The present invention concerns a safety arrangement for hoists as
described in the preamble to claim 1.
Demands on safety zones above and below hoist cages have been made
more stringent during recent years and further restrictions are expected. These
new demands can usually be met by new installations but increasing the depth and/or
raising the roof on existing hoist shafts is often impossible in practice.
These conditions have resulted in the use of known technology to create
solutions in which electronic control systems for hoists interact with some form
of mechanical safety device, often in the form of manual extendable support being
arranged to abut either the hoist cage directly or particular surfaces on the hoist
cage through inelastic engagement.
For example, WO 99/47447 illustrates an arrangement in which the mechanical
safety device comprises a tilting support, which in a tilted down passive position
is located flat on the shaft floor, allowing normal hoist cage operation, and in
a tilted up active vertical position has its free upward facing end intended to
abut against a downward moving hoist cage, thereby ensuring a safety zone and putting
the hoist in a second operating position for service and maintenance. The position
of the support must be changed manually by the operator from inside the shaft.
US 5 727 657 discloses travel blocking apparatus mounted in an elevator
shaft for blocking the travel of an elevator into a temporary working space. The
blocking apparatus comprise a swivel buffer which can be tilted into an active blocking
position. The apparatus having a remotely controlled means comprising a linear actuator
and a buffer for returning the swivel buffer to its inactive position. In order
to overcome possibly failings for example in the event of a power failure the swivel
buffer is tilted into a travel blocking active position solely by its own weight
due to an asymmetrical mass distribution.
It would be preferable to have guaranteed safety zones in all situations
where it is possible for a person to enter the shaft outside the hoist cage for
service, maintenance, repair, inspection, forced entry, etc. To guarantee this state,
it should be virtually impossible to enter the hoist shaft outside the hoist cage
without the hoist being in position for service and the safety zone being secured.
One object of the present invention is to alleviate or even overcome
the aforesaid failings in known techniques.
This object can be reached with the employment of the aforesaid arrangement,
which exhibits the characteristics defined in the following Claim 1.
These and other objects, distinctive features and advantages with
the invention will be evident in the dependent patent claims and the following detailed
description of a preferred embodiment of the invention. This embodiment constitutes
a specimen and accordingly does not limit the scope of protection of the invention.
References to attached drawings, in which equivalent or similar components have
been given the same reference designation, have been inserted in the text to facilitate
Fig. 1 illustrates a schematic of a hoist in a hoist shaft
with an arrangement according to an embodiment of the present invention,
figs. 2 and 3 illustrate part of the preferred embodiment of the arrangement
according to the present invention, figs 4 and 5 illustrate another part
of the embodiment according to figs. 3 and 4, fig. 6 illustrates a detailed
large scale view of an embodiment according to the present invention.
Special expressions and designations of component parts have been
used in the following detailed description for reasons of clarity of the embodiments.
These expressions and designations shall consequently not be interpreted as limitations
for the scope of protection of the invention but as examples within it.
With reference to fig. 1, a hoist cage 1 arranged in a hoist shaft
2 with doors 3 at different stopping points (e.g. floors) is illustrated schematically.
For reasons of simplicity, only two stopping points are illustrated but it should
be understood that between the top and bottom stopping points there can be an additional
one or more stopping points.
The operation of the hoist takes place through the interaction of
a drive unit 4, e.g. a hydraulic unit, rack and pinion system or other known unit
intended for operating hoists, and a control system for the drive unit and for assisting
auxiliary functions such as door operation, etc. The control system is initiated
e.g. by pushbuttons by the door or in the hoist cage and control the movement of
the hoist cage 1, operation of the doors 3, etc.
Furthermore, integrated in the said control system or in a special
control system is a means of identifying safety situations, e.g. if a door 3 is
open without the hoist cage fully surrounding the opening and preventing access
to the hoist shaft. If this should occur, a safety zone under the hoist cage and
a safety zone above the hoist cage must immediately be secured in the hoist shaft.
Once the hoist has entered safety operation mode, e.g. for service,
inspection, forced door entry, etc., the mechanical means of limitation according
to a preferred embodiment of the present invention must be released and block the
movement of the hoist, one above and/or one below the hoist cage. Since the mechanical
means of limitation are arranged unstably in their respective inactive states, they
will enter an active state after the said releasing action. Through additionally
arranging the means of securement so that they will be released also in case of
a power cut to the systems, the risk of a door being opened during a power cut to
gain access to the hoist shaft under the hoist cage will be eliminated without the
safety zone being mechanically secured.
With reference to fig. 1, such a means of limitation intended to secure
a safety zone under the hoist cage can comprise a vertical leg 5. The leg 5 is arranged
so that it can be moved between active state 5, standing on the floor of the hoist
shaft and extending upwards in the direction of the hoist cage in order to abut
against the hoist cage 1 with its free end, and an inactive and contracted position
5', arranged by the side of the path of the hoist cage in the hoist shaft.
The length of the leg 5 is chosen so that the safety zone is sufficient
when the hoist cage is resting on the leg.
Furthermore, the arrangement can include one or more legs arranged
under the hoist cage around or by one side of the shaft.
In the illustrated embodiment, the leg 5 is mounted on two parallel
arms 6, which extend horizontally from their respective attachments outside the
path of the hoist cage when the leg is in an active state to thereby in combination
with the leg reach sufficiently into the path of the hoist cage.
The arms 6 are furthermore arranged to tilt at the side of the shaft,
e.g. on one wall of the shaft or by a pillar along which the hoist cage runs, so
that when the leg is being withdrawn to its contracted state 5', they tilt up to
raise the leg in an arced movement but still, however, with its extension length
in parallel with the direction of travel of the hoist cage. The tilting movement
of the arms 6 is limited so that together with the mounted leg in a raised state,
they are still unstable, whereby striving to return to the leg's active state 5.
In one embodiment, this means that the arms do not tilt far enough to pass their
As the leg 5 in its contracted state also extends in parallel to the
direction of movement of the hoist cage and the extent of the hoist shaft, only
a minimum of space is required to raise the leg and, which is important, no special
space is required beneath the hoist cage.
In order to retain the leg 5' in its contracted state, there is a
retaining device arranged to hold the leg in its contracted state until a risk situation
In the present embodiment, the retaining device is an electromagnet
7. Should the hoist with drive and control systems lose its power supply, the electric
magnet will then lose its retaining power and the leg will take its active state
5 due to its own weight, securing the required safety zone.
The upper means of limitation in the present embodiment is a tilting
projection 8 arranged on one wall of the shaft. The projection 8 is stably suspended
and so designed and balanced that when inactive, it extends into the path of the
hoist cage, thereby preventing its movement. By selecting the distance from the
roof of the shaft that the projection 8 is arranged, the safety zone above the hoist
cage 1 can be secured. The projection 8 is also balanced so that it is unstable
in a contracted state. A retaining device, such as an electromagnet 9, is arranged
to keep the projection in an inactive state 8' at the side of the path of the hoist
during normal operation.
The upper retaining device may well be governed simultaneously and
on the same circuit as the aforesaid lower retaining device 7.
The means of limitation furthermore may well comprise a surface for
interacting with a limit switch on the hoist cage or a limit switch for interacting
with a surface on the hoist cage. The object is that when the means of limitation
are in an active state, the drive will be shut off to the hoist cage as it approaches
them. Hereby, a hoist cage will not hit a stable means of limitation at full speed
but will stop just before contact is made.
The means of limitation can furthermore be equipped with a buffer
to dampen the jolt in case a hoist cage should hit the means of limitation with
full force. Such a buffer can be arranged on the hoist cage, in the hoist shaft
or on the means of limitation, on top or underneath it, or be integrated in the
means of limitation between its upper and lower stop surfaces.
Buffers are usually arranged on the bottom of the shaft in the unlikely
event that a hoist cage should crash to the floor. In such a case, the lower mechanical
means of limitation shown in the embodiment illustrated in fig. 1 could in another
version be arranged in an active state to be brought to rest on such a buffer 10
instead of against the bottom of the shaft. This is shown schematically in figs.
2 and 3.
The leg 5 in the embodiment illustrated in figs. 2 and 3 is arranged
in active state to rest against a shock absorbing surface, which is consequently
deformable. For this reason, the leg 5 exhibits an almost sleeve-shaped retaining
part 11 and a shock absorbing part 12 supported by the arms.
The retaining part 11 exhibits basically the same construction and
movement as the leg in the embodiment described in fig. 1. The shock absorbing part
12 is a means arranged axially in relation to the retaining part 11 and can be displaced
in relation to the direction of movement of the hoist. This is so that the shock
absorbing part 12 can be displaced downward when the retaining part 11 is extended
and convey forces from the hoist cage to the buffer.
The shock absorbing part 12 is accordingly mounted axially displaceable
in the retaining part 11. Furthermore, it is so arranged that in an inactive state,
it will protrude above the top of the retaining part for a distance corresponding
to the stroke of the buffer and thereby corresponding to the maximum load that can
Furthermore, a spring or similar device can be arranged in an inactive
state to keep the shock absorbing part in its initial raised position.
The upper means of limitation is illustrated in an additional embodiment
in figs. 4 and 5. Fig. 4 shows a schematic of a hoist cage 1 travelling along a
mast 4 and an upper means of limitation in the form of a frame-shaped projection
8 equipped with an expanded plastic buffer 13 on the surfaces that are intended
to encounter the hoist cage.
Also arranged on the frame is a breaker cam 14, see fig. 5, intended
to interact when the means of limitation is in an active state with a limit switch
15 arranged on the hoist cage 1 in order to shut off the hoist drive at the new
safety end limit.
In an additional embodiment, the means of limitation can be equipped
with a means of return. One embodiment of such a means of return is illustrated
in figs. 4 and 6, acting on the upper and lower means of limitation respectively.
This means of return can comprise a leaf spring 16 arranged with one end on the
means of limitation, e.g. the projecting frame 8, and the other end on the output
shaft of a gear motor 17. When the motor 17 is activated, the leaf spring will be
wound onto the motor shaft and be pulled in towards the retaining device. A limit
switch 18, for example, can be used to indicate that this has taken place. Once
the retaining device 9 has gripped the means of limitation 8, the motor 17 will
be shut off. When the means of limitation is later released, the leaf spring will
assist in returning it to its active state.
Fig. 6 illustrates the said embodiment of the means of return applied
on the lower means of limitation in the embodiment illustrated in figs. 2 and 3.