimed in claim 5, which further includes an adjustably variable friction means which controls the pivoting of the swingable member about said horizontal axis.
19. 19. The apparatus claimed in claim 11, further including an adjustably variable friction means controlling the movement of the swingable arm about the said horizontal axis.