Apparatus for detecting magnetostrictive resonator and traffic system

Abstract: A magnetostrictive resonator detection apparatus includes a transmission section for transmitting a resonance frequency of a magnetostrictive resonator, and a reception section for detecting a resonance frequency oscillated by the magnetostrictive resonator.

Description: This invention relates to a magnetostrictive resonator detection apparatus for detecting the presence of a magnetostrictive resonator and a traffic system for detecting the position and orientation of a magnetostrictive resonator buried in a road, thereby checking the vehicle position on the road and providing safety information for vehicle driving and road maintenance management. Hitherto, a median strip and a roadside on a road have been displayed by white lines, etc., and visually checked by vehicle drivers. However, a snowplow at the snowfall time loses sight of the roadside or to again draw white lines, the road is closed to traffic and the white lines must be drawn by human power, interfering with labor saving and automatization. In road facilities, it is difficult to provide a safe marker and a safe on-vehicle detection apparatus capable of identifying a median strip and a roadside in a non-contact manner and at low costs because of economics restrictions. US-A-550 617 describes a magnetostrictive apparatus for determining a resonant spectrum of a material sample. A material sample having magnetostrictive properties is placed within an exciting coil for producing an oscillating magnetic field. A detection coil is placed about the sample to detect the sample response to the exciting magnetic field. JP-A-07 244 788 describes an alarm system indicating if a vehicle comes close to a marker placed in a road. The described alarm system comprises a transmission section and a receiving section. The transmission section generates an excitation signal for exciting a marker placed in a road. The receiving section receives a resonance signal from a marker excited by the excitation signal and transmits a received signal to an alarm-level detecting element. In case the received signal exceeds a predetermined threshold, an alarm is initiated. GB-A-2 069 209 describes an abnormal tyre pressure detection system. The described system comprises a first device to be positioned on a rotating wheel and a second device fixed on a non-rotating part of the vehicle. The first device comprises a pressure responsive element mounted within the tyre, a crystal resonator and a first antenna. The second device comprises a transmitter, a receiver, an alarm device, a second antenna and a transmitting/receiving switchover circuit. The transmitter produces an exciting energy of a frequency corresponding to the resonance frequency of the resonator to excite the resonator during a pre-determined time period. After termination of the transmitter's operation, the receiver starts to receive the attenuating oscillation of the crystal resonator radiated to the antenna of the second device. Upon detecting an abnormal internal tyre pressure, the pressure responsive element of the first device opens the switch to prevent a further excitation of the crystal resonator. If no oscillatory energy from the crystal resonator is detected by the receiver, an alarm is initiated in order to inform the driver of the abnormal drop in the internal tyre pressure. In case a plurality of tyres is to be monitored which are disposed next to each other, crystal resonators having different resonance frequencies are provided on each of the tyres. The invention has been made to eliminate the above problems with the prior art, and therefore an object of the invention is to provide a magnetostrictive resonator detection apparatus that can be installed on a vehicle for detecting markers made of magnetostrictive resonators that can be installed in conventional roads and reinforced concrete roads and a traffic system intended for safety of road maintenance management and labor saving. This is achieved by the magnetostrictive resonator detection apparatus of claim 1 and by a traffic system of claim 8. In the accompanying drawings: FIG. 1A is an illustration to show the detection principle of a magnetostrictive resonator detection apparatus in one embodiment of the invention, and FIG. 1B is an illustration to show a detection signal detected by the apparatus; FIG. 2 is an illustration to show an example of applying the magnetostrictive resonator detection apparatus to a traffic system; and FIG. 3 is a block diagram of the magnetostrictive resonator detection apparatus. A first magnetostrictive resonator detection apparatus of the invention oscillates a magnetostrictive resonator and can detect the resonance frequency of the magnetostrictive resonator, thereby detecting the presence of the magnetostrictive resonator. In the magnetostrictive resonator detection apparatus of the invention, the reception section detects the resonance frequency oscillated by the magnetostrictive resonator after the transmission section terminates transmission, so that the magnetostrictive resonator detection apparatus can detect the presence of the magnetostrictive resonator reliably. The magnetostrictive resonator detection apparatus, which further includes the switch section, can transmit and receive a signal through one antenna. The magnetostrictive resonator detection apparatus of the invention transmits and receives one of a plurality of different resonance frequencies and then transmits and receives a resonance frequency different from that resonance frequency, whereby the apparatus can reliably detect a plurality of magnetostrictive resonators. A second magnetostrictive resonator detection apparatus of the invention further includes the intermediate frequency conversion section. Thus, if a plurality of different resonance frequencies are received, they can be detected by one detection section. Another magnetostrictive resonator detection apparatus activates the discharge resistor at the switching time from transmission to reception, thus can prevent reception interference caused by reverberation of transmission output. In another magnetostrictive resonator detection apparatus of the invention, the intermediate frequency conversion section adds output of the local oscillation section to the received frequency to produce the intermediate frequency. Thus, an advantage similar to that of the fifth magnetostrictive resonator detection apparatus can be provided by the simple configuration. Another magnetostrictive resonator detection apparatus of the invention, which simply comprises one direct digital synthesizer, can provide an advantage similar to that of the fifth magnetostrictive resonator detection apparatus. Another magnetostrictive resonator detection apparatus of the invention can reliably transmit and receive a plurality of different resonance frequencies by selecting one of the tuning capacitors in conformance with the oscillated resonance frequency. Another magnetostrictive resonator detection apparatus of the invention enables the user to easily see the detection levels of magnetostrictive resonators. The traffic system of the invention comprises a road having magnetostrictive resonators and a vehicle having a agnetostrictive resonator detection apparatus and thus can provide a system wherein the vehicle is driven safely. In the traffic system of the invention, the magnetostrictive resonators oscillate different resonance frequencies, so that a safe and reliable driving system can be provided. In the traffic system of the invention, the vehicle detects the magnetostrictive resonators and is driven automatically. Thus, a safe and reliable traffic system fitted to a graying society can be provided. The traffic system of the invention can easily and reliably keep track of the vehicle position on the road. In another traffic system of the invention, the magnetostrictive resonators are buried in the road, so that durability of the magnetostrictive resonators is improved. Now, a description will be given in more detail of preferred embodiments of the invention with reference to the accompanying drawings. Generally, when an AC electric field or an AC magnetic field at a specific frequency is given to a magnetostrictive resonator like a thin plate or a rod given a magnetic bias, vibration is produced longitudinally and amplitude reaches the maximum at a resonance frequency. At the same time, the amplitude is in a mechanical resonance state for a short time if electromagnetic field is removed, whereby AC magnetization is generated and an electromagnetic wave is emitted. (Refer to (4) Jiwaisouhakinogenri on pages 34-36 of kaiteizouho "jiwaishindoutochouonpa" by YOSHIMITSU KIKUCHI, published by Coronasha.) FIG. 1A is an illustration to show the detection principle of the magnetostrictive resonator detection apparatus in the embodiment of the invention and FIG. 1B is an illustration to show a detection signal detected by the apparatus. In FIGs. 1A and 1B, an electromagnetic wave at a resonance frequency is transmitted for a short time from an antenna 7 (1) and a magnetostrictive resonator 1 is made to resonate (2). Then, the resonance echo is detected through the antenna 7 (3). In the embodiment, one antenna 7 is used for both transmission and reception. FIG. 2 is an illustration to show an example of applying the magnetostrictive resonator detection apparatus in the embodiment of the invention to a traffic system; it shows the positional relationship between the antenna 7 attached to a vehicle 21 and magnetostrictive resonators 1a, 1b, and 1c buried in a road 20. Referring now to the accompanying drawings, the magnetostrictive resonator detection apparatus in the embodiment of the invention will be discussed. FIG. 3 is a block diagram of the magnetostrictive resonator detection apparatus in the embodiment of the invention. In the figure, numeral 14 is a microprocessing unit (MPU) for controlling the magnetostrictive resonator detection apparatus, numeral 4 is a direct digital synthesizer (DDS) for oscillating the resonance frequency of each magnetostrictive resonator and the difference frequency between the resonance frequency and intermediate frequency; numeral 5 is a transmission and reception switch section for switching transmission and reception, numeral 6 is a transmission amplifier, numeral 7 is an antenna used for both transmission and reception, numeral 8 is a tuning capacitor section wherein an optimum capacitor is selected in response to transmitted or received resonance frequency, numeral 9 is a discharge resistor activated for a short time at the transmission termination time (at the switching time from transmission to reception), numeral 10 is a reception amplification section for amplifying a received signal, numeral 11 is an intermediate frequency conversion section for converting a received frequency into an intermediate frequency, numeral 12 is a filter section for attenuating noise other than the intermediate frequency, numeral 13 is an amplification detector section, and numeral 15 is a display section. The resonance frequencies of the magnetostrictive resonators la, 1b, and 1c can be set roughly at 30-kHz steps from 90 kHz and can be selected up to 445 kHz preceding commercial medium wave broadcasting frequencies. The embodiment assumes that the buried median strip magnetostrictive resonator la is set to resonance frequency f1 = 210 kHz, that the buried up road shoulder magnetostrictive resonator 1b is set to resonance frequency f2 = 240 kHz, and that the buried down road shoulder magnetostrictive resonator 1c is set to resonance frequency f3 = 270 kHz. The operation of the magnetostrictive resonator detection apparatus installed on the vehicle 21 in the embodiment is performed as follows: The MPU 14 causes the DDS4 to oscillate the resonance frequency of the median strip magnetostrictive resonator la, f1, sets the transmission and reception switch section 5 to transmission, amplifies power by the transmission amplifier 6, and outputs an electromagnetic wave from the antenna 7. At this time, an optimum capacitor for the frequency to be transmitted (in this case, fl) is selected in the tuning capacitor section 8 and is connected to a return terminal of the antenna 7 in series. The electromagnetic wave is thus emitted to the median strip magnetostrictive resonator la. If the median strip magnetostrictive resonator la is in the resonance range, a resonance state is entered. Next, reception mode is entered. At this time, the discharge resistor 9 is activated for a short time. Next, the difference frequency between intermediate frequency fc (for example, 3.58 MHz) and the resonance frequency f1 of the median strip magnetostrictive resonator 1a is oscillated from the DDS 4 as local oscillation of the intermediate frequency conversion section 11. At the same time, the transmission and reception switch section 5 is set to reception. An electromagnetic wave echo signal generated due to resonance of the median strip magnetostrictive resonator la is input through the antenna 7 to the reception amplification section 10, which then amplifies the signal. At this time, the same value remains selected in the tuning capacitor section 8. The echo signal is converted into an intermediate frequency by the intermediate frequency conversion section 11. Next, noise other than the intermediate frequency fc is attenuated through the'filter section 12. Further, the signal is set as reception level by the amplification detector section 13 and is input to the MPU 14 through A/D converter input thereof and operation processing is performed on the signal. The result is displayed on the display section 15. Subsequently, the up road shoulder magnetostrictive resonator 1b and the down road shoulder magnetostrictive resonator 1c are detected cyclically in sequence for determining the position on the road. At this time, selection is executed in the DDS4 and the tuning capacitor section 8 in a similar manner to that described above. In the magnetostrictive resonator detection apparatus of the embodiment, the display section 15 specifies the magnetostrictive resonators and displays the detection levels thereof on a bar graph. The display section 15 may also display the road, the vehicle, and the vehicle position on the road. Thus, in the embodiment, electromagnetic waves at specific resonance frequencies are emitted through the antenna 7 attached to the vehicle 21 in sequence to the median strip magnetostrictive resonator la, the up road shoulder magnetostrictive resonator 1b, and the down road shoulder magnetostrictive resonator 1c buried in the road 20. When the magnetostrictive resonator la, 1b, 1c is in the electromagnetic wave reception range in which it can enter a resonance state, a vibration echo of the magnetostrictive resonators 1a, 1b, 1c is input through the antenna 7, amplified, and detected for determining the positional relationship between the vehicle 21 and the road 20. An electromagnetic wave is selectively emitted to the magnetostrictive resonators la, 1b, 1c for a short time and a bleeder current is made to flow, thereby terminating the electromagnetic wave emission. The antenna 7 is provided with tuning circuits in a one-to-one correspondence with resonance frequencies (tuning capacitor section 8). At the reception time, to efficiently distinguish the vibration echo of the magnetostrictive resonator in the resonance range, a signal received by a heterodyne system is converted into an intermediate frequency signal, which is then amplified and detected as reception level. The result is input to the A/D converter section of the MPU 14, determination processing is performed, and display output and control output are performed. Therefore, by installing the magnetostrictive resonator detection apparatus of the embodiment on the vehicle 21, the magnetostrictive resonators la, 1b, and 1c buried in the road 20 can be detected in real time in a non-contact manner and by detecting a road shoulder and a median strip, automatization and labor saving of clearing snow and drawing white lines safely; the role of the magnetostrictive resonator detection apparatus of the embodiment for road maintenance is great. If the infrastructure is furthermore constructed, the magnetostrictive resonator detection apparatus is useful for automatic driving support of vehicles. Thus, the road facilities manager can efficiently carry out road maintenance while providing safety. The magnetostrictive resonators 1a, 1b, and 1c buried in the road 20 may be placed only in the proximity of the shoulder of a narrow road or may be added between lanes on a wide road having more than one lane on one side. The detection order of the magnetostrictive resonators (resonance frequency oscillating order) is not limited to that in the embodiment; the magnetostrictive resonators can be detected in various orders, for example, in the order of the median strip magnetostrictive resonator la, the up road shoulder magnetostrictive resonator 1b, the median strip magnetostrictive resonator 1a, and the down road shoulder magnetostrictive resonator 1c. Further, the magnetostrictive resonators may be installed at the center of a lane for automatically driving the vehicle 21 and more than one piece of information may be contained in one magnetostrictive resonator. In the embodiment, one antenna is used for both transmission and reception, but a transmission antenna and a reception antenna may be provided separately or more than one transmission antenna and more than one reception antenna may be installed. As seen from the description made so far, the first magnetostrictive resonator detection apparatus of the invention oscillates a magnetostrictive resonator and can detect the resonance frequency of the magnetostrictive resonator, thereby detecting the presence of the magnetostrictive resonator. In the magnetostrictive resonator detection apparatus of the invention, the reception section detects the resonance frequency oscillated by the magnetostrictive resonator after the transmission section terminates transmission, so that the magnetostrictive resonator detection apparatus can detect the presence of the magnetostrictive resonator reliably. The magnetostrictive resonator detection apparatus, which further includes the switch section, can transmit and receive a signal through one antenna. The magnetostrictive resonator detection apparatus of the invention transmits and receives one of a plurality of different resonance frequencies and then transmits and receives a resonance frequency different from that resonance frequency, whereby the apparatus can reliably detect a plurality of magnetostrictive resonators. Another magnetostrictive resonator detection apparatus activates the discharge resistor at the switching time from transmission to reception, thus can prevent reception interference caused by reverberation of transmission output. The second magnetostrictive resonator detection apparatus of the invention further includes the intermediate frequency conversion section. Thus, if a plurality of different resonance frequencies are received, they can be detected by one detection section. In another magnetostrictive resonator detection apparatus of the invention, the intermediate frequency conversion section adds output of the local oscillation section to the received frequency to produce the intermediate frequency. Thus, an advantage similar to that of the fifth magnetostrictive resonator detection apparatus can be provided by the simple configuration. Another magnetostrictive resonator detection apparatus of the invention, which simply comprises one direct digital synthesizer, can provide an advantage similar to that of the fifth magnetostrictive resonator detection apparatus. Another magnetostrictive resonator detection apparatus of the invention can reliably transmit and receive a plurality of different resonance frequencies by selecting one of the tuning capacitors in conformance with the oscillated resonance frequency. Another magnetostrictive resonator detection apparatus of the invention enables the user to easily see the detection levels of magnetostrictive resonators. The traffic system of the invention comprises a road having magnetostrictive resonators and a vehicle having a magnetostrictive resonator detection apparatus as claimed in any of claims 1 to 10 and thus can provide a system wherein the vehicle is driven safely. In the traffic system of the invention, the magnetostrictive resonators oscillate different resonance frequencies, so that a safe and reliable driving system can be provided. In another traffic system of the invention, the vehicle detects the magnetostrictive resonators and is driven automatically. Thus, a safe and reliable traffic system fitted to a graying society can be provided. In another traffic system of the invention, the magnetostrictive resonators are buried in the road, so that durability of the magnetostrictive resonators is improved. The traffic system of the invention can easily and reliably keep track of the vehicle position on the road.

Claims: A magnetostrictive resonator detection apparatus, comprising: a transmission section (4-9, 14) for transmitting a plurality of different resonance frequencies including the resonance frequency of a magnetostrictive resonator (1), a reception section (7, 10-14) for detecting a resonance frequency oscillated by the magnetostrictive resonator (1), characterized by an intermediate frequency conversion section (11) for converting the resonance frequency of the magnetostrictive resonator (1) received by said reception section (7, 10-14) into an intermediate frequency, and a detection section (13) for detecting output from said intermediate frequency conversion section (11). A magnetostrictive resonator detection apparatus according to claim 1, further comprising a local oscillation section for oscillating a difference frequency between a transmitted frequency and intermediate frequency, wherein said intermediate frequency conversion section (11) adds output of said local oscillation section to the received frequency to produce the intermediate frequency. A magnetostrictive resonator detection apparatus according to claim 2, wherein said local oscillation section is one direct digital synthesizer for oscillating a difference frequency between a transmitted frequency and intermediate frequency and oscillating the transmitted frequency. A magnetostrictive resonator detection apparatus according to any of claims 1 to 3, further comprising tuning compacitors (8) in a one-to-one correspondence with said plurality of different resonance frequencies, one of said tuning capacitors (8) being selected in conformance with the oscillated resonance frequency. A magnetostrictive resonator detection apparatus according to any of claims 1 to 4, wherein one of said plurality of resonance frequency is transmitted and received and then another of said plurality of resonance frequencies, different from said one resonance frequency, is transmitted and received. A magnetostrictive resonator detection apparatus according to any of claims 1 to 5, further comprising a discharge resistor (9), said discharge resistor (9) being activated at the switching time from transmission to reception. A magnetostritive resonator detection apparatus according to any of claims 1 to 6, further comprising a display section (15) for specifying a magnetostrictive resonator (1) and displaying a detection level thereof on a bar graph. A traffic system comprising: a road (20) having a plurality of resonators (1), a vehicle (21) having a resonator detection apparatus (4-14), said resonator detection apparatus (4-14) comprising: a transmission section (4-9, 14) for transmitting a resonance frequency of a resonator (1), and a reception section (7, 9-14) for detecting a resonance frequency of said resonator (1) characterized in that said resonators being magnetostrictive resonators (1) and said resonator detection apparatus being a magnetostrictive resonator detection apparatus (4-14), said transmission section (4-9, 14) transmitting a plurality of different resonance frequencies in correspondence with the resonant frequencies of said plurality of magnetostrictive resonators (1), said reception section (7, 9-14) detecting a resonance frequency oscillated by each of said plurality of magnetostrictive resonators (1), wherein said reception section (7, 9-14) detects the resonance frequency oscillated by said magnetostrictive resonators (1) after said transmission section (4-9, 14) terminates transmission, and said traffic system further comprises an intermediate frequency conversion section (11) for converting the resonance frequency of the magnetostrictive resonator (1) received by said reception section (7, 9-14) into an intermediate frequency, and a detection section (13) for detecting output from said intermediate frequency conversion section (11). A traffic system according to claim 8, wherein the plurality of magenetostrictive resonators (1) consists of a first magnetostrictive resonator (1a) installed between up and down lanes on said road (20), a second magnetostrictive resonator (1b) installed in the proximity of a road shoulder of the up lane, and a third magnetostrictive resonator (1c) installed in the proximity of a road shoulder of the down lane, and the first, second and third magnetostrictive resonators (1a-1c) oscillate different resonance frequencies. A traffic system according to claim 8 or 9, wherein said vehicle (21) detects the magnetostrictive resonators (1) and is driven automatically. A traffic system according to any of claims 8 to 10, wherein the magnetostrictive resonators (1) are buried in said road (20). A traffic system according to any of claims 8 to 11, further comprising a display section (15) for displaying said road (20), said vehicle (21), and a vehicle position on said road (20). A traffic system according to any of claims 8 to 12, further comprising tuning capacitors (8) in a one-to-one correspondence with said plurality of resonance frequencies, one of said tuning capacitors (8) being selected in conformance with the oscillated resonance frequency. A traffic system according to claim 13, wherein one of said plurality of resonance frequencies is transmitted and received and then another of said plurality of resonance frequencies, different from said one resonance frequency, is transmitted and received. A traffic system according to claim 14, wherein said transmission section (4-9, 14) and said reception section (7, 9-14) share a common antenna (7).

Inventors: TANJI YOSHIHIKO, YOSHIOKA TOSHIHIRO, TANJI, YOSHIHIKO, YOSHIOKA, TOSHIHIRO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1998
Main classification: G08G1
IPC codes: G05D1, G08G1, G01S13