JP2001133549A - Obstacle determining method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an obstacle determining method capable of discriminating an obstacle even in a short range by using an ultrasonic sensor. SOLUTION: A reference time is inputted to the memory 11 of a microcomputer 4, the end time of a received wave signal received simultaneously with transmission of an ultrasonic wave is compared with the reference time in a discriminating circuit 12, and when the end time exceeds the reference time, short range obstacle present is determined. The reference time is inputted in two ways: the case of inputting the end time of the received wave signal received simultaneously with transmission of the ultrasonic wave as the measurement time, and the case of inputting the set time obtained by previously measuring the reverberation time of the ultrasonic sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for determining an obstacle by mounting an ultrasonic sensor on a vehicle or the like and detecting a surrounding state.

[0002]

2. Description of the Related Art Conventionally, an ultrasonic sensor mounted on a vehicle or the like detects a reflected wave from an object within a detection range, and transmits an ultrasonic pulse transmitted from an ultrasonic transmitter and reflected by an object. After the signal is input to the ultrasonic receiver, the received signal is amplified, detected, and shaped, and the control circuit measures the time from the start of transmission of the ultrasonic pulse signal to the reception of the reflected wave, thereby obstructing the obstacle. The distance to the vehicle was calculated, and the presence or absence of an obstacle was determined based on the calculated distance.

A conventional obstacle determination method using an ultrasonic sensor will be described with reference to FIG. Here, FIG. 3A shows an ultrasonic pulse of the ultrasonic wave transmitter, and FIG. 3B shows a received wave of the ultrasonic wave receiver. Also, (c) shows an envelope signal from which noise has been removed and extracted by an envelope detector, and (d) shows a rectangular wave pulse output from the waveform shaper when the detected signal level is equal to or higher than a predetermined reference voltage V0. Indicates a signal. The rectangular pulse signal is input to the arrival time measuring device, and the emission time and reflection time of the ultrasonic pulse are calculated.

In FIG. 3, the ultrasonic pulse is generated at times t1, t2,
It is emitted at t3, and its reflected wave is received at times t4, t5, and t6. And these time differences (t4-t
From 1), (t5-t2), and (t6-t3), the distance to the object in each state has been calculated.

By the way, the ultrasonic wave receiver detects a received wave simultaneously with the emission of each ultrasonic pulse.
It has been received until t21 and t31. This is because a portion where the emitted ultrasonic pulse directly affects the receiver and the reverberation of the housing of the ultrasonic sensor itself appear as a transmission waveform. Therefore, when the target object is very close, the time when the reflected wave appears, for example, t4 approaches t11, and finally the transmission waveform and the reception waveform overlap.

In general, when measuring the distance by ultrasonic waves, the oscillation time applied to the ultrasonic transmission sensor is shortened when the object is at a short distance, and the oscillation time is increased when the distance is long (1.5 to 10 m). It needs to be lengthened to some extent. This is because, since the ultrasonic transmission sensor itself is a resonator, even if the energy such as the applied voltage is increased, a physically large vibration energy cannot be obtained in a short time even if the energy is increased, and therefore the transmission ultrasonic energy is reduced. By adding this for a long time, the vibration energy is increased to extend the reach to a long distance. On the other hand, when the oscillation time is long, the resolution is reduced, and it is not possible to separate the reflection of a nearby obstacle or the like from the transmitted sound wave, the reverberation time of the housing itself, and the like.

[0007] These relationships will be described with reference to FIG. FIG. 4A shows a reception waveform when the transmission time is short, and a short-range reflection waveform 2 appears after the transmission waveform 1. By measuring the time until the appearance time, that is, the time ta from the time of oscillation to the time of appearance of the reflected waveform, the distance to the short-range obstacle can be calculated. However, in this case, a long-distance reflected waveform 3
Is small, and cannot be detected.

On the other hand, FIG. 4B shows a reception waveform when the transmission time is long, and a short-range reflection waveform 12 appears without separation following the transmission waveform 11. In this case, the reflected waveform 13 at a long distance can be detected, and the distance to the long-distance obstacle can be calculated by measuring the time tb.

[0009]

Conventionally, since the transmission time of the ultrasonic wave was about 0.5 ms, it was impossible to measure the reflected wave within this transmission time in the first place, and its resolution was about 30 c.
m. The duration of the reception waveform (reverberation waveform) during transmission is 1.0 to 1.5 ms when there is no short-range reflection.
About. However, if there is an obstacle or the like at a short distance (about 30 cm to 60 cm) and there is a reflected wave, the reverberation waveform due to transmission and the reflected waveform are added, and the duration of the reverberation waveform is increased to 2.0 ms or more. Become.

If an obstacle is present within 20 cm, the transmitted wave hits the obstacle and is reflected. However, the reflected wave is reflected again by the sensor and travels toward the obstacle. I do. Also, if there is an obstacle immediately before the sensor, a growling sound may occur. In this case, the reverberation time is particularly prolonged. If such a phenomenon exists, it is not possible to determine the distance to a nearby obstacle.

As described above, in the conventional obstacle determination method, the distance to the obstacle is calculated based on the appearance time of the reflected waveform. Therefore, if the transmission time is shortened, a reflected waveform at a long distance cannot be detected. Also, if the transmission time is lengthened, the reflection waveform at a short distance cannot be separated, and the distance to a short-range obstacle cannot be calculated.

An object of the present invention is to solve the above-mentioned problems of the conventional obstacle judging method and to provide an obstacle judging method capable of judging an obstacle even at a short distance by using an ultrasonic sensor. I have. Also, it is possible to detect a smaller obstacle, to reliably detect even if an obstacle is already present at the first measurement start time, and to provide an obstacle determination method in consideration of an error. I have.

[0013]

In order to solve the above-mentioned problems, an obstacle judging method according to the present invention transmits an ultrasonic wave from a transmitter, outputs a received wave signal output from a receiver and an output signal from a control circuit. In the method of determining the obstacle by inputting a control signal to the determination circuit, the determination circuit, the end time of the received wave signal received at the same time as the ultrasonic wave transmission and the reference time of the control signal input from the control circuit And if the end time exceeds the reference time, it is determined that there is a short-range obstacle. If it is within the reference time, it is determined that there is no change from the initial state, and it is determined that there is no short-range obstacle.

In the obstacle judging method according to the present invention, the ultrasonic wave is transmitted prior to judging the presence / absence of an obstacle, and the ending time of the received wave signal received simultaneously with the transmission of the ultrasonic wave is set as the measurement time and the control is performed. It stores in the circuit, then performs ultrasonic transmission for obstacle determination, in the determination circuit, the end time of the received wave signal for obstacle determination and the measurement time as the reference time input from the control circuit In comparison, when the end time exceeds the measurement time, it is determined that a short-range obstacle is present. The measurement time measures the reverberation time in the case where there is no obstacle. Based on this measurement, a smaller change in the reverberation time can be detected, so that the sensitivity is increased and a small obstacle can be detected.

According to a third aspect of the present invention, in the obstacle judging method, a predetermined set time is stored in the control circuit, and in the judgment circuit, the end time of the received wave signal and the reference time inputted from the control circuit are stored. The set time as a time is compared, and when the end time exceeds the set time, it is determined that a short-range obstacle is present.
For the set time, the reverberation time of the ultrasonic sensor is measured in advance, and the time is stored in a computer program. In this case, short distance measurement can be performed from the first transmission, and even if an obstacle is already present at the start of the first measurement, it can be reliably detected.

According to a fourth aspect of the present invention, in the obstacle determining method, a predetermined set time stored in advance in the control circuit is compared with the measured measurement time, and one of the measured times is adopted as the reference time. It is characterized by the following. For example, when the measurement time is within the set time, the measurement time is set as the reference time. If the set time is shorter, it is determined that there is an obstacle at a short distance at the start of the measurement.

According to a fifth aspect of the present invention, in the obstacle determining method, the reference time is determined by adding or multiplying a predetermined value to the stored measurement time and / or the set time. is there. The reverberation time value is not constant and analog fluctuations occur.However, even if the reverberation time becomes longer to some extent, it is determined that there is an obstacle nearby by adding or multiplying a predetermined value and considering the error. Don't do it.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram illustrating a configuration of an apparatus that performs obstacle determination using an ultrasonic sensor.
FIG. 2 is a flowchart showing an obstacle determination method. The ultrasonic sensor has a configuration in which an ultrasonic transmitter 2 and an ultrasonic receiver 3 are provided inside a case 1 attached to a vehicle body.

A pulse generation circuit 5 connected to the microcomputer 4 sends a control signal to an ultrasonic wave generation circuit 6 in the case 1 and receives an ultrasonic wave from the ultrasonic wave transmitter 2 for a predetermined period at regular intervals. The pulse signal is transmitted to the target 7. This transmission time is about 0.5 ms. When the transmitted and reflected ultrasonic pulse signal enters the ultrasonic wave receiver 3, the received signal is amplified to a certain level by the amplifier 8, detected by the envelope extracting circuit 9, and then detected in the upper half or lower half of the envelope (envelope). ) The component is extracted and shaped into a rectangular pulse signal representing the reception timing by the waveform shaper 10.

The reference time is input to the memory 11 of the microcomputer 4, and the discrimination circuit 12 compares the end time of the received wave signal received simultaneously with the transmission of the ultrasonic wave with the reference time. When the time exceeds the reference time, it is determined that there is a short-range obstacle, and the microcomputer 4 sends an obstacle detection signal to the alarm unit. Specifically, a display 13 such as a lamp or an LED is turned on, or a warning is issued by a speaker 16 via a voice synthesis circuit 14 and an amplifier 15.

The reference time input to the memory 11 is such that the ultrasonic wave is transmitted prior to the determination of the presence or absence of an obstacle, and the end time of the received wave signal received simultaneously with the transmission of the ultrasonic wave is input as the measurement time. There are two cases: inputting a set time obtained by measuring the reverberation time of the ultrasonic sensor in advance.

When the measurement time is used as a reference, it is effective even when the obstacle is a small object, and there is an advantage that even if there is a difference in characteristics due to variations in the sensor itself, it can be reduced. However, the sensor itself has temperature, humidity,
It can be said that it is not suitable for long-time measurement because it changes over time due to the influence of rainfall or the like.

Next, when the set time is used as a reference, the reverberation time of the sensor is measured in advance and the time is stored in a computer program. The duration of the received waveform (reverberation waveform) when the transmission time is about 0.5 ms is usually about 1.0 to 1.5 ms when there is no short-distance reflection. 2.0 ms to 2.
0 ms is used.

When it is determined whether to use the measurement time or the set time in the obstacle determination, FIG.
As shown in FIG. 7, after the initial processing and the like are completed, first, before the determination of the presence or absence of an obstacle, an ultrasonic wave is transmitted, and the reception levels of the transmission waveform and the reverberation waveform are measured. When it does, measure the duration until then. The measurement time is compared with a preset time stored in advance, and one of them is input to the discrimination circuit 12 as a reference time. This reference time is generally set to about 2.0 ms, which is equivalent to about 30 cm. When the measurement time is within the set time, it is desirable to use the measurement time as the reference time.

Thereafter, ultrasonic waves for obstacle determination are transmitted,
Similarly, the reception level is measured, and when the reception level becomes equal to or less than the set value, the duration is measured.

When the reference time is exceeded, the determination is made based on an error consideration time obtained by adding or multiplying a predetermined value to the reference time.
This is because if the operation of the sensor is repeated, the value of the reverberation time will not always be constant, and fluctuations due to surrounding conditions, analog fluctuations, etc. will occur, so these fluctuations will change the reverberation time, so the reverberation time will be somewhat longer This is to prevent the determination that there is an obstacle nearby in the event that this happens.

Therefore, when the error is within the error consideration time, it is determined that there is no short-range obstacle, and when it exceeds this, it is determined that there is a short-range obstacle. The numerical value used for the addition or the multiplication is required particularly when the measurement time is used as a reference. The designated coefficient used for the multiplication usually takes a number of about 1.0 to 2.0, and multiplies this by the measurement time to obtain the error consideration time. For example, when the measurement time is 1.3 ms and the designated coefficient is 1.2, the error consideration time is 1.56 ms. Note that the error consideration time can be obtained by adding a certain time to the measurement time. For example, the measurement time is 1.3 ms + the designated value 0.2 = 1.5 ms.

In the case where the reference time is set as the set time, if this error consideration time is set in advance, this determination part can be omitted. In addition, the process of transmitting the ultrasonic waves and calculating the measurement time prior to the determination of the presence / absence of an obstacle can be omitted, so that a short-distance obstacle can be measured from the first transmission, and the obstacle is already detected at the start of the first measurement. Even if there is, it can be reliably detected.

[0029]

As described above, according to the obstacle judging method of the present invention, the end time of the received wave signal received simultaneously with the transmission of the ultrasonic wave is compared with the reference time. Can be determined. In the obstacle determining method according to the second aspect, since the measurement time is used as the reference time, a smaller change in reverberation time can be detected, and the sensitivity increases and a small obstacle can be detected. Since the set time is used as the reference time in the obstacle determining method according to the third aspect, even if an obstacle is already present at the first measurement start time, the obstacle can be reliably detected.

In the obstacle judging method according to the present invention, the set time and the measuring time are compared and one of them is adopted as the reference time, so that the respective advantages of both judging methods can be used.
In the obstacle determination method according to the fifth aspect, since the determination is performed by adding or multiplying a predetermined value to the reference time, even if the reverberation time becomes longer to some extent, it is possible to perform an effective obstacle determination in consideration of an error. Become.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an apparatus that performs obstacle determination.

FIG. 2 is a flowchart illustrating an obstacle determination method.

FIG. 3 is a signal waveform diagram of a conventional ultrasonic sensor.

FIG. 4 is a reception waveform chart when an obstacle exists at a short distance.

[Explanation of symbols]

 2 Ultrasonic wave transmitter 3 Ultrasonic wave receiver 4 Microcomputer 11 Memory 12 Discrimination circuit

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Tadashi Kamemura 2111 No. 6 tiled roof tiles, Ageo-shi, Saitama F-term (reference) in Nissei Giken Co., Ltd. 5J083 AA01 AB12 AC05 AD07 AE01 AE08 AE10 AF05 BA01 BB05 BE18 BE38 CA02 CC02 EB11

Claims (5)

[Claims] 1. A method for transmitting an ultrasonic wave from a transmitter and receiving a received wave signal output from a receiver and a control signal output from a control circuit to a determination circuit to determine an obstacle. The circuit compares the end time of the received wave signal received simultaneously with the transmission of the ultrasonic wave with the reference time of the control signal input from the control circuit, and when the end time exceeds the reference time, there is a short-range obstacle. And an obstacle determination method. 2. An ultrasonic wave is transmitted prior to the determination of the presence or absence of an obstacle, and an end time of the received wave signal received simultaneously with the transmission of the ultrasonic wave is stored in the control circuit as a measurement time,
Thereafter, ultrasonic transmission for obstacle determination is performed, and the determination circuit compares the end time of the reception wave signal for obstacle determination with the measurement time as the reference time input from the control circuit. 2. The obstacle determining method according to claim 1, wherein it is determined that a short-range obstacle exists when a time exceeds the measurement time. 3. A predetermined set time is stored in the control circuit, and the determination circuit compares an end time of the received wave signal with the set time as the reference time input from the control circuit. 2. The obstacle determining method according to claim 1, wherein when the end time exceeds the set time, it is determined that there is a short-range obstacle. 4. The obstacle determination method according to claim 2, wherein a predetermined set time stored in advance in the control circuit is compared with the measured time to be measured, and one of the measured times is adopted as the reference time. An obstacle determining method. 5. The method according to claim 1, wherein the reference time is determined by adding or multiplying a predetermined value to the stored measurement time and / or the set time. Or the obstacle judging method according to claim 4.