SE2150299A1

SE2150299A1 - Robotic garden tool

Info

Publication number: SE2150299A1
Application number: SE2150299A
Authority: SE
Inventors: Anton Mårtensson; Beppe Hellsin; Jimmy Petersson; Olof Lydén; Per-Ola Svensson
Original assignee: Husqvarna Ab
Priority date: 2021-03-17
Filing date: 2021-03-17
Publication date: 2022-09-18
Also published as: DE102022104749A1; SE545146C2

Abstract

The present disclosure relates to a robotic garden tool (1) comprising a set of wheels (3, 5) and means for self-navigation across an area to be processed. In order to avoid that the robotic garden tool drown in puddles that are formed during heavy rains in the processed area there is provided an electric sensor (21) for recording an electric property of the surface under the robotic garden tool and a detector (23) configured to determine, based on the electric property, a condition where the robotic garden tool is entering a puddle of water. Control means (25) of the robotic garden tool are configured to initiate a puddle-avoidance maneuver in the case where such a condition is detected.

Description

ROBOTIC GARDEN TOOL Technical field The present disclosure relates to a robotic garden tool comprising a set of wheels and means for self-navigation across an area to be processed.

Background Use of such robotic garden tools have become very widespread. Usually, a predefined working area is processed, within which the robotic garden tool moves autonomously.

One problem associated with such robotic garden tool is to increase their reliability during long-term use in sometimes difficult conditions.

Summary One object of the present disclosure is therefore to provide a robotic garden tool with improved reliability. This object is achieved by means of a robotic garden tool as defined in claim 1. More specifically, in a robotic garden tool of the initially mentioned kind, an electric sensor is provided for recording an electric property of the surface under the robotic garden tool. A detector determines, based on the electric property, whether a condition has occurred where the robotic garden tool is entering a puddle of water. lf so, control means initiate a puddle-avoidance maneuver.

Heavy rains can cause temporary deep puddles of water in a part of the robotic garden tool's working area that is processed under normal circumstances. A robotic garden tool that runs into such a puddle may damage its motors or vital electronics and therefore become temporarily or permanently inoperable. This is especially inconvenient as periods with heavy rains also result in rapid grass growth where an operable device is much needed.

By providing a puddle-avoidance functionality as described above, the robotic garden tool can be kept operable resulting in improved overall reliability. The area corresponding to the puddle is kept within the overall working area and can be processed at a later stage when the water has been absorbed by the soil beneath the lawn.

The electric property may typically be a measured resistance or generally an impedance. A puddle under the robotic garden tool presents a rather small electric resistance between two probes that extend towards the ground and this low resistance may be detected.

The measured resistance may include a first resistance, between a first wheel arrangement and the ground under the first wheel arrangement, and typically a second resistance, between a second wheel arrangement and the ground under the second wheel arrangement. This makes efficient use of one or more wheels, for instance non-driving swiveling wheels, as probes for sensing electric resistance under the robotic garden tool.

A wheel arrangement, where the resistance is measured, may comprise a metal hub and a non-metal wheel spinning around the hub. This implies that a resistance level drops rapidly when a water level reaches the hub. Additionally, there may be provided a conductive rod at the hub projecting towards the ground, so that a lower water level may be detected.

Typically, the electric property is measured at a front portion of the robotic garden tool, in the normal travel direction thereof.

The electric property may generally be measured in between two wheels of the robotic garden tool.

The detector may detect the condition based on the resistance falling below a threshold.

The puddle-avoidance maneuver may include reversing the robotic garden tool and altering its heading so that another area can be processed instead.

The robotic garden tool is typically configured to operate within a pre-defined working area and to detect puddles within that working area.

The present disclosure further considers a corresponding method for controlling a robotic garden tool comprising a set of wheels and means for self-navigation across an area to be processed. The method includes recording an electric property of the surface under the robotic garden tool, determining, based on the electric property, a condition where the robotic garden tool is entering a puddle of water, and initiating a puddle-avoidance maneuver, in the case where said condition is detected.

Brief description of the drawinqs Fig 1 shows a robotic garden tool in the form of a lawn mower.

Fig 2 illustrates a working area processed by a robotic garden tool. Fig 3 shows a robotic garden tool about to enter a puddle of water.

Fig 4 illustrates one configuration of a sensor provided to detect a condition where the robotic garden tool of fig 3 is entering a puddle of water.

Fig 5 illustrates elements of a puddle detection and avoidance system in and/or connected to a robotic garden tool. Fig 6 illustrates movements of a puddle-avoidance maneuver. Fig 7 illustrates a wheel configuration useful for recording an electric parameter.

Fig 8 shows a flow chart of a method for puddle avoidance.

Detailed description The present disclosure relates to robotic garden tools, such as the one illustrated in fig 1. Fig 1 shows a robotic lawn mower 1, configured to process a working area in the form of a lawn. The lawn mower 1 moves autonomously over the lawn while cutting grass, driven by a pair of driving wheels 3 and additionally supported by a pair of swiveling non-driving wheels 5. lt should be noted that, with regard to this disclosure, several other different wheel configurations are possible, such as four- wheel driven configurations, articulated configurations, etc. ln addition to lawn mowers, other robotic garden tools may be considered.

The autonomous operation of the robotic garden tool 1 is illustrated in fig 2. The processed working area 11 is defined by an outer boundary 7 that may be defined by a buried boundary wire that is detected by the robotic garden tool 1 to keep it within the working area 11. Other navigation means are possible such as using GPS or other satellite navigation systems conceivably enhanced with real-time kinematics, RTK, for instance.

The present disclosure is primarily directed towards avoiding that the robotic garden tool drowns or is otherwise damaged by driving into a puddle of water 9 that temporarily exists within the working area defined by the outer boundary 7. Such puddles 9 of water may typically be formed by heavy rains during the summer and may be several centimeters deep. Within the timespan of a few hours or less, the water is usually absorbed by the soil underneath the lawn, but during that period it is advantageous that the robotic garden tool avoids the puddle in order to reduce the risk of drowning or otherwise damaging the robotic garden tool. Also, cutting soaked grass is very inefficient.

The present disclosure provides an efficient way of detecting that the robotic garden tool is about to drive into a puddle 9 of water, such that the puddle 9 can be avoided. ln a self-navigating robotic garden tool 1 of the type shown in fig 1, there is provided with reference to fig 5 an electric sensor 21 for recording an electric property of the surface under the robotic garden tool. This takes advantage of the fact that a relatively large volume of water has recognizable electric properties that deviates from comparatively dry soil covered with growing grass.

A detector 23 is connected to the sensor 21 and detects, based on the measured electric property, a condition where the robotic garden tool is about to enter a puddle of water. The detector in turn may be connected to a control unit 25 which is configured to initiate a puddle-avoidance maneuver, in the case where such a condition is detected. lt is possible also to update a mapping unit 27 in the case a puddle is detected to include a spot where puddles are prone to be formed in case of heavy rains into mapping data. This allows for instance to avoid areas where such spots exist directly after a heavy rain as may be registered by a separate weather unit.

Although different layouts are possible, it is noted that the detector unit 23, the control unit 25 and the mapping unit 27 may typically be integrated in the robotic garden tool's computer system as software routines.

Fig 3 shows a robotic garden tool 1 about to enter a puddle of water 9. Running in the normal heading of the garden tool 1, the front part of the garden tool 1 first enters water and for this reason it is advantage to locate at least parts of the sensor in the front half of the garden tool 1 or in front of the driving wheels 3, such that those wheels remain out of deep water and are capable of providing enough friction to move the garden tool 1 out of the puddle 9 as will be described. Generally, it is more advantageous the further to the front the sensor is located.

Fig 4 illustrates one configuration of a sensor provided to detect a condition where the robotic garden tool of fig 3 is entering a puddle of water. ln this configuration, the sensor arrangement measures an electric resistance below the robotic garden tool 1, specifically between the two front wheels 5.

Each front wheel 5 is connected to the chassis of the garden tool 1 by means of a metal wheel holder 13, which in one example be bent to have one end oriented substantially horizontally at the hub of the wheel 5 and the other end oriented vertically and being pivotably connected to the chassis of the garden tool 1. This allows the wheel 5 to roll on the ground and to swivel such that it can have any heading on the ground as determined by the garden tool 1 movements.

The resistance below the garden tool 1 can then be measured by forming an electric circuit between the wheel holders 13 of the wheels 5. A DC voltage source 15 is connected in between the wheel holders 13, and the current therethrough is measured with a current meter 17. lf the robotic garden tool 1 runs into a puddle 9 that is deep enough for the water to reach the hubs of the wheels 5, the resistance in the circuit drops significantly and an increased current is detected. lt is possible to form a corresponding circuit in various other ways, for instance by connecting to one wheel holder and a cable dragged on the ground by the robotic garden tool 1.

The sensing can be made more sensitive in different ways. ln the case illustrated in fig 4, the wheel holder 13 is made of metal such as steel and the wheel 5 is non- metal, typically plastic. This means that the resistance changes abruptly when the water reaches the hub of the wheel 5. lt would also be possible to provide the wheel 5 or parts thereof in a somewhat conductive material such as a low resistive plastic. This means that the resistance in a circuit drops gradually as the robotic garden tool 1 drives deeper into a puddle 9, and the resistance can be compared to a threshold in the control unit 25 (cf. fig 5) to determine whether a puddle avoidance maneuver should be initiated. This provides an earlier warning, making it possible to react at an earlier stage if needed.

A similar effect can be achieved as illustrated in fig 7 by means of a conductive or somewhat resistive rod 31 projecting from the wheel holder 13 towards the ground at the hub 33 of the wheel 5. This feature functions like a tactile rod, sensing water at a lesser depth. lt should be noted that other parameters than DC resistance may be used to detect a puddle. Generally, an impedance at the ground under the robotic garden tool can be determined. For instance, it would be possible to carry out a capacitive detection by providing one electric connection to the ground, as discussed above, and a connection to a metal plate at the bottom side for instance at the front of the robotic garden tool 1. lf an amount of water is present a few centimeters below the plate a capacitor is formed, the capacitance of which can be detected by providing an AC voltage to the circuit.

Fig 6 illustrates a puddle-avoidance maneuver when a robotic garden tool 1 is travelling towards a puddle 9 with an initial heading 41. At a point 43 where the puddle 9 is detected, the robotic lawn mower 1 stops. Then, it reverses 45 while changing its heading. The robotic garden tool 1 then proceeds along the new heading 47, thereby avoiding the puddle 9. The reversing length and the changing of heading may be varied in various ways. The reversing and changing of heading need not take place simultaneously.

Fig 8 illustrates briefly a puddle-avoidance method. ln a first step, an electric property of the surface under the robotic garden tool is recorded 81. Based on the electric property it is determined 83 whether the robotic garden tool is entering a puddle of water. lf so, a puddle-avoidance maneuver is initiated 85.

The present invention is not limited to the above described examples, and can be altered and varied in different ways within the scope of the appended claims.

Claims

1. A robotic garden tool (1) comprising a set of wheels (3, 5) and means for self-navigation across an area to be processed characterized by an electric sensor (21) for recording an electric property of the surface under the robotic garden tool a detector (23) configured to determine, based on the electric property, a condition where the robotic garden tool is entering a puddle of water (9), and control means (25) configured to, in the case where said condition is detected, to initiate a puddle-avoidance maneuver.

2. Robotic garden tool according to claim 1, wherein said electric property is a measured impedance.

3. Robotic garden tool according to claim 2, wherein said electric property is a measured resistance.

4. Robotic garden tool according to claim 3, wherein the measured resistance includes a first resistance, between a first wheel arrangement and the ground under the first wheel arrangement.

5. Robotic garden tool according to claim 4, wherein the measured resistance further includes a second resistance, between a second wheel arrangement and the ground under the second wheel arrangement.

6. Robotic garden tool according to claim 4 or 5, wherein the at least one wheel arrangement, where the resistance is measured, comprises a metal hub and a non-metal wheel spinning around the hub.

7. Robotic garden tool according to claims 6, wherein the hub comprises a conductive rod projecting towards the ground.

8. Robotic garden tool according to any of the preceding claims, wherein the electric property is measured at a front portion of the robotic garden tool, in the normal travel direction thereof.

9. Robotic garden tool according to any of the preceding claims, wherein the electric property is measured in between two wheels of the robotic garden tool.

10. Robotic garden tool according to any of the preceding claims 3-8, wherein the detector detects said condition based on the resistance falling below a threshold.

11. Robotic garden tool according to any of the preceding claims, wherein puddle-avoidance maneuver includes reversing the robotic garden tool and altering its heading.

12. Robotic garden tool according to any of the preceding claims, wherein the robotic garden tool is configured to operate within a pre-defined working area (11) and to detect puddles (9) within the working area.

13. A method for controlling a robotic garden tool (1) comprising a set of wheels and means for self-navigation across an area to be processed, the method characterized by recording (81) an electric property of the surface under the robotic garden tool determining (83), based on the electric property, a condition where the robotic garden tool is entering a puddle of water (9), and initiating (85) a puddle-avoidance maneuver, in the case where said condition is detected.