ELEVATING DEVICE FOR THE MAST SECTIONS OF A SECTIONAL MAST, ESPECIALLY A MOVABLE AERIAL MAST OF FRAMEWORK TYPE

Abstract: The invention refers to an elevating device for mast sections of a sectional mast, particularly a movable aerial mast of framework type and comprising a foot portion with a mast support and guide jacket (4), said device (5) comprising a power­ -operated screw mechanism (12). In order to avoid a time-con­ suming idle or return movement of conventional reciprocating raising and lowering mechanism and to provide for a faster erection and dismounting, respectively of the mast it is suggested according to the invention that an elongated transport screw (12) extends vertically along one side of the guide jacket (4) and approximately contacts externally with its periphery the peri­ pheral 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 serving as a nut segment meshing with the threads of the transport screw (12).

Description: 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. 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 dis­ mountable. Conventional mast structures usually are of frame­ work 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. In another kind of mast design which has mutually tele­ scopically movable sections it has also been suggested to utilize a centrally mounted transport screw for expansion and retraction of the mast. 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. 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 inven­ tion 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 peri­ pheral 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. 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 pre­ ceding 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. 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. 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. 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 corres­ ponding 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. 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. 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. 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. 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.

Claims: 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 approxi­ mately 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).

Inventors: JONSSON, BERTIL
Applicants: JONSSON PROCESSMEKANIK  AB
Application year: 1987
Main classification: B66F11
IPC codes: E04H12