JP7039323B2 - Road surface condition determination device, road surface condition determination method and road surface condition determination program - Google Patents

Description

The present invention relates to a road surface condition discriminating device for discriminating an object existing on the road surface, a road surface condition discriminating method, and a road surface condition discriminating program.

Conventionally, there is known a technique of receiving a reflected wave reflected on a road surface by a receiving antenna and determining freezing of the road surface based on the reflected amount of the reflected wave (see Patent Document 1). In Patent Document 1, the distance between the road surface and the receiving antenna (distance between the point A and the road surface) is fixed, and when the voltage output by the receiving antenna changes, the reflectance on the road surface changes and becomes wet from a dry state. It is disclosed that it is determined that the state has changed (Fig. 2, paragraph 0019).

Japanese Unexamined Patent Publication No. 2001-235555

In the measurement mode as in Patent Document 1, the combined electric field of the transmitted wave and the reflected wave is measured. The measured combined electric field is simultaneously affected by not only the amplitude change of the reflected wave but also the phase change of the standing wave according to the road surface condition. Therefore, in the discrete measurement by the fixed sensor as in Patent Document 1, the influence of the amplitude change of the reflected wave and the phase change of the standing wave cannot be separated, so that the road surface state cannot be discriminated with high accuracy.

The present invention is intended to solve the above-mentioned problem, and an object of the present invention is to provide a technique capable of discriminating an unknown road surface condition with high accuracy.

In order to achieve the above object, the road surface condition determination device of the present invention has a transmission / reception shared antenna that transmits radio waves to the road surface and receives reflected waves generated by reflection of radio waves from the road surface, and a predetermined moving section. Within, a moving unit that moves the antenna so that the height of the antenna with respect to the road surface changes, and a discriminant unit that determines the road surface state based on the amplitude of the reflected wave received by the antenna when moving in the moving section. Be prepared.

In the above configuration, the antenna is shared for transmission and reception, and the circulator has a function of separating the transmission and reception signals, but the separation between transmission and reception is not perfect, and there is a component in which the transmission wave wraps around the reception circuit. Therefore, when the reflected wave is received, it is combined with the wraparound signal, and the amplitude of the combined electric field increases or decreases not only by the amplitude change of the reflected wave but also by the position on the propagation direction axis of the radio wave (phase of the standing wave). In such a situation, even if the road surface condition is unknown, the maximum and minimum amplitudes of the combined electric field of the reflected wave and the wraparound signal can be obtained by moving the antenna within the moving section and performing continuous measurement. be able to. Further, the change in the difference between the maximum value and the minimum value of the amplitude of the combined electric field is proportional to the change in the amplitude of the reflected wave and does not depend on the change in the amplitude due to the phase of the standing wave (spatial standing wave method). That is, since the change in the amplitude of the reflected wave can be measured from the increase / decrease in the difference between the maximum value and the minimum value of the amplitude of the combined electric field of the reflected wave and the wraparound signal, the unknown road surface condition can be discriminated with high accuracy.

The length of the moving section may be ½ or more of the wavelength of the radio wave transmitted by the antenna. Here, the spatial period in which the maximum value of the amplitude of the combined electric field of the reflected wave and the wraparound signal is continuous and the spatial period in which the minimum value is continuous are 1/2 of the wavelength of the radio wave transmitted by the antenna, and the maximum value and the minimum value are The alternating continuous spatial period is 1/4 of the wavelength of the radio wave. Therefore, by setting the length of the moving section to 1/2 or more of the wavelength of the radio wave transmitted by the antenna, the antenna makes the position where the amplitude of the combined electric field becomes the maximum value and the position where the amplitude becomes the minimum value at least once. Can be made to pass.

Further, the length of the moving section may be 1/2 of the wavelength of the radio wave transmitted by the antenna. As a result, the antenna can pass through the position where the amplitude of the combined electric field of the reflected wave and the wraparound signal becomes the maximum value and the position where the amplitude becomes the minimum value once, and the length of the moving section can be kept to a minimum. can. Therefore, it is possible to suppress the required period for determining the road surface condition.

Further, the discriminator may discriminate the road surface state based on the difference frequency component (low frequency component) obtained by multiplying the radio wave transmitted by the antenna and the combined electric field of the reflected wave and the wraparound signal (heterodyne detection method). ). In particular, when there is no frequency change between the transmitted radio wave and the reflected wave, the amplitude of the combined electric field can be taken out as a DC voltage. Further, in a situation where there is a frequency change, not only the road surface condition but also the vehicle on the road surface can be detected by the Doppler effect, and the road surface condition discriminating device can also serve as the vehicle detection device. Therefore, the Doppler sensor used in a general vehicle detection device can be diverted to the road surface condition determination device.

It is explanatory drawing about the generation of a standing wave. It is a block diagram of a road surface condition discriminator. It is a schematic diagram of a Doppler sensor. 4A to 4C are graphs of the output voltage of the Doppler sensor. It is a flowchart of a road surface condition determination process. 6A to 6C are graphs of the output voltage of the Doppler sensor.

Here, embodiments of the present invention will be described in the following order.
(1) Explanation of the generation of standing waves:
(2) Configuration of road surface condition determination device:
(3) Road surface condition determination process:
(4) Vehicle detection:

(1) Explanation of the generation of standing waves:
First, the relationship between the height L of the transmitting antenna 1 and the receiving antenna 2 and the standing wave will be described. As shown in FIG. 1, the transmitted wave (electric field) and the reflected wave (electric field) are represented by E _i and _Er , respectively, the reflection coefficient of the road surface R is represented by Γ, and the wavelength of the transmitted wave in the height direction is represented by λ. k ₀ represents the wave number of the transmitted wave, and k ₀ = 2π / λ. The combined electric field E of the transmitted wave E _i and the reflected wave E _r at an arbitrary position Z in the height direction with the positions of the transmitting antenna 1 and the receiving antenna 2 as the origin is at an arbitrary position Z as shown in the following equation (1). It can be represented by a function.

前記の（２）式に示すように、送信波Ｅ_iと反射波Ｅ_rの合成電界Ｅの振幅は高さＬ方向において波長λの１／２の長さの空間周期を持つこととなる。すなわち、送信波Ｅ_iと反射波Ｅ_rの合成電界Ｅの振幅が最大値となる位置の間隔は送信波の波長λの１／２となり、最小値となる位置の間隔も送信波の波長λの１／２となる。また、最大値となる位置と最小値となる位置との間隔は、送信波の波長λの１／４となる。このことから、送信波Ｅ_iと反射波Ｅ_rの合成電界Ｅは定在波であることが分かる。 According to the above equation (1), the amplitude (absolute value) of the combined electric field E of the transmitted wave E _i and the reflected wave _Er at the position (Z = 0) of the receiving antenna 2 can be expressed by the following equation (2). .. φ represents the initial phase.

As shown in the above equation (2), the amplitude of the combined electric field E of the transmitted wave E _i and the reflected wave E _r has a spatial period having a length of 1/2 of the wavelength λ in the height L direction. That is, the distance between the positions where the amplitude of the combined electric field E of the transmitted wave E _i and the reflected wave E _r becomes the maximum value is 1/2 of the wavelength λ of the transmitted wave, and the distance between the positions where the amplitude becomes the minimum value is also the wavelength λ of the transmitted wave. It becomes 1/2 of. Further, the distance between the position where the maximum value is reached and the position where the minimum value is reached is 1/4 of the wavelength λ of the transmitted wave. From this, it can be seen that the combined electric field E of the transmitted wave E _i and the reflected wave E _r is a standing wave.

(2) Configuration of road surface condition determination device:
FIG. 2 shows a schematic configuration of the road surface condition discriminating device 10 according to the present embodiment. In the figure, the road surface condition determination device 10 includes a control unit 20, a recording medium 30, a drive device 40, a Doppler sensor 50, a communication unit 60, and a support unit 70.

The support portion 70 is a structure for supporting the drive device 40 and the Doppler sensor 50 on the road surface R. The support portion 70 supports the drive device 40 and the Doppler sensor 50 on the traveling lane in which the vehicle travels. The drive device 40 is interposed between the support portion 70 and the Doppler sensor 50, and moves the Doppler sensor 50 up and down in the vertical direction. The mechanism for the drive device 40 to move the Doppler sensor 50 is not particularly limited. The communication unit 60 is a communication circuit for communicating with an external server or the like. For example, the communication unit 60 transmits data or the like indicating the road surface condition determined by the control unit 20 to a server that manages road information.

FIG. 3 is a schematic diagram of the Doppler sensor 50. The Doppler sensor 50 includes an oscillator 51, a distributor 52, a circulator 53, a transmission / reception shared antenna 54 (hereinafter, simply referred to as an antenna 54), a multiplier 55, and an amplifier 56. The oscillator 51 is an oscillator that generates a transmitted wave E _i that periodically vibrates at a predetermined frequency. In this embodiment, the oscillator 51 generates a transmitted wave E _i of 24.15 GHz. The distributor 52 distributes the transmitted wave E _i to the antenna 54 and the multiplier 55. The circulator 53 switches between transmission and reception of radio waves from the antenna 54. The antenna 54 transmits the transmitted wave E _i perpendicularly to the road surface R, and receives the reflected wave E _r reflected by the road surface R. The multiplier 55 multiplies the transmitted wave E _i distributed from the distributor 52 and the reflected wave E _r received by the antenna 54, and outputs a difference frequency signal between them. The amplifier 56 has a role of amplifying the output of the multiplier 55 and filtering high frequency signal components. As a result, among the difference frequency signal components output by the multiplier 55, the low frequency signal component is output from the amplifier 56. At this time, if the road surface to be reflected is stationary and there is no frequency change between the transmitted wave E _i and the reflected wave E _r , the amplitude of the reflected wave E _r is output as a DC signal component.

In the present embodiment, the circulator 53 has a function of separating the transmitted / received signals, but the separated of the transmitted / received signals is not perfect, and there is a component (wrap-around signal E _c ) in which the transmitted wave E _i wraps around the receiving circuit. That is, since the combined electric field E _m of the reflected wave E _r and the wraparound signal E _c is input to the multiplier 55 of the Doppler sensor 50 of the embodiment, the amplitude of the combined electric field E _m of the reflected wave E _r and the wraparound signal E _c . Is output from the multiplier 55.

また、前記の（３）式により、反射波Ｅ_rと回り込み信号Ｅ_cの合成電界Ｅ_mの振幅（絶対値）は、次の式によって求めることができる。

よって、（４）式のように、反射波Ｅ_rと回り込み信号Ｅ_cの合成電界Ｅ_mの振幅は、送信波Ｅ_iと反射波Ｅ_rの合成電界Ｅと同様の空間周期を持つ関数で表すことができる。このことから、反射波Ｅ_rと回り込み信号Ｅ_cの合成電界Ｅ_mは定在波の性質を持つことが分かる。 Next, the combined electric field E _m of the reflected wave E _r and the wraparound signal E _c obtained by synthesizing the reflected wave E _r and the wraparound signal E _c will be described. As shown in FIG. 1, the combined electric field E _m of the reflected wave E _r and the wraparound signal E _c at the antenna position (L = 0) obtained by the heterodyne type Doppler sensor 50 is such that the transmitting antenna 1 and the receiving antenna 2 are independent. Unlike the combined electric field E of the transmitted wave E _i and the reflected wave E _r when the antenna 54 is provided, when the reflected wave E _r is input to the antenna 54, it is combined with the wraparound signal E _c , and _Em = E _c + _Er. The combined electric field E _m of the reflected wave E _r and the wraparound signal E _c will be measured. Therefore, the combined electric field E _m of the reflected wave E _r and the wraparound signal E _c at the position of the antenna 54 (L = 0) is expressed by the following equation.

Further, the amplitude (absolute value) of the combined electric field E _m of the reflected wave _Er and the wraparound signal E _c can be obtained by the above equation (3) by the following equation.

Therefore, as shown in Eq. (4), the amplitude of the combined electric field E _m of the reflected wave E _r and the wraparound signal E _c is a function having the same spatial period as the combined electric field E of the transmitted wave E _i and the reflected wave E _r . Can be represented. From this, it can be seen that the combined electric field E _m of the reflected wave _Er and the wraparound signal E _c has the property of a standing wave.

As shown in FIG. 3, the height L of the antenna 54 with respect to the road surface R is variable by moving the Doppler sensor 50 by the drive device 40. The drive device 40 moves the antenna 54 so that the height L changes within the moving section W, which is a section between the lower limit height L2 and the upper limit height L1. The Doppler sensor 50 when the upper limit height L1 is reached is shown by a solid line, and the Doppler sensor 50 when the lower limit height L2 is reached is shown by a broken line. The length M of the moving section W is the length obtained by subtracting the lower limit height L2 from the upper limit height L1. The height L of the antenna 54 is represented by the amount of descent m from the upper limit height L1.

The control unit 20 shown in FIG. 2 is a computer composed of a CPU, ROM, and RAM (not shown), and executes processing necessary for determining the road surface state using various information recorded on the recording medium 30. As shown in FIG. 2, the control unit 20 executes the road surface condition determination program 21. The software configuration of the road surface condition determination program 21 will be described later. The control unit 20 is connected to the Doppler sensor 50 and the drive device 40.

The recording medium 30 records the measurement data 30a and the threshold data 30b. The measurement data 30a is data in which the values measured by the control unit 20 are temporarily recorded. The threshold value data 30b is data indicating a discrimination threshold value for discriminating the road surface state.

The road surface condition determination program 21 includes a movement module 21a and a determination module 21b. The control unit 20 that executes the moving module 21a and the discriminating module 21b constitutes the moving unit and the discriminating unit of the present invention.

By the function of the movement module 21a, the control unit 20 moves the antenna 54 so that the height L of the antenna 54 with respect to the road surface R changes within the predetermined movement section W. Specifically, the control unit 20 controls the drive device 40 so that the amount of descent m from the upper limit height L1 of the antenna 54 increases by a minute amount Δm by the function of the mobile module 21a. Then, the control unit 20 ends the movement of the Doppler sensor 50 when the amount of descent m from the upper limit height L1 of the antenna 54 becomes equal to the length M of the movement section W.

Next, the output voltage _Ed of the Doppler sensor 50 will be considered. As described above, the Doppler sensor 50 is a heterodyne type detector including a multiplier 55 and an amplifier 56, and a low frequency signal component is output from the amplifier 56 among the difference frequency signal components output by the multiplier 55. Will be done. At this time, if the road surface to be reflected is stationary and there is no frequency change between the transmitted wave E _i and the reflected wave E _r , the amplitude of the combined electric field E _m of the reflected wave E _r and the wraparound signal E _c is amplified. The voltage is output as the output voltage _Ed . Therefore, by measuring the output voltage E _d of the Doppler sensor 50, it is possible to measure the amplitude of the combined electric field E _m of the reflected wave E _r and the wraparound signal E _c .

4A to 4C are _graphs showing the output voltage Ed of the Doppler sensor 50 at an arbitrary height L. In _FIGS . 4A to 4C, the horizontal axis indicates the height L, and the vertical axis indicates the output voltage Ed of the Doppler sensor 50. As shown in _FIGS . 4A to 4C, the output voltage Ed of the Doppler sensor 50 is a periodic function of height L, and its spatial period is 1/2 of the wavelength λ of the transmitted wave E _i . 4A to 4C are plots of the results of experimentally investigating the output voltage _Ed at a position higher than the upper limit height L1.

Next, FIGS. 4A to 4C are compared. In FIGS. 4A to 4C, the output of the Doppler sensor 50 when the transmitted wave E _i is transmitted to each of the metal plate (black solid line), the water film (gray solid line), and the ice film (black broken line) having a thickness of 2 mm. The voltage _Ed is shown. FIG. 4A shows the output voltage E _d of the Doppler sensor 50 when the transmitted wave E _i is transmitted to each of the metal plate, the water film, and the ice film on the acrylic container on which the metal plate is laid below. FIG. 4B shows the output voltage E _d of the Doppler sensor 50 when the transmitted wave E _i is transmitted to each of the metal plate, the water film, and the ice film on the acrylic container on which the metal plate is not laid below. FIG. 4C shows the output voltage E _d of the Doppler sensor 50 when the transmitted wave E _i is transmitted to each of the metal plate, the water film, and the ice film on the asphalt piece on which the metal plate is not laid below. Note that FIG. _4C shows the output voltage Ed in the situation closest to the actual road surface R.

From _FIGS . 4A to 4C, it can be seen that the output voltage Ed is deviated not only from the magnitudes of the maximum value and the minimum value but also from their positions (phases) according to the reflection coefficient Γ. However, the spatial period of the output voltage E _d does not depend on the reflection coefficient Γ, and the maximum and minimum values of the output voltage E _d appear for every 1/2 of the wavelength λ of the transmitted wave E _i . There is no change.

In the present embodiment, the length M of the moving section W is ½ of the wavelength λ of the transmitted wave E _i . That is, the length M of the moving section W has the same length as the spatial period of the combined electric field E _m of the reflected wave E _r as the output voltage E _d of the Doppler sensor 50 and the wraparound signal E _c . When the frequency of the transmitted wave E _i is 24.15 GHz as in the present embodiment, the length M of the moving section W is about 6.2 mm.

As described above, since the spatial period of the output voltage _Ed of the Doppler sensor 50 does not depend on the reflection coefficient Γ, the length M of the moving section W can be set even if the reflection coefficient Γ of the road surface R is unknown. Of the heights L shown in _FIGS . 4A to 4C, the section having the lowest height L is set as the moving section W, and the section where the output voltage Ed of the Doppler sensor 50 is the least attenuated is set. It is set as a moving section W. The moving section W is preferably closer to the road surface R, but is provided at a position higher than the maximum vehicle height of a vehicle that can travel on the road surface R.

By the function of the discrimination module 21b, the control unit 20 discriminates the road surface state based on the maximum value and the minimum value of the intensity of the standing wave _Em received by the antenna 54 when moving in the moving section W. Hereinafter, the function of the discrimination module 21b will be described with reference to the flowchart of the road surface condition discrimination process.

(3) Road surface condition determination process:
FIG. 5 is a flowchart of the road surface condition determination process. First, the control unit 20 resets the descending amount m to 0 by the function of the moving module 21a (step S100). That is, as shown by the solid line in FIG. 3, the control unit 20 resets the descending amount m so that the height L of the antenna 54 becomes the upper limit height L1. Next, the control unit 20 moves the Doppler sensor 50 by the function of the movement module 21a (step S105). That is, the control unit 20 drives the drive device 40 so that the height L of the antenna 54 becomes a height corresponding to the descending amount m. The control unit 20 stops the movement of the Doppler sensor 50 when the height L of the antenna 54 reaches a height corresponding to the descending amount m.

Next, the control unit 20 starts transmitting the transmission wave E _i by the function of the discrimination module 21b (step S110). That is, the control unit 20 controls the Doppler sensor 50 so as to transmit the transmission wave E _i to the road surface R. Next, the control unit 20 receives the reflected wave _Er by the function of the discrimination module 21b (step S120). That is, the control unit 20 receives the reflected wave _Er at the antenna 54 of the Doppler sensor 50. As a result, among the difference frequency signal components obtained by multiplying the transmitted wave E _i , the reflected wave E _r , and the combined electric field E _m of the wraparound signal E _c , the amplified low frequency signal component is the Doppler sensor 50. It is output as the output voltage _Ed of.

Next, the control unit 20 acquires the output voltage _Ed of the Doppler sensor 50 by the function of the discrimination module 21b (step S130). As described above, when the road surface to be reflected is stationary and there is no frequency change between the transmitted wave E _i and the reflected wave E _r , the output voltage E _d of the Doppler sensor 50 is the reflected wave E _r and the wraparound signal E r. It is a DC voltage having a magnitude proportional to the amplitude of the combined electric field E _m of _c .

Next, the control unit 20 records the output voltage _Ed of the Doppler sensor 50 by the function of the discrimination module 21b (step S140). That is, the control unit 20 records the output voltage Ed of the Doppler sensor 50 in the measurement data _30a of the recording medium 30.

Next, the control unit 20 determines whether or not the descending amount m is equal to the length M of the moving section W by the function of the moving module 21a (step S150). That is, the control unit 20 determines whether or not the height L of the antenna 54 has dropped to the lower limit height L2.

When it is not determined that the descending amount m is equal to the length M of the moving section W (step S150: N), the control unit 20 adds a small amount Δm to the descending amount m by the function of the moving module 21a (step S160). ). Here, the minute amount Δm is the length obtained by dividing the length M of the moving section W by a predetermined natural number (for example, 10 to 20).

Next, the control unit 20 returns to step S105. By performing the above loop processing (steps S105 to S160), the amplitude of the combined electric field E _m of the reflected wave E _r and the wraparound signal E _c obtained at each position of each minute amount Δm in the moving section W can be obtained. It can be accumulated in the measurement data 30a.

6A to 6C are _graphs showing the output voltage Ed of the Doppler sensor 50 in the moving section W. In _FIGS . 6A to 6C, the horizontal axis indicates the height L, and the vertical axis indicates the output voltage Ed of the Doppler sensor 50. In the measurement data 30a, the output voltage Ed of the Doppler sensor 50 shown in _FIGS . 6A to 6C is recorded. 6A to 6C show the output voltage Ed of the Doppler sensor 50 under the same conditions as those of _FIGS . 4A to 4C, respectively.

However, by setting the length M of the moving section W to ½ of the wavelength λ of the transmitted wave E _i , the maximum and minimum values of the output voltage E _d of the Doppler sensor 50 are recorded in the measurement data 30a. Can be done. That is, when the maximum and minimum values of the output voltage _Ed recorded in the measurement data 30a are measured, the antenna 54 is present at each position. Since the road surface condition is unknown, the position where the amplitude of the combined electric field E _m of the reflected wave E _r and the wraparound signal E _c becomes the maximum and minimum values is unknown, but the antenna 54 is used only for the length M of the moving section W. By moving it, the maximum and minimum values of the output voltage _Ed and their positions can be obtained.

For example, in FIG. 6C, which is the closest to the actual road surface R situation, the phase of the output voltage Ed of the Doppler sensor 50 in the water film shown by the gray solid line and the output voltage E of the _Doppler sensor 50 in the ice film shown by the black dashed line. It is out of phase with _d . However, by securing the length M of the moving section W by half the length of the wavelength λ of the transmitted wave E _i , the maximum value (white square) of the output voltage E _d of the Doppler sensor 50 in the water film can be obtained. The minimum value (black square) can be obtained. Further, even if the water film freezes and changes to an ice film, the maximum value (white triangle) and the minimum value (black triangle) of the output voltage _Ed of the Doppler sensor 50 on the ice film can be obtained.

When it is determined that the amount of descent m is equal to the length M of the moving section W (step S150: Y), the control unit 20 uses the function of the moving module 21a to set the maximum and minimum values of the output voltage _Ed of the Doppler sensor 50. The difference E _dif of is calculated (step S170).

前記の（５）式に示すように、差分Ｅ_difは、反射係数Γに比例した値となっている。 When the difference E _dif is derived from the above equation (2), the difference E _dif can be expressed by the following equation (5). In the above equation (2), when cos (2k ₀ L−φ) becomes 1, the amplitude of the combined electric field E _m of the reflected wave _Er and the wraparound signal E _c becomes the maximum value, and the Doppler sensor 50 has a maximum value. The output voltage E _d becomes the maximum value. On the other hand, when cos (2k ₀ L−φ) becomes -1, the amplitude of the combined electric field E _m of the reflected wave _Er and the wraparound signal E _c becomes the minimum value, and the output voltage E _d of the Doppler sensor 50 becomes the minimum value. It becomes. Further, α is a coefficient representing the amplification factor by the amplifier 56.

As shown in the above equation (5), the difference E _dif is a value proportional to the reflection coefficient Γ.

Next, the control unit 20 determines whether or not the difference E _dif is equal to or greater than the discrimination threshold value by the function of the discrimination module 21b (step S180). Then, when it is determined that the difference E _dif is equal to or greater than the discrimination threshold value (step S180: Y), the control unit 20 determines that the water film exists on the road surface R by the function of the discrimination module 21b (step S190). On the other hand, when it is not determined that the difference E _dif is equal to or greater than the discrimination threshold value (step S180: N), the control unit 20 determines that the ice film exists on the road surface R by the function of the discrimination module 21b (step S200). .. The discrimination threshold can be set in advance by measuring the difference E _dif in the situation where the water film and the ice film exist by an experiment or the like. Further, by determining the threshold value of the difference E _dif , the reflection coefficient Γ can be substantially determined as the threshold value.

(3) Vehicle detection:
Next, vehicle detection will be described. By the function of the discrimination module 21b, the control unit 20 detects the vehicle on the road surface R based on the frequency of the output voltage _Ed . Specifically, the control unit 20 acquires the output voltage _Ed of the Doppler sensor 50 for a certain period of time in a state where the Doppler sensor 50 is fixed at a constant height L by the function of the discrimination module 21b, and the output voltage is within that period. Determine if _Ed has fluctuated. When the transmitted wave E _i is reflected by the vehicle as a moving object, the frequency of the reflected wave E _r changes from the frequency of the transmitted wave E _i due to the Doppler effect, and the output of the multiplier 55 is not DC but the transmitted wave E _i . It becomes a difference frequency component (low frequency component) from the reflected wave _Er . That is, the output voltage _Ed has a frequency component that cannot be removed by the filter of the amplifier 56.

Therefore, the control unit 20 can detect a vehicle moving on the road surface R by the fact that the output voltage _Ed of the Doppler sensor 50 fluctuates. When the output voltage Ed of the Doppler sensor 50 acquired in step _S140 of the road surface condition determination process shown in FIG. 5 fluctuates, the passage of the vehicle is completed and the output voltage Ed of the _Doppler sensor 50 is constant. You may wait until it becomes.

In the present embodiment described above, even in a situation where the road surface condition is unknown and the positions where the maximum and minimum values of the output voltage _Ed of the Doppler sensor 50 are unknown are unknown, the antenna 54 is moved within the moving section. By performing continuous measurement, the maximum and minimum values of the output voltage _Ed can be obtained. The difference between the maximum value and the minimum value of the output voltage E _d is proportional to the amplitude change of the reflected wave E _r , and is not affected by the phase of the standing wave. That is, since the increase / decrease in the amplitude of the reflected wave _Er can be detected from the increase / decrease in the difference between the maximum value and the minimum value of the output voltage E _d , the unknown road surface condition can be discriminated with high accuracy.

Further, the length M of the moving section W is ½ of the wavelength λ of the transmitted wave E _i . As a result, the antenna 54 can pass through the position where the output voltage _Ed becomes the maximum value and the position where the output voltage becomes the minimum value once, and the length M of the moving section W can be kept to a minimum. Therefore, it is possible to suppress the required period for determining the road surface condition.

Further, the control unit 20 determines the road surface state based on the difference E _dif obtained from the output voltage Ed of the Doppler sensor 50, and detects the vehicle on the road surface R based on the frequency of the output voltage _{Ed .} .. As a result, not only the road surface condition but also the vehicle on the road surface R can be detected, and the road surface condition determination device 10 can also serve as the vehicle detection device. Further, the Doppler sensor 50 used in a general vehicle detection device can be diverted to the road surface condition determination device 10.

(4) Other embodiments:
In the above embodiment, the road surface condition is determined based on the difference E _dif obtained from the output voltage _Ed of the Doppler sensor 50, but the reflection coefficient Γ may be calculated based on the above equation (5). Then, the control unit 20 may determine the road surface state by determining the calculated reflection coefficient Γ as a threshold value. Further, the control unit 20 may determine not only the water film or the ice film but also the dry state. Of course, the road surface condition determination device 10 is not limited to the one provided only with the configuration of the above-described embodiment, and for example, a configuration for determining whether or not the road surface condition is dry by infrared light may be added.

Further, the length M of the moving section W does not necessarily have to be 1/2 of the wavelength λ of the transmitted wave E _i , and is secured longer than 1/2 of the wavelength λ in consideration of the error of the position control of the drive device 40. May be done. Further, it is not always necessary to detect the vehicle by using the Doppler sensor 50, and the road surface condition discriminating device 10 may have only a function of discriminating the road surface condition. Further, the road surface condition determination device 10 may not only detect the presence or absence of a vehicle by using the Doppler sensor 50, but also detect the speed of the vehicle based on the frequency of the output voltage _Ed of the Doppler sensor 50. Further, when detecting the speed of the vehicle, the Doppler sensor 50 may be configured to be rotatable so that the transmission direction of the transmission wave E _i is close to the horizontal direction.

In the above embodiment, the output voltage E _d of the Doppler sensor 50 is recorded in step S140, but the amplitude of the output voltage E _d and the combined electric field E _m of the reflected wave E _r and the wraparound signal E _c are in a proportional relationship. Therefore, the combined electric field E _m of the reflected wave _Er and the wraparound signal E _c may be recorded.

The frequency of the transmitted wave E _i does not necessarily have to be 24.15 GHz, and other millimeter wave frequencies such as 76.5 GHz and 79.5 GHz may be adopted. Further, the frequency of the transmitted wave E _i does not necessarily have to be the frequency of the millimeter wave. The length M of the moving section W may be set according to the frequency of the transmitted wave E _i . For example, the frequency of the transmitted wave E _i is selected according to the resolution (minimum moving distance) of the position control of the drive device 40. You may. Further, the frequency of the transmitted wave E _i in which the reflection coefficient Γ changes greatly according to the dielectric constant of the substance on the road surface R to be discriminated may be selected.

The control unit 20 does not necessarily have to move the antenna 54 so that the height L becomes lower in order, and may move the antenna 54 so that the height L becomes higher in order. Further, the control unit 20 does not necessarily have to move the antenna 54 over the entire movement section W, and the output voltage Ed of the _Doppler sensor 50 changes from decreasing to increasing, and the output voltage _Ed of the Doppler sensor 50 changes. The movement of the antenna 54 may be terminated when both the increase and the decrease occur. Therefore, the road surface condition can be discriminated with high accuracy without necessarily moving the antenna 54 over the entire moving section W.

10 ... Road surface condition discrimination device, 20 ... Control unit, 21 ... Road surface condition discrimination program, 21a ... Mobile module, 21b ... Discrimination module, 30 ... Recording medium, 30a ... Measurement data, 30b ... Threshold data, 40 ... Drive device, 50 ... Doppler sensor, 51 ... Oscillator, 52 ... Distributor, 53 ... Circulator, 54 ... Antenna, 55 ... Multiplier, 56 ... Amplifier, 60 ... Communication unit, 70 ... Support unit, E _i ... Transmitted wave, _Er ... Reflection Wave, E ... Combined electric field of transmitted wave E _i and reflected wave E _r , E _c ... Wrap signal, E _m ... Combined electric field of reflected wave E _r and wraparound signal E _c , _Ed ... Output voltage, E _dif ... Difference, L ... height, L1 ... upper limit height, L2 ... lower limit height, R ... road surface, W ... moving section, M ... moving section length, Z ... transmitting antenna 1 and receiving antenna 2 (or antenna 54) are the origins. Arbitrary position in the height direction, m ... descent amount, Γ ... reflection coefficient, Δm ... minute amount

Claims (6)

An antenna for both transmission and reception that transmits radio waves to the road surface and receives reflected waves due to the reflection of the radio waves from the road surface.
A moving unit that moves the antenna so that the height of the antenna with respect to the road surface changes within a predetermined moving section.
A discriminator that determines the road surface condition based on the maximum and minimum amplitudes of the reflected wave received by the antenna when moving in the moving section.
A road surface condition discriminating device. The length of the moving section is ½ or more of the wavelength of the radio wave transmitted by the antenna.
The road surface condition discriminating device according to claim 1. The length of the moving section is ½ of the wavelength of the radio wave transmitted by the antenna.
The road surface condition discriminating device according to claim 1. The discrimination unit is
A difference frequency component (low frequency component) obtained by multiplying the combined electric field of the wraparound signal of the radio wave transmitted by the antenna and the reflected wave and the radio wave transmitted by the antenna is input, and the difference frequency component (low frequency component) is input. The road surface condition is determined based on the difference between the maximum value and the minimum value of (frequency component), and the road surface condition is determined.
A vehicle on the road surface is detected based on the frequency of the difference frequency component (low frequency component).
The road surface condition discriminating device according to any one of claims 1 to 3. This is a road surface condition determination method for determining the road surface condition using a transmission / reception shared antenna that transmits radio waves to the road surface and receives reflected waves due to the reflection of the radio waves from the road surface.
A moving step of moving the antenna so that the height of the antenna with respect to the road surface changes within a predetermined moving section.
A discriminating step of discriminating the road surface condition based on the maximum and minimum values of the amplitude of the reflected wave received by the antenna when moving in the moving section, and a discrimination step.
Road surface condition determination method including. A road surface condition determination program that enables a computer to determine the road surface condition using a transmission / reception shared antenna that transmits radio waves to the road surface and receives reflected waves due to the reflection of the radio waves from the road surface.
A movement function for moving the antenna so that the height of the antenna with respect to the road surface changes within a predetermined movement section.
A discriminating function for discriminating the road surface condition based on the maximum and minimum values of the amplitude of the reflected wave received by the antenna when moving in the moving section.
A road surface condition determination program that makes a computer realize.

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