WO2004032091A1

WO2004032091A1 - Proximity detection system and method

Info

Publication number: WO2004032091A1
Application number: PCT/AU2003/001308
Authority: WO
Inventors: Brian Crute; Richard Wilkins
Original assignee: Rf Innovations Pty Ltd
Priority date: 2002-10-04
Filing date: 2003-10-03
Publication date: 2004-04-15
Also published as: AU2002951852A0

Abstract

A proximity detection system (1) for detecting the proximity of a first mobile unit (2a) to a second mobile unit (2b). A transceiver (16) is provided to transmit a first signal from the second mobile unit (2b). The first signal is received by a transponder (12) on a first mobile unit (2a). After a selected time delay, the transponder (12) transmits a second signal in response to the first signal. The second signal is received by the transceiver (16). The time elapsed between transmission of the first signal and receipt of the second signal is computed. The computation is compared with a value, stored in a memory (22), by a computation unit (20). The value stored in the memory (22) represents a predefined distance that forms the boundary of an alarm condition zone (30a, 30b) around the second mobile unit (2b). A comparator (24) compares the computed time elapsed with the value stored in the memory (22) to determine whether the proximity of the first mobile unit (2a) to the second mobile unit (2b) is such that the first mobile unit (2a) is in an alarm condition zone (30a, 30b). If the first mobile unit (2a) is within an alarm condition zone (30a, 30b), a control unit (10) activates a device on the second mobile unit (2b), such as a warning light or siren or the brakes of the second mobile unit (2b) are activated.

Description

"Proximity Detection System and Method"

Field of the Invention

The present invention relates to a proximity detection system and a method for detecting the proximity of a first mobile unit to a second mobile unit.

The term "mobile unit" is used herein to refer to an object or body that is capable of movement. The nature of the mobile units in relation to which the present invention is used varies upon the application of the invention. For example, the invention may be used in an underground mine to detect the proximity of a vehicle, or personnel, to another vehicle. In such an application of the invention, the mobile units are the vehicles and personnel.

Disclosure of the Invention

In accordance with one aspect of the present invention there is provided a proximity detection system for detecting the proximity of a first mobile unit to a second mobile unit comprising

at least one transmitter means to transmit a first signal,

at least one transponder to receive said first signal and transmit a second signal in response to said first signal after a selected time delay,

at least one receiver means to receive said second signal,

said transmitter means and said receiver means arranged to be provided on said second mobile unit and said transponder arranged to be provided on a said first mobile unit,

computation means to compute the time elapsed between transmission of a said first signal by said transmitter means and receipt of said second signal by said receiver means, memory means to store at least one value that represents a predefined distance that forms the boundary of an alarm condition zone around said second mobile unit,

comparator means to compare the computed time elapsed with said at least one value to determine whether the proximity of the first mobile unit to the second mobile unit is such that the first mobile unit is within the alarm condition zone, and

control means to activate at least one device on said second mobile unit if said first mobile unit is determined to be within said alarm condition zone.

In accordance with another aspect of the present invention there is provided a method for detecting the proximity of a first mobile unit to a second mobile unit comprising

transmitting a first signal from the location of said second mobile unit,

receiving said first signal at the location of said first mobile unit,

transmitting a second signal from the location of said first mobile unit in response to said first signal after a selected time delay,

receiving said second signal at the location of said second mobile unit,

computing the time elapsed between transmitting said first signal and receiving said second signal,

comparing the computed time elapsed with at least one stored value that represents a predefined distance that forms the boundary of an alarm condition zone around said second mobile unit,

determining whether the proximity of said first mobile unit to said second mobile unit is such that said first mobile unit is within said alarm condition zone, and activating at least one device on said second mobile unit if said first mobile unit is determined to be within said alarm condition zone.

Brief Description of the Drawings

The present invention will now be described, by way of example, with reference to the accompanying drawing, in which:

Figure 1 is a schematic illustration of an embodiment of the proximity detection system of the present invention;

Figure 2 is a functional block diagram of an embodiment of the circuitry of the master interrogating unit of the proximity detection system shown in Figure 1; and

Figure 3 is a functional block diagram of an embodiment of the circuitry of the transponder of the proximity detection system shown in Figure 1.

Best Mode(s) for Carrying Out the Invention

In Figure 1 there is shown a proximity detection system 1 for detecting the proximity of one or more first mobile units, in the form of vehicles 2a and 2b, to a second mobile unit, in the form of a remotely operated vehicle 4. Whilst only two first mobile units, being vehicles 2a and 2b, have been shown in the embodiment illustrated in Figure 1 , the proximity detection system 1 of the present invention can operate with any suitable number of first mobile units. Depending upon the application of the proximity detection system 1 of the present invention, the number of first mobile units may number from the tens to the hundreds, or more.

The proximity detection system 1 comprises a master interrogating unit 6 having an antenna 8 for transmitting and receiving signals, a control unit 10, and at least one transponder 12 having an associated antenna 14. The master interrogating unit 6 and the control unit 10 are installed on the remotely operated vehicle 4 whilst a transponder 12 and antenna 14 are installed in each of the vehicles 2a and 2b. The antennas 8 and 14 are mounted on top of the vehicles 4, 2a, and 2b in suitable locations that are clear from any line of sight obstructions. The master interrogating unit 6 is installed as close as possible to the antenna 8 on the remotely operated vehicle 4. Similarly, the antennas 14 are mounted as close as possible to the transponders 12 on the vehicles 2a and 2b. The control unit 10 is mounted at a suitable location on the remotely operated vehicle 4 as close as possible to the control box of the remotely operated vehicle 4.

The master interrogating unit 6 comprises a transceiver 16 and logic components 18. The logic components 18 comprise a computation unit 20, a memory store 22 and a comparator 24. The control unit 10 is provided with slave relays 26a, 26b, 26c and 26d. Whilst four relays have been shown, a greater or lesser number of slave relays may be provided. The slave relays 26a - 26d allow operation of devices of the remotely operated vehicle 4 by the control unit 10. Such device or devices may, for example, be warning lights, the horn of the remotely operated vehicle 4 and the brakes of the remotely operated vehicle 4. This operation will be further described later herein.

The transceiver 16 is able to transmit a pulsed signal, referred to herein as the first signal, via the antenna 8. The first signal is received by the transponders 12 on the vehicles 2a and 2b, via their respective antennas 14. In response to receiving the first signal, each transponder 12 transmits a return signal, referred to herein as the second signal, via its respective antenna 14. Each second signal is received by the transceiver 16 via the antenna 8.

Figure 2 illustrates an embodiment of the circuitry for the master interrogating unit 6. A switch 50 is provided to control transmission and reception of signals via the antenna 14. A low PRF (Pulse Repetition Frequency) generator 52 provides the switching between signal transmission and signal reception.

The front end of the circuitry has a transmit signal section 54 and a receive signal section 56. Detection of the second signals transmitted by the transponders 12 and received by the master interrogating unit 6 is detected by the detector 58. An ASP (Analogue Signal Processing) section 60 forms the requisite signal processing for measuring range and providing proximity feedback. The ASP section 60 comprises four discrete modules being a ramp generator 62 to determine the transponder 12 range using the detected second signal, an integrator and associated missed pulse reset circuitry 64 to determine the average range to a transponder 12, a negative peak detector 66 to hold the minimum detected range to the transponder 12 and a bank of comparators 68 to facilitate identification of the alarm condition zones 30a and 30b. Alternatively, the functions of the ASP 60 can equally be achieved using digital signal processing.

Figure 3 shows an embodiment of a functional block diagram of the circuitry of a transponder unit 12 provided on the vehicles 2a. The front end signal transmit section 70 and signal receive section 71 of the transponder 12 on the vehicles 2a is similar to those (54 and 56) of the master interrogating unit 6. Similarly, the detector 72 is similar to the detector 58 of the master interrogating unit 6. A signal timing unit 74 performs signal delay and may use the same discrete delay elements as implemented in the signal timing unit 69 of the master interrogating unit 6.

Preferably, the first and second signals have a frequency of 2.4 GHz. The transceiver 16 transmits the first signal as a narrow pulse at the 2.4 GHz frequency and at approximately 100 milliwatts. However, the invention is not limited to use at the 2.4 GHz frequency and any suitable frequency can be used. The duly cycle of the transceiver 16 is approximately 1 in 4500. Each of the transponders 12 receives the first signal and translates it into a recovered pulse which is then digitally delayed for a predetermined time, as will be later herein described. After the selected time delay, i.e. the predetermined time delay, has elapsed the transponders 12 transmit the second signals which are also narrow pulse.

The transceiver 16 receives each second signal and translates it into a recovered signal. The computation unit 20 uses the time that the first signal was sent and the time that a second signal is received to compute the time elapsed between transmitting the first signal and receiving the second signal. The memory 22 stores threshold values that represent predefined distances. The predefined distances represent the outer perimeters, or boundaries, 28a and 28b of alarm condition zones 30a and 30b, respectively, around the remotely operated vehicle 4.

The comparator 24 compares the time elapsed, computed by the computation unit 20, with the threshold values stored in the memory 22. Since the threshold values stored in the memory 22 represent the predefined distances from the remotely operated vehicle 4, the comparison of the computed time elapsed with the stored threshold values can be used to determine whether a vehicle 2a, 2b has crossed the perimeters 28a, 28b and entered the alarm condition zones 30a and 30b. This can be done since the time elapsed computed by the computation unit 20 is the time taken for the first signal to travel from the remotely operated vehicle 4 to a transponder 12, any potential delay time, and the time for the second signal to travel from the transponder 12 to the master interrogating unit 6. The first and second signals travel at the speed of light (3 X 10⁸ ms^"1) and thus take about 3.3 X 10^"9 seconds to travel each metre. The predetermined time delay may be, for example, from about 200 X 10^~9 seconds to about 500 x 10^"9 seconds.

If the comparator determines that a vehicle 2a, 2b has crossed the perimeter 28a or 28b into an alarm condition zone 30a or 30b, a signal is sent to the control unit 10.

The signal sent to the control unit 10 is indicative of the zone 30a or 30b into which a vehicle 2a or 2b has crossed. The control unit 10 then activates one or more relays 26a, 26b, 26c and 26d to operate a device or devices of the remotely operated vehicle 4. For example, if a vehicle 2a or 2b crosses the perimeter 28a into the zone 30a, warning lights and the horn of the remotely operated vehicle 4 may be activated. Thus, the relays 26a and 26b may be connected to the warning lights and horn, respectively, of the remotely operated vehicle 4. In the event that a vehicle 2a or 2b crosses the perimeter 28b into the zone 30b, which may be designated as a danger zone, the brakes of the remotely operated vehicle 4 may be activated. Thus, the relay 26c may be connected to the brakes of the remotely operated vehicle 4. The brakes of the vehicle 4 may remain activated until the distance between the vehicle 2a or 2b and the remotely operated vehicle 4 increases so that the vehicle 2a, 2b is no longer in the danger zone 30b. The relay 26d may be left spare.

The proximity detection system of the present invention can also determine the relative velocity and acceleration between a vehicle 2a and any of the vehicles 2b (that are provided with the transponders 12).

Whilst the embodiment of the proximity detection system described herein uses two alarm condition zones 30a and 30b, any suitable number of such alarm condition zones may be used. This is readily achieved by storing values in the memory 22 that correspond to the perimeters of the required alarm condition zones. Similarly, the control unit 10 may be arranged such that particular devices of the remotely operated vehicle 4 are activated to correspond with entry of a vehicle 2a or 2b into one of the alarm condition zones.

The proximity detection system 1 as hereinbefore described provides a warning in the event that a vehicle 2a or 2b comes within a predefined distance of the remotely operated vehicle 4 that may constitute a potential hazard. A suitable warning is then given of the potentially hazardous condition, e.g. by warning lights of the remotely operated vehicle being activated and/or the horn of the remotely operated vehicle 4 being activated. In cases where a vehicle 2a or 2b comes sufficiently close to the remotely operated vehicle 4 that a highly hazardous situation may arise, the remotely operated vehicle 4 can be completely stopped by the brakes of the remotely operated vehicle 4 being activated. This significantly reduces the likelihood of the vehicle 2a or 2b colliding with the remotely operated vehicle 4.

The proximity detection system 1 as hereinbefore described can also be used with personnel in place of the vehicles 2a and 2b. Personnel would carry suitable transponders 12 and antennae 14. In the event that personnel came within the alarm condition zones around the remotely operated vehicle 4, the devices of the remotely operated vehicle 4 would be activated as hereinbefore described. This significantly reduces the possibility of personnel being struck by the remotely operated vehicle 4.

The perimeters 28a and 28b may be configured as required. As an example, in an underground mine situation the perimeter 28a may be set at 15 metres and the perimeter 28b set at 8 metres, respectively, from the remotely operated vehicle 4.

The present invention permits more than one master interrogating unit 6 to operate in the same area. In such a case, the transponders 12 respond to the first signals transmitted by all of the master interrogating units 6. In the event that a second signal received from any transponder 12 by any master interrogating unit 6 indicates that the mobile unit carrying the transponder 12 had entered into an alarm condition zone, that master interrogating unit 6 could activate the appropriate devices of its mobile unit 2b.

The proximity detection system 1 of the present invention also permits the transponders 12 of the vehicles 2a to be uniquely identified, referred to herein as coding. This is done by assigning a predetermined time delay (previously referred to herein) to each transponder 12. This predetermined time delay is the time delay between the transponder 12 receiving a first signal from a master interrogating unit 6 and transmitting its second signal in return. The predetermined time delays are set in multiples of a fixed time delay such that each of the transponders 12 has a unique time slot in which to send its second signal in return to the first signal it received from a master interrogating unit 6. This unique time slot uniquely identifies each of the transponders 12 to the master interrogating unit 6. Typically, the number of available time slots is 1000 which is a quantity sufficient to ensure that no two transponders 12 in a given site would have the same code. In the event that a site required more than 1000 separate transponders 12, intra slot coding may be introduced to expand the number of transponders 12 that may be used at the site.

The first signals are emitted by the master interrogating unit 6 as two consecutive timing pulses at a PRF (Pulse Repetition Frequency) of approximately 4 kHz. Two pulses may be generated, for example, 200ns apart so transponders 12 on the vehicles 2a are able to differentiate between first signals being transmitted by master interrogating units 6 and second signals transmitted by transponders 12 on other vehicles 2a.

After the transmission of the second of the two consecutive pulses of each first signal by a master interrogating unit 6, the master interrogating unit 6 waits for a preselected time (being the fixed predetermined time delay previously referred to herein with reference to the transponders 12). After this time period, it starts timing of 2 microsecond respond code bins for the transponders 12 of the vehicles 2a. Approximately 500ns of guard time exist between adjacent code bins, thus providing 1.5 microseconds of range determination time.

A transponder 12 of a vehicle 2a will respond to a master interrogating unit 6 if two consecutive pulses separated by 200ns are detected. As soon as a transponder of a vehicle 2a detects the rising edge of the second pulse of the first signal transmitted by a master interrogating unit 6, it waits so that its predetermined time delay matches that programmed at the master interrogating unit 6 and then begins counting the bins (using its own timer synchronised to this rising edge). When the transponder 12 of a vehicle 2a reaches its allocated bin number it responds by sending one transmit pulse back to the master interrogating unit 6 at the start of its bin. The timing of the transponders 12 of the vehicles 2a is offset from that of the master interrogating unit 6 by an amount equal to the transmit pulse time of flight of the master interrogating unit 6.

The master interrogating unit 6 at the beginning of each bin will enable the interrogator and start a measurement. The received pulse (if any) for each coded transponder 12 of a vehicle 2a will stop the interrogator and thus generate a distance measurement for each time coded transponder 12 of the vehicles 2a. If there is no response from a transponder 12 of a vehicle 2a, the interrogator will saturate and thus report the maximum distance.

By way of example, the following is a functional description of the operation of the master interrogating unit 6 with particular reference to Figure 2. The low PRF generator (waveform A) forms the heart of the master interrogating unit 6 providing the switching between Tx (mark period) and Rx (space period), as-well-as the requisite timing for pulse transmission and received (detected) pulse processing.

Timing information is for the most part derived from the rising edge of pulses. The exception is the +/-330ns delay {waveform I), which is derived from the falling edge of the mark pulse. This is highlighted in Figure 2 through the use of the (logic) inversion symbol (°).

The rising edge of the mark pulse is used to generate a 33ns transmit pulse (waveform C), delayed by 72.6ns (waveform B). As the PA section is turned off during the receive cycle or inter-pulse period (so as to conserve power, especially in the case of the battery operated transponders 12), the 72.6ns delay allows for the PA turn on time.- The 33ns pulse then modulates the 2.45GHz CW carrier (waveform D), which is (wideband) filtered and amplified by the Tx RF front end, before being transmitted (waveform E).

No pulse shaping is implemented to reduce bandwidth occupancy, so the transmitted mainlobe bandwidth for a pulse of duration of τ = 33ns is given by :

2

BW- ma-in-,,lo-^be = - Hz

= 60.61 MHz

A delayed version of the 33ns pulse is (waveform J) sets the FF output (waveform FF O/P).

Setting the FF (Flip-Flop) O/P enables the CCS (Constant Current Source), but the current is shorted to ground until the transponder 12 turn-around delay of 500ns times-out (waveform L). On time-out, the ramp generator is enabled (waveform RAMP) and the capacitor starts to charge. The return pulse from the transponder 12 is (wideband) filtered, amplified (waveform F) and detected using a "biased" envelope detector (waveform G). A limiter is used to extract a useable pulse (waveform H), which then clears the Q output of a D-type FF, switching off the CCS and therefore causing the ramp generator to hold the voltage attained. The ramp generator capacitor is discharged on the rising edge of the PRF mark pulse (waveforms A and RAMP).

If no return pulse is detected, the FF output is reset after 2.2μs (waveform K .

The ramp voltage is averaged to provide a DC measurement that is proportional to the master interrogating unit 6 and transponder 12 proximity, with the minimum measured separation distance recorded using a negative peak detector. A missed pulse integrator reset circuit prevents the ramp generator from biasing the average DC level in cases where no return pulse is detected.

The final DC voltage is used to provide a raw range measurement, as-well-as zone identification using a bank of comparators.

By way of example, the following is a functional description of the operation of the transponder 12 with particular reference to Figure 3.

Functionally the transponder 12 differs from the master interrogating unit 6 in that it actively regenerates and retransmits a detected pulse. In essence the unit performs no ASP per se, but it does use the recovered pulse to generate the requisite timing for pulse retransmission.

The Rx pulse is (wideband) filtered, amplified (waveform A) by the Rx RF front end and detected using a "biased" envelope detector (waveform B). The detected envelope is video amplified and limited to extract a useable pulse (waveform C). The falling edge of the regenerated pulse initiates :

1. a 1μs pulse extender (waveform D). The extended pulse controls the transponder 12 Tx/~Rx line, switching the unit into Tx. 2. a ±490ns delay (waveform E) to allow for the PA turn on time, prior to retransmitting back to the master interrogating unit 6. Since the transponder 12 is battery powered, the PA is turned off during the Rx period so as to conserve power and therefore extend battery life.

The Tx pulse (waveform F) delayed by ±490ns (i.e. the predetermined time delay time), modulates the 2.45GHz CW carrier (waveform G), which is (wideband) filtered and amplified by the Tx RF front end, before being transmitted (waveform H).

The falling edge of the extended pulse initiates an 11 μs delayed, which is used to provide a visual indication to the user that the unit is fully functional (waveform I).

The proximity detection system of the present invention may be used in various applications, e.g. under ground and above ground mine sites to give warnings of potentially hazardous conditions; on locomotives to give warnings of impending collisions with other rolling stock on the same railway line; provide warnings to protect children from being struck by reversing vehicles.

Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

1. A proximity detection system for detecting the proximity of a first mobile unit to a second mobile unit characterised in that it comprises:

at least one transmitter means to transmit a first signal,

at least one receiver means to receive said second signal,

computation means to compute the time elapsed between transmission of a said first signal by said transmitter means and receipt of said second signal by said receiver means,

memory means to store at least one value that represents a predefined distance that forms the boundary of an alarm condition zone around said second mobile unit,

2. A proximity detection system according to claim 1 , characterised in that said transponder is provided with timing means to delay transmission of said second signal by said transponder by said selected time delay.

3. A proximity detection system according to claim 1 or 2, characterised in that each said transponder has a unique selected time delay different from the selected time delay of any other said transponder.

4. A proximity detection system according to claim 3, characterised in that each selected time delay is a unique multiple of a basic fixed time period.

5. A proximity detection system according to any one of the preceding claims, characterised in that said first signal comprises two consecutive pulses that are separated by a predetermined time interval.

6. A proximity detection system according to claim 5, characterised in that said transponder transmits said second signal after it starts to receive the second of said two consecutive pulses.

7. A proximity detection system according to any one of the preceding claims, characterised in that said second mobile unit is a vehicle and said at least one device is an audio or visual warning device.

8. A proximity detection system according to any one of the preceding claims, characterised in that said second mobile unit is a vehicle and said at least one device comprises the brake of said vehicle.

9. A method for detecting the proximity of a first mobile unit to a second mobile unit comprising

transmitting a first signal from the location of said second mobile unit,

receiving said first signal at the location of said first mobile unit, transmitting a second signal from the location of said first mobile unit in response to said first signal after a selected time delay,

receiving said second signal at the location of said second mobile unit,

determining whether the proximity of said first mobile unit to said second mobile unit is such that said first mobile unit is within said alarm condition zone, and

activating at least one device on said second mobile unit if said first mobile unit is determined to be within said alarm condition zone.

10. A method according to claim 9, characterised in that each said transponder has a unique selected time delay that is different from the selected time delay of any other said transponder.

11. A method according to claim 10, characterised in that each unique selected time delay is a unique multiple of a basic fixed time period.

12. A method according to claim 10 or 11 , characterised in that the method further comprises transmitting said first signal as two consecutive pulses separated by a predetermined time interval.

13. A method according to claim 12, characterised in that the method further comprises detecting the second of said two consecutive pulses and then transmitting said second signal after said selected time delay.

14. A method according to any one of claims 10 to 13, characterised in that said second mobile unit is a vehicle and said at least one device is an audio or visual warning device.

15. A method according to any one of claims 10 to 13, characterised in that said second mobile unit is a vehicle and said at least one device comprises the brakes of said vehicle.