WO2022229750A1

WO2022229750A1 - System for collecting litter in an urban area, corresponding method of operation and computer program product

Info

Publication number: WO2022229750A1
Application number: PCT/IB2022/053210
Authority: WO
Inventors: Andrea SALIOLA; Pier Paolo CECCARANELLI; Flavio CECCARELLI
Original assignee: Pixies S.R.L.
Priority date: 2021-04-27
Filing date: 2022-04-06
Publication date: 2022-11-03
Also published as: IT202100010655A1

Abstract

A system (1) for collecting litter in an urban area comprises a mobile robot (10) that includes litter- collecting means (14), a local control unit, and a respective GNSS receiver. The system further comprises an urban fixture (20), which includes a shelter (22), a central control unit, and a respective GNSS receiver, The central control unit is configured to calculate a position error of the GNSS system as a function of a known position of the urban fixture (20) and of the GNSS signals received thereby, and transmit a correction signal indicative of the position error of the GNSS system. The local control unit is configured to determine a current position of the robot (10) as a function of the GNSS signals received and of the correction signal received from the central control unit, and moving the robot as a function of the current position of the robot. The robot (10) further comprises a distance sensor configured to detect data comprising the distances of a set of points in a region of interest in the direction of movement of the robot, and the local control unit is configured to process the data detected by the distance sensors, during an operation of re-entry of the robot into the shelter, to produce data indicative of the position of an entrance to the shelter and move the robot during said operation of re-entry as a function of the current position of the robot and of the data indicative of the position of the entrance.

Description

"System for collecting litter in an urban area, corresponding method of operation and computer program product"

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TEXT OF THE DESCRIPTION

Technical field

The present description relates to systems for collection of litter in an urban area, of the type comprising a robot that moves autonomously in the urban area for collecting litter and periodically returns to a sheltering and electrical-charging station ("hub").

Technological background

Known in the art are systems for cleaning domestic environments (mainly dwellings) that comprise a robot capable of moving autonomously in the domestic environment while carrying out a cleaning operation (for example, sweeping the floor) and returning periodically to an electrical-charging point to recharge its battery.

In some known systems of simple conception, the robot moves around in the domestic environment, proceeding in substantially random directions and varying its own direction of movement when it encounters an obstacle that prevents its movement in the current direction. In other more sophisticated known systems, the robot is able to store a map of the domestic environment following upon a configuration step and determine one or more paths that cover the entire extension of the domestic environment.

Litter-collection systems have been proposed for use in urban areas (for example, squares, public gardens and parks, pedestrian areas, etc.) based on an architecture similar to the one implemented in known systems for domestic use. In such systems for urban use, the robot moves autonomously in the urban environment while collecting litter from the road surface, and periodically returns to a charging station to charge its batteries. The charging station also provides a shelter to protect the robot from external agents (for example, adverse weather conditions).

Due to the greater complexity of urban environments as compared to domestic environments (due, for example, to the variable degree of crowding of the urban environment or to the presence of numerous objects), navigation of an autonomous robot in the urban environment requires a more accurate and sophisticated navigation system as compared to navigation systems implemented in domestic devices.

In the present description, the term "navigation" is used in the wider sense of "determining the position and a path of displacement", that can also be applied to terrestrial navigation.

Object and summary

In view of the above, autonomous robots for the collection of litter in urban environments comprising advanced navigation systems are desirable.

An object of one or more embodiments is to provide a system for collecting litter in which an autonomous mobile robot co-operates with a sheltering and battery charging station to navigate and move in an accurate way in an urban area.

According to one or more embodiments, such an object may be achieved by a system for collecting litter having the features set forth in the claims that follow. In brief, the system comprises an autonomous mobile robot for collecting litter and an urban fixture that functions as sheltering and charging station for the mobile robot. The robot and the station exchange radio signals to facilitate navigation of the autonomous robot in the urban area.

One or more embodiments may refer to a corresponding method of operating the system.

One or more embodiments may refer to a corresponding computer program product that can be loaded into the memory of at least one processing circuit (e.g., a control unit of the autonomous robot and/or a control unit of the station) and comprises portions of software code for executing the steps of the method when the product is run on the at least one processing circuit. As used herein, reference to such a computer program product is understood as being equivalent to reference to a computer-readable medium containing instructions for controlling the processing system in order to co ordinate implementation of the method according to one or more embodiments. Reference to "at least one" processing circuit is understood as highlighting the possibility of one or more embodiments being implemented in modular and/or distributed form: for example, one or more embodiments may envisage interaction between a control unit of the autonomous robot and a control unit of the station, where part of the processing is carried out by the autonomous robot and part of the processing is carried out by the station.

The claims form an integral part of the technical teaching provided herein in relation to the embodiments.

In brief, one or more embodiments refer to a system for collecting litter in an urban area. In various embodiments, the system comprises a mobile robot including means for autonomous movement, means for collecting litter, a local electronic control unit, and a respective GNSS receiver configured to receive radio signals from a global positioning satellite system. The system further comprises an urban fixture including a shelter accessible to the mobile robot, a central electronic control unit, and a respective GNSS receiver configured to receive radio signals from the global positioning satellite system. The central electronic control unit is configured to calculate a position error of the global positioning satellite system as a function of a known position of the urban fixture and of the radio signals received from the global positioning satellite system, and transmit a correction signal indicative of the position error of the global positioning satellite system. The local electronic control unit is configured to determine a current position of the mobile robot as a function of the radio signals received from the global positioning satellite system and of the correction signal received from the central electronic control unit, and moving the mobile robot along at least one litter-collection path defined in the urban area as a function of the current position of the mobile robot, operating the means for collecting litter during the displacement of the mobile robot along the at least one litter-collection path. The mobile robot further comprises a distance sensor configured to detect data that include the distances of a set of points in a region of interest in the direction of movement of the mobile robot. The local electronic control unit is further configured to process the data detected by the distance sensors, during a re-entry operation of the mobile robot to the shelter, in order to produce data indicative of the position of an entrance to the shelter, and move the mobile robot during the re-entry operation as a function of the current position of the mobile robot and of the data indicative of the position of the entrance to the shelter.

In one or more preferred embodiments, the local electronic control unit and/or the central electronic control unit include/includes a memory configured to store data indicative of the at least one litter- collection path defined in the urban area.

In one or more preferred embodiments, the central electronic control unit is configured to impart to the mobile robot commands for exit from the shelter and/or re-entry to the shelter as a function of a weather condition detected in the urban area and/or as a function of a detected condition of crowding of the urban area.

In one or more preferred embodiments, the entrance to the shelter comprises an automated door, and the central electronic control unit is configured to open the automated door in response to the fact that the mobile robot carries out the re-entry operation and is located within a limit distance from the urban fixture.

In one or more preferred embodiments, the local electronic control unit is configured to process the data detected by the distance sensor during the displacement of the mobile robot along the litter- collection path in order to detect obstacles along the litter-collection path, and divert the mobile robot from the litter-collection path in response to the fact that an obstacle is detected.

In one or more preferred embodiments, the urban fixture includes a bench, and the shelter is positioned underneath the sitting surface of the bench.

In one or more preferred embodiments, the GNSS receivers receive radio signals from at least one global positioning satellite system selected from among the Global Positioning System (GPS), the Galileo system, the Global Navigation Satellite System (GLONASS), the BeiDou Navigation Satellite System (BDS), and the Indian Regional Navigation Satellite System (IRNSS).

In one or more preferred embodiments, the distance sensor comprises a stereoscopic-image sensor and/or a LIDAR (Light Detection And Ranging) sensor.

In one or more preferred embodiments, the urban fixture comprises an electrical-charging device for charging a battery of the mobile robot when the mobile robot is sheltered inside the shelter.

In one or more preferred embodiments, the urban fixture is configured to connect to an electric power mains and/or comprises a photovoltaic panel.

One or more embodiments refer to a method for controlling a system for collecting litter in an urban area according to one or more embodiments. The method comprises:

- calculating a position error of the global positioning satellite system as a function of a known position of the urban fixture and of the radio signals received from the global positioning satellite system;

- transmitting via radio a correction signal indicative of the position error of the global positioning satellite system;

- determining a current position of the mobile robot as a function of the radio signals received from the global positioning satellite system and of the correction signal received from the central electronic control unit;

- moving the mobile robot along at least one litter- collection path defined in the urban area as a function of the current position of the mobile robot, operating the means for collecting litter during displacement of the mobile robot along the at least one litter-collection path;

- processing the data collected by the distance sensor, during a re-entry operation of the mobile robot to the shelter, to produce data indicative of the position of an entrance to the shelter; and

- moving the mobile robot during the re-entry operation as a function of the current position of the mobile robot and of the data indicative of the position of the entrance to the shelter.

Brief description of the drawings

Various embodiments will now be described, purely by way of example, with reference to the annexed drawings, wherein:

- Figure 1 is a view exemplary of a system for collecting litter in an urban area according to one or more embodiments of the present description; and

- Figure 2 is a circuit block diagram exemplary of the electronics of a system according to one or more embodiments of the present description.

Detailed description

In the ensuing description one or more specific details are illustrated, aimed at enabling an in-depth understanding of examples of embodiments of the present disclosure. The embodiments may be obtained without one or more of the specific details, or with other methods, components, materials, etc. In other cases, known structures, materials, or operations are not illustrated or described in detail so that certain aspects of the embodiments will not be obscured.

Reference to "an embodiment" or "one embodiment" in the context of the present description is intended to indicate that a particular configuration, structure, or characteristic described in relation to the embodiment is comprised in at least one embodiment. Consequently, phrases such as "in an embodiment" or "in one embodiment" that may be present in one or more points of the present description do not necessarily refer to one and the same embodiment. Moreover, particular conformations, structures, or characteristics may be combined in any adequate way in one or more embodiments.

In all the figures annexed herein, unless the context indicates otherwise, similar parts or elements are designated by the same references/numbers, and a corresponding description will not be repeated for brevity.

The references used herein are provided merely for convenience and consequently do not define the extent of protection or the scope of the embodiments.

One or more embodiments relate to a system for collecting litter in an urban area, as illustrated, for example, in Figure 1. The system 1 comprises an autonomous robot 10 and an urban fixture 20, for example a bench. In the sequel of the present description, reference will be made for brevity to a bench 20, without this implying any limitation of the embodiments described herein insofar as the urban fixture could assume other forms (purely by way of further examples, the urban fixture could be a table, a fountain, etc.).

The robot 10 comprises means for autonomous movement, such as two wheels 12 driven independently by respective electric motors, and a set of sensors for navigation, described in greater detail hereinafter. The robot 10 also comprises means for collecting litter, such as two brushes 14 driven by respective electric motors, one or more containers to store the litter collected, and possibly a litter-suction system.

The bench 20 comprises a shelter 22 accessible to the robot 10, possibly via an access door 24. As illustrated in Figure 1, in the case here exemplified where the urban fixture is in the form of a bench, the shelter may be positioned under the sitting surface of the bench, at the level of the road surface.

Figure 2 is a circuit block diagram that exemplifies some of the electronic components of the robot 10 and of the bench 20.

As illustrated in Figure 2, the robot 10 comprises a battery 101 (for example, a battery with a nominal voltage of 42 V), which stores electrical energy for supplying the sensors, the actuators, and in general the electronic systems of the robot 10. The battery 101 is connected to a control board 102, which is in turn connected to an electronic control unit 103 (for example, a microprocessor or a microcontroller) of the robot 10, for example via a UART communication interface. The control board 102 is connected to the electric motors 104a, 104b that drive the wheels 12 of the robot, and receives one or more control signals C from the control unit 103 for driving the motors 104a, 104b. Moreover, the control board 102 may supply one or more feedback signals F to the control unit 103.

The control unit 103 is connected via respective controllers 105a, 105b to further electric motors 106a, 106b that drive the brushes 14. For instance, the motors 106a, 106b comprise stepper motors, and the controllers 105a, 105b are stepper controllers. In the case where the robot comprises means for suction of the litter, also these can be controlled by the control unit 103.

The control unit 103 is moreover connected to a wireless communication module 107 that enables the robot 10 to exchange (transmit and/or receive) signals with the bench 20, for example by means of a connection to an Internet-type network. For instance, the wireless communication module 107 may comprise a module for connection to a Wi-Fi network, and the exchange of signals between the robot 10 and the bench 20 may be achieved by way of a local Wi-Fi network available in the urban area in which the robot 10 operates and in which the bench 20 is installed. In addition or as an alternative, the wireless communication module 107 may comprise a module for connection to a mobile- communication network (e.g., by means of 3G/4G/5G connectivity) and the exchange of signals between the robot 10 and the bench 20 may be obtained by way of the Internet-type network through connection to a remote server.

The control unit 103 is moreover connected to a GNSS receiver 108 for receiving radio signals from a global positioning satellite system. In particular, the GNSS receiver 108 is of the RTK (Real-Time Kinematic) type.

The control unit 103 is moreover connected to one or more distance sensors 109a and/or 109b configured for detecting the distances of a set of points (for example, a point cloud) in a region of interest in the direction of movement of the robot 10. For instance, the distance sensor 109a may comprise a LIDAR (Light Detection And Ranging) sensor, and the distance sensor 109b may comprise a stereoscopic-image sensor (also referred to as "stereo camera", "stereoscopic photographic camera", or "stereoscopic video camera"). The sensors 109a and/or 109b are positioned in a front region of the robot 10 in order to detect obstacles and/or objects in the direction of movement of the robot. In various embodiments, the robot 10 may comprise just one distance sensor (109a or 109b), a pair of sensors 109a and 109b, or even a plurality of sensors 109a and/or 109b (for example, two or more stereoscopic-image sensors).

As illustrated in Figure 2, the bench 20 comprises an electronic control unit 201 (for example, a microprocessor or a microcontroller). The control unit 201 is connected via a controller 202 to an electric motor 203 that drives (i.e., opens and closes) the access door 24 to the shelter 22. For instance, the motor 203 comprises a stepper motor, and the controller 202 is a stepper controller.

The control unit 201 is moreover connected to a battery 204 (for example, a battery with a nominal voltage of 12 V) that supplies the electronic systems of the bench 20. In one or more embodiments, the bench 20 comprises a photovoltaic panel 205 connected to the battery 204 via a recharge management circuit 206 in such a way that the battery 204 can be recharged with solar energy collected by the photovoltaic panel 205. In addition or as an alternative, the bench 20 may comprise an electrical connection 207 to an electric power mains (for example, a 220-VAC mains supply of a domestic type). The battery 204 may be selectively connected to the mains supply via an inverter 208 in such a way that the battery 204 can be recharged by the mains supply. In particular, the electrical connection between the mains supply and the battery 204 may be selectively activated via an electronic switch 209 controlled by the control unit 201 via a control circuit 210.

The electronic switch 209 may alternatively couple the battery 204 (via the inverter 208) to a d.c. charging circuit 211 (for example, a 42-VDC charging circuit, or in any case a charging circuit configured to supply an output voltage equal to the nominal voltage of the battery 101 of the robot 10). The charging circuit 211 is coupled to two electrical terminals 212a, 212b positioned in the shelter 22 in such a way that, when the robot 10 is sheltered in the shelter, an electrical coupling is created between the charging circuit 211 and the battery 101 for charging the battery 101 of the robot 10. In addition or as an alternative, the electrical coupling between the charging circuit 211 and the battery 101 of the robot can be formed by a coupling of an inductive type, without the use of physical electrical connectors. The control unit 201 is moreover connected to a GNSS receiver 213 for receiving radio signals from the same global positioning satellite system used by the robot 10. In particular, also the GNSS receiver 213 is of the RTK (Real-Time Kinematic) type.

The control unit 201 is moreover connected to a wireless communication module that enables the bench 20 to exchange (transmit and/or receive) signals with the robot 10, for example by means of the Internet-type network referred to previously. Consequently, the wireless communication module of the bench 20 may comprise a module for connection to a Wi-Fi network and/or a module for connection to a mobile-communication network, like the robot 10.

In the system 1 described herein, the robot 10 and the bench 20 co-operate by exchanging radio signals (via the respective wireless communication modules, possibly via connection to an Internet-type network) in order to determine precisely the position of the robot 10 and facilitate navigation thereof in the urban area. In particular, the positioning system is based upon an architecture of a satellite (GNSS, Global Navigation Satellite System) RTK (Real-Time Kinematic) type, where the satellite positioning device of the bench 20 operates as base station for determining the position error of the GNSS signals, and transmits to the robot 10 a correction signal indicative of the error of the GNSS system, which the robot 10 uses for compensating the position determined just via GNSS signals received thereby. Consequently, the control unit 201 and/or the RTK positioning device 213 are configured for calculating a position error of the GNSS positioning system as a function of the position of the bench 20, which is known at the moment of its installation in the urban area, and of the signals received from the GNSS positioning system, according to known methodologies of so-called differential satellite location, of which the RTK technology forms part. The bench 20 then transmits the correction signal indicative of the error inherent in the data received from the satellite system so that the aforesaid correction signal is received by the robot 10. For this reason, in the present description reference is made to the urban fixture 20 also using the term "central station" 20 or "base station" 20, by virtue of the role of master device that this element plays in the navigation system of the robot 10.

In turn, the robot 10 is configured to determine its own current position as a function of the signals received from the GNSS system and of the correction signal received from the bench 20, thus being able to achieve a positioning accuracy in the order of a few centimeters (for example, approximately 2 cm). Once its own position is determined precisely, the robot 10 moves in the urban area following a predefined litter- collection path, at the same time actuating its brushes 14 for collecting litter from the road surface.

In one or more embodiments, one or more litter- collection paths for the robot 10 can be stored, during a configuration step, in a memory of the robot 10 itself. In this case, it is sufficient for the bench 20 to issue an activation command to the robot 10, possibly associated to a command identifying a particular collection path, in order for the robot to exit from the shelter 22 and move in an autonomous way along the path indicated. The robot can re-enter the shelter 22 at the end of the pre-set path, or else if it receives a specific command for re-entry transmitted by the central station 20, or else again if it detects a level of low charge of the battery 101.

In addition or as an alternative, the litter- collection paths can be stored in a memory of the central station 20, and the robot 10 may be configured to follow a given litter-collection path under the continuous supervision of the central station 20, which sends control signals to the robot 10 in a continuous way.

In various embodiments, the global positioning satellite system (GNSS) used by the receivers 108 and 213 is the Global Positioning System (GPS). Alternative embodiments may use another satellite positioning system, such as the Galileo system, the Global Navigation Satellite System (GLONASS), the BeiDou Navigation Satellite System (BDS), or the Indian Regional Navigation Satellite System (IRNSS). In one or more embodiments, the robot 10 and the central station 20 can receive signals from more than one of the aforesaid systems.

As anticipated, the robot 10 also comprise a distance sensor, such as a LIDAR sensor 109a and/or at least one stereoscopic-image sensor 109b, configured to detect the distances of a point cloud in a region of interest in the direction of movement of the robot. Such a distance sensor enables the robot 10 to detect possible obstacles during navigation along the litter-collection path. The robot 10 can hence be configured for diverting from the pre-set paths in order to avoid obstacles detected by the sensors 109a and/or 109b.

In addition, the distance sensor 109a, 109b may be used by the robot 10 for improving the precision of positioning during navigation in the urban area. For instance, the robot 10 may use computer-vision algorithms for detecting the presence of one or more digital markers on the bench 20, which make it possible to determine with greater precision the position of the robot in space.

In various embodiments, the data detected by one or more distance sensors 109a and/or 109b, processed by means of computer-vision algorithms, are merged with the position data determined by the GPS RTK system in such a way as to increase the precision of positioning of the robot 10 and to perform a correction (for example, continuous, instant by instant) of the position of the robot 10 in the urban space during navigation.

In particular, a computer-vision algorithm for processing data collected by the distance sensor is advantageously used by the robot 10 during the operation of re-entry to the shelter 22. Once cleaning of the surrounding urban area is completed, or when it is necessary to carry out a stop for charging the battery 101, or in any one other case where the robot 10 is called back by the central station 20 into the shelter 22, the robot 10 moves towards the bench 20. During re entry, exploiting the possibility of continuous wireless communication between the robot 10 and the central station 20, the central station 20 can detect when the robot 10 is located in its vicinity (for example, within a certain limit distance of a few meters) and can consequently open the door 24 to enable the robot 10 to access the shelter 22. When the robot 10 is located in the proximity of the opening 24, the distance sensor of the robot 10 can detect a point cloud at the opening 24 of the bench 20, identifying the empty space and its geometrical center. The data detected by the distance sensor and processed according to a computer-vision algorithm can be combined (merged) with the position data determined via the differential satellite positioning system (GPS RTK), thus enabling the robot 10 to navigate in a precise way through the opening 24.

In addition, the data detected by the distance sensors and processed according to a computer-vision algorithm may be combined with the position data determined via the differential satellite positioning system also during navigation of the robot 10 in the urban area (in the open field), resorting to an initial configuration step. For instance, the robot 10 may be configured for storing a map of the urban area obtained by collecting data via the distance sensor during the initial configuration stage, where the robot 10 "explores" the urban area. Once the aforesaid map (which may comprise data indicative of the position of various obstacles and/or artefacts, such as trees, pavements, flower beds, fixed installations of various kinds) has been stored, the robot 10 can use the information contained therein for correcting its own position continuously, preventing accumulation in time of a position error (drift error).

Consequently, in one or more embodiments, the robot 10 navigates in the urban environment following predefined paths, avoiding static and dynamic obstacles detected by means of the sensors 109a and/or 109b. Autonomous navigation is supported by the differential satellite positioning system, which makes it possible to determine, instant by instant and with a precision of just a few centimeters (even just 2 cm), the co-ordinates (x, y) of the robot in the urban area and its angle of relative rotation (and hence its direction of movement) thanks to the relation of sub-ordinance to the master device, i.e., the central station 20.

In one or more embodiments, the central station 20 operates as central control and data-collection device, remaining in constant wireless communication with one or more autonomous robots 10, in addition to constituting an electrical-charging station for the robots. The exchange of data between the robots 10 and the central station 20 may enable the central station 20 to carry out an energy analysis of the system (for example, by monitoring the state of charge and the electrical efficiency of the robots 10), as well as analyze the logistic and operating efficiency of the system. In particular, the central control unit 201 can analyze one or more parameters for programming the exits of the robot 10. For example, the central station 20 may issue operating commands (exit and/or re-entry) to the robot 10 according to the weather conditions in the urban area of reference, which can be detected by means of appropriate sensors of the central station 20 and/or by accessing online weather forecasts in order to prevent possible damage to the robot. According to another example, the robots 10 may be configured for collecting statistical data on crowding of the urban area where they operate (for example, by storing the number of obstacles encountered during each operating session), and the central station 20 may be configured to process these data in order to program future exits of the robots 10.

In one or more embodiments, the central station 20 and/or the robots 10 may be equipped with sensors configured for analyzing the type of litter collected in the urban area (for example, video cameras for distinguishing plastic from other materials), and/or the amount of litter collected. The central station 20 may process these data and consequently program the exits of the robots 10 (for example, establishing the frequency of exit of the robot, or else assigning to each litter- collection path a parameter that indicates the optimal frequency of cleaning of that path).

In various embodiments, the robot 10 may be configured for unloading the litter when it is sheltered inside the shelter 22. For instance, the urban fixture 20 may comprise a litter-collection space underneath the shelter 22, possibly separated by a trapdoor. Alternatively, the urban fixture 20 may be installed over a ditch previously provided in the ground.

Alternatively, the robot 10 may be configured for unloading the litter in some pre-set dumping points along the path that it follows. According to a further alternative, the robot 10 may be unloaded manually by an operator when the robot is located in the shelter 22 or at some other moment.

Various embodiments have been described herein with reference to the interaction between a central station 20 and an autonomous robot 10. In one or more embodiments, the system may comprise a plurality of autonomous robots 10 that exchange signals with one and the same central station 20 in the way described previously. A single central station 20 may be provided with a shelter 22 suited to containing a number of autonomous robots, possibly comprising a corresponding number of electrical-charging interfaces.

Without prejudice to the underlying principles, the details and the embodiments may vary even considerably with respect to what has been described herein merely by way of example, without thereby departing from the extent of protection.

The extent of protection is defined by the annexed claims.

Claims

1. A system (1) for collecting litter in an urban area, comprising: - a mobile robot (10) comprising means for autonomous movement (12), litter-collecting means (14), a local electronic control unit (103), and a respective GNSS receiver (108) configured to receive radio signals from a global positioning satellite system; and - an urban fixture (20) comprising a shelter (22) accessible to said mobile robot (10), a central electronic control unit (201), and a respective GNSS receiver (213) configured to receive radio signals from said global positioning satellite system, wherein said central electronic control unit (201) is configured to:

- calculate a position error of said global positioning satellite system as a function of a known position of the urban fixture (20) and of said radio signals received from said global positioning satellite system; and

- transmit a correction signal indicative of said position error of said global positioning satellite system, wherein said local electronic control unit (103) is configured to:

- determine a current position of the mobile robot (10) as a function of said radio signals received from the global positioning satellite system and said correction signal received from the central electronic control unit (201); and

- move said mobile robot (10) along at least one litter-collection path defined in said urban area as a function of said current position of said mobile robot, actuating said litter-collecting means (14) during displacement of said mobile robot along said at least one litter-collection path, wherein the mobile robot (10) further comprises a distance sensor (109a, 109b) configured to detect data comprising the distances of a set of points in a region of interest in the direction of movement of the mobile robot, and wherein said local electronic control unit (103) is further configured to:

- process the data detected by said distance sensor (109a, 109b), during an operation of re-entry of the mobile robot (10) into said shelter (22), to produce data indicative of the position of an entrance to said shelter; and

- moving said mobile robot (10) during said operation of re-entry as a function of said current position of said mobile robot and of said data indicative of the position of the entrance to said shelter (22).

2 . The system (1) according to claim 1, wherein said local electronic control unit (103) and/or said central electronic control unit (201) includes a memory configured to store data indicative of said at least one litter-collection path defined in said urban area.

3 . The system (1) according to claim 1 or claim 2, wherein said central electronic control unit (201) is configured to issue to said mobile robot (10) commands for exit from said shelter (22) and/or re-entry into said shelter (22) as a function of a weather condition detected in said urban area and/or as a function of a detected condition of crowding of said urban area.

4 . The system (1) according to any one of the preceding claims, wherein said entrance to said shelter (22) comprises an automated door (24), and wherein said central electronic control unit (201) is configured to open the automated door in response to the fact that the mobile robot (10) carries out said operation of re-entry and is located within a limit distance from said urban fixture (20).

5 . The system (1) according to any one of the preceding claims, wherein said local electronic control unit (103) is configured to:

- process the data detected by said distance sensor (109a, 109b) during displacement of said mobile robot (10) along said at least one litter-collection path for detecting obstacles along said at least one litter- collection path; and

- divert said mobile robot (10) from said at least one litter-collection path in response to the fact that an obstacle is detected.

6. The system (1) according to any one of the preceding claims, wherein said urban fixture (20) includes a bench, and said shelter (22) is positioned underneath the sitting surface of the bench.

7 . The system (1) according to any one of the preceding claims, wherein said GNSS receivers (108, 213) receive radio signals from at least one global positioning satellite system selected amongst the Global Positioning System (GPS), the Galileo system, the Global Navigation Satellite System (GLONASS), the BeiDou Navigation Satellite System (BDS), and the Indian Regional Navigation Satellite System (IRNSS).

8. The system (1) according to any one of the preceding claims, wherein said distance sensor comprises a LIDAR sensor (109a) and/or a stereoscopic-image sensor (109b).

9. The system (1) according to any one of the preceding claims, wherein said urban fixture (20) comprises an electrical-charging device (211) for charging a battery (101) of said mobile robot (10) when said mobile robot is sheltered inside said shelter (22).

10. The system (1) according to any one of the preceding claims, wherein said urban fixture (20) is configured (210) for connecting to an electric power mains (207) and/or comprises a photovoltaic panel (205).

11. A method of controlling a system (1) for collecting litter in an urban area according to any one of the preceding claims, the method comprising:

- calculating a position error of said global positioning satellite system as a function of a known position of the urban fixture (20) and of said radio signals received from said global positioning satellite system;

- transmitting a correction signal indicative of said position error of said global positioning satellite system;

- determining a current position of the mobile robot (10) as a function of said radio signals received from the global positioning satellite system and said correction signal received from the central electronic control unit (201);

- moving said mobile robot (10) along at least one litter-collection path defined in said urban area as a function of said current position of said mobile robot, actuating said litter-collecting means (14) during displacement of said mobile robot along said at least one litter-collection path;

- processing the data detected by said distance sensor (109a, 109b), during an operation of re-entry of the mobile robot (10) to said shelter (22), to produce data indicative of the position of an entrance to said shelter; and

12 . A computer program product that can be loaded into the memory of at least one processing circuit (103, 201) and comprises portions of software code for executing the steps of the method according to claim 11 following upon execution of the computer program product by said at least one processing circuit (103, 201).