GB2246654A

GB2246654A - Vehicle presence detection system

Info

Publication number: GB2246654A
Application number: GB9116631A
Authority: GB
Inventors: Michael Raymond Hutchinson; Martin Graeme Holmes
Original assignee: H B DETECTION Ltd
Current assignee: H B DETECTION Ltd
Priority date: 1990-08-02
Filing date: 1991-08-01
Publication date: 1992-02-05
Anticipated expiration: 2011-08-01
Also published as: GB9016944D0; GB9116631D0; GB2246654B

Abstract

A vehicle presence detection system comprises a first part 10 disposed at an elevated position above or to one side of a vehicle pathway, e.g. on top of a traffic signal 11, a second part 12 disposed in or on the surface of the vehicle pathway, means for transmitting a microwave signal between the two parts 11 and 12, and means for detecting an interruption of said signal when a vehicle passes between, or comes to rest between, the two parts 11 and 12. In one embodiment, the part 10 includes a microwave transmitter and a microwave receiver and the part 12 includes means for modifying microwave energy incident thereon from the transmitter and for transmitting modified microwave energy to the microwave receiver. In another embodiment, the part 12 includes a microwave transmitter and the part 10 includes a microwave receiver. <IMAGE>

Description

Vehicle Presence Detection System This invention relates to a vehicle presence detection system.

It is known to use Doppler radar detectors to detect moving vehicles to assist in traffic control. In practice these known detectors are placed at an elevated position on a pole located at the side of a road, and are directed at oncoming vehicles to detect vehicles approaching, for example, a road junction and, in this case, signals from the detector may be fed to a computerised control system for operating traffic signals at the junction. There is, however, a requirement for above ground detection of stationary vehicles to complement the Doppler radar detectors and for use, inter alia, in motorway incident detection.

Doppler radar depends on the measurement of a change of frequency of a continuous wave after reflection by a moving target, and, consequently, is unable to detect stationary vehicles. It is known to use inductive loops which are capable of detecting the presence of a stationary vehicle for a limited period of time after the vehicle comes to rest, but such loops are of necessity buried in the road and are therefore expensive to install and maintain. Time-of-flight radar could be used but the cost of providing this type of radar for measuring short distances is prohibitive.

According to the present invention there is provided a vehicle presence detection system comprising a first part disposed at an elevated position above or to one side of a vehicle pathway, e.g. a road, a second part disposed in or on the surface of the vehicle pathway, means for transmitting a microwave signal between the two parts, and means for detecting an interruption of said signal when a vehicle passes between, or comes to rest between, the two parts.

In one embodiment of the invention, the first part includes a microwave transmitter and a microwave receiver, and the second part includes means for modifying microwave energy incident thereon from the microwave transmitter and for transmitting modified microwave energy to the microwave receiver.

The modifying means may include either a passive or an active circuit, although a passive circuit is preferred, and may for example introduce a phase shift or a harmonic component into the incident signal or in the case of an active circuit may modulate or otherwise encode the received signal.

In another embodiment of the invention, the second part includes a microwave transmitter, and the first part includes a microwave receiver.

Microwaves have wavelengths within the range of 1GHz to 300GHz, and it is envisaged that the microwaves towards the lower end of this range will be used for reasons of cost and simplicity. Indeed, a typical wavelength of about 1OGHz or 24GHz may be most appropriate.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic side view of one embodiment of a vehicle presence detection system according to the present invention, Figure 2 is a plan view of part of the detection system shown in Figure 1, Figure 3 is a circuit diagram of the detection system shown in Figures 1 and 2, Figure 4 is a plan view of another embodiment of a vehicle presence detection system according to the present invention, Figure 5 is a schematic view of yet another embodiment of a vehicle presence detection system according to the present invention, and Figure 6 is a circuit diagram of part of a further embodiment of a vehicle presence detection system according to the present invention.

Figure 7 is a sectional view of a road stud incorporating the circuit of Figure 6, Figure 8 is a plan view of the road stud of Figure 7, Figure 9 is a circuit diagram of another part of the embodiment of Figure 6, and Figure 10 is a sectional view of a detector incorporating the circuit of Figure 9.

Referring firstly to Figures 1 and 2 of the drawings, the vehicle presence detection system shown therein comprises a part 10 mounted at an elevated position, e.g. on top of a traffic signal 11, and a part 12 mounted on or in the road surface behind a stop line 13.

The part 10 includes a microwave transmitter and a microwave receiver which are directed towards the part 12 and the part 12 is in the form of a stud-like housing containing a circuit which will modify microwave energy incident on the part 12. The part 12 also includes waveguides or antennae for feeding incident energy to the circuit and for directing modified energy back towards the part 10.

The modifying circuit of the part 12 is preferably a passive circuit which may for example introduce a phase shift or a harmonic component into the microwaves fed thereto. The modifying circuit could however be an active circuit and in this case it may modulate or otherwise encode the microwaves fed to the circuit as an alternative to introducing a phase shift or harmonic component therein.

When a vehicle passes over or comes to rest above the part 12, the receiver detects the absence of a modified signal and this can be used to control the traffic signal 11, possibly in addition to a Doppler radar detector which detects movement of vehicles upstream of the traffic signal 11.

Figure 3 shows one example of the circuitry which can be used in the detection system of Figures 1 and 2. The part 10 comprises a transmitter 14 in the form of a Gunn diode cavity or Dielectric Resonant Oscillator, operating at typically 10.5 GHz or 24 GHz, connected to an antenna 15. The transmitter 14 may be driven from a modulating oscillator 16 to provide encoding of the output signal.

The part 12 comprises one or more non-linear devices 17 which convert some of the incident energy into the second harmonic. An integral antenna 18 may be included to improve efficiency although an omnidirectional beam pattern is generally preferred.

The part 10 also comprises a receiving antenna 19, a receiver 20, an amplifier 21 and signal processing circuitry 22 for detecting the presence or absence of -the second harmonic signal at the receiver 20, including any encoding. The receiver 20 may be in the form of a Schottky diode sensitive to the second harmonic frequency of the transmitter 14.

The components of the part 10 may be conventional waveguide type components or may be combined in "micro-strip" form. The components of the ,part 12 are preferably combined in "micro-strip" form and encapsulated in the stud-like housing referred to above.

If the system described above can be made to operate reliably over a distance of 40 metres or more, it is envisaged that it could also be used as an alternative to a Doppler radar system.

If there is a two lane approach to the traffic signal 11, a second transmitter/receiver 10a could be directed at a further modifying device 12a mounted in the second lane. Differing modulation could be employed in devices 12 and 12a to facilitate discrimination between lanes.

Figure 4 illustrates a detection system similar to that shown in Figures 1 and 2, but, in this case, there are two modifying devices 32a and 32b and two transmitter/receiver units 3Oa and 3orb. The devices 32a an 32b are spaced apart in the direction of traffic movement, e.g. by about 2 metres, and the units 30a and 30b are directed at the two devices 32a and 32, respectively. This will enable the system to not only detect the presence of a vehicle passing through the microwave beams but to also measure the speed of the vehicle. Differing modulation could be employed in devices 32a and 32b.

Figure 5 shows three transmitter/receiver units 4ova, 40b and 40c mounted on a bridge or gantry 41 above a three lane highway or motorway and directed respectively at three modifying devices 42a, 42k and 42c. This system can be used for vehicle counting or incident detection. Differing modulation could be employed in devices 42a, 42b, 42c.

Instead of using the modifying device(s) described above, the road mounted part could include a small battery powered microwave transmitter. The part mounted at an elevated position would then only comprise a microwave receiver and associated components. An example of such an arrangement will now be described with reference to Figures 6 to 10 of the accompanying drawings.

As shown in Figures 6, 7 and 8, the road mounted part 52 comprises a stud-like housing 61 containing a free running oscillator 56, a monostable multivibrator 62, a drive transistor 63, a microwave transmitter 54, a "patch" antenna 58, and a power supply consisting of a lithium battery 64, a magnetic reed switch 65 in series with the battery 64, and a linear voltage regulator 67.

This circuit is activated by inserting a magnet 66 into the housing 61 at the time of final installation of the system to close the magnetic reed switch 65. If the modifying circuit of the part 12 of the embodiment of Figures 1 and 2 is an active circuit, it may have a similar power supply.

The free running oscillator 56 produces a square-wave signal whose frequency is governed by a resistor 68. If it is required to "code" the transmission from the road mounted part 52 the value of this resistor can be selected at installation by inserting a further magnet (not shown) into the housing to operate one of a plurality of further reed switches (not shown) allowing selection of one of several frequencies. The corresponding detector unit would then be configured to decode only this frequency to allow discrimination between road mounted parts 52 and/or avoid cross-talk. Using magnet reed switches in this way allows the road mounted part to be activated and configured at the point of installation without any access to the interral circuitry ensuring that the assembly can be completely encapsulated and weatherproof.

The monostable vibrator 62 produces a short pulse signal once every cycle of the oscillator 56.

This is used to activate transistor 63 which then switches the power supply to the microwave transmitter 54. In a typical configuration the transistor 63 is switched on for 5 microseconds at a repetition rate of between 100 and 500Hz.

When power is applied to the microwave transmitter 54, during the 5 microsecond pulse, it transmits a continuous wave microwave signal at a frequency in the region of 10.5GHz (X-Band). It would be equally possible to implement a system using 'frequencies in the region of 24 GHZ (K-Band) or any other microwave band. The microwave transmitter 54 can be any device capable of producing the narrow pulsewidth signal without excessive distortion and with the minimum of power drain and may, for example, be a transistor configured as a Dielectric Resonant Oscillator (DRO) which produces in the region of 50mW of power.

The microwave signal is transmitted via the patch antenna 58 designed to give a low directivity beam pattern.

The housing 61 comprises inner and outer parts 61a and 61, respectively, bonded together with adhesive. The outer part 61b is a casting of aluminum alloy or iron which is used to anchor the assembly in a pre-drilled hole in the road surface and which may be dimensionally equivalent to a standard reflecting road stud housing. It has a flange which rests on the road surface providing stability. During installation the housing 61 is bedded into molten bitumen compound or an epoxy adhesive. The inner housing part 61a is made of a wear resistant material capable of passing microwave frequencies, such as polycarbonate or glass. The circuit components are encapsulated in the inner housing part 61a using a rigid waterproof compound.

The base of the housing has one or more threaded holes into which a small permanent magnet can be inserted and retained with a screw in order to activate and/or configure the device.

As shown in Figures 9 and 10, the other part, which is in the form of a detector unit 50, comprises a horn antenna 59, a microwave receiver 60 in the form of a waveguide cavity containing a Schottky receiver diode, a pulse amplifier 69, a comparator 70, a pulse detector 71, an output circuit 72, an output device 73, and a power supply circuit 74.

The signal from the road mounted part 52 is collected by the horn antenna 59 and the receiver 60 produces an electrical pulse corresponding to the envelope of the received microwave signal.

The amplifier 69 amplifies the pulse to enable it to be resolved by the comparator 70. The output of the comparator 70 is a series of logic level pulses at a frequency corresponding to the pulse repetition rate of the signal produced by a road mounted part within its field of view.

The presence or absence of the pulses is determined by the pulse detector 71. If the road mounted part 52 has a facility to code the frequency of its transmitted signal, the logic level pulses produced by the comparator 70 are passed to a frequency selective circuit 75 tuned to the desired frequency. Only when this frequency is present is the output of the pulse detector 71 validated and passed to the output circuit 72.

The output circuit 72 includes timing functions to give a defined response time and decay time at its output in response to the presence or absence of a signal from the road mounted part 52. This circuit 72 drives the output device 73, typically a relay, which conveys the state of the detector unit to external equipment, such as a traffic control system.

The electrical circuit of the detector unit 50 is implemented on a printed circuit board 75. This is connected to the receiver 60, antenna 59 and a transformer 76 to form a sub-assembly. This subassembly is fitted into an outer case 77 of durable material, such as aluminum alloy or thermo-plastics material, to provide environmental protection. The case 77 has a screen 78 through which microwaves can pass to the antenna 59. The base of the case 77 has projecting studs 79 for mounting purposes and a glanded exit 80 for one or more cables for connection to external circuits.

The detector unit 50 is mounted at an elevated position, e.g. on top of a traffic signal or on a bridge or gantry.

The circuit arrangement described with reference to Figures 6 to 10 may be used as an alternative to the circuit arrangement of Figure 3 in the detection system of Figures 1 and 2, or Figure 4, or Figure 5.

The embodiments described above are given by way of example only and various modifications may be apparent to persons skilled in the art without departing from the scope of the invention defined b the appended claims,

Claims

CLAIMS 1. A vehicle presence detection system comprising a first part disposed at an elevated position above or to one side of a vehicle pathway, a second part disposed in or on the surface of the vehicle pathway, means for transmitting a microwave signal between the two parts, and means for detecting an interruption of said signal when a vehicle passes between, or comes to rest between, the two parts.
2. A vehicle presence detection system as claimed in claim 1, wherein the first part includes a microwave transmitter and a microwave receiver, and the second part includes means for modifying microwave energy incident thereon from the microwave transmitter and for 'transmitting modified microwave energy to the microwave receiver.
3. A vehicle presence detection system as claimed in claim 2, wherein the modifying means includes a passive circuit for introducing a phase shift or a harmonic component into the incident signal.
4. A vehicle presence detection system as claimed in claim 2, wherein the modifying means includes an active circuit for modulating or otherwise encoding the incident signal.
5. A vehicle presence detection system as claimed in claim 1, wherein the second part includes a microwave transmitter and the first part includes a microwave receiver.
6. A vehicle presence detection system as claimed in claim 4 or claim 5, wherein the second part has a power supply including a battery and a magnetic reed switch which can be closed by inserting a magnet into the second part at the time of final installation of the system.
7. A vehicle presence detection system as claimed in any one of the preceding claims, wherein the transmitting means includes means for selectively altering the frequency of the transmitted signal and the detecting means includes frequency discriminating means which can be tuned to a selected transmission frequency.
8. A vehicle presence detection system as claimed in any one of the preceding claims, wherein the second part includes a stud-like housing mounted in the vehicle pathway.
9. A vehicle presence detection system as claimed in any one of the preceding claims, including two first parts disposed at an elevated position above, or to one side of, a vehicle pathway and two second parts disposed in or one the surface of the vehicle pathway and spaced apart in the direction of traffic movement along the pathway, the two first parts being directed respectively at the two second parts.
10. A vehicle presence detection system substantially as hereinbefore described with reference to Figures 1 to 3, Figure 4, Figure 5, Figure 6, or Figures 7 to 10 of the accompanying drawings.