JPH0721489A - Ultrasonic vehicle sensor - Google Patents

Abstract

PURPOSE:To sense a vehicle without reducing sensitivity even under an environment in which a large background reflection wave exists. CONSTITUTION:When a power supply ON detecting part 1 detects the ON of a power supply, a time counter 15 is started and a background reflection wave depending threshold storing part 13 stores a threshold. Then an ultrasonic wave is radiated to an object to be detected and the ultrasonic reflected wave is detected by a reflected wave level detecting part 6. The detection level of the detecting part 6 is compared with the threshold of the storing part 13 by a comparing part 7, and when the detection level exceeds the threshold, a vehicle is sensed. The threshold stored in the storing part 13 is successively changed in accordance with the detection time of the reflected wave detected by the detecting part 6. Thereby even when the level of a vehicle reflection wave approaches the level of a background reflection wave, the vehicle can be sensed without reducing sensitivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle detector, and more particularly to an ultrasonic vehicle detection suitable for detecting a traveling vehicle using ultrasonic waves.

[0002]

2. Description of the Related Art A conventional ultrasonic type vehicle detection is shown in FIG.
Those shown in are known. This sensor includes a power-on detection unit 1, a uniform threshold value initialization unit 2, a uniform threshold value storage unit 3, a uniform threshold value change unit 4, a reflected wave level detection unit 6, and a comparison unit 7. The reflected wave signal 5 is input to the reflected wave level detector 6.

In the above-mentioned conventional vehicle detector, when the power is turned on, the power-on detection unit 1 detects this and activates the uniform threshold value initialization unit 2. When the uniform threshold value initialization unit 2 is activated, the initial value is input to the uniform threshold value storage unit 3. At this time, when there is no vehicle to be sensed, as shown in FIG. 5, the reflected wave input to the reflected wave level detection unit 6 is only the road surface reflected wave 10 and the vehicle reflected wave 8 is not detected. On the other hand, when the vehicle enters and the vehicle reflected wave 8 is detected, the level of the vehicle reflected wave 8 and the uniform threshold value 11 stored in the uniform threshold value storage unit 3 are detected.
Are compared by the comparison unit 7. At this time, when the level of the vehicle reflected wave 8 exceeds the level of the uniform threshold value 11, the vehicle is sensed.

However, when an obstacle is present in the vicinity of the installed ultrasonic vehicle sensor, the background reflected wave 9 is generated, and the vehicle may be erroneously detected by the background reflected wave 9. Therefore, in order to prevent such false detection,
The uniform threshold value is changed by the uniform threshold value changing unit 4. That is, the uniform threshold value changing unit 4
Then, only when the vehicle is not sensed, the level of the background reflected wave 9 is obtained, the uniform threshold value 11 is determined accordingly, and the level is stored in the uniform threshold value storage section 3. There is. The uniform threshold value 11 thus determined does not change during the period T1 from the emission of ultrasonic waves to the reception of the road surface reflected wave 10, and is fixed at a constant level.

[0005]

However, in the prior art, when the background reflected wave 9 having a large level is present, the background reflected wave 9 is adjusted according to the level of the background reflected wave 9 in order to prevent it from being erroneously sensed. The level of the uniform threshold value 11 must be raised uniformly regardless of time. If such a level change is performed, the level of the vehicle reflected wave 8 necessary for vehicle detection also rises, and as a result, the sensitivity of vehicle detection decreases, and the vehicle cannot be detected even though the vehicle has entered. Problems arise. On the other hand, in order to prevent such a problem, if the level of the uniform threshold value 11 is not increased, the background reflected wave 9 is erroneously sensed as a vehicle. In the example of FIG. 5, the vehicle reflected wave 8 cannot be detected because the levels of the vehicle reflected wave 8 and the background reflected wave 9 are close to each other.

Further, as a conventional technique of this kind, the technique disclosed in Japanese Patent Laid-Open No. 64-61900 can be cited.

The present invention solves such a conventional problem, and provides an ultrasonic vehicle detector capable of detecting a vehicle without lowering the sensitivity even in an environment where a large background reflected wave exists. The purpose is to do.

[0008]

In order to achieve the above-mentioned object, the present invention measures the time from power-on in response to a power-on detector for detecting power-on and a detection output of the power-on detector. A time measurement unit, a reflected wave detection unit that emits ultrasonic waves toward the detection target and detects the reflected waves of these ultrasonic waves, and a threshold value memory that stores the threshold value that depends on the reflected waves from the background of the vehicle Section, a threshold value changing section that sequentially changes the threshold value of the threshold value storage section according to the reflected wave detection time in response to the measurement time of the time measuring section, and the detection output and threshold value of the reflected wave detection section. An ultrasonic system equipped with a comparison unit that compares the threshold value of the storage unit and outputs a vehicle detection signal when the former level exceeds the latter level and outputs a background reflected wave detection signal otherwise It is a component of a vehicle detector.

Further, in the ultrasonic type vehicle detector, the threshold value changing unit is configured to sequentially change the threshold value of the threshold value storage unit according to the level of the background reflected wave by the detection output of the reflected wave detection unit. It can be composed of

[0010]

Therefore, according to the present invention, when the power is turned on, the time since the power is turned on is sequentially measured, and the threshold value is sequentially changed according to the reflected wave detection time. Therefore, the vehicle can be sensed without lowering the sensitivity even in an environment where a strong background reflected wave exists. Furthermore, the threshold is changed sequentially according to the level of the background reflected wave,
Even if the background reflected wave fluctuates, the vehicle can be detected without lowering the sensitivity.

[0011]

FIG. 1 shows an embodiment of the present invention. In FIG. 1, the ultrasonic vehicle detector includes a power-on detection unit 1, a background reflected wave dependent threshold value initialization unit 12, a background reflected wave dependent threshold value storage unit 13, a time counter 15, a comparison unit 7, a reflected wave. The level detection unit 6 and the background reflection wave-dependent threshold value changing unit 14 are provided, and the reflection wave signal 5 is reflected by the reflection wave level detection unit 6.
Has been entered in.

When the sensor is powered on, the power-on detection unit 1 detects the power-on and outputs the detection output to the time counter 15 and the background reflected wave dependence threshold value initialization unit 12. It has become. In response to the detection output of the power-on detection unit 1, the time counter 15 initializes the measurement value to 0 when the power is turned on, and thereafter, as shown in FIG. 2, receives the road surface reflected wave 10 from the ultrasonic wave emission. Cycle T1
Each time is repeated, the count value is incremented by one and the time from power-on is measured to measure the time.
The background reflected wave dependent threshold value initialization unit 12 is activated by the detection output of the power-on detection unit 1, and sets the threshold level stored in the background reflected wave dependent threshold value storage unit 13 to the initial value 10
It is designed to be initialized to 0. Further, the background reflected wave dependent threshold value storage unit 13 is configured to sequentially store the threshold level at each time in order to change the background reflected wave dependent threshold value 16 according to the background reflected wave 9. . Further, the threshold value 16 stored in the storage unit 13 is sequentially changed according to the measurement time of the time counter 15. On the other hand, the comparison unit 7 compares the threshold value 16 stored in the threshold value storage unit 13 with the detection level detected by the reflected wave level detection unit 6, and the detection level exceeds the level of the threshold value 16. When the vehicle detection signal is output, the background reflected wave detection signal is output at other times. Further, the background reflected wave dependent threshold value changing unit 14 inputs the detection information of the vehicle from the comparison unit 7 and the detection signal from the reflected wave level detecting unit 6 to input the background reflected wave 9
The value of the threshold value 16 stored in the threshold value storage unit 13 is sequentially changed according to the level of.

Next, the operation of the embodiment in which the threshold value is changed according to the measured value of the time counter 15 will be described.

In this embodiment, when the power is turned on, the power-on detector 1 detects this and the time counter 1
5 is initialized and the background reflected wave dependent threshold value initialization unit 12 is initialized, whereby an initial value is given to the background reflected wave dependent threshold value storage unit 13. At this time, an ultrasonic wave is emitted from the reflected wave level detection unit 6 toward the detection target, and the reflected wave of this ultrasonic wave is input to the reflected wave level detection unit 6 as a reflected wave signal 5. The reflected wave signal 5 is converted into a level by the reflected wave level detecting section 6 and compared with the threshold value 16 stored in the background reflected wave dependent threshold value storage section 13 by the comparing section 7. At this time, when the level of the vehicle reflected wave 8 exceeds the level of the background reflected wave dependent threshold value 16, it is determined that the vehicle is sensed. On the other hand, when there is no vehicle to be sensed, the reflected wave is only the road surface reflected wave 10, and the vehicle reflected wave 8 does not exist.

Next, when the vehicle enters and the reflected wave 8 of the vehicle is detected, it is determined that the vehicle is sensed. At this time, the level of the background reflected wave dependent threshold value 16 is the uniform threshold value 11
Unlike FIG. 2, it changes depending on the background reflected wave 9 with time as shown in FIG. As a result, the vehicle reflected wave 8
Even if the level of the background reflected wave is close to the level of the background reflected wave 9, the vehicle can be accurately sensed without reducing the sensitivity, and the background reflected wave 9 is prevented from being mistakenly determined as the vehicle reflected wave 8. be able to.

Next, the operation of changing the threshold value according to the level of the background reflected wave will be described with reference to the flowchart of FIG.

First, when the power is turned on (step 1), the power-on detector 1 detects this, and in response to this detection output, the count time t of the time counter 15 is initialized to 0 (step 1). 2). At the same time, the background reflected wave dependent threshold value initialization unit 12 is activated and an initial value is given to the background reflected wave dependent threshold value storage unit 13 (step 3). At this time, the threshold 16 is a constant value independent of the time and the background reflected wave 9.

Next, the processing from step 5 to step 14 is performed within a time period sufficiently shorter than the period T1 immediately after the period T1 from the emission of ultrasonic waves to the reception of the road surface reflected wave 10 is completed. That is, the processing from step 5 to step 14 is executed in the same cycle as the cycle T1. Immediately after the period T1 until the road surface reflected wave 10 is received, the count value t of the time counter 15 is incremented by 1 (step 5). That is,
The count time t of the time counter 15 is incremented by 1 each time the cycle T1 from the emission of ultrasonic waves to the reception of the road surface reflected wave 10 is repeated. On the other hand, the background reflected wave dependence threshold value 16 needs to be changed only when the vehicle is not sensed, so it is first determined whether or not the vehicle is sensed (step 6). In this step, if the vehicle is sensed, do nothing and wait for the next cycle.

On the other hand, if the vehicle is not sensed, the level of the reflected wave is detected (step 7). Since the level of this reflected wave does not include the level of the vehicle reflected wave 8, this directly becomes the background reflected wave 9. Next, the count time t of the time counter 15 is compared with 13 (step 8). If the count time t exceeds 13, then t2 = 1.
3 (step 9) When t is 13 or less, t2 = t (step 10). This is because when the background reflected wave-dependent threshold value 16 is made to follow the background reflected wave 9 in the next step, it is made to immediately follow immediately after the power is turned on, and then the following speed is gradually decreased to finally (t> 13). ) Is to follow slowly.

Next, a new threshold value SH is obtained (step 11). This threshold value S1 is obtained by the following equation.

[0021]

[Equation 1]

Here, OFFSET is a constant indicating the level difference for distinguishing the background reflected wave 9 and the vehicle reflected wave 8.

The threshold value S1 is set as described above because it immediately follows the environment of the surrounding background reflected wave 9 immediately after the power is turned on, and after a sufficient time has passed since the power was turned on, the background reflected wave 9 is changed to the background reflected wave 9. This is to prevent the background reflected wave dependent threshold value 16 from being affected by the sudden noise and to perform a stable operation.

Next, the threshold value 16 calculated in this way
For safety, it is judged whether or not the value exceeds a predetermined value 100 (step 12). At this time, when the threshold value exceeds 100, the threshold value is corrected to 100 or less (step 13), and the corrected value is substituted into the background reflected wave dependent threshold value 16 (step 14).

As described above, according to the present embodiment, the background reflected wave dependent threshold 16 is automatically changed to an appropriate value according to the level of the background reflected wave 9, so that the background reflected wave is changed due to the environmental change. Even if the level of the wave 9 changes, the vehicle can be sensed without lowering the sensitivity, and erroneous sensing of the vehicle can be prevented.

[0026]

As is apparent from the above embodiment, the present invention changes the threshold value according to the detection time of the reflected wave, so that the sensitivity is lowered even in the environment where a large background reflected wave exists. The vehicle can be sensed without it. Furthermore, since the threshold value is changed according to the level of the background reflected wave, the vehicle can be sensed with sufficient sensitivity even if the level of the background reflected wave changes due to environmental changes. In addition, it is possible to prevent a decrease in sensitivity and the occurrence of false detection.

[Brief description of drawings]

FIG. 1 is a schematic block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram for explaining a method of setting a threshold level of a vehicle detector.

FIG. 3 is a flowchart for explaining the operation of the ultrasonic vehicle detector according to the present invention.

FIG. 4 is a schematic block diagram of a conventional example.

FIG. 5 is a diagram for explaining a conventional threshold value setting method.

[Explanation of symbols]

 1 Power-on detection unit 5 Reflected wave signal 6 Reflected wave level detection unit 7 Comparison unit 12 Background reflected wave dependent threshold value initialization unit 13 Background reflected wave dependent threshold value storage unit 14 Background reflected wave dependent threshold value changing unit 15 Time counter

Claims (2)

[Claims] 1. A power-on detection unit for detecting power-on,
A time measurement unit that measures the time from power-on in response to the detection output of the power-on detection unit, a reflected wave detection unit that emits ultrasonic waves toward a detection target and detects reflected waves of the ultrasonic waves,
The threshold value storage unit that stores the threshold value that depends on the reflected wave from the background of the vehicle and the threshold value of the threshold value storage unit that corresponds to the reflected wave detection time in response to the measurement time of the time measurement unit Compares the detection output of the reflected wave detection unit with the threshold value of the threshold value storage unit, which sequentially changes the threshold value, and outputs the vehicle detection signal when the former level exceeds the latter level, and otherwise In the case of, an ultrasonic type vehicle detector including a comparison unit that outputs a background reflected wave detection signal. 2. A power-on detection unit for detecting power-on,
A time measurement unit that measures the time from power-on in response to the detection output of the power-on detection unit, a reflected wave detection unit that emits ultrasonic waves toward a detection target and detects reflected waves of the ultrasonic waves,
The threshold value storage section that stores the threshold value that depends on the reflected wave from the vehicle background, and the threshold value of the threshold value storage section that is changed in sequence according to the level of the background reflected wave detected by the reflected wave detection section The threshold value changing unit and the detection output of the reflected wave detection unit and the threshold value of the threshold value storage unit are compared, and when the former level exceeds the latter level, the vehicle detection signal is output and at other times. An ultrasonic vehicle detector, comprising: a comparison unit that outputs a background reflected wave detection signal.