Abstract:
A locating system and method for determining the location of an article relative to a crop row. The system comprises a plurality of marker means substantially linearly disposed at intervals substantially parallel to the crop row. A sensor means is provided to generate a sensor signal indicative of the location of the sensor means and hence the article in relation to the crop row.

Description:
BRIEF DESCRIPTION OF THE INVENTION 
     The present invention relates to a locating system and method and, in particular, to a locating system and method for determining the location of an article relative to a crop row. 
     FIELD OF THE INVENTION 
     It is common in the agricultural industry to plant food crops in rows, each row being spaced from an adjacent row by a predetermined distance and the rows being generally parallel to each other. The areas between the crop rows facilitate access to the crops for the purpose of tending the crops. 
     In order to reduce the presence of weeds both in such areas between the rows and amongst the crops, it has been common to spray the crops with herbicides. However, such use of herbicides on food crops is becoming of greater concern to the public as excessive use of herbicides and fertiliser cause contamination of produce and excessive levels of nutrients in waterways. The use of herbicides for this purpose also introduces additional expense into the growth of the crops. 
     A solution to the above mentioned problem is to employ a manually controlled mechanical weeding apparatus to remove weeds between the crop rows. However, in order to remove the weeds with such mechanical weeding apparatus, it is necessary to accurately steer the mechanical weeding apparatus between the crop rows so as to avoid damaging the crop. This is often extremely difficult as the crop rows are generally not perfectly straight. Manual movement of the weeding apparatus is also very slow. 
     An alternative method of guiding a mechanical weeding apparatus incorporates a vision based system using CCD imaging and computer analysis to determine the location of the apparatus relative to the crop rows. However, although such a system operates satisfactorily in determining the location of the crop rows, the system is complex and expensive, and the accuracy of the system is dependent on weed density, the shape of the crop and wind and lighting conditions. 
     The present invention seeks, among other things, to provide a system which overcomes the above mentioned disadvantages. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, there is provided a locating system for determining the location of an article relative to a crop row, the system characterised by including a set of markers capable of being buried, the set of markers being substantially linearly disposed at spaced intervals substantially parallel to and along the length of the crop row, the set of markers having a predetermined characteristic selectable from a range of possible characteristics such that the predetermined characteristic is specific to the set and a sensor unit mounted relative to the article, in use, substantially above the markers, the sensor unit being arranged to detect a signal corresponding to the predetermined characteristic of the set of markers and to generate a sensor signal indicative of the location of the sensor unit relative to the set of markers and thereby of the article relative to the crop row. 
     In accordance with a further aspect of the present invention, there is provided a method of determining the location of an article relative to a crop row, the method including the steps of selecting a set of markers having a specific predetermined characteristic from a range of possible characteristics, the markers being capable of being buried, disposing the set of markers substantially linearly at spaced intervals substantially parallel to and along the length of the crop row, and providing a sensor unit mounted relative to the article, substantially above the set of markers, the sensor unit detecting a signal corresponding to the predetermined characteristic of the set of markers and generating sensor signal indicative of the location of the sensor unit relative to the set of markers and thereby of the article relative to the crop row. 
     The article may be a mechanical weeding apparatus and the weeding apparatus may include a movement actuator adapted to adjust the lateral position of the weeding apparatus relative to the crop rows in response to the control signal from the control means. In this way, the location of the weeding apparatus may be adjusted so that the weeding apparatus is maintained in the desired location relative to the crop row whereby weeds are removed without damaging the crop. 
     Alternatively, the article may be a herbicide spraying apparatus or fertiliser disposing apparatus which includes a movement actuator adapted to adjust the lateral position of the spraying apparatus or disposing apparatus relative to the crop rows in response to the control signal from the control means. In this way, the location of the spraying apparatus or disposing apparatus relative to the crop may be maintained, and herbicide may be sprayed only on weeds in areas between adjacent crop rows or fertiliser may be disposed only on crops. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a diagrammatic representation of a first embodiment of a sensing unit and a control unit of a locating system in accordance with the present invention; 
     FIGS. 2 a ,  2   b  and  2   c  are diagrammatic representations of the sensing unit shown in 
     FIG. 1 located, in use, in different locations relative to a crop row; 
     FIG. 3 is a diagrammatic representation of a second embodiment of a sensing unit and a control unit of a locating system in accordance with the present invention; 
     FIG. 4 is a diagrammatic representation of a mechanical weeding apparatus including the sensing unit and the control unit of FIG. 3; 
     FIG. 5 is a diagrammatic side view of a marker and seed disposal unit of the locating system of the present invention; 
     FIG. 6 a  is a diagrammatic side view of a lower portion of a marker disposal unit of the marker and seed disposal unit shown in FIG. 5; and 
     FIG. 6 b  is a diagrammatic plan view of a portion of the marker disposal unit shown in FIG. 6 a.   
    
    
     DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1 and 2, there is shown a first embodiment of a locating system  8  including a sensing unit  10  and a control unit  12 . The locating system  8  also includes marker means in the form of markers  13 , shown in use in FIGS. 2 a ,  2   b  and  2   c.    
     The sensing unit  10  includes a signal generation means, in this example a source of magnetic radiation in the form of a transmitting coil  14 , and sensor means responsive to the transmitting coil  14 , in this example in the form of first and second receiving coils  16  and  18  respectively. The first receiving coil  16  includes a first coil output  20  and the second receiving coil  18  includes a second coil output  22 . The first and second receiving coils  16 ,  18  are of substantially the same configuration and are spaced substantially the same distance from the centre of the transmitting coil  14 . The arrangement of the sensing unit  10  is such that the transmitting coil  14  emits magnetic radiation which is receivable by the first and second receiving coils  16 ,  18 , the first and second receiving coils each generating a current through the first and second receiving coils  16 ,  18  and a voltage across the first and second receiving coils  16 ,  18  in response to the received magnetic radiation. Under normal circumstances, since the configuration of the first and second receiving coils  16 ,  18  is substantially the same and the first and second receiving coils  16 ,  18  are spaced substantially the same relative to the transmitting coil  14 , the magnitude of the current and voltage generated by the first receiving coil  16  in response to the received magnetic radiation is substantially the same as the magnitude of the current and voltage generated by the second receiving coil  18  in response to the received magnetic radiation. Preferably, the first and second receiving coils  16  and  18  are arranged to be nulled under normal conditions such that no signal is generated on either of the first or second coil outputs  20  and  22  as a result of the radiation generated by the transmitting coil  14 . 
     The control unit  12  includes a logic circuit  24  having first and second logic circuit inputs  26  and  28  respectively. The logic circuit  24  also includes first and second logic circuit outputs  34  and  36  respectively and a power supply (not shown) for supplying the required power to all components of the locating system. 
     The logic circuit  24  is arranged so that, in use, the logic circuit  24  receives a signal on the first logic circuit input  26  from the first coil output  20  and a signal on the second logic circuit input  28  from the second coil output  22 . The signals received on the first and second logic circuit inputs  26  and  28  are indicative of the magnitudes of currents generated in the first and second receiving coils  16  and  18  respectively. The logic circuit  24  then compares the respective magnitudes of the signals received on the first and second logic circuit inputs  26  and  28  and generates output signals indicative of the difference between the two signals on the first and second logic circuit outputs  34 ,  36 . 
     The control unit  12  also includes a tolerance circuit  38  which allows a user to set the level of accuracy of the locating system, and a driver interface connection  40  which connects the logic circuit  24  to a control panel (not shown) for use by a user. 
     The sensing unit  10  of FIG. 1 is shown in use above a crop row  42  in FIGS. 2 a ,  2   b  and  2   c . Markers  13  are interspersed with crops  44  in the crop row  42  such that the markers  13  are disposed substantially linearly and parallel to the crop row  42 . The markers  13  are arranged to generate a signal or to distort the field produced by the transmitting coil  14  such that the result is detectable by the first and second receiving coils  16  and  18 . For example, the markers  13  may comprise a metallic object. The magnetic field generated by the transmitting coil  14  will induce current flow in the metallic object, which will in turn generate a magnetic field detectable by the first and second receiving coils  16  and  18 . Each of the first and second receiving coils  16  and  18  along with the transmitting coil  14  therefore acts in a manner similar to known metal detectors. 
     The metallic markers are preferably arranged to degrade over time to reduce the incidence of metallic markers from previous crops being detected within a current crop. 
     Preferably, the markers  13  are in the form of tuned markers. The tuned markers are arranged to generate a magnetic field when exposed to a magnetic field from the transmitting coil  14  of a predetermined frequency. The tuned markers may be constructed by known methods. For example, a resonant circuit tuned to a desired frequency could be incorporated within the marker  13 . Alternatively, the marker  13  may be of a cavity resonator type, wherein the physical characteristics of a cavity within the marker  13  determined the frequency to which it will respond. Further, the markers  13  may be transponders capable of transmitting additional information. The transponder may include sensors capable of measuring soil conditions and could transmit this information when activated to a data storage means included in the locating system  8 . This information could then be used to evaluate land conditions for crop planning. 
     The tuned markers would have the advantage that the interference from other metal objects, such as parts of the machinery on which the locating system  8  is mounted, would be reduced. Further, tuned markers of different frequencies could be used in subsequent crops to ensure that markers left in the soil from previous crops are not detected. A number of frequencies could be used alternatively to ensure that the tuned markers have degraded by the time the tuned markers of a certain frequency are used again. 
     In a further embodiment, the markers may be remotely deactivated so that they will not be detectable by the sensing unit  10 . Transponders of such type are known. This would allow the markers to become inactive at a time specified by the user in relation to the time requirements of the current crop. 
     In FIG. 2 b , the markers  13  are located closer to the first receiving coil  16  than the second receiving coil  18  and, therefore, the magnitude of the current generated in the first receiving coil  16  is greater than the magnitude of the current generated in the second receiving coil  18 . 
     In FIG. 2 c , the markers  13  are located closer to the second receiving coil  18  than the first receiving coil  16  and, therefore, the magnitude of the current generated in the second receiving coil  18  is greater than the magnitude of the current generated in the first receiving coil  16 . 
     It will also be understood that the difference in the magnitude of the currents generated in the first and second receiving coils  16 ,  18 , which is determined by the logic circuit  24 , is indicative of the lateral position of the transmitting coil  14  relative to the markers  13  and thereby to the crop row  42 . 
     It will also be appreciated that the configuration of the transmitting coil  14  and the sensing coils  16 ,  18  may be adjusted to suit the type of crop or the distance between markers  13 , for example by increasing or decreasing the length of the transmitting coil  14  and the sensing coils  16 ,  18 . 
     The tolerance circuit  38  operates so as to allow a user to set a maximum permitted distance of deviation of the transmitter coil  14  from a central location relative to the markers  13 . In this way, a signal indicative of a required movement of the sensing unit  10  does not appear on the first and second logic circuit outputs  34 ,  36  until the difference in signals corresponds to the maximum permitted distance. 
     FIG. 3 shows an alternative embodiment of a locating system  8  in accordance with the present invention. The locating system  8  of FIG. 3 includes a first antenna  80 , a second antenna  82  and an antenna controller circuit  84 . 
     The markers  13  in this embodiment are in the form of tuned transponders, arranged to transmit a response signal on receiving a signal from either of the first or second antennas  80  and  82 . 
     The antenna controller circuit  84  is capable of providing a driving signal to each of the first and second antennas  80  and  82  and also of detecting response signals received by the first and second antennas  80  and  82 . 
     In use, the antenna controller circuit  84  first provides a driving signal to the first antenna  80  while the second antenna remains idle. The first antenna  80  is arranged such that if a marker  13  is positioned directly below the area of the first antenna  80 , the transmitted signal from the first antenna  80  will activate the marker  13  to emit a response signal. The response signal from the marker  13  may then be received by the first antenna  80  and detected by the antenna controller circuit  84 . The antenna controller circuit  84  then deactivates the first antenna  80  and provides a driving signal to the second antenna  82 . If a marker  13  is positioned directly below the area of the second antenna  82 , then the marker  13  is activated to generate a response signal. The response signal may be received by the second antenna  84  and detected by the antenna controller circuit  84 . The antenna controller circuit then continues to drive the first and second antennas  80  and  82  alternately. The frequency at which the first and second antennas  80  and  82  are alternately driven is set so that sufficient information can be obtained regarding the position of the markers  13  for the speed of travel of the article on which the locating system  8  is mounted. 
     The antenna controller circuit  84  further includes first and second signal outputs  86  and  88 . The first and second signal outputs  86  and  88  provide signals to the logic circuit  24  on first and second logic circuit inputs  26  and  28 . The signals generated on first and second signal outputs  86  and  88  are indicative of whether a response signal from a marker  13  is received by either the first or second antenna  80  or  82  respectively. The logic circuit  24  includes logic circuit outputs  34  and  36  on which are generated signals indicative of the required movement of the sensing means  10  relative to the crop row  42 . 
     In a further embodiment of the locating system  8  of FIG. 3, the first and second antennas  80  and  82  are arranged such that they are positioned the same distance from the row of markers but with the first antenna  80  being positioned forward of the second antenna  82 . The would result in a lower level of interference between the first and second antennas  80  and  82  so that both may be turned on at the same time. 
     The locating system  8  of FIGS. 1 and 2 is shown mounted on a mechanical weeding apparatus  46  in FIG.  4 . 
     The weeding apparatus  46  includes a tool bar  48  and a plurality of harrows  50  adapted to remove weeds from the ground when the weeding device  46  is moved in the direction of the arrow. 
     Mounted on the tool bar  48  is a movement actuator  52  which is adapted to move the tool bar  48  and thereby the harrows  50  in left and right lateral directions parallel to the tool bar  48  in response to an appropriate signal from the processing unit  8 . The weeding apparatus  46  also includes tool bar arms  54  for attachment to a suitable pulling vehicle, for example a tractor (not shown). 
     The movement actuator  52  is connected to the first and second logic circuit outputs  34 ,  36  of the control unit  12 , the movement actuator  52  thereby receiving the output signals from the control unit  12  and, in response to the output signals, returning the sensing unit  10  to a central location relative to the markers  13 , and thereby moving the tool bar  48  and the harrows  50  in a left lateral or right lateral direction parallel to the tool bar  48 . The type of control signal output generated by the control unit  12  and the corresponding left lateral or right lateral movement of the tool bar  48  depends on whether the transmitting coil  14  is disposed to the left, to the right or centrally relative to the crop row  42  under inspection. 
     In this way, the harrows  50  are maintained between the crop rows  42  thereby ensuring that weeds are removed from between the crop rows  42  without damaging the crops  44 . 
     In FIG. 5, there is shown a marker and seed disposal unit  56  of the locating system  8 , the marker and seed disposal unit  56  including a marker disposal unit  58  and a seed disposal unit  60 . 
     The marker disposal unit  58  includes a marker receptacle  62 , a marker tube  64  and a foot portion  66 . 
     The foot portion  66  is shown in more detail in FIGS. 5 a  and  5   b , the foot portion  66  including a foot member  70  adapted to create a groove in the ground as the foot member  70  is drawn through the ground in the direction of the arrows in FIGS. 5 a  and  5   b , and backfill arms  72  adapted to urge soil adjacent the groove to fill the groove as the foot member  70  is drawn through the ground. 
     The arrangement is such that as the foot portion  66  is drawn through the ground the foot member  70  creates a groove, markers  13  are periodically dispensed into the groove from the marker receptacle  62  by passing through the marker tube  64 , and the groove is filled in by the backfill arms  72 . In FIGS. 6 a  and  6   b , the markers  13  which have been dispensed and covered with soil are shown in broken lines and the markers  13  which are not covered with soil are shown in full lines. 
     The seed disposal unit  60  includes a seed receptacle  74  and a seed tube  76 , the arrangement being such that as the foot portion  66  is drawn through the ground in the direction of the arrows in FIGS. 6 a  and  6   b , seeds  78  are periodically dispensed. 
     It will be understood that the marker and seed disposal unit  56  operates, in use, to substantially linearly dispense seeds  78  and markers  13 , with the markers  13  interspersed with the seeds  78  in a line substantially parallel to the seeds  78 . 
     It will be appreciated that various forms of movement actuator  52  are envisaged. The movement actuator may be hydraulically or electrically operated. For example, the movement actuator may include an electric driven worm drive which acts against a fixed surface. Alternatively, the movement actuator may include an actuating arm mounted between the weeding apparatus and a disk in contact with the ground, the disk providing a fixed lateral location relative to which the apparatus can be laterally moved. 
     Also, the movement actuator  52  of a locating system  8  may be interconnected to a steering mechanism of a vehicle such as a tractor, where a device such as the weeding apparatus  46 , described above, is towed by the vehicle. The steering of the vehicle would then be controlled by the locating system  8  such that the position of the vehicle is also controlled in relation to the position of the crop rows. 
     Furthermore, it will be appreciated that although the above embodiment has been described in relation to a mechanical weeding apparatus, the present invention is also applicable to other applications such as herbicide spraying apparatus where it is desired to spray only between adjacent crop rows or to placement apparatus where it is desired to accurately place substances, for example, fertiliser, adjacent the crop rows. 
     It will also be appreciated that although the above embodiment has been described in relation to markers and sensing means utilising magnetic and electromagnetic fields. Other marking and sensing arrangements are equally applicable to the locating system of the present invention. For example, a marker of a specific shape could be used, the sensing means utilising radar to locate the position of the marker by recognising the specific shape. 
     Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.