The present invention relates to a rolling door or roll-up door comprising a flexible door leaf which is rolled up round an upper roller and which, when unrolled therefrom, closes a door opening; a motor for turning the roller in both the unrolling and the rolling-up direction; two upper pulleys which are coaxial with the roller and disposed one at each end of the roller so as to turn with the roller; and two ropes each travelling over a lower pulley provided in the lower part of the door opening, each rope being fixed, at one end, to the free end of the door leaf and, at the other end, to an upper pulley, so as to be rolled up round the upper pulley when the roller is turned in the unrolling direction and be unrolled from the upper pulley when the roller is turned in the rolling-up direction.

The object of the present invention is to provide a roll-up door of this type, which is equipped with a parti- cularly simple device for stretching the door leaf when wholly or partly unrolled, the stretching force produced by the device increasing as the door leaf is unrolled. In addition, this device should make it possible to so coun¬ terbalance the weight of the door leaf that the latter, when the motor is disengaged, either is retained in its position without dropping, or is rolled up round the roller.

According to the invention, this object is achieved by a roll-up door which is of the type stated above and which is characterised in that the two upper pulleys are of larger diameter than the roller and are connected to the roller by a spring means which is adapted, when the roller is turned in the unrolling direction, to entrain the two upper pulleys in this movement, said spring means being so mounted that its spring tension increases when the roller is thus turned owing to the fact that the

upper pulleys turn more slowly than the roller because of the difference in diameter.

The invention will be described in more detail below with reference to the accompanying drawing, in which Fig. 1 is a schematic side view showing a roll-up door according to the invention, the door leaf being part¬ ly unrolled;

Fig 2 corresponds to Fig. 1, the door leaf being un¬ rolled to a larger extent than in Fig. 1; and Fig. 3 is a schematic side view showing an alterna¬ tive embodiment of a roll-up door according to the inven¬ tion.

The roll-up door illustrated in Figs 1 and 2 has a door leaf 1 of flexible material, e.g. a plastic-coated woven fabric. The door leaf 1 is supported by an upper roller 2 which is disposed above a door opening (not shown) and whose shaft 3 is rotatably mounted in a side stand (not shown). The door leaf 1 is rolled up round the roller 2 and, when unrolled, closes the door opening. The roller 2 is rotatable in both the unrolling and the roll¬ ing-up direction by means of a motor (not shown) driving the shaft 3.

Two upper pulleys 4, which are of larger diameter than the roller 2, are supported in freely rotatable man- ner by the shaft 3 on both sides of the roller 2. Two lower pulleys 5 are arranged in the lower part of the door opening, each pulley being disposed straight below an upper pulley 4. A rope 6 travels over each pulley 5, and is, at one end, fixed to the free end edge of the door leaf 1 and, at the other end, fixed to the upper pulley 4 straight above, so as to be rolled up round and unrolled from the upper pulley 4 when the roller 2 is rotated in the unrolling and the rolling-up direction, respectively. Each upper pulley 4 is connected to the roller 2 by a spring 7 which, for reasons of clarity, is illustrated as a tension spring mounted on the outside of the roller 2 and the respective pulley 4. As will be appreciated by

anyone skilled in the art, the spring may be of any suit¬ able type able to perform the function described below. The springs 7 are so mounted on the roller and the pulley that they, when the roller is turned in the unrolling direction, entrain the pulleys 4 in this movement while their spring tension is increased, as will be explained in more detail below.

When the door leaf 1 is to be unrolled further from the partly unrolled position shown in Fig. 1, the shaft 3, and consequently the roller 2, is turned clockwise

(Fig. 1) by means of the motor. Thus, a certain length of the door leaf 1 is unrolled from the roller 2, while the same length of the ropes 6 is rolled up round each pulley 4. When the roller 2 is thus turned, the springs 7 entrain the pulleys 4 in this movement. Since the pulleys 4 are of larger diameter than the roller 2, they are, however, not turned as much as the roller 2, and the springs 7 are thus increasingly tensioned as the roller 2 is turned. This fact is illustrated in Figs 1 and 2 with the aid of refe- rence marks 8 and 9 provided on the roller 2 and the pul¬ ley 4, respectively. The marks 8 and 9 are situated oppo¬ site to one another when the door leaf 1 is in the partly unrolled position shown in Fig. 1. When the door-leaf length L has been unrolled from the roller 2, the latter has been turned clockwise to the position shown in Fig. 2, in which the reference mark 8 on the roller 2 is slightly ahead of the reference mark 9 on the pulley 4, as illu¬ strated. As also appears from Fig. 2, the spring 7 has been extended a corresponding distance. As appears from the foregoing, the door leaf 1 is stretched by the springs 7 via the ropes 6 connected to the free end edge of the door leaf 1, the stretching force produced by the springs 7 increasing as the door leaf 1 is unrolled. The desired stretching force is obtained by a suitable choice of the springs 7 and the difference in diameter between the roller 2 and the pulleys 4. Suitably chosen, the springs 7 obviously ensure that the weight of

the door leaf 1 is counterbalanced in such a manner that the door leaf either is retained in its position without dropping, or is rolled up round the roller 2, if the motor is disengaged, e.g. in the event of a power failure. Compared with the roll-up door illustrated in Figs 1 and 2, the space-saving embodiment shown in Fig. 3 re¬ quires very little space outside the wall in which the door opening is formed. The roll-up door of Fig. 3 differs from that of Figs 1 and 2 only in that a guide roller 10 is provided for each rope 6. The guide roller 10 is dis¬ posed slightly below the upper pulley 4 and is closer to the wall. The lower pulleys 5 are then disposed closer to the wall, straight below the guide rollers 10.