JP7634377B2 - Vehicle detection device, vehicle detection method, and determination device - Google Patents

Description

The present invention relates to a vehicle detection device, a vehicle detection method, and a determination device.

Patent Document 1 discloses a vehicle detection device that includes light-projecting units arranged on one side of the lane in the width direction and arranged in a plurality of units in the height direction, and light-receiving units arranged in a plurality of units in the height direction, facing the light-projecting units in the width direction across the lane and paired with each light-projecting unit, and that detects whether or not a vehicle is present in the lane based on a light-receiving signal that indicates whether or not the optical axis connecting the detection light projected by the light-projecting units and the light-receiving units that receive the detection light is blocked.

JP 2019-185436 A

However, in a vehicle detection device such as the one described above, in rainy weather, the light projected from the light-projecting unit may be reflected by the road surface and enter the light-receiving unit, which may result in false detection.

The present invention was made in consideration of the above problems, and its main objective is to provide a vehicle detection device, a vehicle detection method, and a determination device that can reduce false detections.

To solve the above problem, a vehicle detection device according to one aspect of the present invention includes a light-projecting unit that projects pulsed light, a light-receiving unit that is disposed opposite the light-projecting unit and receives the pulsed light from the light-projecting unit to generate a received light signal, a comparison unit that compares the signal voltage of the received light signal with a reference voltage, a measurement unit that measures the time during which the signal voltage of the received light signal is greater than the reference voltage, and a determination unit that determines the presence or absence of an object between the light-projecting unit and the light-receiving unit based on the length of the time.

In another aspect of the vehicle detection method of the present invention, a light-projecting unit projects a pulsed light, a light-receiving unit disposed opposite the light-projecting unit receives the pulsed light from the light-projecting unit to generate a light-receiving signal, compares the signal voltage of the light-receiving signal with a reference voltage, measures the time during which the signal voltage of the light-receiving signal is greater than the reference voltage, and determines the presence or absence of an object between the light-projecting unit and the light-receiving unit based on the length of time.

In addition, the determination device of another aspect of the present invention includes a receiving unit that receives an output signal from a comparing unit that compares the signal voltage of the received light signal generated by a light receiving unit that receives pulsed light from a light projecting unit with a reference voltage, a measuring unit that measures the time during which the signal voltage of the received light signal is greater than the reference voltage based on the output signal, and a determining unit that determines the presence or absence of an object between the light projecting unit and the light receiving unit based on the length of the time.

The present invention makes it possible to reduce false positives.

FIG. 1 is a diagram illustrating an example of a vehicle detection device according to an embodiment. 1A and 1B are diagrams illustrating an example of object detection by a vehicle detection device. 4 is a circuit diagram showing an example of a light receiving section and a comparison section. FIG. FIG. 1 is a block diagram illustrating an example of a determination device. FIG. 11 is a diagram illustrating an example of a determination made by a determining unit. FIG. 13 illustrates an example of time measurement. FIG. 1 is a diagram illustrating an example of object detection. FIG. 13 is a diagram illustrating an example of detection time. FIG. 13 is a diagram illustrating an example of detection time. FIG. 13 is a diagram illustrating an example of detection time. FIG. 13 is a diagram illustrating an example of detection time. FIG. 11 is a circuit diagram showing a reference example. FIG. 13 is a diagram showing a modified example of the determination device.

The following describes an embodiment of the present invention with reference to the drawings.

Figures 1 and 2 are diagrams showing an example of a vehicle detection device 1 according to an embodiment. The vehicle detection device 1 includes a light-projecting unit 2 and a light-receiving unit 3, and the light-receiving unit 3 receives light projected from the light-projecting unit 2. The light is, for example, infrared light.

In this embodiment, the vehicle detection device 1 is a transmission type multi-optical axis photoelectric sensor, and the light-projecting unit 2 and the light-receiving unit 3 form multiple optical axes arranged in the vertical direction. The light-projecting unit 2 has multiple light-emitting elements 21 arranged in the vertical direction, and the light-receiving unit 3 has multiple light-receiving elements 31 arranged in the vertical direction.

The light-projecting unit 2 and the light-receiving unit 3 are arranged opposite each other, sandwiching the road RD on which the vehicle VH travels. When the light traveling from the light-projecting unit 2 to the light-receiving unit 3 is blocked by an object such as the vehicle VH, the object is detected.

As shown in FIG. 2, at the bottom of the vehicle detection device 1, some of the light projected from the light projecting unit 2 may be reflected by the road surface and enter the light receiving unit 3. In that case, even if an object B is present between the light projecting unit 2 and the light receiving unit 3, the object B may not be detected.

In addition, the detection resolution of the vehicle detection device 1 depends on the number of pairs of light-emitting elements 21 and light-receiving elements 31, so if you want to detect even small objects relative to the vehicle VH, such as a tow bar, it is necessary to arrange a large number of light-emitting elements 21 and light-receiving elements 31 with a narrow pitch.

Therefore, in this embodiment, as described below, these problems are solved by measuring the length of time during which the signal voltage of the received light signal is greater than the reference voltage, and using the measured length of time for judgment.

Figure 3 is a circuit diagram showing an example of the light receiving unit 3 and the comparison unit 4. The figure also shows an example of the signal waveform of each element. The configuration shown in the figure is provided for each of the multiple light receiving elements 31 included in the light receiving unit 3.

In this embodiment, the light-projecting unit 2 projects pulsed light having a predetermined time width. The light-receiving element 31 receives the pulsed light projected from the light-projecting unit 2 and generates a light-receiving signal. The light-receiving signal is a rectangular wave corresponding to the pulsed light.

The received light signal is input to a comparison section (e.g., a comparison circuit) 4 via a differentiation circuit 32 and an amplification/filtering circuit 33. The amplification/filtering circuit 33 includes multiple amplifiers, and amplifies the received light signal and extracts components in a specified frequency band.

The comparator 4 compares the signal voltage of the received light signal with the reference voltage RF. The comparator 4 outputs a high-level voltage when the signal voltage of the received light signal is greater than the reference voltage RF, and outputs a low-level voltage when the signal voltage of the received light signal is less than the reference voltage RF.

The length of time during which the signal voltage of the received light signal is greater than the reference voltage RF (hereinafter referred to as detection time _tdet ) corresponds to the intensity of the pulsed light. That is, the higher the intensity of the pulsed light, the longer the detection time _tdet , and the lower the intensity of the pulsed light, the shorter the detection time _tdet .

For this reason, the detection time _tdet is relatively long when the pulsed light directly enters the light receiving element 31. On the other hand, when the pulsed light does not directly enter the light receiving element 31 and only the light reflected by the road surface enters the light receiving element 31, the detection time _tdet is relatively short.

FIG. 4 is a block diagram showing an example of the functional configuration of the determination device 5. The determination device 5 is, for example, an FPGA (Field Programmable Gate Array). However, the determination device 5 is not limited to this and may be another PLD (Programmable Logic Device) or a computer including a CPU, etc.

The determination device 5 has, as its functional parts, a receiving part 51, a measuring part 52, and a determining part 53. The receiving part 51 receives the output signal of the comparing part 4. The measuring part 52 measures, based on the output signal of the comparing part 4, the length of time during which the signal voltage of the received light signal is greater than the reference voltage RF (detection time t _det ).

The judgment unit 53 judges the presence or absence of an object B between the light projector 2 and the light receiver 3 based on the length of the detection time _tdet . The judgment unit 53 further judges the quality of the installation or maintenance of the light projector 2 and the light receiver 3 based on the length of the detection time _tdet .

5 is a diagram showing an example of a determination made by the determination unit 53. The thresholds t1, t2, and t3 have a relationship of t1>t2>t3. The determination unit 53 determines that an object B is present between the light projector 2 and the light receiver 3 when the length of the detection time _tdet is equal to or shorter than the threshold t3 (an example of a first threshold).

Furthermore, when the length of the detection time t _det exceeds the threshold value t1 (an example of a second threshold value), the determination unit 53 determines that there is no object B between the light projecting unit 2 and the light receiving unit 3, and that the installation or maintenance of the light projecting unit 2 and the light receiving unit 3 is good (i.e., there is no defect).

Furthermore, when the length of the detection time _tdet exceeds the threshold value t3 and is equal to or smaller than the threshold value t1, the determination unit 53 determines that the installation or maintenance of the light projector 2 and the light receiver 3 is defective. In more detail, when the length of the detection time _tdet exceeds the threshold value t3 and is equal to or smaller than the threshold value t2, the determination unit 53 determines that the maintenance is defective, and when the length of the detection time _tdet exceeds the threshold value t2 and is equal to or smaller than the threshold value t1, the determination unit 53 determines that the installation is defective.

Poor installation occurs when insufficient light enters due to, for example, misalignment of the optical axes of the light-projecting unit 2 and the light-receiving unit 3 during installation. Poor maintenance occurs when insufficient light enters due, for example, to dirt on the lenses of the light-projecting unit 2 and the light-receiving unit 3 caused by long-term use.

In this way, by making a judgment based on the length of the detection time t _det , which indicates the intensity of the pulsed light, it is possible to distinguish between a state in which the pulsed light directly enters the light receiving element 31 and a state in which the pulsed light does not directly enter the light receiving element 31 and only light reflected by the road surface enters the light receiving element 31, thereby making it possible to suppress erroneous detection. Furthermore, it is also possible to judge not only the presence or absence of an object but also the quality of installation or maintenance.

As shown in FIG. 2 above, the light reflected by the road surface enters only some of the lower light receiving elements 31 out of the multiple light receiving elements 31 provided in the light receiving unit 3. Therefore, for these light receiving elements 31, the presence or absence of an object may be determined based on the length of the detection time _tdet , and for the remaining light receiving elements 31, the presence or absence of an object may be determined based on the presence or absence of light received, as in the conventional manner.

6 is a diagram showing an example of a measurement window _tWIN for measuring the detection time _tdet . The measurement unit 52 may measure the detection time _tdet in accordance with the projection timing of the pulsed light by the light projection unit 2. That is, the measurement unit 52 provides a predetermined measurement window _tWIN based on the light projection timing, and measures the detection time _tdet during that period. This makes it possible to reduce the influence of disturbances and the like.

Figure 7 is a diagram showing an example of detecting an object smaller than a vehicle, such as a tow bar P, in the vehicle detection device 1. According to this embodiment, as described below, it is possible to maintain the detection resolution even if the number of light-emitting elements 21 and light-receiving elements 31 is reduced and the pitch is increased compared to conventional methods.

As shown in the figure, the light emitted from the light-emitting element 21 has a certain spread, so for example, light L2 emitted from the second light-emitting element 21b is received not only by the second light-receiving element 31b in its pair, but also by the light-receiving elements 31a and 31c above and below it. Similarly, light L3 emitted from the third light-emitting element 21c is received not only by the third light-receiving element 31c in its pair, but also by the light-receiving elements 31b and 31d above and below it.

When considering a state in which a tow bar P is positioned between the light projector 2 and the light receiver 3, the shadow created by the light L2 being blocked by the tow bar P is located between the second and third light receivers 31b and 31c, so the amount of light received by the light receivers 31b and 31c for the light L2 does not change. On the other hand, the shadow created by the light L3 being blocked by the tow bar P is located on the second light receiver 31b, so the amount of light received by the light receiver 31b for the light L3 changes.

As described above, according to this embodiment, the intensity of the amount of received light can be determined by the length of the detection time _tdet , and therefore in the example shown in the figure, it is possible to detect the tow bar P by the change in the amount of received light at the second light receiving element 31b. In this way, even if the number of light emitting elements 21 and light receiving elements 31 is reduced and the pitch is widened compared to the conventional case, it is possible to maintain the detection resolution by determining the intensity of the amount of received light by the length of the detection time _tdet .

8 is a diagram for explaining an example of detecting an object by comparing detection times _tdet . In the case where the light emitting element 21 and the light receiving element 31 are arranged in the vertical direction as shown in FIG. 7, the determination unit 53 may determine the presence or absence of an object between the light projecting unit 2 and the light receiving unit 3 based on the difference in the length of a plurality of detection times _tdet measured by the plurality of light receiving elements 31.

The figure shows detection times _tdet1 to _tdet3 measured by the first to third light receiving elements 31a to 31c. When there is no object between the light projecting unit 2 and the light receiving unit 3, the detection times _tdet1 to _tdet3 are approximately equal in length, but when there is an object between the light projecting unit 2 and the light receiving unit 3, some of the detection times _tdet1 to _tdet3 are shorter than the others.

For example, as shown in the figure, the judgment unit 53 judges that an object is present _{between the light-projecting unit 2 and the light-receiving unit 3 when there are two or more detection times t det1 and} t _det2 whose difference from the longest detection time t det3 is greater than or equal to a threshold value.

Also, for example, as shown in FIG. 9, if the detection time t _det3 of the light receiving element 31c is shorter than the detection times t _det1 and t _det2 of the light receiving elements 31a and 31b, it can be estimated that an object is present between the light emitting element 21b and the light receiving element 31c.

10 and 11 are diagrams illustrating another example of object detection based on the variation of the detection time _tdet . The determination unit 53 may determine the presence or absence of an object between the light projector 2 and the light receiver 3 based on the difference between the length of the measured detection time _tdet and the length of the previously measured detection time _tdet .

10 shows detection time t _det(n-1) measured when there is no object between the light projector 2 and the light receiver 3, and detection time t det(n) measured when there is an object between the light projector 2 and the light receiver 3. The detection time t _{det( n)} is shorter than the detection time t _det(n-1) .

For example, the judgment unit 53 judges that an object is present between the light-projecting unit 2 and the light-receiving unit 3 when the difference between the length of the measured detection time t _{det(n) and} the length of the detection time t _det(n-1) measured before the length of the detection time t det(n) is measured is equal to or greater than a threshold value.

In the above embodiment, the determination device 5 is configured as an FPGA or a computer, which has the following advantages:

In the conventional method, it is determined whether the signal voltage of the light receiving signal is equal to or greater than a threshold value _Vth , but the threshold value _Vth is a fixed value. In this case, it is necessary to determine the threshold value _Vth according to the condition where the distance between the light projecting unit and the light receiving unit is the longest. However, if this is done, the threshold value _Vth cannot be said to be the optimal threshold value under the condition where the distance between the light projecting unit and the light receiving unit is shorter than that.

In contrast, in this embodiment, since an FPGA or a computer is used, it is possible to freely change the threshold value _tth applied to the detection time _tdet . For example, the detection time _tdet measured when the light projecting unit 2 and the light receiving unit 3 are installed is set as the initial value _tdet0 , and a value obtained by multiplying the initial value _tdet0 by a predetermined value such as 0.8 is set as the threshold value _tth , thereby making it possible to set an appropriate threshold value.

In addition, in the conventional method, the light projecting unit and the light receiving unit are installed while checking that the signal voltages of all light receiving signals are equal to or higher than the threshold value _Vth , but this is not necessarily the optimal installation. Alternatively, the light projecting unit and the light receiving unit are installed while checking with an oscilloscope that the waveform of the light receiving signal is maximized, but in this case, an oscilloscope is required, which makes the installation time-consuming.

In contrast, in this embodiment, since the length of the detection time _tdet is measured using an FPGA or a computer, it is easy to adjust the light projecting unit 2 and the light receiving unit 3 to the optimum installation that maximizes the length of the detection time _tdet . Also, since the length of the detection time _tdet can be confirmed using a PC or the like, confirmation is easier than using an oscilloscope.

Figure 12 is a circuit diagram showing a reference example. As shown in the figure, multiple comparison units 41-43 with different reference voltages RF1-RF3 may be provided to determine the strength of the signal voltage of the received light signal. The reference voltages RF1-RF3 in the figure have the relationship RF1>RF2>RF3.

For example, similar to the judgment example shown in FIG. 5 above, when all of the comparison units 41 to 43 output a high-level voltage, the judgment unit 53 judges that there is no object B between the light-projecting unit 2 and the light-receiving unit 3, and that the installation or maintenance of the light-projecting unit 2 and the light-receiving unit 3 is good.

In addition, when the comparison unit 41 outputs a low-level voltage and the comparison units 42 and 43 output a high-level voltage, the determination unit 53 determines that there is a maintenance defect.In addition, when the comparison units 41 and 42 output a low-level voltage and the comparison unit 43 outputs a high-level voltage, the determination unit 53 determines that there is an installation defect.

In addition, when all of the comparison units 41 to 43 output a low-level voltage, the judgment unit 53 judges that an object B is present between the light-projecting unit 2 and the light-receiving unit 3. In this way, by measuring the strength of the signal voltage of the light-receiving signal with multiple comparison units 41 to 43, it is also possible to suppress false detections and judge whether the installation or maintenance is satisfactory.

[Modification]
The determination device 5 in the modified example described below is composed of a computer including a CPU, etc., and uses a learned model to identify the type of vehicle VH passing between the light-projecting unit 2 and the light-receiving unit 3 from time-series data of the length of the detection time t _det .

FIG. 13 is a block diagram showing an example of the functional configuration of a determination device 5 according to a modified example. In addition to a receiving unit 51, a measuring unit 52, and a determination unit 53, the determination device 5 according to the modified example further includes a normalization unit 54, a vehicle type identification unit 55, and a model holding unit 56.

The receiving unit 51, the measuring unit 52, the determining unit 53, the normalizing unit 54, and the vehicle type identification unit 55 are realized by the CPU of the determining device 5 executing information processing according to a program. The model holding unit 56 is constructed in the memory of the determining device 5.

The normalization unit 54 is connected to a vehicle speed detection unit 6 that detects the speed of the vehicle VH, and acquires vehicle speed data from the vehicle speed detection unit 6. The vehicle speed detection unit 6 is provided near the light projecting unit 2 and the light receiving unit 3, and detects the speed of the vehicle VH traveling on the road RD.

The measurement unit 52 provides time series data of the lengths of the detection times _tdet measured for each of the light receiving elements 31 (see FIG. 2, etc.) to the normalization unit 54 and the vehicle type identification unit 55. The time series data represents a change over time in the detection time _tdet measured each time the light projector 2 projects a pulsed light.

The normalization unit 54 normalizes the time series data acquired from the measurement unit 52 in accordance with the vehicle speed data acquired from the vehicle speed detection unit 6. Specifically, the normalization unit 54 divides the time axis of the time series data by the vehicle speed.

The vehicle type identification unit 55 uses the trained model stored in the model storage unit 56 to identify the vehicle type of the vehicle VH passing between the light projector 2 and the light receiver 3 from the normalized time series data acquired from the normalization unit 54. The vehicle type may be, for example, a light vehicle, a standard vehicle, or a medium-sized vehicle.

The trained model stored in the model storage unit 56 is generated in advance by machine learning, for example, using time-series data for training as input data and vehicle models as training data.

The time series data for learning is time series data that is measured and normalized in the same manner as the time series data having the length of the detection time t _det described above.

The vehicle type used as training data is determined based on, for example, tire width calculated from detection data of treads buried in the road. A learning dataset is created by associating the determined vehicle type with time-series data for learning.

The trained model is, for example, a convolutional neural network, which includes a convolutional layer, a pooling layer, a fully connected layer, and an output layer. In particular, a deep neural network that combines neurons in multiple stages is preferable.

Learning is achieved by inputting the learning time series data into the model as input data, performing calculations, outputting the vehicle model as output data, calculating the difference between the vehicle model as the output data and the vehicle model as the training data, and adjusting the model parameters to reduce the difference. In addition, between learning rounds, the validity of the model is evaluated using a test dataset.

According to the modified example described above, it is possible to identify the type of vehicle VH passing between the light-projecting unit 2 and the light-receiving unit 3 from the time series data of the length of the detection time t _det , even without providing a step board on the road RD.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible for those skilled in the art.

REFERENCE SIGNS LIST 1 vehicle detection device, 2 light projection unit, 21 light emitting element, 3 light receiving unit, 31 light receiving element, 32 differentiation circuit, 33 amplification and filtering circuit, 4 comparison unit, 5 determination device, 51 reception unit, 52 measurement unit, 53 determination unit, 54 normalization unit, 55 vehicle type identification unit, 56 model storage unit

Claims (12)

a light projection unit that projects pulsed light;
a light receiving section disposed opposite to the light projecting section, receiving the pulsed light from the light projecting section and generating a light receiving signal;
a comparison unit that compares a signal voltage of the light receiving signal with a reference voltage;
a measurement unit that measures a time during which a signal voltage of the light reception signal generated by receiving the pulsed light once is greater than the reference voltage;
a determination unit that determines whether or not an object is present between the light projecting unit and the light receiving unit based on the length of time;
A vehicle detection device comprising: The determination unit further determines whether installation or maintenance of the vehicle detection device is good or bad based on the length of time.
The vehicle detection device of claim 1 . The determination unit is
If the length of time is equal to or less than a first threshold value, it is determined that an object is present between the light projecting unit and the light receiving unit;
If the length of time exceeds the first threshold and is equal to or less than the second threshold, it is determined that there is no object between the light projecting unit and the light receiving unit, but the installation or maintenance of the vehicle detection device is defective;
If the length of time exceeds the second threshold, it is determined that there is no object between the light projecting unit and the light receiving unit, and that the installation or maintenance of the vehicle detection device is good.
The vehicle detection device of claim 2. the measurement unit measures the length of time in a measurement window that is set based on the timing at which the light projector projects the pulsed light.
4. A vehicle detection device according to claim 1. The light projecting unit includes a plurality of light emitting elements arranged in a vertical direction,
The light receiving unit includes a plurality of light receiving elements arranged in a vertical direction,
The comparison unit is provided for each of the plurality of light receiving elements.
5. A vehicle detection device according to claim 1. the determination unit determines that there is an object between the light projecting unit and the light receiving unit when a predetermined number or more of the lengths of time are measured for the plurality of light receiving elements and the difference between the length of time and the longest length of time is equal to or greater than a threshold value, or when a part of the lengths of time are shorter than the remaining lengths of time .
6. The vehicle detection device of claim 5. the determination unit determines the presence or absence of an object between the light projecting unit and the light receiving unit based on the length of time measured for a portion of the light receiving elements located on a lower side among the plurality of light receiving elements.
7. A vehicle detection device according to claim 5 or 6. the determination unit determines that an object is present between the light projecting unit and the light receiving unit when a difference between the length of the time and a length of the time measured before the length of the time is measured becomes equal to or greater than a threshold value.
A vehicle detection device according to any one of claims 1 to 7. The present invention further includes an identification unit that identifies a type of vehicle passing between the light projecting unit and the light receiving unit from time series data of the lengths of the times measured for the plurality of light receiving elements by using a trained model.
6. The vehicle detection device of claim 5. A detection unit for detecting a speed of the vehicle is further provided.
The identification unit identifies the type of the vehicle from the time-series data normalized according to the speed of the vehicle.
10. The vehicle detection device of claim 9. The light-emitting unit emits pulsed light,
a light receiving section disposed opposite to the light projecting section receives the pulsed light from the light projecting section and generates a light receiving signal;
Comparing a signal voltage of the received light signal with a reference voltage;
measuring a time during which a signal voltage of the light reception signal generated by receiving the pulsed light once is greater than the reference voltage;
determining whether or not an object is present between the light projecting unit and the light receiving unit based on the length of time;
Vehicle detection methods. a receiving section for receiving an output signal from a comparing section for comparing a signal voltage of a light receiving signal generated by a light receiving section for receiving a pulsed light from a light projecting section with a reference voltage;
a measurement unit that measures, based on the output signal, a length of time during which a signal voltage of the light reception signal generated by receiving the pulsed light once is greater than the reference voltage;
a determination unit that determines whether or not an object is present between the light projecting unit and the light receiving unit based on the length of time;
A determination device comprising:

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