US 3558103 A
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United States Patent r  Inventor Alois Lodige Frankfurter Weg 13, Paderbarn, Germany [21 1 Appl. No. 670,332  Filed Sept. 25, 1967  Patented Jan. 26, 1971  Priority Sept. 26, 1966 [3 3] Germany [31 1454642  SCISSOR ACTION HOIST WITH COMPONENTS SHAPED S0 AS TO NEST WITHEN ONE ANOTHER 12 Claims, 19 Drawing Figs.
 U.S. Cl 254/122  1366f 3/22  Field of Search 254/ i 22 (Cursory), 8, 9; l87/l8;,214/512  References Cited UNITED STATES PATENTS 3,282,566 11/1966 Clarke 254/122 3,246,876 4/1966 Larson Primary Examiner-Andrew R. J uhasz Assistant Examiner-David R. Melton Attorney Molinare, Allegretti, Newitt & Witc0ff.
I (\(TT 32 s 4 E 2 18 KO PATENTEU JAN26 IBYI sum 01 [1F PATENTED M26197! FIG. 8
PATENTED JAN26 I97! SHEET 05 [1F PATENTED M26 IBYI 3558.103
SHEET 08 0F 1 1 PATENTEUJANZBIBYI I 3558.103
- sum USOF 11 PATENTED JAN26 I97l SHEET 1 0 HF PATENTEU JANZS IHYI SHEET 1 1 BF SCISSOR ACTION HOIST WITH COMPONENTS SHAPED SO AS TO NEST WITHIN ONE ANOTHER Scissor-action hoists for all purposes, with two, three or more (usually four) scissor arms, are known to technology. The drive is obtained very simply from a driving unit such as a hydraulic cylinder mounted in the direction of lift. This method has the disadvantage that the driving unit must be sunk in the ground. In the case of scissor-action hoists, where small overall height is of no great importance and a high lift is not required, a beam joining the inner and a beam joining the outer scissor arms are used, with the aid of a hydraulic system, perhaps telescopic, for forcing the associated pairs of scissor arms apart. To give a higher lift, the driving units are then frequently place obliquely.
Placing the driving units directly between the inner and outer scissor arms has the advantage that the scissor-arm end assemblies are not required to transmit the forces applied by the driving units, which forces are large in relation to the load. In such arrangements, the ratio between the travel of a platform carried at one end of the arms and the stroke of the driving unit is determined by the ratio between the scissor-arm length and the leverage of the driving unit in relation to the central scissor-arm articulation. In the usual form of construction, the central scissor-arm articulation lies approximately halfway up the overall height. The leverage available for the driving unit is thus less than half the overall height, so that this height is required to be large. The smaller the overall height, the greater the technical difficulties arising, because of the increased hydraulic forces necessary. The minimum possible height is achieved when the necessary thickness of the scissorarm to withstand the maximum bending moment, plus the plate thickness of the platform, if any, equals the overall height in the retracted condition of the arms.
In the present state of the art, scissor-action hoists having a particularly small minimum height do not allow the provision of a completely closed, distortion-resistant scissor-arm frame that is a frame joining the ends of associated scissor arms to one another, because the frames in the minimum height condition of the arms would have to extend into one another to give the minimum possible height overall. In the usual forms of construction, therefore, part of the lift is sacrificed and the minimum overall height in increased, in order to enable such frames to be provided. The scissor-arms then remain, when in the retracted position, spread apart by an angle necessitated by the design and the scissor-action hoist can never be lowered far enough to bring all the scissor-arm points of attachment into a single plane.
Some scissor-arm hoists exist in which the scissor arms can be lowered until the arms lay parallel side-by-side; however, the formation of complete distortion-resistant frames has then been dispensed with.
In other known examples, the inner scissor arms are cut away in the vicinity of the maximum bending moment, to enable a flat connecting bearer for the outer scissor arms, which is capable of distortion and resistant to vertical bending, to be passed through below the inner pair of arms, this carrying a wheeled towage yoke through the agency of two tension rods. This wheeled yoke is supported on flat irons fixed to the ground frame. As these flat irons, on which the towage yoke of the driving unit rolls, are not proof against bending the flat connecting bearer has to be capable of distortion, in order to allow for uneven ground, with which the flat irons lie in contact. Because the flat bearer which pulls the supporting yoke lies on the flat irons when lowered, the flat irons cannot be made more highly resistant to bending, unless the overall height is to be increased.
The total retracted height consists of the height of the track on which the towage yoke rolls, plus the thickness of the fiat bearer carrying the yoke, plus the thickness of the scissor arms, plus the thickness of the platform. Thus, four load-bearing members are added to form the total minimum height. This form of construction with four bearing members can be reduced in height to some extent, but only by making the rails with flat iron, subject to bending, and by keeping the yoke bearer as low as possible, so as to retain an adequate depth of bend for the scissor arms and the platform stiffening. As the yoke transmits the forces as it rolls along the ground, it must necessarily follow all unevenness in the track arising within the outer scissor articulations, the effect of which is to distort the flat bearer.
Where the ground is convex, the scissor-arm ends do not bear on the ground at all: the stable width is then very small. Particularly when the highest point in the convex track is situated below one roller of the yoke, such a form ot'construction has only three-point contact with the ground, with a one-sided moment effect and central loading. The stability becomes even more uncertain when the load lies on the freely over hanging end of the platform, because the cantilever position approaches one-point support. The system of forces in the scissor-end articulations is upset by the yoke, which is important to stability, since the moving scissor-end articulations do not absorb any lifting power when the ground surface is con vex.
There are also scissor-action hoist systems incorporating rolling curves, thrust wedges, rolling chain pulls, rotary pistons and so forth.
All systems fail to attain even approximately the position where the requisite scissor arm thickness is approximately equal to the overall height, and especially not when distortion resistance is to be produced with the aid of closed frames.
The present invention sets out to eliminate the drawbacks mentioned above, by providing a scissor-action hoist having at least two scissor arms arranged as a pair of scissor assemblies articulated at an intermediate point about a first axis after the manner of Nuremberg scissors, the scissor arms having their ends pivotally attached at end articulation points to a support by means of articulation support brackets, for pivotal movement about second axes parallel to the first axis, the articulation points at one end of the hoist being capable of longitudinal movement, the articulation support brackets being so arranged that they can fit one around the other in the retracted condition of the hoist so that they at least partially overlap in the plane parallel to said axes with the scissor arms closed to a very small, nil or negative angle, and a driving unit arranged for extending or retracting the hoist. Preferably a scissor assembly comprises a closed frame joining the ends of scissor arms in that assembly.
Two driving units can be fitted between the scissor arms in such a way that the torque acts simultaneously on both scissor arms and adequate leverage is possible with minimum overall height. The minimum total constructional height is derived from the thickness of the scissor arms needed to withstand the maximum bending moment. The closed-frame construction of the scissor assemblies, made possible by the method here proposed, whereby nesting" is obtained by shaping components to fit round one another, ensures that the hoist is highly resistant to distortion when loaded by offeenter vertical forces or by horizontal forces.
At the points where the bending moments in the scissor arms are smaller, the scissor arms may be set back to back to accommodate the bend-resistant bearing members of the platform. The points of application of power for one or more driving units are connected, on the one hand, to a transverse beam not subject to bending, which rigidly connects the outer scissor arms at their ends and fits round the inner scissor arms, and, on the other hand, to a transverse beam resistant to bending and twisting, which joins the inner scissor arms together in the vicinity of the central articulation of the scissor arms.
The method of nesting by fitting components round one another also enables the possible lift to be further increased by fitting those scissor -end acticulations which support the platform to be hoisted as low down as possible on the platform chassis, while those scissorO scissor-end articulations which do not carry out the hoist raising movement are raised high as possible below the platform deck in its retracted condition. The scissor angle thereby passes from the positive range in the hoisted condition through Zero to the negative range in the retracted condition. The central articulations of the scissor arms should preferably be arranged as high as possible below the platform deck, to give high leverage for the driving units. The lines joining the scissor-end articulations then lie no longer, in the retracted position, in the horizontal, but are dropped beyond this, to the extent of the overall height minus the end articulation diameter and minus the thickness of the platform deck.
The possible increase in lift amounts in practice to about per cent. If the symmetrically placed central articulation lies at the point ofintersection of the lines joining the end articulations, every point in the platform moves vertically i upwards.
If the central articulation lies, for reason of driving unit leverage above the point of intersection, every point in the platform will describe, in the course of the parallel upward movement, a curve with a continuously increasing displacement towards the side of the fixed articulations. In many applications, this slight displacement of the platform at the higher levels in the lift is not troublesome, but may even be an advantage.
With this scissor-action hoist, which is particularly distortion-resistant and is capable of lifting and lowering and in which the scissor-end articulations or frames are fitted round one another for nesting purposes, the base frame can be made relatively light, there being no over heavy bending beams to take the driving units. There is thus a technical advance, in that the scissor-action hoist can be made mobile, if desired, by using the downward-moving weights of scissor arms, driving units and platform to raise the base framerelatively light by reason of the method of construction-and thus providing wheel mounting, the lowering effort being necessarily greater than the lifting effort plus friction, all of which in the unloaded condition.
With the scissor-action hoist here proposed, with nesting achieved by fitted components round one another, and the driving unit or units connected between the arms, the base frame may be omitted, since it is not called upon to absorb any forces from the driving units. The free scissor-end articulations, situated high up which do not carry out the hoist raising movement, are then carried by two wheeled axle mountings or by pivoted articulated saddle-type tractors. The dual-axle wheeled mounting carrying one scissor-arm end bearing has the advantage that when there are foreign bodies on the track the force of collision is halved. The other scissorarm end bearing is carried by a swiveling bogie construction or a three-wheeled or four-wheeled saddle-type tractor, the scissor'action hoist then acting as the follower. Driving up with saddle-type tractors, as is well known, is far easier than with swiveling bogie constructions.
The usual, normal design for a hoist conforming to the invention, with one or more hydraulic driving units between the scissor arms, is a four-arm construction. It is also possible, however, to work with an odd number of scissor arms, when, for example, with a three-anned design, one doubly strong distortion-resistant scissor arm is enclosed between two scissor arms side-by-side. In that case, the driving unit or units can be fitted between the central and outer scissor arms. Whether an even or odd number of scissor arms be used, the constructional principle of the method of fitting components round one another to make nesting possible remains the same, even with only two scissor arms.
This nesting system, with its possibility of making complete distortion-resistant frames for all the associated scissor-arms, has the particular advantage that the hoist as a whole is unaffected to a very high degree by offcenter vertical forces or by horizontal forces. This makes it possible to weld larger platform decks to unit-constructed types of chassis, the thrust forces being transmitted by stays to the load-bearing members of the standard platform chassis.
By virtue of the particularly shallow, distortion-resistant design, a hoist embodying the invention can be bolted in multiples one on the other to give lifts several times greater with small scissor-arm length than for known hoists.
A preferred feature of the hoist is that those end articulations which carry out the hoist raising movement are shifted up as high as the articulation diameter permits within the overall height, so as not to sacrifice any lift and also so as to take full advantage of the method of undercutting using a negative angle of the scissor arms. The scissor system can be reversed so that the movable platform is at the lower end of the arms and then these articulations lie as low as possible. With this arrangement, the scissor arms must be correspondingly nested by shaping, so as to provide the substituted lifting side, at a point where the bending moment is smaller, with the necessary height for the load-bearing members of any platform used. However, the structure incorporating the method of fitting components round one another be designed, it remains possible for the scissor-arm thickness at a point of low bending movement, plus the depth of bend for any platform or base-frame stiffening members, to equal the overall height. Irrespective of the platform deck, no more than two members ever lie one above the other and form part of the overall retracted height.
This invention will now be explained in greater detail with the aid of practical examples, these being shown in the accompanying drawings, in which:
FIG. I shows a scissor-action hoist in accordance with the invention in the extended position, the method of fitting whereby good nesting is achieved being clearly visible, as well as the drive arrangement and its leverage:
FIG. 2 shows a scissor-action hoist in the retracted condition,
FIG. 3 is a plan of the hoist shown in FIG. 2 minus the platform deck,
FIG. 4 shows an alternative retracted scissor-action hoist with drive applied at both ends,
FIG. 5 shows the same hoist as in FIG. 4 with obliquely cut scissor-arm profiles, the method of fitting and the nesting of the base frames, scissor arms and platform begin clearly visible,
FIG. 6 is a plan of the hoist shown in FIGS. 4 and 5,
FIG. 7 shows a modified driving arrangement with lowloaded central bolt,
FIG. 8 shows a further embodiment of hoist with three scissor arms and the method of fitting the components to ensure nesting,
FIG. 9 is a longitudinal section corresponding to FIG. 8,
FIG. I0 is a diagrammatic representation of a further hoist in accordance with the invention,
FIG. 11 shows the same hoist as in FIG. 10, minus the base frame, but including the wheel mounting;
FIG. I2 shows an alternative hoist, in which the descending weights raise the chassis so that it is supported on wheels, make making it movable.
FIG. 13 is a sectional view showing the method of stiffening an enlarged platform on a standardized platform chassis,
FIG. I4 is a plan showing the method of stiffening an enlarged platform,
FIG. 15 shows a further scissor-action hoist in which the load on the beams that join the scissor arms and on which the driving members act is relieved by means of tension rods;
FIG. 16 shows a scissor-action hoist with rack and pinion drive;
FIG. I7 shows the arrangement of the pulls for producing the lift;
FIG. 18 shows the same arrangement as in FIG. 17, with pressure cylinders; and
FIG. 19 is a side elevation of the arrangement shown in FIG.
FIG. 1 shows a center-intersection scissor-action hoist having four scissor arms. In this drawing, 1 is the base frame, 2 is the platform chassis, 3 are the outer scissor arms, which have their ends joined to one another by beams to a frame, and 4 are the inner scissor arms, which again have their ends joined to one another by beams to form a frame. The driving unit 5 is pivotally attached at one end to bear on the beam 18, which is secured against turning and bending and joins the hoisting end of the outer scissors arms 3 together. At its other end the driving unit 5 acts on the inner scissor arms, by being pivotally attached to an articulation bracket 21 of the beam 22, which is secured against turning and bending and joins the inner scissor arms 4 together.
The two opposing turning moments produced on the two scissor arms assemblies act about a fist axis being the axis of the center pin 19. The pressure beam I8, in its lowered position, is shown in chain line in relation to the scissor arms 4 and numbered 23, to show how the pressure beam, when lowered, fits round the scissor arms 4 and end beam 24 joining the fixed ends of the inner arms. The frame beam 23 in turn has beam 24 and the articulation bracket 20, by means of which beam 24 is pivotallyattached to the base I, fitted round it. The articulation bracket 25 by means of which the beam 18 and the scissor arms 3 are pivotally attached to the platform 4 fits round the articulation bracket 20 belonging to the scissor arms 4, as can be seen particularly clearly (sideways from above) in FIG. 3. The articulation brackets 25 support the platform at one end at the fixed articulation 11 for pivotal movement about an axis parallel to the first axis. The fixed ar ticulation brackets 20 on the inner scissor frame 4 are supported by the articulation bracket 6, which is welded to one end of the base frame 1 for pivotal movement about a further parallel axis. This serves to show the method of nesting, as far as the fixed-pivot is concerned.
At the horizontally mobile pivot end, the end beam 26, which holds the hoist ends of the inner scissor arms 4 together to form part of the inner frame assembly, has been drawn in chain line at 27 in relation to the scissor arm 3, to show how the connecting beam ,28 (which joins the lower ends of the outer scissor arms 3) fits therearound. The beam 28 carries the articulation bracket 9, the pin 29 of which supports the roller carried within the U-sectioned rail 8. This rail is welded firmly to the base frame 1. The pin 29 has an iron flat, 30 (FIG. 3), welded to it, which draws the pin forwards or backwards in conjunction with a tension/pressure screw (not shown). This adjustment, provided on all the pins, is for truing purposes. The other mobile pivot supporting the platform consists of the articulation bracket 31 carrying the pin 14, which in turn supports the roller 32. This roller 32 travels within the U-sectioned rail fixed to the platfonn chassis. The rail 15 is secured to the platform chassis 2 as well as to the platform bearer 17, which withstands bending.
The inner scissors assembly, formed by the scissor arms 4 and the tie beams 24 and 26, is rigidly attached to the'articulation bracket 31. It can be seen in FIG. 2 how the articulation bracket 31 fits round the beam, 28, of the outer scissor assembly formed by the scissor arms 3 and beams 18 and 28.
FIG. 4 shows a modification in which the beam 26, which is low down in FIG. 2, is raised to provide room for an additional driving unit 33. The articulation bracket 31 in FIGS. 4 and 5 is welded both the scissor arm 4 and to the beam 26, to provide the closed frame construction.
From FIGS. 4, 5 and 6 can be seen how the method of nesting is carried out in three dimension. v
In FIG. 7, the center pin is situated at midheight. Two pull or thrust drive units are here working in opposite directions, so that the center pin is stress-relieved as far as the driving forces are concerned. The disadvantage of this arrangement is that the forces act with only half the leverage in comparison with the previous drawings. This drive arrangement is always suitable and even necessary when the scissor arms are very short, so that the length of the retracted driving units and hence the stroke can be only very short.
The power of the driving units is twice as great with this arrangement. The lifting speed, for one and the same speed of driving unit, is particularly good.
FIGS. 8 and 9 in which the same reference numerals have been used, show a three-armed scissor construction designed on the same principle of fit-round nesting. It allows of a reduction in width.
In the examples shown diagrammatically in FIGS. 10 and 11, the fit-round method results in the lift beginning in the negative range ofangles. FIGS. 10 and 11 are side views.
As can be seen, this form of construction provides a possible increase in lift, 34, on account of moving end articulations having been positioned lower. The magnitude of the possible increase in lift is derived from the height of construction minus the roller diameter or articulation diameter or the depth of the U-sectional rail. At the same time, the degree of fitround become greater, namely by the magnitude 34.
For illustration purposes, the arm lengths have been made unequal in FIGS. 10 and II. The more the arm lengths differ. the greater the sideways displacement, indicated by the curve 35. As a long as adequate scissor-arm length is provided, the angled shape--that is to say with the nonmobile end articula tion positioned high and the center pin moved upis suitable as regards leverage. With smaller scissor-arm lengths, where the stroke of the driving unit can no longer be made long enough, the central articulation 36 is moved half way up, halving the leverage (cf. FIG. 7).
FIG. 11 shows a mobile hoist embodying the invention in which the lower end of the scissor assemblies are mounted on a saddle-type tractor and a follower. The follower has double axles, 37, with flexible suspension. The saddle tractor consists of the rear running-wheel assembly 38 and the pivoted bogie 39.
FIG. 12 shows an example of an optional wheel and extension mechanism.
The invention-type lifts-lower hoist with base frame, because of its high resistance to distortion, makes it possible to set the hoist on wheels when desired, the descending weights acting through the platform frame or directly from the scissor assemblies to operate a wheel lowering mechanism, so that the lowering effort is greater than the lifting effort of the base frame. The travelling gear is in the form of a pivoted bogie construction. In the case of special stability, stub axle pin steering with track rod which could be fitted should be fitted in its place. The lowering weights should be provided, for example, with projections such as 40, which, during the downward movement, move the slides 41 downwards, these in turn imparting downward motion to the rockers 42 and 43.
The front and rear thrust arrangements, each of which constitutes a reverse image of the other, are interconnected, for example, bya change-over lever, 46.
In position a, the side faces 44 and 45 lie one below the other, with side play. This means that the wheels are not extended when the lifting mechanism is lowered.
In position b, the projections 40 force the slides down, so
that the rockers 42 lower the wheels or raise the base frame. In
position b, the wheels are lowered only when the hoist comes together. When the hoist is extended, the frame automatically settles on the ground again.
In position 0, the spring-loaded lever automatically slips into place, so that the hoist remains mobile, however extended.
In position b, in which the slide is only half forward, the locking lever 47 is in the position48because the slide 41 is drawn back, so that the lever 49 has lifted off the lever 47 and is in the position 53, since the lever 49 has come to bear against the stop 50. The lever 47 has thereupon taken up position at 48 and is bearing against the stop 51 under the action of the tension spring 52.
FIGS. 13 and 14 show the method of strengthening whereby larger platforms may be welded ontoa standard platform chassis.
For this purpose, the stiffeners of the standard frame 2 are extended to form similar body faces 54, 55 and 56 and joined if necessary with vertical profiles 47, the platform 58 then being secured in its place. Working in this way, mass produetion with suitable platform sizes is possible, since the hoist is not affected by loads offcenter.
FIG. 15 shows how the driving units 5 are fitted, as in FIG. 7, symmetrically about the central scissor joint, so that none of the driving forces acts on the central bearing of the scissor arms. They can be connected either to the torque member 22, by which the inner scissor arms 4 are rigidly joined, or directly to the scissor arms 4. The other sides of the driving units bear against the beams 18, by which the outer scissor arms 3 are rigidly joined. Since, when more than one driving unit is employed, large bending moments arise in both the beams 18, especially when the scissor arms are far apart, these beams should be stress-relieved by the tie 59 at points, 61, as close as possible to the driving units 5.
In order to dodge the torque member 22, the tie 59, is pro vided with a bored diamond-shaped spreader, 60, which has freedom to turn. For ease of assembly, the tie 59 is secured by a detachable connector either to the spreader 60 or to the two beams 18. Similarly, the torque member may be spread out so as to pass round the tie 59, this being carried straight through, or it may be divided. This is particularly suitable when the scissor arms turn through a wide angle.
According to how they are placed, the beams 18 may also be stress-relieved by means of two ties, 62, mounted in bearings, 63, on the scissor arms 3. The inward pull then arising can be taken by a compression rod joining the two op posite bearings 63.
FIG. 16 shows a driving mechanism in which the torque is transmitted to the scissor arms by on or more toothed racks 64 acting in opposite directions on a pinion wheel fixedly attached to the central spindle 22 of the inner scissor assembly. The racks 64 are acted on by the driving units 67.
Because a wide angle of rotation between the scissor arms is possible with undercut hoists, the transmission ratio arising is very irregular when the driving units act on the scissor arms through articulations.
FIGS. l7, l8 and 19 show how the scissor arm 4 is turned, with the nonrotary spindle 22 by which the inner scissor arms are joined, by tension members, 70, attached to the bearing points 68, or by two hydraulic pressure cylinders, 72, connected by a chain, 71, to the nonrotary spindle by which the scissor arms are joined, to operate the hoist. The chain height should preferably be greater than the piston diameter. The chains are attached on both side sides of the piston, so as not to touch the nonrotary spindle. The same effect can be obtained by using a guide groove in the spindle. The arrangement shown in FIG. I8 has the advantage that the hydraulic cylinder can extend almost to the nonrotary spindle, since the piston advances to the opposite side of the spindle.
With undercut hoists, the load leverage varies sinusoidally with the lift an and attains its maximum when the scissor arms lie horizontal, that is to say at the midway height of the lift. The transmission ratio can be kept uniform if the radius of the developed curve varies equally with the angle of rotation. The radius variations are indicated in FIGS. l7 and I8 by the curves 69. FIG. 19 is a side elevation of the arrangement shown in FIG. 18.
l. A scissor hoist construction comprising, in combination, a platform which may be elevated from a base, at least three scissor arms pivotally connected together at a point intermediate their opposite ends, each of said arms having a base end, a platform end, and a platform chassis member extending from each of said platform ends, two of said arms being parallel and structurally connected at their base ends, the base end of said two arms or alternatively of said remaining arm being pivotally connected to said base, and correspondingly the remaining arm or alternatively said two arms being in sliding engagement with said base, the platform ends of said two arms each including the platform chassis member extending from said am ends to the platform for sliding or alternatively pivotal engagement therewith, the remaining one of said arms being disposed between the said two arms and including the platform chassis member extending from the platform end, said platform chassis member of said one arm pivotally connected.with said platform when said chassis members of said two arms are slidably engaging said platform and alternatively slidably engaging said platform, the platform end of said remaining arm extending to a position short of the structural connection between said two arms when said hoist is in a nesting position, and scissor-action lift means for driving said two arms in relation to said one arm about said pivotal connection between said arms.
2 The construction as set forth in claim I wherein said scissor action lift men means includes an expansive cylinder having its opposite ends connected respectively to a pivot point adjacent the pivotal connection at the end of one of said arms and a separate pivot point adjacent the pivotal connection between said arms sufficient to provide a lever arm about said pivotal connection between said arms.
3 The construction of claim 2 including an additional cylinder operative to expand in the opposite sense of said expansive cylinder, said additional expansive cylinder having one end connected to a second separate pivot point adjacent the pivotal connection between said arms and on the opposite side of said pivotal connection from said other separate pivot point, and the other end of said additional expansive cylinder connected to the opposite ends of said scissor arms, to which said expansive cylinder in connected.
4. The construction of claim I wherein said pivotal connection between said arms is at substantially the midpoint of said arms.
5. A scissor-action hoist construction comprising, in com bination, a platform may be elevated from a base, an inside pair and an outside pair of parallel, pivotally connected scissor arms, each arm having a base end, a platform end and a platform chassis member extending from said platform end, said outer pair being structurally connected at their base ends, one pair of arms being pivotally connected to the base at one end and including the chassis members extending from each platform end for slidably or alternatively pivotally engaging said platform, the other pair of arms slidably engaging the base and having its chassis members pivotally connected to the platform when the chassis members of the one pair of arms are slidably engaging said platform or alternatively slidably engaging said platform when the chassis members of the one paid of arms are pivotally connected with said platform the platform end of said inside arms extending to a position short of the structural connection between said outside arms when said hoist is in a nesting position, and scissor-action lift means for driving one pair of arms in relation to the other pair of arms about said pivotal connection between said pairs of arms.
6. The construction as set forth in claim 5 wherein said scissor-action lift means include an expansive cylinder having its opposite ends connected respectively to a pivot point adjacent the pivotal connection at the end of one of said arms and a separate pivot point adjacent the pivotal connection between said arms sufficient to provide a lever arm about said pivotal connection between said arms.
7. The construction of claim 6 including an additional cylinder operative to expand in the opposite sense of said expansive cylinder, said additional expansive cylinder having one end connected to a second separate pivot point adjacent the pivotal connection between said arms and on the opposite side of said pivotal connection from said other separate pivot point and the other end of said additional expansive cylinder connected to the opposite ends of said scissor arm, to which said expansive cylinder is connected.
8. The construction of claim 5 wherein said pivotal connection between said arms is at substantially the midpoint of said arms.
9. The construction of claim 1 wherein said chassis members of said outside two arms are connected by a crossmember adjacent the pivotal or slide connection to said platform.
It) The construction of claim 5 wherein said inside arms are structurally connected at their platform ends.
11. The construction of claim 5 wherein said chassis members of said outside arms are interconnected adjacent the pivotal or slide connection to said platform.
12. The construction of claim 5 wherein said inside arms are connected together at their base ends.