KR100601195B1 - Piezoelectric detector and system for collecting traffic informations using the same - Google Patents

Abstract

The present invention relates to a piezoelectric detector which is embedded in a road so as to measure a temperature, and uses the same to collect traffic information such as the number of vehicles passing through, speed, and weight, and a traffic information collecting system using the same. A piezoelectric detector including a piezoceramic sensor, a temperature sensor, an output compensator connected to the piezoceramic sensor and a temperature sensor to compensate for the output of the piezoelectric ceramic sensor according to a measurement temperature, and a piezoelectric sensor connected to the connector of the output compensator. A piezoelectric detector comprising an input unit for receiving load information of the vehicle passing through the detector, and an operation unit for calculating the number, speed, type, or weight of the vehicle passing through the piezoelectric detector by receiving real-time load information input therefrom. And it provides a traffic information collection system using the same.

As described above, the present invention can reduce the error of the output signal of the piezoelectric detector according to the temperature change by output compensation according to the road temperature, which could not be achieved in the conventional piezoelectric detector, thereby providing reliable traffic information such as vehicle speed and vehicle weight. There is an effect that can be collected.

Traffic information, piezoelectric detector, collection system, temperature sensor, output compensator, piezoceramic

Description

Piezoelectric Detector and Traffic Information Collection System Using It {PIEZOELECTRIC DETECTOR AND SYSTEM FOR COLLECTING TRAFFIC INFORMATIONS USING THE SAME}

1 is a block diagram of a traffic information collection system using a general loop detector;

2 is a graph showing changes in temperature dependence of dielectric constant of piezoelectric ceramics;

3 is a perspective view of a piezoelectric detector according to the present invention;

4 is a cross-sectional view showing the internal structure of a piezoelectric detector according to the present invention;

5 is a block diagram of a traffic information collection system using a piezoelectric detector according to the present invention.

<Description of Symbols for Main Parts of Drawings>

1: piezoelectric sensor 2: temperature sensor 3: protective case

4: molding material 5: connector 6: external cable

7: Cable connector 8: Intermediate cable 10: Output compensator

11: Piezoelectric Detector 20 of the Present Invention

30: calculation unit 40: communication unit

The present invention relates to a piezoelectric detector and a traffic information collection system using the same, and more particularly, to construct a piezoelectric detector capable of temperature compensation of a piezoelectric ceramic sensor embedded in a road to measure a load. The present invention relates to a piezoelectric detector capable of collecting traffic information such as speed and weight, and a traffic information collection system using the same.

The current traffic situation in Korea is very poor due to the rapidly increasing traffic demand and the road situation that cannot accommodate it. In order to improve this, it is necessary to accurately and stably collect traffic information (vehicle passing number, weight, speed, etc.), which are very important basic data for efficient operation and management of existing roads and planning and design of new roads.

As a method for collecting traffic information of the road as described above, the global survey by the mobile survey equipment and the continuous survey by the fixed equipment are performed in parallel. In the case of a global survey, there is a problem that it takes a long time to derive the final result due to the huge manpower requirements, the deterioration of the reliability of the survey results by non-specialized personnel, and the complexity of the survey / aggregation / analysis process.

As an alternative to the problem described above, the continuous inspection by the fixed detector can collect important traffic information such as speed, traffic volume, type of vehicle, and occupancy in the installed detector continuously. Can be collected. Therefore, it is attracting attention as a major component of the transportation system as a core infrastructure that forms the basis of the intelligent traffic information collection system.

As a continuous inspection method using the fixed detector described above, there are many methods for measuring real-time traffic volume on an image or other methods, but a traffic information system using a loop detector and a piezoelectric detector, which still show superior performance in terms of cost and efficiency. This is used a lot.

Using the loop detector and the piezoelectric detector, it is possible to measure the vehicle speed, the number of vehicles, the vehicle length, the number of axles, the distance between the wheels, and the recognition of traffic accidents in real time. Traffic information such as occupancy rate, average speed per unit time, and average number of vehicles can be obtained.

In the traffic information collection system using a general loop detector, as illustrated in FIG. 1, a loop detector 21 embeds a loop detector 21 having two loop coil sensors per lane on an asphalt road surface of a highway. It is connected to the 22 and the cable (23). When the vehicle passes through the loop detector 21 installed above, the loop detection controller 22 measures the change amount of the fine loop coil inductance, and amplifies the measured data to amplify the presence of the passing vehicle. You will measure speed. In addition, the traffic information collection system using the loop detector 21 is configured to store and analyze the vehicle information detected by the loop detection control unit 22 and to transmit the traffic information required for elements requiring information such as a traffic control center.

However, the traffic information collection system using the loop detector 21 having the above-described configuration is a method for changing the fine loop coil inductance of the loop coil sensor embedded in the road surface when the vehicle passes. Since the loop detection control unit 22 measures the vehicle type and the vehicle speed according to the simple number of vehicle passages and the distance between the axes, it only collects the vehicle speed, and there is no control function of the overload vehicle through the weight measurement of the vehicle.

In particular, the operation of overload vehicles can cause damage to roads and bridge structures, which can shorten the service life of the roads, increase maintenance costs, and reduce the ability to control and brake due to heavy weight, which can cause large traffic accidents. . In addition, overload vehicles deteriorate the performance of the road because the driving performance is relatively reduced, and also acts as a factor of deteriorating the roadside environment due to noise and vibration, exhaust emissions, etc. when driving. As the damage caused by overloading vehicles is directly related to the well-being of the people's life, the government has established and promoted an enforcement policy to eradicate the operation of overloading vehicles through related laws such as road law and road traffic law. It is rarely eradicated.

Traffic information using a piezoelectric detector to measure the weight of the vehicle to eliminate the operation of the overload vehicle and to collect traffic information such as the number of passages of the vehicle, the vehicle speed, and the type of vehicle using the loop detector. A traffic information collection system using a collection system or the above-described loop detector and piezoelectric detector is used.

The traffic information collection system using the piezoelectric detector is embedded in the road in a manner similar to the traffic information collection system using the loop detector, but the sensor elements introduced to the detector differ. That is, the loop detector uses a coil loop coil sensor, but the piezoelectric detector uses a piezoelectric ceramic element.

The piezoelectric ceramic is a device that generates a voltage proportional to it when a pressure is applied, and a mechanical deformation proportional to it when an electric field is applied. It is a material that can be converted to vibration energy and has high conversion efficiency. PZT [Pb (Ti, Zr) O ₃ ] is a representative material of such piezoelectric ceramics.

Therefore, when the piezoelectric detector using the piezoelectric ceramic as the sensor element is applied to the traffic information collection system, the number of passages of the vehicle, the speed of the vehicle, the type of the vehicle, and the weight of the vehicle can be measured.

The stationary survey equipment of the traffic information collection system with the loop + piezoelectric detector operated at all times is superior to other survey equipment in terms of accuracy and type of data collected, but almost all of them are imported and used in foreign countries. There are many difficulties in investigating and measuring the appropriate traffic characteristics.

In addition, as various kinds of different products are supplied to Korea, there are difficulties in compatibility and integrated maintenance between devices, and there are many difficulties in improving functions and applying advanced algorithms.

In addition, as in Korea, four seasons are distinct, and the yearly crossover is large, there may be a difference in output depending on the vehicle load depending on the season.However, the currently used vehicle classification detection sensor has a function to compensate for the influence of temperature. Because it does not have a disadvantage that is difficult to use in areas with large temperature difference, such as Korea.

In addition, the piezoelectric detector is greatly influenced by the output characteristics depending on the shape of the piezoceramic sensor used. In other words, the cable shape that receives a lot of horizontal stress causes a strong magnetic force to cause magnetic fields in the adjacent lane sensors, resulting in mutual interference, resulting in deterioration of the sensor's detectability.

In view of the above, it is very necessary to develop a sensor having a performance and function suitable for domestic situations such as more reliable traffic collection and easy maintenance.

In order to solve the problems of the conventional traffic information collection system using a piezoelectric detector, the present invention is manufactured in the form of a flat plate in consideration of the ease of installation and measurement accuracy of the piezoelectric ceramic sensor embedded in the road, The purpose of the present invention is to provide a piezoelectric detector that can be used even in a region with a large temperature difference by compensating the influence of temperature on the output value of the piezoelectric ceramic by embedding a temperature sensor inside the detector to measure the temperature inside the road.

In addition, the present invention by applying a piezoelectric detector capable of temperature measurement to the traffic information collection system, traffic using a piezoelectric detector that can collect traffic information, such as the number of passes, speed, type, weight, etc. of the road vehicle regardless of the season There is another purpose to provide an information collection system.

In order to achieve the above object, the present invention is a piezoelectric detector for measuring the load of the vehicle, the piezoelectric ceramic sensor, the temperature sensor, the piezoelectric ceramic sensor and the piezoelectric ceramic sensor according to the measurement temperature connected to the temperature sensor It provides a piezoelectric detector comprising an output compensator for compensating the output of.

The output compensator compensates the dielectric constant according to the temperature information input from the temperature sensor to compensate for the output of the piezoelectric ceramic sensor.

According to the present invention, the piezoceramic sensor, the temperature sensor and the output compensator are surrounded by a molding material, or the piezoceramic sensor and the temperature sensor are surrounded by a molding material, and the output compensator is the piezoceramic sensor and the temperature sensor outside the molding material. It provides a piezoelectric detector connected to, the molding material is to be covered with a protective case of a metal material except the upper portion.

In addition, the present invention includes an epoxy resin as the molding material, the piezoceramic sensor is manufactured in the form of a plate to remove the horizontal stress to the load.

On the other hand, the present invention is a piezoelectric detector embedded on the road surface, the input unit connected to the connector of the output compensation portion of the piezoelectric detector receives the load information of the vehicle passing through the piezoelectric detector and receives the real-time load information input to the input unit It provides a traffic information collection system including a calculation unit for calculating the number, speed, type or weight of the vehicle passing through the piezoelectric detector.

The present invention may further include a communication unit for transmitting the calculation information to the external system.

Hereinafter, a theoretical background of a piezoelectric detector capable of temperature measurement according to the present invention will be described.

As described above, the piezoelectric detector to which the present invention is applied is a detector in which the piezoceramic sensor element generates electric charge in accordance with mechanical stress. Piezoelectric detectors used for vehicle detection utilizes the generation of proportional electrical signals when stress is applied to the piezoelectric ceramic elements by the vehicle weight when the vehicle passes through the detector embedded in the road. In this method, the number of axles can be accurately measured, and when the two sensors are placed at a constant distance, the speed of the vehicle can be accurately measured.

In addition, if the effect on temperature is properly compensated, it is likely to be used as WIM (Weighing-In-Motion). Therefore, among the methods of measuring the number of shafts and the load of the car, it is widely used in traffic survey equipment because of its economical, durable and easy installation.

Also, depending on the shape of the sensor element, the output characteristics of the sensor are greatly affected. In other words, the shape that receives a lot of horizontal stress (cable type) forms a strong magnetic force, which causes the magnetic field of the next lane sensor to interfere with each other. In order to remove the horizontal stress of the sensor of this shape, a method such as inserting a shock absorber or the like to block the transmission of the horizontal stress around the cable is used. Therefore, considering the ease of installation and measurement accuracy, the thin plate-type sensor is better.

Therefore, if the sensor element is manufactured in the form of a flat plate to minimize the horizontal stress applied to the sensor, and the detector itself can detect the temperature inside the road and feed it back to the controller, the influence of temperature on the output value can be compensated. do. As such, when temperature compensation is appropriate, it can be used as a WIM.

Piezoelectric constants are used to express the relationship between mechanical deformation and resulting voltage in piezoelectric ceramics. There are two types of piezoelectric constants: d (piezoelectric strain constant) and g (voltage output constant), and g (voltage output constant) is mainly used as a constant representing the generated voltage due to external shock. d is defined as in Equation 1, and the relationship between d and g is shown in Equation 2.

At this time, the voltage (V) output when an external shock occurs in the vertical direction is as shown in Equation 3.

Equation 1 to Equation 3 are summarized as Equation 4.

It is generally possible to ignore changes in modulus of elasticity at low temperatures below 100 ° C. Therefore, the output voltage varies with the change of the electromechanical coupling coefficient and the dielectric constant, and the electromechanical coupling coefficient changes with the resonance frequency and the anti-resonance frequency. In addition, it can be seen from Equations 2 and 4 that the smaller the dielectric constant, the larger the electromechanical coupling coefficient, the larger the output voltage.

Therefore, if the electromechanical coefficient and dielectric constant change with temperature of the material used are known, it is possible to predict the change of output voltage with temperature.

The permittivity of ferroelectrics behaves according to the Curie-Weiss law (Equation 5).

Where C is the Curie constant, θ is the Curie-Weiss temperature, and can generally be thought of as the phase transition temperature of the ferroelectric, and A and B are constants.

FIG. 2 is a graph showing the temperature dependence of the dielectric constant of piezoelectric ceramics, and may show a very different trend depending on the type of material, but shows the temperature dependence of general piezoelectric ceramics. Table 1 shows the change in permittivity according to linear fitting, assuming the minimum temperature in Korea is -20 ℃ and the summer maximum temperature is about 60 ℃.

The change rate in the said Table 1 is a change rate at -20 degreeC and 60 degreeC on the basis of 20 degreeC. Therefore, since the voltage output is inversely proportional to the square root of the dielectric constant according to Equation 4, the output change at each temperature can be estimated as shown in Table 2, assuming that other variables are constant.

Therefore, the change of the output by temperature can expect the error of about ± 10%. In general, to be used for WIM, the linearity of output should be kept below 10%. Therefore, even in the case of a WIM sensor having a linearity of 10% or less at room temperature, if the error due to temperature and the error of the sensor itself are combined, the error may be 20% or more depending on the season, which may cause problems in practical use. This is very high.

Therefore, in the present invention, the piezoelectric ceramic element of the piezoelectric detector is manufactured in a flat plate shape to block the transfer of horizontal stress, thereby collecting traffic information of the road by accurate measurement, and at the same time, a temperature sensor capable of measuring the temperature of the road By constructing a piezoelectric detector, the influence of temperature on the output value of the piezoelectric ceramic was compensated according to the above-described relationship of temperature and permittivity based on the measured road temperature data.

Hereinafter, with reference to the accompanying drawings will be described in detail the configuration of the present invention.

3 is a perspective view of a piezoelectric detector according to the present invention, Figure 4 is a cross-sectional view showing the internal structure of the piezoelectric detector according to the present invention.

3 to 4, in the piezoelectric detector according to the present invention, a conventional piezoceramic sensor is positioned at the center portion. The piezoceramic sensor 1 may use a representative PZT [Pb (Ti, Zr) O ₃ ] element that generates a voltage when pressure is applied, as mentioned in the prior art. The piezoceramic sensor 1 is manufactured in the form of a flat plate to enable accurate measurement of the sensor by removing horizontal stress when a vehicle load is applied.

In addition, in the present invention, in order to measure the temperature of the environment in which the piezoelectric ceramic sensor 1 is used, that is, the road temperature, a temperature sensor 2 is installed in the piezoelectric detector 11.

The temperature sensor 2 may be any material capable of sensing a temperature and outputting a numerical value for the temperature. In the present invention, a thermocouple type commonly used is used.

In addition, the temperature sensor 2 of the present invention is installed in the lower or both sides of the piezoelectric ceramic sensor 1 in close proximity to the sensor to accurately measure the temperature of the environment in which the piezoelectric ceramic sensor 1 is used.

The piezoelectric ceramic sensor 1 and the temperature sensor 2 installed as described above are connected to the output compensator 10 of the present invention. That is, the output compensator 10 receives the output voltage generated from the piezoelectric ceramic sensor 1, receives the road temperature detected from the temperature sensor 2, and receives the road temperature based on the theoretical background mentioned above in detail. Compensating the output voltage of the piezoelectric ceramic sensor 1 according to.

The output compensator 10 may be installed integrally with the piezoelectric ceramic sensor 1 and the temperature sensor 2 or separately from the outside thereof. That is, as shown in (a) of FIG. 3 and (a) of FIG. 4, the output compensation unit 10 of the present invention inside the molding material 4 surrounding the piezoelectric ceramic sensor 1 and the temperature sensor 2. ) May be molded together, as shown in FIGS. 3 (b) and 4 (c), seen outside the molding material 4 surrounding the piezoceramic sensor 1 and the temperature sensor 2. The output compensator 10 of the present invention can be installed.

As described in the theoretical background of the present invention, the function of the output compensator 10 compensates the output voltage by compensating the dielectric constant of the piezoelectric ceramic sensor 1 according to the road temperature measured and input from the temperature sensor 2. Will be done.

In addition, the piezoelectric detector 11 of the present invention molded into the molding material 4 as described above is covered with a protective case 3 to reduce the bending stress (Bending Stress) generated by the application of the vehicle load to the detector itself It is desirable to make it. In particular, the protective case (3) is applicable to all plastics, metals, composites having good flexural strength, but it is preferable to use those of excellent metal material in terms of economy.

Epoxy resin was selectively applied to the piezoelectric ceramic sensor 1 and the temperature sensor 2 or the molding member 4 having a protective function surrounding the output compensator 10. As the material of the molding material 4, all polymer materials may be used. However, the epoxy resin having a high bonding strength of the protective case 3 and having a certain elastic force capable of applying a stress due to the vehicle load to the piezoelectric ceramic sensor 1 may be used. The resin was used to protect it from the outside.

When the piezoelectric ceramic sensor 1 and the temperature sensor 2 and the output compensator 10 constituting the piezoelectric detector 11 of the present invention configured as described above are integrally molded to the molding material 4, output compensation The connector 5, which is a terminal from which the output value can be transmitted to the outside, is formed at one side of the detector, and the cable connector 7 of the external cable 6 is connected to transmit the output value.

In addition, the piezoelectric ceramic sensor 1 and the temperature sensor 2 constituting the piezoelectric detector 11 of the present invention are molded in the molding material 4, and the output compensator 10 is installed outside the molding material 4. When the piezoelectric ceramic sensor 1 and the temperature sensor 2, the connector 5 for transmitting the measurement data to the outside is formed on one side of the detector, which is connected to the external output compensation unit 10 The cable 8 is connected to transmit the measurement data to the output compensator 10. The output compensator 10 compensates the output voltage of the piezoelectric ceramic sensor 1 according to the temperature based on the input measurement data and then requires an output value through an external cable 6 connected to the connector 9 thereof. Will be sent to.

Hereinafter, a traffic information collection system using the piezoelectric detector 11 of the present invention will be described.

5 is a block diagram of a traffic information collection system using the piezoelectric detector 11 according to the present invention. The traffic information collection system of the present invention is configured by using the piezoelectric detector 11 capable of temperature compensation according to the present invention described above. That is, as shown in FIG. 5, one or more, preferably two, piezoelectric detectors 11 of the present invention are spaced at predetermined intervals in a pair and embedded in the road surface of each lane.

The embedded piezoelectric detector 11 is connected to the input unit 20 using an output compensator 10 and an external cable 6 connected to the piezoelectric ceramic sensor 1 and the temperature sensor 2 and connected to the piezoelectric detector 11. Passing and load information of the vehicle passing through is input. The input unit 20 receives the real-time load information input therefrom and calculates a vehicle type or vehicle weight according to the number of vehicles passing through the piezoelectric detector 11, the vehicle speed, and the distance between the axles for a given time. ) And the cable is connected. In addition, the operation unit 30 further includes a communication unit 40 for transmitting operation information to an external system, and a transmission cable extended from a place requiring traffic information may be connected to the communication unit 40. Can be.

Hereinafter, the operation of the present invention will be described.

When the vehicle passes through the piezoelectric detector 11 of the present invention buried in the lane road surface of the road, the voltage according to the applied stress is output from the piezoelectric ceramic sensor 1 built in the piezoelectric detector 11 according to the weight of the vehicle. The output voltage is input to the output compensator 10 built in the piezoelectric detector 11 or externally installed, and at the same time, the real-time road temperature is compensated for by the temperature sensor 2 embedded in the piezoelectric detector 11. It is input to the unit 10.

The output voltage and temperature information input to the output compensator 10 are processed by the output compensator 10. That is, if the real-time road temperature measured from the temperature sensor 2 does not affect the output voltage of the piezoelectric ceramic sensor 1 (for example, the rate of change of permittivity is within ± 10% of the reference value), the piezoelectric ceramic sensor 1 Output voltage inputted from the output compensator 10 as it is, the real-time road temperature affects the output voltage of the piezoelectric ceramic sensor 1 (for example, the rate of change of dielectric constant is ± 10% or more), the output voltage of the piezoelectric ceramic sensor 1 is compensated by the output compensator 10 as much as that value.

As described above, the output voltage compensated by the output compensator 10 is input to the input unit 20 to transmit load information of the vehicle according to the output voltage to the calculation unit 30.

The real-time compensation output voltage from the piezoelectric detector 11 input to the calculating unit 30 is used to calculate the vehicle type or vehicle weight according to the number of vehicles passing through the piezoelectric detector 11, the vehicle speed, and the distance between the axes. The operation information output from the operation unit 30 is transmitted in real time to an external system connected to the communication unit 40 of the operation unit 30.

The real-time traffic information transmitted according to the traffic information collection system of the present invention can be used in the urban traffic control center for determining the time of congestion or the degree of congestion, or in the highway control center that checks the traffic volume or moving speed of the highway, and the weight of the passing vehicle. In particular, it is possible to install the piezoelectric detector 11 of the present invention in the place of frequent traffic jams and to display the traffic volume and the passing speed according to the information of the piezoelectric detector 11 at a position spaced behind the predetermined distance. If the display device is installed, it is possible to solve the traffic jam by providing real-time traffic information to the driver of the subsequent vehicle. In addition, the weight of the overload vehicle passing through the road can be measured and cracked down.

As described above, the present invention improves the ease of installation and measurement accuracy by making the piezoceramic sensor of the piezoelectric detector embedded in the road in the form of a flat plate, and output compensation according to the road temperature which could not be achieved in the conventional piezoelectric detector. In this case, in Korea, where the four seasons are clear, the use of such a detector can reduce the error of the output signal according to the temperature change regardless of the road temperature, so that it is possible to collect traffic information such as reliable vehicle speed and vehicle weight. have.

In addition, if the traffic information collection system using the piezoelectric detector of the present invention is used to share the real-time traffic information to reduce traffic congestion on the road, as well as to measure and crack down on the weight of the overload vehicle passing through the road in real time. There is a side effect of prolonging road life.

Claims (11)

In the piezoelectric detector for measuring the load of the vehicle, A piezoceramic sensor in the form of a plate, With a temperature sensor, An output compensator connected to the piezoelectric ceramic sensor and the temperature sensor and compensating for and outputting a dielectric constant of the piezoelectric ceramic sensor according to temperature information input from the temperature sensor; A molding material surrounding the piezoceramic sensor and the temperature sensor; Piezoelectric detector comprising a protective case for covering the lower portion of the molding material. delete The piezoelectric detector of claim 1, wherein the molding material surrounds the output compensation unit. delete The piezoelectric detector of claim 1 or 3, wherein the temperature sensor is located at the bottom or both sides of the piezoceramic sensor. delete The piezoelectric detector of claim 1, wherein the protective case is made of metal. The piezoelectric detector according to claim 1 or 3, wherein the molding material comprises an epoxy resin. delete In the traffic information collection system using a piezoelectric detector, A piezoelectric detector according to claim 1 embedded in a road surface, An input unit connected to a connector of an output compensator of the piezoelectric detector and receiving load information of a vehicle passing through the piezoelectric detector; And a calculation unit for receiving the real-time load information inputted to the input unit and calculating the number, speed, type, or weight of the vehicle passing through the piezoelectric detector. The traffic information collection system according to claim 10, wherein the calculation unit further includes a communication unit for transmitting the calculation information to an external system.

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