[0001] The present invention refers to an elevating device for the mast sections of a sectional
mast, especially a movable aerial mast of framework type and comprising a foot portion
with a mast support and guide jacket, said elevating device including a power-operated
screw mechanism.
[0002] Movable aerial masts have to fill a plurality of partly contradictory requirements.
Thus, they have to be strong and rigid but still relatively light and easily mountable
and dismountable. Conventional mast structures usually are of framework type and
the masts are put together from a number of sections. The mast is erected by arranging
at a desired place a foot portion of the mast having a support and guide jacket therefor
and introducing into said jacket the sections one by one, coupling them together with
the nearest preceding section and raising them by means of any suitable raising and
lowering mechanism a sufficient distance for allowing the introduction of the subsequent
mast section into the jacket. For this purpose the conventional raising and lowering
mechanisms have been rope blocks or chain winches having a hook which is connected
with the lower end of each mast section after the same has been inserted into the
guide jacket after which raising is made, the mast is locked, the hook released and
the raising and lowering mechanism returned to the initial position for again connecting
the hook to the lower end of the subsequent mast section. When lowering the mast and
dismounting thereof, the operation of course is carried out in the same way although
in reversed order.
[0003] In another kind of mast design which has mutually telescopically movable sections
it has also been suggested to utilize a centrally mounted transport screw for expansion
and retraction of the mast.
[0004] Conventional framework masts of the kind referred to above and put together in sections
have turned out to serve their purpose rather well but at many occasions of use in
which the time aspect is essential the conventional raising and lowering mechanism
has been considered to operate too slow since it has to be returned to the initial
position after each working movement. There is thus a need for a faster operating
device for this purpose.
[0005] Quite surprisingly it has now turned out that this can be achieved very easily by
means of a differently designed screw mechanism which does not require any return
movement between the working movements. The object of the present invention now is
to suggest such a device and the invention is essentially characterized in that an
elongated transport screw extends vertically along one side of the guide jacket and
approximately contacts externally with its periphery the peripheral contour of a
mast section housed parallel therewith within the jacket and in that each mast section
in its lower portion at the point of contact on the peripheral contour is provided
with a mechanical component serving as a nut segment meshing with the threads of the
transport screw.
[0006] Owing to said design, the transport screw certainly operates intermittently but permanently
in the same direction during the erection of the mast and in the opposite direction
during the lowering of said mast. The respective mast sections only need to be inserted
into the support and guide jacket of the foot portion in order to be brought directly
into meshing with the transport screw with its nut segment, after which the screw
is rotated and the mast section together with the preceding sections is raised a
distance substantially corresponding to the length of one section, after which the
subsequent mast section is introduced into the guide jacket, coupled to the preceding
mast section and thereafter raised by means of the transport screw in cooperation
with the nut segment of the last-mentioned section.
[0007] By way of example, the invention is further described below with reference to the
accompanying drawing, in which Fig 1 is a side elevational view of a mast with an
elevating device according to the invention with a support and guide jacket in a foot
portion of the mast and Fig 2 is a plan view from above of said guide jacket.
[0008] As is evident from the drawing a movable aerial mast of framework type comprises
a foot portion 1 and a plurality of mutually equal mast sections 2 of framework type
and in the present case having triangular cross section. The uppermost section carries
in its upper end an aerial element such as a paraboloidal aerial 3. At each end the
sections 2 are provided with suitable mountings for some suitable kind of coupling
means such as a bolt connection of easy-coupling type. In its erected position the
mast rests with its lowermost sections in a support and guide jacket 4 having an elevating
device 5. The jacket has the same general cross sectional shape as the mast sections
2, in the present case thus triangular shape, and surrounds the lowermost mast sections
2 with moderate clearance. The height of the jacket substantially corresponds to the
total length of two mast sections 2 and for stabilizing the mast the jacket 4 is provided
with support legs 6 and side struts 7 protruding from the corners of the triangular
cross section. From the top as well as from other levels of height of the mast, if
desired, usually also extend span wires 8.
[0009] In order to provide for the individual mast sections 2 one by one into the support
and guide jacket 4 when erecting the mast as well as for removal of said sections
in the corresponding manner when dismounting the mast, the jacket which suitably
also is of framework type, is provided in the lower portion of one of its sides with
an opening 10 in said side wall. Within the guide jacket the mast sections 2 are guided
by means of suitable guide members 11, preferably in the form of guide rollers cooperating
with the corner edges of said mast sections 2.
[0010] According to the invention the elevating or raising and lowering mechanism 5 comprises
an elongated vertical transport screw 12 which is along another side of the guide
jacket 4 also provided with a suitable opening. The screw 12 has a length which at
least corresponds to the length of each mast section 2 and extends from a bottom of
the guide jacket 4 and upwardly to a position above the level of a mast section 2
standing on the bottom of the jacket 4 or, in other words above the open portion of
the framework at the insertion and removal side of the jacket 4. At said position
the transport screw 12 is connected with some suitable kind of drive mechanism 13
not further illustrated, such as a worm drive driven by an electric motor for 12 or
24 volts. Suitably the device also is provided with a connection for mounting of a
hand crank for allowing manual operation of the transport screw in case of lack of
electric current.
[0011] According to the invention the transport screw 12 is arranged in a plane coinciding
with the center line of the adjacent jacket side such that the screw with its periphery
approximately contacts externally one of the sides of a mast section 2 located in
the jacket 4 and oriented parallelly thereto along an axis extending in said side,
said axis preferably being the longitudinal center line of said side. At least at
one of its sides each mast section 2 according to the invention is provided at the
lower end of said center line with a nut segment 14 adapted for meshing with the threads
of said transport screw 12. The nut segment may be constituted by a slide block of
suitable material such as bronze or by a roller.
[0012] The mast provided with the elevating device according to the invention is erected
in the following way. Firstly, the support and guide jacket 4 is arranged and levelled
at the desired place and thereafter a first mast section 2 is inserted into the guide
jacket 4 through the opening in one of the sides thereof, said section 2 of course
being oriented in such a way that a side provided with a nut segment 14 is turned
towards the side of the jacket 4 at which transport screw 12 is located. After that
the rotation of the transport screw 12 is started and owing to the movement of the
nut segment 14 along the threads of the screw 12 a raising of the mast section 2 through
the jacket 4 is obtained. When the mast section 2 has been raised to such an extent
that a subsequent mast section 2 can be inserted into the guide jacket 4, the rotation
of the transport screw 12 is stopped. This can easily be provided by a limit switch
for the electric drive motor or any similar manner obvious to the artisan. The subsequent
mast section 2 which has been inserted into the jacket 4 is coupled with its upper
end to the lower end of the preceding mast section 2 by means of a bolt connection
of easy-coupling type not further illustrated, after which the rotation of the transport
screw 12 again is started, now in the same direction as during the first transport
movement and without any need of a return movement such as in rope blocks or other
raising and lowering mechanisms previously used for the same purpose. This is repeated
until all, in the present case 19, mast sections have been brought into position and
been coupled to each other.
[0013] When dismounting the mast the same operation is repeated although in reversed order.
For locking at each occasion the respective mast section 2 next to the lowermost one
in the guide jacket 4 it is suitable that the transport screw 12 or the screw 12 together
with the drive mechanism 13 is of a self-braking type. Said locking also can be provided
by locking means, not illustrated.
1. Elevating device for the mast sections of a sectional mast, especially a movable
aerial mast of framework type and comprising a foot portion with a mast support and
guide jacket, said elevating device including a power-operated screw mechanism, characterized
in that an elongated transport screw (12) extends vertically along one side of the
guide jacket (4) and approximately contacts externally with its periphery the peripheral
contour of a mast section (2) housed parallel therewith within the jacket and in that
each mast section (2) in its lower portion at the point of contact on the peripheral
contour is provided with a mechanical component (14) serving as a nut segment meshing
with the threads of the transport screw (12).
2. A device according to claim 1 for mast sections and a support and guide jacket
(4) having a polygonal cross sectional shape and particularly triangular shape, characterized
in that the transport screw (12) is arranged with its longitudinal axis located in
a plane coinciding with the longitudinal center line of the jacket side and in that
the nut segment (14) of each mast section (2) is mounted at the lower end of the longitudinal
center line of at least one of the sides of the sections (2), the transport screw
(12) furthermore extending from a bottom of the jacket (4) and upwardly to a level
exceding the length of a mast section (2).
