JPH11337657A - Loop-coil type metal-detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly and accurately perform detection by detecting the initial frequency of an oscillation circuit for dividing the frequency with a specific division ratio, and by detecting the presence or absence of a metal object, according to change in a pulse signal being counted based on a frequency-divided signal. SOLUTION: A loop coil 1 is embedded under the surface of the road of a crossing, the entrance of a parking, or the like for laying. It is so constituted that oscillation can be made by inductance due to the coil 1 and a capacitor provided in an oscillation circuit 2. A division ratio is set at a logic part according to the initial count of an initial frequency counter 4d for measuring the output of a filter circuit 3. Since the presence or absence of a metal object is detected by counting a pulse signal within measurement time based on the division ratio of a oscillation frequency, without detecting the presence or absence of the metal object according to the increase and decrease of the oscillation frequency of the oscillation circuit 2, the metal object can be detected quickly and accurately, even if the oscillation frequency fluctuates. Consequently, this device can be suitably provided as a device for quickly and accurately detecting a vehicle on a crossing road.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a loop coil type metal detector for detecting the presence or absence of a metal object such as an automobile using a loop coil laid on a road surface or the like.

[0002]

2. Description of the Related Art Conventionally, this kind of loop coil type metal detector has an oscillation circuit composed of, for example, a loop coil embedded on a road surface of a level crossing and a capacitor connected to the loop coil. The oscillation frequency of this oscillation circuit is determined by the inductance of the loop coil and the constant (capacity) of the capacitor, and is determined, for example, in the range of 15 to 70 KHz.

When a metal object of an automobile (vehicle) approaches the loop coil, the inductance of the loop coil changes, and the oscillation frequency changes according to the change. Therefore, the presence or absence of the vehicle on the loop coil can be detected from the change in the oscillation frequency.

The change in the oscillation frequency is detected by counting the frequency in a predetermined measurement time set by a logic unit formed mainly by a CPU that controls the loop coil type metal object detecting device. Like that.

[0005]

However, since the conventional loop coil type metal object detecting device described above counts the frequency in the measuring time set by the logic section, the measuring time is required to detect the metal object with high accuracy. Has to be set long, and there is a disadvantage that it takes a long time to detect a metal object.

In addition, since the above-mentioned logic unit controls not only the operation of setting the measurement time but also the loop coil type metal detecting device, it performs other operations in parallel. In addition, there is a possibility that unevenness may occur in the setting of the measurement time.

Further, the constant of the capacitor included in the oscillation circuit changes due to aging or ambient temperature change.
Since the oscillation frequency changes, there is a disadvantage that the detection accuracy is reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks, and has as its object to provide a loop coil type metal object detector capable of detecting a metal object in a short time and with high accuracy. It is to provide a device.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above object, a loop coil type metal object detecting device according to the present invention sets the initial frequency of an oscillation circuit having a loop coil installed at a place where a metal object is detected. Initial frequency detecting means for detecting, pulse signal generating means for generating a pulse signal at a predetermined constant interval, frequency dividing means for dividing the detected initial frequency by a predetermined frequency dividing ratio, Counting time setting means for setting a counting time for counting a pulse signal generated based on the pulse signal; counting means for counting a pulse signal in the set counting time; and presence or absence of a metal object based on a change in the counted pulse signal. And detecting means for detecting the

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating a schematic configuration of a loop coil type metal object detection device according to one embodiment.

The loop coil 1 is buried and laid on, for example, a road surface of a level crossing or a road surface at the entrance of a parking lot. The oscillation is achieved by the inductance of the loop coil 1 and a capacitor (not shown) provided in the oscillation circuit 2. Usually, the number of turns of the loop coil 1 and the constant of the capacitor are determined so that the oscillation frequency is in the range of 15 KHz to 70 KHz.

The oscillation frequency output from the oscillation circuit 2 is
It is configured to be input to the detection unit 4 via a filter circuit 3 including a band-pass filter.

The detecting section 4 includes four counter circuits. That is, it includes a frequency dividing counter 4a, a first pulse counter 4b, a second pulse counter 4c, and an initial frequency counter 4d.

The frequency dividing counter 4a is configured to divide the signal input from the filter circuit 3, that is, the oscillation frequency at a predetermined frequency dividing ratio set by a logic unit (not shown).

The above-mentioned division ratio is an initial count (frequency) of an initial frequency counter 4d for measuring (counting) the output (initial frequency) of the filter circuit 3 (this is referred to as "initial frequency" in the present invention). ) Is set by a not-shown logic unit.

The logic section is composed of an arithmetic circuit formed mainly of a CPU, and is configured so as to be able to control the present loop coil type metal detector in a comprehensive manner.

The first pulse counter 4b receives a predetermined oscillation frequency (10 MHz in the illustrated example) from a crystal oscillator (not shown).
z) is configured to be input. The second pulse counter 4c is configured to count the pulse signal output from the first pulse counter 4b based on the gate signal from the frequency dividing counter 4a and output the counted pulse signal to the logic unit.

The detection control operation of the loop-type metal detection device having the above configuration will be described with reference to the time chart of FIG.

FIG. 2A shows the state of the oscillating frequency output from the filter circuit 3 to the frequency dividing counter 4a. FIG. 2B shows a one-shot output state, which is a signal output from the frequency dividing counter 4a obtained when the oscillation frequency is divided by a predetermined frequency dividing ratio. Here, the one-shot interval is 100
Shown as ms.

With a slight delay from this one-shot signal (at a maximum of 67 μs in the example shown), as shown in FIG. 2C, a gate for dividing the interval between the one-shot signals from the frequency dividing counter 4a into two. The signal is the first pulse counter 4b
And the second pulse counter 4c.

FIG. 2D shows a pulse signal based on an oscillation signal of a crystal oscillator (not shown) input to the first pulse counter 4b. Of these pulse signals, FIG.
The pulse signal in the range indicated by “count” in (d) indicates the count number of the pulse signal without a measurement time obtained by dividing the interval of the one-shot signal from the frequency dividing counter 4a into two. . The count value of the pulse signal during the measurement time is configured to be output to a logic unit (not shown).

If the measured pulse signal count value has increased from the previous count value, the logic unit determines that there is a metal object (vehicle) on the loop coil 1 and the increased count value decreases. For example, it is determined that the metal object has moved from above the loop coil 1 (there is no metal object).

The above-described loop coil type metal detecting device does not detect the presence or absence of a metal object based on the increase or decrease of the oscillation frequency of the oscillation circuit 2 but instead detects a pulse signal within a measurement time based on the frequency division ratio of the oscillation frequency. Since the presence / absence of a metal object is detected by counting, even if the oscillation frequency fluctuates, the metal object can be accurately detected in a short time. Therefore, it can be suitably used for vehicle detection on a railroad crossing that requires high accuracy in a short time.

[0024]

According to the present invention, there is provided a loop coil type metal detecting device comprising: an initial frequency detecting means for detecting an initial frequency of an oscillation circuit having a loop coil laid at a place for detecting a metal object; Pulse signal generating means for generating a pulse signal, frequency dividing means for dividing the detected initial frequency by a predetermined frequency dividing ratio, and counting time for counting the pulse signal generated based on the divided frequency. Counting time setting means for setting, pulse signal counting means for counting pulse signals in the set counting time, and detecting means for detecting the presence or absence of a metal object from a change in the counted pulse signal, so that in a short time A metal object can be detected with high accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a loop coil type metal detecting device according to an embodiment of the present invention.

FIG. 2 is a time chart.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Loop coil 2 Oscillation circuit 3 Filter circuit 4 Detector 4a Frequency dividing counter 4b First pulse counter 4c Second pulse counter 4d Initial frequency counter

Claims (1)

[Claims] 1. An initial frequency detecting means for detecting an initial frequency of an oscillation circuit having a loop coil laid at a place for detecting a metal object, a pulse signal generating means for generating a pulse signal at predetermined constant intervals, Frequency dividing means for dividing the divided initial frequency by a predetermined frequency dividing ratio; counting time setting means for setting a counting time for counting a pulse signal generated based on the divided frequency; A loop coil type metal detecting device, comprising: pulse signal counting means for counting a pulse signal with time; and detecting means for detecting the presence or absence of a metal object from a change in the counted pulse signal.