GB2135967A

GB2135967A - Vertically displaceable platform

Info

Publication number: GB2135967A
Application number: GB8305715A
Authority: GB
Inventors: Raimo Pelto-Huikko
Original assignee: Elevator GmbH
Current assignee: Elevator GmbH
Priority date: 1981-09-03
Filing date: 1983-03-02
Publication date: 1984-09-12
Also published as: DE3232475A1; SE456419B; FI812722L; GB8305715D0; DE3232475C2; FR2541984A1; FI65762B; FR2541984B1; GB2135967B; FI65762C; SE8301156D0; SE8301156L

Abstract

A vertically movable platform (1) having between the platform and the base (2) at least one shearlegs member (3,4) by the aid of which the platform maintains unchanged orientation regardless of vertical motions, and where the vertical movements of the platform have been accomplished by the aid of a screw (5) connected to the shearlegs member. The screw (5) is connected with the shearlegs member (3,4) by means of transmission members (6,7) by the aid of which the movement of the platform is constantly nearly linear in relation to the rotation of the screw. <IMAGE>

Description

SPECIFICATION Vertically displaceable platform The present invention concerns a vertically displaceable platform having between the platform and the base at least one shearlegs member by the aid of which the platform maintains the same orientation regardless of the vertical movements, and where the vertical movements of the platform have been obtained with the aid of a screw connected to the shearlegs member. A platform of this kind is employed, for instance, as a theatrical stage platform, as a load pallet, as a servicing platform, etc.

In order that the rotary motion of the screw might have a linear effect on the speed and moving force of the platform, the screw should be mounted vertically between the base and the platform. This would however cause the screw to project upwards over the platform when the platform is at an elevation lower than the maximum elevation. This problem has been solved by replacing the screw with a contracting hydraulic cylinder which can be accommodated vertically between the platform and the base when the platform is in its lowest position. The drawback encumbering a hydraulic system is that the platform will present some degree of elastic yielding, and if there is even the slightest leakage in the system the platform will slowly descend by effect of its weight.

If the lifting movement of the platform is arranged with the aid of a screw horizontally connected with the shearlegs member that has been connected to the legs of the shearlegs member, the ratio between the screw's rotational motion and the lifting movement of the platform will be greatly variable and the lifting motor has to be dimensioned for unnecessarily high power at maximum force. The lifting of the platform close to the lower position requires a multiple of the lifting force which is necessary to lift the platform when it is close to the top position.

The object of this invention is to eliminate the drawbacks mentioned. The platform of the invention is characterized in that the screw has been connected to the shearlegs member by means of transmisson members by the aid of which the movement of the platform is nearly linear all the time, related to the rotation of the screw.

It is possible with the aid of the invention to manage with a smaller lifting motor because the required lifting force is the same both in the lower and upper positions of the platform. When the platform has been halted on a given level, it is firmly held stationary because the screw has no elastic yielding nor any leakage, as is the case with a hydraulic cylinder.

An advantageous embodiment of the invention is characterized in that the transmission members consist of two linkage arms pivotally interconnected, one end of the linkage arm pair being pivotally attached to one linkage rod of the shearlegs member and the opposite end to the other linkage rod, and that the screw force acts on the common pivotal point of the linkage arms. Therefore it is achieved by a simple design that the vertical movement of the platform is linear in relation to the rotation of the screw.

Another embodiment of the invention, comprising two shearlegs members located one above the other and pivotally interconnected, and each shearlegs member having its own linkage arm pair, is characterized in that the lower end of the linkage arm pair of the upper shearlegs member has been pivotally attached at one common pivotal point of the shearlegs members and that the upper end of the linkage arm pair of the lower shearlegs member has been pivotally attached at the other common pivotal point of the shearlegs members, and that one and the same screw acts on both linkage arm pairs. Thereby it is achieved that with one and the same screw the lifting movements act on both shearlegs members, whereby the forces are more uniformly distributed over the whole lifting system.

Athird embodiment of the invention is characterized in that the screw is a ball screw, the threads of the nut belonging thereto being constituted by a moving sequence of balls. Hereby the friction between the screw and the nut is reduced to be negligible and it need not be taken into account as a braking force. The thread of the ball screw is not subject to wear, nor does it cause any lost motion.

One embodiment of the invention is further characterized in that on the screw has been mounted a brake arresting the movement of the screw. If the screw is not arrested, or locked, it may as a result of its minimal friction start to rotate unintentionally owing to the weight of the platform.

The invention is described in the following with the aid of an example, with reference to the attached drawing, wherein Figure 1 presents a platform according to the invention, in perspective.

Figure 2 shows the platform viewed from the front.

Figure 3 presents another design of the linkage arm system.

Between the platform 1 and the base 2 there are two pivotally interconnected shearlegs members 3,4, by the aid of which the platform maintains the same orientation regardless of its vertical movements. The vertical movements of the platform 1 have been accomplished with the aid of a screw 5 connected to the shearlegs members. The screw 5 has been connected to the shearlegs members by means of transmission members 6,7, by the aid of which the movement of the platform 1 is constantly nearly linear in relation to the rotation of the screw 5.

The transmission members 6,7 consist of two pivotally interconnected linkage arms 8,9 and 10,11 respectively, one end 12,13 of each linkage arm pair being pivotally attached to one linkage rod 18,19 of the shearlegs member 3,4 and the opposite end 16,17 to the other linkage rod 14,15. The screw force acts in both pairs at the common pivotal point 20,21 of the linkage arms 8,9 and 10,11. The lower end 17 of the linkage arm pair 10,11 of the upper shearlegs member 3 has been pivotally attached at one common pivotal point 22 of the shearlegs members 3,4. The upper end 16 of the linkage arm pair 8,9 of the lower shearlegs member 4 has been pivotally attached at the other common pivotal point 23 of the shearlegs members 3,4. One and the same screw 5 acts on both linkage arm pairs 8,9 and 10,11.The end 24 of the thread of the screw has been rotatably carried in the extension 25 of the linkage arm 8, and the nut 26 belonging to the screw has been attached to the extension of the linkage arm 11. The screw 5 is a ball screw, and the thread of the nut 26 consists of a moving sequence of balls. On the screw 5, in conjunction with the operating mechanism 27, has been mounted a brake 28 arresting the motion of the screw.

By the platform construction described in the foregoing is obtained a platform simply movable vertically, of which the movement is nearly linear in relation to the rotation of the screw. Therefore the power output of the operating mechanism 27 can be minimized, as can the power requirements of the operating mechanism and the power which the brake requires, etc., It is obvious to a person skilled in the art that the invention may vary within the scope of the claims stated below. For instance, the location of the linkage arms 8,9,10,11 is not necessarily as in the example presented: they may also be located and move e.g. in the horizontal plane at the lower end of the linkage rods of the shearlegs members 29,30, as has been shown in Figure 3. Thereby the screw 31 also lies in the same plane.

The platform may be raised and lowered not only by the operating mechanism depicted in the drawing, but also manually e.g. with the aid of a crank.

Claims

1. Vertically displaceable platform (1) having between the platform and the base (2) at least one sheariegs member (3,4) by the aid of which the platform maintains unchanged orientation regardless of vertical movements and where the vertical movements of the platform have been accomplished with the aid of a screw (5) connected to the shearlegs member, characterized in that the screw (5) has been connected to the shearlegs member (3,4) by transmission members (6,7), by the aid of which the movement of the platform is constantly nearly linear in relation to the rotational movement of the screw.

2. Platform according to claim 1, characterized in that the transmission members (6,7) consist of two pivotally interconnected linkage arms (8,9 and 10,11), one end (12,13) of the linkage arm pair being pivotallyattachedto one linkage rod (18,19) of the shearlegs member (3,4) and the opposite end (16,17) to the other linkage rod (14,15), and that the screw force acts at the common pivotal point (20,21) of the linkage arms.

3. Platform according to claim 1 or 2, comprising two shearlegs members (3,4) located one above the other and pivotally interconnected, and each shearlegs member having its own linkage arm pair (6,7), characterized in that the lower end (17) of the linkage arm pair (6) of the upper shearlegs member (3) has been pivotally attached at one common pivotal point (22) of the shearlegs members and that the upper end (16) of the linkage arm pair (7) of the lower shearlegs member (4) has been pivotally attached at the other common pivotal point (23) of the shearlegs members, and that one and the same screw (5) acts on both linkage arm pairs (6,7).

4. Platform according to any one of the preceding claims, characterized in that the screw (5) is a ball screw, the thread of the nut (26) belonging thereto consisting of a movable sequence of balls.

5. Platform according to any one of the preceding claims, characterized in that on the screw has been mounted a brake (28) arresting the motion of the screw.

6. Vertically displaceable platform substantially as herein described with reference to the accompanying drawings.