[0001] The present invention relates to a lifting device for lifting a load, comprising
a rigid carrier arm to be placed over the load, means for receiving the load, the
carrier arm supporting said means for receiving the load, and transfer means connected
to said carrier arm for parallel movement thereof in its lateral direction.
[0002] Primarily, the lifting device is intended for lifting and/or moving a patient confined
to bed between two places.
[0003] Such lifting devices, often referred to as patient lifters, are previously known
for facilitating the work of the medical staff in hospitals and similar institutions
for lifting and moving patients having reduced faculty of motion or being confined
to their beds for other reasons. Prior art lifting devices are often bulky and difficult
to handle and require for handling often more than one person. Moreover, prior art
lifting devices generally are mounted on the floor or a wall and so valuable space
is lost in the room where the lifting device is accomodated.
[0004] There are previously knwon patient lifters attached to the ceiling of a room, such
lifters including a rigid carrier bar to be placed along and over a person to be lifted.
The bar is supported at its both ends by two cables which over pulleys in the ceiling
are connected to a telfer having two cable exits. A device for receiving and supporting
a patient can be attached to the carrier bar. This type of lifting device only allows
vertical movement. Therefore, when moving a patient from e.g. a stretcher to a bed,
first the patient has to be lifted from the stretcher which then has to be removed
whereupon the bed is brought in under the patient which is then lowered down onto
the bed.
[0005] The Swedish laid-open specification 7508892-2 discloses a patient lifter including
a carrier bar supported by a lever which is pivotably supported by a horizontal shaft.
The carrier bar is movable in its lateral direction by rotation of said shaft. This
patient lifter can be handled by one operator and allows movement of a patient between
two support surfaces, e.g. a stretcher and a bed, without intermediate movement of
said support surfaces. However, this patient lifter occupies a relatively large floor
area.
[0006] The object of the present invention is to provide a new lifting device which obviates
the above-mentioned drawbacks of prior art lifting devices and is particularly suited
for operation in narrow spaces.
[0007] This object is achieved by means of a lifting device for lifting a load which device
comprises a rigid carrier arm to be placed over said load, said carrier arm supporting
means for receiving said load, a transfer means connected to said carrier arm for
parallel movement of the carrier arm in its lateral direction. Said transfer means
includes two similar transfer assemblies, each having a rigid link member pivotably
connected at separate ends of the carrier arm, and a lever pivotably connected at
one end to the associated link member and pivotably supported at its other end. Said
transfer assemblies are symmetrically arranged for pivoting said levers in opposite
directions, thereby allowing the ends of the link members connected to the carrier
arm and so the carrier arm to be lifted and moved in lateral direction.
[0008] For the purpose of elucidation the invention will be described in greater detail
in the following with reference to the accompanying drawings, wherein
Fig. 1 is a simplified view showing the principle structure of a lifting device according
to the invention;
Figs. 2A and 28 are partial detail views on a large scale showing essential portions
of the lifting device in Fig. 1;
Fig. 3 illustrates a realization of the lifting device according to the invention;
Figs. 4A and 4B illustrate in two different positions in simplified manner a modified
structure of the lifting device according to Fig. 1; and
Fig. 5 illustrates a stabilizing means for the lifting device according to the invention,
said stabilizing means being connected to the link members of the lifting device.
[0009] The following description of the lifting device according to the invention is directed
to an application as a patient lifter. However, as mentioned below the lifting device
provided with a suitably structured load receiving means can be used for lifting any
type of load.
[0010] Referring to Fig. 1 which schematically illustrates the principle structure of a
lifting device according to the invention occupying its top position, the lifting
device has a rigid carrier arm 1 with a longitudinal extension suitable for the particular
application of the lifting device. Preferably, the carrier bar 1 includes a pipe or
two parallel side members which are rigidly connected by means of cross members (Fig.
3).
[0011] In Figs. 1, 4A and 48 most of the components of the lifting device are illustrated
in a simplified manner by means of straight lines, crossing lines showing the presence
of articulations for allowing mutual movement. However, it is emphasized that the
components illustrated as straight lines in practice also have a lateral extension.
[0012] A load receiving means 2 for receiving and supporting a patient is connected to the
carrier arm 1 and supported thereby. Said receiving means can be made releasable from
the lifting device and can also include the carrier arm. In Fig. 1 said load receiving
means 2 is shown as consisting of several rigid yokes 3 connected to the carrier bar
1, lifting bands 4 being releasably attached to the legs of said yokes. However, said
load receiving means 2 can be embodied in various other ways, another suitable embodiment
for receiving patients being shown in Fig. 3.
[0013] Rigid, preferably straight link members 5a and 5b are pivotably connected to both
the ends of the carrier arm 1 which link members at their other ends are pivotably
connected to a respective lever 6a and 6b. These levers 6a and 6b are in turn pivotably
supported and rigidly fixed to separate pivot shafts 7a and 7b, respectively. The
pivot shafts 7a, 7b are supported in a frame 27 which is bolted to the ceiling of
a room. In the embodiment of the lifting device which is described here the pivot
shafts are vertical. However, as mentioned below, they can have other directions.
[0014] At their ends facing away from the levers 6a and 6b the vertical pivot shafts 7a
and 7b have transmission members 8a and 8b which for transmitting a rotating movement
to the pivot shafts engage corresponding transmission members 9a, 9b of a shaft 10.
In the embodiment of the lifting device shown in Fig, 1, the shaft 10 is an elongated
worm of a worm gear 12 the input shaft of which is coupled to a motor 13 which may
be pneumatically or hydraulically driven but preferably electrically driven.
[0015] The above mentioned components 13, 12, 10, 9a, 9b, 8a, 8b, 7a, 7b, 6a, 6b and 5a,
5b constitute transfer means for parallel movement of the carrier bar 1 in its lateral
direction. Said transfer means including drive means and transmission means is provided
to drive said pivot shafts 7a and 7b in opposite rotational directions.
[0016] Apparently said transfer means includes two transfer assemblies interconnected by
means of said drive means and transmission means. The two transfer assemblies are
similar, the components thereof having identical lengths and structure. The length
of the carrier arm 1 is equal to the distance between the pivot shafts 7a and 7b.
[0017] It is appreciated that the members having the same reference figures, e.g. levers
6a and 6b, have the same longitudinal extensions and so when rotating the pivot shafts
7a and 7b in opposite directions the carrier arm 1 will be transferred perpendicularly
to its longitudinal extension. From an initial lifting position where the levers 6a
and 6b are parallel and facing in the same direction the levers can be rotated either
inwardly or outwardly thereby achieving the same lifting action on the carrier arm
1.
[0018] The connection of the link members 5a and 5b to the carrier arm 1 has such a structure
that the link members can pivot around an axis essentially perpendicular to the longitudinal
extension of the carrier arm which axis is horizontal when the lifting device is mounted
on place. Preferably a shaft 17 (Fig. 2B) is used for this connection, thereby counter-acting
the tendency of lateral swinging of the load receiving means. Another suitable articulation
for this connection is a universal joint, such as a ball and socket. Such an articulation
also allows movement between the link members 5a and 5b and the carrier arm around
an axis parallel to the carrier arm and so lateral swinging motion of said load receiving
means will not be counter-acted. The connection of the link members 5a and 5b to the
respective levers 6a and 6b is made for allowing pivot around both a vertical and
a horizontal axis perpendicular to the carrier arm. A suitable articulation in this
case is a universal joint, such as a ball and socket (Fig. 3). However, as shown in
Fig. 2A also a vertical pivot 19 can be pivotably mounted at the end of the respective
lever 6b facing away from the associated pivot shaft which pivot at its lower end
has a lateral through shaft 16 which is connected to the associated link member 5b.
This latter articulation with rigid shafts counter-act unfavourable swing motions
of said load receiving means.
[0019] Of course, the transmission between the output shaft 10 of the worm gear 12 and the
two pivot shafts 7a and 7b can be constituted in many different ways. However, these
transmissions are preferably embodied as bevel drives 8a, 9a and 8b, 9b respectively,
the shafts 10, 7a and 7b being supported and carried in bearings in a suitable manner.
The exchange gear reduction between the shaft 10 and the pivot shafts 7a and 7b preferably
is 2:1 in order that the load on the levers 6a and 6b is kept at reasonable values
when operating the lifting device. The drive means and transmission means described
above sometimes may be too heavy to be fixed to the ceiling of rooms in older buildings.
A considerably lighter drive means and transmission means (not shown) are based on
a chain drive. In this case the transmission can include sprockets fixed at the ends
of each pivot shaft 5a, 5b which sprockets are rotatable in different directions by
means of an endless chain having crossing parts. A central sprocket fixed on an additional
shaft engages the chain and said shaft is driven over a gear connected by means of
a motor.
[0020] The levers 6a and 6b are rigidly fixed to a respective pivot shaft 7a and 7b and
extend downwardly therefrom under an angle of declination which is less than 90
0. However, it is appreciated that in other embodiments of the lifting device the levers
can form any angle to the pivot shafts and also extend upwardly therefrom.
[0021] In fig. 1 the transfer means of the lifting device is shown entirely over the carrier
arm and is mounted to the ceiling of a room by means of the frame 27 (see also Fig.
3). However, said transfer means and the associated frame can be mounted on the floor
of a room, the pivot shafts 7a and 7b thereby extending upwardly from the floor. This
latter alternative embodiment is of interest only in the case of ample space in the
room where the lifting device is placed.
[0022] In said alternative embodiment of the lifting device the levers can however only
be rotated inwardly in order that the carrier arm 1 shall be able to pass through
its top position, in which the levers are directed towards each other and located
in the same vertical plane.
[0023] In this alternative embodiment the carrier arm should be somewhat shorter than the
distance between the pivot shafts 7a, 7b since otherwise the latter will obstruct
the carrier arm when passing through its top position.
[0024] The operation of ;.he lifting device is described below with reference to the embodiment
of Fig. 1.
[0025] For lifting and transferring between two supporting surfaces a patient supported
in said receiving means 2 the lifting device is put into a position where the levers
6a and 6b are parallel and the link members 5a and 5b are essentially vertical. The
bed or similar resting place on which the patient to be lifted lies is inserted under
the carrier arm 1 so that the latter takes a position along the person in question.
Then the person is placed in sa;d receiving means 2 and the lifting device can be
activated. When starting the motor 13 the shafts 7a and 7b will rotate in opposite
directions, e.g. so that the levers6a and 6b are pivoted outwardly from the carrier
arm as shown in Fig. 1. Since the ends of the levers 6a and 6b facing away from the
pivot shafts 7a and 7b are turned outwardly the link members 5a and 5b will be brought
along and so the ends of the link members connected to the carrier arm will be urged
in a direction perpendicular to its longitudinal extension.
[0026] During the movement of the carrier arm from its bottom position to its top position
(rotation of the pivot shafts over 90°) where the levers are located in the same vertical
plane, the carrier arm describes a curve. When the rotation of the shafts are continued
over another 90° the carrier arm performs a reverse movement downwardly to a laterally
displaced second bottom position, the carrier arm thereby describing a curve which
in relation to a vertical plane through the two pivot shafts 7a and 7b is symmetrical
to said first mentioned curve.
[0027] By suitable selection of the lengths of the levers 6a, 6b, the link members 5a, 5b
and the carrier arm as well as the angled between the levers and the shafts 7a, 7b
a desired shape of said curve is achieved. For a patient lifter said curve should
have an intial steep slope upwardly which slope successively decreases. In this way
a very appropriate movement is achieved for the lifting device in which movement the
carrier arm in an initial stage principally is lifted whereupon the movement in horizontal
direction gradually will increase until the top position of the carrier arm is reached.
From this position the reverse movement takes place and the carrier arm is lowered
on to the other side of the lifting device.
[0028] In accordance with a further feature of the invention a biasing device 15 is provided
between two members lla, llb fixed to the pivot shafts 7a and 7b. The biasing device
15 may be shaped as a tension spring which has its most biased or extended state when
the carrier arm takes any of its bottom positions. When the biasing device 15 is a
tension spring said members lla, llb can be either rigid arms or cables the latter
to be wound around the pivot shafts. The biasing device 15 is completely unloaded
when the levers 6a and 6b are situated in the same vertical plane, i.e. when the carrier
arm 1 takes its top position. When operating the lifting device the biasing device
will contribute to the rotation of the pivot shafts during the lifting stage while
during the lowering stage the biasing device will smooth the movemenc at the same
time as a bias is built up in the biasing device.
[0029] It is appreciated that the biasing device 15 can be embodied in a variety of ways.
Thus, it may also be hydraulic or penumatic.
[0030] Fig. 3 illustrates a preferred embodiment of the lifting device. In this figure the
same reference numerals are used as in Fig. 1 and 2 for denoting the same components.
[0031] As shown in Fig. 3 the carrier arm 1 has two side members la and lb which are rigidly
connected by means of cross members. One cross member at each end of the carrier arm
serves as a horizontal shaft 17 for the respective link member 5a, 5b for connecting
the same to the carrier bar. The link members 5a and 5b are connected at their upper
ends to a respective lever 6a, 6b by a ball and socket articulation 18.
[0032] The upper portions of the pivot shafts 7a and 7b are accommodated in a casing 14
together with the worm gear 12, the motor 13 and the biasing device 15.
[0033] In accordance with another embodiment of the lifting device shown in Fi
g. 4A and 4B the carrier bar 1 is shorter than the distance between the two vertical
pivot shafts 7a and 7b.
[0034] Fig. 4A illustrates the lifting device in a position where the levers 6a and 6b are
rotated outwardly at a relative angle of 180 in which position the carrier arm 1 takes
its top position. In Fig.4B the lifting device is illustrated with the carrier arm
1 in its bottom position and the link members 5a and 5b are parallel and vertical.
In this bottom position the two levers 6a and 6b are directed slightly towards each
other from the respective pivot shafts.
[0035] In this embodiment of the lifting device the relative longitudinal extensions of
the carrier arm 1 the link members 5a and 5b and the levers 6a and 6b are defined
such that the link members take parallel position (bottom position of the carrier
arm) when the two levers from parallel positions have been rotated inwardly towards
each other a small angle, substantially 20°.
[0036] It is ipreciated that in this embodiment the lifting height will be greater than
for the embodiments <own in Figs. 1 and 3. From the initial bottom position of the
lifting device shown in Fig. 4B the two pivot shafts 7a and 7b are rotated counter-clockwise
and clockwise, respectively (seen from above), the levers 6a and 6b thereby lifting
the carrier arm 1 by intermediation of the link members 5a and 5b. In the movement
of the levers from the position shown in Fig. 4B to the position where the levers
are parallel, i.e. after a rotation of approximately 20° of the pivot shafts, the
carrier arm 1 principally performs a movement upwardly while its movement in horizontal
direction is small. Upon further rotation of the pivot shafts the movement in vertical
direction will continue to dominate but gradually decreases in relation to the movement
in horizontal direction until the carrier arm takes its top position where the levers
are facing away from each other and located in the same vertical plane. When the rotation
of the pivots shafts are continued the levers are brought out on the other side of
the lifting device, the reverse movement taking place and the carrier arm being lowered
to its bottom position. Similar to the embodiment shown in Fig. 1 the initial lifting
and the final lowering of the carrier arm, when transferring the same, will be smooth
and the speed of these stages is slower than the intermediate lateral movement of
the carrier arm. Thus; it is appreciated that the embodiment of the lifting device
shown in Fig. 4A and 4B makes it possible to lift the carrier arm 1 higher than can
be achieved by means of the embodiment shown in Fig. 1.
[0037] In a particularly preferred embodiment of the lifting device shown in Fig. 4A and
4B the distance between the pivot shafts 7a and 7b is 80 cm, the length of the levers
6a and 6b is 65 cm, the length of the link members 5a and 5b is 80 cm, the length
of the carrier arm 1 between its connecting points to the link members is 60 cm and
the angle OG between the levers and the pivot shafts is 80°. Thus, it is realized
that the lifting device occupies a very small space.
[0038] The above described embodiments of the lifting device can be modified within the
scope of the invention. Thus, the carrier arm 1 can be longer than the distance between
the two vertical shafts. In such an embodiment the carrier arm takes its bottom position
when the two levers are turned outwardly from each other. In order to achieve the
greatest lifting height by means of this embodiment the pivot shafts are first pivoted
in a direction towards each other until they are parallel and after continued movement
they fall in the same vertical plane, in which position the carrier arm takes its
top position. Then the levers are brought out on the other side of the lifting device
and the reverse movement is obtained, i.e. the carrier arm is lowered.
[0039] As mentioned above the pivot shafts 7a and 7b need not be parallel to each other.
Thus, the pivot shafts can be arranged in the same vertical plane with their bottom
ends located at a greater distance from each other thar their upper ends. This arrangement
can be used when the carrier arm is shorter than the distance between the points on
the pivot shafts from where the levers extend. On the other hand the pivot shafts
can also be arranged in the same vertical plane with their bottom ends located at
a smaller distance from each other than their upper ends. This arrangement can be
used when the carrier arm is longer than the distance between the points on the pivot
shafts from where the levers extend. When the two pivot shafts 7a and 7b are arranged
at an angle a still greater lifting height can be obtained for the carrier arm. However,
the bearings of the pivot shafts as well as their transmissions will be more complicated
than in the embodiments of the lifting device shown in Figs. 1 to 48.
[0040] The above described embodiments of the lifting device are relatively sensible to
unsymmetrical load, namely the condition where the centre of gravity of the load is
displaced from a vertical plane of symmetry across the carrier arm. Thus, if the patient
is placed in said load receiving means such that the centre of gravity of the patient
is displaced a considerable distance from said plane of symmetry the carrier arm will
tend to incline relative the horizontal plane and the lifting device will not operate
satisfactorily. In order to counteract said inclining tendency of the carrier arm
a stabilizing means 20 shown in Fig. 5 is provided.
[0041] Said stabilizing means 20 includes two rigid bars 21a and 21b which at their ends
are pivotably connected between the link members 5a and 5b in a crossing relation.
Stabilizing means 20 shown in Fig. 5 is arranged between the bottom ends of the link
members, and the carrier arm 1 is suspended between spacers 22a and 22b under said
stabilizing means. However, it-is appreciated that the stabilizing means 20 also can
be connected to the link members at a distance from their bottom ends and so it may
simply be mounted on the above described embodiments of the lifting device.
[0042] Said stabilizing means 20 comprises U-shaped clevises 23a, 23b having opposite lugs
and a connecting web the latter being rigidly fixed to the respect'ive link members
at the lower ends thereof such that the clevises open up towards each other. The bars
21a and 21b are disposed in parallel vertical planes and have their ends inserted
between the lugs of a respective clevis 23a, 23b where they are pivotably supported
by mear
'f horizontal shafts. From Fig. 5 it is seen that the bars 21a and 21b are symmetrically
arranged such that the bar 21a at one end is mounted below the bar 21b but at its
other end is mounted over the bar 21b, the corresponding relation applying to the
bar 21b. The upper ends of the spacers 22a and 22b which are connected to the clevises
have two legs which reach around the associated clevis 23a and 23b, respectively.
A horizontal shaft through the legs and the clevis allows the necessary rotation between
the link members and the carrier bar 1, in this case the spacers.
[0043] If e.g. the spacer 22a is subjected to a greater load than the spacer 22b the lower
end of the link member 5a will tend to sink in relation to the lower end of the link
member 5b. However, this sinking of the link member 5a is counter-acted by the stabilizing
means 20 in that a couple of forces is transmitted over the clevises and the bars
21a and 21b for urging the lower end of the link member 5b down to the same lever
as the lower end of the link member 5a. In this way the link members 5a and 5b will
be maintained at the same level of height and the carrier arm will be horizontal.
Of course the corresponding conditions hold if instead the lower end of the link member
5b is subjected to a greater load than the lower end of the link member 5a.
[0044] It is realized that said stabilizing means 20 can be constructed in several other
ways as long as it includes elements coupled to the link members which elements in
response to loads on the link members transfer from each link member to the other
link member a force corresponding to the difference in the load.
[0045] In the embodiment of the lifting device provided with said stabilizing means shown
in Fig. 5 the distance between the link members is kept more or less constant by means
of the bars 21a and 21b and so the carrier arm 1 can be rotatably supported by the
spacers.22a, 22b and displaceable through the spacers. In this case the carrier arm
is cylindrical and each connecting member 24a and 24b of the spacers for connecting
the respective spacer to the carrier arm consists of a cylindrical sleeve having a
bearing, preferably made of TeflonQ9, which allows the carrier arm to be rotated around
its own axis.
[0046] From the two ends of the carrier arm wide bands or belts 25a and 25b, e.g. of plastic
material, extend downwards for supporting said load receiving means (not shown) having
a suitable structure, e.g. of that kind shown in Fig. 3 where the belts 25a and 25b
also are shown. The belts 25a, 25b have a suitable length such that the individual
lifting bands 4 of said load receiving means reach desired height level when the carrier
arm takes its bottom position.
[0047] The lifting device has been described above in connection with a load receiving means
2 suited for lifting a person confined to bed or having reduced faculty of motion.
However, any type of load receiving means can be connected to the carrier arm in order
to lift and/or transfer other types of loads.
1. Lifting device for lifting a load, comprising a rigid carrier arm (1) to be placed
over the load, means (2) for receiving the load, the carrier arm supporting said means
for receiving the load, and transfer means (13, 12, 10, 9a, 9b, 8a, 8b, 7a, 7b, 6a,
6b, 5a, 5b) connected to said carrier arm for parallel movement thereof in its lateral
direction, characterized in that said transfer means includes two similar transfer
assemblies each having a rigid link member (5a; 5b) pivotably connected at separate
ends of the carrier arm (1), and a lever (6a; 6b) pivotably connected at one end to
the associated link member (ba; 5b) and pivotably supported at its other end, the
transfer assemblies being symmetrically arranged for pivoting the levers (6a; 6b)
in opposite directions, thereby allowing the ends of the link members (5a; 5b) connected
to the carrier arm and so the carrier arm to be lifted and moved in lateral direction.
2. Lifting device as claimed in claim 1, wherein in each transfer assembly the pivotable
connection between the link member (5a; 5b) and the carrier arm (1) is an articulation
(17) permitting movement around a horizontal axis.
3. Lifting device as claimed in claim 2, wherein in each transfer assembly the articulation
between the link member (5a; 5b) and the carrier arm (1) also permits movement around
a vertical axis.
4. Lifting device as claimed in any one of claims 1 to 3, wherein in each transfer
assembly the lever (6a; 6b) is mounted on a separate pivot shaft (7a; 7b) for allowing
the lever to pivot in rotating the pivot shaft.
5. Lifting device as claimed in any one of claims 1 to 4, said device being placed
in a room, and wherein the pivot shafts (7a; 7b) are supported in an overhead frame
(27), e.g. fixed to the ceiling of the room.
6. Lifting device as claimed in any one of claims 1 to 5, wherein in each transfer
assembly the pivotable connection between the link member (5a; 5b) and the lever (6a;
6b) is an articulation (19, 16; 18) permitting movement around a horizontal and a
vertical axis.
7. Lifting device as claimed in any one of claims 1 to 6, wherein the distance between
the connections of the link members (5a; 5b) to the carrier arm (1) is equal to the
distance between the mounting places of the levers (6a; 6b) on the pivot shafts (7a;
7b).
8. Lifting device as claimed in any one of claims 1 to 6, wherein the distance between
the connections of the link members (5a; 5b) to the carrier arm (1) is less than the
distance between tne mounting places of said levers (6a; 6b) on the pivot shafts (7a;
7b).
9. Lifting device as claimed in any one of claims 4 to 8, wherein the pivot shafts
(7a; 7b) are vertical.
10. Lifting device as claimed in any one of claims 1 to 9, wherein said transfer means
comprises drive means (13, 12) and transmission means (10, 9a, 9b, 8a, 8b) for pivoting
said levers (6a; 6b) in opposite directions.
11. Lifting device as claimed in claim 10, wherein said transmission means comprises
a worm gear (12) mounted between said pivot shafts (7a; 7b), the worm (10) of said
worm gear at its ends being rotatably engaged to said pivot shafts (7a; 7b).
12. Lifting device as claimed in claim 11, wherein first bevel gear wheels (9a, 9b)
are fixed at the ends of said worm (10) and second bevel gear wheels (8a, 8b) are
fixed to the pivot shafts (7a, 7b), one first and one second bevel gear wheel being
rotatably engaged.
13. Lifting device as claimed in any one of claims 6 to 12, wherein in each transfer
assembly the articulations between the link member (5a; 5b) and the carrier arm (1),
on one hand, and the lever (6a; 6b) on the other hand are universal joints.
14. Lifting device as claimed in any one of claims 4 to 13, wherein in each transfer
assembly the lever (6a, 6b) extends downwards from the associated pivot shaft (7a,
7b) and declines therefrom an angle less than 90°.
15. Lifting device as claimed in any one of claims 1 to 14, characterized by stabilizing
means (20) mounted between the link members (5a, 5b) for transferring forces therebetween
when the centre of gravity of the load in said receiving means (2) is displaced from
a vertical plane of symmetry across the carrier arm (1), thereby compensating for
, uneven load and maintaining the carrier arm horizontally.
16. Lifting device as claimed in claim 15, wherein said stabilizing means (20) comprises
two rigid bars (21a, 21b) each of which connects the two link members (5a, 5b), the
ends of said bars being pivotably connected to the link members for movement around
horizontal shafts, each bar at one end being connected to one of said link members
at a level below the connection of the other bar, while the other end of each bar
being connected to the other link member at a level over the connection of the other
bar.
17. Lifting device as claimed in any one of claims 1 to 16, characterized by biasing
means (15) provided to cooperate with said pivot shafts (7a, 7b) over members (lla,
llb) fixed to each pivot shaft (7a, 7b), said biasing means being non-actuated when
the carrier arm (1) takes its top position, rotation of the pivot shafts for lowering
the carrier arm resulting in charging of said biasing means.