TECHNICAL FIELD

The invention relates to a navigation system for a vehicle arranged at a working space. The invention also relates to a method of navigating a vehicle arranged at a working space. The invention further relates to a computer program, a computer readable medium and a control unit.

The invention is applicable on various types of vehicles such as cars, busses, trucks, boats, etc. For instance, the invention is advantageously applicable on working machines within the fields of industrial construction machines or construction equipment, such as wheel loaders, articulated haulers, excavators, forwarders and backhoe loaders, etc. Although the description of the invention will focus on working machines, the invention is not restricted to this particular vehicle, but may also be used for navigating other types of vehicles.

BACKGROUND

Working machines in the form of articulated haulers, wheel loaders, trucks, forwarders and dumpers are frequently used for loading and transporting of material loads at construction sites, in forestry and the like. A load-receiving container of a hauler or dump truck may for instance be loaded with unprocessed material, such as rock fragments, at a loading location, transport the material to another location and dump the material (in)to a material processing device, such as into a buffering feeder of a crusher arranged to crush the rock fragments into smaller fragments.

A challenge in connection with autonomous working machines, and also in connection with other autonomous vehicles, is how to determine the current location of the vehicle in relation to its environment. The awareness of its current location may, for instance, be needed in order to determine on what road or in which part of a work site (such as a quarry site) the vehicle is located, or how far away the vehicle is located or is travelling from an obstacle, or how much the vehicle deviates from its currently specified trajectory. The use of GPS and other Global Navigation Satellite Systems (GNSS) are widely spread for supporting navigation of vehicles, and are also used in various industrial applications. However, for certain work sites or under certain conditions, GPS systems (and other GNSS systems) are not adequate. For instance, in underground mining, GPS signals may not be correctly communicated. Even when operated outdoors GPS systems may be subject to disturbances due to nearby buildings or other objects, such as trees, next to the vehicle to be navigated.

It would be desirable to provide a navigation solution which may advantageously be used at a working space, which may be either indoors or outdoors, and which is less affected by disturbance at the working space.

SUMMARY An object of the invention is to provide a navigation system, a method, a computer program, a computer readable medium and a control unit, which can be used for providing an adequate navigation of a vehicle at a working space, and which alleviates the drawbacks of the prior art. According to a first aspect of the invention, the object is achieved by a navigation system for a vehicle arranged at a working space, the navigation system comprising:

- an on-board subsystem adapted to be located on the vehicle, and

- an off-board subsystem adapted to be located at the working space separately from the vehicle, wherein the off-board subsystem comprises:

- at least one vehicle presence detector configured to generate data indicative of the presence of a vehicle,

- a processing unit configured to receive the generated data from the at least one vehicle presence detector, the processing unit being configured to determine a position of the vehicle based on the received data, and

- a transmitter configured to wirelessly transmit a signal representative of said position of the vehicle, wherein the on-board subsystem comprises:

- a receiver configured to wirelessly receive said signal from the transmitter, and - a control unit configured to control the navigation of the vehicle based on the received signal.

By the provision of a system in which one or more off-board detectors cover an area of interest (e.g. part of the working space or the entire working space) and detect the presence of a vehicle, the position of the vehicle may be determined and transmitted to the vehicle whereby the on-board control unit can control the navigation of the vehicle. Off-board detectors may advantageously be used outdoors or indoors, and even under ground or in a tunnel. Furthermore, by providing a processing unit off-board, the position calculating capacity needed at the vehicle is reduced, and therefore the cost of the individual on-board control units may be kept low. This is particularly advantageous in connection with working machines, in which a control unit including a high-end computer would need to be sufficiently rugged to withstand the often shaky and dirty environments in which working machines operate, and would therefore become much more expensive.

The vehicle presence detector may advantageously be located at an open working space outdoors, or in a relatively concealed working space, such as a tunnel. For instance, in a tunnel the vehicle presence detector may generate data which the processing unit receives. The processing unit may uses the received data to determine the distance to a tunnel wall. In a tunnel, it may be enough to detect the lateral position of the vehicle, i.e. to avoid that the vehicle hits the tunnel wall (the orientation and the longitudinal position along the tunnel may be less relevant). Thus, in at least some exemplary embodiments, said position may be a lateral position, such as a lateral position relative to an intended trajectory of the vehicle (i.e. the lateral position is along a direction transverse to the intended trajectory).

The vehicle may suitably be an autonomous vehicle. However, in some exemplary embodiments the vehicle may be controlled by a human operator, and the control unit may function to correct inadequate manoeuvring of the vehicle by the human operator, or the control unit may provide suggested corrections to the human operator.

In some exemplary embodiments, two or more vehicle presence detectors may be included in the system to determine the presence of the vehicle and to generate data based on which the processing unit may determine the position of the vehicle. In other exemplary embodiments, a single vehicle presence detector may suffice for enabling the processing unit to determine the position of the vehicle. For instance, a single vehicle presence detector including, or being in the form of, a camera may be used to detect visual fiducial marks/tags provided on the vehicle. For example, by looking at which pixels and the number of pixels present in the image of the visual fiducial mark/tag the processing unit can (based on the received data representative of the image) even determine the rotational orientation of the vehicle, although only a single vehicle presence detector (such as a camera) is used.

The placement of the various components may be designed in various ways. For instance, the off-board transmitter may in some exemplary embodiments be integrated in the processing unit, while in other exemplary embodiments the off-board transmitter may be a separately located component or entity in operative communication with the processing unit. Likewise, the on-board receiver may in at least some exemplary embodiments be integrated in the control unit, while in other exemplary embodiments the on-board receiver may be a separately located component or entity in operative communication with the control unit.

As mentioned previously, the vehicle may advantageously be a working machine, however, it should be understood that the invention is not limited to this, but as will be readily understood, the inventive concept can be implemented for navigating other types of vehicles, be it on land, in air or on/under water.

According to at least one exemplary embodiment, said position is a three-dimensional position in said working space. By determining the three-dimensional position the vehicle can be navigated over a large variety of different working spaces, including outdoors and indoors.

Information relating to the position of the vehicle may suitably be complemented with information relating to the orientation of the vehicle. This is reflected in at least one exemplary embodiment, according to which the processing unit is configured to determine an orientation of the vehicle based on the received data, wherein said signal is also representative of said orientation. By having information of the orientation of the vehicle, the navigation may be further improved. For instance, the control unit may in a timely manner decide if the vehicle should be turned, or steered in some other direction than its current heading. It should be understood that the term “orientation” of the vehicle includes one or more of yaw, pitch and roll. For a vehicle, such as a truck or a working machine, in a Cartesian x-,y-,z-coordinate system: the roll defines the rotation around the longitudinal axis (x), the pitch defines the rotation around the lateral axis (y) and the yaw defines the rotation around the normal or heave axis (z).

As mentioned previously, under certain conditions or in certain working spaces, it may suffice to provide the on-board control unit with limited positional information. An example of such a case is when the working space is located in a tunnel or shaft or the like. The vehicle may in such cases have a defined or programmed trajectory (or part of a trajectory) starting from one part of the tunnel to another part further ahead in the tunnel. In such cases it may be enough to make sure that the vehicle is not too close to the wall of the tunnel. Thus, if the tunnel has a main direction of extension, it may suffice to provide information to the control unit with respect to the lateral position of the vehicle relative to the tunnel wall, i.e. its position in a direction transverse to the main direction of extension. This is reflected in at least one exemplary embodiment of the invention, according to which the working space is located in a tunnel, which is laterally defined by tunnel walls, wherein said position is a lateral position relative to one of the tunnel walls. This provides for a simple yet effective navigation of the vehicle. In the tunnel example, the working space may be regarded as a confined working space. It is also conceivable, to have a confined working space outdoors. Such a confined working space may be a real working space, for instance confined by physical limitations/borders, such as walls, trees, objects, etc., or the confined working space may be a virtually confined working space, created for instance by a control unit (the on-board control unit or a different control unit). Thus, in some exemplary embodiments the working space is a confined working space. In other exemplary embodiments, the working space is not a confined working space, but may, for instance, be a public road or similar.

According to at least one exemplary embodiment, the at least one vehicle presence detector is an image capturing unit, such as a camera. As mentioned above, a single camera may be enough for determining the position and/or the orientation of the vehicle, for instance, by detecting characteristic features of the vehicle or provided on the vehicle. Such features may, for instance, include one or more visual fiducial marks or tags provided on the vehicle. It should, however, be understood that in at least some exemplary embodiments, two or more vehicle presence detectors may be used, in order to increase the accuracy of the position and/or orientation determination of the processing unit.

The expression “processing unit” as used above should be understood to include any type of computing device, such as an ASIC, a micro-processor, etc. It should also be understood that the actual implementation of such a processing unit may be divided between more than a single device/circuit. For instance, one device/circuit of the processing unit may receive data generated by a first vehicle presence detector, while another device/circuit of the processing unit may receive data generated by a second vehicle presence detector, and a third device/circuit of the processing unit may, based on the received data, determine the position of a vehicle. In other embodiments. For instance, one device/circuit of the processing unit may be located at or connected to the first vehicle presence detector, while the other device/circuit of the processing unit is located at or connected to the second vehicle presence detector. In other embodiments, a device/circuit of a processing unit may be operatively connected to both (or a plurality of) vehicle presence detectors, for instance by wired or wireless connection, and may be physically located at one of the vehicle presence detectors, or located separate/spaced apart from the vehicle presence detectors.

According to at least one exemplary embodiment, the vehicle presence detector comprises a wave emitter and a wave receiver for receiving a reflected wave, wherein the vehicle presence detector is suitably one of a Lidar, radar or ultrasonic detector. One Lidar, radar or ultrasonic detector may suffice to accurately determine the position of the vehicle. For instance, a Lidar or a radar provides a point cloud, the orientation of the point cloud being usable for determining the position of the vehicle.

It should be understood that in exemplary embodiments in which two or more vehicle presence detectors are used, they may be of the same type or of different types. For instance, if two or more vehicle presence detectors are used, in some exemplary embodiments, both detectors are in the form of cameras, while in other exemplary embodiments both detectors are wave-emitting and wave receiving detectors such as Lidar, radar or ultrasonic detectors. In still further exemplary embodiments, one of the detectors may be a camera, and the other one of the detectors may be one of the above exemplified wave-emitting and wave receiving detectors. The use of two or more vehicle presence detectors is reflected in at least one exemplary embodiment, according to which the off-board subsystem comprises at least two vehicle presence detectors, wherein the processing unit is configured to receive the generated data from each one of the at least two vehicle presence detectors, the processing unit being configured to determine a three-dimensional position and orientation of the vehicle based on the received data. The use of two detectors may facilitate determination of the position and/or orientation, although as discussed above, one detector may suffice.

In the case of using two vehicle presence detectors, they may be located and facing in numerous different directions. In some exemplary embodiments, the detectors may have different fields of view. However, to facilitate the mapping to a three-dimensional position of the vehicle, it may be advantageous to have overlapping fields of view. Thus, according to at least one exemplary embodiment, the at least two vehicle presence detectors have a field of view overlapping each other at an area of interest at the working space. By having overlapping fields of view parts of the vehicle will be detected by both detectors, and any calculations performed by the processing circuit may accurately determine the position and/or orientation of the vehicle relative to its environment.

According to at least one exemplary embodiment, the control unit is configured to control the navigation of the vehicle along a predefined trajectory, including controlling speed and steering of the vehicle. Thus, based on the received signal representative of the position of the vehicle (and suitably also the orientation of the vehicle) the control unit may navigate the vehicle towards a determined destination or the like. For instance, a predetermined trajectory may be to deliver a load of material, such as gravel, stones, sand etc. from a pick-up point to a delivery point, such as a container. One or more vehicle presence detectors may be located along the trajectory to generate data that will later be used to calculate and send signals representative of the position of the vehicle. The control unit will based on the received signals navigate the vehicle from the pick-up point to the delivery point.

According to at least one exemplary embodiment, the processing unit is configured to determine if the vehicle has escaped its intended working area, and upon such determination initiate a wireless transmission of a stop signal, wherein the control unit is configured to stop the vehicle based on a reception of said stop signal. By providing a forced stop, when the vehicle is outside its intended working area, hazardous situations may be avoided, and any malfunctioning of the vehicle or the system may be timely checked and corrected. The stop signal may be sent to said on-board control unit or to a separate emergency stop system on the vehicle. The stop signal, may be sent from said off-board transmitter or from a different separate off-board transmitting module comprised in or being operatively connected to the processing unit. In a physically or virtually confined working space, or in a physically or virtually partly confined working space, said intended working area may correspond to the working space or part of the working space. In a non-confined working space, the working area is suitably defined as part of said working space, for instance an area along an intended trajectory. The signal representative of the position of the vehicle, may be referred to as a “position signal”, which is primarily provided for navigational purposes, in contrast to the “stop signal”, which is primarily provided for emergency purposes.

According to a second aspect of the invention, the object is achieved by a method of navigating a vehicle arranged at a working space, comprising the off-board steps of:

- generating, by means of at least one vehicle presence detector, data indicative of the presence of a vehicle,

- receiving, by means of a processing unit, the generated data,

- determining, by means of the processing unit, a position of the vehicle based on the received data,

- transmitting wirelessly a signal representative of said position of the vehicle, the method further comprising the on-board steps of:

- receiving wirelessly said signal,

- controlling, by means of a control unit, the navigation of the vehicle based on the received signal.

The advantages of the various embodiments of the second aspect are largely analogous to the advantages of the corresponding embodiments of the first aspect. Exemplary embodiments of the method of the second aspect include the following.

According to at least one exemplary embodiment, the method comprises the further off- board steps of

- determining, by means of the processing unit, an orientation of the vehicle based on the received data, wherein said transmitted signal is also representative of said orientation. According to at least one exemplary embodiment, the on-board step of controlling comprises controlling the navigation of the vehicle along a predefined trajectory, including controlling speed and steering of the vehicle. According to at least one exemplary embodiment, the method comprises the further off- board steps of:

- determining, by means of the processing unit, if the vehicle has escaped its intended working area, and upon such determination,

- initiating a wireless transmission of a stop signal.

According to at least one exemplary embodiment, the method comprises the further on board step of:

- stopping the vehicle based on a reception of said stop signal. According to a third aspect of the invention, the object is achieved by means of a computer program comprising program code means for performing the on-board steps of the method according to the second aspect, including any embodiments thereof, when said program is run on a computer. According to a fourth aspect of the invention, the object is achieved by means of a computer readable medium comprising a computer program comprising program code means for performing the on-board steps of the method according to the second aspect, including any embodiments thereof, when said program is run on a computer. According to a fifth aspect of the invention, the object is achieved by a control unit for controlling the navigation of a vehicle in a working space, the control unit being configured to perform the on-board steps of the method according to the second aspect, including any embodiments thereof. The control unit may include a microprocessor, microcontroller, programmable digital signal processor or another programmable device. The control unit may also, or instead, include an application specific integrated circuit, a programmable gate array or programmable array logic, a programmable logic device, or a digital signal processor. Where the control unit includes a programmable device such as the microprocessor, microcontroller or programmable digital signal processor mentioned above, the processor may further include computer executable code that controls operation of the programmable device.

The advantages of the third, fourth and fifth aspect of the invention are largely analogous to the advantages of the first and second aspects of the invention.

Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

In the drawings:

Fig. 1 illustrates an example of a vehicle, for which the inventive navigation system and method may be implemented.

Fig. 2 illustrates schematically a vehicle at a working space which is navigated by the inventive navigation system according to at least one exemplary embodiment.

Fig. 3 illustrates schematically a vehicle at a working space which is navigated by the inventive navigation system according to at least another exemplary embodiment.

Fig. 4 illustrates navigation of a vehicle in a confined environment, such as a tunnel, in accordance with at least one exemplary embodiment of the invention. Fig. 5 illustrates schematically a vehicle at a working space navigated by the inventive navigation system according to at least a further exemplary embodiment.

Fig. 6 is a schematic illustration of components of an inventive navigation system according to at least one exemplary embodiment. Fig. 7 illustrates a method of navigating a vehicle according to at least one exemplary embodiment of the invention.

Fig. 8 illustrates a method of navigating a vehicle according to at least another exemplary embodiment of the invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

Fig. 1 illustrates an example of a vehicle 1 , for which the inventive navigation system and method may be implemented. In the present illustration, the vehicle 1 is a working machine in the form of a wheel loader. However, it should be understood that the inventive system and method may be implemented for other types of vehicles, such as cars, busses, trucks, boats, etc. Furthermore, it should be understood that the inventive system and method may be implemented for autonomous vehicles or semi-autonomous vehicles, such as vehicles provided with Advanced Driver Assistance Systems (ADAS).

The wheel loader comprises a lift arm unit 3 to which a work tool 5 is connected. In this example, the work tool 5 is illustrated in the shape of a bucket which is mounted on the lift arm unit 3. It should be understood that although the work tool 5 has been illustrated as a bucket, other types of work tools may also be connected to the lift arm unit 3, such as shovels, forks, gripping tools, material arms or excavating tools. Although some of the following figures illustrate a wheel loader transporting material in its bucket from one location to another, it is again emphasized that this is just one of many possible implementations. Thus, it should be understood that other implementations, such as a for instance busses transporting passengers, are also readily conceivable.

Inside the vehicle 1, there may be a control unit (not shown in Fig. 1) configured to navigate the vehicle 1. The control unit is part of an on-board subsystem which interacts with an off-board subsystem of the inventive navigation system. The control unit is configured to perform the on-board steps of the inventive method of navigating a vehicle. The control unit may comprise or may be comprised in a processing circuitry. The processing circuitry may include a microprocessor, microcontroller, programmable digital signal processor or another programmable device. The processing circuitry may also, or instead, include an application specific integrated circuit, a programmable gate array or programmable array logic, a programmable logic device, or a digital signal processor. Where the processing circuitry includes a programmable device such as the microprocessor, microcontroller or programmable digital signal processor mentioned above, the processor may further include computer executable code that controls operation of the programmable device. It should be understood that all or some parts of the functionality provided by means of the processing circuitry (or generally discussed as “processing circuitry”) may be at least partly integrated with the control unit.

Fig. 2 illustrates schematically a vehicle 1 at a working space which is navigated by the inventive navigation system according to at least one exemplary embodiment. The vehicle 1 is illustrated at three different location. At a first location (area A), to the left in the figure, the vehicle 1 starts its intended trajectory, for instance to transport a load of material to a destination. At a second location (area B), in the middle of the figure, the vehicle 1 is on its way along its intended trajectory, and is supervised by the navigation system. In the third location (area C), to the right in the figure, the vehicle 1 has reached its destination and has unloaded the material.

The navigation system comprises an on-board subsystem adapted to be located on the vehicle 1 and an off-board subsystem adapted to be located at the working space separately from the vehicle 1. In Fig. 2 the off-board subsystem is illustrated to include two vehicle presence detectors 22, such as cameras, Lidars, radars or ultrasonic detectors. However, it should be understood that in other exemplary embodiments the off- board subsystem may include only one vehicle presence detector, or three or more vehicle presence detectors. Furthermore, in case of a plurality of vehicle presence detectors being provided in the off-board subsystem they may be arranged pairwise (for instance, each pair of detector having an overlapping field of view) or not pairwise. In Fig. 2, the two vehicle presence detectors 22 are illustrated as having an overlapping field of view 12. The details of the on-board subsystem and the off-board subsystem are illustrated in Fig. 6.

Thus, turning to Fig. 6, there is shown a schematic illustration of components of an inventive navigation system 10 according to at least one exemplary embodiment. The navigation system comprises said off-board subsystem 20 and said on-board subsystem 40. The off-board subsystem 20 comprises at least one vehicle presence detector 22 configured to generate data indicative of the presence of a vehicle. The off-board subsystem 20 also comprises a processing unit 24 configured to receive the generated data 23 from the at least one vehicle presence detector 22. The processing unit 24, which may comprise suitable computational circuitry, is configured to determine a position of the vehicle based on the received data 23. The processing unit 24 provides position data 25 to a transmitter 26, such as a radio transmitter. The transmitter 26 is configured to wirelessly transmit a signal 27 representative of said position of the vehicle. The processing unit 24 may, in at least some exemplary embodiments, be configured to determine if the vehicle has escaped its intended working area. An optional emergency controller module 28 may be provided in the off-board subsystem. The processing unit 24 may instruct 29 the emergency controller module 28 to send a stop signal 30, if the processing unit 24 has, based on the received data 23, determined that the vehicle has escaped its working area. Although the emergency controller module 28 is in Fig. 6 illustrated as a separate off-board transmitting module, in other exemplary embodiments the stop signal may be sent from said off-board transmitter or from a transmitting module comprised in the processing unit. It should also be noted that the transmitter may, in other exemplary embodiments, form part of the processing unit 24.

The on-board subsystem 40 comprises a receiver 42, such as a radio receiver, configured to receive the position signal 27 from the transmitter. The on-board-subsystem 40 also comprises a control unit 44 configured to control the navigation of the vehicle based on the received signal 27, i.e. based on the positional information contained in said received position signal 27. The navigational control of the control unit 44 is illustrated by a control output 47. The receiver 42 may transform said received position signal 27 into position data 43 readable by the control unit 44. The receiver may in other exemplary embodiments form part of the control unit 44. In the case of the off-board subsystem 20 having being designed with the above-described, or similar, emergency stop functionality, the on-board subsystem 40 may comprise an emergency stop relay 45 for receiving the stop signal 30, and upon receipt of the stop signal 30 send an emergency brake signal 46 to the control unit 44, whereby the control unit stops the vehicle by means of its control output 47. In other exemplary embodiments, the stop signal 30 may be received directly by the control unit 44. Turning back to Fig. 2, as the vehicle travels from its start (at area A) to its destination (at area C) it will be detected (at area B) by the vehicle presence detectors 22. The processing unit may suitably be provided in one of the vehicle presence detectors 22, or may be provided separately from the vehicle presence detectors 22, but in operative (wired or wireless) communication with the vehicle presence detectors. The processing unit will by means of a connected transmitter (such as illustrated and discussed above in connection with Fig. 6) send a position signal to a receiver provided in the on-board subsystem of the vehicle, whereby the control unit can control the navigation of the vehicle based on the received signal, so that the vehicle keeps its intended trajectory towards its destination (at area C). Thus, if the control unit determines that the vehicle is off its trajectory, corrective measures, such as change of direction, speed, etc. can be taken by the control unit, to get the vehicle on the right track again. Another example is when the control unit determines that the vehicle has almost reached its destination, it may initiate a controlled braking of the vehicle so that it smoothly stops at the destination and potentially in a desired orientation, for instance facing a certain direction. Thus, the processing unit may, in some exemplary embodiments be configured to determine an orientation of the vehicle based on the received data, wherein the position signal is also representative of said orientation. The determined position as such may, suitably, be a three-dimensional position in said working space. In the exemplary embodiment of Fig. 2, the processing unit may thus be configured to receive the generated data from each one of the two vehicle presence detectors, and the processing unit may being configured to determine a three-dimensional position and orientation of the vehicle based on the received data.

Fig. 3 illustrates schematically a vehicle 1 at a working space which is navigated by the inventive navigation system according to at least another exemplary embodiment (such as the one illustrated in Fig. 6 or described elsewhere in this disclosure). The vehicle 1 , here illustrated as a wheel loader, is instructed to move material from a starting location, such as a pile of sand 50, to a destination location, such as a container 52 of a waiting truck. In this exemplary embodiment, a plurality of vehicle presence detectors 22 are arranged so as to pairwise have overlapping fields of view 54. For a small working space, or small intended working area, one or two vehicle presence detectors may be enough for adequate control and navigation of the vehicle, but for a larger working space, for instance when the intended trajectory of the vehicle is over a longer distance, it may be advantageous to have a plurality of vehicle presence detectors along the way. They do, however, not necessarily need to be arranged as close to each other as in Fig. 3; for instance, in some cases there may be larger blank areas between the areas covered by the fields of view of the vehicle presence detectors. For instance, some central parts of the working space may be void of vehicle presence detectors, while peripheral parts of the area, including starting and destination locations and boarder areas may be provided with vehicle presence detectors. These are, of course just a few examples, and the distribution of vehicle presence detectors is suitably designed based on the conditions of the actual environment in which they will be used, and suitably on a case by case basis.

Fig. 4 illustrates navigation of a vehicle 1 in a confined environment, such as a tunnel 60, in accordance with at least one exemplary embodiment of the invention. When the working space is located in a tunnel 60 which is laterally defined by tunnel walls 62, or a similar confined environment, the position determined by the system may be a lateral position L1, L2 relative to at least one of the tunnel walls 62. Thus, relatively simple vehicle presence detectors 22 may be used, if desired. Of course, a three-dimensional position as well as the orientation of the vehicle in the tunnel may also be determined, however, oftentimes it may suffice to know the lateral position L1, L2. In either case, the vehicle presence detectors 22 may, for instance, suitably be ultrasonic detectors, cameras, Lidars, radars, or any other appropriate detector type. The vehicle 1 will often have an intended trajectory which is along the main direction of extension of the tunnel 60. By making sure that the vehicle 1 does not deviate too much transversely (i.e. laterally) from the main direction of extension and thereby risking hitting a tunnel wall 62, the control unit may make appropriate corrections to the lateral position L1 , L2 as the vehicle 1 continues along its trajectory in the tunnel 60. In the present illustration, a plurality of vehicle presence detectors 22 are provided along both lateral tunnel walls 62. They, do, however, not necessarily need to be arranged pairwise as in Fig. 4, but can be appropriately distributed, for example taking into account bends or other irregularities in the tunnel 60 which may advantageously have a more dense collection of vehicle presence detectors than straight passages.

Fig. 5 illustrates schematically a vehicle 1 at a working space navigated by the inventive navigation system according to at least a further exemplary embodiment. The example is similar to the one illustrated in Fig. 2, however, only one vehicle presence detector 22 is provided. As explained previously in this disclosure, in some exemplary embodiments the navigation system only has a single vehicle presence detector. This may suffice for enabling the processing unit to determine the position of the vehicle 1. For instance, a single vehicle presence detector 22 including, or being in the form of, a camera may be used to detect visual fiducial marks/tags provided on the vehicle. For example, by looking at which pixels and the number of pixels present in the image of the visual fiducial mark/tag the processing unit can (based on the received data representative of the image) even determine the rotational orientation of the vehicle 1, although only a single vehicle presence detector (such as a camera) is used. It is also conceivable to provide the vehicle with a plurality visual fiducial marks/tags, for instance individual marks/tags, distributed around the vehicle, and depending on which marks/tags that are viewed by the vehicle presence detector, the processing unit can determine the position and orientation of the vehicle.

It should be understood that in each one of the exemplary embodiments, the one or more vehicle presence detectors 22 may be of any suitable type. Each vehicle presence detector has a field of view, and the processing unit can determine based on the received data where in the field of view, i.e. where in the working space, the vehicle is located. In the exemplary embodiments, each vehicle presence detector may, for instance be an image capturing unit, such as a camera. In other exemplary embodiments, each vehicle presence detector may comprise a wave emitter and a wave receiver for receiving a reflected wave (for instance Lidar, radar or ultrasonic detector). In further exemplary embodiments, different types of vehicle presence detectors may be used in the off-board subsystem.

Fig. 7 illustrates a method 100 of navigating a vehicle according to at least one exemplary embodiment of the invention.

The method 100 comprises the off-board steps of:

- in a step S1 , generating, by means of at least one vehicle presence detector, data indicative of the presence of a vehicle,

- in a step S2, receiving, by means of a processing unit, the generated data,

- in a step S3, determining, by means of the processing unit, a position of the vehicle based on the received data,

- in a step S4, transmitting wirelessly a signal representative of said position of the vehicle.

The method 100 further comprising the on-board steps of:

- in a step S5, receiving wirelessly said signal, - in a step S6, controlling, by means of a control unit, the navigation of the vehicle based on the received signal.

Fig. 8 illustrates a method 200 of navigating a vehicle according to at least another exemplary embodiment of the invention. The method 200 in Fig. 8 includes the step of the method 100 in Fig. 7.

Additionally, the method 200 in Fig. 8 includes the following optional steps:

-in an off-board step S7, determining, by means of the processing unit, an orientation of the vehicle based on the received data, wherein said transmitted signal is also representative of said orientation,

- in an on-board step S8, controlling comprises controlling the navigation of the vehicle along a predefined trajectory, including controlling speed and steering of the vehicle,

- in an off-board step S9, determining, by means of the processing unit, if the vehicle has escaped its intended working area, and upon such determination, - in an off-board step S10, initiating a wireless transmission of a stop signal,

- in an on-board step S11 , stopping the vehicle based on a reception of said stop signal.

It should be understood that not all the steps S7-S11 are required to be performed in the method 200 of Fig. 8. However, if off-board step S9 is performed, then suitably, off-board step S10 and on-board step S11 are also performed. Furthermore, it should be understood that the listed order of steps S1-S11 in Fig. 8 is not necessarily the order in which the steps must be performed. For instance, the off-board step S7 may suitably performed simultaneously with the off-board step S3. The on-board step S8 is suitably performed simultaneously with (or is included in) the on-board step S6.

It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.