Abstract:
A method of preventing a collision of two elevator cars of an elevator installation, which cars move substantially independently of one another in a common shaft, and an elevator installation includes a collision protection system that produces a retardation of each moved elevator car by a stopping brake as soon as the effective distance between the elevator cars falls below a critical minimum distance. After retardation of the cars by the stopping brakes, an emergency stop system comes into function. A control system of this emergency stop system ascertains the instantaneous movement state of the elevator cars. With the help of the car brakes, which are associated with the elevator cars, an additional retardation of each moved elevator car is triggered when the movement state thereof fulfils definable emergency stop criteria.

Description:
FIELD OF THE INVENTION 
     The invention relates to a method of preventing collision of two elevator cars, which are movable in the same elevator shaft of an elevator installation. 
     BACKGROUND OF THE INVENTION 
     Elevator installations with several elevator cars in the same shaft, which are also termed multi-mobile elevator installations, usually have a respective driving and braking system per elevator car. Moreover, such elevator installations are equipped with a collision protection system by which collisions of the elevator cars are to be avoided. 
     Apart from conventional electronically controlled collision protection systems an elevator installation with a collision protection system with electromechanical switching mechanisms able to be mechanically triggered has been described by European Patent Application EP 06 120 359. The disclosure of this European Patent Application is regarded as an integral part of the present application. The mentioned collision protection system is simple in construction and reliable in its operation. However, it is disadvantageous that its triggering takes place merely when a critical minimum distance between two approaching elevator cars is fallen below without further braking criteria such as, for example, the relative speed between the elevator cars or the instantaneous effective distance, in each instance after triggering of the stopping brake, being taken into consideration. Particularly in the case of high car speeds and emergency situations it cannot be guaranteed with ultimate certainty that a further elevator car disposed above or below still stops at the right time to avoid a collision. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to propose a method in order to trigger, in the case of a multi-mobile elevator installation, an additional braking when the distance between the elevator cars further reduces, notwithstanding triggering of stopping brakes by means of a collision protection system, so that an immediate emergency stop is required, and to create a multi-mobile elevator installation operable according to this method. 
     The emergency stop system shall in this connection be conceived as far as possible so that it does not oblige any enlargement of the shaft cross-section. 
     The new elevator installation comprises at least one upper elevator car and at least one lower elevator car. The two elevator cars can move vertically upwardly and downwardly, substantially independently of one another, in a common elevator shaft of the elevator installation. 
     The upper elevator car has a first driving and braking system comprising a first stopping brake (preferably a motor brake). The lower car has a second driving and braking system which includes a second stopping brake (preferably a motor brake). According to the present invention the first elevator car is additionally equipped with a first car (emergency) brake and the second elevator car with a second car (emergency) brake, the function of which is explained in more detail further below. 
     Moreover, the elevator installation has a collision protection system in order to avoid collisions between the elevator cars. The collision protection system preferably comprises a first electromechanical switching mechanism at the upper elevator car and a second electromechanical switching mechanism at the lower elevator car, by which retardation of the upper elevator car by the first stopping brake and/or retardation of the lower elevator car by the second stopping brake can be triggered. However, the elevator cars and the collision protection system can, in particular, be constructed—but do not necessarily have to be constructed—in accordance with EP-06120359. 
     According to the present invention an emergency stop system is in addition provided. The emergency stop system is so designed that after triggering of the retardation or braking by the stopping brakes it continuously or repeatedly ascertains the instantaneous movement state of the two elevator cars and triggers an additional braking of one or both moved elevator cars by means of an associated car brake if this, with consideration of the movement state of the elevator cars on the one hand and with consideration of ascertainable braking criteria on the other hand, is necessary. 
     The movement state of the elevator cars is inter alia and substantially a function of their relative speed. 
     Braking criteria can in principle be ascertained in advance, but advantageously the instantaneous movement state of the elevator cars is included. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which: 
         FIG. 1  is schematic side elevation view of a multi-mobile elevator installation according to the state of the art; 
         FIG. 2  is an enlarged schematic view of a collision protection system and an emergency stop system at the multi-mobile elevator installation of  FIG. 1  according to the present invention; 
         FIG. 3  is a flow diagram of the method according to the present invention; and 
         FIG. 4  is an exploded perspective view of the upper switching mechanism shown in  FIG. 2 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following detailed description and appended drawings describe and illustrate various exemplary embodiments of the invention. The description and drawings serve to enable one skilled in the art to make and use the invention, and are not intended to limit the scope of the invention in any manner In respect of the methods disclosed, the steps presented are exemplary in nature, and thus, the order of the steps is not necessary or critical. 
       FIG. 1  shows a simple elevator installation  10 . Such elevator installations are, as mentioned further above, known under the designation multi-mobile elevator installations. The elevator installation  10  has an elevator shaft  11  in which an upper elevator car Al and a lower elevator car A 2  can move vertically. As long as a critical minimum distance “d(0)” between the two elevator cars A 1 , A 2  is maintained, i.e. during normal operation where the instantaneous spacing “di” is greater than the critical minimum distance “d(0)”, the elevator cars A 1 , A 2  can move independently of one another in the elevator shaft  11 . The elevator installation  10  has a driving and braking unit, wherein preferably each of the elevator cars A 1 , A 2  has an individual driving and braking system. 
     The elevator installation  10  additionally has a collision protection system  20 . The collision protection system  20  comprises a first electromechanical switching mechanism  21  which is arranged in a lower region of the upper elevator car A 1  and a second electromechanical switching mechanism  22  which is arranged in an upper region of the lower elevator car A 2 . The two switching mechanisms  21 ,  22  are mounted in vertical alignment one above the other, 
     The collision protection system  20  of the elevator installation  10  preferably comprises, for each elevator car A 1 , A 2 , an individual safety circuit in which several safety elements such as, for example, safety contacts and safety switches, are arranged in series. The corresponding elevator car A 1  or A 2  can be moved only if its safety circuit and thus all safety contacts integrated therein are closed. The safety circuit is connected with the driving and braking unit of the elevator installation  10  or the driving and braking systems of the elevator cars A 1 , A 2  in order to interrupt travel operation of the corresponding elevator car A 1  and/or A 2  if the safety circuit is opened by actuation of the corresponding electromechanical switching mechanism  21  and/or  22 . 
     The first switching mechanism  21  comprises a weighting body  23  with a weight G suspended at an elongate flexible support element  24 , which in turn is fastened at the lower region of the upper elevator car A 1 . The entire vertical dimension of the support element  24  and the weighting body  23  substantially corresponds with the critical distance “d(0)” to be maintained between the elevator cars A 1 , A 2 . 
     The second switching mechanism  22  comprises a mechanical sensor in the form of a lever  28  (see  FIG. 2 ), which acts on a contact switch  34 . 
     In the normal case, i.e. when the spacing “di” between the elevator cars A 1  and A 2  is greater than the critical distance “d(0)”, the weighting body  23  hangs freely at the support element  24 , which is disposed under tensile stress and kept stretched by the weight G of the waiting body  23 . 
     If the elevator cars A 1 , A 2  approach to such an extent that the instantaneous space “di” thereof falls below the critical distance “d0” then the weighting body  23  impinges on the lever  28  of the second electromechanical switching mechanism  22 . The tensile force exerted by the weighting body  23  on the support element  24  thereby reduces and thus substantially the tensile stress in the support element  24 . 
     Due to the considerable reduction in the tensile stress in the support element  24  the safety circuit of the first driving and braking unit of the upper elevator car A 1  is opened. Retardation of the upper elevator car A 1  by means of the first stopping brake (for example, designed as a motor brake) is thereby triggered. Through the impinging of the waiting body  23  on the lever  28  the safety circuit of the second driving and braking unit of the lower elevator car A 2  is opened at virtually the same time. Retardation of the lower elevator car A 2  by means of the second stopping brake (for example, designed as a motor brake) is thereby triggered. 
     However, the emergency stop system according to the present invention can also be used in elevator installations  10  of which the collision protection system is of different design or of which the stopping brakes can be triggered in a different manner and/or which are equipped with a safety bus system instead of the mentioned safety circuits. 
     According to the present invention the elevator installation  10  has, in addition to the collision protection system  20 , the emergency stop system by which after retardation of one or both elevator cars A 1 , A 2  by one or both stopping brakes an additional retardation of the moved elevator cars A 1  and/or A 2  can be achieved. Triggering of this additional retardation takes place with consideration of the instantaneous movement state of the elevator cars A 1 , A 2  and on the basis of emergency stop criteria. 
     The emergency stop system of the present invention can comprise constructional elements of the collision protection system  20  and additional constructional elements, i.e. the emergency stop system in this case is at least partly integrated in the collision protection system  20 . 
     In the case of a collision protection system of an elevator installation  10  according to the present invention and in accordance with  FIG. 2  it is provided that the flexible support element  24  is not fastened directly or fixedly at the lower region of the upper elevator car A 1  or at a lever disposed there, but is mounted at a roller  30 . The roller  30  is in turn rotatably fastened at the lower region of the upper elevator car A 1 . This fastening is not shown in  FIG. 2 . The roller  30  has an internal energy store  31  (or an attached energy store  31 , as shown in  FIG. 4 ), preferably in the form of a spiral spring, which exerts a force having a tendency to so rotate the roller  30  (in the illustrated example this rotation would act in a clockwise sense) that the flexible support element  20  is wound up on the roller  30 . In the normal case, i.e. when the instantaneous spacing “di” between the elevator cars A 1  and A 2  is greater than the critical distance “d0”, the roller  30  is blocked against rotation and, in particular, by the tension force which the flexible support element  24  loaded by the weight G of the weighting body  23  exerts. This means that the roller  30  cannot, due to this blocking, be brought by means of its internal energy store  31  into rotation. As soon as a retardation of the elevator cars A 1 , A 2  has been initiated by the stopping brakes because the instantaneous distance “di” between the elevator cars A 1  and A 2  falls below the critical distance “d0”, the emergency stop system or its control system is activated. In the present case this takes place by impinging of the weighting body  23  on a sensor (for example the lever  28  in conjunction with a switch  34 ) of the switching mechanism  22  of the lower elevator car A 2 . After impinging of the weighting body  23  the tension force in the flexible support  24 , by which the roller  30  was blocked, diminishes. The roller  30  is now freed and rotates under the winding-up torque delivered by its internal force store  31  so that the flexible support element  24  is wound up on the roller  30 . The release of the roller  30  takes place virtually simultaneously with the actuation of the electromechanical switching mechanisms  22  and the retardation of the elevator cars A 1 , A 2  by the stopping brakes thereof. 
     The roller  30  rotates after release thereof and in that case that part of the flexible element  24  substantially corresponding with the difference between the critical distance “d0” and the instantaneous spacing “di” of the elevator cars A 1 , A 2  is wound up. In this connection, however, the weighting body  23  does not have to be drawn upwardly. The winding-up torque exerted by the internal energy store  21  on the roller  30  thus has to exert on the flexible support element  24  a winding force which is less than the weight “G(23)” of the weighting body  23 , but greater than the weight “G(24)” of the flexible support element  24 , wherein the frictional forces also have to be taken into consideration. 
     The rotation of the roller  30  allows detection of the instantaneous movement state of the elevator cars A 1 , A 2  proceeding from the instantaneous angular speed “ωI” and the instantaneous distance “di” between the elevator cars A 1  and A 2 . As soon as the roller  30  rotates, its angular speed “ωI”, which is a function of time, is detected by an incremental transmitter  32 . The instantaneous relative speed “vi(rel)” of the elevator cars A 1 , A 2  can then be ascertained from this angular speed “ωI”. The instantaneous distance “di” between the elevator cars A 1 , A 2  can then be similarly ascertained, either by means of a travel measuring sensor  35  or in computerized manner with utilization of the instantaneous angular speed “ωI” of the roller  30 . Subsequently, it is clarified with consideration of the thus-ascertained movement state and the emergency stop criteria whether an additional retardation of one or both elevator cars A 1 , A 2  is to be triggered by the car brakes thereof. 
     How this can be realized is explained by way of example in the following. The following symbols are used:
         d 0  critical distance (maximum detection distance)   di instantaneous distance of the elevator cars A 1 , A 2     ωi instantaneous angular speed of the roller  30     vi(rel) instantaneous relative speed of the elevator cars A 1 , A 2     vi instantaneous speed of one of the elevator cars   vi(A 1 ) instantaneous speed of the upper elevator car A 1     vi(A 2 ) instantaneous speed of the lower elevator car A 2     a(min) minimum attainable retardation in an emergency stop   s stop (min)I minimum stopping distance if only one elevator car A 1  or A 2  is in motion (i.e. if vi(rel)=vi actual)   s stop (min)II minimum stopping distance if both elevator cars A 1  and A 2  are in motion (i.e. if (v(rel)/2)=vi actual)       

     In addition, the following assumptions or rules apply: 
     If in the context of the present description both elevator cars A 1  and A 2  are moving, then they approach at the same speeds vi(A 1 )=vi(A 2 ), wherein vi(A 1 ) and vi(A 2 ) are absolute values. 
     If a contact switch  34  of the safety circuit of the lower elevator car A 2  is open and/or the instantaneous distance “di” between the elevator cars A 1  and A 2  is less than the critical distance “d0”, then a retardation of each moved elevator car A 1 , A 2  takes place through retardation by means of the stopping brakes thereof. 
     Emergency stop criteria—An emergency stop or a braking by one or both car brakes is triggered, additionally to braking by the stopping brakes, if one of the following two emergency stop criteria is fulfilled: 
     Emergency stop criterion A: If an elevator car A 1  or A 2  is moving and the instantaneous distance “di” between the cars A 1  and A 2  is less than or equal to the corresponding minimum stopping distance s stop (min)I then braking is triggered by the car brake of the moving elevator car A 1  or A 2 . 
     Emergency-stop criterion B: If both elevator cars are moving and the instantaneous distance “di” between the elevator cars A 1  and A 2  is less than or equal to the corresponding minimum stopping distance s stop (min)II then retardation is triggered by car brakes of both elevator cars A 1  and A 2 . 
     For ascertaining the movement state and comparison with the emergency stop criteria, the following are detected or calculated: 
     By measurement: Is one car not in motion? 
     Is contact  34  of the safety circuit of the lower elevator car A 2  open? 
     Through calculations: vi(A 1 )=vi(A 2 )=vi=0.5 vi(rel)
         s stop (min)I=(vi(rel)) 2 /(2*a(min))   s stop (min)II=(0.5 vi(rel)) 2 /(2*a(min))       

       FIG. 3  shows a flow diagram by which the sequence of the entire braking process is explained by way of example with use not only of the stopping brakes, but also of the car brakes. 
     Box F 1  shows measured or available values, namely vi(rel); di; vi( 1 ); vi( 2 ); setting of the contact  34 ; A 1   
     After these values are available, question Q 1  takes place. 
     It is ascertained by question Q 1  whether the contact  34  may be open and/or di&lt;d 0 . 
     If question Q 1  is answered by no N, then obviously no braking, neither by the stopping brakes nor by the car brakes, is required. 
     If question Q 1  is answered by yes J, then according to box F 2  triggering of the stopping brakes takes place, i.e. the emergency stop system is not caused to trigger an additional braking by the car brakes. 
     Then it is ascertained by question Q 2  whether both elevator cars are in motion. 
     If question Q 2  is answered by no N, thus only one of the elevator cars is in motion, then question Q 3  is set. 
     By question Q 3  it is ascertained whether “di” may be equal to or even smaller than s stop (min)I. 
     If question Q 3  is answered by yes J, thus the minimum stopping distance for this case is reached or exceeded, then according to box F 3  an additional retardation by the corresponding car brake takes place for an emergency stop. 
     If question Q 3  is answered by no N, then a further question Q 4  takes place. 
     It is clarified by question Q 4  whether the relative speed of the elevator cars may be zero. 
     If question Q 4  is answered by yes J, then this can only mean that now both cars are no longer in motion, because according to box F 2  the stopping brakes are triggered and according to answer no N to question Q 2  only one elevator car A 1  or A 2  is in motion. According to box F 4  no further braking by use of car brakes is then required, since obviously the braking action of the stopping brake has sufficed. 
     If question Q 4  is answered by no N, then question Q 2  is posed again. 
     If question Q 2  is answered by yes J, thus both elevator cars A 1  and A 2  are in motion, then subsequently question Q 5  is posed. 
     It is clarified by question Q 5  whether “di” is the same as or even smaller than s stop (min)II. 
     If question Q 5  is answered by no N, then question Q 4  is posed for further clarification, i.e. it is clarified by question Q 4  whether the relative speed vi(rel) of the elevator cars A 1 , A 2  may be zero. If this is the case, then according to box F 4  no additional braking by car brakes is necessary. 
     If, thereagainst, question Q 5  is answered by yes J, then according to box F 3  an additional braking by the car brakes for an emergency stop takes place. 
     If more than two elevator cars move in the same elevator shaft  11 , then an appropriate emergency stop system can also be fitted between these elevator cars. 
     A currently particularly preferred embodiment of a significant part of the emergency stop system  21  is shown in  FIG. 4 . The roller  30  on which the support means  24  is wound up when it is not loaded by the weighting force of the weighting body  23  suspended thereat can be seen. Seated on the same shaft  42  as the roller  30  is a spring drive  31  which is here also termed an energy store. An incremental transmitter  32  is attached by way of a coupling  40 . A connection takes place by way of an adapter  41 . 
     In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiment. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.