JPS5911958B2 - How to determine the end of vehicle signal waveform - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for determining the end of a vehicle signal waveform in a traffic flow measuring device.

Traffic flow measurement devices include those that use loop coils buried under the road surface, those that use ultrasonic waves, and those that use optical systems, but in any case, they process vehicle detection signals output from sensors. The system collects traffic flow information such as vehicle speed, headway distance, number of passing vehicles, and degree of congestion.

The output signal of such a sensor normally rises when a vehicle is detected, continues with a waveform depending on the shape of the vehicle, and then falls back to the original level as the vehicle passes, but the signal waveform varies depending on the speed of the vehicle. Also changes into species.

For example, when two or more fast-moving vehicles pass in succession, two peaks appear one after another.

In addition, when a slow vehicle passes by, an almost flat peak level continues for a while, but depending on the shape of the vehicle, a valley may appear in the middle of this peak level.
This makes it difficult to distinguish from when two high-speed vehicles pass in succession.

Therefore, in order to clearly identify passing vehicles one by one, it is necessary to reliably know the end of the signal from that vehicle.

The present invention has been made in view of the above circumstances, and provides a method that can reliably determine the end of a vehicle detection signal regardless of the traveling speed of the vehicle.

Hereinafter, the content of the present invention will be explained in detail with reference to the drawings.

The example shown below is a case where a traffic flow measuring device installed at a position overlooking a road and having a large number of light receiving elements is used.

This device has the advantage of being able to collect vehicle information from many points on the road at one location and being easy to install.

FIG. 1 shows how the camera of the traffic flow measuring device is installed.

The camera 1 is mounted at a required height position (for example, 6 m) above the road using a support 3 or the like, and within a required range (for example, 6 m) in the length direction of the road.
For example, it is installed so that it overlooks 100 meters).

As shown in FIG. 4, the camera 1 is equipped with an optical system 4 including a lens 5 and a large number of light receiving elements.

In this example, within the field of view of the camera 1, there are six detection points P1 to P6 along the lane in which traffic flow is to be measured.

On the imaging plane of the optical system 4 in the camera 1 and corresponding to these detection points, one pair of light receiving elements ds1.
dR1 to dS6 and dR6 are arranged.

These light receiving elements are composed of photodiodes, for example.

When measuring traffic flow in two lanes with one camera, a large number of light receiving elements are arranged in two rows on the imaging plane of the optical system 4.

At each detection point (represented by P), as shown in Figure 2,
A set area S and a reset area R are set apart from each other by a required interval l.

A pair of light receiving elements (represented by dS and dR) correspond to these six regions S and H, respectively.

When the vehicle CA passes the detection point P from the set area S to the reset area R, as shown in FIG.
Then, a vehicle detection signal shifted by time t from dR is output.

Here, the rising edge of the output of each of the light receiving elements ds and dR is detected, and the difference between the rising edges of both signals is defined as the detection time t.

Since this detection time t is the time required for the vehicle to travel between the set area S and the reset area R (distance l), the traveling speed V of this vehicle is determined by the following equation.

However, K is a constant.

V = K - The distance that the vehicle actually moves during the detection time t is affected by the shape of the vehicle, vehicle height, etc., and differs slightly from vehicle to vehicle, and is not actually equal to the above distance l. .

However, a detection surface is assumed to be at a position above the road surface by a required height, and the detection surface S is defined on this detection surface.

By measuring the distance between R and statistically correcting this distance, it is possible to measure the traveling speed of the vehicle with high accuracy.

Furthermore, if necessary, the average value of the traveling speeds of the same vehicle measured at the six detection points P1 to P6 may be determined.

Vehicle spacing and congestion level can also be calculated based on this traveling speed.

For example, when a vehicle at the detection point P1 is detected, the headway distance can be determined from the product of the speed of the preceding vehicle detected at the detection point P1 and the elapsed time.

The degree of congestion can be determined, for example, by the number of points among the six points P1 to P6 where the measured travel speed is less than or equal to a predetermined speed (for example, 20/cIrl/h).

Now, the various processes described above are performed by the processing device 2.

With reference to FIG. 4, each light receiving element dS, d in the camera 1
The R output signal is amplified by an amplifier 6 equipped with an automatic gain control function, and then sent to a multiplexer channel device 7, where the outputs of each of the 12 light receiving elements are sequentially switched to the A- is sent to converter 8.

The A-D converter 8 performs AD conversion on the input output of the light receiving element at a predetermined sampling period (4.8 m5 in this example), and sends the result to a central processing unit (referred to as CPU) 11.

The processing device 2 is equipped with two CPUs 11 and 12.

The CPU II analyzes the output signal waveform of each light-receiving element based on the data sent from the A-D converter 8, and also analyzes the output signal waveform of the multiplexer channel device 7 and the A-D converter 8.
- Control the D converter 8.

Based on the data obtained by the CPU 11, the CPU 12 performs end confirmation time selection processing, calculation of vehicle travel speed, detection of congestion degree, and other traffic flow calculation processing, which will be described later, and creates necessary traffic flow information. Transmission section (not shown)
The data is then transmitted to the center.

Each CPU 11.12 is equipped with a program memory (not shown) that stores an execution program, and local memo IJ 13, 14 that stores data, respectively. There is a shared memory 15 that can be accessed by.

In order to detect the rise or fall of the output signal waveform of the light receiving element, it is necessary to determine the change in the signal.

The output signal of the light receiving element is A-D at each sampling period.
Since it is AD-converted by the converter 8, the current AD-converted result is used as the current data Dt.

In order to determine whether the current data Di is increasing, decreasing, or in equilibrium compared to the previous data, it is necessary to find the deviation Δω between the current data Dt and the previous data. .

Previous data to be used for determining this deviation Δω is defined as preprocessed data DO.

This preprocessed data DO is, for example, the previous sample-linked data, and is updated every sampling period.

Furthermore, for the above determination, the reference amount to be compared with the deviation Δω between the current data Dt and the preprocessed data DO is defined as a deviation reference amount ω0.

Then, if Di-Do≧ωO, it is in an increasing state, Dt-D
If O≦−ωO, it is in a decreasing state, and if 1Dt-DOI<ωO, it is in an equilibrium state.

FIG. 5 shows how the change in the signal is determined for each sampling period in this manner.

CPUI 1 performs waveform analysis processing of the output video signal of the light receiving element.
The memos 1J13 and 15 have areas for storing various data, and the memory 14 has areas for storing data necessary for the CPU 12 to perform the end confirmation time selection process.

The memory 13 has an area for storing current data Di, preprocessed data DO1 deviation Δω, and road surface level LO.

The road surface level LO is the level of the light reception signal when the light receiving element is detecting the road surface, and at this level LO, the signal maintains a balanced state.This road surface level LO is measured as appropriate.

The memory 13 also contains a vehicle signal flag F1, a temporary end flag F2. There is an area used as a post-completion time counter C and a vehicle speed counter.

Referring to FIG. 6, the vehicle signal flag F1 indicates that one vehicle is passing through the detection point and a vehicle detection signal is being output, and the output of the light receiving element is at the road surface level LO.
After that, it falls to the road surface level LO and returns to the road surface level LO, and then remains on while maintaining the road surface level LO until a certain period of time (this is referred to as the completion confirmation time T) has elapsed.

The end confirmation time T is a time provided to confirm that one vehicle has passed the detection point in order to clearly distinguish individual vehicles.

The temporary termination flag F2 indicates that the termination confirmation time T is being counted, and is turned on when the signal returns to the road surface level LO, and is turned off when the termination confirmation time T has elapsed.

The post-completion time counter C measures the completion confirmation time T.

The vehicle speed counter measures the speed of a passing vehicle.The time from the rise of the output signal of the light receiving element dS that detects the set area S to the rise of the output signal of the light receiving element dR that detects the reset area R (detection time t).

The shared memory 15 has an area for storing deviation reference amount ω0, road surface identification level L1, end confirmation time T1, end confirmation time transfer flag F3, and speed data.

Of course, the signal maintains a balanced state at road level LO, but
Even at the peak level of the vehicle detection signal, the equilibrium state may continue for a while (see FIG. 5).

The road surface discrimination level L1 is used to identify whether the equilibrium state is continuous at the road surface level or at the peak level of the vehicle detection signal, and is a difference between the road surface level LO and the peak level. It is set at a level between.

The end confirmation time transfer flag F3 indicates that the end confirmation time T has elapsed, and is turned off when this time T elapses.

The contents of the vehicle speed counter are transferred to the speed data area when the measurement of the detection time t ends.

The memory 14 includes an area for storing the speed v1 of the preceding vehicle, and three types of end confirmation times TI.

Area for setting T2 and T3, comparison speed Va,
An area for setting Vb is provided.

The end confirmation time T can be changed in three stages depending on the speed v1 of the preceding vehicle.

The times of these three stages are T1 to T3, and constants for dividing the vehicle speed v1 are comparison speeds Va and Vb.

The end confirmation time is selected as follows.

When 0≦v1×va, T3 V a≦V l <V b (7) and kiLtT2Va≦
When v1, T is straight, but va<vb, and the relationship is TI<T2<T3 (7).

The faster the speed v1 is, the shorter the completion confirmation time T becomes.

As will be clear from what will be described later, when the transfer flag F3 is off, the CPU 12 transfers the end confirmation time selected according to the front vehicle speed v1 to the end confirmation time area of the memory 15.

The processing procedure by CPU II is shown in FIG.

This process is executed, for example, every 4.8 mS.

First, the AD-converted current data Dt is read, and the preprocessed data DO is subtracted from the current data Dt to obtain the deviation Δω (step 21).

Then, the absolute value of this deviation Δω is compared with the reference amount ω0 to determine whether the change in the set signal is increasing, decreasing, or balanced (Step 22), and if it is increasing or decreasing, the temporary end flag F2 is turned off. (Step 23).

This flag F2 is always off when the signal is increasing or decreasing, and is turned off if it was on when the signal moves from equilibrium to increasing or decreasing.

Next, it is checked whether the vehicle signal flag F1 is off.

Since the change state of the signal is an increase or a decrease (\ES in step 22), if the vehicle signal flag F1 is off, it means that the signal has started rising or falling from the road surface level LO.

Therefore, if the vehicle signal flag F1 is off, it is turned on (step 25).

In the case of a vehicle detection signal, the signal normally rises from the road surface level LO, but when the shadow of a vehicle is detected, it falls from the road surface level LO.

Since the same processing is performed when the shadow of a vehicle is detected, no distinction is made between increase and decrease.

After that, the vehicle speed counter measures the detection time t and performs other signal waveform processing (step 26).Finally, the current data Dt is used as preprocessed data DO to update the preprocessed data (step 27), and finish.

If the balance is found in step 22, the process moves to step 28 to check whether the temporary termination flag F2 is on.

When this flag F2 is off, the vehicle is in an equilibrium state at the peak level during vehicle detection, or an equilibrium state at the road surface level LO where no vehicle is detected (excluding the end confirmation time period).

Therefore, it is checked whether the vehicle signal flag F1 is on (step 29). If the flag F1 is off, it means that the road surface level LO is in an equilibrium state, so the process proceeds to step 27 and processes the current data Di as the preprocessed data DO. (Step 27).

When the vehicle signal flag F1 is on, the signal is in an equilibrium state at the peak level, or is falling to just the road surface level L.
Either it reaches O and transitions to an equilibrium state.

Therefore, the current data Di is compared with the road surface identification level L1 (step 30).

If the data Di is level 1 or higher this time, step 27
Move to.

If the data Dt is less than level 1 this time, it has just reached the road surface level LO, so the temporary end flag F2 is turned on (step 31), and after the end, the time counter C is cleared and the end is confirmed by this counter C. Prepare to start measuring time (step 32).

Then, the process proceeds to step 27.

If the temporary end flag F2 is on (YES in step 28), the end confirmation time is being measured, so the contents of the after-end time counter C are incremented by 1 (step 33), and the contents of this counter C and the end confirmation time T are (Step 3)
4).

If the content of the counter C is less than time T, the process moves to step 27, and if the content of the counter C reaches time T, the counter C is cleared (step 35) and the vehicle signal flag F1 is turned off. 36), temporary end flag F
2 is turned off (step 37), and the end confirmation time transfer flag F3 is also turned off (step 38), and the process proceeds to step 27.

The processing shown in FIG. 7 is common to both signals from the light receiving elements dS and dR, except for the processing at step 26.

FIG. 8 shows the processing procedure by CPUI2.

This process is executed, for example, every 19.2 mS.

First, it is checked whether the end confirmation time transfer flag F3 is off (step 41), and if this flag F3 is off, the time is determined according to the traveling speed v1 of the preceding vehicle, which has been fetched from the speed data area of the memory 15 and calculated in advance. Save the selected completion confirmation time (any of T1 to T3) in a shared memo IJT
15 to the end confirmation time area (step 42).
).

Then, turn off the transfer flag F3 (step 43).
Finish processing.

Note that if the headway time interval between the preceding vehicle one vehicle ahead and the currently detected vehicle is longer than a predetermined time, the shortest time T1 may be selected as the end confirmation time regardless of the speed of the preceding vehicle. .

As described in detail above, the present invention measures and stores vehicle speed based on the detection signal of a sensor that detects a vehicle passing through a traffic flow measurement point, and the vehicle detection signal output from the sensor is set to a predetermined value. It is determined that the test has returned to the reference level, and from this determination point, the end confirmation time starts to be measured.
It is determined whether a predetermined end confirmation time has elapsed while maintaining the above reference level, and it is assumed that vehicle detection has ended when the above end confirmation time has elapsed, and based on the memorized measured vehicle speed. Since the present invention is characterized in that a new completion confirmation time is set in advance, each vehicle can be clearly distinguished and traffic flow measurement processing can be performed regardless of the traveling speed of the vehicle.

[Brief explanation of drawings]

Figure 1 is a diagram showing the installation status of the camera of the traffic flow measurement device.
Fig. 2 is an enlarged view of the detection point, Fig. 3 is a waveform diagram showing the vehicle detection signal, Fig. 4 is a configuration and block diagram showing the inside of the camera and processing device, and Fig. 5 shows detection of the waveform pattern. An explanatory diagram, FIG. 6 is a time chart for explaining the vehicle signal termination determination process, and FIGS. 7 and 8 are flow charts showing the processing procedure when the vehicle signal termination determination process is executed by the CPU. It is. ds1 to dR6... Light receiving element, LO...
・Road surface level, T, T1-T3... End confirmation time, Di... Current data, DO... Preprocessing data, Δω... Deviation, ω0・・・・・・
Reference amount.

Claims (1)

[Claims] 1. Vehicle speed is measured and stored based on a detection signal of a sensor that detects a vehicle passing through a traffic flow measurement point, and the vehicle detection signal output from the sensor returns to a predetermined reference level. start measuring the completion confirmation time from this judgment point; determine whether the predetermined completion confirmation time has elapsed while maintaining the above reference level; and when the above completion confirmation time has elapsed. A method for determining the end of a vehicle signal waveform, which assumes that vehicle detection has ended and also sets a new end confirmation time based on a stored measured vehicle speed.