JPS59210389A - Earth magnetism type vehicle sensor - Google Patents

Abstract

PURPOSE:To correct automatically the variation in earth magnetism and to detect a vehicle by winding a core with the primary winding connected to an exciting circuit, the secondary winding which is connected to a magnetism variation detecting circuit and generates an induced voltage, and the feedback winding. CONSTITUTION:An exciting current of specific frequency is supplied from the exciting circuit 2 to the primary winding 11 of a detection coil 1 to establish exciting magnetic fields around two cores 10a and 10b in the opposite directions. Voltages having the opposite characteristics are induced at winding parts 12a and 12b of the secondary winding 12. The induced voltage is outputted by the whole secondary winding 12 because of earth magnetism applied to the cores 10a and 10b and a circumferential magnetic field. The induced voltage is detected by the detecting circuit 31 of the magnetism variation detecting circuit 3 and fed back to the feedback winding 13 through an amplifier 32, delay circuit 51, and current limiting circuit 52, so magnetic field variation depending upon the environment is canceled. Thus, the vehicle is detected accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device that detects changes in a magnetic field to detect the passage or presence of a vehicle running or stopping on a road surface, and in particular, the present invention relates to a device that detects changes in a magnetic field to detect the passage or presence of a vehicle running or stopping on a road surface. The present invention relates to a vehicle sensor equipped with means for automatically correcting.

2. Description of the Related Art Conventionally, vehicle sensors used for detecting traffic volume, etc., are generally of an ultrasonic pulse type or an inductance loop type. In the former method, an ultrasonic transmitter and a receiver are attached to an inverted pole placed on the road, and a vehicle is detected based on the difference in the reflection time of ultrasonic waves. However, this system has drawbacks such as the time-consuming installation work, the high power consumption of the ultrasonic transducer, and the possibility of miscalculation due to differences in the shape of the top of the vehicle, snow accumulation, etc. . On the other hand, the main part of the latter is several meters below the road surface.
The system has an insulated wire looped at a depth of 1.5, and detects a vehicle by detecting changes in the loop's inductance caused by the vehicle running. However, since this type of heel requires a groove to be provided on the road surface, it is time-consuming to install the loop, and the insulation of the sill rapping wire may be poor due to vibrations caused by passing vehicles, cracks in the road surface, deformation, etc.) Additionally, there are drawbacks such as wire breakage.

In contrast, due to changes in the magnetic field,! A possible method is to detect seven vehicles. A vehicle sensor according to this method includes a detection coil that detects changes in the magnetic field by winding a primary winding and a secondary winding around a core made of a ferromagnetic material, and an excitation circuit that excites the primary winding. It is configured to include a magnetic change detection circuit that detects changes in the magnetic field based on the induced voltage of the secondary winding, and a vehicle detection circuit that detects a vehicle from the detected changes in the magnetic field. This sensor is buried in the road surface as shown in Figure 1.
The presence of the vehicle is determined by detecting changes in the magnetic field that occur when the vehicle V passes over the heavy equipment M, which is different from the conventional vehicle detectors described above, and is easy to install. It is unaffected by shape, snow accumulation, etc., and is not damaged by vibrations, etc.

However, geomagnetic sensors have a problem in that they are easily affected by the environmental conditions at the location where they are installed. For example, the normal level of geomagnetism differs depending on the magnetic field state of the location, so when installing a sensor, initial adjustments such as zero point adjustment are required, which has the drawback of requiring time and effort.

Furthermore, the geomagnetic field itself fluctuates, and also changes due to changes in the environmental conditions at that point, such as the construction of buildings. That is, as shown in FIG. 4(a), when a vehicle passes, the magnetic field strength H at the point where the heavy equipment M is present changes upward and downward from the normal magnetic field level HB as shown by Hv in the same figure. death,
The part of the magnetic field that exceeds the magnetic field strength corresponding to the detection level is detected by the sensor, but if a building is constructed after heavy equipment is installed, the normal magnetic field level Ha becomes gradual (changes due to vehicle running). ), which is a sufficiently long time compared to Hn
If it exceeds k, it will be judged as the vehicle width, resulting in erroneous measurements. Therefore, this type of sensor has the disadvantage that it is affected by the installation location and that the detection operation becomes inaccurate due to changes in the environment after installation.

The present invention 1 has been made in view of the above-mentioned drawbacks, and by automatically correcting magnetic field fluctuations caused by environmental conditions, it is possible to eliminate the need for adjustment at the time of installation regardless of the installation location. It is an object of the present invention to provide a geomagnetic vehicle@sensor that can easily detect magnetic fields and accurately detect them without erroneous measurements even if there are magnetic field fluctuations due to environmental changes after installation.

In order to achieve such an object, the present invention provides a detection coil that detects changes in a magnetic field by winding a primary winding and a secondary winding around a core, an excitation circuit that excites the primary winding, and the above-mentioned 2. A feedback winding wound around the core, which is equipped with a magnetic change detection circuit that detects a change in the magnetic field based on the induced voltage of the next winding, and a vehicle detection circuit that detects a vehicle from the detected magnetic field change. and a feedback circuit that accumulates the output of the magnetic change detection circuit at a predetermined time constant and applies it to the feedback winding, and is provided with means for correcting magnetic field fluctuations caused by environmental conditions.

Hereinafter, the present invention will be explained based on embodiments shown in the drawings.

FIG. 2 is a block diagram showing an example of the geomagnetic vehicle sensor of the present invention. The sensor of the present invention shown in the figure includes a detection coil 1, an excitation circuit 2 that excites the coil 1, a magnetic change detection circuit 3 that detects changes in the magnetic field by the detection coil 1,
It comprises a vehicle detection circuit 4 that detects a vehicle based on the detected magnetic field change, and a feedback circuit 5 that constitutes a correction means that corrects the magnetic field fluctuation.

As shown in FIG. 3, the detection coil 1 has two cores 10a and 10b made of a ferromagnetic material that has high magnetic permeability and is easily saturated.
It is constructed by winding a primary winding 11, a secondary winding 12, and a feedback winding 13. The primary winding 11 has two cores 10a.
, 10b to generate an excitation magnetic field in the opposite direction.
and llb are wound. The secondary winding 12 has both cores l
Windings 12g and 12b are provided to be wound in the same direction around Qa and 10b so as to cancel the induced voltage caused by the excitation magnetic field.

The feedback winding lm13 constitutes a correction means together with the feedback circuit 5, and is wound in the same direction around both upper sb cocoas 0a and 10b.

The excitation/retraction path 2 includes an oscillator 21 and an amplifier 22, and excites the primary winding 11 to generate an excitation magnetic field. The excitation frequency is, for example, 5 IIG(y).The excitation current is set so that it oscillates in a linear region immediately before the cores 10a and 10b are saturated.

The magnetic change detection circuit 3 includes a detection circuit 31 and an amplifier 32, and detects a change in the magnetic field from the induced voltage generated in the secondary winding 12. - As described above, since the secondary winding 12b and each winding 12a, 12b are wound so as to cancel the induced voltage caused by the excitation magnetic field, the cores 10a, 10. If no external magnetic field is applied to b, the combined output 'yri pressure is O.

On the other hand, when an external magnetic field is applied to the core 10a and Job, a difference is generated in the induced voltage between the windings 12a and 12b, and a voltage is generated across the secondary winding 12. The detection circuit 31 detects the external magnetic field in addition to this voltage. This external magnetic field is the earth's magnetism in the present invention. Since the magnetic flux distribution of this earth's magnetism changes due to the presence of ferromagnetic material, this is used to detect vehicles made of ferromagnetic material.

The vehicle detection circuit 4 includes a bandpass filter 41, a rectifier circuit 42, a detection circuit 43, and an output circuit 44, and detects a vehicle from the magnetic field change detected by the magnetic change detection circuit 3. do.

That is, a bandpass filter 41 removes a high frequency component from the induced voltage (signal voltage) detected by the magnetic change detection circuit 3, a rectifier circuit 42 rectifies the positive and negative induced voltages, and a detection circuit 43 rectifies the induced voltage. , the feedback circuit 5 includes a delay circuit 51 and a current limiting circuit. 52 constitutes a correction means together with the feedback winding 13, and a feedback output is applied to the feedback winding 13, and the cores 10a, 10
A return magnetic field is generated at b. As shown in FIG. 3, the delay circuit 51 includes an integrating circuit 53 connected to the output of the magnetic change detection circuit 3 and accumulating the output at a predetermined time constant, and an amplifier amplifying the output of the integrating circuit 53. 54. Although the feedback signal is delayed due to the accumulation, the purpose of such accumulation is to cancel the change in the induced voltage due to the passage of a vehicle and prevent it from being returned. On the other hand, changes in the magnetic field due to building construction, etc. increase or decrease very slowly, so even if changes in induced voltage due to this change are accumulated, they will not be canceled out. The current limiting circuit 52 controls the output of the delay circuit 51 to convert it into a corresponding excitation current and supply it to the feedback winding 13.

In this embodiment, the integration circuit 53 is used as the delay circuit 51, but other circuits may be used as long as they have a so-called low-pass filter function that blocks magnetic change output from the vehicle and passes a gentle magnetic change output. A circuit may also be used.

Next, the operation of the vehicle sensor of the present invention will be explained.

First, in the vehicle sensor of the present invention, the entire circuit is hermetically housed in a capsule-shaped container, and this is buried in the road surface as shown in FIG. 1 for use on land.

When all the circuits are connected to a power supply (not shown) and started, an excitation current of a predetermined frequency is supplied to the primary winding 11 of the detection coil 10 from the excitation circuit 2, and excitation magnetic fields in opposite directions are applied to the two cores 10a and 10b. It is formed. Voltages of opposite polarity are induced in each core winding portion 12a, 12b of the secondary winding 12. If no external magnetic field is applied to both cores 10a and 10b, both induced voltages will cancel each other out, and the output of the entire secondary winding 12 will be zero, but in reality, the core 10
Since the earth's magnetism and surrounding magnetic fields are applied as external magnetic fields to cores 10a and 10b, the strength of the magnetic fields between cores 10a and 10b becomes unbalanced, causing each core 10a to become unbalanced.

A difference is generated in the induced voltage between the coils 10b, and the remaining induced voltage that is not canceled out is output across the secondary winding 12 as a whole. The geomagnetism and surrounding magnetic fields are at a level determined by the installation location of this sensor M when the vehicle V is not passing through.
When the vehicle V passes by, the distance changes greatly as shown by the arrow in FIG. 4(a).

The induced voltage is detected by the detection circuit 31 of the magnetic change detection circuit 3, and sent to the vehicle detection circuit 4 and feedback circuit 5 via the amplifier 32. The vehicle detection circuit 4 rectifies the signal voltage due to the earth's magnetism, and then detects whether the magnetic field exceeds a preset detection level (ID). The detection level T (D is set so that it cannot be exceeded by normal magnetic field fluctuations, but can be exceeded by magnetic field fluctuations Hv when a vehicle passes. Figure 5 (al) shows the detection signal. The signal is processed by the output circuit 44 and output as a signal (see FIG. 5(b)) indicating that the car #j odor has passed.

On the other hand, in the feedback circuit 5, the induced voltage is inputted to an integrating circuit 51, accumulated at a predetermined time constant, that is, a time constant larger than the time constant of magnetic field change caused by the vehicle, and passed through a current limiting circuit 52 to the sensing coil 51. It is supplied as a feedback current to the feedback winding 13 of. This time constant is, for example, set to a value larger than the magnetic field fluctuation period when the vehicle speed is IKm/h or less. As a result of the above-mentioned integration, as shown in FIG. 4 (bl), the magnetic field variation output by the vehicle is canceled out, and only the magnetic field variation output due to the environment is fed back. As a result, the cores 10m and 10b have no external magnetic field and A return magnetic field is formed in the opposite direction, canceling out the external magnetic field, and when the vehicle is not running, the output voltage of the secondary winding 12 becomes 0. Therefore, as shown in FIG. 4(c),
It is possible to automatically correct the effects of the magnetic field at the installation point, including those caused by environmental changes.

As explained above, the present invention provides a detection coil that has a primary winding for excitation and a secondary winding for signal detection and detects changes in a magnetic field, and is provided with a feedback winding for canceling an external magnetic field. In addition, by providing a feedback circuit that controls the feedback current to the feedback winding, it automatically compensates for magnetic field fluctuations caused by the influence of the magnetic field at the installation location and environmental conditions, eliminating the need for adjustments during installation. As a result, the installation work can be completely simplified, and even if there are magnetic field fluctuations due to environmental changes after installation,
This has the effect of accurately detecting a vehicle without causing erroneous measurements. Furthermore, the present invention can be expected to operate stably semi-permanently even if the installation conditions change, and therefore has the advantage that the detection coil and other circuits can be installed in the same container in a hermetically sealed manner.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the installation state of the geomagnetic vehicle detector;
Fig. 2 is a block diagram showing an example of the implementation of the geomagnetic vehicle sensor of the present invention, Fig. 3 is a block diagram showing details of the detection coil and feedback circuit constituting the above embodiment, Fig. 4(a),
(b) and (c) are waveform diagrams showing magnetic field changes and the operation of each part in the above embodiment, respectively, and Fig. 5 (at, (b))
1 is a waveform diagram showing a detection signal and an output signal of magnetic change due to vehicle running; FIG. 1...Detection coil 11...Primary winding 12...
Secondary winding 13... Feedback winding 2... Excitation circuit
21... Oscillator 22... Amplifier 3.
...Magnetic change detection circuit 31...Detection circuit 32.
... Amplifier 4 ...] Desired vehicle detection circuit 41 ... Band pass filter 42 ... Rectifier circuit 43 ... Detection circuit 44 ... Output circuit 5 ... Feedback circuit 51
...Delay circuit 52...Current limiting circuit applicant
Kyosan Seisakusho Co., Ltd. Figure 3 4 Figure 4 = 559- Figure 5 (b)

Claims (1)

[Scope of Claims] A detection coil configured by winding a primary winding and a secondary winding around a core and detecting changes in a point magnetic field, an excitation circuit that excites the primary winding, and the secondary winding. a magnetic change detection circuit that detects changes in the magnetic field based on the induced voltage of the magnetic field; a vehicle detection circuit that detects a vehicle based on the detected magnetic field deformation; and means for correcting magnetic field fluctuations and gradual changes in the magnetic field due to environmental conditions. The correction means comprises a feedback winding wound around the core, and a feedback circuit that accumulates the output of the magnetic change detection circuit at a predetermined time constant and applies it to the feedback winding. A geomagnetic vehicle sensor characterized by comprising: