Lifting apparatus

Lifting apparatus including a base, a platform disposed above the base, a thrust device therebetween to lift the platform relative to the base, and a platform stabilizer enclosed within the thrust device to connect the platform and base in parallel. The platform stabilizer includes an upper extensible linkage device having upper end portions connected to the platform, a lower extensible linkage device having lower end portions connected to the base, and connecting arrangement connecting lower end portions of the upper extensible linkage device to upper end portions of the lower extensible linkage device so that the linkage devices are constrained to move in unison.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention concerns a lifting apparatus of a type which 
comprises a base, a platform disposed above the base, thrust means 
therebetween to lift the platform relative to the base, and platform 
stabilizing means enclosed within the thrust means to connect the platform 
and base in parallel. The platform stabilizing means comprises an upper 
extensible linkage device having upper end portions which are connected to 
the platform, a lower extensible linkage device having lower end portions 
which are connected to the base, and connecting means which connect lower 
end portions of the upper extensible linkage device to upper end portions 
of the lower extensible linkage device, so that the linkage devices are 
constrained to move in unison. 
2. Description of the Prior Art 
Apparatus of the aforementioned type is known from U.S. Pat. No. 2,725,578 
Keller dated Dec. 5, 1955. However, in this known apparatus, several of 
the linkage devices form parts of a vertically and horizontally extending 
bracing means, incorporating three separate lazytongs arranged at the 
sides of an equilateral triangle to provide vertical bracing in three 
mutually inclined vertical planes. Each of the lazy-tongs is slidably 
connected to the base and to the platform, and includes upper and lower 
linkage devices, as well as an intermediate linkage device which serves as 
a connecting means to connect the upper and lower linkage devices. A 
central pivot of each of the three upper linkage devices is connected to 
an upper peripheral circular ring member, and central pivots of the three 
intermediate and three lower linkages are similarly connected respectively 
to an intermediate ring member and a lower ring member. The three ring 
members are arranged horizontally to form part of the bracing means, and 
are secured to the inside of a pleated bellows which serves as the thrust 
means. In this known apparatus, the three surrounding ring members and the 
three separate lazy-tongs necessary for platform stabilization give rise 
to various problems, e.g. an extremely high manufacturing cost, 
complexity, and, most importantly, poor stabilization of the platform due 
to uneven or unequal movement (extension or contraction) of the lazy-tongs 
which allows the platform (and/or ring members) to tilt relative to the 
horizontal. Furthermore, the bearing or pivot clearances, which are 
necessary for relative pivotal movement of the parts of the lazy-tongs 
relative to each other and relative to the ring members, allow the 
platform to move linearly in any direction in or near to the plane of the 
platform. In any lifting position of the platform intermediate its maximum 
upper and minimum lower positions, the bracing means allows the platform 
to rotate freely through a restricted but unacceptably large angle, thus 
failing to stabilize the platform and allowing twisting torsion loads to 
be applied to the relatively weak bellows. Thus, the platform can pitch, 
roll and yaw to an unacceptable extent. 
A further drawback of this known apparatus is that the ring members have to 
be directly attached to the bellows and subject the lazy-tongs to lifting 
forces which are produced by the bellows; thereby giving rise to the 
further problems of wear, friction and malfunction of the platform 
stabilizing means. 
However, this known apparatus has the advantage that the horizontal 
dimensions of the linkage devices are relatively small in relation to the 
overall lift distance which can be produced by the apparatus, so that the 
apparatus is compact when the platform is lowered. 
An object of the present invention is to enable the problems encountered 
with heretofore known lifting apparatus to be reduced or avoided. 
SUMMARY OF THE INVENTION 
The present invention is characterized primarily in that the upper and 
lower extensible linkage devices each comprise a single inner rigid 
member, which is pivotally secured between two outer rigid members by 
median pivot means, so that the outer rigid members are held in spaced 
apart relationship for constrained arcuate movement about a common median 
axis. Also, the linkage devices are connected, so that said median axes 
are parallel. 
A lifting apparatus according to the present invention is further 
characterized in that a first two of said upper end portions of the upper 
extensible linkage device are secured to the platform by upper pivot 
means, so as to be constrained to pivotal movement about an upper common 
axis fixed in relation to the platform, in order that a second two of the 
upper end portions of the upper extensible linkage device are movable 
linearly of the platform and perpendicular to said upper common fixed 
axis. A first two of said lower end portions of the lower extensible 
linkage device are secured to the base by lower pivot means, so as to be 
constrained for pivotal movement about a lower common axis which is fixed 
relative to the base and is disposed vertically below, and parallel with, 
the upper common axis, in order that a second two of said lower end 
portions of the lower extensible linkage device are movable linearly 
relative to the base and perpendicular to the lower common axis. 
In particular, the present invention provides an apparatus of the 
aforementioned type wherein linkage devices comprise rigid members, which 
are pivotally connected, so as to be arcuately movable about axes which 
are maintained mutually in parallel by said rigid members. An upper one of 
these axes is fixed in relation to the platform and a lower one of these 
axes is fixed in relation to the base so that the platform is constrained 
against arcuate movement, relative to the base, in all positions of the 
platform. 
The thrust means is preferably pneumatically inflatable to apply lifting 
forces directly to the platform independently of the platform stabilizing 
means. 
The present invention also provides apparatus of the aforementioned type 
wherein each linkage device comprises a rigid member pivotally secured 
between two outer rigid members by means of a median pivot, so that the 
outer rigid members are held in spaced apart relationship for constrained 
arcuate movement about a common median axis. In addition, the connecting 
means comprise a plurality of intermediate axes, each of which passes 
through end portions of the inner rigid member of one of the linkage 
devices and the outer rigid members of the linkage devices, in order to 
confine these outer rigid members to arcuate movement relative to the 
inner rigid member. The upper linkage device is pivotally connected to the 
platform about an upper common axis fixed in relation to the platform, and 
the lower linkage device is pivotally connected to the base about a lower 
common axis fixed in relation to the base and, parallel with and 
vertically below, the upper common axis. The inner rigid members thereby 
locate the median and the intermediate axes parallel with the common axes. 
The present invention further provides a lifting apparatus of the 
aforementioned type wherein: 
(a) the upper and lower extensible linkage devices each comprise an inner 
rigid member, which provides two of said upper end portions and two of 
said lower end portions in rigid spaced apart relationship; and the inner 
rigid member is pivotally secured between two outer rigid members by 
median pivot means, so that the outer rigid members are held in spaced 
apart relationship for constrained arcuate movement about a common median 
axis; and 
(b) a first two of said upper end portions of the upper extensible linkage 
device are secured to a platform by upper pivot means, so as to be 
constrained to pivotal movement about an upper common axis fixed in 
relation to the platform in order that a second two of the upper end 
portions of the upper extensible linkage device are movable linearly of 
the platform and perpendicular to said upper common fixed axis; and a 
first two of said lower end portions of the lower extensible linkage 
devices are secured to the base by lower pivot means, so as to be 
constrained for pivotal movement about a lower common axis, which is fixed 
relative to the base and is disposed vertically below and parallel with 
the upper common axis, in order that a second two of said lower end 
portions of the lower extensible linkage device are movable in unison 
linearly relative to the base and perpendicular to the lower common axis. 
The apparatus of the present invention thus provides complete stability for 
the platform by the use of stabilizing means that is smooth (i.e. 
non-jerky) in operation, compact in relation to the lift which can be 
produced, and of relatively light and simple construction. 
The inner rigid members preferably provide stop means which is abutted by 
the outer rigid members when the apparatus is in the lowered (i.e. minimum 
height) position. The outer rigid members of each linkage device are 
preferably connected, by tie means, to further secure the outer rigid 
members in a parallel relationship. 
The inventive apparatus is particularly suitable for low pressure pneumatic 
operation, e.g. those operations using a pneumatic supply of less than 1 
kilogram per square centimeter, and preferably less than 0.5 kilograms per 
square centimeter (0.5 kg/cm.sup.2). 
Since the platform stabilizing means is of a particularly rigid 
construction in relation to movement about the axes, and is substantially 
relieved of all lifting loads, the extended angle between the inner and 
outer rigid members may be very large at a maximum lift. The inventive 
lifting apparatus is preferably arranged so that this angle can be at 
least 130.degree., and preferably at least 135.degree., or more, so that 
the maximum distance between the platform and base can be about 80% of the 
combined overall length (height) of the inner rigid members, without loss 
of platform stability. 
The connecting means preferably comprises intermediate pivot means which 
directly pivotally connect the upper and lower linkage devices. 
The platform stabilizing means is particularly effective, is simple and 
inexpensive to construct, and is reliable in use. 
The platform and base preferably each have a pair of parallel guides 
secured rigidly thereto, so as to be offset outwardly from the linkage 
devices and to slidably receive sliders supporting pairs of coaxial main 
pivots which project outwardly from the linkage devices. 
The inner rigid members each preferably integrally incorporate two parallel 
main elongate portions, from which the upper and lower end portions 
project, and a plurality of rigid transverse portions extending between 
and supporting the main elongate portions 
Each of the intermediate and the median pivot means preferably comprises a 
rigid rod, which extends transversely across the platform stabilizing 
means and through axially elongate cylindrical bearings of the inner and 
outer rigid members. 
The lower pivot means preferably comprise a lower rigid rod, and the upper 
pivots may comprise an upper rigid rod, which rods extend across the 
platform stabilizing means and are secured in end portions of the guides. 
Each main pivot means preferably comprises a rigid rod which extends 
across the platform stabilizing means and is secured in the sliders. 
The inventive apparatus may be provided with a part, such as a seat, seat 
and backrest assembly, cushion, cradle, flank panel or mattress mounted, 
e.g. releasably located, upon the platform, while the platform may be 
shaped to receive such a part. 
The present invention provides a backrest assembly in a particularly easy 
to fit and remove form. The backrest assembly comprises a frame, a facing 
supported on the frame, oppositely directed lugs which are located on the 
frame and which fit into first recesses provided by the platform, and 
manually retractable bolts which are biased to outwardly projecting 
positions for engaging second recesses which are located on the platform. 
The side edges of the platform, and optionally also the front and rear 
edges of the platform, may be provided with protuberances which extend 
longitudinally of the edges to receive slide-on fittings for adjustably 
locating arm-rest, leg-support panels, or flank panels on the platform. 
The present invention further provides a flank panel assembly for use with 
a form of the inventive apparatus having, along the side edges of the 
platform, an elongate headed protuberance joined to the platform by a 
neck, with the assembly comprising a panel and a hinge. The hinge 
comprises a first relatively rigid part having an elongate recess shaped 
to accept the protuberance, a second relatively rigid part secured to the 
panel, and a thin flexible elongate intermediate part. This hinge is a 
co-extrusion of rigid and flexible plastics materials. 
The base may be provided with feet, suction cups, castors, or wheels or may 
form part of a bath, chair, bed, floor, wheelchair, trolley, or vehicle. 
Biasing means and/or motion damping means may be enclosed in the thrust 
means to act on the platform stabilizing means. Lift limiting means may 
also be provided to limit the maximum distance between the base and the 
platform. 
The pneumatic thrust means include a flexible wall, and in experiments with 
various forms of the apparatus, it has been found that distortions of the 
flexible wall can arise under certain conditions. However, advantageous 
wall constructions will overcome this problem. According to one example of 
an advantageous wall construction, the flexible wall is preferably 
provided with vertically spaced horizontal stiffeners which are bonded to 
inwardly projecting flexible portions of the wall within the extensible 
member. These stiffeners may be of flattened or tapered section, and are 
preferably cast or injection molded.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings in detail, lifting apparatus shown therein 
comprises a base 10 and a platform 11, together with low pressure 
pneumatic thrust means 12, means 13 to admit pressurized fluid into the 
thrust means 12, and platform stabilizing means 14, which is located 
between the base 10 and platform 11 and is surrounded by the thrust means. 
The thrust means 12 has a flexible wall 15, of a large area concertina 
bellows form, which extends between and is sealed to the base 10 and 
platform 11 (e.g. as hereinafter described). The means 13 is provided, for 
example, in the form of a valve and fluid plug socket, in the base 10 or 
in the platform 11 or in the wall 15. 
The platform stabilizing means 14 generally comprises an upper extensible 
linkage device 20, a lower extensible linkage device 21, and connector 
means 18, which may include an extensible linkage device, for example, as 
hereinafter described. 
Each extensible linkage device 20, 21 is an assembly comprising two 
elongate outer rigid members 16, which are connected by median pivot means 
17 to opposite sides of an inner rigid member 19 so as to be relatively 
angularly movable. Thus, when the linkage device increases in height and 
decreases in width, an angle A (which formed between the inner member 19 
and the outer members 16) is increased, and vice versa. 
The rigid members 16 and 19 are of a strong metal or alloy, e.g. aluminum 
alloy, and are cast or machined so that, in transverse cross-section, the 
members 16 and the main portions 22 of the members 19 are substantially as 
wide as they are thick. The main portions 22 of each member 19 are secured 
in rigid parallel relationship by rigid integral transverse portions 23, 
which are disposed adjacent the median pivot means 17 and between 
projecting end portions 24 and 25 or 26 and 27 of the main portions 22, as 
shown in FIGS. 3 and 4. One or more of the extreme transverse portions 23 
may be hollow and extend to the ends of the rigid member 19 to close the 
gap between the end portions 24 and 24; 25,25; 26,26; and/or 27 and 27, 
and to further integrally unite said end portions. 
The median pivot means 17 each comprise a rigid metal rod 28, which extends 
through axially elongate bearing sockets 29 (FIG. 4) and transversely 
horizontally across the linkage device 20 or 21. 
The connector means 18 comprises parallel intermediate pivot means 30, each 
of which comprises a metal rod 31 or 32, which extends across the linkage 
devices and through the bearing sockets 29. The rod 32 connects the upper 
end portions 26 of the member 19 of the linkage device 21 to the lower end 
portions 33 of the members 16 of the upper linkage device 20. Similarly, 
the rod 31 connects the lower end portions 25 to the upper end portions 34 
of the members 16 of the lower linkage device 21. 
The platform and base have, releasably secured thereto, respective pairs of 
mutually opposed upper guides 35 or lower guides 36. These guides are of 
channel form, are arranged in parallel, and are offset outwardly from the 
linkage devices 20, 21. The upper end portions 24 support a further metal 
rod 37 in bearing sockets 29. This rod is provided with outwardly 
projecting end portions (not shown), each of which is secured fixedly to 
an end part of an upper guide 35, and is bedded in a plastics block 38 
which is fixed in the guide 35. The lower end portions 27 similarly 
support a further metal rod 39. This rod 39 is provided with outwardly 
projecting end portions (not shown), which are bedded in plastics-block 
sliders 40 that maintain a tight sliding fit within the lower guide 36. 
The end portions 24 and 27 extend outwardly adjacent to the guides 35, 36 
in order to further support the rods 37, 39. 
The rods 28, 31, 32, 37, and 39 provide bracing for the end portions and 
are a close, or push, fit in the bearing sockets 29. 
The upper end portions 41 of the members 16 of the upper linkage device 20 
may support a rod, which is similar to the rod 39, having end portions 
embedded in plastics block sliders 42 in the upper guides 35. The lower 
end portions 43 of the members 16 of the lower linkage device 21 may 
support a rod, which is similar to the rod 37, having end portions 
embedded in plastics blocks 44 which are fixed in the lower guides 36. 
However, in the embodiment shown, the linkage devices 20, 21 are provided 
with tie means 45, which comprises a rigid upper bar 46 that extends 
horizontally between, and is secured to, the upper end portions 41 and a 
similar lower bar 47 which is secured to the lower end portion 43. This 
tie means 45 is proximal to the end portions 25 and 26 when the apparatus 
is in the lowered position shown in FIG. 1. The tie means 45 provides 
rigid spacing and bracing for the end portions 41 and 43, so that a weight 
saving can be made by mounting respective individual short rods 48, 49 in 
the end portions 41 and 43 to engage in the sliders 42 and blocks 44. 
As an alternative to the use of plastics block sliders 40 and 42, the 
outwardly projecting end portions may be slidable in low-friction plastics 
channel section inserts within the guides, e.g. as indicated at 142 in 
FIG. 3. 
While in use, the rods 37 and 49, respectively, serve as upper pivot means 
and lower pivot means, and provide an upper horizontal common fixed axis 
and a lower horizontal common fixed axis which is vertically below, and 
parallel with, the upper common fixed axis, so that the end portions 24 
and 43 are restricted solely to pivoted movement relative to the platform 
11 and base 10. The rods 39 and 48, respectively, serve as lower main 
pivot means and upper main pivot means, and provide lower and upper 
horizontal common main axes 50, 51 (FIG. 3) for pivotal movement of the 
end portions 27 and 41 relative to the sliders 40, 42. The axes 50 and 51 
are solely horizontally movable in unison in relation to the guides 36, 
35, so that the upper main axis 51 remains vertically above, and parallel 
with, the lower main axis 50. 
In the fully raised maximum lift position (FIGS. 3 and 4) the sliders 40, 
42 abut the blocks 44, 38 (which thus serve as stop means to prevent 
further lift which would increase the angle A beyond a maximum of 
140.degree.). The sliders move forwards (away from the blocks) as the 
platform 11 is lowered, and causes the linkage devices 20, 21 to retract 
downwards and to extend forwards, thereby decreasing the angle A, until 
further movement is halted by the end portions 34 and 33 which abut the 
end portions 27 and 24. These end portions 27 and 24 are outwardly 
extended to serve as stop means in the lowered position, so that the 
guides and pivots are not subjected to any major stresses. 
During movement of the platform, the relatively large axial length to 
diameter ratio (e.g. at least 2:1) of the bearing sockets, in combination 
with the close or tight fit of the rods in the bearing sockets, blocks and 
sliders, prevent any significant unwanted movements of said axes from 
their precisely parallel relationships. This also serves to minimize wear. 
Furthermore, only the linearly sliding surfaces of the sliders are 
subjected to any slow but significant wear during repeated operation. In 
addition, these sliders can be replaced cheaply and easily after simply 
removing the guides, which thus serve as releasable connecting means that 
connect the stabilizing means 14 to the base and to the platform 11. 
Referring in general to FIGS. 2 and 3, the flexible wall 15 is of segmental 
construction and, as indicated in FIG. 3, comprises strips 52 of 
impervious, and flexible but substantially inelastic, material which is 
bonded together at outer junctions 53, and is bonded together and to 
stiffeners 54 at inner junctions 55. The stiffeners 54 are of flattened 
cross-section, have rounded or tapered edges, and are substantially 
rectangular in plan. The lowermost and uppermost strips 52 are 
respectively clamped to the base 10, e.g. by a clamping ring 56 and 
fasteners 57, and similarly to the platform 11, in order to effect a seal 
therewith which renders the thrust means 12 airtight except for the means 
13. This allows the platform to be raised or lowered by inflation or 
deflation of the thrust means. Since the large area bellows allows a large 
load to be lifted by a direct thrust on the platform, the stabilizing 
means is not subjected to any lifting loads. For example, a load of about 
100 kg can be lifted on a platform of about 0.15 m.sup.2 in area through a 
distance of 40 cm by a pneumatic supply pressure of only about 0.35 
kg/cm.sup.2. 
Referring to FIGS. 1, 2, 5 and 6, the lifting apparatus may be arranged to 
support and lift a person. In this embodiment, the inventive apparatus 
comprises a backrest assembly 60, which, in turn, comprises a frame 61, a 
molded plastics facing 62, oppositely directed lugs 63 which are located 
on lower portions 64 of the frame, bolts 65 which are slidably mounted on 
the lower portions 64, crossed levers 66 which are connected to the bolts 
and are pivotally mounted by means of a central pivot 67 and guides 68 on 
the frame, and a cross-rope 69 which connects the upper ends of the levers 
66. The rope 69, when pulled upwards, causes the bolts 65 to be retracted 
inwards, against a bias provided by springs 70. 
The rear of the platform 11 is shaped to provide a pair of mountings 71, 
each of which provides an upwardly open socket 72 for one of the lugs 63, 
and a parallel downwardly open socket 73 which accepts one of the bolts 65 
and thereby secures the backrest assembly for the platform. When the bolts 
are retracted, as indicated in broken lines in FIG. 6, the backrest 
assembly 60 can be simply lifted off the platform. 
The platform 11 also has, along each side, an elongate and headed 
protuberance 74 which is joined to the platform by a neck 75. The 
protuberances 74 serve as mountings for slide-on supports 76 (for armrests 
or similar fittings) having clamping screws 77 that secure the supports 76 
in fixed positions on the platform as shown in FIG. 6, or as mountings for 
flank panels 78 shown in FIG. 7 and indicated in broken lines in FIG. 1. 
The flank panels 78 operate, and are used, as described in British Patent 
Specification No. 2110527. The flank panels 78 are secured to the 
mountings 74,75 by a plastics hinge 79 which comprises a first elongate 
portion 80 that is shaped to fit onto the mounting, a second portion 81 
that is secured to the panel 78, and a thin flexible portion 82 that 
connects the portions 80 and 81. The hinge is a unitary/coextrusion of 
relatively rigid plastics material, which forms the portions 80, 81, and a 
relatively flexible plastics material, which forms the portion 82. 
The base 10 is provided with four swivel mounted suction feet 84, and a 
lift limiting cord 85 that actuates the means 13 and thereby limits 
inflation of the thrust means. The cord 85 may be adjustably secured to 
the platform, backrest, or armrest. 
The present invention is not confined to details of the foregoing examples, 
and many variations are possible within the scope of the invention. For 
example, the longitudinal orientation of the devices 20 and 21, as shown 
in FIG. 4, may be reversed so that the upper pivots locate the upper end 
portions 41. The connecting means may also comprise an intermediate 
extensible linkage device and two additional rods similar to the rods 32, 
31. 
Clearly, the, or any of the rods, which extend across the linkage devices, 
may be replaced by pairs of co-axially aligned pairs of short rods, e.g. 
similar to the rods 48 and 49, which act to connect together the rigid 
members or to connect the rigid members to the blocks or sliders, and 
permit arcuate movement about said axes, thereby providing the, or any one 
of the, several pivot means. 
The rigid members, guides, mountings, and pivots may be of any suitable 
construction and configuration. The rigid members may also be cast so as 
to have rounded edges. 
The stabilizing means may incorporate stops, dampers, shock absorbers, or 
bias means, in order to limit, smooth, or bias the movement of the rollers 
or sliders relative to the guides. 
The flexible wall may be of any suitable form and of any suitable 
construction; and may be secured to the platform and base in any suitable 
manner. The corners of the wall may also be rounded to facilitate sealing. 
Connectors may be includes to enable several units of the apparatus to be 
arranged in a stack or row and to be connected so as to operate 
sequentially or in unison. The connectors may also incorporate self 
sealing fluid couplings. 
The inventive apparatus is particularly suitable for operation in 
connection with a low pressure compressed air supply; and preferably 
includes a manually operable valve means, in order to control admission 
and release of air into and out from the thrust means, along with a 
pressure relief valve which acts to limit the maximum working air pressure 
within the thrust means. 
The inventive apparatus may also include manually releasable safety means 
which hold the platform at a selected or predetermined height. 
The inventive apparatus is capable of being used in a wide variety of 
applications, may carry a variety of fittings, and may be mounted on a 
variety of supports. The base and platform may be shaped to suit the 
supports and fittings, and may include a removable or openable inspection 
or maintenance hatch or panel which provides access to the linkages and 
other components within the thrust means. The apparatus may also be 
operated in any required orientation, e.g. may be inclined to the vertical 
or may be horizontal (the terms "vertical", "horizontal", and "front" 
being used herein in relation to the apparatus when it is orientated as 
shown in the drawings). 
The present invention is, of course, in no way restricted to the specific 
disclosure of the specification and drawings, but also encompasses any 
modifications within the scope of the appended claims.