The invention is particularly concerned with driving a double-deck elevator to a landing level in a building having unequal distances between floors. The problem is generally an uneven distribution of load between elevator cars, with the result thatthe internal mechanism of the common car frame that moves the elevator cars undergoes an elastic deformation. As a consequence, the elevator cars sink independently of each other through distances that are proportional to the car loads and thus often unequal. Besides, when the elevator is to be driven to a landing level, there is the additional difficulty that the main hoisting ropes used to move the two elevator cars by means of their common car frame undergo an elastic elongation proportional to the sum of the loads of the elevator cars.

In prior art, e. g. US patent no. 6,334, 511 discloses a control arrangement for the control of a double-deck elevator in a building with varying floor-to-floor distances.

In the solution according to the US patent, the lower car is moved in relation to the upper car by means of either an articulated jack or a separate hoisting motor and hoisting ropes. This moving is carried out in accordance with a pre-calculated floor-to-floor distance between the target floors. The specification contains no mention of the control system bringing the elevator cars accurately to the floor levels even when the cars have unequal loads and the elastic rope elongations cause a change in the relative positions of the cars. Therefore, the solution dis- closed in this specification involves the problem that there is no compensation for the effect of unequal load on the relative position of the elevator car, which is why the elevator cars can not be brought sufficiently accurately to the landing levels.

The object of the present invention is to overcome the above-mentioned draw- backs and to enable a reliable and economical double-deck elevator arrangement

in which each elevator car can be driven accurately and quickly to its respective level regardless of unequal loads of the elevator cars.

The apparatus of the invention is characterized by what is disclosed in the char- acterization part of claim 1. Other embodiments of the invention are characterized by what is disclosed in the other claims. Inventive embodiments are also pre- sented in the description part of this application. The inventive content of the ap- plication can also be defined in other ways than is done in the claims below. The inventive content may also consist of several separate inventions, especially if the invention is considered in the light of expressions or implicit subtasks or in view of advantages or sets of advantages. Therefore, some of the attributes contained in the claims below may be superfluous in respect of separate inventive concepts.

The solution of the invention has the advantage of enabling the elevator cars of a double-deck elevator to be driven accurately to their respective landing levels re- gardless of the load of the elevator cars. Effective compensation of the loads of the elevator cars is achieved. A further advantage is that the apparatus of the in- vention works reliably in a building having floor-to-floor distances of mutually dif- ferent heights.

In the following, the invention will be described in detail with reference to an em- bodiment example and the attached drawings, wherein Fig. 1 presents a simplified side view of an elevator solution applying the invention, wherein unequal loads of the elevator cars have resulted in unequal elastic elongations, Fig. 2 presents a simplified side view of the elevator solution in Fig. 1, wherein the unequal loads of the elevator cars have been compen- sated, and Fig. 3 presents a simplified side view of the elevator solution in Fig. 1, wherein the elevator cars have been driven accurately to their re- spective landing levels.

Fig. 1 presents a typical situation which may occur in a double-deck elevator solu- tion when the loads in the two cars are unequal. The figure shows a double-deck elevator solution comprising a car frame 1 which is supported and moved verti- cally in an elevator shaft by means of main hoisting ropes 4 driven by an elevator machine 2. In addition, the elevator solution comprises a counterweight 3 and a diverting pulley 5, by means of which the counterweight has been removed to a correct horizontal distance from the car frame 1 of the elevator. The elastic elon- gation of the main hoisting rope 4 in a loading situation is represented by refer- ence kl. The car frame 1 contains an upper elevator car 6 and a lower elevator car 7, which are connected to each other by a hoisting rope 10 so that the eleva- tor cars 6 and 7 function as each other's counterweights. In addition, provided in conjunction with the car frame 1 is an auxiliary hoisting machine 8 for moving the elevator cars 6 and 7 vertically in relation to each other, and a diverting pulley 9 for guiding the hoisting rope 10. This solution permits the elevator cars 6 and 7 to be moved in a manner ensuring that the nominal vertical distance between them always corresponds to the distance between the floors at which the elevator is to stop.

The elastic elongations for each elevator car caused by their loads are repre- sented by references k2 and k3. In Fig. 1, the elevator cars are intended to stop at levels 11 and 12 of the building in such manner that the upper elevator car 6 stops exactly at level 11 and the lower elevator car 7 stops correspondingly at the lower level 12. Due to the unequal loads of the elevator cars, the hoisting rope 10 of the elevator cars 6 and 7 has undergone elastic elongation k2 and k3, and thus the elevator cars remain at mutually unequal distances below their respective landing levels 11 and 12. The elastic elongations k2 and k3 are independent of each other because, in the example situation according to the invention, the fric- tion or structure of the traction sheave 8 is such that no slip of the hoisting rope 10 occurs over the traction sheave 8. The upper elevator car 6 is at elongation distance h2 below landing level 11, and the lower elevator car 7 is at elongation distance h3 below landing level 12. Since the lower elevator car 7 carries a larger

load, its elongation distance h3 is also greater than the elongation distance h2 of the upper elevator car.

Fig. 2 presents a situation where the unequal elongation distances caused by the unequal loads of the elevator cars have been compensated. The compensation is accomplished by using a suitable control device, such as an auxiliary hoisting machine 8, in such manner that the positions of the elevator cars 6 and 7 relative to the respective landing levels 11 and 12 are corrected. The car 7 for which the elongation distance is larger is raised upwards by means of the auxiliary hoisting machine 8, thereby causing the upper elevator car 6 forming the counterweight of car 7 to descend correspondingly through an equal distance downwards. The dis- tance Si to be moved equals half the difference between the elongation distances h2 and h3 of the cars, i. e. Si = (h3-h2)/2. After this correcting movement, the dis- tances h1 of the elevator cars 6 and 7 from their respective landing levels 11 and 12 are mutually equal. Exact position data for the elevator cars 6 and 7 is ob- tained e. g. by means of different position detectors, from whose output signal it is possible to determine the absolute position of the elevator cars. The determina- tion of the position data for the elevator cars 6 and 7 can also be accomplished by utilizing the signal obtained from the car load weighing devices or by some other corresponding applicable location method allowing the position data for the eleva- tor cars to be computed.

The apparatus additionally comprises a control unit 13 or equivalent, which is connected at least to the main hoisting machine 2 or to its specific control unit, to the auxiliary hoisting machine 8 and to the position data for the elevator cars 6 and 7. For the sake of clarity, the connection of the control unit 13 to the auxiliary hoisting machine 8 is not shown in the drawings. The control unit 13 calculates the aforesaid required moving distance Si on the basis of the position data for the elevator cars 6 and 7 and gives the auxiliary hoisting machine 8 instructions for moving the elevator cars so as to equalize the distances h1 of the two elevator cars 6,7 from their respective landing levels.

The control unit 13 a Iso g ives t he m ain h oisting m achine 2 d ata i ndicating t he magnitude of the distance of the movement to be effected by the main hoisting machine. Thus, the final correction can be made using the main hoisting machine 2 by moving the car frame through a distance equaling hi plus the elastic elonga- tion k1 of the main hoisting rope 4, i. e. through distance S2 as shown in Fig. 3, this distance being equal to h1 + kl. In practice, the correction required by the loads of the elevator cars 6 and 7 which is to be performed by means of the auxiliary hoist- ing machine 8 and the overall correction to be performed by means of the main hoisting machine 2 are carried out simultaneously, the elevator cars being thus brought exactly to the landing levels as quickly and smoothly as possible.

By using the solution described above, the compensation of elastic and other elongations of the hoisting ropes can be performed economically and reliably by the same basic technical solution that is used for adjusting the mutual distance between the elevator cars of a double-deck elevator because of varying floor-to- floor distances to make it correspond to the mutual distance between the target floor levels.

It is obvious to the person skilled in the art that different embodiments of the in- vention are not limited to the example described above, but that they may be var- ied within the scope of the claims presented below. Thus, to change the mutual distance between the elevator cars in the car frame 1, it is also possible to use control devices other than an auxiliary hoisting machine 8 operating by means of a hoisting rope. As control devices it is possible to use e. g. hydraulic cylinders, screws, e tc. L ikewise, t he c onnection a nd o peration o f t he c ontrol unit 13 may differ from the above description. It is further obvious to the skilled person that the apparatus of the invention can also be applied by way of a method of compensat- ing elastic elongations in a double-deck elevator.