BRAKE CONTROL APPARATUS AND A METHOD OF CONTROLLING AN ELEVATOR BRAKE

Abstract

The invention concerns a brake control apparatus and a method of controlling an elevator brake. The brake control apparatus comprises a first switch and a second switch connected in series with each other for selectively supplying current from a power source to an electrically operated actuator of an elevator brake. The control pole of the first switch and the control pole of the second switch are associated with an elevator safety circuit. The brake control apparatus further comprises a first monitoring circuit configured to indicate operation of the first switch and a second monitoring circuit configured to indicate operation of the second switch.

Claims

1. A brake control apparatus, comprising: a first switch and a second switch connected in series with each other for selectively supplying current from a power source to an electrically operated actuator of an elevator brake, the control pole of the first switch and the control pole of the second switch being associated with an elevator safety circuit; wherein the brake control apparatus comprises: a first monitoring circuit configured to indicate operation of the first switch; and a second monitoring circuit configured to indicate operation of the second switch.

2. A brake control apparatus according to claim 1, wherein the second monitoring circuit is configured to indicate operation of the first switch while the second switch is open.

3. A brake control apparatus according to claim 1, wherein the first switch is a change-over switch and the second switch is a change-over switch.

4. A brake control apparatus according to claim 3, wherein the first change-over switch and the second change-over switch have their inputs as well as first outputs in the current supply path, and in that the second output of the first change-over switch in coupled to the first monitoring circuit, and the second output of the second change-over switch is coupled to the second monitoring circuit.

5. A brake control apparatus according to claim 1, wherein the first monitoring circuit and the second monitoring circuit are configured to indicate opening and closing of the first switch while the second switch is open.

6. A brake control apparatus according to claim 1, wherein the first switch is fitted in the current supply path closer to the power source than the second switch.

7. A brake control apparatus according to claim 1, wherein the second monitoring circuit is configured to indicate opening of the first switch only when the second switch is open.

8. A brake control apparatus according to claim 1, wherein the brake control apparatus comprises a processor and a memory with a processor-implemented monitoring program stored therein, the processor having inputs coupled to the first monitoring circuit and to the second monitoring circuit as well as an output associated with the control pole of the second switch; and in that the monitoring program comprises instructions for comparing operation data of the first switch as received from the first monitoring circuit and the operation data of the first switch as received from the second monitoring circuit to a monitoring criteria, and for indicating an operational anomaly when the operation data does not fulfill the monitoring criteria.

9. A brake control apparatus according to claim 8, wherein the processor has an output for selectively sending a start permit signal to the safety circuit, and in that the monitoring program comprises instructions for sending a start permit signal when the operation data fulfills the monitoring criteria.

10. A brake control apparatus according to claim 1, wherein the brake control apparatus comprises a rectifier fitted into the current supply path, for rectifying AC current to DC current for the electrically operated actuator of an elevator brake; and in that the first switch is fitted to AC side of the rectifier and the second switch is fitted to DC side of the rectifier.

11. A brake control apparatus according to claim 1, wherein the brake control apparatus comprises a third switch; and in that there are two elevator brakes each having an electrically operated actuator operable to selectively open or apply the elevator brake; and in that the third switch is connected in series with the first switch for selectively supplying current from power source to one of the electrically operated actuators, independent of the switching state of the second switch; and in that the second switch is connected in series with the first switch for selectively supplying current from power source to the other of electrically operated actuators, independent of the switching state of the third switch; and in that the brake control apparatus comprises a third monitoring circuit configured to indicate operation of the third switch.

12. A brake control apparatus according to claim 1, wherein the electrically operated actuator is an electromagnet of an electromagnetic brake.

13. A brake control apparatus according to claim 8, wherein the first switch and the second switch are relays having each a change-over switch configuration; and in that the safety circuit is coupled to the control coil of the first relay and the second relay for supplying current to the control coils of the first relay and the second relay; and in that the control coil of the second relay is coupled to electrical reference ground via a transistor; and in that an output of the processor is coupled to the transistor for controlling the second relay.

14. A brake control apparatus according to claim 13, wherein the control coil of the first relay is coupled to electrical reference ground via a transistor; and in that an output of the processor is coupled to the transistor for controlling the first relay.

15. A method of controlling an elevator brake, the method comprising: a) causing, responsive to a control signal from a safety circuit, a first switch to close for supplying power from power source to an electrically operated actuator of an elevator brake, b) measuring, by a first monitoring circuit, operation of the first switch, c) measuring, by a second monitoring circuit, operation of the first switch, d) comparing, by a computer, the measuring data received from the first monitoring circuit and the second monitoring circuit to a monitoring criteria, which is valid when a second switch is open.

16. The method according to claim 15, comprising: after step d), causing, by the computer, the second switch to close for supplying power from power source to an electrically operated actuator of an elevator brake, if the measuring data received from the first monitoring circuit and the second monitoring circuit fulfills the monitoring criteria.

17. The method according to claim 15, comprising: after step a) and before step b), causing, by a computer, a second switch to open for interrupting power supply from power source to an electrically operated actuator of an elevator brake.

18. The method according to claim 17, comprising: after causing the second switch to open, and before step b), further causing, responsive to a control signal from a safety circuit, a first switch to open for interrupting power supply from power source to an electrically operated actuator of an elevator brake.

19. The method according to claim 18, comprising: after step d), sending, by the computer, to the safety circuit a start permit signal when the operation data fulfills the monitoring criteria.

20. The method according to claim 15, comprising: after step d), indicating, by the computer, an operational anomaly if the measurement data does not fulfill the monitoring criteria.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In the following, the invention will be described in more detail by the aid of some examples of its embodiments, which in themselves do not limit the scope of application of the invention, with reference to the attached drawings, wherein

[0037] FIG. 1 shows a brake control apparatus according to an exemplary embodiment.

[0038] FIG. 2 shows an exemplary brake control sequence when starting a new elevator run.

[0039] FIG. 3 shows an exemplary brake control sequence in connection with normal stop of an elevator.

[0040] FIG. 4 shows an exemplary brake control sequence in connection with emergency stop of an elevator.

[0041] FIG. 5 shows a brake control apparatus according to a second exemplary embodiment.

[0042] FIG. 6 shows an exemplary brake control sequence in connection with normal stop of an elevator, according to a second exemplary embodiment.

MORE DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0043] For the sake of intelligibility, in FIGS. 1-6 only those features are represented which are deemed necessary for understanding the invention. Therefore, for instance, certain components/functions which are widely known to be present in corresponding art may not be represented.

[0044] In the description same references are always used for same items.

First Embodiment

[0045] FIG. 1 is a schematic of a main circuit of a brake control apparatus according to an exemplary embodiment. As is known, electromagnetic brakes are used in elevator systems for braking movement of elevator car or hoisting machine driving an elevator car, for example. Preferably two separate brakes are used to enhance safety, e.g. if one brake fails the other is still available for braking movement of the elevator car. The electromagnetic brake is opened by feeding sufficient amount of DC current to the magnetizing coil 5A, 5B, and the electromagnetic brake is applied by interrupting supply of current to the magnetizing coil 5A, 5B. The brake control apparatus of FIG. 1 has a current supply path for supplying current from AC power source 4 (e.g. mains) to magnetizing coils 5A, 5B of two electromagnetic elevator brakes. In some refinements, the brake control apparatus is supplied with one-phase alternating current (AC) system having phase conductor L and neutral conductor N coming from a supply transformer 4 connected to the mains. In some refinements, neutral conductor N is also earthed near the supply transformer 4 (protective earth).

[0046] The brake control apparatus comprises a first switch 1, a second switch 2 and a third switch 3. The first switch 1, the second switch 2 and the third switch 3 are low-cost relays having change-over switch configuration. They have their their inputs 1″, 2″, 3″ as well as first outputs 1″′, 2″′, 3″′ in the current supply path. Each relay has a two change-over switch configuration. The two change-over switches of each relay 1, 2, 3 are connected in series to improve current switch-off properties.

[0047] Instead of relays 1, 2, 3 also solid-state switches such as mosfet-transistors or igbt-transistors could be used. In some refinements a combination of relays and solid-state switches may be used.

[0048] The second relay 2 is connected in series with the first relay 1 for selectively supplying current from the mains 4 to the first magnetizing coil 5A. The third relay 3 is connected in series with the first relay 1 for selectively supplying current from the mains 4 to the second magnetizing coil 5B. A rectifier 37 is fitted to the current path to supply DC current to the magnetizing coils 5A, 5B. First relay 1 is fitted to AC side of the rectifier 37 and second and third relay 2, 3 and fitted to DC side of rectifier 37. As can be seen from FIG. 1, the second relay 2 and the third relay 3 may supply current to the magnetizing coils 5A, 5B independent of each other, such that both magnetizing coils 5A, 5B may be energized and de-energized separately and therefore the elevator brakes may be applied and opened independently. This is advantageous for example when testing braking force of the independent brakes by opening the brakes one at a time.

[0049] Further, the brake control apparatus comprises monitoring circuits 7, 8, 9 for indicating operation states (e.g. open/close states) of the change-over relays 1, 2, 3. The first monitoring circuit 7 is coupled to the second output 1″″ of the first relay 1 and is configured to read voltage status (e.g. voltage on/voltage off) of the second output 1″″. The second monitoring circuit 8 is coupled to the second output 2″″ of the second switch 2 and is configured to read voltage status of the second output 2″″. The third monitoring circuit 9 is coupled to the second output 3″″ of the third relay 3 and is configured to read voltage status of the second output 3″″. Each monitoring circuit 7, 8, 9 comprises a resistor connected in series with an optocoupler to isolate the monitoring signal 14A, 14B, 14C from the mains 4. When the relay 1, 2, 3 opens or closes, voltage status in the corresponding second output 1″″, 2″″, 3″″ changes and opening/closing of the relay 1, 2, 3 can be read from the monitoring signal 14A, 14B, 14C.

[0050] Further, because of the advantageous topology of the brake control apparatus of FIG. 1, the second 8 and third 9 monitoring circuits may be used for monitoring operation of the first relay 1 when the second relay 2 and the third relay 3 are open. At the same time, the advantageous monitoring sequence also provides monitoring of second 2 and third 3 relays, by comparing results of second 8 and third monitoring 9 circuits when first relay 1 is operated. Therefore, a high level of safety may be achieved with the brake control apparatus of FIG. 1, even when ordinary low-cost relays 1, 2, 3 are used in current supply paths of the magnetizing coils 5A, 5B.

[0051] The brake control apparatus comprises a processor 10 and a memory 11 with a processor 10-implemented monitoring program stored therein. The main processor is preferably the main processor of the inverter of the elevator hoisting motor of the hoisting machine; however it may also be a separate component dedicated to brake control purpose. The processor 10 takes care of control and monitoring functions of the brake control apparatus. Monitoring signals 14A, 14B, 140 from the monitoring circuits 7, 8, 9 are connected to processor 10 inputs.

[0052] Control coil 1′ of the first relay 1 is coupled to an elevator safety circuit 6. Also control coils 2′, 3′ of second 2 and third 3 relay are coupled to the elevator safety circuit 6; in addition to this, control coils 2′, 3′ of second 2 and third 3 relay are coupled to electrical reference ground via transistors 15, 16. Transistors 15, 16 are further coupled to processor 10 outputs such that switching state of second 2 and third 3 relay may be controlled by the processor 10. In come refinements, the safety circuit 6 is implemented with electromechanical safety control components, such as safety contacts and safety relays/contactors. In some refinements, the safety circuit 6 comprises a microprocessor-based safety computer according to elevator safety regulations.

[0053] The processor 10 has also an output for selectively sending a start permit signal through a communication channel 13 to the safety circuit 6. The monitoring program comprises instructions for sending a start permit signal when the operation data received from the monitoring circuits 7, 8, 9 fulfills the monitoring criteria.

[0054] When the safety circuit 6 indicates that elevator is in safe state, current is supplied from a 24 V power supply to control coils 1′, 2′, 3′. A dangerous situation in elevator system is notified by interrupting power supply to control coils 1′, 2′, 3′. This has the effect that relays 1, 2, 3 open to interrupt current to the magnetization coils 5A, 5B of the elevator brakes. Consequently, elevator brakes are applied immediately and elevator car will be stopped. A dangerous o situation in elevator system may result, for example, if elevator shaft door opens to elevator shaft or elevator car arrives to end limit switch in elevator shaft.

[0055] The operation sequence of the brake control apparatus is disclosed hereinafter in details in connection with three different operating situations: normal elevator start, normal elevator stop and emergency stop of an elevator.

[0056] Normal Start

[0057] FIG. 2 shows an exemplary brake control sequence when normal elevator start is issued. In normal start, hoisting motor of elevator car is energized, elevator brakes are opened and elevator car starts a new elevator run according to service request from elevator passengers.

[0058] In step 18 of the brake control sequence, processor 10 receives an elevator run start request from elevator traffic controller.

[0059] In step 19, elevator safety circuit 6 determines that elevator safety is not endangered, and enables supply of current to control coils 1′, 2′, 3′.

[0060] In step 20, relay 1 closes, conducting mains 4 voltage further to inputs 2″, 3″ of second 2 and third 3 relays. If the relays 1, 2 and 3 are operating properly, the voltage status in the second outputs 1″″, 2″″, 3″″ changes as follows (on means that mains 4 voltage is present in the corresponding second output 1″″, 2″″, 3″″; off means that mains 4 voltage is not present in the corresponding second output 1″″, 2″″, 3″″):

[0061] 1″″: on.fwdarw.off

[0062] 2″″: off.fwdarw.on

[0063] 3″″: off.fwdarw.on.

[0064] In step 21, processor 10 reads the voltage statuses with the monitoring circuits 7, 8, 9. If voltage in all the second outputs 1″, 2″, 3″ changes as required, processor 10 concludes that the relays 1, 2, 3 operate properly. Then the processor 10 controls hoisting motor inverter to energize the hoisting motor. At the same time processor 10 controls transistors 15 and 16 to cause relays 2 and 3 close, thereby energizing the magnetizing coils 5A, 5B to open elevator brakes. After this the normal start sequence proceeds to step 22.

[0065] On the other hand, if processor determines that signal status of one or more of the second outputs 1″″, 2″″, 3″″ does not change as required, processor 10 determines a brake control failure and proceeds to step 23 wherein processor cancels elevator operation and sends a fault-indicating signal to safety circuit 6 via the communication channel 13 (or rejects sending of start permit signal).

[0066] In step 22, processor 10 reads the voltage statuses of the second outputs 2″″, 3″″ with the monitoring circuits 8 and 9. If voltage status in both second outputs changes from on to off, processor 10 concludes that the relays 2 and 3 operate properly and normal start may proceed (step 24). Otherwise processor 10 determines a brake control failure and proceeds to step 23 to cancel elevator start.

[0067] Normal Stop

[0068] FIG. 3 shows an exemplary brake control sequence when normal elevator stop is issued. In normal stop, hoisting motor of elevator car is de-energized and elevator brakes are applied as elevator car arrives to the destination floor.

[0069] In step 26, processor 10 receives an elevator normal stop request from elevator traffic controller.

[0070] In step 27, processor 10 controls transistors 15 and 16 to cause relays 2 and 3 open. When relays 2, 3 open, current of the magnetizing coils 5A, 5B commutates through the dissipation circuits 40, thereby de-energizing the magnetizing coils 5A, 5B to apply elevator brakes.

[0071] In step 28, processor 10 reads the voltage statuses of the second outputs 2″″, 3″″ with the monitoring circuits 8 and 9. If voltage status in both second outputs changes from off to on, processor 10 concludes that the relays 2 and 3 operate properly and normal stop may proceed to step 29. Otherwise processor 10 determines a brake control failure and proceeds to step 23 to indicate brake control failure and cancel further elevator operation.

[0072] In step 29, when brakes have been applied the safety circuit 6 interrupts current supply to control coils 1′, 2′, 3′, which has the effect that also relay 1 opens.

[0073] In step 30, processor 10 reads the voltage statuses in the second outputs 1″″, 2″″, 3″″ with the monitoring circuits 7, 8, 9. If voltage in all the second outputs 1″″, 2″″, 3″″ changes as follows:

[0074] 1″″: off.fwdarw.on

[0075] 2″″: on.fwdarw.off

[0076] 3″″: on.fwdarw.off,

[0077] processor 10 concludes that the relays 1, 2, 3 operate properly and sends a status signal via communication channel 13 to safety circuit 6 indicating that next elevator start is allowed (step 31). On the other hand, if processor determines that signal status of one or more of the second outputs 1″″, 2″″, 3″″ does not change as required, sequence proceeds to step 23 wherein processor 10 determines a brake control failure, cancels elevator operation and sends a fault-indicating signal to safety circuit 6 via the communication channel 13 (or rejects sending of start permit signal).

[0078] Emergency Stop

[0079] FIG. 4 shows an exemplary brake control sequence when emergency stop of an elevator is issued. In emergency stop situation, elevator brakes are applied as soon as possible for stopping movement of an elevator car. Hoisting motor is also de-energized, but only after certain brake control delay (appx. 150-200 ms) to make sure that elevator brakes have been applied and braking has started before motor torque is removed.

[0080] In step 32, processor 10 receives an elevator emergency stop request from safety circuit 6 via the communication channel 13.

[0081] In step 33, processor 10 controls transistors 15 and 16 to cause relays 2 and 3 open, thereby de-energizing the magnetizing coils 5A, 5B.

[0082] In step 34, processor 10 reads the voltage statuses of the second outputs 2″″, 3″″ with the monitoring circuits 8 and 9. If voltage status in both second outputs 2″″, 3″″ changes from off to on, processor 10 concludes that the relays 2 and 3 operate properly, and sequence proceeds to step 35. Otherwise processor 10 determines a brake control failure and proceeds to step 23 to indicate brake control failure and cancel elevator operation.

[0083] In step 35, after the brake control delay, when brakes have been applied the safety circuit 6 interrupts current supply to control coils 1′, 2′, 3′, which has the effect that also relay 1 opens. Processor 10 reads the voltage statuses in the second outputs 1″″, 2″″, 3″″ with the monitoring circuits 7, 8, 9. If voltage in all the second outputs 1″″, 2″″, 3″″ changes as follows:

[0084] 1″″: off.fwdarw.on

[0085] 2″″: on.fwdarw.off

[0086] 3″″: on.fwdarw.off,

[0087] processor 10 concludes that the relays 1, 2, 3 operate properly and sends a start permit signal via communication channel 13 to safety circuit 6 indicating that next elevator start is allowed (step 36). On the other hand, if processor determines that signal status of one or more of the second outputs 1″″, 2″″, 3″″ does not change as required, sequence proceeds to step 23 wherein processor 10 determines a brake control failure, cancels elevator operation and sends a fault-indicating signal to safety circuit 6 via a communication channel 13 (or rejects sending of start permit signal).

Second Embodiment

[0088] FIG. 5 shows a brake control apparatus according to second exemplary embodiment. In the second embodiment, in connection with normal elevator stop, relay 1 is opened first while relays 2 and 3 are kept closed. This has the effect that magnetizing coil 5A, 5B current commutates through diode rectifier 37 instead of dissipation circuits 40, causing magnetizing coil current to decrease with a lower decrease rate. Therefore movement of brake armature is slower and noise level when brake armature engages the hoisting machinery is very low, e.g. the brake is more silent.

[0089] Monitoring of relays 1, 2, and 3 differs from first embodiment such that in second embodiment operation of relay 1 is monitored in normal stop situation but not in normal start situation. Further, operation of second 2 and third 3 relays is monitored in normal start situation. During emergency stop all relays 1, 2, 3 are monitored as in the first embodiment.

[0090] FIG. 5 is a schematic of a main circuit of a brake control apparatus according to a second embodiment. The brake control apparatus of FIG. 5 differs from that of FIG. 1 in such a way that also control coil 1′ of the first relay 1 is coupled to the electrical reference ground via a transistor 17, in the same way as control coils 2′, 3′. Transistor 17 is also coupled to processor 10 output such that switching state of first relay may be controlled by the processor 10.

[0091] The operation sequence of the brake control apparatus according to second embodiment is disclosed hereinafter in details in connection with three different operating situations: normal elevator start, normal elevator stop and emergency stop of an elevator. Because of similarities, normal start is disclosed in connection with same FIG. 2 and emergency stop is disclosed in connection with same FIG. 4 as in the first embodiment above. FIG. 6 shows normal stop according to second embodiment.

[0092] Normal Start

[0093] Normal start according to second embodiment is disclosed in connection with FIG. 2.

[0094] In step 18 of the brake control sequence, processor 10 receives an elevator run start request from elevator traffic controller.

[0095] In step 19, elevator safety circuit 6 determines that elevator safety is not endangered, and enables supply of current to control coils 1′, 2′, 3′. Processor 10 has already turned on control signal of transistor 17 appx. 2 seconds after previous (successful) elevator stop. Therefore, in step 20, relay 1 closes, conducting mains 4 voltage further to inputs 2″, 3″ of second 2 and third 3 relays.

[0096] If the relays 1, 2 and 3 are operating properly, the voltage status in the second outputs 1″″, 2″″, 3″″ changes in the same way as in embodiment 1:

[0097] 1″″: on.fwdarw.off

[0098] 2″″: off.fwdarw.on

[0099] 3″″: off.fwdarw.on.

[0100] In step 21, processor 10 reads the voltage statuses with the monitoring circuits 7, 8, 9. If voltage in all the second outputs 1″, 2″, 3″ changes as required, processor 10 concludes that the relays 1, 2, 3 operate properly. Then the processor 10 controls hoisting motor inverter to energize the hoisting motor. At the same time processor 10 controls transistors 15 and 16 to cause relays 2 and 3 close, thereby energizing the magnetizing coils 5A, 5B to open elevator brakes. After this the normal start sequence proceeds to step 22.

[0101] On the other hand, if processor determines that signal status of one or more of the second outputs 1″″, 2″″, 3″″ does not change as required, processor 10 determines a brake control failure and proceeds to step 23 wherein processor cancels elevator operation and sends a fault-indicating signal to safety circuit 6 via the communication channel 13 (or rejects sending of start permit signal).

[0102] In step 22, processor 10 reads the voltage statuses of the second outputs 2″″, 3″″ with the monitoring circuits 8 and 9. If voltage status in both second outputs changes from on to off, processor 10 concludes that the relays 2 and 3 operate properly and normal start may proceed (step 24). Otherwise processor 10 determines a brake control failure and proceeds to step 23 to cancel elevator start.

[0103] Normal Stop

[0104] Normal stop according to second embodiment is disclosed in connection with FIG. 6.

[0105] In step 50, processor 10 receives an elevator normal stop request from elevator traffic controller.

[0106] In step 51, processor 10 controls transistor 17 to cause relay 1 open. At the same time, processor 10 controls transistors 15 and 16 to keep relays 2 and 3 closed. When relay 1 opens, current of the magnetizing coils 5A, 5B commutates through the diode (full) bridge rectifier 37, thereby de-energizing the magnetizing coils 5A, 5B to apply elevator brakes in a silent manner.

[0107] In step 52, processor 10 reads the voltage status of the first output 1″″ with the monitoring circuit 7. If voltage status in first output 1″″ changes from on to off, processor 10 concludes that the relay 1 operates properly and normal stop may proceed to step 53. Otherwise processor 10 determines a brake control failure and proceeds to step 23 to indicate brake control failure and cancel further elevator operation.

[0108] In step 53, processor 10 controls transistors 15 and 16 to open relays 2 and 3, after a given time delay has passed from opening of relay 1. The given time delay may be for example 150 . . . 200 milliseconds and the purpose of it is to wait until magnetizing coil 5A, 5B currents have vanished and brakes have been applied before opening relays 2 and 3.

[0109] In step 54, when brakes have been applied the safety circuit 6 interrupts current supply to control coils 1′, 2′, 3′ to turn the elevator into safe state. In the safe state, brake control by means of processor 10 is blocked.

[0110] Emergency Stop

[0111] Emergency stop according to second embodiment is disclosed in connection with FIG. 4.

[0112] In step 32, processor 10 receives an elevator emergency stop request from safety circuit 6 via the communication channel 13.

[0113] In step 33, processor 10 controls transistors 15 and 16 to cause relays 2 and 3 open, thereby de-energizing the magnetizing coils 5A, 5B.

[0114] In step 34, processor 10 reads the voltage statuses of the second outputs 2″″, 3″″ with the monitoring circuits 8 and 9. If voltage status in both second outputs 2″″, 3″″ changes from off to on, processor 10 concludes that the relays 2 and 3 operate properly, and sequence proceeds to step 35. Otherwise processor 10 determines a brake control failure and proceeds to step 23 to indicate brake control failure and cancel elevator operation.

[0115] In step 35, after the brake control delay, when brakes have been applied the safety circuit 6 interrupts current supply to control coils 1′, 2′, 3′, which has the effect that also relay 1 opens. Processor 10 reads the voltage statuses in the second outputs 1″″, 2″″, 3″″ with the monitoring circuits 7, 8, 9. If voltage in all the second outputs 1″″, 2″″, 3″″ changes as follows:

[0116] 1″″: off.fwdarw.on

[0117] 2″″: on.fwdarw.off

[0118] 3″″: on.fwdarw.off,

[0119] processor 10 concludes that the relays 1, 2, 3 operate properly and sends a start permit signal via communication channel 13 to safety circuit 6 indicating that next elevator start is allowed (step 36). Processor 10 also keeps transistor 17 closed. On the other hand, if processor determines that signal status of one or more of the second outputs 1″″, 2″″, 3″″ does not change as required, sequence proceeds to step 23 wherein processor 10 determines a brake control failure, cancels elevator operation and sends a fault-indicating signal to safety circuit 6 via a communication channel 13 (or rejects sending of start permit signal).

[0120] It is obvious to a skilled person that the above-disclosed brake control apparatus may be used to control a brake of an escalator or a conveyor also.

[0121] The invention is described above by the aid of exemplary embodiments. It is obvious to a person skilled in the art that the invention is not limited to the embodiments described above and many other applications are possible within the scope of the inventive concept defined by the claims.