WO2001044830A1

WO2001044830A1 - Device for locating a person or an object in a liquid environment

Info

Publication number: WO2001044830A1
Application number: PCT/CH2000/000665
Authority: WO
Inventors: Michel Declercq; Patrick Favre
Original assignee: Ecole Polytechnique Federale De Lausanne
Priority date: 1999-12-16
Filing date: 2000-12-15
Publication date: 2001-06-21
Also published as: FR2802651A1; AU1686101A; FR2802651B1

Abstract

The invention concerns a device for automatically and rapidly locating (10) a person or an object at sea in poor meteorological conditions, comprising a radio wave transmitting device (20) provided on the person or the object and a reception device (30), provided in a boat, and designed to receive directly said waves and to process them without any other intermediary than the radio link (40) established between them. The transmitting device (20) comprises a transmitter (21) supplied by a power source (23), and delivering a radio signal to an antenna (22). Said transmitter is activated by an actuating member (24). The reception device (30) consists of a receiver (31) for the signal transmitted by the transmitter (21) and picked up by an antenna array (32) co-operating with an antenna switch (33). The antenna array (33) is connected to the receiver (31) whereof an output is connected to said unit processing (34) the received signal. A display unit (37), connected to said processing unit (34) via a user interface (35), enables the display of the information delivered by said unit (34). An audio warning (36) is connected to the activation of the transmission device (20).

Description

DEVICE FOR LOCATING A MAN OR AN OBJECT IN A LIQUID MEDIUM

Prior art

The present invention relates to a device for locating a man or an object in a liquid medium, comprising a device for transmitting radio waves, placed on the man or on the object, and a receiving device, arranged in a navigation vessel, arranged to directly receive the waves emitted by the emission device.

Navigation at sea, by sail or by engine, being done with more and more advanced and faster and faster boats, the risks of the navigator falling into the sea or sinking during bad weather conditions are very important. It is therefore necessary to equip these men with devices intended to locate them quickly in order to be able to recover them as soon as possible.

In the detection technique, there are currently on the market several embodiments of this type of device which are based on the reception of a signal emitted by a beacon carried by the shipwrecked.

The best known and most commonly used devices in racing are the EPIRB beacons with which many navigators are equipped and which make it possible to locate them by means of a satellite relay.

Also known, in particular from US Pat. No. 5,886,635, is a detection device comprising a device carried by the navigator and intended for transmitting an FM signal, which cooperates with a station for receiving and processing this signal on a lifeboat. In this device, the location of the shipwrecked person is done by the navigation system of the boat, which can be of the GPS or Loran type, and which is linked to the station of signal reception via an interface.

Publication EP O 360 671 relates to a device formed by a submerged acoustic source arranged to emit acoustic signals in water to an alarm box carried by the shipwrecked person and provided with an acoustic sensor and a transmitter arranged for transmit a radio signal received by a receiver located in a boat.

The device which is the subject of US Pat. No. 5,463,598 is based on an ultrasonic transmitter worn by the person to be rescued and engaging in contact with water. The reception of ultrasound by a receiver placed on a boat allows the triggering of an alarm and the display of the speed of the boat compared to the transmitter.

The rescue device described by the international publication WO 90 08060 allows the location of a man overboard by means of a signal emitted by a transmitter carried by the shipwrecked person, this signal being detected by a directional receiving antenna. This antenna is a portable antenna. When the transmitter is triggered, to be able to locate the shipwrecked person, the antenna is held by one of the occupants of the boat and moved around this boat in order to determine the direction in which the man to be recovered is, this direction being the one with the strongest signal.

The German publication DE 43 11 473 relates to a man overboard rescue device in which an intermediate remote-controlled float is launched when the transmitter of the shipwrecked person is activated. This float will be directed towards the transmitter and allow its location.

The devices described by these last two publications require the presence of an intermediate connecting element between the transmission means and the reception means, namely the person carrying the directional antenna in the first device and the remote-controlled float in the second. This is not the case with the device according to the invention which has only two elements and which makes it possible to automatically determine, without human intervention and through its network of antennas, the direction in which the shipwrecked man is located. .

US-A 4,186,396 relates to an active radar beacon which requires the presence of a radar on board the rescue boat. This type of beacon is rather intended to be carried on life rafts.

The direction finding object of US Pat. No. 5,945,947 is intended for searching for transmitters whose signal is coded in FSK, which is not the case for the signal emitted by the tracking device of the invention.

US Patent 4,053,883 describes a radar allowing automatic tracking of a target and which is used in a context other than the device of the invention.

All these known devices are expensive devices since they consist, in most cases, of three elements, namely a transmitter, a receiver and an interface allowing the connection. In addition, they are very slow in reaction. In addition, the devices based on the transmission of acoustic waves have a very short range and, in the event of bad weather conditions, in particular of rough sea, they do not present a good reliability because of the cuts of transmission caused by the waves.

Statement of the invention

The present invention proposes to overcome these drawbacks by providing a device comprising only two elements and therefore having a rapid reaction time, the operation of which is not very sensitive to fluctuating waves and which makes it possible to determine automatically, without intervention. human, the direction in which the shipwrecked is. This object is achieved by the device as defined in the preamble and characterized in that said receiving device comprises an array of antennas switched sequentially by an antenna switching device in order to automatically determine the direction in which the man or object

The use of such an antenna array associated with an automatic switching device makes it possible to quickly and safely locate the man or the object to be recovered.

Advantageously, said antenna switching device is arranged to operate in progressive or abrupt mode.

In a preferred embodiment, the reception device comprises a receiver and a processing unit, said processing unit comprising a filtering and amplification block linked to the output of the receiver, a clock generation block linked to the device switching antenna, and a microcontroller respectively connected to said blocks and arranged to measure the phase difference between the rotating antenna simulated by the antenna array and the signal demodulated by the receiver.

The receiving device also includes a user interface arranged to convert, in the form of the value of an angle relative to a reference value, the phase information defining the direction in which the man or the object is located, supplied by the processing unit and display this angle via display means.

In this preferred embodiment, the receiving device preferably comprises means for reducing the effect of the cuts in the transmitted waves, said cuts being caused by movements of the liquid medium. Advantageously, the microcontroller of the processing unit comprises a first programmed algorithm, said algorithm making it possible to reduce the effect of the cuts in the transmitted waves.

In an alternative embodiment, the reception device may include means for determining an estimate of the time necessary to travel the distance separating the navigation vessel from the man or from the object.

To determine this estimate, the microcontroller of the processing unit can comprise a second programmed algorithm.

The device may also include means for displaying this estimate of the time necessary to cover the distance separating the navigation vessel from the man or from the object.

The emission device advantageously comprises an automatic or manual triggering element in contact with the liquid medium.

In one embodiment, the reception device may include means for triggering an audible alarm system when the transmission device is switched on.

Brief description of the drawings

The present invention will be better understood with reference to the description of a preferred embodiment and the accompanying drawings in which:

FIG. 1 is a schematic representation of the device according to the invention,

FIG. 2 is a detailed schematic representation of the antenna array associated with the switching device of the device in FIG. 1, and FIG. 3 is a detailed schematic representation of the signal processing unit of the device in FIG. 1.

Best way to realize the invention

With reference to the figures, the locating device 10 according to the invention comprises two elements, namely a device for transmitting radio waves 20 and a receiving device 30 intended for directly receiving and processing these waves without any other intermediary than the radio link 40 established between these two devices.

The emission device 20 is placed on the man or on the object that we want to locate and recover. This device comprises a transmitter 21 supplying a radio signal to an antenna 22. This transmitter is supplied with energy by a source 23 and is switched on manually or automatically in contact with water by an interlocking member 24.

The reception device 30 is on board the ship intended for the recovery of man or object at sea. This device consists of a frequency demodulation receiver 31 receiving the signal transmitted by the transmitter 21 and picked up by an antenna array 32 cooperating with an antenna switching device 33. The antenna array 32 is connected to an input of the receiver 31, an output of which is connected to a processing unit 34 of the received signal. A display unit 37, linked to this processing unit 34 by means of a user interface 35, allows the conversion and the display, via a logic demutiplexer 371 connected to a display 372, of the information delivered by said processing unit 34. An alarm 36 connected to the display unit 37 allows the emission of an audible signal as soon as the emission device 20 is switched on.

This emission device 20 can be in the form of a stand-alone device or be integrated into a life jacket, life jacket or the like. When it is integrated into a flotation element of this type, it can be triggered manually or coupled to the latching member 24.

This latching member 24 comprises two contacts 241 directly linked with the external environment. A resistance measurement block 242 measures the resistance that exists between these two contacts and determines whether the external medium is water or air. When the resistance measured corresponds to that of water, a switch 243 is activated in order to activate the emission device 20.

The transmitter 21 of the transmission device 20 includes a synthesis block by phase-locked loop 211. This block is followed by a power amplifier 212 in order to impose sufficient power on the antenna 22. The transmitter 21 further comprises an amplitude modulation block 213 arranged to effect modulation of the gain of the power amplifier 212 in order to identify the transmission device 20.

The reception device 30, associated with the transmission device 20, makes it possible to determine the source of a radio wave by measuring the apparent variation of the frequency of a transmitted wave, by simulating the rotation of a reception antenna. When the simulated rotating antenna approaches the source of transmission, the received frequency increases and, conversely, when it moves away from the source, the frequency decreases. A frequency demodulation receiver connected to this antenna therefore demodulates the sinusoidal signal whose frequency is equal to the frequency of rotation of the antenna and whose phase indicates the direction from which the transmitted wave originates. However, when using this type of system in a moving liquid medium, in particular at sea, since most of the time the recovery of the shipwrecked person is done in heavy weather, the transmission of the signal emitted by the emission device is strongly disturbed by the movements of the sea, and locating the man to be fished becomes difficult. The antenna array 32 of the reception device 30, as illustrated in more detail in FIG. 2, is constituted by a group of three antennas 50, or more, which can be of the monopoly or dipole type. The switching device 33, which cooperates with this array of antennas 32, is responsible for sequentially switching these antennas. Depending on the desired variant, it can operate in progressive or abrupt mode. In order to obtain a good sensitivity of the device, the connection between the antenna array 32 and the switching device 33 is done by means of gain gain amplifiers 51 linked to each of the antennas 50 and controlled by a block of gain distribution 52, these elements being integrated into the switching device 33. This switching device 33 is controlled by the processing unit 34 and makes it possible to keep a phase synchronization between the antenna array 32 and the received and demodulated signal by the receiver 31.

The gain distribution block 52, controlling the amplifiers 51 which make it possible to obtain a device which is reliable in all circumstances, comprises a counter 521 arranged to drive the address bus of a memory 522 whose data bus attacks an analog converter -digital 523 containing the waveform necessary for the scanning of the amplifiers with voltage-controlled gain 51. The output of this converter 523 is arranged to drive an analog demutiplexer 524 which distributes the control voltages on the various amplifiers 51.

The receiver 31, the input of which is connected to the antenna array 32, is a receiver allowing the demodulation of the signals in frequency modulation transmitted by the transmitter 21. Its central frequency is tuned to the transmission frequency of this transmitter . The demodulated output of this receiver is connected to the processing unit 34. This processing unit 34, as illustrated in more detail in FIG. 3, is a low frequency unit and makes it possible to convert the signal transmitted by the transmitter 21 into information that can be viewed by the rescuers, by measuring the relative phase of the signal demodulated by the receiver 31. To this end, it includes a filtering and amplification block 60 linked to the output of the receiver 31 and arranged to remove a large part of the noise, a clock generation block 61 linked to the antenna switching device 33 and arranged to synthesize all the necessary signals, and a microcontroller 62 connected respectively to the two blocks 60 and 61 and arranged to measure the phase difference between the rotating antenna simulated by the antenna array 32 and the signal demodulated by the frequency demodulation receiver 31, and supply, to the user interface 35, the phase information obtained.

In order to be able to perfectly eliminate a large part of the noise, the filtering and amplification block 60 comprises a first amplifier 601 intended for a first increase in the voltage of the demodulated signal emitted by the receiver 31. This increased signal is then filtered by a low-pass filter 602, the cut-off frequency of which is lower than the sampling frequency of a switched-capacity filter 603. The use of such a filter makes it possible to reduce the bandwidth of the signal to a width of 10 Hz. Furthermore, a smoothing filter 604 allows the elimination of the clock frequency of the filter 603, and a zero-crossing detector 605, which transforms the processed analog signal into a digital signal, then allows the use of this signal. digital by the microcontroller 62. This microcontroller 62 is arranged to process the signal indicating the level of the signal received, delivered by the receiver 31, and to measure the growth of this signal so as to be able to calculate, using a programmed algorithm appropriate, the time remaining before finding the carrier of the transmitting device 20.

The microcontroller 62 also makes it possible, by measuring the signal indicating the level of the received signal or the demodulated signal, to detect, using a another programmed algorithm, the periods during which the radio link 40 between the transmitting device 20 and the receiving device 30 is cut by a wave. During this period, the last measured direction remains memorized and displayed and the user of the device can be warned of the disappearance of the link 40 by the user interface 35.

This user interface 35 is arranged to convert, in the form of the value of an angle relative to a reference value, and display, via the display unit 37, the phase information supplied by the processing unit 34. To this end, the display 372 of this display unit includes a device for displaying the value of this angle. This display device can be in the form of a wind rose 70 which will indicate the direction of the emission device 20. This wind rose 70, as shown, is provided with light indicators 71 arranged in a circle, the lit indicator 72 indicating the direction of the man overboard. This display 372 is also provided with a digital display element 73 intended to indicate an estimate of the time remaining before the recovery, this time being determined at starting from an appropriate algorithm programmed in the microcontroller 62, as well as from a general switch 74 of the device 10. The alarm 36, linked to the display unit 17, can be triggered by an appropriate button.

This device is particularly advantageous in that, on the one hand, it is very reliable since it takes into account all the parameters liable to disturb the emission of the signal and, on the other hand, that it only comprises two elements, which greatly reduces its cost price.

In an alternative embodiment, the system for displaying the direction in which the shipwrecked is located can be replaced by any other known device, such as in particular a screen allowing the digital display of the value of the angle relative to a reference value.

Claims

1. Device for locating (10) a man or an object in a liquid medium comprising a device for transmitting radio waves (20) disposed on the man or on the object and a receiving device ( 30), arranged in a navigation vessel, arranged to directly receive the waves emitted by the transmitting device, characterized in that said receiving device (30) comprises an array of antennas (32) switched sequentially by a device antenna switching (33) to automatically determine the direction of the man or object.

2. tracking device according to claim 1, characterized in that the antenna switching device (33) is arranged to operate in progressive or abrupt mode.

3. Locating device according to claim 1, characterized in that the reception device (30) further comprises means for converting the phase differences between a control signal from said reception device (30) and the signal transmitted by the transmitting device (20) at an angle to define the direction in which the man or object is located.

4. Locating device according to claim 3, characterized in that the receiving device (30) comprises a receiver (31) and a processing unit (34), said processing unit comprising a filtering and amplification block ( 60) linked to the output of the receiver (31), a clock generation block (61) linked to the antenna switching device (33), and a microcontroller (62) connected respectively to the blocks (60) and (61 ) and arranged to measure the phase shift between the rotating antenna simulated by the antenna array (32) and the signal demodulated by the receiver (31).

5. Locating device according to claims 3 and 4, characterized in that the receiving device (30) comprises a user interface (35) arranged to convert, in the form of the value of an angle relative to a reference value, the phase information defining the direction in which the man or the object is located, supplied by the processing unit (34) and displaying this angle via display means (70).

6. Locating device according to claim 1, characterized in that the receiving device (30) comprises means arranged to reduce the effect of cuts in the transmitted waves, said cuts being caused by movements of the liquid medium.

7. tracking device according to claims 4 and 6, characterized in that the microcontroller (62) of the processing unit (34) comprises a first programmed algorithm, said algorithm making it possible to reduce the effect of the cuts in transmitted waves.

8. Locating device according to claim 1, characterized in that the receiving device (30) comprises means for determining an estimate of the time necessary to travel the distance separating the navigation vessel from the man or from the object.

9. tracking device according to claims 4 and 8, characterized in that the microcontroller (62) of the processing unit (34) comprises a second programmed algorithm, said algorithm allowing this estimation of time.

10. Locating device according to claim 8, characterized in that the receiving device (30) comprises means (73) for displaying this estimate of the time necessary to cover the distance separating the man or object navigation vessel.

11. Locating device according to claim 1, characterized in that the emission device (20) comprises a triggering element (24) automatic or manual, in contact with the liquid medium.

12. Locating device according to claim 1, characterized in that the reception device (30) comprises means (36) for triggering an audible alarm system when the transmission device is switched on.