WO2020120601A1

WO2020120601A1 - Controlling movement of an autonomous device

Info

Publication number: WO2020120601A1
Application number: PCT/EP2019/084703
Authority: WO
Inventors: Elof WINROTH
Original assignee: Nordluft Automation Ab
Priority date: 2018-12-12
Filing date: 2019-12-11
Publication date: 2020-06-18

Abstract

The disclosure relates to a method and a control device (15) for controlling movement of at least one autonomous device (10) over an area (14). In an aspect a method of a control device (15) of controlling movement of at least one autonomous device (10) over an area (14) is provided. The method comprises segmenting (S101) a representation of the area (14) into parallelly arranged segments (A-G), and instructing (S102) the at least one autonomous device (10) to move over the area (14) along a selected segment (A) until an end of the area is reached in the selected segment, wherein the at least one autonomous device (10) is instructed to move over the area (14) along a next segment (B), in a direction opposite to the movement performed when moving along the preceding segment (A), until an end of the area (14) is reached in the next segment (B), wherein movement from one segment to a next segment is performed either until the area (14) has been completely covered or a capacity threshold of the at least one autonomous device (10) has been reached, in which case the at least one autonomous device (10) is instructed to return to a base from which the at least one autonomous device (10) started.

Description

CONTROLLING MOVEMENT OF AN AUTONOMOUS DEVICE TECHNICAL FIELD

The disclosure relates to a method and a control device for controlling movement of at least one autonomous device over an area. BACKGROUND

Autonomous devices, such as autonomous cars, unmanned aerial vehicles (UAVs), commonly known as a drones, robots in the form of for instance robotic lawn mowers, autonomous sea vessels, automated guided vehicles, etc., are being utilized in society in many different applications. Typically, these autonomous devices are controlled to move over a designated area and simultaneously performing a particular operation, such as mowing a lawn, capturing photos of their surroundings or removing ocean oil spill by disposing an absorber.

A challenge with these autonomous devices is that their movement needs to be controlled and such controlling is a complex process.

SUMMARY

An objective is to solve, or at least mitigate, this problem in the art and to provide an improved method of controlling movement of an autonomous device. This objective is attained in a first aspect by a method of a control device of controlling movement of at least one autonomous device over an area. The method comprises segmenting a representation of the area into parallelly arranged segments, and instructing the at least one autonomous device to move over the area along a selected segment until an end of the area is reached in the selected segment, wherein the at least one autonomous device is instructed to move over the area along a next segment, in a direction opposite to the movement performed when moving along the preceding segment, until an end of the area is reached in the next segment, wherein movement from one segment to a next segment is performed either until the area has been completely covered or a capacity threshold of the at least one autonomous device has been reached, in which case the at least one autonomous device is instructed to return to a base from which the at least one autonomous device started. This objective is attained in a second aspect by a control device configured to control movement of at least one autonomous device over an area. The control device comprises a processing unit and a memory, said memory containing instructions executable by said processing unit, whereby the control device is operative to segment a representation of the area into parallelly arranged segments, and instruct the at least one autonomous device to move over the area along a selected segment until an end of the area is reached in the selected segment, wherein the at least one autonomous device is instructed to move over the area along a next segment, in a direction opposite to the movement performed when moving along the preceding segment, until an end of the area is reached in the next segment, wherein movement from one segment to a next segment is performed either until the area has been completely covered or a capacity threshold of the at least one autonomous device has been reached, in which case the at least one autonomous device is instructed to return to a base from which the at least one autonomous device started.

Initially, a representation of the area is acquired by the control device being configured to control the movement of the autonomous device, being for instance a UAV. This representation may be acquired by importing map data with coordinates such that the area can be navigated. The representation of the area is divided into parallelly arranged segments. The orientation of the parallelly arranged segments are preferably, but not necessarily, aligned in a direction from a starting point of the UAV to a center point of the area.

Upon leaving the starting point, the UAV is instructed by the control device to move - i.e. to fly - to a selected one of the segments and move over the area along the selected segment until an end of the area is reached in the selected segment.

When reaching the end of the area in the selected segment, the UAV is instructed to move to a next segment and moves over the area in the next segment in a direction opposite to the direction of movement in the preceding segment while disposing material, such as e.g. fertilizer, over the area. The UAV is then instructed to move to an end of the area in the next segment whereupon the UAV moves to yet a next segment, and so on, until having covered the complete area upon reaching the end of the area in a final segment, wherein the UAV is instructed by the control device to return to its starting point.

Advantageously, the UAV will be controlled to systematically and orderly travel across the area to be fertilized, with the number of turning maneuvers kept low in order to keep energy consumption down. Should a capacity threshold of the UAV have been reached (or is close to being reached) before the complete area has been covered, the UAV will be instructed to return to the base from which it started in order to restore capacity. Advantageously, the control device plans the route of the UAV well in advance, and will thus timely instruct the UAV to return to the starting point when deemed necessary.

In an embodiment, the segmenting further comprises dividing one or more of the segments into sub-segments.

In an embodiment, the autonomous device is a device being configured to move over the area to deposit material (e.g. fertilizer) over the area, wherein the autonomous device is instructed not to deposit material over at least one selected sub-segment over which it moves.

In an embodiment, the autonomous device may for instance be a robotic lawn mower, wherein it is instructed not to move over at least one selected sub- segment. In an embodiment, at least two autonomous devices are controlled to move over the area, and are instructed to move over the area without colliding.

In an embodiment, at least two autonomous devices are controlled to move over the area such that queues among the two or more autonomous devices are avoided at the starting point.

In an embodiment, the capacity threshold is stipulated by one or more of a capacity property selected from: amount of material that the autonomous device can carry, spreading radius over which the autonomous device deposits material, energy capacity of an energy source from which the autonomous device is powered, speed with which the autonomous device moves and memory capacity of the autonomous device for storing data.

In an embodiment, the control device continuously acquires a current status regarding the capacity of the autonomous device.

In an embodiment, the width of each segment is adapted to a working width of the autonomous device.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are now described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 illustrates a system in which embodiments may be applied, where UAVs are used to dispose fertilizer over an area comprising woodland; Figure 2 illustrates segmenting of an area into parallelly arranged segments according to an embodiment;

Figure 3a illustrates controlling of movement of a UAV over the segmented area of Figure 2 according to an embodiment;

Figure 3b illustrates a flowchart of a method of controlling movement of a UAV over the segmented area of Figure 2 according to an embodiment;

Figure 4 illustrates controlling of movement of a UAV over the segmented area of Figure 2 including an intermediate refill of fertilizer according to an embodiment;

Figure 5 illustrates segmenting some of the segments of Figure 2 into sub- segments according to an embodiment;

Figure 6 illustrates controlling of movement of two UAVs over the segmented area of Figure 2 according to an embodiment;

Figure 7 illustrates a further embodiment, where movement of a robotic lawn mower is controlled;

Figure 8 illustrates a further embodiment of controlling movement of UAVs; and

Figure 9 illustrates yet a further embodiment of controlling movement of UAVs.

DETAILED DESCRIPTION

Embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments are shown. The disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope to those skilled in the art. Like numbers refer to like elements throughout the description. In the following, the autonomous device to be controlled is exemplified in the form of an UAV, a so called drone, which is to be controlled to move over a designated area, for instance a stretch of woodland to be fertilized by having the UAV fly over the area for disposing fertilizer onto the woodland.

It is envisaged that one or more embodiments may be applied to any appropriate autonomous device to be controlled to move over a designated area, such as a robotic lawn mower, an autonomous tractor for harvesting a field, an autonomous sea vessel for removing oil spill at sea, or a UAV configured to capture photos of a designated area.

Hence, in the exemplifying embodiments shown in the following, one or more UAVs are used to fertilize a designated area. The UAVs may be embodied in the form of multicopters, fixed-wing aircrafts, vertical take-off and landing (VTOL) aircrafts, etc.

In practice, capacity of a UAV must be taken into account when planning its air route over the area to be fertilized.

A number of capacity properties of the UAV can be considered; for instance (a) the amount of fertilizer that UAV can carry, (b) spreading radius over which the UAV deposits fertilizer, (c) energy capacity of an energy source from which the UAV is powered, (d) speed with which the UAV flies, (e) memory capacity (for instance for a UAV capturing images of an area), etc.

The energy source may be a rechargeable battery, a diesel motor, a gasoline motor, etc.

With reference to Figure l, the route of the one or more UAVs to, n, 12 start from a base station where fertilizer can be refilled and batteries can be charged if necessary. In an example, such a base station is embodied by a truck 13 having a UAV landing facility where fertilizer can be refilled from a container and the batteries can be recharged or even changed before the UAVs 10, 11, 12 returns to fertilizing a designated area 14 consisting of woodland. The base station/truck 13 thus acts as a starting point for the one or more UAVs 10, 11, 12. It should be noted that the truck can move during the flight of the UAVs and hence that a UAV may return a base having moved.

In Figure 1, three UAVs 10, 11, 12 are utilized, but it is understood that any number of UAVs may be used depending on fertilizing capacity required. In the application illustrated with reference to Figure 1, the UAVs 10, 11, 12 are started and instructed to fly over the area 14 to be fertilized (the UAVs may already have been pre-configured with such an instruction before arrival at the site from which they will start their route). Typically, the UAVs 10, 11, 12 will shuttle between the base station 13 and the area 14 for refilling of fertilizer and/ or battery recharge.

Now, as is understood, in order to provide an efficient UAV fertilizing system, it is important that the UAVs are controlled to move over the area 14 for dropping fertilizer over the woodland in an ordered and systematic manner. Figure 2 illustrates an embodiment of a method of controlling the UAV 10 to move over the area 14.

Initially, a representation of the area 14 is acquired by a control device 15 being configured to wirelessly control the movement of the UAV 10. This may be a remote control device 15 located far away from the actual site where the system of Figure 1 is located.

It may further be envisaged that such a control device is implemented within the UAV 10 itself in the form of a processing unit executing appropriate software from a local memory. If so, the control device in the UAV 10 may have to be capable of communicating with corresponding control device(s) implemented in other UAV(s) configured to move over the area 14.

This representation may be acquired by importing map data with coordinates such that the area 14 can be navigated. This representation may further comprise sub-areas within the area 14 where fertilization not should be performed, such as a rocky sub-area where no trees grow. It should be noted that the appearance of the area 14 may change during the operation of the UAV 10 moving over the area 14, in which case the representation may have to updated before the complete area 14 has been covered. The representation of the area 14 is divided into parallelly arranged segments, in this particular embodiment seven segments A-G.

The orientation of the parallelly arranged segments are preferably, but not necessarily, aligned in a direction from a starting point of the UAV 10 to a center point of the area 14. In an embodiment, a width of each segment A-G is adapted to the spreading radius over which the UAV 10 deposits fertilizer over the area 14. If the spreading radius is 5 m, the segment width will be selected to be 10 m, or just under or above 10 m. It should further be noted that the width not necessarily is equal for all segments A-G. In case of for instance a lawn mower, the width of the segments would be adapted to the operational width of a cutting mechanism of the mower, while for an autonomous harvester the width would be adapted to the operational range of a harvesting tool of the harvester.

Hence, the width of each segment is in an embodiment adapted to a working width of the autonomous device, which typically differs depending on the type of autonomous device being utilized.

With reference to Figure 2, the steps of the method performed by the control device 15 of controlling movement of at least one autonomous device 10 over an area 14 according to embodiments are in practice performed by a processing unit 20 embodied in the form of one or more microprocessors arranged to execute a computer program 21 downloaded to a suitable storage medium 22 associated with the microprocessor, such as a Random Access Memory (RAM), a Flash memory or a hard disk drive. The processing unit 20 is arranged to cause the control device 15 to carry out the method according to embodiments when the appropriate computer program 21 comprising computer-executable instructions is downloaded to the storage medium 22, being e.g. a non-transitory storage medium, and executed by the processing unit 20. The storage medium 22 may also be a computer program product comprising the computer program 21. Alternatively, the computer program 21 may be transferred to the storage medium 22 by means of a suitable computer program product, such as a Digital Versatile Disc (DVD) or a memory stick. As a further alternative, the computer program 21 may be downloaded to the storage medium 22 over a network. The processing unit 20 may alternatively be embodied in the form of a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a complex programmable logic device (CPLD), etc.

With reference to Figures 3a and 3b, after the area 14 has been segmented in step S101; upon leaving the base station (i.e. the truck 13), the UAV 10 is instructed in step S102 by the control device 15 to move - i.e. to fly - to a selected one of the segments A and move over the area 14 along segment A until an end of the area 14 is reached in the segment A.

When reaching the end of the area 14 in segment A, the UAV 10 is instructed to move to a next segment B and moves over the area in segment B in a direction opposite to the direction of movement in segment A while disposing fertilizer over the area 14. The UAV 10 is then instructed to move to an end of the area 14 in segment B whereupon the UAV 10 moves to next segment C, and so on, until having covered the complete area 14 upon reaching the end of the area 14 in segment G, wherein the UAV 10 is instructed by the control device 15 to return to its starting point at the base station.

Advantageously, with the described embodiment the UAV 10 will be controlled to systematically and orderly travel across the area 14 to be fertilized, with the number of turning maneuvers kept low in order to keep energy consumption down. Should a capacity threshold of the UAV 10 have been reached (or is close to being reached) before the complete area 14 has been covered, the UAV 10 will be instructed to return to the starting point, i.e. the truck 13, in order to restore capacity. Advantageously, the control device 15 plans the route of the UAV 10 well in advance, and will thus timely instruct the UAV 10 to return to the truck 13.

Figure 4 illustrates such a scenario, where the UAV 10 is instructed to move through segments A-C as previously has been described with reference to Figures 3a and 3b. However, after having traversed the area 14 in segment D, the control device 15 concludes that a capacity of the UAV 10 is close to being reached.

Hence, information regarding operational capacity of the UAV 10 is acquired by the control device 15.

For example, a maximum carrying capacity of the UAV 10 is 30 kg, the spreading radius is 5 m, while 0.055 kg of fertilizer is to be disposed over each square meter of the area 14. This means that the UAV 10 can travel a total distance of 30 / (0.05 x 10) = 54.5 m at a given speed before running out of fertilizer. As previously mentioned, battery capacity is also an important parameter. Weather and wind conditions may also affect utilization of capacity.

Assuming for instance that the length of the area 14 in segment A is e.g. 26 m while the length of the area 14 in segment B is 28 m; the control device 15 would than instruct the UAV 10 to fertilize the part of the area 14 enclosed by segments A and B and then return to the truck 13 for a refill of fertilizer. In a more elaborate example, the control device 15 makes the assessment that the UAV 10 will be able to cover segments A and B if a speed of X km/h are held, while being able to cover (after a fertilizer refill) the longer segments C and D if a lower speed Y is held. Further, the control device 15 could e.g. concluded that after segments C and D has been covered at the lower speed Y, not only is a fertilizer refill required, but also a battery charge, upon the UAV 10 returning to the truck 13..

In an embodiment, current status regarding the capacity of the UAV 10 is continuously communicated from the UAV 10 to the control device 15 with respect to e.g. amount of fertilizer left, travelled distance, battery capacity, speed, etc. Further, travel data of the UAV 10, such as position, speed and heading, is continuously communicated to the control device 15.

After having moved through segment D, the UAV 10 is thus instructed by the control device 15 to return to the base station to refill fertilizer. After having been refilled, the UAV 10 is instructed to move to segment E and dispose fertilizer over the area 14 in segments E and F, thereby fertilizing the complete area 14 before returning to the base station.

Figure 5 illustrates a further embodiment, where it is taken into account that the acquired representation further comprises a sub-area 16 within the area 14 where fertilization not should be performed, such as a rocky sub-area where no trees grow.

In such a scenario, in addition to segmenting the area 14 into parallelly arranged segments A-F as previously has been described in detail, the control device 15 will further create sub-segments within the segments where the rocky sub-area 16 is located.

In Figure 5, it can be seen that in segment A, no sub-segment will be created for the sub-area 16, since the UAV 10 still will have to dispose fertilizer over the area 14 which is adjacent to the sub-area 16 in segment A.

However, in segment B, fertilizer is disposed as the UAV 10 travels along segment B until the sub-area is 16 are encountered. Hence, segment B is further segmented into three sub-segments Bi, B2 and B3. The control device 15 will instruct the UAV 10 to dispose fertilizer over first sub-segment Bi, discontinue the fertilization when travelling over second sub-segment B2, and resume the disposing upon reaching third sub-segment B3. It is noted that the movement of the UAV 10 will be the same as that discussed with reference to Figure 3a.

Thus when reaching the end of the area 14 in segment B, i.e. after having travelled over the third sub-segment B3, the UAV 10 will be instructed to move to segment C. Again, fertilizer will be disposed over first sub-area Cl, while the disposing is discontinued over second sub-segment C2, and finally resumed upon reaching third sub-segment C3. As in the case of segment A, no sub-segmentation will be performed for segment D.

The UAV 10 will fertilize the complete area 14 and return to the starting point after having travelled along segment G.

Advantageously, with the sub-segmentation being applied to segments B and C, no unnecessary disposal of fertilizer is performed, and premature exhaustion of fertilizer is avoided.

This is further advantageous for sustainability reasons, since no fertilizer is disposed over areas where little (or no) vegetation exists.

With reference to Figures 3 or 4, the UAV 10 is instructed to start at segment A, cover segment A, and then move to a next segment until last segment G is covered, wherein the UAV 10 returns to the starting point. However, it is envisaged that the UAV 10 could start at any segment and move through the segments until the complete area 14 has been fertilized. For instance, the UAV 10 could start at segment D and travel along segment D before moving to segment E and then on to segment F. After having completed segment G, the UAV 10 will move to segment A - being the next segment - and then to segments B and C before returning to the starting point.

In a further embodiment, with reference to Figure 6, a plurality of UAVs 10,

11 are utilized to fertilize the area 14.

In this exemplifying embodiment, first UAV 10 is instructed to fertilize the part of the area 14 enclosed by segments A-D while second UAV 11 is instructed to fertilize the part of the area 14 enclosed by segments E-G. When utilizing more than one UAV, a number of considerations must be made. As in the case with a single UAV, it is desirable to minimize the travelled distance while still fertilizing the complete area 14. However, the controlling of the movement of the UAVs 10, 11 should further be performed such that no queue occurs at the truck 13 when batteries are to be

charged/changed or fertilizer is to be refilled, and - importantly - such that collisions are avoided.

When controlling the two UAVs 10, 11 to move over the area 14, it may for instance be envisaged that the first UAV 10 is instructed to move to segment A, and the second UAV is instructed to move to segment E.

However, in order to avoid any queues at the base station, the second UAV 11 will not start until the first UAV 10 reaches, say, the end of the area 14 in segment A. Hence, the first UAV 10 will return to the base station for a fertilizer refill after having covered segments A and B. Alternatively, the control device 15 assigns a task to the second UAV 11 to be performed simultaneously as the task of the first UAV 10, the tasks of the first and second UAVs 10, 11 being planned by the control device 15 to avoid queues at the base station.

When the second UAV 11 has covered segments E and F and returns to the base station for fertilizer refill, the first UAV has already been refilled and leaves the base station and heads towards segment C.

In this way, the control device 15 may assign a service time slot for the first UAV 10 and the second UAV 11 already before the controlling process starts. In line with the previous example where the length of the part of the area 14 in segment A has a length of 24 m, while the length in segment B is 27 m, the total travel distance of the UAV 10 is 51 m (excluding a turn from segment a to segment B and the distance from the base station to the area 14).

If the travel speed of the UAVs 10, 11 are assumed to be 5 km/h, the control device 15 estimates that the first UAV 10 will be back for a fertilizer recharge in about (51/5000) x 3600 = 37 s. With the turn from segment A to B and the distance to/from the area 14 from the base station, the control device 15 will assign a service time slot in about 40 s from the starting time for the first UAV. A similar estimation is performed for the second UAV 11.

Advantageously, this avoids a queue at the base station, and thus ensures that the UAVs 10, 11 do not unnecessarily spend idle time on the ground, and even more important that the UAVs 10, 11 do not unnecessarily spend idle time in the air.

It should be noted that these estimates may change during an assignment being performed by any one of the UAVs 10, 11, for instance due to wind or other weather conditions.

In another example, should for instance battery capacity of a UAV be low, a number of assignments may be cancelled, but a close assignment may still be performed.

Further with reference to Figure 6, by assigning a flight route and timing to each UAV 10, 11 which do not coincide with the route and timing of the other UAV, collisions are advantageously avoided. Hence, the routes UAVs 10, 11 may be allowed to cross each other, as long as the timing of UAVs 10, 11 is not such that both UAVs will be at the crossing simultaneously.

Figure 7 illustrates a further embodiment. In this embodiment, the autonomous device is a robotic lawn mower 17.

As in the embodiment described with reference to Figure 5, it is taken into account that the acquired representation further comprises a sub-area 16 (being identical to that of Figure 5) within the area 14 where the lawn mower 17 should not travel, such as a rocky sub-area where the lawn mower 17 could be damaged.

Compared to the sub-segmenting discussed with reference to Figure 5, the creation of sub-segments is slightly different when the autonomous device 17 is a device which should not move over the sub-area 16 at all. As can be seen, created segment A is divided into four sub-segments A1-A4, and the lawn mower 17 is instructed to move to Ai and then to A2, but to avoid A3 altogether. Thereafter, the lawn mower 17 moves to segment A4 before travelling to sub-segment Bi in segment B. As it approaches the rocky sub-area 16, the lawn mower 17 will move to sub- segment C3 in next segment C. Thereafter, the lawn mower 17 moves along segments D-G, where it approaches the end of the area 14.

Now, instead of returning directly to the starting point (such as for instance a base in the form of a charging station), the lawn mower 17 travels to sub- segment Cl in segment C and then to sub-segment B3 in segment B before retuning to the starting point.

Advantageously, with the sub-segmentation being applied to segments A, B and C, the risk of damaging cutting parts of the lawn mower 17 decreases. Further, in case the sub-area 16 for instance is a hill, there is a risk that the lawn mower 17 cannot travel there without tipping over.

Figure 8 illustrates a further embodiment of controlling movement of UAVs. Again, the representation of the area 14 is divided into parallelly arranged segments, in this particular embodiment seven segments A-G. The orientation of the parallelly arranged segments A-G are preferably aligned in a direction from a starting point of the first UAV 10 and the second UAV 11 to a center point of the area 14.

The width of each segment A-G is typically adapted to the spreading width of each UAV, which in this example deposits fertilizer over the area 14.

Now, the UAVs 10, 11 are given the assignment to cover the area 14 with fertilizer.

The control device 15 will compute for instance a length of a full fertilizer spreading run of each of the UAVs 10, 11. Assuming e.g. that time for emptying a fertilizer tank is 15 seconds and the speed of each UAV is 5 m/s; one spreading run will then be 15 x 5 = 75 m. As is understood, the speed and amount of fertilizer being disposed of the UAVs may be adapted to the length of the segments; in this exemplifying embodiment, it is assumed that total length of segments A and B, including the stretch where the UAV must go from segment A to segment B, is about 73-74 m. The first UAV 10 is thus given the assignment to fertilize the area of segments A and B.

As is understood, the length of a segment may be longer than the computed spreading run of the first UAV 10, in which case the UAV 10 would have to return to the base when having disposed all the fertilizer. The first UAV 10 may thus be given this assignment by the control device 15, implying that the first UAV 10 must return to the base embodied e.g. by previously discussed truck 13 (not shown in Figure 8) for refilling fertilizer, since the tank of the first UAV 10 is practically empty after having performed the spreading run including segments A and B. Thus, after having given the assignment to the first UAV 10, the control device 15 is aware that the first UAV 10 will return in about 15 s. Upon starting their first assignment, the battery of the respective UAV 10, 11 is typically fully charged.

The control unit 15 may further estimate or measure energy consumption of the first UAV 10 for performing the assignment. The energy consumption is updated after each performed assignment in order for the control device 15 to keep track of when the battery of the first UAV 10 requires charging.

Now, after the first UAV 10 has been given the assignment, the second UAV 11 is given an assignment. It is assumed that the spreading run of the second UAV 11 also is 15 x 5 = 75 m, and that total length of segments G and F, including the stretch where the second UAV 11 must go from segment G to segment F, is about 73-74 m.

Now, the control device 15 will aim to optimize the assignments being given to the UAVs 10, 11. In this particular exemplifying embodiment, if the two UAVs 10, 11 begin their respective assignment at about the same point in time, the UAVs will return to the base for refilling fertilizer at the same time.

This is disadvantageous for a number or reasons. Firstly, there is a risk for collision if the two UAVs 10, 11 return to the base at the same time. Secondly, one of the UAVs will have to wait while the other fills up its tank with fertilizer.

Hence, in this exemplifying embodiment, to avoid the UAVs 10, 11 returning to the base at the same time for refilling of fertilizer, the control device 15 will estimate the time required for the first UAV 10 to refill fertilizer. Assuming that the refill time is estimated to 10 s, the control device 15 will upon giving the assignment to the second UAV 11 select between a number of possible assignments and in this exemplifying embodiment give to the second UAV 11 an assignment which is expected to take about 15 + 10 = 25 s, i.e. the time the assignment of the first UAV 10 is expected to take including refilling of fertilizer.

In this example, since the second UAV 11 should not return to the base for 25 s, the control device 15 will instruct the second UAV 11 to wait for 10 s before travelling towards segment G to dispose fertilizer over the area of segments G and F as shown in Figure 8. Since the spreading run of the second UAV 11 lasts for about 15 s, the second UAV 11 arrives at the base 10 s after the first UAV 10 which then has performed refill of fertilizer and is off on a new assignment as illustrated with the arrow indicating that the first UAV 10 proceeds to segment C.

In an alternative, the control device 15 could have given an assignment to the second UAV 11 to dispose fertilizer over a section of the area being located further away from the base as compared to the section of the area over which the first UAV 10 is instructed to move (i.e. segments A and B), such that the second UAV 11 will return to the base 10 s later than the first UAV 10 (but with the same length of the spreading run). The second UAV 11 will thus arrive at the base when the first UAV 10 has refilled fertilizer, meaning that there is no risk for collision.

In another embodiment, a UAV currently disposing fertilizer (i.e. being in operational mode) will fly at a lower altitude than a UAV in transport flight mode to further reduce risk of collision.

Figure 9 illustrates a further embodiment illustrating a situation where the length of the segments exceeds a maximum length of a spreading run. Hence, a UAV may have to return to the base 13 without having finished fertilizing the area of a complete segment. In this example, the first UAV 10 nearly finishes segment A, but needs to turn back to the base 13 for fertilizer refill (along line V2).

If such a situation occurs, the control device 15 computes a first vector Vi from the base 13 to a position where the fertilizer assignment starts and a second vector V2 from the base 13 to a position where the UAV 10 needs to return to the base 13 for refilling of fertilizer. In order to avoid collision, or at least mitigate the risk of collision, the second UAV 11 will not be given an assignment where it would need to pass over the area formed by the first vector Vi and the second sector V2.

Thus, in this embodiment, the second UAV 11 would not be given an assignment which includes segment B, but could be given an assignment which includes segment C, even though segment C is close to being off limits for assigning due to the starting point of segment C being very close to the second vector V2.

Hence, with reference to the embodiments of Figure 8 and Figure 9, an UAV may be given an assignment unless:

• the point in time of the UAV returning to the base 13 overlaps with the point at which another UAV returns to the base 13; • there is a risk for collision, i.e. the UAV need to pass over the area formed by the first vector Vi and the second vector V2 for another

UAV; and

• if the estimated energy consumption exceeds a current energy capacity of the battery of the UAV (if so, an operator may be alerted to charge the battery).

Further, when all UAVs are in operation (even though only two UAVs are included hereinabove for illustrative purposes, a fleet may in practice comprises tens of UAVs), the control device 15 shall change from short term planning to long term planning of the complete mission, in the above to fertilize the whole area 14. This is necessary in order to avoid queues at the base station 13 because of unexpected battery swaps caused by UAV battery discharge. To plan the time for occupying the base station 13 due to battery swap, the control device 15 needs an estimation of which UAV will handle which assignment and at what moment in time. The result will be a flight plan with all UAVs and assignments included. When something does not happen according to plan, e.g. a battery swap taking more time than estimated, the control device 15 will need to modify the assignment planning.

The disclosure has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the disclosure, as defined by the appended patent claims.

Claims

1. A method of a control device (15) of controlling movement of at least one autonomous device (10) over an area (14), comprising:

segmenting (S101) a representation of the area (14) into parallelly arranged segments (A-G); and

instructing (S102) the at least one autonomous device (10) to move over the area (14) along a selected segment (A) until an end of the area is reached in the selected segment, wherein the at least one autonomous device (10) is instructed to move over the area (14) along a next segment (B), in a direction opposite to the movement performed when moving along the preceding segment (A), until an end of the area (14) is reached in the next segment (B), wherein movement from one segment to a next segment is performed either until the area (14) has been completely covered or a capacity threshold of the at least one autonomous device (10) has been reached, in which case the at least one autonomous device (10) is instructed to return to a base (13) from which the at least one autonomous device (10) started.

2. The method of claim 1, the segmenting (S101) further comprising: dividing at least one of the segments (B) into sub-segments (Bi, B2, B3).

3. The method of claim 2, the autonomous device (10) being configured to move over the area (14) to deposit material over the area (14), wherein the autonomous device (10) is instructed not to deposit material over at least one selected sub-segment (B2) over which it moves.

4. The method of claims 2 or 3, wherein the autonomous device (17) is instructed not to move over at least one selected sub-segment (B2).

5. The method of any one of the preceding claims, wherein at least two autonomous devices (10, 11) are controlled to move over the area (14), and the instructing (S101) of the at least two autonomous devices (10, 11) further comprises instructing the at least two autonomous devices (10, 11) to move over the area (14) without colliding.

6. The method of claim 5, wherein the instructing (S101) of the at least two autonomous devices (10, 11) further comprises instructing the at least two autonomous devices (10, 11) to move over the area (14) such that queues among said at least two autonomous devices (10, 11) are avoided at the base (13).

7. The method of claims 5 or 6, wherein the at least two autonomous devices (10, 11) are instructed to move over the area (14) such that upon giving a first instruction to a first device (10) of the at least two autonomous devices (10, 11), the control device (15) computes a timing when the first autonomous device is expected to return to the base (13) and leave for a new assignment, wherein the control device is configured to give a second instruction to a second device (11) of the at least two autonomous devices (10, 11) to move over the area (14) and return to the base (13) after the first autonomous device (10) has left the base (13) for the new assignment,

8. The method of claim 7, wherein the control device (15) is configured to instruct the second autonomous device (11) to move over a section of the area (14) being located further away from the base (13) than a section of the area over which the first autonomous device (10) is instructed to move.

9. The method of claim 7, wherein the control device (15) is configured to instruct the second autonomous device (11) to wait for a time period before moving over the area (14) as instructed.

10. The method of any one of the claims 5-9, the control device (15) computing a first position where an assignment starts for a first device (10) of the at least two autonomous devices (10, 11) and a second position here the assignment ends and the first autonomous device (10) returns to the base, wherein the second autonomous device (11) is instructed not to move over an area delimited by a first vector (V 1) from the base (13) to the first position and by a second vector (V 2) from the base (13) to the second position.

11. The method of any one of the preceding claims, wherein the capacity threshold is stipulated by one or more of a capacity property selected from: amount of material that the autonomous device (io) can carry, spreading radius over which the autonomous device (io) deposits material, energy capacity of an energy source from which the autonomous device (io) is powered, speed with which the autonomous device (io) moves and memory capacity of the autonomous device (io) for storing data.

12. A control device (15) configured to control movement of at least one autonomous device (10) over an area (14), the control device (15) comprising a processing unit (20) and a memory (22), said memory containing instructions (21) executable by said processing unit (20), whereby the control device (15) is operative to:

segment a representation of the area (14) into parallelly arranged segments (A-G); and

instruct the at least one autonomous device (10) to move over the area

(14) along a selected segment (A) until an end of the area is reached in the selected segment, wherein the at least one autonomous device (10) is instructed to move over the area (14) along a next segment (B), in a direction opposite to the movement performed when moving along the preceding segment (A), until an end of the area (14) is reached in the next segment (B), wherein movement from one segment to a next segment is performed either until the area (14) has been completely covered or a capacity threshold of the at least one autonomous device (10) has been reached, in which case the at least one autonomous device (10) is instructed to return to a base (13) from which the at least one autonomous device (10) started.

13. The control device (15) of claim 12, further being operative to, when performing the segmenting:

divide at least one of the segments (B) into sub-segments (Bi, B2, B3).

14. The control device (15) of claim 13, the autonomous device (10) being configured to move over the area (14) to deposit material over the area

(14), wherein the control device (15) further is operative to instruct the autonomous device (10) not to deposit material over at least one selected sub- segment (B2) over which it moves.

15. The control device (15) of claims 13 or 14, the control device (15) further being operative to instruct the autonomous device (17) not to move over at least one selected sub-segment (B2).

16. The control device (15) of any one of claims 12-15, wherein at least two autonomous devices (10, 11) are controlled to move over the area (14), and the control device (15) further is operative to, when instructing the at least two autonomous devices (10, 11), instruct the at least two autonomous devices (10, 11) to move over the area (14) without colliding.

17. The control device (15) of claim 16, the control device (15) further being operative to, when instructing the at least two autonomous devices (10, 11), instruct the at least two autonomous devices (10, 11) to move over the area (14) such that queues among said at least two autonomous devices (10, 11) are avoided at the base (13).

18. The control device (15) of claims 16 or 17, wherein the at least two autonomous devices (10, 11) are instructed to move over the area (14) such that upon giving a first instruction to a first device (10) of the at least two autonomous devices (10, 11), the control device (15) computes a timing when the first autonomous device is expected to return to the base (13) and leave for a new assignment, wherein the control device is configured to give a second instruction to a second device (11) of the at least two autonomous devices (10, 11) to move over the area (14) and return to the base (13) after the first autonomous device (10) has left the base (13) for the new assignment,

19. The control device (15) of claim 18, wherein the control device (15) is configured to instruct the second autonomous device (11) to move over a section of the area (14) being located further away from the base (13) than a section of the area over which the first autonomous device (10) is instructed to move.

20. The control device (15) of claim 19, wherein the control device (15) is configured to instruct the second autonomous device (11) to wait for a time period before moving over the area (14) as instructed.

21. The control device (15) of any one of the claims 16-20, the control device (15) being configured to compute a first position where an assignment starts for a first device (10) of the at least two autonomous devices (10, 11) and a second position here the assignment ends and the first autonomous device (10) returns to the base, wherein the second autonomous device (11) is instructed not to move over an area delimited by a first vector (Vi) from the base (13) to the first position and by a second vector (V2) from the base (13) to the second position.

22. The control device (15) of any one of claims 12-21, wherein the capacity threshold is stipulated by one or more of a capacity property selected from: amount of material that the autonomous device (10) can carry, spreading radius over which the autonomous device (10) deposits material, energy capacity of an energy source from which the autonomous device (10) is powered, speed with which the autonomous device (10) moves and memory capacity of the autonomous device (10) for storing data.

23. The control device (15) of any one of claims 12-22, the at least one autonomous device (15) being one of an autonomous vehicle moving on the ground, an autonomous sea vessel and an unmanned aerial vehicle, UAV.

24. The control device (15) of any one of claims 12-23, further being operative to continuously acquire a current status regarding the capacity of the autonomous device (10) or travel data of the autonomous device (10).

25. The control device (15) of any one of claims 12-24, further being operative to, when segmenting (S101) a representation of the area (14) into parallelly arranged segments (A-G):

adapt of width of each segment to a working width of the autonomous device (10).

26. A computer program (21) comprising computer-executable instructions for causing a control device (15) to perform the method recited in any one of claims 1-11 when the computer-executable instructions are executed on a processing unit (20) included in the control device (15).

27. A computer program product comprising a computer readable medium (22), the computer readable medium having the computer program (21) according to claim 26 embodied thereon.