AU2012227260B9

AU2012227260B9 - Method and device for generating proximity warnings

Info

Publication number: AU2012227260B9
Application number: AU2012227260A
Authority: AU
Inventors: Urs Martin Rothacher; Andrea Boris Schlapbach; Peter Arnold Stegmaier
Original assignee: Safemine AG
Current assignee: Safemine AG
Priority date: 2012-09-21
Filing date: 2012-09-21
Publication date: 2014-05-29
Anticipated expiration: 2032-09-21
Also published as: CA2885095A1; CA2885095C; AU2012227260B1; ZA201501814B; WO2014043824A1

Description

Australian Patents Act 1990 - Regulation 3.2 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Invention Title Method and device for generating proximity warnings The following statement is a full description of this invention, including the best method of performing it known to me/us: P/00/0 I I H:Adl\lnterwovnc\NRPortbl\DCC\DXL\5 911394 l.doc-24/12/2013 1A Technical Field The invention relates to a method and device for generating proximity warnings, for example for use in a 5 mining environment. Background Art Surface mines and similar sites or areas are 10 generally operated by means of a large number of vehicles and staff. Some of the vehicles may be exceedingly large, heavy, and difficult to control. It has been proposed to use GNSS-devices (GNSS = global navigation satellite system, such as GPS) on board of 15 vehicles and other objects, such as cranes, to generate proximity warnings in order to reduce the risk of collisions between vehicles. Such a system is e.g. described in WO 2004/047047 and it is based on devices mounted to the objects. Each device comprises a GNSS receiver, a control 20 unit deriving positional data using the signal of the GNSS receiver, a radio circuit for wireless exchange of the positional data with the other devices, and an output device for outputting proximity warnings. Such systems allow the driver of a vehicle to 25 obtain information on some of the obstacles nearby. Disclosure of the Invention Embodiments of the invention may provide a method 30 and a monitoring apparatus of a similar type that enables improved safety and/or positioning accuracy, even in situations with poor or absent GNSS reception.

H:\dsl\Jnterwoven\NRPobl\DCC\DXL\5911394_ .doc-24/12/2013 1B According to the present invention there is provided a method for generating a proximity warning on an area, by means of a plurality of monitoring devices mounted on movable objects on said area, 5 wherein at least a first monitoring device at a first position and a second monitoring device at a second position each comprises a radio transceiver and a receiver for a radio based positioning system, said method comprising steps of 10 - determining said first position of said first monitoring device by means of said receiver for said radio based positioning system of said first monitoring device, - determining a first positioning accuracy of said determined first position by means of said first 15 monitoring device, - determining said second position of said second monitoring device by means of said receiver for said radio based positioning system of said second monitoring device, - transmitting said determined second position by 20 means of said radio transceiver of said second monitoring device, - receiving said transmitted second position of said second monitoring device by means of said radio transceiver of said first monitoring device, and steps of 25 a) transmitting a first radio pulse by means of said radio transceiver of said first monitoring device, b) receiving said first radio pulse from said first monitoring device by means of said radio transceiver of said second monitoring device, 30 c) transmitting a second radio pulse by means of said radio transceiver of said second monitoring device, H:Wxl\l nten oven\NRPonb\DCC\DXL\5911394_ .doc-24/122013 1C d) receiving said second radio pulse by means of said radio transceiver of said first monitoring device, e) measuring by means of said first monitoring device a first flight time between said transmitting of said 5 first radio pulse and said receiving of said second radio pulse, and wherein the method comprises a further step of - deriving by means of said first monitoring 10 device a first distance value between said first and said second monitoring devices using * said measured first flight time, * said determined first position of said first monitoring device, 15 * said first positioning accuracy of said determined first position, and * said received second position of said second monitoring device, and wherein the method comprises a further step 20 of - issuing by means of said first monitoring device a proximity warning as a function of said first distance value between said first and said second monitoring devices. The invention also provides a method for 25 generating a proximity warning on an area, by means of a plurality of monitoring devices mounted on movable objects on said area, wherein at least a first monitoring device at a first position and a second monitoring device at a second 30 position each comprises a radio transceiver and a receiver for a radio based positioning system, said method comprising steps of H:\dxl\!nienvovcn\NRPortbl\DCC\DXL\5911394 I.doc-24/12/2013 1D - determining said first position of said first monitoring device by means of said receiver for said radio based positioning system of said first monitoring device, - determining a first positioning accuracy of 5 said determined first position by means of said first monitoring device, - determining said second position of said second monitoring device by means of said receiver for said radio based positioning system of said second monitoring device, 10 - transmitting said determined second position by means of said radio transceiver of said second monitoring device, - receiving said transmitted second position of said second monitoring device by means of said radio 15 transceiver of said first monitoring device, and steps of a) transmitting a first radio pulse by means of said radio transceiver of said second monitoring device, wherein said first radio pulse comprises a synchronized timestamp or wherein said first radio pulse is transmitted 20 at a predefined synchronized time, b) receiving said first radio pulse by means of said radio transceiver of said first monitoring device, c) measuring by means of said first monitoring device a first flight time between said transmitting of said 25 first radio pulse and said receiving of said first radio pulse, and wherein the method comprises a further step of - deriving by means of said first monitoring 30 device a first distance value between said first and said second monitoring devices using * said measured first flight time, * said determined first position of said first monitoring device, H:\dxl\lntcnvovcn\NRPorb\DCC\DXL\5911394_1 doc-24/12/2013 lE * said first positioning accuracy of said determined first position, and * said received second position of said second monitoring device, 5 and wherein the method comprises a further step of - issuing by means of said first monitoring device a proximity warning as a function of said first distance value between said first and said second monitoring 10 devices. The invention also provides a monitoring device comprising - a radio transceiver for transmitting and receiving a radio pulse, 15 - an interface for issuing a proximity warning, - an analysis and control unit adapted and structured to carry out the steps of a method of the invention. The invention also provides a computer program 20 element comprising computer program code means for, when executed by a processing unit, implementing a method according to a method of the invention. In embodiments there is provided a method for generating a proximity warning on an area (e.g., in a 25 surface mine) is carried out by a plurality of monitoring devices which can be mounted on movable objects like vehicles, persons, etc. on said area. At least a first H:\dx\lntrwoven\NRPoribl\DCC\DXL\5911394 I.doc-24/12/2013 2 monitoring device at a first position and a second monitoring device at a second position each comprises a radio transceiver for transmitting and receiving radio pulses and position information. It should be noted here 5 that the radio receiver is not necessarily a single device but can comprise a plurality of physical devices. The first and the second monitoring devices additionally comprise a receiver for a radio based positioning system such as a GNSS (e.g., GPS, Galileo, ...) each. The method comprises the 10 following steps: - A determination of a first position of the first monitoring device and a determination of a second position of the second monitoring device using the respective receivers for the radio based positioning system. 15 The determined second position is then transmitted (advantageously together with a unique identifier of second monitoring device) by means of the radio transceiver of the second monitoring device such that other monitoring devices in range are aware of the second position. Specifically, the 20 transmitted second position of the second monitoring device is received by means of the radio transceiver of the first monitoring device such that the first monitoring device knows about the second position. The method comprises further steps of 25 a) A transmission of a first radio pulse by said radio transceiver of said first monitoring device. The first radio pulse advantageously comprises a unique identifier of the first monitoring device. Furthermore, 3 this first radio pulse is advantageously a frequency chirped pulse (i.e., a radio pulse with a frequency modu lation over time). Preferred frequencies of the first ra dio pulse are in the range between 0.3 and 6 GHz, par s ticularly in the range between 868 and 928 MHz, in the range between 2 and 3 GHz, in the range between 2.3 and 2.5 GHz, or in the range between 5 and 6 GHz. Thus, the signal-to-noise ratio and radio range can be improved, e.g., also by means of suitable post-processing steps 10 (e.g., correlation algorithms, filtering, etc.). b) Then, the first radio pulse from the first monitoring device is received by means of said radio transceiver of said second monitoring device. Advanta geously, suitable post-processing steps such as, e.g., is filtering, are applied to the received radio pulse as it is obvious to the person skilled in the art. c) Then, after processing, the second moni toring device transmits a second radio pulse (reply pulse) by means of its radio transceiver. As discussed 20 above, the second radio pulse advantageously also com prises a unique identifier of the second monitoring de vice such that the first monitoring device is aware that the reply pulse originates from the second monitoring de vice. Furthermore, the second radio pulse is advanta 25 geously also a frequency chirped pulse. Preferred fre quencies of the second radio pulse are in the range be tween 0.3 and 6 GHz, particularly in the range between 868 and 928 MHz, in the range between 2 and 3 GHz, in the range between 2.3 and 2.5 GHz, or in the range between 5 30 and 6 GHz. d) Then, the second radio pulse is received by means of the radio transceiver of the first monitoring device, and - again - suitable post-processing is advan tageously applied to the received radio pulse. As part of 3s this, coarse (i.e., + 20 degrees) relative bearing infor mation can be derived, e.g., using at least one direc tional antenna. As discussed below, ambiguities in posi SU/CE 20/09/2012 4 tion determinations using, e.g., triangulation methods, can be resolved. e) Then, the first monitoring device measures a first flight time tTOF of the first and second radio s pulses between the transmission of the first radio pulse (from its own radio transceiver) and the receiving of said second radio pulse which originates from the second monitoring device. As an alternative to the bidirectional ex 10 change of the first and second radio pulses as discussed above under the steps a) - d), an unidirectional trans mission and receiving of a single first radio pulse is also possible: a) The second monitoring device transmits a is first radio pulse by means of its radio transceiver. This first radio pulse advantageously comprises a unique iden tifier of the second monitoring device such that the first monitoring device is aware that the first radio pulse originates from the second monitoring device. Fur 20 thermore, the first radio pulse is advantageously a fre quency chirped pulse. Preferred frequencies of the first radio pulse are in the range between 0.3 and 6 GHz, par ticularly in the range between 868 and 928 MHz, in the range between 2 and 3 GHz, in the range between 2.3 and 25 2.5 GHz, or in the range between 5 and 6 Ghz. b) Then, the first radio pulse is received by means of the radio transceiver of the first monitoring device, and - advantageously - suitable post-processing is applied to the received first radio pulse. As part of 30 this, coarse (i.e., + 20 degrees) relative bearing infor mation can be derived, e.g., using at least one direc tional antenna. As discussed below, ambiguities in posi tion determinations using, e.g., triangulation methods, can be resolved. 35 c) Then, the first monitoring device measures a first flight time tTOF of the first radio pulse be tween the transmission of the first radio pulse (from the SU/CE 20/09/2012 5 radio transceiver of the second monitoring device) and the receiving of said first radio pulse by means of the first monitoring device's radio transceiver. For this, the first radio pulse comprises a synchronized timestamp s or equivalent time information. The term "synchronized timestamp" herein relates to a transmission timestamp at tached to the radio pulse, wherein clocks of the first and the second monitoring device are synchronized. Such synchronized time information/clocks is/are advanta 1o geously derived by means of the receiver for the radio based positioning system, e.g., from information trans mitted by GPS satellites. As an alternative to transmis sion timestamps, the first radio pulse can also be trans mitted at a predefined synchronized time between the is first and the second monitoring device. The term "prede fined synchronized time" herein relates to a predefined transmission time of the radio pulse, wherein clocks of the first and the second monitoring device are synchro nized. 20 In both scenarios, i.e., the bidirectional radio pulses scenario (ping-pong-scenario) and the unidi rectional radio pulse scenario (pong-scenario), the method comprises the following further steps: - The first monitoring device derives a first 25 distance value d_12 or a value indicative of this dis tance value between said first and said second monitoring devices, i.e., between the first and the second posi tions. This is achieved using * said measured first flight time tTOF and 3o advantageously a known response delay of the second moni toring device in the ping-pong-scenario as described above. This known response delay is due to necessary processing steps in the second monitoring device between receiving the first radio pulse and transmitting the sec 3s ond radio pulse. Thus, the precision of the derivation of the first distance value d_12 can be improved. SU/CE 20/09/2012 6 In addition to solely using radio pulse time of-flight measurements as discussed above for deriving the first distance value d_12, also * the determined first position of the first 5 monitoring device and the received second position of the second monitoring device are used. Both distance derivation schemes, i.e., the position based and the time-of-flight based scheme, are weighted and combined to improve the precision and/or re 10 liability of the derivation of the first distance value d_12. One possibility of deriving the first distance value is based on the equation: d_12 = wTOF * dTOF + wPOS * dPOS 15 with dTOF and dPOS being the time-of-flight based and the position based distance values, respec tively, and with wTOF and wPOS being associated weight ing factors with wTOF + wPOS = 1. The weighting factors 20 can be fixed or changed on the fly, e.g., based on the reliability and/or accuracies of the respective position determinations (see below). - Then, an, e.g., acoustic, tactile (vibra tional), electric shock, or optical proximity warning or 25 approach warning is issued to, e.g., a driver of a vehi cle or an operator of an object as a function of said first distance value d 12. As an example, an acoustic beeping can be triggered as soon as the first distance value decreases below a threshold, e.g., 10 or 50 m. An 30 other warning can be triggered as soon as, e.g., a cur rent approach speed of the first monitoring device and the second monitoring device would result in an impact in less than a threshold time, e.g., 4 s. In an advantageous embodiment, a first posi 3s tioning accuracy of the first position of the first moni toring device is determined. The positioning accuracy of the first position as determined by the receiver for the SU/CE 20/09/2012 7 radio based positioning system can vary, e.g., due to changing satellite reception levels and/or signal reflec tions. Thus, a reliability level or precision of the de termined first position can be assessed. 5 In another advantageous embodiment, a second positioning accuracy of the second position of the second monitoring device is determined. As discussed above, the positioning accuracy of the second position as determined by the receiver for the radio based positioning system io can also vary, e.g., due to changing satellite reception levels and/or signal reflections. Thus, a reliability level of precision of the determined second position can also be assessed. This second positioning accuracy is then transmitted by means of the radio transceiver of the is second monitoring device. Then, the transmitted second positioning accuracy is received by the radio transceiver of the first monitoring device. Thus, the first monitor ing device is aware of the accuracy/precision of the sec ond position of the second monitoring device. 20 Then, preferably, the first positioning accu racy of the first position and/or the second positioning accuracy of the second position are used in the step of deriving the first distance value d_12 between the first and the second monitoring device. Thus, e.g., the above 25 described radio-pulse time-of-flight contribution can be uprated (i.e., its weighting factor is increased) in the derivation of the first distance value d_12 in a case when one or both determined positions have a decreased reliability. In a border case, when the first and/or the 30 second position cannot be determined at all, e.g., due to a lack of satellite reception, a fallback to solely using the time-of-flight based distance value derivation is also possible (i.e., with wTOF = 1 in the above exam ple). This improves the reliability of the proximity 3s warning generation method. In another advantageous embodiment, the prox imity warning issued by, e.g., the first monitoring de SU/CE 20/09/2012 8 vice, comprises the second position of the second moni toring device. Then, an operator of a machine who re ceives the proximity warning is aware of the position of the second monitoring device and can take suitable ac 5 tion. Thus, the overall safety is increased. In an advantageous embodiment, the derived first distance value d_12 between the first and the sec ond monitoring devices is transmitted to all or selected other monitoring devices in range, such that these moni 10 toring devices are aware of the distance value d_12 be tween the first and the second monitoring devices. Thus, a more complete "picture" of the spatial distribution of the monitoring devices on the area is derivable. Advanta geously, using additional positional data from the re 1s ceiver(s) for said radio based positioning system and, e.g., triangulation methods (see below), also position information of monitoring devices without a receiver for the radio based positioning system are derivable. Thus, the overall safety is increased. 20 As another aspect of the invention, a moni toring device comprises a radio transceiver for transmit ting and for receiving a radio pulse. Furthermore, the monitoring device comprises an interface (e.g., an acous tic, tactile, e.g., vibrating, and/or optical user inter 25 face or - in another embodiment - a computer interface) for issuing a proximity warning as a function of the de rived distance value(s). Furthermore, the monitoring de vice comprises an analysis and control unit which is adapted and structured to carry out the steps of a method 30 as described. Specifically, the analysis and control unit can comprise a computer program element comprising com puter program code means for, when executed by the analy sis and control unit, implementing a method for generat ing a proximity warning as described. 35 Note: SU/CE 20/09/2012 H:\dxl\lntenwovcn\NRPor41\DCC\DXL\59 1394 I doc-24/12/2013 9 The described embodiments and/or features similarly pertain to both the apparatuses and the methods. Synergetic effects may arise from different combinations of these embodiments and/or features although they might not be 5 described in detail. The invention is further described by way of example only with reference to the accompanying drawings. Brief Description of the Drawings 10 The invention and its embodiments will be more fully appreciated by reference to the following detailed description of presently preferred but nonetheless illustrative embodiments in accordance with the present 15 invention when taken in conjunction with the accompanying drawings. Fig. 1 schematically shows a surface mine 100 with a monitoring apparatus comprising three monitoring devices 1,2,3, 20 Fig. 2 shows a monitoring apparatus 1,2,3 comprising a radio transceiver 10, an interface 5, an optional receiver for a radio based positioning system 20, and an analysis and control unit 6. 25 Modes for Carrying Out the Invention Definitions: A "movable object" is any object that can change and is expected to change its position and/or orientation or 30 configuration in space. It may e.g. be a truck or any other vehicle that moves from place to place and changes its orientation in respect to the general north-south direction, e.g., by steering, or it may be an object positioned at a fixed location but able to rotate about its axis or to 35 change its physical configuration, e.g. by extending an gripper or shovel, in such a manner 10 that the volume of safety space attributed to it varies in significant manner. The term GNSS stands for "Global Navigation Satellite System" and encompasses all satellite 16 based s navigation systems, including GPS and Galileo. The term "radio based positioning system" stands for a GNSS or for any other type of positioning system using radio signals, such as a pseudolite system. The term "monitoring apparatus" as used 10 herein designates an assembly of monitoring devices dis tributed over several locations, with the single monitor ing devices communicating with each other as described. Some of the monitoring devices are installed on movable objects while others may be installed at fixed locations, 15 e.g., fixed obstacles. The term "mounting a device to a person" can be understood as affixing the monitoring device to the person in such a manner that the person will carry it without requiring the use of his/her hands. For example, 20 the term expresses that the monitoring device is affixed to a piece of clothing or equipment, such as a belt or a helmet, that the person is wearing. The area: 25 Fig. 1 schematically depicts an area, such as a surface mine 100, to be monitored by the present sys tem. Typically, such a site covers a large area, in the case of a surface mine, e.g., in the range of several square kilometers, with a network of roads (bold lines) 30 and other traffic ways, such as rails. A plurality of ob jects is present in the mine, such as: - Large vehicles, such as haul trucks 40, cranes, or diggers. Vehicles of this type may easily weigh several 100 tons, and they are generally difficult 3s to control, have very large braking distances, and a large number of blind spots that the vehicle operator is unable to visually monitor without monitoring cameras. SU/CE 20/09/2012 11 - Medium sized vehicles, such as regular trucks 50. These vehicles are easier to control, but they still have several blind spots and require a skilled driver. s - Small vehicles. Typically, vehicles of this type weigh 3 tons or less. They comprise passenger vehi cles and small lorries. - Trains. - Individual persons 8, in particular pedes 10 trians. A further type of object within the mine is comprised of stationary obstacles, such as temporary or permanent buildings, open pits, boulders, non-movable ex cavators, stationary cranes, deposits, etc. 15 The risk of accidents in such an environment is high, specifically under adverse conditions as bad weather, during night shifts, etc. In particular, the large sized vehicles can easily collide with other vehi cles, or obstacles. 20 For this reason, the mine is equipped with a monitoring apparatus comprising a plurality of monitoring devices 1,2,3 that allows to generate proximity warnings for the personnel of the site, thereby reducing the risk of collisions and accidents. 25 The monitoring apparatus: Basically, the monitoring apparatus comprises a plurality of monitoring devices 1,2,3 that are affixed to fixed objects and/or movable objects and/or persons. 30 Specifically, monitoring device 1 is affixed to haul truck 40 which is at position P_1, monitoring device 2 is affixed to truck 50 which is at position P_2, and moni toring device 3 is affixed to person 8 who is at position P_3. These components communicate in a wireless manner, 35 in particular by radio signals by means of integrated ra dio transceivers 10. They are described in more detail in the following sections. SU/CE 20/09/2012 12 In addition, the monitoring apparatus can comprise a central server (not shown), whose role is also explained below. 5 The monitoring devices: As stated above, the monitoring devices 1,2,3 are affixed to different objects in the area. In general, the larger the number of in stalled monitoring devices 1,2,3, the higher the safety 10 level. The monitoring devices 1,2,3 comprise an analysis and control unit 6, such as a microprocessor system, which controls the operations of the monitoring device and the communication with the other monitoring 15 devices. The monitoring devices 1,2,3 further comprise a radio transceiver 10 comprising a first and a second transceiver unit. The second transceiver unit comprises a digital transceiver for exchanging digital data such as 20 position information, positioning accuracies, distance values, etc. with other monitoring devices 1,2,3. Due to the digitally exchanged signals, error detection/ correc tion algorithms can be used which increase the reliabil ity of the data exchange. The radio transceiver 10, spe 25 cifically its first transceiver unit, is also adapted to transmit and receive time-of-flight radio pulses and op tionally timestamp information. By measuring a flight time of these radio pulses (e.g., first pulse PTOF from first monitoring device 1 to second monitoring device 2, 30 reply pulse R TOF from second monitoring device 2 to first monitoring device 1) between two monitoring devices 1,2, a first distance value d_12 of a distance between the two monitoring devices, i.e., between the first posi tion P_1 of the first monitoring device 1 and the second 3s position P 2 of the second monitoring device 2 can be de rived (dotted line and dotted circle segment). SU/CE 20/09/2012 13 The monitoring devices 1,2 further comprises a GNSS receiver 20. Although it is called a GNSS receiver in the following, it can also be a receiver interoper ating with any other radio based positioning system for s determining its position. The present invention can be used on various types of radio based positioning systems. Control unit 6 accesses a memory (e.g., RAM, ROM) that comprises programs as well as various parame ters, such as a unique identifiers of the monitoring de 10 vices which is transmitted with each message over the ra dio transceiver. Thus, the identity or origin of the transmitted signals can be determined. An interface 5, here, an acoustic and optical user interface 5 advantageously comprises an optical dis is play 22 as well as an acoustic signal source 23, such as a loudspeaker. Furthermore, a tactile interface such as a vibrating unit (not shown) for alerting a user can be comprised in the interface 5. The primary purpose of monitoring device 20 1,2,3 is to generate proximity warnings or approach warn ings in case that there is a danger of collision between two or more objects. This is achieved by a two-step ap proach: a) By receiving position signals through GNSS 25 receiver 20, a position of the respective monitoring de vice(s) is determined. This position(s) is or are advan tageously transmitted by means of the radio transceiver 10 to all the other monitoring devices 1,2,3 that are in range such that all monitoring devices 1,2,3 are aware of 30 the respective positions, velocities, and probabilities for collisions. b) By deriving distance values (e.g., d_12) between the monitoring devices 1,2,3 using position based and time-of-flight based measurements of radio pulses 3s that are exchanged between the two monitoring devices. Again, advantageously, the distance values are exchanged with other monitoring devices 1,2,3 in order to calculate SU/CE 20/09/2012 14 relative positions, velocities, and probabilities for collisions. The method for calculating relative positions is described in the next section, while further informa tion about various aspects of the monitoring device fol s lows later. The advantage of using such a two-step ap proach is that proximity warnings or approach warnings can also be issued in a case where one or more of the monitoring devices 1,2,3 do not or only have poor GNSS 10 reception and thus positioning accuracy and/or where one or more of the monitoring devices 1,2,3 are not equipped with a GNSS receiver 20. In an advantageous embodiment, monitoring de vice 1,2,3 can also comprises an acceleration detector 1s (not shown here). Acceleration values can also be trans mitted by means of the radio transceiver 10. This accel eration detector can be used to reduce the energy con sumption of the monitoring device. Since GNSS receiver 20 is one of the major power drains, GNSS receiver 20 can 20 have a "disabled mode" where it is not operating and an "enabled mode" where it is operating. When analysis and control unit 6 detects an acceleration by means of the acceleration detector, it puts GNSS receiver 20 into its enabled state to obtain the current position of the moni 25 toring device. Otherwise, it puts GNSS receiver 20, e.g., after a predetermined amount of time, into its disabled state. In addition to this, to account for the unlikely event that no acceleration is measured even though the monitoring device 1,2,3 is moving, control unit 6 can be 3o adapted to put GNSS receiver 20 into its enabled state at regular intervals in order to perform sporadic position measurements. In addition or alternatively to switching GNSS receiver 20 between a disabled an enabled state, 3s other parts of monitoring device 1,2,3 can be switched between an idle and an active state in response to sig nals from the acceleration detector. In general terms, SU/CE 20/09/2012 15 monitoring device 1,2,3 can have an "idle state" and an "active state", wherein, in said idle state, monitoring device 1,2,3 has a smaller power consumption than in said active state. Control unit 6 is adapted to put monitoring s device 1,2,3 into its active state upon detection of an acceleration by the acceleration detector, while the monitoring device is, e.g., brought back to its inactive state if no acceleration has been detected for a certain period of time. 10 Monitoring device 1,2,3 advantageously com prises a rechargeable battery (not shown) for feeding power to its components. A battery charger comprises cir cuitry for charging the battery. The battery charger can draw power from at least one power source. Such power is sources can, e.g., be - a power plug for directly connecting moni toring device 1,2,3 to an external power supply; - an inductive coupler comprising a coil adapted to generate electrical current from an alternat 20 ing magnetic field generated by an external primary coil; such inductive power couplers are known to the skilled person; and/or - a solar power supply mounted at the outer surface of the monitoring device 1,2,3 or in a separate 25 unit electrically connected to the monitoring device 1,2,3. Relative position determination: If all monitoring devices 1,2,3 would have a 30 GNSS receiver 20, the operation of the monitoring devices could be basically as in conventional systems of this type, such as, e.g., described in WO 2004/047047 and need not be described in detail herein. In such a simple approach, each monitoring 3s device 1,2, and 3 would obtain information about its re spective position P_1, P_2, and P_3 derived from a signal from GNSS receiver 20. This data is stored in a "device SU/CE 20/09/2012 16 status dataset". The device status dataset also contains a unique identifier (i.e. an identifier unique to each of the monitoring devices 1,2,3 used on the same area 100). The device status dataset is then transmitted s as a digital radio signal through radio transceiver 10. At the same time, the monitoring device receives the cor responding signals from neighboring monitoring devices and, for each such neighboring monitoring device, it cal culates the relative distance dxy (where x and y denote 10 the index of the involved monitoring devices, e.g., d_12 relates to a distance between monitoring device 1 and monitoring device 2) by subtracting its own coordinates from those of the neighboring monitoring device. In the present invention, however, the deri is vation of the distance values d xy does not simply rely on the described position based procedure but also on a radio pulse flight time approach. Both distance deriva tion schemes are weighted and combined as described to improve the reliability and safety of the system, in par 20 ticular in situations with poor GNSS reception. Proximity warnings: Proximity warnings can be generated by means of various algorithms. Examples of such algorithms are 25 described in the following. In a very simple approach, it can be tested if the absolute value of the relative distance d_xy is below a given threshold. If yes, a proximity warning can be issued. This corresponds to the assumption that a cir 30 cular volume in space is reserved for each object. The radius of the circular volume attributed to an object can, e.g., be encoded in its device status dataset. A more accurate algorithm can, e.g., take into account not only the relative position, but also the 3s driving velocities and directions of the vehicles. An improvement of the prediction of colli sions can be achieved by storing data indicative of the SU/CE 20/09/2012 17 size and/or shape of the object that a monitoring device 1,2,3 is mounted to. This is especially true for large vehicles, e.g., haul truck 40, which may have non negligible dimensions. In a most simple embodiment, a ve s hicle can be modeled to have the same size in all direc tions, thereby defining a circle/sphere "covered" by the vehicle. If these circles or spheres of two vehicles are predicted to intersect in the near future, a proximity warning can be issued. It should be noted here that it is 10 also possible to affix more than one monitoring device to an object which, e.g., enables the monitoring of orienta tions. These multiple monitoring devices on the same ob ject would then, e.g., be configured not to exchange time-of-flight radio pulses with each other. 15 Instead of modeling an object or vehicle by a simple circle or sphere, a more refined modeling and therefore proximity prediction can be achieved by storing the shape (i.e. the bounds) of the vehicle in the data set. In addition, not only the shape of the vehicle, but 20 also the position of the GNSS-receiver 20 (or its an tenna) in respect to this shape or bounds can be stored in memory. In some cases, the signal strength of a re ceived radio signal can be used to determine a range of 2s distance where the monitoring device may be, thus improv ing warning accuracy in such a case. Hence, a first moni toring device receiving a signal from a second monitoring device assesses the signal strength of said signal and generates a proximity warning based on the assessed sig 30 nal strength, in particular by comparing it to a maximum value. Other functions: In addition to issuing proximity warnings as 35 described above, monitoring devices 1,2,3 can provide other uses and functions. SU/CE 20/09/2012 18 In one embodiment, which is particularly use ful if monitoring device 1,2,3 is worn on a person, the monitoring device 1,2,3 can issue a warning when it leaves the site or enters a "restricted area" of the s site. This can, e.g., happen when a user of the monitor ing device forgets to return the apparatus when leaving the site or tries to steal it, or when a user enters an area, such as a blast area, that is not safe for him. This type of warning can be generated by exe 10 cuting the following steps: 1) In a first step, analysis and control unit 6 obtains the position of the monitoring device by means of GNSS receiver 20 or via time-of-flight triangulation (see below). 15 2) In a second step, analysis and control unit 6 compares this position to a predefined geographi cal area. This geographical area can, e.g., be stored in memory and describes the area where the monitoring device is allowed to be operated. If it is found that the posi 20 tion is not within the geographical area, the following step 3 is executed: 3a) A warning which can comprise one or more positions of monitoring devices is issued. This warning can, e.g., be displayed on a display or issued as a sound 25 by acoustic signal source 23. 3b) Alternatively, or in addition to step 3a, the warning can be sent, e.g., by means of a cellular phone transceiver (not shown) integrated into the moni toring device 1,2,3 or by means of the radio transceiver 30 10 to a central monitoring system (i.e. a central server), together with the current position and identity of the respective monitoring device 1,2,3. Then, the warning can be displayed by the central server and brought to the attention of personnel that can then take 3s further necessary steps. SU/CE 20/09/2012 19 3c) Alternatively or in addition to steps 3a and/or 3b, the apparatus can be made unusable by blocking and/or destroying at least part of its functionality. In general, a cellular phone network (or any s other wireless network) can be used to transmit informa tion from the monitoring devices 1,2,3 to the central server. As mentioned, this information can, e.g., com prise any warnings issued by the monitoring devices 1,2,3, and/or it may comprise the position of the moni 10 toring device. Another application of a cellular phone transceiver integrated into monitoring device 1,2,3 is to send messages from the central server to any monitoring device 1,2,3. Such messages are received the respective i5 monitoring device 1,2,3 and displayed or brought to the operator's attention acoustically. This, e.g., allows to issue warnings, alerts or information to the person using the monitoring device 1,2,3. The monitoring devices 1,2,3 can also be used 20 for generating automatic response to the presence of a vehicle or person at a certain location. For example, when a pedestrian with a monitoring device approaches a gate, such as door of a building, that door can open automatically. Similarly, an entry light can switch to 25 red or to green, depending on the type of object that a monitoring device is attached to, or a boom can open or close. This can be achieved by mounting a receiver device to a selected object (such as a door, a gate, boom or an entry light). The receiver device is equipped with a ra 30 dio receiver adapted to detect the proximity of monitor ing devices 1,2,3. When the receiver device detects the proximity of a monitoring device 1,2,3, it actuates an actuator (such as the door, gate or entry light) after testing access rights of the object attributed to the 35 monitoring device 1,2,3. For example, the actuator may be actuated depending on the type of the object that the monitoring device is attached to and/or to its distance SU/CE 20/09/2012 20 from the receiver. The type and/or distance information is transmitted as part of the device status dataset of the monitoring device 1,2,3. Furthermore, the control unit of the monitor ing device 1,2,3 can have an "alert mode", which can be activated by a user, e.g., by pressing an alert button on a keyboard of the monitoring device 1,2,3 and/or by voice control. It can, e.g., be used to indicate that the per son using the monitoring device is in need of urgent help 10 or needs all activity around it to be stopped immedi ately. The device status dataset comprises a flag indica tive of whether the monitoring device is in alert mode. Another monitoring device receiving a device status data set that indicates that the sender is in alert mode may 15 take appropriate action. For example, the central control room operator can be informed, closeby machinery can be shut down, etc. Persons on the site: 20 As mentioned above, the monitoring devices 1, 2, 3 can not only be mounted to vehicles in the area, but also to individual persons on the site. By using the same type of device for persons as well as vehicles, costs can be reduced. In such a situation, the monitoring device 25 1,2 mounted to vehicles can cooperate with the monitoring device 3 mounted to a person in such a manner that a) the drivers of the vehicles are alerted of the presence of pedestrians, and/or b) the pedestrians are alerted of the pres 30 ence of the vehicles 40,50. While option a) is the primary purpose of the present invention, option b) may also have its advan tages, too. In order to alert the drivers of the presence 3s of a pedestrian, each pedestrian-mounted monitoring de vice can transmit a flag indicative of the fact that it is mounted to a pedestrian, e.g., as part of its device SU/CE 20/09/2012 21 status dataset. Thus, all other monitoring devices in range are aware of this fact and can adapt their warning strategy accordingly. s Time of flight measurement/triangulation: Under adverse conditions, e.g. when one or more satellite signals are partially or fully blocked by obstacles, GNSS receiver 20 of a given monitoring device 1,2 may not be able to reliably derive its position -10 P_1,P_2, or the determined position P_1,P_2 will be inac curate. In another situation, one monitoring device 3 may not equipped with a GNSS receiver 20 at all (therefore, GNSS receiver 20 is dotted in fig. 2). Therefore, in order to improve the reliabil 1s ity and versatility of the proximity warning method, the monitoring devices 1,2,3 are adapted and structured for mutual time-of-flight distance derivation. For this, the monitoring devices 1,2,3 are equipped with radio trans ceivers 10 to perform a "time-of-flight (TOF) measurement 20 and/or triangulation". This TOF measurement/triangulation allows to at least approximately determine the mutual distances and/or positions of several monitoring devices 1,2,3, even if the monitoring device 3 is unable to de termine its position P_3 because of the lack of a GNSS 25 receiver 20. In the given example situation, a first posi tion P_1 of the first monitoring device 1 and a second position P_2 of the second monitoring device 2 are deter mined using the GNSS receivers 20 of the respective moni 30 toring devices 1,2. The first and second positions P 1 and P_2 are then transmitted by the monitoring devices 1,2 such that all monitoring devices 1,2,3 are aware of these positions P_1 and P_2. Then, using a bidirectional exchange of TOF 3s pulses P TOF and RTOF (see above) between the first and the second devices 1,2 and using the first and second po sitions P_1 and P_2, the first monitoring device 1 de SU/CE 20/09/2012 22 rives a first distance value d_12 (dotted lines and cir cle segments in figure 1) between the first and the sec ond monitoring devices 1,2. Then, this distance value d_12 is transmitted in a way that all monitoring devices s 1,2,3 in range are aware of it. As another step, by means of a bidirectional exchange of TOF-pulses PTOF (i.e., a third radio pulse) and RTOF (see above) between the second and the third monitoring devices 2,3, the second monitoring device 2 to derives a second distance value d 23 (dotted lines and circle segments in figure 1) between the second and the third monitoring devices 2,3. It should be noted here that this distance value d_23 is not derivable because position P 3 is not (yet) known. Then, the distance value is d_23 is also transmitted in a way that all monitoring de vices 1,2,3 in range are aware of it. As another step, by means of a bidirectional exchange of TOF-pulses PTOF and RTOF (see above) be tween the first and the third monitoring devices 1,3, the 20 first monitoring device 1 derives a third distance value d_13 (dotted lines and circle segments in figure 1) be tween the fist and the third of the monitoring devices 1,3. The P TOF pulse can be the first radio pulse which is also used for deriving d_12 as discussed above or it 25 can be a fourth radio pulse. It should be noted here that this distance value d_13 is also not derivable from the respective positions because the third position P_3 is not yet known. Then, the distance value d_13 is also transmitted in a way that all monitoring devices 1,2,3 in 30 range are aware of it. Now, the monitoring apparatus (specifically all the monitoring devices 1,2,3 in range) are aware of P_1, P_2, d_12, d_13, and d_23. From this information, the position P_3 of the third of the monitoring device 3 3s is derived and optionally transmitted by means of the ra dio transceiver(s). An ambiguity between P_3 and an also possible "mirrored position P_3'" is resolved by means of SU/CE 20/09/2012 23 a radio transceiver antenna with directional resolution, i.e., a direction sensitive antenna, in any of the moni toring devices 1,2,3. Then, a proximity warning can be issued as a s function of the first, the second, and/or the third dis tance values d_12, d_23, d_13 and/or optionally of the first, second, and/or third position P_1, P_2, P_3. Thus, even without a GNSS receiver 20 in the third of the monitoring devices 3, the position P 3 is 10 derivable which leads to higher reliability and increased safety of the monitoring apparatus. Note: 1s The above mentioned steps of transmitting a determined position P_1, P_2, and/or P_3 of a monitoring device 1,2,3 by means of the radio transceiver 10 of the respective monitoring device 1,2,3 can comprise absolute position information, e.g., altitude, longitude, and 20 latitude and/or relative position information with regard to a predefined position or regular grid points on the surface mine 100. Furthermore, an incremental position information transmission is possible as well in which only position changes are transmitted. 25 While there are shown and described presently preferred embodiments of the invention, it is to be dis tinctly understood that the invention is not limited thereto but may be otherwise variously embodied and prac ticed within the scope of the following claims. 30 Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "com prising", will be understood to imply the inclusion of a 3s stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. SU/CE 20/09/2012 H:WI\l nicm-ocn\NRPonbl\DCC\DXL\5911394 _Ldoc-24112/2013 24 The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that S that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Claims

1. A method for generating a proximity warning on an area, by means of a plurality of monitoring devices 5 mounted on movable objects on said area, wherein at least a first monitoring device at a first position and a second monitoring device at a second position each comprises a radio transceiver and a receiver for a radio based positioning system, 10 said method comprising steps of - determining said first position of said first monitoring device by means of said receiver for said radio based positioning system of said first monitoring device, - determining a first positioning accuracy of 15 said determined first position by means of said first monitoring device, - determining said second position of said second monitoring device by means of said receiver for said radio based positioning system of said second monitoring device, 20 - transmitting said determined second position by means of said radio transceiver of said second monitoring device, - receiving said transmitted second position of said second monitoring device by means of said radio 25 transceiver of said first monitoring device, and steps of a) transmitting a first radio pulse by means of said radio transceiver of said first monitoring device, b) receiving said first radio pulse from said first monitoring device by means of said radio transceiver 30 of said second monitoring device, c) transmitting a second radio pulse by means of said radio transceiver of said second monitoring device, d) receiving said second radio pulse by means of said radio transceiver of said first monitoring device, -26 e) measuring by means of said first monitoring device a first flight time between said transmitting of said first radio pulse and said receiving of said second radio pulse, 5 and wherein the method comprises a further step of - deriving by means of said first monitoring device a first distance value between said first and said second monitoring devices using 10 * said measured first flight time, * said determined first position of said first monitoring device, * said first positioning accuracy of said determined first position, and 15 * said received second position of said second monitoring device, and wherein the method comprises a further step of - issuing by means of said first monitoring 20 device a proximity warning as a function of said first distance value between said first and said second monitoring devices.

2. A method for generating a proximity warning on 25 an area, by means of a plurality of monitoring devices mounted on movable objects on said area, wherein at least a first monitoring device at a first position and a second monitoring device at a second position each comprises a radio transceiver and a receiver 30 for a radio based positioning system, said method comprising steps of - determining said first position of said first monitoring device by means of said receiver for said radio based positioning system of said first monitoring device, H:\mas Inrovn\NK'ODfl)jWLL\MA5\0U9065_I dOC-13/03/2014 -27 - determining a first positioning accuracy of said determined first position by means of said first monitoring device, - determining said second position of said second 5 monitoring device by means of said receiver for said radio based positioning system of said second monitoring device, - transmitting said determined second position by means of said radio transceiver of said second monitoring device, 10 - receiving said transmitted second position of said second monitoring device by means of said radio transceiver of said first monitoring device, and steps of a) transmitting a first radio pulse by means of said radio transceiver of said second monitoring device, 15 wherein said first radio pulse comprises a synchronized timestamp or wherein said first radio pulse is transmitted at a predefined synchronized time, b) receiving said first radio pulse by means of said radio transceiver of said first monitoring device, 20 c) measuring by means of said first monitoring device a first flight time between said transmitting of said first radio pulse and said receiving of said first radio pulse, and wherein the method comprises a further step 25 of - deriving by means of said first monitoring device a first distance value between said first and said second monitoring devices using * said measured first flight time, 30 * said determined first position of said first monitoring device, * said first positioning accuracy of said determined first position, and l OVIC]IrOI O lfl~I\JL\]\'l/\3\I) . j.[JUL [-I // i/IllI-I -28 * said received second position of said second monitoring device, and wherein the method comprises a further step of 5 - issuing by means of said first monitoring device a proximity warning as a function of said first distance value between said first and said second monitoring devices. 10

3. The method of claim 1 wherein a frequency of said first radio pulse and/or of said second radio pulse is in the range between 0.3 and 6 GHz, particularly in the range between 868 and 928 MHz, in the range between 2 and 3 GHz, in the range between 2.3 and 2.5 GHz, or in the range 15 between 5 and 6 GHz.

4. The method of any one of claims 1 or 3 wherein said first radio pulse and/or said second radio pulse is or are frequency chirped. 20

5. The method of any of the preceding claims comprising further steps of - determining a second positioning accuracy of said determined second position by means of said second 25 monitoring device, - transmitting said second positioning accuracy of said determined second position by means of said radio transceiver of said second monitoring device, and - receiving said transmitted second positioning 30 accuracy of said second position by means of said radio transceiver of said first monitoring device.

6. The method of claim 5 wherein said received second positioning accuracy of said second position is used H.\ns\Inn v e\NRPorbI\DCC\MAS\6090625_ I.doc-13/03/2014 -29 in said step of deriving said first distance value between said first and said second monitoring devices.

7. The method of any of the preceding claims 5 wherein said proximity warning comprises said received second position.

8. The method of any of the preceding claims wherein said proximity warning comprises at least one of the 10 group consisting of - an optical warning, - an acoustic warning, - an electric shock, and - a tactile warning, in particular a vibration. 15

9. The method of any one of claims 1 or claims 3 to 8 wherein said radio transceiver comprises a first transceiver unit for transmitting and receiving said first and/or said second radio pulse and wherein said radio 20 transceiver comprises a second transceiver unit for transmitting and receiving - said first and/or second position and/or - said first and/or second positioning accuracy and/or 25 - said first distance value, and in particular wherein said second transceiver unit comprises a digital transceiver.

10. The method of any of the preceding claims 30 comprising a further step of - transmitting by means of said radio transceiver of said first monitoring device said first distance value between said first and said second monitoring devices. H:\a\Ineove\NKPorbIl\DCC\MAS\6090625_ I.doc- 13/03/2014 -30

11. The method of claim 10 wherein a third monitoring device at a third position comprises a radio transceiver, and wherein the method comprises further steps of 5 - deriving by means of said second monitoring device a second distance value between said second and said third monitoring devices using a second measured flight time of a third radio pulse transmitted by said second monitoring device, 10 - transmitting by means of said radio transceiver of said second monitoring device said second distance value between said second and said third monitoring devices, - deriving by means of said first monitoring device a third distance value between said first and said 15 third monitoring devices using a third measured flight time of said first or of a fourth radio pulse transmitted by said first monitoring device, - transmitting by means of said radio transceiver said first monitoring device said third distance value 20 between said first and said third monitoring devices, - issuing by means of said first, said second, and/or said third monitoring device a proximity warning as a function of said first, said second, and/or said third distance value between said first and said second, between 25 said second and said third, and/or between said first and said third monitoring devices.

12. The method of claim 11 comprising further steps of 30 - transmitting by means of said radio transceiver of said first monitoring device said determined first position of said first monitoring device, - determining by means of said first, said second, and/or said third monitoring device said third 35 position of said third monitoring device using said first -31 position, said first distance value, said second distance value, and said third distance value, wherein an ambiguity of said third position is resolved using at least one directional antenna. 5

13. A monitoring device comprising - a radio transceiver for transmitting and receiving a radio pulse, - an interface for issuing a proximity warning, 10 - an analysis and control unit adapted and structured to carry out the steps of a method of any of the preceding claims.

14. A computer program element comprising 15 computer program code means for, when executed by a processing unit, implementing a method according to any of the claims 1 to 12.

15. The method of any one of claims 1 to 12, for 20 generating said proximity warning in a surface mine.

16. A computer program element as claimed in claim 14, the processing unit being an analysis and control unit. 25

17. A method for generating a proximity warning on an area substantially as hereinbefore described with reference to the accompanying drawings. 30

18. A monitoring device substantially as hereinbefore described with reference to the accompanying drawings. H:\maslnin, oven\NRPorbi\DCC\MAS\6)90625_I doc-1033/20)14 -32

19. A computer program element substantially as hereinbefore described with reference to the accompanying drawings. 5

20. The method of claim 2 wherein a frequency of said first radio pulse is in the range between 0.3 and 6 GHz, particularly in the range between 868 and 928 MHz, in the range between 2 and 3 GHz, in the range between 2.3 and 2.5 GHz, or in the range between 5 and 6 GHz. 10

21. The method of claim 2 wherein said first radio pulse is frequency chirped.

22. The method of claim 2 wherein said radio 15 transceiver comprises a first transceiver unit for transmitting and receiving said first radio pulse and wherein said radio transceiver comprises a second transceiver unit for transmitting and receiving - said first and/or second position and/or 20 - said first and/or second positioning accuracy and/or - said first distance value, and in particular wherein said second transceiver unit comprises a digital transceiver. 25