SE542918C2 - Robotic tool with boundary wire loop - Google Patents

Abstract

The present disclosure relates to a self-propelled robotic tool (1) comprising a work implement (3), a driving arrangement (5, 7, 9, 11) for moving the robotic work tool, a control device (13) for controlling the driving arrangement, and an acquisition device (23, 25), configured to record a signal (27; 31) transmitted in bursts by a boundary wire loop (19), wherein the control device is configured to determine whether the robotic work tool is located within an area (17) defined by the boundary wire loop based on the recorded signal. There is provided a digital signal processor (39) which is configured to provide an output corresponding to an average of a plurality of recorded transmitted signal bursts, wherein the control device (13) is configured to determine whether the robotic tool (1) is located within said area (17) at least partly based on said output.

Description

FšOBOTIC TOOL WETH BOUNDÅRY WlRE LQOF* Technical field The present disclosure relates to a self-propelled robotic tool comprising a workimplement, a driving arrangement for moving the robotic work tool, a control devicefor controlling the driving arrangement, and an acquisition device, configured torecord a signal transmitted in bursts by a boundary wire loop, wherein the controldevice is configured to determine whether the robotic work tool is located within anarea defined by the boundary wire loop based on the recorded signal.

Further, a correspondlng method for controlling a self-propelled robotic tool isconsidered.

Background Such a self-propelled robotic tool is disclosed for instance in EP-2741160-A1, wherea recorded signal is correlated with a reference signal, or the like, in order todetermine whether the robotic work tool is located within the area in question.

One general problem associated with tools of this type is how to increase thereliability in determining whether the robotic tool remains located within the areadefined by the boundary wire loop.

Summary One object of the present disclosure is therefore to provide a self-propelled robotictool which determines with an increased reliability whether the tool is located within a work area.

This object is achieved by means of a self-propelled robotic tool as defined in claim1. More particularly, in a self-propelled robotic tool of the initially mentioned kind, adigital signal processor is provided which is configured to provide an outputcorrespondlng to an average of a plurality of recorded transmitted signal bursts. Thecontrol device is configured to determine whether the robotic tool is located withinsaid area at least partly based on said output. This allows the determining of whetherthe robotic tool remains located within the area in question in a more reliable mannerin particular to deal with noisy conditions.

The output may correspond to an average of a sequence of bursts repeated with anestimated period time (P). ln this average burst, the order of flanks or other pulse characteristic may then bedetermined and compared to a reference. Alternatively, the determined average maybe correlated with a reference pattern.

Typically, the average may be made up from between 2 and 20 of the most recentlyreceived pulses.

The estimated period time may be determined using a recursive algorithm.Typically, the self-propelled robotic tool may be a robotic lawn mower.

The present disclosure further considers a corresponding method comprising thesteps carried out in a self-propelled robotic tool as defined above.

Brief description of the drawinds Fig 1 illustrates schematically a self-propelled robotic tool operating in a work area.Fig 2 schematically illustrates system units of the self-propelled robotic tool in fig 1.Fig 3 illustrates an example of burst with certain signatures or patterns.

Fig 4 shows an example of a signal with burst having specific flank orders.

Fig 5 illustrates digital signal processing using a number of successive bursts.

Fig 6 illustrates schematically units in a system carrying out a detection method andfig 7 illustrates an example flowchart of such a detection method.

Detailed description The present disclosure relates generally to self-propelled robotic work tools, of thekind disclosed for instance in EP-2741160-A1, where a robotic mower for cuttinglawns is shown as an example. Such a mower is shown schematically in figs 1 and 2where a mower 1 has a cutting implement 3, e.g. a rotating knife, and wheels 5, 7typically driven by electric motors 9, 1 1. There may also be provided non-driven, e.g. swiveling wheels, and various other wheel configurations are possible.

The steering of the robotic work tool is carried out by controlling the driving motors 9,11 by means of a control unit 13, cf. fig 2. A battery arrangement 15 powers themotors 9, 11 as well as the control unit 13.

By controlling the motors 9, 11, the control unit 13 moves the robotic work tool 1 overa work area 17, typically a lawn. A boundary wire 19, which may typically be buried afew centimeters deep in the ground, defines the work area 17, the boundary wire 19forming a loop, which is typically closed at a transmission unit 21, transmitting asignal on the boundary wire 19. The ends of the boundary wire 19 are typicallyconnected to the transmission unit 21 which may be integrated with a charging station that can be used to intermittently charge the battery arrangement 15.

The transmission unit 21 thus feeds an electric signal to the boundary wire 19 thatoperates as a form of antenna, radiating an electromagnetic signal which the roboticwork tool 1 can pick up using one or more coils. Based on the signal, the robotic worktool can be controlled, typically making sure that the robotic work tool remains withinthe work area 17. ln the aforementioned document, the transmitted signal comprisesbursts of signals with predetermined patterns and separated by pauses. Within thebursts, the signal switches between high and low states, where the duration of thehigh states is different from the duration of the low states within a burst.

The electromagnetic signals transmitted by the boundary wire 19 are thus picked upby two or more coils 23, 25 connected to the control unit 13 in the robotic work tool 1.The picked-up signal may be more or less equivalent to the first order derivative ofthe current fed to the boundary wire 19, and therefore also the signals fed to thecontrol unit 13 have a distinguishable pattern. lf all of the two or more coils 23, 25 arelocated inside the work area 17 defined by the boundary wire 19, the patterns will besimilar, and any disturbances will also affect both signals similarly. When the robotictool 1 is about to move outside the work area, however, one of the coils 23 will belocated outside and another one 25 inside the work area 17. At this point, the signalsacquired by the first and second coils 23, 25 will become diametrically different. lt has also been suggested to use a transmission unit 21, transmitting a signal 27with bursts having a predetermined pattern 29 or signature as illustrated in fig 3.When receiving a signal, using one single coil, the self-propelled robotic tool maycorrelate the received signal with an internally stored template. As long as thecorrelation between the received signal's pattern and the template is high, the self-propelled robotic tool is considered to remain within the work area 17. When the self-propelled robotic tool moves outside this area however, the phase of the received signal reverses and the correlation drops, which can be determined by the controlunit 13.

Another example of a signal transmitted via a boundary wire is described in EP-1512053-A1. ln that example, a signal 31 with bursts comprising a set of pulses withpositive and negative flanks (voltage) having a predetermined order is transmitted, asillustrated in fig 4. lt may be determined, on the receiving side, for instance that aburst beginning with a positive pulse with a certain length is received, followed by anegative pulse of a certain length. This may be sufficient to determine whether or notthe self-propelled robotic tool remains within the work area. Bursts are repeated witha period time P or offset time. The order of flanks is one example of a pulsecharacteristic, other examples include lengths of pulses in a burst and/or delaystherebetween. ln both the initially described schemes however, noise and interference may makethe detection difficult. This has been addressed by using a high enough burstamplitude such that correct detecting takes place. That however may lead to highpower consumption and, more importantly, to excessive interference disturbing othersystems nearby. ln the present disclosure, correct detection is instead achieved by using a digitalsignal processor which provides an output based on an average of a plurality ofrecorded transmitted signal bursts. The control device is configured to determinewhether the robotic tool is located within said area at least partly based on saidoutput.

An example of this is illustrated in fig 5 where a received signal 33 corresponding tothe transmitted signal of fig 4 is shown. As illustrated, the received signal may bevery noisy, and it may be difficult to assess e.g. the order of flanks, positive-negative-positive based on an individual burst 35. However, by using a digital signal processorit is possible to superpose a plurality of such individual burst to form a sum corre-sponding to an average burst 37 thereof. ln this signal e.g. the order of flanks can bedetected more easily. By a burst is here generally meant a varying signal that lastsfor a certain amount of time.

Fig 6 illustrates schematically units in a system carrying out a detection method andfig 7 illustrates an example flowchart of such a detection method. The method may be carried out by a digital signal processor 39, DSP, in the control unit 13, althoughother hardware configurations are conceivable. Further, a buffer 41 and a timing unit43 may be provided, which are shown as individual units although they may beintegrated for instance in the DSP 39.

With reference to fig 7, the method may begin with clearing 45 the buffer 41 ormemory. The system waits 47 an estimated period time Pest, and thereafter samples49 data input from the coil 23. The sampled data is added 51 to the buffer 41. Byadding is here meant that the received signal is added to corresponding data fromprevious pulses such that the value at a time t, vi is added to the corresponding valueof previous pulses vl-P+vl-2P+...etc. The sum in the buffer thus corresponds to anaverage of pulses received since the last clear event, even if not divided by the number of pulses.

Detection 53 is then done on the data in the buffer, whether by testing the order offlanks or other pulse characteristic, or carrying out a correlation procedure. lf thedetection is considered successful 55, the process may go on to report the condition(inside/outside work area) to other functions in the control unit 13. lf, however, theaccumulated data is insufficient to carry out detection, the process in the DSP 39may instead wait another period P, sample a new burst and add to the buffer 49, 51,and again attempt to detect 53 the condition.

Once a condition has been reported 57, it may be useful to update the estimatedperiod time. This may be done by adjusting the previously estimated period Pestwhich was used during the last accumulation as a linear combination with the periodtime Pdel that can be determined from the last accumulated bursts, e.g. such that thenew estimated period time Peslnew can be defined as: Peslnew= 0.9*Pesl+0.1*Pdel .

This provides a recursive algorithm that adapts the detection to the transmitted signaland may be further developed using Kalman filters and the like.

The present disclosure is not limited to the above-described examples and may bevaried and altered in different ways within the scope of the appended claims.

For instance, even if the transmitted signals have been shown as short burstsinterleaved with long pauses, the burst may be as long as the period time such as thesignal appears to be transmitted continuously.

Claims (8)

1. A self-propelled robotic tool (1) comprising a work implement (3), adriving arrangement (5, 7, 9, 11) for moving the robotic work tool, a control device(13) for controlling the driving arrangement, and an acquisition device (23, 25),configured to record a signal (27; 31) transmitted in bursts by a boundary wire loop(19), wherein the control device is configured to determine whether the robotic worktool is located within an area (17) defined by the boundary wire loop based on therecorded signal, characterized by a digital signal processor (39) which is configuredto provide an output corresponding to an average of a plurality of recordedtransmitted signal bursts, wherein the control device (13) is configured to determinewhether the robotic tool (1) is located within said area (17) at least partly based onsaid output.

2. Self-propelled robotic tool according to claim 1, wherein the outputcorresponds to an average of a sequence of pulses repeated with an estimatedperiod time (P).

3. Self-propelled robotic tool according to claim 2, wherein a pulsecharacteristic in the determined average is compared to pulse characteristicreference.

4. Self-propelled robotic tool according to claim 2, wherein thedetermined average is correlated with a reference pattern.

5. Self-propelled robotic tool according to any of claims 2 to 4, whereinthe average is made up from between 2 and 20 of the most recently received pulses.

6. Self-propelled robotic tool according to any of claims 2 to 5, whereinthe estimated period time is determined using a recursive algorithm.

7. Self-propelled robotic tool according to any of the preceding claims,wherein the self-propelled robotic tool is a lawn mower.

8. A method for controlling a self-propelled robotic tool comprising a workimplement, a driving arrangement for moving the robotic work tool, a control devicefor controlling the driving arrangement, and an acquisition device, configured torecord a signal transmitted in bursts by a boundary wire loop, wherein the controldevice determines whether the robotic work tool is located within an area defined by the boundary wire loop based on the recorded signal characterized by a providingan output corresponding to an average of a plurality of recorded transmitted signalbursts, and determining whether the robotic tool is located within said area at leastpartly based on said output.