JP2006048524A - Vehicle detection system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vehicle detection system with lighter weight and excellent in detection accuracy. <P>SOLUTION: The vehicle detection system 1 detects a vehicle which passes through a monitoring range on a road and is provided with a sensor 2 which senses infrared rays generated by an object to be detected, an infrared transmission lens 3 arranged in front of the detecting direction of the sensor 2 and a heat alleviation member 4 which alleviates change in an amount of infrared rays except the infrared rays which pass through the lens 3 among the infrared rays to be transmitted to the sensor 2 by external environment. The heat alleviation member 4 is formed of materials with low heat conductivity so that the amount of infrared rays to be irradiated is hard to change by the external environment. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a vehicle detection system that detects a vehicle passing through a monitoring range on a road. In particular, the present invention relates to a lighter vehicle detection system that is less affected by temperature changes in a housing that houses a sensor, can detect a vehicle with high accuracy, and is lighter.

  Conventionally, loop detectors, ultrasonic detectors, and the like are well known as vehicle detectors that detect vehicles in order to examine traffic flow such as traffic volume and occupation rate. However, the loop detector is not applicable to bridges where it is difficult to secure a buried space in addition to the need to bury the loop coil in the road. In addition, the ultrasonic detector needs to be arranged so as to be located almost directly above the vehicle, which is detrimental to the appearance, and because the detector itself uses an active sensor that emits ultrasonic waves, power consumption tends to be large. It was.

  In view of this, the present inventors have proposed a vehicle detection system using an infrared detection sensor which is a passive sensor in order to eliminate the problems of the conventional detector described above (Patent Document 1). This vehicle detection system measures infrared rays emitted from vehicles and infrared rays emitted from objects other than vehicles (such as roads) by sensors that sense infrared rays, such as thermopile elements, and the presence or absence of vehicles is determined based on the amount of these infrared rays. It is the structure which determines. In addition, it is proposed to arrange an infrared transmission lens in front of the detection direction of the sensor in order to condense the infrared detection area, condense the infrared light efficiently on the sensor, and limit the transmitted wavelength to the infrared region. (See Patent Document 1 FIG. 17).

JP2003-317186A

  As a result of various investigations on the vehicle detection system proposed by the present inventors, there is a case where the vehicle detection may not be performed properly when a large temperature change occurs in the housing that houses the infrared sensor. I understood. When the present inventors investigated, the sensor senses infrared rays other than infrared rays that have passed through the lens, specifically infrared rays emitted from a casing or a lens support portion that exists around the sensor. When the case or support part is made of a metal material such as aluminum with high thermal conductivity, depending on the thickness of the case or support part, if the temperature of the case or support part changes due to environmental changes outside the case, It was found to be strongly affected.

  Therefore, a main object of the present invention is to provide a vehicle detection system capable of reducing the deterioration of the vehicle detection rate and increasing the detection accuracy.

  This invention achieves the said objective by setting it as the structure which can hold | maintain substantially constant the quantity of infrared rays other than the infrared rays which permeate | transmitted the lens among the infrared rays transmitted to the detection surface of a sensor.

  That is, the present invention is a vehicle detection system that detects a vehicle that passes through a monitoring range on a road, a sensor that detects infrared rays emitted from a detection target, and an infrared transmission lens that is disposed in front of the detection direction of the sensors. A heat relaxation material is provided for reducing the amount of infrared light transmitted to the sensor other than infrared light transmitted through the lens, depending on the external environment.

  In order to reduce the weight of the vehicle detection system, the present inventors tried to form the casing and the support portion of the infrared transmission lens with aluminum. And in order to further reduce the weight, when the thickness of the housing and the support portion is made as thin as possible, the housing and the support portion are warmed by sunlight or the case and the support portion are cooled by blowing wind. For example, when the temperature of the housing or the support changes greatly, the sensor may detect the change in the amount of infrared rays accompanying the temperature change, and the vehicle presence / absence may not be properly determined. all right. Even if the case and the support are formed of aluminum with high thermal conductivity, if the thickness is increased to some extent, the inside of the case or the inside of the support, ie, the case or the support, Since the temperature of the surface facing the sensor is unlikely to change, the amount of infrared radiation radiated from the inside of the housing or the support portion is held almost constant regardless of sunlight or wind. Therefore, the presence or absence of the vehicle can be detected properly regardless of the external environment. That is, by increasing the thickness, it is possible to reduce the change caused by the external environment of the amount of infrared rays emitted from the inside of the housing or the support portion, and the sensor is hardly affected by the infrared rays. However, increasing the thickness increases the weight. Therefore, the present inventors have achieved a further reduction in weight and a thermal relaxation material that reduces the change in the amount of infrared rays due to the external environment in order to reduce the influence of infrared rays radiated from the housing received by the sensor. To provide Hereinafter, the present invention will be described in more detail.

  The vehicle detection system of the present invention measures the amount of infrared rays emitted from an object, and detects the presence or absence of a vehicle based on the amount of infrared rays. The amount of infrared rays emitted by an object is proportional to the fourth power of the absolute temperature of the object and proportional to the emissivity ε of the object according to Stefan-Boltzmann law. The emissivity ε of an object on the road, for example, a road surface or a vehicle traveling on the road, is usually substantially the same (usually 0.9 or more), and there is often no significant difference. Therefore, if a sensor that detects infrared rays is installed in the direction of the road surface, the amount of infrared light detected by the sensor changes when a vehicle with a temperature different from that of an object other than a vehicle such as a road passes through the road surface. By doing so, the vehicle can be detected. As such a sensor, the present invention stipulates that the sensor itself does not actively emit infrared rays but includes a so-called passive sensor that senses infrared rays emitted from a detection target. This sensor is preferably one that can detect a change in electrical properties caused by a rise in temperature that is warmed by the thermal effect of infrared rays. For example, a thermopile element that outputs a temperature change generated in a thermocouple by infrared rays as a thermoelectromotive force Is mentioned. In particular, when a thermopile element having a large thermoelectromotive force output is used, the vehicle can be detected by sufficiently sensing infrared rays using only the thermopile element without using another sensor such as a pyroelectric sensor.

  Further, in the present invention, an infrared transmission lens is disposed in front of the detection direction of the sensor in order to adjust the infrared detection area in the sensor to an appropriate range and to efficiently collect the infrared light on the sensor. The infrared transmitting lens is not particularly limited as long as it transmits infrared light. For example, one surface may be spherical. The infrared transmitting lens is particularly preferably made of ZnS. Conventional infrared transmission lenses made of Ge (germanium) or the like are known, but conventional lenses require glass-based or silicon-based auxiliary materials. On the other hand, a lens made of ZnS is preferable because it has excellent weather resistance and can withstand sufficient use even if the lens itself is exposed to the outside.

  The most characteristic feature of the present invention is that, among infrared rays transmitted to the sensor, the amount of infrared rays other than the infrared rays transmitted through the infrared transmission lens (hereinafter referred to as second infrared rays) is the outside such as temperature and wind. The purpose is to provide a thermal relaxation material that mitigates changes caused by the environment. In the present invention, in order to reduce the weight of the entire system and to effectively suppress the deterioration of the vehicle detection rate due to the temperature change of the casing, a thermal relaxation material is arranged to restrict infrared rays detected by the sensor. That is, the heat relaxation material makes the amount of the second infrared ray transmitted to the sensor difficult to change depending on the external environment, and keeps it almost constant. Such a heat relaxation material may be formed of a material having a low thermal conductivity compared to a material having a high thermal conductivity such as aluminum. Specific examples include those made of a non-metallic material of 10 W / mK or less. The thermal conductivity is preferably as low as possible, and particularly preferably 1.5 W / mK or less. Examples of such a nonmetallic material include at least one selected from rubber, ceramics, paper, and plastic. In particular, rubber, paper, and plastic are relatively inexpensive and can reduce costs. Specific rubbers include soft rubber (thermal conductivity 0.14 to 0.16 W / mK), hard rubber (thermal conductivity 0.17 W / mK), and the like. Specific ceramics include alumina and zirconia. By forming the heat relaxation material with a material having low thermal conductivity, for example, even if the housing is warmed by sunlight and the amount of infrared rays emitted from the housing increases, the heat relaxation material is difficult to warm. That is, the temperature change hardly occurs. Therefore, the amount of infrared rays radiated from the heat relaxation material transmitted to the sensor disposed inside the heat relaxation material can be reduced. That is, the amount of infrared rays radiated from the heat relaxation material transmitted to the sensor can be kept substantially constant regardless of the external environment.

  The shape of the heat relaxation material is not particularly limited as long as it does not prevent the infrared rays transmitted through the infrared transmission lens from being transmitted to the detection surface of the sensor. For example, it is possible to form a cylinder so that the sensor is surrounded by one opening, and the other opening is in contact with the lens, that is, between the sensor and the lens. At this time, the infrared light transmitted through the infrared transmission lens passes through the cylindrical heat relaxation material and is transmitted to the detection surface of the sensor. On the other hand, infrared rays from the outer periphery of the cylindrical heat relaxation material, for example, infrared rays from the housing are shielded by the heat relaxation material, and are hardly transmitted directly to the detection surface of the sensor. Such a thermal relaxation material is preferably disposed as close as possible to the sensor, and is preferably disposed inside the housing, particularly inside the support portion of the infrared transmission lens. For example, if a lens hole for attaching an infrared transmission lens is provided in the housing and the housing itself is used as a lens support portion, the heat relaxation material is disposed in the housing, so that heat can be generated inside the lens support portion. Mitigating material will be placed.

  The sensor, the infrared transmitting lens, the heat relaxation material, and other vehicle presence / absence determining means described later constituting the vehicle detection system of the present invention may be housed in a casing. The casing is preferably made of lightweight aluminum or the like. In addition, a support portion for the infrared transmitting lens is provided. As described above, the support portion may be integrated with the housing in which the lens hole is provided in the housing, or may be provided separately. In the former case, it is preferable to provide a sensor fixing portion in the housing at a position where the focal length matches the infrared transmission lens. In the latter case, the support part of the infrared transmission lens is shaped so that the sensor can be arranged, and when the sensor and the lens are arranged in the support part, the sensor, the lens, and the support part are integrated into the housing. It is preferable that the installation work can be easily performed. In addition, it is preferable that the support portion be formed so as to have an appropriate focal length when the sensor and the infrared lens are arranged, because it is not necessary to adjust the focal length when the support portion is arranged at a predetermined position of the housing.

  The casing may include an aiming unit for adjusting the directivity angle of the infrared transmission lens in a target direction. The aiming unit may be any unit that can adjust the directivity angle in a target direction. For example, the aiming unit may be provided with a mark such as a combination of a concave projection and a convex projection, or a laser pointer. It is done.

  In addition, the vehicle detection system of the present invention includes determination means for determining the presence or absence of a vehicle using the input level value obtained from the sensor. Moreover, when using a thermopile element as a sensor, you may provide the amplifier which amplifies the electromotive force of an element. Furthermore, a configuration may be provided in which the determination result is transmitted to a signal controller, a management center, or the like by wire or wirelessly.

  In the present invention, the presence / absence of the vehicle is determined using the input level value obtained from the sensor. As the input level value, it is preferable to use a calculated value obtained by performing an appropriate calculation rather than using it as it is. For example, a value based on the amount of infrared rays emitted from an object other than a vehicle is used as a background level, and a value based on the difference between the background level and the input level value is used as a comparison value. If the comparison value is less than the threshold value, it may be determined that there is no vehicle.

As for the background level, the amount of infrared rays from other than the vehicle is detected at any time by the sensor, and if the value is based on the detected amount of infrared rays, it is approximated to the value of the actual environment and more precise detection is performed. be able to. For example, you may use the average value of the data which detected the infrared rays from those other than vehicles in multiple times, and the calculated value by an exponential smoothing method. The exponential smoothing method is generally expressed as f ₀ = α × d ₋₁ + (1-α) f ₋₁ = f ₋₁ + α × (d ₋₁ −f ₋₁ ) (f ₀ : next predicted value, α: Smoothing coefficient, d _-1 : Actual value of the previous term, f _-1 : Predicted value of the previous term), Actual value of the previous term (here, input level value) can be reflected, so the background level is the actual environment (road surface condition) ) Can be more accurate value. In particular, when the smoothing coefficient α is changed according to the previous vehicle determination result, the background level can be more reliably grasped regardless of the amount (temperature) of the infrared rays of the vehicle. If the same sensor for detecting the background level and the sensor for detecting the vehicle are used, it is not necessary to provide a sensor for detecting the background level.

  The value based on the difference between the background level and the input level value, that is, the comparison value to be compared with the threshold value, is a value obtained by integrating the input level values within a certain time rather than using the difference between the input level value and the background level as it is. When used, it is preferable because an essential tendency in the change in the amount of infrared radiation can be grasped and the vehicle can be detected with higher accuracy. In addition to the difference between the background level and the input level value, it is preferable to use the amount of change per unit time of the input level value as a comparison value. Since this amount of change does not take into account the background level, it is not affected by the background level.Therefore, even if the difference between the input level value and the background level is small, there is a vehicle while the input level value is changing. It is easy to obtain the determination that the vehicle is in the vehicle, and the case where the vehicle cannot be recognized is reduced. It is more effective that the amount of change is the difference between the input level value just before and the current input level value than immediately before.

  The threshold (threshold) used for the determination is preferably changed according to the actual environment.For example, when the change in the amount of infrared rays (temperature change) is large (that is, the dispersion is large), the threshold is set to a relatively large value. When it is small (that is, the variance is small), a relatively small value may be used. These threshold values may be obtained by calculation. For example, the threshold value may be changed by setting the threshold value as a set value + correction value and changing the correction value.

  The algorithm for determining the presence or absence of the vehicle may be configured in the same manner as in Patent Document 1.

  Such a vehicle detection system of the present invention can be installed in a so-called side fire type with respect to a support provided on the road, and can detect infrared rays from the side of the road.

  In the vehicle detection system of the present invention having the above-described configuration, by arranging the heat relaxation material, the amount of infrared rays other than infrared rays transmitted through the lens is hardly changed by the external environment, and the infrared rays transmitted to the detection surface of the sensor The amount can be kept almost constant regardless of the external environment. Therefore, it is possible to reduce the deterioration of the vehicle detection rate due to the temperature change of the housing. Further, by using a heat relaxation material made of rubber, ceramics, or the like, it is possible to reduce the metal material such as aluminum constituting the support portion of the housing or the lens, thereby realizing further weight reduction.

  Furthermore, since the vehicle detection system of the present invention uses a sensor that detects infrared rays emitted from a detection target without sensing infrared rays emitted by itself, there is a risk of being affected by wind and rain even when installed on the side of the vehicle. The number of vehicle misidentifications can be reduced. That is, both improvement in aesthetics and detection accuracy are realized. In addition, since the system of the present invention uses a passive sensor, it consumes less power than an active sensor used in a conventional ultrasonic detector. Therefore, for example, sufficient power can be supplied by a solar cell or the like.

Embodiments of the present invention will be described below.
FIG. 1 is a schematic view showing a state in which the vehicle detection system of the present invention is attached to a column near a road, and FIG. 2 is a schematic cross-sectional view showing the configuration of the vehicle detection system of the present invention. A vehicle detection system 1 shown in the present example is attached to a support column 130 disposed near a road 100 and detects a vehicle 120 passing through a monitoring range 110 of the road 100 from its side. Specifically, the system 1 detects infrared rays from the vehicle 120, infrared rays from other than the vehicle 120 such as the road 100, and checks the presence or absence of the vehicle based on the amount of these infrared rays. A sensor 2 that senses infrared rays emitted from a detection target such as 100, and an infrared transmission lens 3 disposed in front of the detection direction of the sensor 2 (see FIG. 2). The most characteristic feature of the present invention is that it includes a heat relaxation material 4 for relaxing the amount of infrared light other than the infrared light transmitted through the lens 3 due to an external environment. This will be described in more detail below.

  In this example, the sensor 2 is housed in a cubic housing 5 and is disposed on a circuit board 6 having vehicle presence / absence judging means, and a fixing member such as a screw is fixed to a fixing portion 5a provided in the housing 5. It is fixed in the housing 5 using The infrared transmitting lens 3 is provided with a lens hole for fitting the lens 3 on one surface of the housing 5 (the surface facing the sensor 2), and is fitted into this hole and is attached to a fixing member such as a screw via the lens presser 5b. And fixed to the housing 5. In this example, when the sensor 2 and the lens 3 are fixed to the housing 5, the fixing portion 5a is provided so as to have an appropriate focal length.

  In this example, the sensor 2 is a thermopile element, and the infrared transmission lens 3 is a lens having a spherical surface formed of ZnS. The housing 5 was made of aluminum. The circuit board 6 has a memory for storing the presence / absence of a vehicle, a memory for storing an input level value and a calculation value from the sensor 2, a central processing unit (CPU) for performing various calculations using the input level value, and an input from the sensor 2. It includes an amplifier that amplifies the level value. Although omitted in FIG. 2, in order to transmit power wiring from the solar cell 10 (see FIG. 1) and the determination result of the circuit board 6 to the signal controller and the management center, Signal wiring is connected to the circuit board 6 so that a signal to a transmission unit (not shown) can be transmitted.

  In the vehicle detection system having the above-described configuration, the support portion of the lens 3 is integrated with the casing 5, and no separate support portion is provided, so that the weight of the entire system is reduced. However, for example, when a sudden temperature change occurs in the casing 5 due to wind blowing or when the casing 5 is heated due to high air temperature, the temperature is transmitted to the sensor 2 due to the temperature change. The amount of infrared rays changes. An electromotive force is generated due to the change in the amount of infrared rays accompanying the temperature change, and it may be determined that the vehicle is present even though the vehicle has not passed the monitoring range. This is because infrared rays other than infrared rays transmitted through the lens 3 (in this example, infrared rays from the housing 5) are transmitted to the detection surface of the sensor 2 (see the broken line arrows in FIG. 2). Therefore, in the present invention, the amount of infrared light other than the infrared light transmitted through the lens 3 is reduced by the external environment such as air temperature and wind, and the amount of infrared light transmitted to the detection surface of the sensor 2 is stabilized. The heat relaxation material 4 is disposed on the side.

  In this example, the heat relaxation material 4 is made of cylindrical soft rubber, and is arranged so that one opening is in contact with the substrate 6 and surrounds the sensor 2 as shown in FIG. The other opening is arranged in contact with the lens 3. That is, in this example, the heat relaxation material 4 is disposed between the substrate 6 and the lens 3. By arranging the heat relaxation material 4 so that there is no gap between the substrate 6 and the lens 3 in this way, it is possible to suppress the infrared rays from the housing 5 from being directly transmitted to the sensor 2. In this example, since the heat relaxation material 4 is formed of a material having low thermal conductivity, for example, when the temperature is high, the amount of infrared rays radiated from the housing 5 is increased by heating the housing 5. Even if it increases, since the heat relaxation material 4 is not easily heated, the change in the amount of infrared rays emitted from the heat relaxation material 4 can be reduced. Therefore, among the infrared rays transmitted to the sensor 2, the amount of infrared rays other than the infrared rays transmitted through the lens 3 hardly changes regardless of the external environment such as the temperature.

  By the said structure, this invention vehicle detection system can reduce effectively the change of the quantity of infrared rays other than the infrared rays which permeate | transmitted the lens among the infrared rays transmitted to the detection surface of a sensor with a thermal relaxation material. Therefore, misidentification of the presence or absence of the vehicle by infrared rays other than the infrared rays that have passed through the lens is reduced.

  The vehicle detection system of the present invention senses infrared rays emitted from a detection target with a sensor (a thermopile element in this example), amplifies an electromotive force generated in the element with an amplifier, and converts it into a digital signal with an A / D converter. Convert to get the input level value. Then, a value (comparison value) based on the difference between the input level value and the background level is calculated, and whether or not the vehicle is present is determined based on whether the comparison value is equal to or greater than a threshold value. The judgment results are aggregated and sent to a signal controller or a traffic management center.

  The operation procedure for vehicle detection will be specifically described. First, the sensor is activated to perform initial learning of the background level and threshold value. At this time, it is preferable not to determine the vehicle. By the initial learning, the background level and the threshold value can be set to values more suitable for the actual environment. The obtained background level and threshold value are stored in a memory.

After the initial learning, the determination of the presence or absence of the vehicle is started. First, an electromotive force obtained from the sensor is amplified by an amplifier to obtain an input level value, and a comparison value and a threshold value are calculated based on the input level value. Then, the comparison value calculated based on the input level value is compared with a threshold value, and if the comparison value is equal to or greater than the threshold value, it is determined that there is a vehicle, “Vehicle presence” is written in the sensing total result, and stored in the memory. As the comparison value, a value calculated based on the difference between the input level value and the background level is used. Specifically, a difference (referred to as a background difference) between the input level value b _n and the previous background level an _n−1 is obtained, and the integrated value of this background difference over a fixed time is used as a comparison value. In addition to this integrated value, a calculated value using the integrated value and the amount of change per unit time of the input level value may be used. Specifically, the difference between the input level value and the previous background level (background difference) is obtained in the same manner as described above, and the integrated value of this background difference for a certain time is obtained. Next, a change amount is obtained, and an average value of the change amounts is obtained. A value obtained by multiplying the average value by a constant is added to the current integrated difference to obtain a comparison value. In this way, by using not only the integrated value but also the value calculated using the amount of change as the comparison value, cases where the vehicle is misidentified or cannot be recognized are further reduced. In addition, by using a value that also takes into account the amount of change in this way, it is possible to detect the presence of a vehicle by sufficiently sensing infrared rays using only a thermopile element without using other sensors such as pyroelectric sensors. can do.

  In this example, the threshold value is changed depending on the change in the amount of infrared rays, that is, the temperature change so that the threshold value can be changed according to the actual environment. Specifically, the threshold value is set to the sum of the set value and the correction value, the set value is set to the minimum value, and various correction values are added to the set value to follow the environment.

On the other hand, if the comparison value is less than the threshold value, it is determined that there is no vehicle, and similarly, “no vehicle” is written in the sensing count result and stored in the memory. At this time, the sensor has detected a background such as a road. Therefore, the input level value used for this determination is stored for use in calculation, and the background level is calculated using this input level value. In this example, an arithmetic value by exponential smoothing is used as the background level. Specifically, when the input level value is b _n , the background level used for the next determination is a _n , and the smoothing coefficient is α, a _n = a _n-1 + α × (b _n -a _n-1 ) Is used as the background level (a _n-1 is the background level used in the previous vehicle determination).

  The vehicle detection system of the present invention is suitable for examining traffic flow such as traffic volume and occupation rate.

It is the schematic which shows the state which attached this invention vehicle detection system to the support | pillar of the roadside. It is a cross-sectional schematic diagram which shows the structure of this invention vehicle detection system.

Explanation of symbols

1 Vehicle detection system 2 Sensor 3 Infrared transmitting lens 4 Thermal relaxation material
5 Housing 5a Fixed part 5b Lens holder 6 Circuit board 10 Solar cell
100 Road 110 Monitoring range 120 Vehicle 130 Prop

Claims (4)

A vehicle detection system for detecting a vehicle passing through a monitoring range on a road,
A sensor for detecting infrared rays emitted by the detection target;
An infrared transmitting lens disposed in front of the detection direction of the sensor;
A vehicle detection system comprising: a heat relaxation material that relieves changes in the amount of infrared light transmitted through the lens other than infrared light transmitted to the sensor, depending on an external environment.   2. The vehicle detection system according to claim 1, wherein the heat relaxation material is made of a non-metallic material having a thermal conductivity of 10 W / mK or less.   2. The vehicle detection system according to claim 1, wherein the heat relaxation material is made of at least one selected from rubber, ceramics, paper, and plastic.   The vehicle detection system according to claim 1, wherein a thermopile element is used as the sensor.

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