AUTOMATIC MINE DETECTION DEVICE

Abstract: A device for scanning a predetermined area (4) for detecting mines (10), where the device comprises a vehicle (1) which is commanded from a base station (2) by a control program to scan the area (4) according to a predetermined pattern, where the vehicle (1) is in addition equipped with sensors (9) for detecting mines (10) within the area (4), comprising with a navigation system which determines the vehicle's position within the area (4). The vehicle (1) has, in addition, means (13) for determining the orientation of the vehicle, and its control program is designed to obtain position data on known obstacles (23) and to detect obstacles within the area. The control program is designed to guide the vehicle so that the obstacles (23) are avoided during scanning of the area (4) according to the pattern. The device comprises means (19) for recording data which describes the zones within the area which have been scanned, as well as the zones which have not been scanned by the mine detection sensors (9).

Description: AUTOMATIC MINE DETECTION DEVICE TECHNICAL FIELD The invention relates to a device for automatic searching of an area according to a control program for detecting mines within the area, for memorizing the position of encountered mines within the area and for accurately recording which areas have been scanned. STATE OF THE ART There is a pressing need to find reliable devices and methods for making safe areas which during period of unrest have been mined with land mines, or areas in which unexploded ammunition is suspected to be present, where the latter area is equated with the mined areas in this document. Such mined areas can, for a long time, cause both people and animals unnecessary suffering. One problem is locating the whereabouts of the mines within the area, another is safely recognizing exactly which areas have been cleared from mines, and which areas have not yet been searched. Safe clearing of mines in areas which either have been part of war zones or within zones which have been mined so as to deter people entering the zone has long been a problem. There are still areas today which were mined as far back as the Second World War and where it is not known for certain if the mines have been cleared, and consequently are unable to be fully utilized. The problem has received attention and various types of mine detection devices have been tested. An example of such a device is where tanks are equipped with long arms extending out in front of the vehicle, where mechanical devices in the form of, for example, heavy chains are rotated or struck against the ground with the purpose of triggering the mines encountered by the chains. These devices have not worked particularly well for many reasons, because of, for example the nature of the ground, and whether or not the ground surface is covered with vegetation that impedes the use of the mechanical devices. Mine fragments, which are difficult to detect, may remain undiscovered. Such fragments can even be thrown out into previously demined areas. Another known solution for mine detection is to use manual methods, whereby a template in the form of a narrow strip is placed within the area that is to be searched, followed by manually sticking needles through holes in the template in order to feel if mines are present. The template is moved accordingly until the whole area has been searched. An example of another known mine detection device is presented in patent document US 5307272. In the said document, there is a presentation of a device which searches an area by means of a vehicle equipped with sensors for detecting mines, and which marks the positions of the detected mines. In the said document there is nothing about guiding the vehicle to ensure that all accessible areas are covered nor about mapping of the parts of the area searched which could not be accessed, and thus could not be scanned with the vehicle's sensors. DESCRIPTION OF THE INVENTION According to an aspect of the invention a robotic device for detecting mines in a mined area is presented here. The robot is made up of a terrestrial vehicle which moves on wheels or conveyor belts and is suitable for moving across rough terrain. A different version of the robot could be comprised of a flying or hovering craft, for example in the form of a low-flying helicopter. The robot is additionally equipped with one or more sensors for detecting mines, and in the case where several sensors are employed algorithms are used for sensor fusion to take into account the various signals from the sensors in order to determine if mines are present or not. Furthermore, the robot is equipped with a navigation system which preferably uses satellites by so called GPS-navigation, which can also use a comparison with GPS- measurements from a fixed reference receiver to establish so called differential GPS- navigation, or alternatively a navigation system based on reference objects arranged at the place next to the area to be searched for mines, where the position of these reference objects can be determined by means of laser. A course reference unit built in to the robot is used to sense the robot's orientation in space, that is to say its current orientation. The robot is controlled by a control system which automatically ensures that the robot systematically scans a given area, at the same time as it avoids known obstacles programmed in the control system, obstacles which it discovers on its own using sensors, as well as mines which it has detected and determined the position of. The robot is connected by a data link to a ground station, in which there is software that accurately records the zones within the searched mined area that have been scanned by the robot sensors, which means that the robot's position, the orientation of the robot in its current position, and the sensors' position in relation to the robot unit are all taken into consideration. The recording includes, in addition, which mines have been detected and their location, as well as sensor data on the same detected mines. An advantage of the device and the method for mine detection presented here is that, using knowledge of the precisely defined position of the robot obtained with the aid of the navigation system, and by compensating for the actual position of the sensors, one obtains from the recording data which can be translated into information on which zones have been scanned, which zones, if any, that could not be reached by the robot, and in addition knowledge about where suspected mines occur within the area searched. DESCRIPTION OF THE DRAWINGS Figure 1 shows schematically the various units and how they are linked together in the mine detection device. Figure 2 is a simplified diagram of a vehicle and a base station to which it is connected for detection of mines within an area. Figure 3 illustrates the use of differential GPS for navigation of the vehicle within the scanned area. Figure 4 illustrates the use of laser reflectors for navigation of a vehicle within the scanned area. Figure 5 depicts the mapping of an area, where it is shown which information on the scanned area is available as scanning proceeds. Figure 6 shows programmed break points within the area to be scanned and the path the robot is to follow between these points. Figure 7 shows prohibited areas for the robot which have been created around obstacles and detected mines. Figure 8 shows new break points created by the control system to guide the robot around an obstacle. DESCRIPTION OF EMBODIMENTS A number of embodiments of the invention are described below with the aid of the attached figures. The invention is represented and exemplified below by a device in which the robot is embodied by a ground vehicle, denoted by 1 in figure 1. The ground vehicle 1 is equipped with either wheels or track for moving across rough terrain. The robot may naturally be of a different character. For example, it can be a helicopter or a hovercraft. The robot communicates with a base station 2 by means of a data link 3. The robot scans the given area 4 in order to detect mines which may be present. The base station 2 is placed outside the given area 4. The vehicle 1 is equipped with a so called sensor rake 5, which can be designed as a manipulator arm 6 with a holder for the sensors at the extremity of the manipulator arm 6, in such a way that the sensor rake can be commanded from the vehicle to adopt the desired position in relation to the vehicle and desired height above the ground surface. The vehicle 1 is additionally equipped with a fusion unit 7 for evaluating data from sensors 9 located on the sensor rake 5 for detecting mines 10 according to known methods, for example according to the account in the previously mentioned document US 5307272. The motor or motors 11 in the vehicle 1 are commanded from the base station 2 to manoeuvre the vehicle 1 and manipulator arm 6 using signals transmitted via the data link 3. The vehicle 1 is equipped with a GPS receiver 12 for reception of satellite signals for determining the position of the vehicle. The GPS receiver merely gives information about the position of the vehicle's antenna. A course reference unit 13 is equipped with a transmitter, for example a gyro based instrument, that provides information about the vehicle's orientation in space, which allows determination of the exact position of the sensor rake relative to the position determined for the antenna of the vehicle 1. The signals from the position finding units 12, 13 are sent by the link 3 to a control unit 14 located in the base station 2 in order to inform a control system in the control unit 14 about the momentary positions of both the vehicle 1 and the mine detecting sensors 9 in the sensor rake 5. Data from a geographically positioned GPS reference station 15 is also sent to the control unit 14. This allows for differential GPS position determination, which means that a more exact position determination can be obtained than when only using the signal from GPS satellites. An alternative for navigation of the vehicle within the area to be scanned involves equipping the vehicle with instrumentation 16 for laser recording. When this version is employed the laser reflectors 17 are positioned close to the area to be scanned. By establishing the position of the laser reflectors, the position of the vehicle 1 can be determined with a high degree of accuracy and reliability. The base station 2 contains an evaluation unit 18 for evaluating data from the sensor fusion unit 7 which compiles data from the sensors 9, whereupon if the evaluation results in the judgement that a mine has been encountered, data about the mine as well as its current position is entered in a data base 19 for recording the position of mines. The sensors' 9 position during the scanning process is continuously registered by a recording device 18b. This recorded sensor position data is continuously entered into the data base 19, which means that one can retrieve from the data base the information that is required, i.e. the position of encountered mines, and information about which zones have been traversed by the mine sensors and which zones have not been scanned. By employing the method which is to be used for the device, it is possible to obtain information about the said zones with an accuracy of about one cm. A user interface 20 is also shown for the device according to figure 1. The interface 20 allows the operator of the device to transmit, to the control program, information about the geographic position of the area to be scanned, in addition to permitting the operator to enter data about obstacles within the area. The control system generates a system of break points 21, which the vehicle is to pass in turn. In the control system there are programmed rules for guiding the vehicle, which forces the vehicle to pass these break points 21. The break points 21 are placed out in the terrain so that the vehicle's sensors 9 will sweep over the entire area to be scanned, taking into consideration the fact that the terrain is undulating, which means that a three-dimensional map of the area has to be used in accordance with the known method within this field of engineering. Using the interface 20, the operator programs the obstacles 23 present within the area into the control system. In this way the control system automatically creates prohibited zones 22 around these obstacles 23, where the extent of these prohibited zones is such that no part of the vehicle can collide with the obstacle 23 if the centre of the vehicle is outside the said prohibited zones 22. Similarly, if the robot in the form of a vehicle 1 discovers a mine 10 while scanning the area, prohibited zones are automatically created around the mine, where the extent of the prohibited zone is such that no part of the vehicle 1 passes over the mine, as long as the centre of the vehicle is outside the prohibited zone. When the robot moves from one break point 21 to a subsequent break point 21 according to the control program, the path the robot is to follow in the terrain to the subsequent break point is determined in the control system. If this path crosses a prohibited zone 22, the control system will supplement a list of existing break points 21 with new break points, as is shown in figure 8, which leads to the prohibited zone 22 being avoided by the vehicle 1. In figure 5 the previously scanned area is represented by reference 24. The above description of automatic scanning of a given area can naturally be modified so that the operator him/herself controls the vehicle 1 with a user interface 20 at a safe distance from the vehicle 1. In this design, discovered mines, as well as scanned and unscanned zones are also mapped and recorded in a similar way to that described above.

Claims: CLAIMS 1. A device for scanning a predetermined area (4) for detecting mines (10), where the device comprises a vehicle (1) which is commanded from a base station (2) by a control program in a control system to scan the area (4) according to a predetermined pattern, where the vehicle (1) is in addition equipped with at least one sensor (9) for detecting mines (10) within the area (4), characterized in that the vehicle (1) comprises a navigation system which determines the vehicle's position within the area (4) with a high degree of accuracy, that the vehicle (1) comprises means (13) for determining the orientation of the vehicle, that the control program is designed to obtain position data on known obstacles (23) within the area (4) and position data on obstacles which obstacle detection sensors on the vehicle discover, as well as position data on obstacles in the form of mines (10) that have been detected, that the control program is designed to guide the vehicle so that the obstacles (23) are avoided during scanning of the area (4) according to the pattern, and that the device comprises means (19) for recording data which describes the zones within the area which have been scanned by the mine detection sensors (9), as well as recording data which describes the zones within the area (4) which have not been scanned by the mine detection sensors (9). 2. A device as claimed in claim 1, characterized in that the control system within the area (4) generates a system of break points (21), which the robot (1) is to pass in turn. 3. A device as claimed in claim 2, characterized in that the control system generates break points (21) around obstacles (23) and detected mines (10) in order to create a new course for the robot (1) to follow. 4. A device as claimed in claim 3, characterized in that the navigation system comprises a GPS receiver (12) for determining the position of the robot (1) by GPS navigation. 5. A device as claimed in claim 4, characterized in that the navigation system uses a separate position reference from a GPS reference station (15) for determining the position of the robot (1) by means of differential GPS navigation. 6. A device as claimed in claim 3, characterized in that laser reflectors (17) are placed out within the area (4), whereupon the robot's (1) navigation system determines the position of the robot by recording the position of the reflectors. 7. A device as in claim 3, characterized in that the means (19) for recording data consists of a memory in the base station (2). 8. A device as in any preceeding claim, characterized in that the means for determining the orientation of the robot (1) consists of a separate course reference unit (13), which contains a gyro.

Inventors: NORDLING PER, SKARMAN ERIK, NORDLING, PER, SKARMAN, ERIK
Applicants: NORDLING PER, SAAB AB PUBL, SKARMAN ERIK, NORDLING, PER, SAAB AB (PUBL), SKARMAN, ERIK
Application year: 1999
Main classification: G01V3
IPC codes: F41H11, G01S5