JP3363947B2 - Loop coil type vehicle detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a loop coil type vehicle sensor for burying a road surface, and in particular, causes less malfunction even if it is installed adjacent to a snow melting road heater or the like. The present invention relates to a configuration of a loop coil type vehicle sensor. 2. Description of the Related Art A loop coil type vehicle sensor is used for controlling traffic of a vehicle and managing vehicles entering and exiting a parking lot. FIG. 6 is a diagram showing an example of installation of such a loop coil type vehicle sensor, and FIG. 6 is a block diagram showing an example of a loop coil type vehicle sensor. The illustrated loop coil type vehicle detector includes a loop coil 1 having a predetermined inductance embedded (or laid) on a road surface on which a vehicle CA to be detected travels, and a vehicle detection circuit unit 2A connected to the loop coil 1. It is composed of The vehicle detection circuit section 2A detects a vehicle according to a change in inductance of the loop coil 1 and sends out a vehicle detection output. The vehicle detection circuit section 2A includes a coupling transformer 3, an oscillation circuit 4, and a detection circuit 100, detects the presence of a vehicle, and sends out a vehicle detection output. FIG. 1 also shows a snow melting road heater 20. Reference numeral 21 denotes a heater buried in proximity to the loop coil 1 and the like. Reference numeral 22 denotes a heater power supply for supplying electric power to the heater 21.
1 forms a closed circuit and exerts an electromagnetic induction action on the loop coil 1. As is well known, in the above circuit, the inductance of the loop coil 1 functions as a circuit element for determining the oscillation frequency (ft) of the oscillation circuit 4. Therefore, when the vehicle passes over the loop coil 1, the inductance changes, and the oscillation frequency (ft) changes correspondingly. This change is monitored by the detection circuit 100 to detect the vehicle. In this type of loop coil type vehicle sensor, the inductance of the loop coil changes slowly (drift) according to changes in the surrounding environment such as temperature.
Usually, a follow-up operation for automatically correcting the reference inductance (reference inductance: Lr) while constantly monitoring the inductance is performed. This tracking is set to follow relatively slowly. Note that if the vehicle continues to stop on the loop for a long time due to this function, the sensing output will eventually be cut off. FIG. 9 shows a case including a vehicle passing as an example.
FIG. 6A is a time chart showing a change in the reference inductance Lr reflecting the output frequency (ft: corresponding to the current value Lt of the inductance) and the correction result of the oscillation circuit 4 and FIG. is there. FIG. 8 is an example of a flow chart showing a conventional operation process of the above-mentioned circuit, and will be briefly described below. First, the current inductance value Lt is read and the reference value Lr is read.
And the timer value T is set to "0" (S0). Next, the current inductance value Lt
(Hereinafter, also referred to as a current value) is read (S1), and it is verified whether a difference from a reference value Lr (a value equal to a previous inductance value) does not exceed a predetermined set value L1 (S2). If the difference exceeds the set value L1 (threshold value), the sensing output is set to be in the sending state as the vehicle is present (S11), and then the reference value Lr is slowly reduced (percentage of the constant value ΔL for each cycle T2). ) Follow the direction of the current value Lt (S12, S13, S14). After that, the timer value T
Is reset (S7) and the process returns to the step (S1). On the other hand, when the difference between the current value Lt and the reference value Lr does not exceed the set value L1 (threshold value), it corresponds to the absence of the vehicle, and in this case, the sensing output is stopped (S1).
1) Subsequently, the current value Lt is substituted for the cycle T1 reference value Lr (S4, S5, S6). In other words, in this case, the reference value Lr is caused to slowly follow the current value Lt at the ratio of “difference between the reference value Lr and the current value Lt for each cycle T1”. Thereafter, the timer value T is reset (S7) and the process returns to the step (S1). As described above, the exemplary circuit sets the vehicle detection output only when there is a difference between the internal reference inductance and the inductance of the loop coil equal to or more than a predetermined threshold value (sensitivity set value), and provides two relatively slow speeds. The reference inductance value held inside is made to slowly follow the current inductance value of the loop coil. As described above, the loop coil 1 which is the sensor of the loop coil type vehicle sensor is used by being embedded in the road surface and connected to the vehicle detection circuit 2A installed at an appropriate position and used by the vehicle CA. (See the top view of FIG. 7). By the way, depending on the area, the road heater device 20 for melting snow is used for melting snow accumulated on the road surface as part of road surface management or for preventing snow accumulation on the road surface.
In this case, the heat generating portion (snow melting road load heater, hereinafter simply referred to as a road heater) 21 is buried in the road surface like the loop coil. Therefore, the loop coil 1 and the load heater 21 are often provided close to each other (FIG. 7). This snow melting road heater (heating wire) 21 is shown in FIG.
Are often laid in a loop as schematically shown in FIG. In addition, a large current is supplied from the heater power supply 22 for the operation. When the loop coil 1 and the road heater for snow melting (hereinafter simply referred to as a heater) are buried close to each other as shown in FIG. A loop-shaped current path is formed. Therefore, during the operation of the heater, an electromagnetic induction action occurs between the loop coil 1 and the heater 21, and the inductance of the loop coil 1 decreases. FIG. 10 shows heater power ON / OF
The state of the inductance change when F is performed is shown. This phenomenon is similar to the phenomenon that occurs when passing a vehicle. FIG. 11 shows an inductance obtained by the loop coil type vehicle sensor shown in FIG. 6 described above corresponding to FIG. 10 (when the road heater is in operation). 6 is a time chart showing a current value Lt and a reference inductance value Lr reflecting a correction result together with a vehicle detection output. At this time, a vehicle detection output (false alarm) is obtained corresponding to the operation of the load heater. As described above, in the conventional loop coil type vehicle sensor, there is a problem that a false alarm is generated due to, for example, a road heater for melting snow. In addition, the same false alarm occurs when high-level external noise enters the measurement system of the apparatus. Needless to say, false alarms are obstacles to the measurement of the number of vehicles, the measurement of travel time, and the like, and high-reliability traffic control cannot be expected. The present invention is
The present invention has been made in view of the above circumstances, and proposes a loop coil type vehicle sensor for burying a road surface that can reliably detect a vehicle without malfunction even when installed adjacent to a snow melting road heater. The purpose is to: It should be noted that the apparatus of the present invention suppresses external noise even when it is mixed and does not malfunction. According to the present invention, there is provided a loop coil, an oscillation circuit connected to the loop coil and oscillating at a frequency corresponding to the inductance of the loop coil. A loop coil type vehicle sensor including a detection circuit subsequent to an oscillation circuit, wherein the detection circuit causes a change of an output frequency of the oscillation circuit between a first set value and a second set value within a predetermined time. The vehicle detection output is sent only when there is. As can be seen from a comparison between FIG. 9 and FIG. 10, the change in inductance due to the ON / OFF of the heater has a sharp rise (a larger change rate) than when the vehicle enters or leaves. According to the present invention, the detection circuit determines that the output of the inductance calculation circuit has a variation greater than or equal to the first set value and less than or equal to the second set value within a predetermined period of time. And only the vehicle is reliably detected. Hereinafter, the present invention will be described in detail with reference to examples. FIG. 1 shows a loop coil type vehicle detector according to an embodiment of the present invention, which has the same configuration as that of FIG. 6 described above, and has a predetermined structure embedded (or laid) on a road surface on which a vehicle to be detected travels. It comprises a loop coil 1 having an inductance, and a vehicle detection circuit section 2A connected to the loop coil 1. The vehicle detection circuit section 2A of the embodiment also includes a coupling transformer 3, an oscillation circuit 4, and an inductance calculation circuit 5, as in the above-described example. The detection circuit 100 is connected to the inductance calculation circuit 5. In the embodiment, as will be described later, the detection circuit 100 performs correction such as elimination of the influence of the snow melting road heater and elimination of the influence of extraneous noise irrespective of the presence of the vehicle in addition to the drift correction of the coil inductance. The vehicle detection output is sent only when there is a change equal to or more than the first set value and equal to or less than the second set value within a predetermined time,
It detects the presence of a true vehicle and sends out a detection output. The following action of the present invention follows slowly in response to a smooth inductance change, but responds to a sudden inductance change such as a sharp rise or a sharp fall due to ON / OFF of a snow melting road heater. Corrects inductance so that it follows quickly, and malfunctions (erroneous sensing) due to heater ON / OFF etc.
It is to try to prevent. In addition to the function of the road heater for melting snow, it functions effectively also for external noise having a sharp waveform to prevent malfunction. FIG. 2 is a diagram showing, as an example, the change in inductance of the loop coil when the operation of the road heater and the passage of the vehicle are included, and FIG. 3 shows the current values Lt and Lt of the inductance in the circuit of the embodiment corresponding to FIG. Detection circuit 100
Inductance value Vr reflecting the result of the correction process at
Is a time chart showing the vehicle detection output together with the vehicle detection output. FIGS. 5A and 5B are enlarged views of a portion M and a portion N in FIG. 3, respectively. In the circuit of the embodiment, the detection circuit 100 including the CPU 6 corrects the drift of the inductance of the loop coil 1 to increase the detection accuracy, and the processing does not detect the vehicle change for a more rapid change in the inductance than set. It is carried out. FIG. 1 shows an example of a flowchart showing the operation process of the circuit of the embodiment. Hereinafter, the operation process of the circuit will be described. First, the current inductance value Lt is held as the read reference value Lr, and the timer value T is set to "0" (S0). Next, the current inductance value Lt (hereinafter also referred to as the current value) is read (S
1) It is verified whether a difference from a reference value Lr (a value equal to the previous inductance value) is equal to or less than a predetermined first set value L1 (S2). The difference between the current value Lt and the reference value Lr is the set value L
If it does not exceed 1 (threshold value), it corresponds to the absence of the vehicle. In this case, the sensing output is stopped (S11).
Subsequently, after the elapse of the cycle T1, the current value Lt is substituted for the reference value Lr (S4, S5, S6). In other words, in this case, the reference value Lr is caused to slowly follow the current value Lt at the ratio of “difference between the reference value Lr and the current value Lt for each cycle T1”. Thereafter, the timer value T is reset (S7) and the process returns to the step (S1). The above process is the same as the conventional process. However, if the difference exceeds the first set value L1 (threshold value) in the above step (S2), the difference between the current value Lt and the reference value Lr is further increased by a predetermined second set value L2.
Is verified (S10). If it exceeds (YES), it is not regarded as a vehicle and the reference value Lr
Is substituted for the current value Lt (S6). In other words, in this case, the reference value Lr immediately follows the current value Lt. Thereafter, the timer value T is reset (S7) and the process returns to the step (S1). Through this series of processes, a steep rising (falling) event other than the vehicle is not sensed by the vehicle but is suppressed. First, the vehicle detection is performed by the above-described process (S
In 2), it is verified whether the difference exceeds the first set value L1 (threshold value) and whether the difference between the current value Lt and the reference value Lr exceeds a predetermined second set value L2 (S10). Only when the condition is not exceeded ("NO"), and only when each condition is satisfied, the sensing output is set to the sending state as the presence of the vehicle (S11). Subsequently, the reference value L
r slowly (the ratio of the constant value ΔL for each cycle T2) in the direction of the current value Lt (S12, S13, S1)
4). Thereafter, the timer value T is reset (S7) and the process returns to the step (S1). As described above, in the loop coil type vehicle sensor according to the embodiment, when the detection circuit has a variation between the first set value and the second set value within a predetermined time in the output of the inductance calculation circuit, Only the vehicle sensing output will be transmitted. As described above in detail, according to the present invention, a loop coil type vehicle sensor is provided with a loop coil, an oscillation circuit connected to the loop coil, and a detection circuit following the oscillation circuit. Since the detection circuit is configured to transmit the vehicle detection output only when the output frequency of the oscillation circuit fluctuates within a predetermined time by a first set value or more and a second set value or less, An effect is obtained that a highly reliable loop coil type vehicle sensor that does not generate a false alarm even when the snow melting road heater is operated or when a high level of external noise enters the measurement system of the apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flowchart showing the operation of the loop coil type vehicle sensor of the present invention. FIG. 2 is an explanatory diagram showing an example of a change in inductance of a loop coil according to the present invention. FIG. 3 is a time chart showing a voltage, a holding value, and the like of each part corresponding to FIG. 3 of the loop coil type vehicle sensor of the present invention. FIG. 4 is an explanatory diagram showing an enlarged main part of the time chart of FIG. 3; FIG. 5 is a block diagram showing an embodiment of a loop coil type vehicle sensor according to the present invention, together with a snow melting road heater. FIG. 6 is a diagram showing an installation example of a loop coil type vehicle sensor according to the present invention. FIG. 7 is a top view showing an installation example of a loop coil type vehicle sensor and a snow melting road heater according to the present invention. FIG. 8 is a flowchart showing the operation of a conventional loop coil type vehicle sensor. FIG. 9 shows the voltage and voltage of each part of a conventional loop coil type vehicle sensor.
It is a time chart which shows a holding value and the like. FIG. 10 is a diagram illustrating an example of a change in inductance when the snow melting road heater of the loop coil according to the present invention is operated. FIG. 11 is a time chart showing voltages, holding values, and the like of respective parts corresponding to the operation of the conventional snow melting road heater of the loop coil type vehicle sensor. [Description of Signs] 1 ... Loop coil 2A ... Vehicle detection circuit section 4 ... Oscillation circuit 100 ... Detection circuit

Claims (1)

(57) [Claims] [Claim 1] A loop coil (1) and the loop coil
An oscillation circuit (4) connected to (1) and oscillating at a frequency corresponding to the inductance of the loop coil (1), and a detection circuit (100) following the oscillation circuit (4) In the vehicle sensor, the detection circuit (100) sends a vehicle detection output only when the output frequency of the oscillation circuit (4) fluctuates between a first set value and a second set value within a predetermined time. A loop coil type vehicle detector characterized by: