Patent Publication Number: US-2019193993-A1

Title: Management of power supply of an elevator system

Description:
TECHNICAL FIELD 
     The invention concerns in general the technical field of elevator systems. More particularly, the invention concerns management of power supply of an elevator system. 
     BACKGROUND 
     Nowadays elevator systems are heavily dependent on a supply of electricity in the system. For example, the elevator hoisting machines are electrical motors, which are operable by supplying electricity to the hoisting machine, and as a result the elevator car may be moved in an elevator shaft. Correspondingly, the machinery brakes of the elevator cars need electrical energy for operating as well as many other devices belonging to the elevator system. 
     In the elevator environment there may be a need to provide power to the elevator system from external sources. The reason for this kind of need may arise in various situations, for example if a power outage is faced in a building of the elevator system. In the worst case passengers of the elevators may get stuck in the elevator car because the power outage happens in a middle of a travel of the elevator car and the elevator car stops between landing floors. For that kind of situations, the elevator system may be equipped with external power storages from which the power may be obtained when needed. Moreover, in some situations serviceman may carry a power source, which may be coupled to the elevator system for supplying power, i.e. electricity, into it. As said the need for external power supply may originate in various reasons. 
     There is also brought out ideas to introduce robots to serve passengers in a use of elevators. For example, the robots may be arranged to roam in a building and provide the passengers an interface e.g. for providing elevator calls to the elevator system. The fundamental idea in this kind of approach is to enhance people flow in buildings and in that manner to improve utilization rate of elevators as well as to increase user satisfaction with the elevators. 
     Hence, the integration the robots into the elevator system provides new approaches also for supplying an electrical energy to the elevator system. 
     SUMMARY 
     The following presents a simplified summary in order to provide basic understanding of some aspects of various invention embodiments. The summary is not an extensive overview of the invention. It is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of exemplifying embodiments of the invention. 
     An objective of the invention is to present an elevator system and a method or transferring electrical energy between entities. Another objective of the invention is that the elevator system and the method enable an improved operation of the elevator system in various situations. 
     The objectives of the invention are reached by an elevator system and a method as defined by the respective independent claims. 
     According to a first aspect, an elevator system is provided, the elevator system comprising: an elevator entity, a mobile robot, wherein in response to a detection that the mobile robot shall provide electrical energy to the elevator entity the mobile robot is configured to: receive an instruction to provide electrical energy to the elevator entity; couple to a coupling station of the elevator entity; and provide electrical energy to the elevator entity via the coupling station of the elevator entity. 
     The elevator system may further comprise a data center communicatively coupled to at least one of the following: elevator entity, mobile robot. 
     The detection may be performed by one of the following: the elevator entity, the mobile robot, the data center. 
     Furthermore, the detection is based on an analysis by comparing a value derived from operational data relating to the elevator system to a reference value and by setting, in accordance with a comparison between the value and the reference value, a detection to express one of the following: (i) the mobile robot shall provide the electrical energy to the elevator entity, (ii) the mobile robot shall not provide the electrical energy to the elevator entity. The value compared to the reference value may represent an electrical characteristic of a drive circuit of a hoisting machine. 
     The mobile robot and the coupling station of the elevator entity may comprise interfaces to interact for providing electrical energy to the elevator entity from the mobile robot. The interface between the mobile robot and the coupling station of the elevator entity may be implemented by one of the following: galvanic coupling, inductive coupling. 
     The electrical energy provided to the elevator entity via the coupling station of the elevator entity may be arranged to be conveyed to a hoisting machine of an elevator car. The electrical energy may be conveyable to the hoisting machine via the drive circuit of the hoisting machine. Moreover, the elevator system may further comprise a wiring arranged in a traveling cable, the wiring being dedicated to transfer the electrical energy from the coupling station residing in the elevator car to the hoisting machine. Alternatively or in addition, the elevator system may further comprise a dedicated wiring in a wire bundle arranged in a shaft, the wiring being dedicated to transfer the electrical energy from the coupling station residing in a hall to the hoisting machine. 
     According to a second aspect, a method for an elevator system to transfer electrical energy is provided, the elevator system comprising: an elevator entity, and a mobile robot, the method comprises: detecting that the mobile robot shall provide electrical energy to the elevator entity; generating an instruction for the mobile robot to provide electrical energy to the elevator entity, coupling the mobile robot to a coupling station of the elevator entity, and providing electrical energy to the elevator entity via the coupling station of the elevator entity. 
     The expression “a number of” refers herein to any positive integer starting from one, e.g. to one, two, or three. 
     The expression “a plurality of” refers herein to any positive integer starting from two, e.g. to two, three, or four. 
     Various exemplifying and non-limiting embodiments of the invention both as to constructions and to methods of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplifying and non-limiting embodiments when read in connection with the accompanying drawings. 
     The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of unrecited features. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or “an”, i.e. a singular form, throughout this document does not exclude a plurality. 
    
    
     
       BRIEF DESCRIPTION OF FIGURES 
       The embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings. 
         FIG. 1  illustrates schematically an example of an elevator system in which the present invention may be implemented to. 
         FIG. 2  illustrates schematically a method according to an embodiment of the invention. 
         FIG. 3  illustrates schematically an example of a method step according to an embodiment of the invention. 
         FIGS. 4A and 4B  illustrate schematically non-limiting examples of an implementation of coupling station. 
         FIG. 5  illustrates schematically an embodiment of the mobile robot according to an embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE EXEMPLIFYING EMBODIMENTS 
     The specific examples provided in the description given below should not be construed as limiting the scope and/or the applicability of the appended claims. Lists and groups of examples provided in the description given below are not exhaustive unless otherwise explicitly stated. 
     The present invention relates at least in part to an elevator system comprising devices and entities of an elevator residing in a location where an elevator is operated. Additionally, the elevator system according to the present invention comprises a mobile robot configured to communicate with one or more other entities belonging to the elevator system. Furthermore, the elevator system may comprise a data center configured to communicate with one or more other entities belonging to the elevator system. 
       FIG. 1  schematically illustrates a non-limiting example of an elevator system in which the present invention may be implemented to. The elevator system may comprise an elevator entity  120  and a mobile robot  110 , which are configured to interact with each other. The interaction comprises at least communication between the entities over an applicable communication technology, but also coupling to each other for transferring electrical energy as will be described. Moreover, the elevator system may comprise a data center  130  wherein the data center  130  may be coupled to, e.g. communicatively, to at least one other entity of the elevator system. The communication between the data center  130  and the elevator entity  120  may be performed over a communication network  135 , such as Internet or mobile communication network as non-limiting examples. Specifically speaking the elevator entity  120  may comprise an elevator controller  122  which may be configured to operate as an interface for other entities, like the data center  130  and the mobile robot  110 . Moreover, the elevator entity  120  may comprise further devices  124 , such as any necessary devices for enabling an operation of the elevator. For example, the other elevator devices  124  may comprise at least one elevator car traveling in a shaft, hoisting means for moving the elevator car, safety related devices, control related devices as well as mechanical devices needed for moving the elevator car in the shaft, for example. Moreover, the other elevator devices  124  may comprise power related devices, which refers to devices and arrangements enabling power supply to the system, for example. The above given examples of the devices belonging to the elevator entity  120  is not comprehensive, but the purpose of the description above is to give at least some understanding of the elevator entity  120  belonging to the elevator system. The relevant devices and entities as regards to the present invention will be described in more detail later. 
     The mobile robot  110  shall in this context be understood as a machine capable of carrying out actions automatically in response to an input provided to the robot. Moreover, in this context the robot comprises means for enabling it to be mobile within the area it operates, such as in the location of the elevator. The means for enabling the mobility may refer to power generating means, such as an electric motor receiving its power from a battery located in the robot. The battery residing in the robot may advantageously be such that its energy density is high for storing electrical energy for the purpose of the present invention. Additionally, the mobile robot  110  may comprise means of transport, such as a drive shaft and a number of tyres, or similar, into which the power is brought from the electric motor. The means for enabling the mobility as described above is a non-limiting example and any means by means of which the robot may be mobile may be applied to. Moreover, the mobile robot  110  may comprise computing resources for controlling an operation of the robot. At least part of the controlling may be received from an external control device, which in the context of the present invention may refer to the elevator controller  122  or the data center  130 , or even a combination of these, or to some other entity, which may be configured to generate and transmit control signals to the mobile robot  110 . Moreover, the mobile robot  110  may comprise a communication interface though which the mobile robot may be communicatively coupled to the data center  130  or to the elevator controller  122  or both. According to some embodiment the mobile robot  110  may be configured to communicate with the data center  130  through the elevator controller  122 . The communication between the mobile robot  110  and the mentioned entities i.e. the data center  130  and/or the elevator controller  122  may e.g. be arranged through the communication network  135 , as already mentioned. Alternatively or in addition, the mobile robot  110  may be configured to communicate with at least one of the mentioned entities locally e.g. over a short range wireless communication technology. For example, the mobile robot  110  and the elevator controller  122  may be coupled to a local Wi-Fi network and the communication may be arranged over it. Still further, the mobile robot  110  may comprise a user interface for receiving input and outputting information. For giving an example of the input given to a robot may e.g. be an indication on a need to use the elevator, i.e. giving an elevator call through the mobile robot  110 , which indication may be signaled from the robot  110  to the elevator controller  122 . Alternatively or in addition, the input given to a robot may indicate another type of control request towards the elevator, such as requesting to control the door of the elevator (e.g. to open or to close). Moreover, the mobile robot  110  comprises an interface for coupling it to a power supply network of the elevator entity  120  so that electrical energy may be transferred to and from the mobile robot  110 . The transfer of electrical energy may be performed through a wireless power transfer or through a mechanical coupling by establishing a galvanic connection between the entities. The mechanical solution may rely on any type of plug-and-socket implementation, for example. 
     To describe at least some aspects of the present invention a method according to an embodiment of the invention is schematically illustrated in  FIG. 2 . At least one aim of the present invention is to enable optimization in transfer of electrical energy between the elevator entity  120  and the mobile robot  110 . Specifically, the present invention relates to a situation in which the mobile robot  110  is instructed to supply power to the elevator entity  120 . In the following method steps according to the embodiment of the present invention are described: 
     Regarding Step  210 : 
     Step  210  relates to a step in which a detection  210  is performed that the mobile robot  110  shall provide electrical energy to the elevator entity  120 . The detection  210  may be based on a number of rules defined for performing the detection. The detection may be performed by any of the entities belonging to the system, such as by the elevator entity  120  (e.g. in the elevator controller  122  therein), by the mobile robot  110 , by the data center  130 , or by any combination of these. The detection may e.g. be implemented so that the entity, or entities, configured to perform the detection  210  is arranged to obtain data, such as sensor data or any other data, from the elevator system, or any external entity, and to compare the data with one or more reference values obtainable by the entity in question. If these values deviate from each other over a predetermined amount, the entity may be configured to generate in indication that a detection is made that the mobile robot  110  shall provide electrical energy stored in a battery of the mobile robot  110  to the elevator entity  120 . 
     In an embodiment of the invention the detection may be performed by the elevator controller  122 . The detection  210  may e.g. be based on a measurement, or a derivation, of a value from operational data relating to the elevator system. The value may e.g. represent an electrical characteristic of a hoisting system, such as a voltage level in a drive circuit of the hoisting machine. The elevator controller may e.g. be configured to obtain the value representing the electrical characteristic, such as a voltage level, from a measurement circuit, compare the value to a reference value and in case the measured voltage level deviates from the reference value over a predetermined amount, an indication may be generated. For example, if the elevator entity  120  experiences a power outage, it may be detected in the described manner. The elevator controller, and any other necessary entities for performing the monitoring and the detection, may be equipped with a battery for performing the detection  210 , and a further communication, even if there is a power outage in the elevator entity  120 . 
     According to another embodiment the detection may be implemented so that the entities, such as the elevator entity  120  and the mobile robot  110  are configured to communicate with each other under a predetermined communication scheme. The communication scheme may e.g. be based on time, i.e. the entities may be arranged to communicate with each other regularly or irregularly under a time scheme, for example. For example, the entities may be configured to communicate so that a first entity, such as the mobile robot  110 , transmits so called polling signal to a second entity, such as to the elevator controller  122 , for checking a status of the second entity, and in normal operation the second entity may respond with a predetermined status value, for example. In case, the polling entity, such as the mobile robot  110 , does not receive the response, the mobile robot  110  may perform the detection  210  that it shall provide electrical energy stored in the battery of the mobile robot  110  to the elevator entity  120 . 
     A further example of the detection  210  may be that the data center  130  may be configured to monitor an operation of the elevator entity  120 . For example, it may be configured to receive data, such as operational data, from the elevator entity  120  under a predetermined communication scheme. If the data is not received the data center  130  may be configured to perform the detection  210 . Alternatively or in addition, there may be arranged a polling solution between the data center  130  and the elevator entity  120  in a similar manner as described above. In case the polling is not successful the detection  210  may be performed. 
     In some embodiment the data center  130 , or any other entity, may be configured to perform the detection  210  based on some external data. For example, the data center  130  may e.g. be configured to receive information on a market price of electricity from an external data source, and it may be configured to generate the detection  210  if the market price of the electricity exceeds a predetermined limit, and in that manner cause the mobile robot  110  to provide electrical energy to the elevator entity  120 . Moreover, the detection may be based to some other specific situation, such as there is need to switch off the power supply to the elevator entity  120  from a power grid, e.g. due to a maintenance work, and obtain the electrical energy from one or more mobile robots  110 . Thus, the data center  130 , or any similar external entity, may be configured to, based on at least one predefined rule, decide the direction in the provision of the electrical energy i.e. if the robot provides electrical energy to the elevator system or vice versa or prevent any transfer of electrical energy. The decision-making may e.g. be based on automatic or manual monitoring, or machine-learning methods applied herein. 
     In the implementation in which the data center  130  may perform the detection  210  the data center  130  may be configured to generate a signal to a mobile robot  110  as will be described. The communication path may be established directly between the data center  130  and the mobile robot  110  e.g. over a mobile communication network by arranging necessary means at both ends for communication. Similarly, the communication path may be established indirectly e.g. through the elevator controller  122 . 
     In still further embodiment the detection may be arranged so that the mobile robot  110  is configured to obtain information from an environment in which it is arranged to operate. For example, the mobile robot  110  may be configured to perform one or more measurements, e.g. with one or more sensors arranged in the mobile robot  110 , in the building, or in the location, and by analyzing the measurement data, e.g. by comparing it with reference data, to determine if the detection shall be made. Alternatively or in addition, the mobile robot  110  may obtain the measurement data from measurement devices residing in the location, for example, and perform the analysis accordingly. The data obtained by the mobile robot  110  may be any other than the measurement data. As already mentioned it may be received from the data center  130   
     Regarding Step  220 : 
     Next, in step  220  of  FIG. 2 , an entity, which has performed the detection  210  that the mobile robot  110  shall provide electrical energy stored in a battery of the mobile robot  110  to the elevator entity  120 , is configured to generate an instruction to the mobile robot  110  to perform accordingly. In other words, depending on the implementation the instruction may e.g. be generated by at least one of the following: the data center  130 , the elevator entity  120 , the mobile robot  110 . In case the entity is the elevator entity  120  it may e.g. be the elevator controller  122 , or any other device therein arranged to generate the instruction under certain circumstances. On the other hand, if the entity generating the instruction is the mobile robot  110  it refers to an internal logic in the mobile robot  110  as a result of which an internal instruction is generated for operating accordingly. 
     In the embodiment in which an external entity to the mobile robot  110 , such as the data center  130  or the elevator entity  120 , is configured to generate the instruction, the corresponding entity is configured to generate a signal carrying pre-defined data for indicating the mobile robot  110  that it shall provide electrical energy to the elevator entity  120 . In some embodiment, the pre-defined data may be a bit indicating the need for the provision of electrical energy. In some other embodiment the pre-defined data may be a code, such as an error code, which may be interpreted by the mobile robot  110  for determining the operational instructions i.e. the mobile robot  110  shall operate so that it may provide the electrical energy to the elevator entity  120 . 
     The mobile robot  110  may be configured to receive the instruction signal from an external entity over any communication technology the mobile robot  110  is configured to implement to. For example, the communication technology may e.g. be a mobile communication technology or Wi-Fi, for example. 
     Regarding Step  230 : 
     In response to a receipt of the instruction signal from an external entity, or through an internal creation of the instruction signal, the mobile robot  110  may be configured to initiate a procedure to couple to the elevator entity  120  for discharging the electrical energy thereto. A non-limiting example of the coupling step  230  is schematically illustrated in  FIG. 3 . According to the example, the mobile robot  110  may be configured to, in response to the receipt of the instruction  220 , to determine its position  310  in the location it operates to. The determination of the position  310  may be implemented with any applicable positioning technology. For example, an indoor positioning technology may be implemented in the location which is utilized by the mobile robot  110 , and the position of the mobile robot  110  may be derived therefrom. Additionally, the mobile robot  110  may be configured to determine one or more locations in which it may couple to the elevator entity  120 . The data indicating the locations may be stored in internal memory of the mobile robot  110  and the mobile robot  110  is configured to retrieve the information therefrom. Alternatively or in addition, the mobile robot  110  may be configured to inquiry the information from an external entity, such as from a server residing in the location and configured to provide such a functionality or even from the data center  130 . In case the information is inquired from an external entity it may be arranged that only those coupling locations are informed to the mobile robot  110 , which are not occupied e.g. by another mobile robot  110 . This kind of implementation may be achieved by implementing a database to store up-to-date information on the statuses of the coupling locations and the information may be obtained from the database. The mobile robot  110  may be configured to execute the steps  310  and  320  concurrently, at least in part, to determine the mentioned pieces of information. Next, in response to a determination of the position and the coupling locations available for the mobile robot  110  in question the mobile robot  110  may be configured to select a coupling location  330 . The selected coupling location may e.g. be the closest to the mobile robot  110  or it may be the one which is available at the time of the selection. Any further criteria may also be used for the selection. Advantageously, a limitation is defined for the coupling location to be selected that it is accessible for the mobile robot  110  in the location, such as a building, at the time the coupling is instructed. For example, the mobile robot  110  may reside in a certain floor and cannot enter to another floor e.g. due to outage of power which blocks a use of elevator in the building. Hence, only those coupling locations may be offered selectable, which reside on the same floor where the mobile robot  110  locates. The selection procedure may be implemented with a computer program product executing a selection algorithm when executed in a processing device. 
     Next, in the non-limiting example illustrated in  FIG. 3  the mobile robot  110  may be configured to generate a route  340  to the selected coupling location from its current location. For generating the route the mobile robot  110  may e.g. access to a floor plan stored in a memory and take into account any boundaries set by the floor plan in the generation of the route. The generation of the route may utilize any known route calculation algorithm, which may be applied in the described environment. 
     In step  350  the mobile robot  110  has reached the coupling location and is instructed exactly to such a position in the coupling location that an electrical coupling may be achieved to the elevator entity  120 . At least some examples of the coupling mechanisms will be discussed later. 
     Regarding Step  240 : 
     The final step according to an embodiment of the invention may be a provision of power  240 , that is the electrical energy from the mobile robot  110  to the elevator entity  120  in the coupling location. The provision of power  240  may be implemented so that in response to the coupling  230  the mobile robot  110  may generate a signal causing an output of electrical energy from an energy storage residing in the mobile robot  110 . For example, the signal may change a state of a switch causing the transfer of energy to the elevator entity  120 . 
     The provision of power to the elevator entity may at least refer to an implementation that the energy is provided to at least one elevator car, such as a battery therein. Alternatively or in addition, the power may be transferred to a battery being common to a plurality of elevator cars i.e. the battery belongs to the elevator entity and is configured to provide electrical energy to the elevator cars e.g. in case of power failure. 
     Next, some aspects of an interface between the mobile robot  110  and the elevator entity  120  are brought out with non-limiting examples as illustrated in  FIGS. 4A and 4B . The implementation as illustrated in  FIG. 4A  is based on a solution in which a galvanic connection may be established between the mobile robot  110  and the elevator entity  120 . Here, a coupling location is in a hall close to elevator door  410  of an elevator car  420 . The coupling location may comprise a coupling station comprising necessary devices and means for receiving electrical energy from a battery  430  of the mobile robot  110 . Among others, the coupling station may comprise an interface  440  to which the mobile robot  110  is configured to be coupled to. Thus, the mobile robot  110  may advantageously comprise an interface  450  for establishing a galvanic connection between the interfaces  440 ,  450 . As a result, the mobile robot  110  may provide at least a part of electrical energy stored in the battery  430  to the elevator entity  120  over the galvanic connection. The galvanic connection established with the interfaces  440 ,  450  is only a non-limiting example and the connection may be established in a plurality of ways. For example, a plug-and-socket type implementation may be used in which the mobile robot  110  is arranged to be driven to the coupling station so that the plug and socket get interconnected. For sake of clarity it is worthwhile to mention that the purpose of a rectangle referred with ‘A’ in  FIG. 4A  is to indicate an entity into which the electrical energy received from the mobile robot  110  is supplied to. 
       FIG. 4B , in turn, schematically illustrates an implementation according to an embodiment of the invention in which a coupling station  460  is arranged in an elevator car  420  and wherein the electrical energy is transferred over a wireless power transfer. In the disclosed embodiment the wireless power transfer is based on inductive coupling. The inductive coupling is based on an idea that the mobile robot  110  is configured to transfer the electrical energy from a battery  430  though arranging an alternating current (AC) to a transmitting coil  466 . The alternating current may be generated from a DC current stored in the battery  430  by arranging an oscillator  468  to change the current to AC for supplying it to the transmitting coil  466 . The coupling station  460  residing in the elevator car  420  comprises a receiving coil  462  for inducing an alternating current therein from the transmitting coil  466 . Depending on an implementation the coupling station may comprise further electronics, such as a rectifier  464  for transforming the induced alternating current back to DC, for supplying the electrical energy in an applicable form to the elevator entity  120 . In some embodiments, the induced AC may be directly supplied to the elevator entity  120 . In the disclosed manner the mobile robot  110  may transfer energy in a wireless manner to the elevator entity e.g. in a situation in which the mobile robot  110  is traveling in the elevator car  420  when a power outage occurs in the elevator entity  120 . The transfer of electrical energy to the elevator entity  120  may enable a drive of the elevator car  420  to a floor for allowing passengers to exit from the elevator car  420  in a safe manner. For sake of reason it is worthwhile to mention that the purpose of a rectangle referred with ‘A’ in  FIG. 4B  is to indicate an entity into which the electrical energy received from the mobile robot  110  is supplied to, such as a battery belonging to the elevator system. 
     In the description herein at least some aspects of the present invention are mainly described by introducing a utilization of galvanic and inductive coupling for the power transfer. However, the invention is not limited to these only, but any applicable technology for transferring the power may be applied to. For example, resonant inductive coupling as well as magnetodynamic coupling may be used, as examples of wireless power transfer. 
     In the non-limiting examples as illustrated in  FIGS. 4A and 4B  it is disclosed different locations for coupling stations. It is also clear that the location of the elevator may comprise one or more charging stations e.g. on different floors and in a plurality of elevator cars  420 . In  FIGS. 4A and 4B  it is illustrated entities into which the electrical energy is supplied to with rectangles referred with ‘A’. The entity may advantageously be a device generating mechanical or electrical power for moving the elevator car  420  in a shaft. Naturally, the device may be any other in the elevator entity  120 , which is considered to need the supplied electrical energy, or at least part of it. An example of such a device may be an elevator controller. When the device into which the electrical energy is to be supplied is a hoisting machine of the elevator car residing e.g. on top of the shaft the electrical energy may be supplied to a drive circuit controlling the hoisting machine. More specifically, the electrical energy may be supplied to an intermediate circuit of the drive circuit. The advantage of this kind of implementation is that the supplied electrical energy remains in the drive circuit and do not enter to power supply network of the whole building. The wiring through which the electrical energy is to be supplied to the drive circuit is dependent on the location of the coupling station. In case the coupling station resides in a hall it may be arranged that the electrical energy is transferred to the drive circuit over a dedicated wiring in a wire bundle e.g. arranged in the shaft. On the other hand, if the coupling station is implemented in an elevator car  420  the electrical energy may be transferred to the drive circuit through a dedicated wiring arranged in a traveling cable. In case the elevator car  420  carries the hoisting machine with it, such as a linear motor, the electrical energy may be directly fed to the device in question from the coupling station without conveying it away from the elevator car  420 . 
     For sake of clarity it may be mentioned that devices and means belonging to the coupling station, such as the ones illustrated in  FIGS. 4A and 4B , shall be considered to be included in the elevator devices  124  of  FIG. 1 . 
       FIG. 5  schematically illustrates an example of a mobile robot  110  belonging to an elevator system. The mobile robot  110  may comprise at least the following entities: processing unit  510 , memory unit  520 , communication unit  530 , user interface (UI) unit  540 , sensor unit  550  and motor unit  560 . The mentioned entities may comprise one or more operating units, e.g. one or more microprocessors or similar, one or more memories, one or more communication devices, such as modems, one or more user interface devices, one or more sensors and one or more motors. Additionally, the mobile robot  110  comprises a battery  430  for storing electrical energy and a coupling interface  450  comprising necessary elements for coupling the mobile robot  110  to a coupling station. The electrical energy stored in the battery  430  may also be used for operating the mobile robot  110  as well as to other purposes as described. The entities belonging to the mobile robot  110  may be communicatively coupled to each other with e.g. a communication bus. Additionally, the entities may be coupled to the battery  430  with a power supply network, for example. The processing unit  510  may be configured to control the operation of the mobile robot  110  as well as communication with any external entity, such as with a data center  130 , an elevator entity  120 , other mobile robots, or other entities. The communication may be performed e.g. in a wireless manner. The users of the elevator system may provide input through the user interface unit  540  with the mobile robot  110  and the mobile robot may, under control of the processing unit  510 , output information, such as prompting, to the user. The user interface unit  540  comprises I/O devices, such as buttons, keyboard, touch screen, microphone, loudspeaker, display and so on. The sensors may comprise any sensors by means of which the mobile robot  110  may obtain information on an environment, but also the sensor unit  550  may comprise sensors enabling positioning and/or navigation within the location. The processing unit  510  may also be configured to generate control signals to the motor unit  560  in order to make the mobile robot  110  to move. Moreover, the mobile robot  110  may comprise means enabling the mobile robot  110  to be mobile, such as the transport means as described earlier. The operation of the processing unit  510  may be achieved by executing portions of computer program code stored e.g. in the memory unit  520  for generating the control signals and, thus, causing the mobile robot  110  to operate in the manner as described. The memory unit  520  may also be used for storing obtained and received information together with any other data either permanently or temporarily. 
     In the above some non-limiting examples with respect to the present invention are disclosed. The elevator system according to an embodiment of the invention comprises an elevator entity  120  into which electrical energy is to be supplied from at least one mobile robot  110  in response to detecting a need for that. This is advantageous because the mobile robots  110  are regularly charged e.g. from the coupling station and they can be used for discharging the electrical energy back to the elevator entity  120  if needed. 
     A further embodiment of the present invention may comprise a feature that in case the detection is made that at least one mobile robot  110  shall provide the electrical energy to the elevator entity, the mobile robots  110  may be arranged to communicate with each other for determining which one of the robots stores the highest level of electrical energy in a battery  430 . In response to the determination the mobile robot  110  storing the highest amount of electrical energy may be instructed to couple to the coupling station for discharging the energy. 
     The specific examples provided in the description given above should not be construed as limiting the applicability and/or the interpretation of the appended claims. Lists and groups of examples provided in the description given above are not exhaustive unless otherwise explicitly stated.