An arrangement for operating an elevator

Abstract

Modern elevators with position dependent maximum allowed speed adjust the travelling according to the location in the elevator shaft (100). When the elevator car (102) is closer to the bottom or the top of the elevator shaft (100) the travelling speed is reduced so that in case of accident the impact force to the safety buffers (116) is reduced. The disclosed arrangement comprises a mechanism that limits the travelling speed of the elevator when the position information is not received so that the elevator can still be operated.

Description

DESCRIPTION OF BACKGROUND

[0001] The following disclosure relates to elevators and particularly to monitoring safety features of an elevator.

[0002] Modern buildings typically have elevators for moving people and other physical objects. Elevators comprise a hoisting machine to which elevator cars are connected to using hoisting ropes. The hoisting ropes run via a traction sheave of the hoisting machine. The hoisting machine moves the connected elevator car and a counterweight so that passengers and transported objects are moved to a correct destination. The elevator car runs in a shaft that has safety buffers in an elevator shaft pit. The buffers are used to reduce the power of an impact in case that the elevator car for some reason would hit the bottom of the elevator shaft. A separate buffer may be provided for the counterweight.

[0003] The elevator also comprises hoisting machinery brakes. The hoisting machinery brakes can be opened or closed so that the brake reduces the speed of the elevator car. The movement by the hoisting machine and brakes is controlled by a controller that receives commands, for example, from control panels, calling devices or other systems and peripherals that have been connected to the elevator.

[0004] During the normal operation elevators may face abnormal situations that without appropriate safety measures could be dangerous to passengers. For this reason, in most countries, the necessary safety measures of elevators are regulated and controlled. It is common that an elevator has separate safety measures that are independent from the normal operation of the elevator. These safety measures commonly comprise one or more independent safety arrangements so that each of the safety arrangements is not disturbed by a failure in another one.

[0005] One component in safety arrangements is so called overspeed governor. This device monitors the speed of the elevator car and ensures it does not exceed a safe operational limit. Should the elevator begin to descend at an unsafe speed, the overspeed governor activates a safety gear mechanism that brings the elevator car to a controlled stop. Modern elevators may also be equipped with an electronic overspeed monitoring function, which may be position dependent so that the safe operational limit is dependent on the location of the elevator car. This monitoring requires reliable and precise feedback from an elevator car position system during an elevator run. If the position system fails or is missing for some reason, the position dependent overspeed monitoring function is not safe anymore. In that case elevator the service must be interrupted, which will increase elevator downtime.

[0006] Elevator downtime is particularly undesired in high rises where using stairs is not an option. Similarly, elevator downtime causes inconveniences in lower buildings and limits, for example, access of handicapped people. Thus, there is a continuous need for developing mechanisms that minimize the downtime while maintaining the elevator safe to operate.SUMMARY

[0007] In the following disclosure an arrangement for setting a speed limit in an elevator having a position dependent travelling speed is disclosed. Modern elevators with position dependent maximum allowed speed adjust the travelling according to the location in the elevator shaft. When the elevator closer to the bottom or the top of the elevator shaft the travelling speed is reduced so that in case of accident the impact force to the safety buffers is reduced. The disclosed arrangement comprises a mechanism that limits the travelling speed of the elevator when the position information is not received so that the elevator can still be operated.

[0008] In an aspect an elevator is disclosed. The elevator comprises an elevator car connected to a hoisting machine using hoisting ropes; an electronic overspeed governor configured to monitor the movement of the elevator car; at least one position measurement sensor configured to measure the position of the elevator car; wherein the electronic overspeed governor is configured to detect a failure in receiving the position of the elevator car from one or more of the at least one position sensors; and as a response to the detected failure the electronic overspeed governor is configured set a limited maximum allowed speed of the elevator car, wherein the limited maximum allowed speed is based on a predetermined maximum buffer impact speed. The benefit of the arrangement is that the elevator can be maintained in the operation instead of disabling the elevator while waiting for repairing. Setting the maximum allowed speed based on the maximum allowed impact speed keeps the elevator safe even when the position is not known.

[0009] In an example implementation the electronic overspeed governor is further configured to limit the speed by instructing the hoisting machine to reduce the speed and / or by activating breaks. It is beneficial to instruct the hoisting machine and / or brakes to reduce the speed of the elevator car so that the elevator can be maintained safe to operate.

[0010] In an example implementation the elevator comprises at least two position measurement sensors. It is beneficial to have at least two position measurement sensors so that the elevator may be used in ordinary mode while waiting for one sensor to be repaired or to improve the reliability so that the sensors can be compared with each other.

[0011] In an example implementation the electronic overspeed governor is further configured to: set the limited maximum allowed speed as a response to the detected failure in one or more of the at least two position sensors. It is beneficial to have a possibility to limit the operation if only one sensor is working as two sensors provide increased security.

[0012] In an example implementation the electronic overspeed governor is further configured to: set the limited maximum allowed speed as a response to the detected failure in all of the at least two position sensors. In that case it is still possible to operate the elevator so that in a possible accident the buffers are not hit too high speed.

[0013] In an example implementation as a response to the detected failure the elevator is further configured to: transmit a request for approving a limited maximum allowed speed of the elevator car to a maintenance person; receive an approval for the transmitted request; and limit the limited maximum allowed speed in accordance with the received approval. It is beneficial to request an approval from the maintenance so that a responsibility for continued operating can be proven and also the speed of operation has been verified to be safe by a person.

[0014] In an example implementation the elevator further comprises a controller that comprises two processors and is configured to: receive an input signal at both of the processors; determine if both of the processors indicate automatic operation at the limited maximum allowed speed; and as a response to both of the processors indicating automatic operation at a limited maximum allowed speed, allow the automatic operation at a limited speed in accordance with the limited maximum allowed speed. It is beneficial to have two redundant processors connected to respective position sensors so that redundant information can be received and malfunctioning of one sensor can be detected from deviating values.

[0015] In an example implementation the electronic overspeed governor is further configured to: transmit a notification of a failure to a maintenance person. It is beneficial to transmit a notification to a maintenance person while keeping the elevator still in operation. The maintenance person may schedule a maintenance break for the elevator so that the operation is not unnecessarily discontinued.

[0016] In an example implementation the electronic overspeed governor is, when controlling the limited maximum allowed speed, further to: receive the current speed value from two different channels. It is beneficial to receive the speed value from two different channels so that they are not dependent on each other and one fault does not affect to the whole system.

[0017] In an example implementation the electronic overspeed governor is, as a response to the detected failure, further configured to stop the elevator car; and continue operating the elevator car in accordance with the limited maximum allowed speed. It is beneficial to stop the elevator car so that it can be assumed that the elevator car hasn't traveled to a dangerous location while traveling at a higher speed than the limited maximum allowed speed during the breaking sequence.

[0018] In an aspect a method for controlling an elevator is disclosed. The method comprises detecting a failure in receiving the position of the elevator car; and as a response to the detected failure, limiting the maximum allowed speed of the elevator car. The benefit of the method is that the elevator can be maintained in the operation instead of disabling the elevator while waiting for repairing.

[0019] In an example implementation the limited maximum allowed speed is a predetermined maximum buffer impact speed. Setting the maximum allowed speed as a maximum allowed impact speed to be the same with the maximum buffer impact speed keeps the elevator safe even when the position is not known.

[0020] In an example implementation the limiting further comprises: transmitting a request for approving a limited maximum allowed speed of the elevator car to a maintenance person; receiving an approval for the transmitted request; and limiting the maximum allowed speed in accordance with the received approval. It is beneficial to request an approval from the maintenance so that a responsibility for continued operating can be proven and also the speed of operation has been verified to be safe by a person.

[0021] In an example implementation the method further comprises: transmitting a notification of a failure to a maintenance person. It is beneficial to transmit a notification to a maintenance person while keeping the elevator still in operation. The maintenance person may schedule a maintenance break for the elevator so that the operation is not unnecessarily discontinued.

[0022] In an example implementation the method further comprises: approving, by a maintenance person, switching back to ordinary operation speed. It is beneficial to allow a maintenance person to finally approve that the elevator is again safe for ordinary operation.

[0023] The aspects and example implementations described in the above provide a possibility to maintain the elevator in operation when the position of the elevator cannot be received or acquired. This is particularly beneficial in high rise buildings, where people flows involve large number of passengers and the elevator system is crucial for the building owner. High rise buildings are very expensive and unnecessary downtime in elevators reduces the user experience and may cause additional expenses while the people flow is not fluent.BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings, which are included to provide a further understanding of the arrangement for operating an elevator and constitute a part of this specification, illustrate embodiments and together with the description help to explain the principles of the arrangement for operating an elevator . In the drawings: Fig. 1 is a block diagram of an example embodiment of the arrangement for operating an elevator, Fig. 2 is a flow chart of an example of a method of operating an elevator, Fig. 3 is a flow chart of an example of a method of operating an elevator, Fig. 4 is a flow chart of an example of a method of operating an elevator, and Fig. 5 is a block diagram of an example implementation of a controller. DETAILED DESCRIPTION

[0025] Reference will now be made in detail to the embodiments, examples of which are illustrated in the accompanying drawings.

[0026] In figure 1 a block diagram of an example embodiment of the arrangement for operating an elevator is disclosed. In the figure an example of an elevator is shown. In the example of figure 1 only one elevator is shown, however, particularly in high rise buildings there are typically a plurality of elevators in an elevator group and some of the services may be shared with other elevators. For example, elevator journeys may be scheduled using the knowledge of other elevators and scheduled calls and journeys. The elevator of the example comprises an elevator shaft 100, wherein an elevator car 102 runs up and down. The elevator car 102 is connected to a hoisting arrangement 104 using one or more ropes 106. The ropes are also connected to a counterweight 108. The counterweight runs into the opposite direction with the elevator car?. The ropes are arranged to run through one or more sheaves.

[0027] The hoisting arrangement 104 is illustrated here in the top of the shaft 100, however, this is only for illustrative reasons. The hoisting machine and other components illustrated in the figure may be located in different locations, which depending on the component, may be located in the shaft or outside the shaft. In very traditional elevators the hoisting machine and machine room were located on the top of the shaft 100, however, in modern elevators separate machine rooms are not needed and hoisting may be arranged also from the bottom of the shaft by arranging the ropes appropriately.

[0028] In the bottom of the shaft the example of figure 1 comprises two safety buffers 116 that are provided separately for the elevator car 102 and the counterweight 108. The buffers are designed to reduce the impact in case of unintentional crash of the elevator car against the bottom of the elevator shaft. The maximum allowed speed for a safe impact can be determined. Using the maximum allowed speed, or a lower speed, when operating elevator near the elevator shaft end, facilitates safe stopping even in case of the rare event that the elevator does not stop at the bottom floor but travels further to the elevator shaft pit, or similarly, travels above the top floor.

[0029] In the example of figure 1 the hoisting arrangement 104 comprises additionally a controller 110 and a position measurement sensor 112. The controller of figure 1 is configured to control all movements of the elevator. It is possible that the controller controls also other things, such as lighting and door opening. The controller is configured to receive information from elevator peripherals and processes the received information so that the passengers can be brought to their destination. In figure 1 the position measurement sensor 112 is used for position dependent travelling speed management and overspeed governing. The position measurement sensor needs not to be of any specific type, however, it needs to capable of indication the position of the elevator car in the elevator shaft. The elevator comprises also an electronic overspeed governor that 114 that is used for preventing the elevator car travelling too fast. The overspeed governor is typically an independent device so that it is not controlled by the controller that is controlling common functionality of the elevator. This is because it is desired to have an independent overspeed governor that will be operable also in the case, wherein the controller fails somehow. The overspeed governor may be implemented in several ways and in the following it will be explained how the present arrangement for operating an elevator may be implemented using information received from the electronic overspeed governor 114 that can send instructions to controller 110, or other similar controller controlling the operating speed of the elevator car. In an alternative embodiment the overspeed governor does not need to communicate with the controller controlling the common functionality. The principles of the present embodiments could be applied also to an implementation without a traditional overspeed governor, however, an alternative arrangement for preventing overspeed in a position-based variable speed elevator must be used in that case.

[0030] As explained in the above, the elevator comprises a position measurement sensor 112. The position measurement sensor 112 is capable of indicating the position of the elevator car 102 in the elevator shaft 100. The position measurement sensor can be implemented in several ways. For example, the sensor may be electro-mechanical sensor or optical sensor. The elevator has been determined to have a maximum allowed speed as a function of a distance to the buffers 116 at the bottom of the elevator shaft and accordingly to the top of the elevator shaft. The shaft may be designed so that the counterweight hits buffers before the elevator car hits the top of the shaft. The buffers have a maximum impact speed, however, when the elevator car is far away from the buffers, it is possible to allow faster speed for the elevator car 102. In the event of possible emergency, the speed of the elevator car 102 can be reduced using the hoisting machine 104 or by using a braking mechanism before the elevator car 102 hits the buffers 116. This is particularly beneficial in high buildings, wherein faster elevator speeds are desired. The variable speed limit facilitates driving elevators faster when they are not near a shaft end.

[0031] In figure 2 a flow chart of an example of a method of operating an elevator is disclosed. In the figure the basic principles of the present arrangement are explained. During the method of the elevator maybe in ordinary use. Instead of ordinary use the elevator may also be in restricted use, for example, during the construction of the elevator.

[0032] First, an electronic overspeed governor, controller or other similar component of the elevator detects a failure in receiving the position of the elevator car from one or more of the at least one position sensors. The failure may be caused by several reasons. Typically the sensors are electro-mechanical devices that may wear in the use. Furthermore, it is possible that dust or other dirt in the elevator shaft may cause malfunctioning. In some cases it is possible that software is involved in position measuring. It is possible that the software has bugs or the arrangement is under a cyber-attack. For the arrangement the reason why the position sensor does not transmit a position information or transmits clearly incorrect information is not important as all reasons for incorrect information may be equally dangerous.

[0033] If the elevator comprises more than one position sensor, it can be decided if a failure to receive from one of the position sensors is considered as a failure requiring an action. It is possible, for example, that the elevator comprises two position sensors and it has been decided that if one of the position sensors works, the elevator can be operated normally. In that case it is sufficient to send a notification to the maintenance so that they can come and check, and replace if needed, the position sensor. The failure can be detected in different ways. For example, the electronic overspeed governor or other controller may be configured to receive the position directly from the position sensor. If the electronic overspeed governor or a controller cannot receive it, there is a failure in a position sensor or in the connection between the controller and the position sensor. The electronic overspeed governor or other controller may also receive an acknowledgement from another controller, such as, an independent safety controller. The safety controller acknowledges the electronic overspeed governor or other similar controller that it cannot receive the position from a position sensor.

[0034] After a failure has been detected, the electronic overspeed governor or other controller limits the maximum allowed speed of the elevator car, step 210. The maximum allowed speed of the elevator car may be considered as a speed limit for the hoisting arrangement. The hoisting arrangement may not move the elevator faster than the speed limit. If the electronic overspeed governor detects that the elevator is running faster than the maximum allowed speed, the electronic overspeed governor reduces the speed. In some implementations the controller controlling moving the elevator car may receive instructions to reduce the speed from the electronic overspeed governor. If the controller does not reduce the speed, the electronic overspeed governor may use alternative ways, such as emergency braking, to stop the elevator car and bring it safely to a landing floor so that passengers can leave the elevator car.

[0035] In the example of figure 2 the limited maximum allowed speed, or the speed limit, is set so that the elevator can be operated safely even without knowledge of the position of the elevator car. The limit may be set, for example, so that it equals the maximum safe speed that the buffers of the elevator can absorb. Naturally, it is also possible to use lower speed limits if it is considered that the speed limit based on buffers is too high. Accordingly, a higher speed can be used, if it can be determined to be safe in the rare event of hitting buffers. However, typically there is a maximum allowed hitting speed and that should not be exceeded when deciding limited maximum allowed speed.

[0036] In figure 3 a flow chart of an example of a method of operating an elevator is disclosed. In the method first a failure in receiving the position of the elevator car is detected, step 300. The failure may be a failure in receiving the position of the elevator car from one position sensor while a second position sensor is fully functional. The failure may also be a failure of receiving from both or all of the position sensors, in case there are more than two sensors.

[0037] In the example of figure 3 the electronic overspeed governor decides to limit maximum allowed speed of the elevator car, step 310, even when the failure is related to one of the position sensors in a two sensors configuration. This may be because of regulation or a decided so that the position is considered to be reliable only when at least two measurement results are the same or at least same enough for determining the position of the elevator car.

[0038] As a response to the detected failure the controller of the elevator, or any other component suitable for the purpose, sends or otherwise transmits a notification to the maintenance of the elevator, step 320. The maintenance crew knows that there is a problem with the position measurement, and they can decide to visit the elevator site with commonly needed spare parts. While waiting for the maintenance crew, the elevator is operated according to the speed limit. The speed limit is typically set so that it is about the maximum allowed speed, or less, allowed for safety buffer impact.

[0039] In the above it is explained that the speed limit is applied when one position sensors of a plurality of position sensors is not providing position information. In another example embodiment the same applies only when all of the position sensors are defect. In such example embodiment even one position sensor is trusted and the elevator can be operated at normal speeds while maintenance is informed and reparation is underway. In a configuration comprising more than two position sensor it is possible to decide that a measurement result from two, or any other number is sufficient. Additionally, it is possible to determine particular sensors that need to be functioning.

[0040] In figure 4 a flow chart of an example of a method of operating an elevator is disclosed. Again, the method is initiated by detecting a failure in receiving the position of the elevator from one, two or even more position sensors, step 400. It is possible, if the regulations allow, that the elevator has only one position sensor, however, in typical installations there are two.

[0041] As a response to the detected failure the elevator is stopped, step 410. Stopping in the context of the application means bringing the elevator into safety and letting the passengers out, preferably at the next possible floor. Further travelling is prevented. Thus, when position information is lost the elevator is appropriately slowed down and stopped typically at the first convenient floor. As the action is taken typically at the earliest convenience the arrangement is possible to estimate if the elevator needs to be stopped fast or in a gentle manner. For example, if the last known position is close to buffers or top of the shaft, the need for stopping is more urgent than in cases where the elevator car was far away from either of the elevator shaft ends.

[0042] After the elevator has been brought into safety, or even before, the elevator sends a request for approving limited speed operation, step 420. The request may have additional information, for example, about which position sensor is not currently providing position for the elevator. It is possible to transmit also additional information that is related to other elevator components and not to the position sensors as such. This may be beneficial as if the maintenance person visits the elevator, he / she can perform also other tasks requiring a visit at the elevator if that is considered useful.

[0043] As a response to the transmitted request, the elevator receives a response to the request, step 430. In the example of figure 4 the response is a speed limit verified by a maintenance person and an approval to operate the elevator according to the received speed limit. The maintenance person may set the speed limit and provide the approval either by visiting the site or remotely, depending on the capability of the elevator system and / or nature of the failure.

[0044] After receiving the approval, the elevator is operated according to the speed limit, step 440. The elevator is returned back to normal operation after a maintenance person has changed incorrectly functioning parts and allowed normal operation. Alternatively, the maintenance person may allow normal operation mode based on consideration that the elevator is safe to operate.

[0045] In the example of figure 4 the method comprises a request for approval after stopping the elevator. In an alternative embodiment the elevator continues operation according to a limited maximum allowed speed without requesting an approval. The alternative embodiment may transmit an information message about the current situation to the maintenance so that they are aware of the situation, however, also that is optional.

[0046] In Figure 5 a block diagram of an example implementation of a controller 500 controlling an elevator car is shown. In the implementation the controller comprises a first processor 502 and a first memory 504 and a second processor 506 and a second memory 508. The example comprises two independent processors and memories as it is common to have two redundant systems in order to increase the safety of the elevator. It is possible to implement the present arrangement also without two independent processors, position sensors and memories if the local regulations allow that. The processor 502 is coupled with an arrangement comprising a position sensor 510 and the processor 506 is coupled with an arrangement comprising a position sensor 512.

[0047] The position sensors 510 and 512 may be independent position sensors, or a part of an electronic position-based overspeed governor. The processors 502 and 506 are independent with regard electronic overspeed governors and cannot impact to functioning of electronic overspeed governors that are configured to prevent operating faster than a predetermined speed limit. The processors may be connected to position sensors 510 and 512 wirelessly or wiredly so that they can read the position of the elevator car. When the elevator has a position-based speed control the controller retrieves a speed limit corresponding with the position of the elevator car and instructs the hoisting machine to accelerate or decelerate the elevator car by taking the maximum allowable speed into account.

[0048] If one of the processors does not receive a position value, it may be considered as a fault and the controller will act as described in the above as an example of a method or a modification of an example of the method. The controller may comprise also additional processors for performing non-safety related activities and processors 502 and 506 may be used for additional tasks provided that the local regulations allow that.

[0049] The memories 504 and 508 comprise computer program code comprising instructions for performing a method as described in the above when the computer program is executed by a processor 502 and / or 506. The computer program may be embodied on a computer readable medium.

[0050] In the above examples of methods and required arrangements have been discussed. The person skilled in the art understands that these are only examples and is able to implement the arrangement also in various other ways provided that the elevator uses position dependent speed management, wherein a speed limit is set in case the position information is considered unreliable or is not received at all.

[0051] As stated above, the components of the exemplary implementations can include computer readable medium or memories for holding instructions programmed according to the teachings of the present inventions and for holding data structures, tables, records, and / or other data described herein. Computer readable medium can include any suitable medium that participates in providing instructions to a processor for execution. Common forms of computer-readable media can include, for example, a floppy disk, hard disk, magnetic tape, any other suitable magnetic medium, a CD-ROM, DVD, Blu-ray Disc, any other suitable optical medium, a RAM, a PROM, an EPROM, a FLASH-EPROM, any other suitable memory chip or cartridge, a carrier wave or any other suitable medium from which a computer can read.

[0052] It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the arrangement for operating an elevator may be implemented in various ways. The arrangement for operating an elevator and its implementations are thus not limited to the examples described above; instead they may vary within the scope of the claims.

Claims

1. An elevator comprising: an elevator car connected to a hoisting machine using hoisting ropes; an electronic overspeed governor configured to monitor the movement of the elevator car; at least one position measurement sensor configured to measure the position of the elevator car; wherein the electronic overspeed governor is configured to detect a failure in receiving the position of the elevator car from one or more of the at least one position sensors; and as a response to the detected failure the electronic overspeed governor is configured set a limited maximum allowed speed of the elevator car, wherein the limited maximum allowed speed is based on a predetermined maximum buffer impact speed.

2. An elevator according to claim 1, wherein the electronic overspeed governor is further configured to limit the speed by instructing the hoisting machine to reduce the speed and / or by activating breaks.

3. An elevator according to claim 1 or 2, wherein the elevator comprises at least two position measurement sensors.

4. An elevator according to claim 3, wherein the the electronic overspeed governor is further configured to: set the limited maximum allowed speed as a response to the detected failure in one or more of the at least two position sensors.

5. An elevator according to claim 3, wherein the the electronic overspeed governor is further configured to: set the limited maximum allowed speed as a response to the detected failure in all of the at least two position sensors.

6. An elevator according to any of preceding claims 1 - 5, wherein as a response to the detected failure the elevator is further configured to: transmit a request for approving a limited maximum allowed speed of the elevator car to a maintenance person; receive an approval for the transmitted request; and limit the limited maximum allowed speed in accordance with the received approval.

7. An elevator according to any of preceding claims 1 - 6, wherein the elevator further comprises a controller and the controller comprises two processors and is configured to: receive an input signal at both of the processors; determine if both of the processors indicate automatic operation at the limited maximum allowed speed; and as a response to both of the processors indicating automatic operation at a limited maximum allowed speed, allow the automatic operation at a limited speed in accordance with the limited maximum allowed speed.

8. An elevator according to any of preceding claims 1 - 7, wherein the electronic overspeed governor is further configured to: transmit a notification of a failure to a maintenance person.

9. An elevator according to any of preceding claims 1 - 8, wherein the electronic overspeed governor is, when controlling the limited maximum allowed speed, further to: receive the current speed value from two different channels.

10. An elevator according to any of preceding claims 1 - 9, wherein as a response to the detected failure the electronic overspeed governor is further configured to: stop the elevator car; and continue operating the elevator car in accordance with the limited maximum allowed speed.

11. A method for controlling an elevator comprising: detecting a failure in receiving the position of the elevator car; and as a response to the detected failure, limiting the maximum allowed speed of the elevator car.

12. A method according to claim 11, wherein the limited maximum allowed speed is a predetermined maximum buffer impact speed.

13. A method according to claim 11 or 12, wherein the limiting further comprises: transmitting a request for approving a limited maximum allowed speed of the elevator car to a maintenance person; receiving an approval for the transmitted request; and limiting the maximum allowed speed in accordance with the received approval.

14. A method according to any of preceding claims 11 - 13, wherein the method further comprises: transmitting a notification of a failure to a maintenance person.

15. A method according to any of preceding claims 11 - 14, wherein the method further comprises: approving, by a maintenance person, switching back to ordinary operation speed.

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