Abstract:
A safety circuit for an elevator system includes a plurality of switch contacts, at least one first switch contact, and a control unit. The at least one first switch contact can be switched electronically and can be bridged using a conductive bridging element, in particular for maintenance or testing purposes. Additionally, the control unit is directly or indirectly connected to the safety circuit. The at least one first switch contact can be switched on the basis of instructions of the control unit in order to change the state of the safety circuit. In the process, the at least one control unit detects the absence of the state change of the safety circuit, in particular when the at least one first switch contact is being bridged by the bridging element

Description:
FIELD 
       [0001]    The invention relates to a safety system and an elevator installation with this safety system and to a method of operating the elevator installation with this safety system. 
       BACKGROUND 
       [0002]    Current elevator installations are equipped with a safety system comprising a safety circuit. This consists of a plurality of switch contacts, which are connected in series, of different safety elements for shaft, door and cable monitoring. Opening one of these switch contacts has the consequence that the entire safety circuit is interrupted. This in turn causes interruption of power supply for the main drive and thus adoption of a rest state. For maintenance purposes or test purposes of the elevator installation individual ones or several of these switch contacts have to be bridged over by means of bridging-over elements. In the case of travel to a buffer it is necessary, for example, for a limit switch to be bridged over so as to be able to travel beyond the travel range, which is permissible in normal operation, in the shaft onto the buffer. Before the elevator installation can resume its normal operation all bridging-over elements would have to be removed from the safety circuit. However, it cannot be excluded that a maintenance engineer forgets to remove a bridging-over element again. Accordingly, reliability of the safety circuit is impaired, since a bridged-over switch contact in a given case may be unable to interrupt the safety circuit. 
       SUMMARY 
       [0003]    It is therefore the object of the invention to create a safety system with a safety circuit for an elevator installation which releases normal operation of an elevator installation only if a previously inserted bridging-over element has been removed. 
         [0004]    A safety system for an elevator installation preferably comprises a safety circuit with a plurality of switch contacts and a control unit. At least one first switch contact is electronically switchable and can be bridged over with use of a conductive bridging-over element, particularly for maintenance purposes or test purposes. In addition, the control unit is indirectly or directly connected with the safety circuit. The first switch contact is switchable on the basis of an instruction of the control unit so as to achieve a change in state of the safety circuit. In that case, the control unit is arranged to detect absence of the change in state of the safety circuit if the at least one switch contact is bridged over by the bridging-over element. 
         [0005]    By “bridging-over element” there is to be understood here a conductive element for temporary bridging-over of a switch contact. 
         [0006]    It is of advantage that a previously bridged-over first switch contact can, for example, be opened in a test and, when the bridging-over element of the safety circuit is removed, interruption of the safety circuit can be detected as expected. Such a change in state arises only when the bridging-over element has been removed. Accordingly, removal of a bridging-over element is reliably recognizable by means of this test and the elevator installation can be released for operation. This test can optionally also be carried out during normal operation so as to detect an incorrectly inserted bridging-over element. In that case, the test can be carried, for example, once per day. 
         [0007]    By electronically switchable switch contact there is to be understood here a switch contact which is switchable by an electronic computer unit such as, for example, the aforesaid control unit. For that purpose a signal is communicated by the computer unit to the switch contact. The switch contact itself can be designed as an electronic component in the form of an analog switch or a semiconductor switch such as, for example, field effect transistors, bipolar transistors, switching diodes, thyristors or the like. Alternatively thereto a switch contact can also be electromechanically designed, such as, for example, a relay, circuitbreaker or the like. 
         [0008]    By “control unit” there is to be understood a unit with at least one processor, which can issue at least switching commands to an electronically switchable switch contact. In addition, the control unit typically comprises a data memory unit and a work memory unit. In a preferred embodiment the control unit is designed as a main control of the elevator installation. Alternatively thereto the control unit can also be designed as a separate safety control unit. 
         [0009]    Operation of the elevator installation can preferably be interrupted by the control unit if on the basis of the instruction of the control unit to switch the first switch contact no change in state of the safety circuit is detectable. 
         [0010]    In that regard it is advantageous that if a bridging-over element is present, operation is not released. Safe starting of operation of the elevator installation is thus ensured. The elevator installation can enter into operation only if the bridging-over element has been removed and switching of the first switch contact has an influence on the state of the safety circuit or opening of the first switch can cause interruption of the safety circuit. 
         [0011]    The safety circuit preferably comprises at least one second electronically switchable switch contact, wherein the second switch contact is switchable by the control unit when on the basis of the instruction of the control unit to switch the first switch contact no change in state of the safety circuit is detectable. 
         [0012]    The safety circuit is thereby interruptible in simple mode and manner by the switching or opening of the second switch contact. Accordingly, power supply of a drive and/or main control of the elevator installation is interrupted and the elevator installation is brought to a rest state. 
         [0013]    Alternatively or in addition thereto the control unit itself can bring itself into a safety mode in which the control unit can no longer execute travel commands and/or accept car calls. 
         [0014]    A fault signal can preferably be stored at a data memory unit, preferably a data memory unit of the control unit, when on the basis of the instruction of the control unit to switch the switch contact no change in state of the safety circuit is detectable. 
         [0015]    By “fault signal” there is to be understood a signal reflecting a negative test result. The control unit in the case of a switching process of the first switch contact expects a change in state in the safety circuit. If no change in state in the safety circuit can be ascertained, the control unit assesses the test as negative and in correspondence with this result stores a fault signal at a data memory unit. The fault signal can preferably also include characteristic information with respect to the first switch contact which was switched. Such characteristic information bears, for example, a value uniquely assignable to the first switch contact. The first switch contact is thus uniquely identifiable. 
         [0016]    This has the advantage that a maintenance engineer when reading out the data memory unit is referred simply and quickly to the cause of the shutdown of the elevator installation and does not waste time on fault investigation. The characteristic information with respect to the first switch contact which was switched, by which information the bridged-over first switch contact can be localized particularly quickly, is of particular advantage. 
         [0017]    The first switch contact after the instruction by the control unit to switch is preferably switched back after a predetermined period of time, in which case the period of time is at least 1 millisecond, preferably lasts not longer than 30 seconds and with particular preference is between 500 milliseconds and 10 seconds. 
         [0018]    In that case, the time period has to last long enough for a voltage drop or power interruption in the safety circuit to be reliably detectable and primarily depends on the response time of the first switch contact. In the case of a semiconductor switch this time period can even be less than 1 millisecond. Similarly, the time period for switching back should not last too long so as to not unnecessarily delay operation of the elevator installation. 
         [0019]    In the case of a positive test result after switching back the first switch contact, the operation of the elevator installation can be started. Conversely, in the case of a negative test result the test is to be repeated after switching back the first switch contact. 
         [0020]    The switching back is preferably undertaken autonomously by the first switch contact. For that purpose the first switch contact has a resetting unit. This resetting unit is designed as a time relay, monoflop or the like, which triggers switching back of the first switch contact. 
         [0021]    The safety system preferably comprises a further control unit connected with the safety circuit. This further control unit is associated with, in particular, a shaft information system. In that case the further control unit is designed in such a way that this switches the first switch contact on the basis of an instruction of the control unit. 
         [0022]    If the further control unit is present, this can trigger switching-back of the first switch contact. In this embodiment resetting can take place not only on the basis of elapsing of the predetermined period of time, but in addition also on the basis of a check for predetermined conditions. 
         [0023]    An excess speed switch contact or a limit switch contact, which interrupts the safety circuit in the case of excess speed or travel beyond a permissible end position in the shaft, is preferably assigned to the further control unit. Obviously, the excess speed switch contact and the limit switch contact can preferably be designed as first switch contacts. 
         [0024]    In the case of an excess speed switch contact a condition for switching back is, for example, fulfilled if the further control ascertains that at the instant of switching back no excess speed of the car is ascertainable. Correspondingly, a limit switch contact can be switched back when the car stops in a permissible position between the two end positions. The further control unit can obtain the two items of information, i.e. car speed and car position, by way of the shaft information system. On the basis of these items of information the further control unit decides whether a condition for switching back the at least one first switch contact is fulfilled and switches back the respective first switch contact if the condition is fulfilled. 
         [0025]    In a preferred embodiment an individual further control unit can be associated with the first electronically switchable switch element. 
         [0026]    A further aspect of the invention relates to an elevator installation with the above-described safety circuit. 
         [0027]    In addition, the invention also relates to a method for checking the safety system of an elevator installation, comprising the steps of:
   switching at least one first electronically switchable switch contact of a safety circuit with use of a control unit for achieving a change in state of the safety circuit; and   detecting absence of a change in state of the safety circuit by the control unit when the first switch contact is bridged over by a bridging-over element.   
 
         [0030]    A further step preferably relates to interruption of operation of the elevator installation by the control unit in the case of detection of absence of the change in state of the safety circuit. Accordingly, a bridging-over element may still be inserted and the first switch contact bridged over. 
         [0031]    A further step preferably relates to switching a second electronically switchable switch contact with use of a command of the control unit for interrupting operation of the elevator installation in the case of detection of absence of the change in state of the safety circuit. 
         [0032]    A further step preferably relates to storage of a fault signal at a data memory unit, preferably a data memory unit of the control unit, in the case of detection of absence of the change in state of the safety circuit. 
         [0033]    For preference, yet a further step relates to switching back, particularly autonomous switching back, of the first switched switch element after a predetermined period of time, wherein the period of time is at least one 1 millisecond, preferably does not last longer than 30 seconds and, with particular preference, is between 500 milliseconds and 10 seconds. 
         [0034]    Finally, a last step preferably relates to switching the first switch contact with use of an instruction of a second control unit, which is associated with, in particular, a shaft information system. In that case, switching-back of the first switch contact is possible as an option with use of an instruction of the further control unit after checking a predetermined condition. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0035]    The invention is better described in the following by way of embodiments, in which: 
           [0036]      FIG. 1  schematically shows a circuit diagram of the safety system according to the invention, comprising a safety circuit of a first embodiment with a control unit; and 
           [0037]      FIG. 2  schematically shows a circuit diagram of the safety system according to the invention, comprising a safety circuit of a second embodiment with a further control unit. 
       
    
    
     DETAILED DESCRIPTION 
       [0038]      FIG. 1  shows a safety system comprising a safety circuit  1  with a plurality of switch contacts  10 . 1 ,  10 . 2 ,  11 ,  12 . 1 ,  12 . 2  connected in series. The switch contacts  10 . 1 ,  10 . 2 ,  12 . 1 ,  12 . 2  monitor a state of a safety-relevant component of the elevator such as, for example, a shaft door, a car door, a speed limiting system, an emergency stop switch or a shaft limit switch. In the illustrated example the safety circuit  1  comprises five switch contacts  10 . 1 ,  10 . 2 ,  11 ,  12 . 1 ,  12 . 2 . The number of switch contacts in the safety circuit  1  is obviously variable and depends on the number of safety-relevant components to be monitored. The safety circuit  1  is in a safe state when all switch contacts  10 . 1 ,  10 . 2 ,  11 ,  12 . 1 ,  12 . 2  are closed. 
         [0039]    The safety circuit  1  is supplied with power from, for example, a 24V source. In a safe state of the safety circuit  1  a corresponding current flows across the switch contacts  10 . 1 ,  10 . 2 ,  11 ,  12 . 1 ,  12 . 2 . A relay  13  is connected at one end of the safety circuit  1  with the same and with a 0V conductor. The relay  13  comprises a switching magnet  13 . 1  and a switch  13 . 2 , the latter being integrated in a power supply  20  of a main drive  21 . The switching magnet  13 . 1  switches the associated switch  13 . 2  in correspondence with a switch state of the safety circuit  1 . In that case the energized switching magnet  13 . 1  keeps the switch  13 . 2  closed. As soon as a switch contact  10 . 1 ,  10 . 2 ,  11 ,  12 . 1 ,  12 . 2  of the safety circuit  1  is open and the current flow in the safety circuit  1  is interrupted, the power feed to the switching magnet  13 . 1  is also interrupted. As a consequence, the associated switch  13 . 2  is opened and the power supply  20  to the main drive  21  interrupted. 
         [0040]    In the depicted illustration, two bridging-over elements  14 . 1 ,  14 . 2  which bridge over the two switch contacts  10 . 1 ,  10 . 2  are inserted. This is carried out, for example, for testing purposes or maintenance purposes of the elevator installation so as to permit certain travel states which otherwise are not permitted in a normal operating mode. After the conclusion of such tests or maintenance operations the bridging-over elements are removed again so as to guarantee safe operation of the elevator installation in a normal mode. Before the elevator installation is again operable in the normal mode it is checked whether the bridging-over elements  14 . 1 ,  14 . 2  have actually been removed. 
         [0041]    For that purpose the safety circuit  1  is connected with a control unit  30 , preferably the main control unit of the elevator installation. The control unit  30  can on the one hand recognize the state of the safety circuit  1  by way of the line  31  and on the other hand transmit control signals for switching the switch contacts  10 . 1 ,  10 . 2 ,  11 . This action of the control unit  30  on the switch contacts  10 . 1 ,  10 . 2 ,  11  is illustrated in  FIGS. 1 and 2  by dashed lines. 
         [0042]    In a test the two switch contacts  10 . 1 ,  10 . 2  are switched by the control unit  30  into an open state. If the two bridging-over elements  14 . 1 ,  14 . 2  have been removed, this opening causes interruption of the safety circuit  1 . This interruption can be recognized by the control unit  30 . Accordingly, the expectation of the control unit  30  has been fulfilled and the elevator installation can be safely operated in the normal mode. The switch contacts  10 . 1 ,  10 . 2  are preferably opened in a predetermined sequence so as to individually test each switch contact  10 . 1 ,  10 . 2 . 
         [0043]    Conversely, the expectation of the control unit is not fulfilled if opening of the switch contacts  10 . 1 ,  10 . 2  does not lead to interruption of the safety circuit  1 . In such a case it has to be assumed that removal of one or both of the bridging-over elements  14 . 1 ,  14 . 2  has not taken place. Accordingly, opening of the switch contacts  10 . 1 ,  10 . 2  has no effect on the state of the safety circuit  1 . For reasons of safety this is not acceptable in the normal mode. Accordingly, the control unit  30  opens the safety contact  11  so as to prevent further operation of the elevator installation. 
         [0044]    In the case of a negative test result a fault signal can be stored in a data memory unit of the control unit  30 . Advantageously, the fault signal contains characteristic information, particularly a unique address about which switch contact or contacts  10 . 1 ,  10 . 2  is or are bridged over. This makes it possible for a maintenance engineer to quickly localize and remove an overlooked bridging-over element  14 . 1 ,  14 . 2 . 
         [0045]    After a predetermined period of time the two switch contacts  10 . 1 ,  10 . 2  are switched back or closed. In that case the time period is at least 1 millisecond and preferably at most 30 seconds. A particularly preferred duration of this time period is 500 milliseconds to 10 seconds. The switch contacts  10 . 1 ,  10 . 2  comprise a resetting unit for the resetting. 
         [0046]    Such a resetting unit is preferably designed as a time relay or monoflop. In that case, the resetting unit is settable to a specific time period. After expiry of this time period the resetting unit triggers resetting of the associated switch contact  10 . 1 ,  10 . 2 . 
         [0047]    The safety circuit  1  can obviously also have additional switch contacts  12 . 1 ,  12 . 2  which are not switchable by means of a control unit  30 . Such non-switchable switch contacts  12 . 1 ,  12 . 2  preferably do not have to be bridged over for maintenance operations. These switch contacts  12 . 1 ,  12 . 2  monitor, for example, the state of shaft doors or car doors as well as an emergency switch. The safety circuit  1  is accordingly designed in such a way that within the scope of maintenance preferably only electronically switchable switch contacts  10 . 1 ,  10 . 2  have to be bridged over by means of a bridging-over element  14 . 1 ,  14 . 2 . 
         [0048]      FIG. 2  shows an alternative embodiment of the safety system with an additional control unit  40 . By contrast to the first embodiment according to  FIG. 1  the two switch contacts  10 . 1 ,  10 . 2  are activated by the control unit  40 . The control unit  40  is connected with the control unit  30  by way of a line  32 . The control unit  40  obtains control signals from the control unit  30  by way of this line  32 . 
         [0049]    In this alternative embodiment the test of the switch contacts  10 . 1 ,  10 . 2  is similarly triggered by the control unit  30  in that the control unit  30  transmits to the control unit  40  by way of the line  32  a control signal for opening the switch contacts  10 . 1 ,  10 . 2 . The control unit  40  correspondingly opens the switch contacts  10 . 1 ,  10 . 2  so as to check whether the two bridging-over elements  14 . 1 ,  14 . 2  have been removed. 
         [0050]    If a further control unit  40  is present, resetting of the associated switch  10 . 1 ,  10 . 2  can be triggered by the control unit  40 . It is therefore possible to dispense with the resetting units of the first embodiment in the design of the safety system. Resetting of the switch contacts  10 . 1 ,  10 . 2  can be triggered not just on the basis of elapsing of a period of time, but alternatively or optionally also on the basis of checking a condition. The test otherwise takes place analogously to the first embodiment. 
         [0051]    The control unit  40  is, for example, associated with a shaft information system. The shaft information system has data with respect to the speed and position of an elevator car available. Accordingly, the switch contact  10 . 1  is switchable on the basis of excess speed of the elevator car and the switch contact  10 . 2  is designed as a limit switch. The switch contact  10 . 1  is to be bridged over in the case of a safety braking test and the switch contact  10 . 2  in the case of test travel onto a buffer. Accordingly, a condition for resetting the switch contact  10 . 1  is linked to maintenance of a permissible car speed and resetting of the switch contact  10 . 2  is linked to maintenance of a permissible car position between two end positions in the shaft. 
         [0052]    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.