JP4157078B2 - Road surface state measuring method and road surface state measuring device - Google Patents

Description

  The present invention is intended to provide road surface information to a driver, each control device, etc. by sensing information such as wetness and freezing on the road surface, which greatly affects the safety and steering performance of a vehicle. The present invention relates to a method and a road surface state measuring apparatus.

  It is very important for the vehicle driver to grasp the road surface condition of the road. In particular, when driving at high speed, the road surface condition greatly affects the safe operation and steering performance of the vehicle, so the vehicle driver always pays attention during traveling. Even in this road surface condition, the wetness and freezing of the road surface greatly deprives the steerability of the car, so that information is very important for the driver.

  On the other hand, for road managers, grasping the road surface condition is listed as the main work of the management work, and information such as wetness and freezing of the road surface is used to perform appropriate work to ensure road safety. We use as judgment material. It also provides road surface information to alert drivers who are driving.

  As devices used for grasping such road surface conditions, the following devices have been conventionally provided.

  First of all, as a stationary type for highways and general roads, we used a thermometer embedded on the road surface and various weather information and predictions to predict wetness and freezing of the road surface, and changes in the amount of reflected light using infrared rays There are various types, such as those using visual observation from a stationary camera and those using a near-infrared semiconductor laser with a road installation type.

  In addition, those for in-vehicle use that are judged by the outside air temperature, those that use infrared light, those that use radio waves, etc. have been proposed. Among them, spatial frequency analysis was used as the one that uses infrared light. There are some (for example, refer to Patent Document 1).

  In this method using spatial frequency analysis, the substance on the road surface is discriminated by calculating based on the light quantity ratio by regular reflection and diffuse reflection of the irradiated light, so the principle on road surfaces other than asphalt and white lines is the principle Moreover, measurement is difficult. Also, in recent years, pavement technology called drainage pavement and high-performance pavement, which is characterized by a high porosity (void ratio) in the pavement, unlike asphalt used on the conventional road surface, has become popular. Yes. In the measurement of water-permeable asphalt by such a pavement technique, aggregates having a particle shape larger than that of conventional asphalt are used. Therefore, in the spatial frequency type measurement method, measurement is difficult due to large spots.

  On the other hand, a method using a method of measuring the amount of water using the water absorption characteristics in the near-infrared wavelength region has been proposed (see, for example, Patent Document 2).

  In this measurement system, a lamp having a broad spectrum including the wavelengths used for the reference light and the measurement light is used as the light source, and the near-infrared light having a wavelength (water absorption wavelength) that is largely absorbed by the filter is absorbed by water. It is divided into near-infrared light having at least two wavelengths and near-infrared light having a wavelength that is difficult to be performed (reference wavelength). And the method of measuring the water | moisture content of a road surface by calculating the ratio of the reflected light quantity of each light is employ | adopted. In this method, it is difficult to be affected by the surface shape of the object, and at the same time, the light irradiated on the object is used, so there is no time lag. However, in this method, whether the water on the road surface is water or ice is determined by measuring the road surface temperature.

  Also, using a near-infrared semiconductor laser, a wavelength of 0.905 μm, which is difficult to be absorbed by water and ice, a wavelength of 1.42 μm, which is easy to be absorbed by water (water absorption peak) and difficult to be absorbed by ice, water Has been proposed that uses three wavelengths with a wavelength of 1.55 μm, which are not easily absorbed by ice and are easily absorbed by ice (ice absorption peak), to distinguish between dry, snowy, wet, and frozen states ( For example, see Patent Document 3.)

  However, in this method, the distinction between water and ice is easily absorbed by water (water absorption peak), and is not easily absorbed by water at a wavelength of 1.42 μm, which is difficult to be absorbed by ice, and is easily absorbed by ice (ice absorption). Peak) Determination is made based only on the magnitude relationship of the reflected light quantity at a wavelength of 1.55 μm, and at the peak wavelength of water and ice absorption, the other material is easily absorbed, so it is difficult to measure the reflected light quantity difference. . Furthermore, no consideration is given to the sherbet-like road surface mixed with water and ice.

  In addition, a method of measuring the road surface state using the polarization characteristics of laser light has been proposed (see, for example, Patent Document 4).

  Generally, as a characteristic of a semiconductor laser, the oscillation wavelength of the laser changes several nm with a temperature change of about 10 ° C., and the optical output fluctuates by about 10 mW. Therefore, a system using a near-infrared wavelength semiconductor laser requires a circuit for controlling the temperature or keeping the optical output constant.

  Furthermore, as shown in FIG. 8, a lamp light source 91 is used to irradiate light on the road surface x, the reflected light is divided into three wavelengths by a filter, and the road surface state is discriminated by the ratio of each wavelength. (For example, refer nonpatent literature 1.).

However, what is described in this document is a system that divides reflected light into three wavelengths, and it has not been clarified which wavelength of the reflected light can be detected to determine the road surface condition. .
International Publication No. WO95 / 01549 Pamphlet JP-A-6-229917 JP-A-9-318766 Japanese Patent Laid-Open No. 10-206314 Plakash Joshi Physical Science Co., Ltd. (Pracash Joshi, Physical Sciences, Inc.) “Mobile Road Condition Sensor As Winter Maintenance Aid 2” -10, p34

  In the above-described prior art, the road surface state is determined by comparing the reflected light amounts of light of two or three wavelengths, but no specific wavelength is mentioned.

  In the technique described in Patent Document 3 in which the wavelength used is described, the wavelength at which each absorption of water and ice reaches a peak is used. In general, the peak position of the absorption wavelength of ice does not vary, but the peak position of the absorption wavelength of water varies depending on the temperature. Measurement becomes impossible. In particular, when a very narrow spectrum is used like a semiconductor laser, the fluctuation of absorption becomes large. Furthermore, for a laser using a near-infrared wavelength semiconductor laser, the oscillation wavelength changes greatly due to mode hopping due to temperature, and the optical output fluctuates. For this reason, when a semiconductor laser is used, it is necessary to add a circuit for keeping the temperature of the semiconductor laser constant regardless of the external temperature and keeping the optical output constant in order to prevent the oscillation wavelength from deviating.

  Also, as can be seen from the water and ice transmittance graph shown in FIG. 3, the difference in transmittance between one material and the other material at the position where each transmittance is at the bottom is small. However, the accuracy is not good for discrimination by the respective light quantity ratios.

  Furthermore, in the prior art, an attempt has been made to determine the road surface condition using a xenon lamp or the like including a near-infrared wavelength in the light source. In this way, the spectrum of the light source using the lamp is broad. There are many light components other than the desired wavelength component. Therefore, the light amount of the wavelength used for the measurement is small in terms of the entire irradiation light amount. When considering use on an actual road surface, it is inevitably necessary to increase the irradiation light quantity of the lamp in order to remove the influence of disturbance light or the like. For this reason, there arises a problem that the apparatus becomes larger and the energy efficiency becomes worse. Also, in such an apparatus, optical components such as prisms and filters, and elements on the light receiving side are required for each wavelength, the number of components increases, and the system becomes large and expensive.

  As described above, the conventional technique using a lamp as a light source increases the size and cost of the apparatus. Furthermore, when using near-infrared light as in the prior art, the difference in reflected light amount of the wavelength to be compared with the complicated road surface condition is small, so the accuracy is deteriorated due to fluctuations in absorption wavelength due to temperature, etc., and accurate discrimination There is a high possibility of not being able to.

  Even in the case of the spatial frequency method using near-infrared light, since the gap is large on the transmissive asphalt road, the accuracy of discrimination is deteriorated.

  The present invention was created in view of such circumstances, and an object of the present invention is to provide a road surface state measuring method and apparatus that can measure a road surface state with high accuracy in real time, and is small and energy efficient. .

  In order to solve the above problems, the present invention provides a wavelength that is not easily absorbed by both water and ice, a wavelength that is hardly absorbed by ice and is easily absorbed by water, and any of water and ice. The irradiation step of irradiating the object with near-infrared light of at least three wavelengths that are absorbed to the same degree from the light source, and the irradiated near-infrared light of each wavelength is reflected by the object. A detection step for detecting the reflected light, and a calculation processing step for determining the road surface state by calculating the detected amount of reflected light.

  Further, the present invention has the same wavelength for both water and ice, the wavelength that is difficult to absorb for both water and ice, the wavelength that is difficult for water to absorb and that is easily absorbed for water. A light source for irradiating the object with near infrared light of at least three wavelengths of wavelengths absorbed to the extent, and detection means for detecting reflected light reflected by the object with the irradiated near infrared light of each wavelength And arithmetic processing means for determining a road surface state by performing arithmetic processing on the detected amount of reflected light.

  Next, the present invention will be described in detail.

  First, the details of light absorption by water and ice, which are the basis of the present invention, will be described.

  When the material is irradiated with light, the energy state of the atoms constituting the material changes from the ground state to the excited state, and at this time, energy is absorbed. The absorbed energy tries to return to the original ground state when light irradiation is stopped, and light corresponding to the absorbed light is emitted. The frequency of absorption and emission of light is very selective with respect to the type and structure of atoms and molecules, and it is widely known that the absorption and emission spectra of light can be used for substance identification and quantification. .

  In the case of water and ice used in the present invention, as shown in FIG. 3, the water has an absorption spectrum peak or transmittance bottom at wavelengths of 0.98 μm, 1.20 μm, 1.45 μm and 1.93 μm. Similarly, ice has absorption spectrum peaks or transmittance bottoms at wavelengths of 1.03 μm, 1.25 μm, 1.50 μm and 1.99 μm. Thus, by measuring the water and ice having different absorption and transmittance depending on the wavelength, it is possible to discriminate the water and ice as the objects.

  The relationship between the absorbance and the transmittance in this case can be derived from the following equation (1) based on Lambert-Beer's law.

A = log (I0 (λ) / It (λ)) (1)
A: Absorbance, I0 (λ): Incident light amount, It (λ): Light amount after passing through the substance. Actually, in addition to the absorption wavelength of water and ice, other wavelengths not affected by water or ice Light is irradiated as reference wavelength light, and the incident light quantity I0 including the influence of the surface state, particle size, etc. of the substance is regarded as the light quantity by the reference wavelength. Light of other wavelengths that are not affected by the moisture is irradiated as reference wavelength light, and the amount of reflected light is measured. The amount of water can be determined by putting this measured value into the following equation (2).

W = a0 + a1 · In (R / s) (2)
s: Reflected light amount of absorption wavelength light a0: Constant R: Reflected light amount of reference wavelength light a1: Proportional constant W: Water content (%)
Next, a method for determining the road surface condition will be described.

  The criteria for determining the dryness (Dry), wetness (Wet, Water), freezing (Ice), snow cover (Snow), and thaw (slush) of the road surface are determined by the position in the matrix shown in FIG. The

  In FIG. 6, the horizontal axis represents the water absorption normalized by I (λ2) / (I (λ1) −I (λ3)), and the vertical axis represents I (λ1) / I (λ3) from the road surface. Whether or not the snow quality is determined by the amount of reflected light.

  According to the present invention, the wavelength that is difficult to absorb for both water and ice, the wavelength that is difficult to absorb for ice and easy to absorb for water, and the same for both water and ice. The road surface state can be determined by detecting reflected light obtained by reflecting near-infrared light of at least three wavelengths of wavelengths absorbed to the extent by the object and performing arithmetic processing as described above.

  Therefore, since the wavelength at which each absorption of water and ice reaches its peak is not used, accurate measurement can be performed without being affected by the peak position of the absorption wavelength of water that varies with temperature. In addition, since the wavelength at which each absorption of water and ice becomes the bottom is not used, a difference in transmittance between one material and the other material can be ensured, so that accurate measurement can be performed. .

  In this invention, you may comprise so that the said near-infrared light may be irradiated from the light source which each outputs the light of at least 3 different single wavelength separately.

  In the present invention, all of the light sources that output light of at least three different single wavelengths may be arranged in one package, and the light from these light sources may be collimated or condensed by optical components. In this case, since all the light sources are arranged in one package, it is possible to measure with a small device.

  In the present invention, a light emitting diode may be used as the light source. In this case, unlike the case where a semiconductor laser is used, there is no need to add a circuit in order to keep the optical output constant. Therefore, the apparatus can be reduced in size. Further, unlike the case of using a lamp light source having a broad spectrum, it is not necessary to increase the amount of light emitted from the light source, and the apparatus can be miniaturized and energy efficiency can be improved.

  In the present invention, a light receiving element having one light receiving surface may be used for detecting the reflected light. In this case, measurement can be performed with a small device, and the cost can be reduced.

  In this invention, you may have a correction means for hold | maintaining the optical distance with respect to the road surface of the light-receiving surface of the said light receiving element. As the correcting means, for example, the objective lens used for collimation or condensing is moved in the direction of the optical axis so that it is always focused on the collimated light or the road surface.

  In the present invention, the timing of irradiating the object with near-infrared light of at least three wavelengths may be set by sequentially controlling each of the light sources with a trigger pulse. In this case, each light source can be irradiated with a single drive circuit, and the number of parts can be reduced. Even if the number of light sources is increased in order to increase accuracy, there is no need to increase the number of drive circuits. Furthermore, energy efficiency can be improved by pulse driving.

  In the present invention, the total time or measurement time during which the object is irradiated by the sequential control of each light source may be 50 μs to 10 ms.

  In the present invention, the timing of irradiating the object with near-infrared light of at least three wavelengths is within the time when light of a wavelength that is difficult to be absorbed by both water and ice is lit. Light with a wavelength that is less likely to be absorbed with respect to water and light with a wavelength that is absorbed to the same extent with respect to both water and ice Thus, the light quantity may be measured when the light of each wavelength is turned on and off. In this case, measurement can be performed in a short time.

  Information detected by the present invention may be fed back to various vehicle control devices. In this case, the vehicle can be controlled safely.

  ADVANTAGE OF THE INVENTION According to this invention, the road surface state can be measured with high precision in real time, and a small and energy efficient road surface state measuring method and apparatus can be provided.

  Embodiments of the present invention will be described below with reference to the drawings.

  The road surface condition detection apparatus 1 according to this embodiment has a wavelength λ1 that is difficult to absorb for both water and ice, a wavelength λ2 that is difficult to absorb for ice and is easily absorbed for water, A light source 2 that irradiates the object with near-infrared light having a wavelength λ3 that is absorbed to the same extent with respect to any of the ice, and the irradiated near-infrared light of each wavelength is reflected by the object. A light-receiving element 3 that detects the reflected light and a calculation device 4 that determines the road surface state by calculating the detected amount of reflected light (see FIG. 1).

  The light source 2 is composed of near-infrared light emitting diodes 21, 22 and 23 having three wavelengths (wavelengths λ 1, λ 2 and λ 3), and these near-infrared light emitting diodes 21, 22 and 23 are mounted in one package 24. (See FIG. 2).

  These three wavelengths (wavelengths λ1, λ2, and λ3) are obtained by utilizing the fact that the ice transmittance does not vary with respect to temperature, and as shown in FIG. 3, the wavelength λ2 immediately before the ice transmittance decreases. (In FIG. 3, 1.40 to 1.42 μm), the wavelength λ3 (in the vicinity of 1.47 μm in FIG. 3) at which the transmittance of water and ice is almost the same, and the wavelength λ1 having good transmittance for water and ice The wavelength is 1.14 μm or less in FIG.

  These near-infrared light emitting diodes 21, 22 and 23 emit light sequentially as shown in FIG. 4, and near-infrared light is irradiated onto the road surface x through the beam splitter 5 and the lens 6.

  Then, the reflected light obtained by reflecting the irradiated near-infrared light of each wavelength on the road surface x is detected by the light receiving element 3, and the detected reflected light amount is arithmetically processed by the arithmetic unit 4 to determine the road surface state. The

  As the light receiving element 3, an InGaAs PIN photodiode is used, and the output of the light receiving element 3 is input to the arithmetic unit 4 as a voltage signal.

  That is, the reflected light from the road surface x enters the light receiving element 4, is photoelectrically converted and amplified by an amplifier (not shown) in the arithmetic unit 4 at the subsequent stage, and then an A / D converter (not shown). ), And the road surface state is determined from the calculation processing result and displayed on the display device 7.

  In this embodiment, at least three types of near-infrared light emitting diodes 21, 22, and 23 are necessary. However, since only one light receiving element 3 is required, this contributes to downsizing and low cost of the apparatus. In addition, the sequential processing as described above can contribute to a reduction in the number of components because only one drive circuit for the light emitting diode is required. Further, even when the number of light sources 2 is increased in order to increase accuracy, it is only necessary to increase the number of near-infrared light emitting diodes, and it is not necessary to increase the number of light receiving elements 3 and driving circuits.

  However, at the light emission timing by the sequential processing as described above, it is conceivable that the object to be measured by the reference light and the measurement light of water or ice is different during high-speed movement. Actually, if the vehicle moves at a speed of 60 km / h, the movement amount is about 17 mm in 1 ms. Therefore, as another embodiment described above, the light-emitting diode 21 for reference light is always turned on, and only the light-emitting diodes 22 and 23 for other measurement objects are sequentially turned on and off, thereby shortening the measurement time. Yes (see FIG. 5).

  In this method, the reference light (λ1) is always applied to the road surface x, the amount of reflected light is detected by the light receiving element 3, and the output signal of the light receiving element 3 is monitored by the arithmetic unit 4. The arithmetic device 4 compares the output signal of the light receiving element 3 with the average value of the front and rear reference light levels, calculates the absorbance due to the wavelength, and determines whether the road surface x is wet or frozen. When performing such a sequential process, it is necessary to design so that the light receiving element 3 may not be saturated.

  Next, the arithmetic processing in the arithmetic device 4 will be specifically described.

  When the reflected light amount from the road surface x of each wavelength is detected and the measured values are I (λ1), I (λ2), and I (λ3), they are set from the respective calculation results as shown in FIG. The road surface condition is determined in light of the determination criteria.

  The discrimination method will be described. As described above, the determination results of the dry (Dry), wet (Wet, Water), freezing (Ice), snow cover (Snow), and thaw (slush) are shown in FIG. Judgment is made according to which position in the matrix shown in FIG.

  In FIG. 6, the horizontal axis represents the water absorption normalized by I (λ2) / (I (λ1) −I (λ3)), and the vertical axis represents I (λ1) / I (λ3) from the road surface. Whether it is snowy or not is determined by the amount of reflected light.

  In this embodiment, the maximum and minimum amounts of reflected light are obtained at two wavelengths that are not affected by water or ice, and water and ice are distinguished at wavelengths having different amounts of reflected light due to differences in absorption between water and ice. There is a feature.

  Note that the example shown in FIG. 6 is one of the determination examples, and the determination method can be changed according to the purpose of determining the road surface condition. That is, depending on the purpose, it is also possible to make a determination by another combination of I (λ1), I (λ2), and I (λ3).

  As an example of use of the road surface state measuring apparatus 1 according to the present invention, information on road surface state determination results can be provided to various vehicle control devices.

  In addition, when mounting on a vehicle, as shown in FIG. 7, the light emitting / receiving device may be installed near the bumper in the traveling direction, but more preferably, by installing a plurality of devices near the front of the tire. It is possible to really know the condition of the road surface through which the tire passes. In particular, it is possible to control the car safely by issuing effective warnings and giving feedback to the control system because the information on the left and right, front and rear tires can be found in the Sanin curve and easy-to-freeze places. .

  Furthermore, by automatically judging the road surface condition during auto cruise function and driving of an automatic vehicle, it is possible to control various drive systems and control the slip warning as a parameter for driving speed control, including suppression of brake system and sudden handle operation. You may make it feed back to the safety device of a lamp display.

  Furthermore, as another application example, by providing road surface information from a vehicle equipped with the device of the present invention to a network, another vehicle connected by the network receives the road surface information, and an information system such as car navigation It is also possible to utilize it effectively.

  INDUSTRIAL APPLICABILITY The present invention can be effectively used for a road surface state measuring method and apparatus that provide road surface information to a driver, each control device, and the like.

It is the schematic which shows an example of the road surface state measuring apparatus of this invention. It is the schematic which shows the structure of the light-emitting device of the road surface state measuring apparatus shown in FIG. It is a figure which shows the transmittance | permeability characteristic of water and ice. It is a figure which shows light emission and the data reading timing of each light emitting diode in embodiment of this invention. It is a figure which shows the other example of light emission of each light emitting diode in embodiment of this invention, and data reading timing. It is a figure which shows the matrix for discrimination | determination of the road surface state in embodiment of this invention. It is a figure which shows the example which mounted the road surface state measuring apparatus of this invention in the vehicle. It is the schematic which shows the conventional road surface state measuring apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Road surface state measuring apparatus 2 Light source 21, 22, 23 Near-infrared light emitting diode 3 Light receiving element (detection means)
4. Arithmetic unit (arithmetic processing means)
5 Beam splitter 6 Collimating lens x Road surface

Claims (11)

Wavelengths that are difficult to absorb for both water and ice, wavelengths that are hard to absorb for ice and easy for water, and wavelengths that are absorbed to the same extent for both water and ice An irradiation step of irradiating an object with near-infrared light having at least three wavelengths of
A detection step of detecting the reflected light reflected by the object with the irradiated near-infrared light of each wavelength;
A road surface state measuring method comprising: an arithmetic processing step of determining a road surface state by processing the detected amount of reflected light. Wavelengths that are difficult to absorb for both water and ice, wavelengths that are hard to absorb for ice and easy for water, and wavelengths that are absorbed to the same extent for both water and ice A light source that irradiates an object with near-infrared light of at least three wavelengths of:
Detecting means for detecting the reflected light of the irradiated near-infrared light of each wavelength reflected by the object;
A road surface state measuring apparatus comprising: arithmetic processing means for determining a road surface state by performing arithmetic processing on the detected amount of reflected light.   3. The road surface state measuring method or the road surface state measuring device according to claim 1, wherein the near infrared light is irradiated from a light source that individually outputs at least three light beams having different single wavelengths.   The light source that outputs the light of at least three different single wavelengths is disposed in one package, and the light from the light source is collimated or condensed by an optical component. Road surface state measuring method or road surface state measuring device.   The road surface state measuring method or the road surface state measuring apparatus according to any one of claims 1 to 4, wherein the light source uses a light emitting diode.   The road surface state measuring method or the road surface state measuring apparatus according to claim 1, wherein a light receiving element having one light receiving surface is used for detecting the reflected light.   The road surface state measuring method or the road surface state measuring apparatus according to claim 6, further comprising a correcting unit for maintaining an optical distance of the light receiving surface of the light receiving element with respect to the road surface.   8. The timing of irradiating an object with near-infrared light of at least three wavelengths is set by sequentially controlling each of the light sources with a trigger pulse. 9. Road surface state measuring method or road surface state measuring device.   9. The road surface state measuring method or the road surface state measuring device according to claim 8, wherein a total time or measurement time for irradiating the object by sequential control of each light source is 50 [mu] s to 10 ms.   The timing of irradiating the object with near-infrared light of at least three wavelengths is within the time when light of a wavelength that is difficult to be absorbed by both water and ice is lit, Light that has a wavelength that is not easily absorbed and is easily absorbed by water, and light that has a wavelength that is absorbed to the same extent by both water and ice, are set to alternately turn on and off. 10. The road surface state measuring method or the road surface state measuring device according to claim 1, wherein the light amount is measured when the light of each wavelength is turned on and off.   A road surface state measuring method or a road surface state measuring device, wherein information detected by the method or device according to claim 1 is fed back to various vehicle control devices.

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