JP4173456B2 - Metal object detection device - Google Patents

Description

  The present invention relates to a metal object detection device, and can be applied to, for example, a vehicle detection device.

  For example, in an unmanned parking system, a vehicle detection device detects whether or not a vehicle is present in a parking area, and when the vehicle detection device detects the presence of a vehicle, a baffle plate (between a front wheel and a rear wheel ( Stand up and lock the flap plate) to prevent unauthorized leaving or start counting the parking time.

  The vehicle detection device embeds a loop coil (for example, a 1 m × 1.5 m rectangle: the vertical direction is the longitudinal direction of the vehicle) in the parking area, and the inductance when the loop coil is energized is the vehicle (metal object). It is detected whether there is a vehicle in the parking area by using the difference depending on whether or not the vehicle exists. In the conventional vehicle detection device, a minute signal in the loop coil is detected by an analog circuit such as a tuning circuit, an amplifier circuit, and a filter circuit.

  However, in the conventional vehicle detection device, since a minute signal in the loop coil is detected by an analog circuit, the detection accuracy is low.

  For example, even if a vehicle exists in a parking area, the vehicle may be a mini vehicle or a vehicle exceeding 3000 cc, and the vehicle height may vary. For this reason, the detection criterion is somewhat relaxed in order to detect the presence of the vehicle regardless of the type of vehicle. Under such circumstances, if there are environmental fluctuations (characteristic changes due to temperature, etc.) that are unique to analog circuits, or if they are affected by external noise, the detection of the presence or absence of the vehicle may be erroneously detected, and the detection accuracy is It was low. Even if an attempt is made to suppress such erroneous detection by adjustment at the time of installation of the vehicle detection device, the adjustment work is complicated, and all the erroneous detections cannot be prevented.

  Further, in the conventional vehicle detection device, if there is a metal object other than the vehicle in the vicinity of the loop coil, it may be impossible to detect, so that the installation position of the loop coil is limited, or the vehicle detection device itself is There were also cases where it was not applicable.

  For example, if the baffle plate and its in / out mechanism are above the loop coil surface, there is a possibility of erroneous detection. Conventionally, the loop coil has been installed at a position avoiding the baffle plate and its in / out mechanism. However, if the positional deviation of the loop coil from the baffle plate and its retracting mechanism is increased, the possibility that the vehicle itself is not stopped above the loop coil is increased. Also, in cold regions, heater wires for thawing snow and ice may be embedded in the road surface of the parking area, but the loop coil as described above was used for such a parking area. The vehicle detection device itself cannot be applied.

  Furthermore, the loop coil detects a change in inductance due to the approach of a vehicle (metal object). However, since the structure is a coil, a current flows around the coil or an electromagnetic wave having a resonance frequency is received. Then, an electromotive force is generated, and the electromotive force has an influence on the measured value, which sometimes hinders measurement of a pure inductance change.

  The problems as described above are caused not only in vehicles but also in devices that detect other metal objects using a loop coil.

  Therefore, there is a demand for a metal object detection device that can detect the presence of a metal object with high accuracy and can increase the degree of freedom of the installation position of the loop coil.

In order to solve such a problem, the metal object detection device of the present invention includes a loop coil, a pulse applying unit that applies a pulse voltage to the loop coil, and a pulse voltage applied to the loop coil from the time when the pulse voltage is applied to the loop coil. measuring means voltage between terminals obtain time data until crosses the threshold, based on the sequence of the time data, have a recognizing decision means a metal object present in the vicinity of the loop coil, the pulse application The means switches the application direction of the pulse voltage to the loop coil for each application, and the determination means is based on a series of updated time data obtained by adding a predetermined number of time data consisting of consecutive even numbers. , Recognizing the presence of a metal object in the vicinity of the loop coil .

  The inductance of a loop coil changes depending on the proximity of a metal object. Here, when a pulse voltage is applied to the loop coil, the terminal voltage of the loop coil changes with a response curve corresponding to the inductance at that time, crossing the threshold value. The time depends on the inductance at that time. That is, the metal object can be detected based on the time data series.

  According to the metal object detection device of the present invention, the change in the voltage between the terminals of the loop coil when the pulse voltage is applied to the loop coil is measured as time data, and based on this, the metal object is detected. A digital circuit can be applied to the part, and the detection accuracy can be improved. Since detection accuracy can be improved, the freedom degree of the installation position of a loop coil can also be raised.

(A) First Embodiment Hereinafter, a first embodiment in which a metal object detection device according to the present invention is applied to a vehicle detection device will be described in detail with reference to the drawings.

  FIG. 1 is an explanatory view showing an outline of the arrangement positions of the components of the parking system to which the vehicle detection device of the first embodiment is applied, and the elements embedded in the ground are drawn as they are.

  In FIG. 1, one parking area 1 is defined by a marking line made of a white line or the like, and a pair of tire stops 2 and 2 are provided on the back side of the parking area 1. An area processing unit 4 is provided outside one of the left and right central portions of the parking area 1. The area processing unit 4 has, for example, a flat unit portion for standing, locking, and tilting a baffle plate (flap plate) 5 in the lower portion, and an adjustment unit portion for taking in a parking fee or the like in the upper portion. Have. As described above, one end portion of the baffle plate 5 is accommodated in the area processing unit 4 (flat unit portion), and the other end portion of the baffle plate 5 is accommodated in the baffle plate receiving portion 6. It is designed to rotate as a center of movement and stand up or fall.

  In addition, a loop coil 3 wound in a rectangular shape of 1 m × 1.5 m in length and width, for example, is embedded in the ground in the center of the portion of the parking area 1 ahead of the pair of tire stops 2 and 2. Yes. The loop coil 3 is embedded, for example, by being sandwiched between a lower cement layer and an upper cement layer. The end of the loop coil 3 enters the area processing unit 4. A detection processing unit (see reference numeral 10 in FIG. 2) based on a minute signal of the loop coil 3 is provided inside the area processing unit 4 or connected via a pipe 7 through a signal line or a power cable. It is provided in a monitoring center device or the like.

  FIG. 2 is a block diagram showing a detailed configuration of the detection processing unit 10 that constitutes the vehicle detection device together with the loop coil 3.

  In FIG. 2, the detection processing unit 10 includes a crystal oscillator 11, a frequency dividing circuit 12, a pulse output circuit 13, a coil drive circuit 14, a comparator circuit 15, a latch circuit 16, an interrupt generation circuit 17, a series resistor 18, and a microcontroller 19. have. Reference numeral 13 a represents a transistor (for example, FET) at the output stage of the pulse output circuit 13. The microcontroller 19 may be provided at a position away from other components.

  In the case of the first embodiment, as a practical structure, other components excluding the crystal oscillator 11, the coil drive circuit 14, the comparator circuit 15 and the microcontroller 19 are incorporated on one programmable logic array. Can be realized.

  The crystal oscillator 11 oscillates a 50 MHz pulse with high stability, for example. For example, a 16-bit synchronous counter circuit is used as the frequency dividing circuit 12, and the frequency dividing circuit 12 divides the output pulse from the crystal oscillator 11 and outputs a pulse having a cycle of about 1.3 ms to the pulse output circuit 13. To supply. The pulse supplied to the pulse output circuit 13 is switched by the transistor 13a of the pulse output circuit 13, is input to the coil drive circuit 14 through the series resistor 18, and is supplied to the loop coil 3 (see FIG. 1) as a pulse voltage. Applied.

  Here, when the change in the voltage between the terminals of the loop coil 3 is measured, when the voltage is applied to the loop coil 3, the current of the loop coil 3 does not immediately flow due to the action of the inductance of the loop coil 3, and as a result As a result, the applied voltage is observed as it is, but the current gradually begins to flow, and finally, the resistance 18 inserted in series with the loop coil 3 and the DC resistance value of the loop coil 3 itself (strictly speaking, It also approaches the voltage divided by the on-resistance value of the transistor 13a). At this time, if the direct-current resistance value of the loop coil 3 itself is sufficiently smaller than the resistance value of the resistor 18 inserted in series, the voltage drops to approximately 0V. The process of this voltage change is determined by the inductance of the loop coil 3.

  Therefore, the change in the voltage is compared with a predetermined threshold value using the comparator circuit 15, and the count number of the frequency dividing circuit 12 is latched in the latch circuit 16 by the output of the comparator circuit 15 when the threshold value is crossed, and the interrupt An interrupt signal is output from the generation circuit 17 to the microcontroller 19.

  Here, the latched count number is the time from when a pulse is applied to the loop coil 3 until the voltage between the terminals of the loop coil 3 reaches a predetermined threshold. Since this time is determined by the inductance of the loop coil 3, by reading the change in this value, it is possible to obtain the change in inductance, that is, the change in and out of the vehicle. As the processing of the microcontroller 19 at this time, for example, the processing of the second embodiment described later can be applied.

  According to the vehicle detection device of the first embodiment, the following effects can be obtained.

  The vehicle detection device according to the first embodiment is mostly composed of a digital circuit and does not include an analog amplifier circuit or a tuning circuit. It is possible to obtain a stable operation that is not easily affected by fluctuations due to environmental changes such as temperature (hereinafter referred to as drift).

  Further, since most of the parts are constituted by digital circuits, there is no part to be adjusted or few (for example, threshold adjustment of the comparator circuit 15), and a simple circuit configuration can be achieved. As described above, the main part of the detection device can be realized by almost one integrated circuit (programmable logic array) except for a few circuits.

  Note that the divider circuit is used not only for the function of dividing, but also for the function of measuring the time (count number) from when the pulse is applied until the loop coil voltage falls below the threshold (the number of these functions). An embodiment in which the realization configuration is constructed with a separate circuit is also an embodiment of the present invention). From this point, it can be said that the apparatus is realized with a simple circuit configuration.

(B) Second Embodiment Next, a second embodiment in which the metal object detection device according to the present invention is applied to a vehicle detection device will be described in detail with reference to the drawings.

  Also in the vehicle detection device of the second embodiment, the loop coil 3 is installed, for example, as shown in FIG. 1 according to the first embodiment.

  FIG. 3 is a block diagram showing a detailed configuration of the detection processing unit 10B that constitutes the vehicle detection device of the second embodiment together with the loop coil 3, and is related to FIG. 2 described above according to the first embodiment. The same and corresponding parts are indicated by the same and corresponding reference numerals.

  In the case of the detection processing unit 10B of the second embodiment, a bridge coil drive circuit 14B that can switch the application direction to the loop coil 3 is applied as a coil drive circuit that applies a pulse voltage to the loop coil 3. In addition, a bridge control signal generation circuit 20 that instructs the application direction to the loop coil 3 is provided for the bridge coil drive circuit 14B.

  The bridge control signal generation circuit 20 is incorporated in one integrated circuit (programmable logic array) together with the frequency divider circuit 12, the pulse output circuit 13, the latch circuit 16, the interrupt generation circuit 17, and the series resistor 18. Preferably it is.

  Also in the second embodiment, one basic measurement operation in which the latch circuit 16 latches data and the interrupt generation circuit 17 outputs an interrupt signal to the microcontroller 19 is the same as in the first embodiment. It is.

  However, in the case of the second embodiment, the application direction of the pulse voltage to the loop coil 3 is switched for each measurement operation.

  The value of the last stage (most significant) of the counter provided as the frequency dividing circuit 12 is given to the bridge control signal generating circuit 20. The bridge control signal generation circuit 20 is made up of, for example, one T-type flip-flop circuit, and inverts the logic polarity when the value of the final stage (highest level) of the frequency dividing circuit 12 changes by counting up. The bridge control signal is output to the bridge coil drive circuit 14B.

  The bridge coil drive circuit 14B has a transistor bridge (FET bridge) for driving by switching the polarity of the terminal of the loop coil 3, controls the gate of each transistor by a bridge control signal, and connects the terminal of the loop coil 3 Invert.

  The reason why the terminal connection of the loop coil 3 is reversed is as follows. When the loop coil 3 is embedded in the ground, an electromotive force is generated in the loop coil 3 when a current flows around the loop coil 3 due to a complicated change in the potential difference in the ground. Similarly, an electromotive force is generated when receiving an electromagnetic wave having a frequency at which the loop coil 3 resonates. These electromotive forces are an obstacle when trying to capture only changes in inductance. This electromotive force is generated, and the direction (polarity) of the current is reversed if the terminal connection of the loop coil is reversed. As described above, each time a measured value is obtained, the polarity of the terminal of the loop coil is switched and measured, and the measured values are combined (for example, added), these electromotive forces can be canceled.

  The microcontroller 19 adds, for example, two measurement values (latch data) obtained by four measurement operations, that is, two each of data at the time of positive connection to the loop coil 3 and data at the time of reverse connection. One measurement value is assumed.

  The microcontroller 19 performs a pre-processing of the following algorithm on the measurement value series in which the unnecessary electromotive force generated in the loop coil 3 is canceled, and reflects only the signal change related to the presence or absence of the vehicle. Convert to

The first stage performs shallow digital filtering to remove extremely high frequency components. Now, assuming that the n-th data in the continuously measured data (measurement value) column is D _n , the n-th calculation result is X _n , and the filter coefficient is k, the first-stage filter processing is (1 ) Expression.

_{X n = {X n-1} × (k-1) + D n} / k ... (1)
In the second stage, differentiation is performed on the result Xn obtained in this way. For example, pseudo differentiation as shown in the equation (2) is performed. The obtained value Y _n represents the degree of change in the measurement data, and this value increases when affected by external noise.

_{Y n = | X n -X n} -1 | ... (2)
In the third stage, a measured value that is considered to be affected by external noise is replaced with a predicted value of the original value. For most external noises, the value Y _n obtained in the second stage is extremely large compared to the change in the vehicle presence / absence signal. A measurement value in which the value Y _n is larger than a certain set value is determined to be external noise, and the n-th measurement value D _n is replaced with X _n−1 .

In the fourth stage, the filtering process is performed again based on the measurement data appropriately replaced with the predicted value by the determination of the external noise. When the n-th data in the data (measurement value) column appropriately replaced with the predicted value is D _n , the n-th calculation result is Z _n , and the filter coefficient is p, the fourth-stage filtering process is (3) It can be expressed by a formula. Here, the value of p is set larger than the value of k used in the first stage. For example, a value in the range of 5 to 25 (for example, 10) is applied as k, and a value in the range of 20 to 80 (for example, 50) is applied as p.

_{Z n = {Z n-1} × (p-1) + D n} / p ... (3)
FIGS. 5 to 8 show the process of removing the external noise almost completely by the pre-processing of this algorithm (k = 10, p = 50) with examples of actual measurement results, and there is no vehicle. This is an example. FIG. 5 shows the original measurement data including extraneous noise, FIG. 6 shows the data after the first stage filtering, FIG. 7 shows the data after the second stage differentiation, and FIG. The data after pre-processing is shown.

  Further, FIG. 9 shows the original measurement data in the process of actually parking the vehicle, and FIG. 10 shows the data after performing the above-described preprocessing on the data of FIG.

  From the two examples shown in FIGS. 5 to 10, it can be confirmed that the external noise is almost completely removed, but the change in the presence or absence of the vehicle can be measured with almost no influence of the preprocessing.

  The microcontroller 19 calculates the change amount versus the elapsed time (the amount changed at a certain time) using the value after the preprocessing. The amount of change vs. elapsed time is known to be extremely small compared to changes in the presence or absence of vehicles in the case of drift due to environmental changes such as temperature. Judge. Further, when it is determined that there is a drift, the determination criterion is followed. Note that this drift determination method is the same as the existing determination method used in various circuit devices using active elements.

  Also according to the second embodiment, the effect obtained by obtaining the measurement value correlated with the inductance of the loop coil by using the response time with respect to the pulse voltage application is the same as that of the first embodiment. According to the second embodiment, the following effects can be further achieved.

  According to the second embodiment, even if an electromotive force is generated when an electric current flows around the loop coil 3 or an electromagnetic wave having a resonating frequency is generated, the pulse voltage is applied to the loop coil 3 with a polarity. Are alternately switched and connected, and the measured signals are added and processed, so that a measurement result that cancels the influence of the electromotive force can be obtained.

  In addition, according to the second embodiment, the influence of external noise, which is a sudden signal change, can be eliminated from the measurement value series by the above-described four-stage processing. Furthermore, since the fluctuation (drift) due to environmental changes such as temperature changes very slowly is also determined based on the amount of change vs. elapsed time (amount changed in a certain amount of time). The presence / absence judgment accuracy can be increased.

  Furthermore, according to the second embodiment, since the determination with high accuracy is possible as described above, for example, even if the baffle plate 5 or the like is located above the loop coil 3 as shown in FIG. The presence or absence of can be detected. In other words, the degree of freedom such as the installation position of the loop coil 3 can be increased as compared with the related art.

  Furthermore, according to the second embodiment, the frequency dividing circuit 12 also provides determination information for switching the application direction of the pulse voltage to the loop coil 3 (regardless of the frequency dividing circuit). A circuit using a counter is another embodiment). In this respect, the circuit configuration can be simplified.

(C) Other Embodiments In the above-described embodiments, the frequency dividing circuit 12 is responsible for a plurality of functions. However, a separate configuration may be used for each function. In addition, although one programmable logic array (integrated circuit) has been realized with a plurality of components, a method for realizing the plurality of components is not limited to this. The part that the microcontroller 19 executes in software may be configured by hardware.

  In the second embodiment, the measurement value obtained by switching the polarity from one loop coil is added to eliminate the influence of unnecessary electromotive force. Loop coils may be provided, the application direction to the loop coils may be reversed, and the measured values from the respective loop coils may be added to eliminate the influence of unnecessary electromotive force.

  In addition, as the arithmetic expression for realizing the four-stage processing for eliminating the external noise described in the second embodiment, other expressions can be applied as long as the function of the stage can be executed. .

  Furthermore, when there is little change in the external environment as applied to a parking system in a building, the countermeasure against drift may be omitted.

  In the above embodiments, the vehicle detection device is applied to a parking system. However, the vehicle detection device may be applied to a system for other purposes. The technique of the present invention may be applied to a metal object detection device other than the vehicle detection device. Furthermore, unlike the embodiment, the loop coil may be provided in the vertical direction, and the shape thereof is not limited to a rectangle.

It is explanatory drawing which shows the schematic arrangement position of each part component of the parking system to which the vehicle detection apparatus of each embodiment was applied. It is a block diagram which shows the detailed structure of the detection process unit of 1st Embodiment which comprises the vehicle detection apparatus with a loop coil. It is a block diagram which shows the detailed structure of the detection process unit of 2nd Embodiment which comprises the vehicle detection apparatus with a loop coil. It is a flowchart which shows the external noise removal process of 2nd Embodiment. It is a graph which shows the primitive measurement data containing an external noise. It is a graph which shows the data after performing the filter process of the 1st step of the external noise removal process of 2nd Embodiment with respect to the data of FIG. It is a graph which shows the data after performing the differentiation process of the 2nd step of the external noise removal process of 2nd Embodiment with respect to the data of FIG. It is a graph which shows the data after all the exogenous noise removal processes of 2nd Embodiment are complete | finished with respect to the data of FIG. It is a graph which shows the primitive measurement data of the process in which a vehicle actually parks. It is a graph which shows the data after all the exogenous noise removal processes of 2nd Embodiment are complete | finished with respect to the data of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 3 ... Loop coil, 11 ... Crystal oscillator, 12 ... Frequency divider circuit, 13 ... Pulse output circuit, 14 ... Coil drive circuit, 14B ... Bridge coil drive circuit, 15 ... Comparator circuit, 16 ... Latch circuit, 17 ... Interrupt generation Circuit, 18 ... Series resistance, 19 ... Microcontroller, 20 ... Bridge control signal generation circuit.

Claims (4)

A loop coil;
Pulse applying means for applying a pulse voltage to the loop coil;
Measuring means for obtaining time data from when a pulse voltage is applied to the loop coil until the voltage between the terminals of the loop coil crosses a threshold;
Based on the sequence of the time data, have a recognizing determining means that there is a metal object to the vicinity of the loop coil,
The pulse applying means switches the application direction of the pulse voltage to the loop coil for each application,
The determination means recognizes that a metal object is present in the vicinity of the loop coil based on a series of updated time data obtained by adding a predetermined number of time data consisting of consecutive even numbers. A metal object detection device. The pulse applying means includes an oscillator and a frequency dividing circuit having a counter configuration that divides a transmission signal from the oscillator to form a cycle of the pulse voltage.
The metal object detection device according to claim 1, wherein the measurement unit causes the time data to be a count value of the frequency dividing circuit when a voltage between terminals of the loop coil crosses a threshold value. The determination means removes the high frequency component from the time data by shallow digital filtering in the first stage, differentiates the data from which the high frequency component is removed in the second stage, and differentiates the result in the third stage. , The time data corresponding to the data whose value is larger than a certain set value is replaced with the predicted value, and in the fourth stage, the time data having a sharp change is replaced with the predicted value. 3. The metal object detection according to claim 1, wherein a digital object is detected to recognize that a metal object exists in the vicinity of the loop coil based on a series of data after the fourth stage process. 4. apparatus. The determination means obtains a data change rate with respect to a data series for recognizing the presence of a metal object in the vicinity of the loop coil, and if the change rate is slower than a predetermined change rate, data based on ambient environment fluctuations. metal object detecting apparatus according to any one of claims 1 to 3, wherein the capturing the variation.

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