AN ARRANGEMENT IN A TWO MAST PLATFORM

Abstract: The invention relates to an arrangement in an elongated working platform (2) which at each end is carried by a mast via a drive support (8) movable along the mast. The drive support includes an electric motor unit by means of which the drive support is drivable along the mast, said drive support pivotally carrying the corresponding end of the platform. At each motor unit an operating means for manual release of a motor brake for lowering the platform in case of power failure, is connected to a levelling device (24-38). The levelling device is arranged to be triggered in order to prevent movement of a drive support resulting in deviation of the platform from a position essentially corresponding to the horizontal position, said transmission being arranged to return the operating means to a position activating the motor brake, if the manual release of the motor brake causes triggering of the levelling device.

Description: An arrangement in a two mast platform. The present invention relates to an arrangement in an elongated working platform which at each end is carried by a mast via a drive support movable along the mast and including an electric motor unit by means of which the drive support is drivable along the mast, said drive support pivotally carrying the corresponding end of the platform. The object of the invention is to make possible, in a platform of the above indicated kind, lowering of the platform in a safe way in case of power failure. According to the invention this is attained in that, at each motor unit, an operating means for manual release of a motor brake, for lowering the platform in case of power failure, is connected to a levelling device which is arranged to be triggered in order to prevent movement of a drive support resulting in deviation of the platform from a position essentially corresponding to the horizontal position, said transmission being arranged to return the operating means to a position activating the motor brake, if the manual release of the motor brake causes triggering of the levelling device. Thus, by means of the invention tilting of the working platform is prevented when the motor brakes are manually released, so that the platform by its own weight slides along the mast. An embodiment of the invention shall now be described more closely below with reference to the attached drawings, on which Figure 1 is a sideview illustrating a two mast working platform of the kind in which the invention can be used, Figure 2 to a greater scale illustrates a part, essential to the invention, in connection with the left hand mast of the platform shown in Figure 1, and Figure 3 likewise to a greater scale shows a view perpendicular to Figure 2 of said part. Figure 1 illustrates how an elongated working platform 2, built up by means of framework sections, at each end is carried by a framework mast 4 and 6, respectively, via a respective drive support 8 and 10 movable along the mast. More particularly, the drive support, in a manner known per se and not shown, by means of rollers can abut against longitudinally extending roller races of the mast and be carried via tooth wheels on a tooth rack extending along the mast. The tooth wheels are driven by an electric motor unit 12 and 14, respectively, only schematically illustrated in Figure 1, so that the respective drive supports 8 and 10 can be driven along the mast. The drive supports 8 and 10 pivotally carry the platform 2 at the upper side thereof at 16 and 18, respectively. By means of the pivoted support of the platform 2 wedging between the platform and the masts is prevented in case of tilting of the platform. Between the drive supports 8 and 10 and the corresponding ends of the platform 2 there is a levelling mechanism comprising means included in an arrangement according to the invention and described below with reference to Figures 2 and 3. Generally such levelling mechanisms are, however, arranged to be triggered for preventing movement of the drive supports which can result in deviation of the platform from a position essentially corresponding to the horizontal position. During normal driving this can be carried through by temporarily stopping, by means of electric breakers, the driving motor unit which is driven too fast, until the platform has taken a horizontal position again. The breakers can be automatically operated as controlled by the position of the platform. The design of such levelling mechanisms for carrying through this function is well known and need therefore not be described more closely here. In the embodiment illustrated and described here the arrangement according to the invention is supposed to form part of a levelling mechanism having the described function, although it could also be imagined to be used separately from such a mechanism. With reference to Figure 2, the levelling mechanism includes a rod 24 which is supported on the drive unit 8 at 20 and 22 to be shiftable transversely to the mast 4 . One end of the rod is connected to the lower part of the platform at 26 by means of a couupling, not shown, which admits mutual tilting of the platform 2 and the rod 24 at movement of the platform about the pivot 16. The rod 24 carries a cam 28 shaped as a double cone, with which one end 30, arranged as a cam follower, of a lever arm 32 can cooperate. Between its ends the lever arm 32 is pivotally supported at 34 and the other end 36 thereof is coupled to a Bowden cable 38. Via guides not shown in more detail the Bowden cable 38 leads to the electric motor unit 12 for cooperating with its motor brake in a way to be described more closely below. In Figure 3 the electric motor unit is shown as comprising two motors 40 and 42, respectively, arranged in parallel with each other and being arranged to drive a respective tooth wheel indicated at 44 and 46, said tooth wheels, as described above, being in engagement with a tooth rack extending along the mast but not shown on the drawing. At 48 a catching mechanism is indicated. The tooth rack drive of the drive supports 8 and 10 along the mast by means of elements 40 - 46, as well as the catching apparatus 48 can be of a conventional kind and need not therefore be described more closely here. Each motor 40 and 42 has a respective motor brake device 50 and 52 of mechanical type arranged, at power failure, to be actuated for locking the motor shaft against rotation and thereby the tooth wheels 44 and 46 to the tooth rack. The design of the motor brakes can be of conventional kind known per see, where the actuating and releasing movements of the brake are linear in the direction of the motor shaft towards and away, respectively, from the tooth rack. The movable elements of the motor brakes 50 and 52 are interconnected by means of a link system 54 designed to be manually available from the drive support for releasing the motor brakes 50 and 52 by movement in the direction of the arrow 55. At 56 the other end of the Bowden cable 38 is connected to the link system in such a way that the cable, at movement contrary to the direction of the arrow 55, can draw the motor brakes 50 and 52 via the link system 54 for activating the motor brakes, and at movement of the link system in the direction of the arrow 56 can follow this movement. At power failure the platform 2 can be lowered by its own weight by releasing the motor brakes at both drive supports 8 and 10, respectively, manually by operating the link system 54 in the way described above. If it is assumed that the platform should tend to tilt downwardly at its left hand end in Figure 1 this results in the platform turning counter clockwise about the pivot 16. This in turn results in the lower side of the platform moving away from the mast 4 and thereby pulling the rod 24 with it, the cam 28 then following this movement and pressing the cam follower 30 upwardly so that the lever arm 32 turns clockwise. Thereby the Bowden cable 38 is pulled downwardly in Figure 2 and contrary to the direction of arrow 55 in Figure 3, the manual force against the link system 54 then being not able to resist this movement, but the motor brake is actuated by movement in a direction contrary to the arrow 55 so that the drive support 8 is stopped temporarily. The platform 2 will then, by means of the continuing unhindered movement of the drive support 10, attain horizontal position again while shifting the rod 24 to the left in Figure 2. Thereby the cam 38 will finally escape from the engagement with the cam follower 30 so that the continued manual force on the link system 54 can again release the motor brakes 50 and 52 and the descending movement of the drive support 8 can be resumed. The breakers mentioned briefly above for the normal operation of the drive motor units are indicated at 60 in Figure 2. They are operated by cams 62 and 64 being likewise positioned on the rod 24. The invention is, of course, not limited to the embodiment shown on the drawing and described above, but can be modified within the scope of the patent claims.

Claims: Claims . 1. An arrangement in an elongated working platform (2) which at each end is carried by a mast (4,6) via a drive support (8,10) movable along the mast and including an electric motor unit (12,14) by means of which the drive support is drivable along the mast, said drive support pivotally carrying the corresponding end of the platform, characterized in that, at each motor unit (12,14), an operating means (54) for manual release of a motor brake (50,52), for lowering the platform in case of power failure, is connected to a levelling device (24-38) which is arranged to be triggered in order to prevent movement of a drive support resulting in deviation of the platform from a position essentially corresponding to the horizontal position, said transmission (38) being arranged to return the operating means (54) to a position activating the motor brake, if the manual release of the motor brake causes triggering of the levelling device. 2. Arrangement according to claim 1, characterized in that the levelling device at each drive support comprises a mechanism (24-32) acting upon tilting of the platform (2) with respect to the corresponding mast, and by means of which the levelling device is connected to the transmission (38). 3. An arrangement according to claim 2, characterized in that the mechanism includes a mechanical means (24) , reacting by a.mechanical movement on tilting of the platform (2) , and being mechanically connected with the transmission, which is deviced as a mechanical transmission device (38) , so that said mechanical movement is transferred to a return movement of the operating means (54). 4. An arrangement according to claim 3, characterized in that the mechanical means comprises a cam (28) , the movement of which being sensed by a cam follower (30) , which is connected to the transmission which is arranged as a Bowden cable (38) , link train or similar. 5. An arrangement according to claim 4, characterized in that the movement of the cam (28) is a translatory movement, and that the cam follower (30) forms part of a two arm lever (32) , which is pivotally carried between its ends, of which one abuts the cam and the other one (36) is connected to the transmission (38) .

Inventors: JOHANSSON AAKE, JOHANSSON, AAKE
Applicants: ALIMAK AB
Application year: 1991
Main classification: E04G1
IPC codes: B66F11, E04G1