JP2002006036A - Sensing method for reflected waves of ultrasonic waves and ultrasonic sensor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To expand the sensing range at a short range of an ultrasonic sensor device. SOLUTION: Received signals are sampled at prescribed intervals, and a level state which is composed of a combination of levels with reference to respective threshold values is found by using a plurality of stages of threshold values A, B, C, D in each sampling operation. The first change point of the level state corresponding to the rise after the fall of a waveform is sensed as the rise of reflected waves Wh. Even when output waves Wo and the reflected waves Wh are brought close so as to be partly overlapped, both are discriminated on the basis of a change in the levels with reference to any level value, and the reflected waves Wh can be sensed. As a result, the sensing range of an obstacle or the like at a short range is expanded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic wave reflected wave detecting method and an ultrasonic sensor device which are mounted on a vehicle and used for detecting an obstacle around the vehicle.

[0002]

2. Description of the Related Art An ultrasonic sensor device transmits an ultrasonic wave from a transmitter, receives a reflected wave from an object within a detection range by a receiver, and detects a reflected wave, that is, a reflected wave from the transmission. The distance to an object such as an obstacle is detected based on the time difference until reception. FIG. 7 briefly illustrates the principle. (A) of the figure shows the ultrasonic wave (output wave Wx) transmitted from the transmitter and the reflected wave Wy returned after the ultrasonic wave hits an obstacle and received by the receiver. (B) shows a waveform obtained by integrating and converting the output wave and the reflected wave, that is, a detected waveform, and (c) is a shaped waveform obtained by shaping the detected waveform of (b) at a predetermined threshold level. is there. The distance from the transmitter / receiver to the obstacle is calculated based on the time difference Tz between the rising points of the output wave and the reflected wave in the shaped waveform.

When such an ultrasonic sensor device is used for a vehicle, an alarm can be issued when a detected obstacle is within a predetermined distance, and a vehicle traveling ahead is monitored according to a set detection distance range. It is possible to easily secure the inter-vehicle distance or to easily park at a predetermined position in a narrow garage without contacting surrounding vehicles or walls. This type of ultrasonic sensor device is also disclosed in, for example, JP-A-56-92483.

[0004]

However, in the ultrasonic sensor device as described above, when the distance to an obstacle or the like is reduced, the output wave Wx is reduced as shown in the detection waveform of FIG. The reflected waves Wy overlap,
As shown in (b), depending on the low threshold value L1, the shaped waveform is continuous, and the reflected wave cannot be identified.

[0005] As a countermeasure, if the threshold value is set to a high value L2, the reflected wave Wy can be identified as shown in (c). However, this is effective only when the intensity of the reflected wave Wy is large. On the other hand, a reflected wave having a small intensity from a relatively long distance does not reach the threshold value L2, and is not detected. For this reason, the shortest distance that can be identified and detected in a practical ultrasonic sensor device is limited to about 30 cm.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the above-mentioned conventional problems, and an ultrasonic reflected wave detection method and an ultrasonic sensor capable of reliably detecting a long-distance obstacle or the like, and detecting a closer distance. It is intended to provide a device.

[0007]

According to the present invention, there is provided a method for detecting a reflected wave of an ultrasonic wave for transmitting an ultrasonic wave and detecting a reflected object from a reflected wave included in a received signal. The received signal is sampled at predetermined intervals, and the level of the received signal is obtained at a plurality of threshold values for each sampling, and it is detected that the level state, which is a combination of levels for each threshold value, has changed in a predetermined direction. Then, the received signal at the time of the detection is determined to be a reflected wave.

According to a second aspect of the present invention, there is provided an ultrasonic sensor device for transmitting an ultrasonic wave and detecting a reflected object from a reflected wave included in the received signal. Level detecting means for obtaining the level of the received signal at a plurality of threshold levels for each, detecting that the level state consisting of a combination of levels for each threshold determined by the level detecting means has changed in a predetermined direction, And a reflected wave detecting means for detecting a reflected wave.

According to the first and second aspects, a plurality of sets of levels for a plurality of threshold values are obtained for each sampling, so that even if the output wave and the reflected wave are close to each other and partially overlap with each other. Since the two can be identified and the reflected wave can be detected by a change in the level with respect to any one of the threshold values, the detection range of an obstacle or the like at a short distance is expanded.

According to a third aspect of the present invention, in addition to the configuration of the second aspect, a reflected wave reception time setting means for determining a reception time of a reflected wave from the transmission of the ultrasonic wave based on the sampling time at which the level state has changed. And a distance calculating means for calculating a distance to the reflecting object based on the reflected wave reception time. Thereby, the distance to the detected reflection object is obtained.

According to a fourth aspect of the present invention, the reflected wave detecting means detects the first change point of the level state corresponding to the rising after the falling of the waveform of the received signal as the rising of the reflected wave. Thereby, the reflected wave is detected without erroneous recognition.

According to a fifth aspect of the present invention, the reflected wave reception time setting means sets the reflected wave detection time from the transmission of the ultrasonic wave to the sampling time at which the rise of the reflected wave is detected, as the reception time of the reflected wave. The reception time can be easily obtained. According to a sixth aspect of the present invention, the reflected wave reception time setting means further corrects the reflected wave detection time in a shortening direction according to the threshold value whose level has been changed. As a result, even a slight shift in the reception time that may occur due to the rising slope of the reflected wave is corrected.

[0013]

Embodiments of the present invention will be described below with reference to examples. FIG. 1 is a block diagram showing the overall configuration of an embodiment in which the present invention is applied to a vehicle alarm device. An ultrasonic microphone 3 for transmitting and receiving ultrasonic waves is connected to the oscillator 1 via a microphone driving unit 2. The ultrasonic microphone 3 is installed, for example, on the front bumper of the vehicle toward the front, or is installed on the rear bumper rearward and obliquely rearward. Here, only one ultrasonic microphone will be described.

The oscillator 1 outputs a pulse signal having a time width τ at a constant period of, for example, 100 μs. The pulse width τ is 0.
It is set in the range of 2 to 0.5 ms. Microphone drive 2
Receives the pulse signal from the oscillator 1 and outputs the time width τ
During this period, a drive signal of, for example, 40 kHz is output, whereby the ultrasonic microphone 3 transmits ultrasonic waves. An amplification / detection unit 4 is further connected to the ultrasonic microphone 3, and the amplification / detection unit 4
The level detector 5, the reflected wave detector 6, and the distance calculator 7 are sequentially connected to the detector 4, and the alarm calculator 8 is connected to the distance calculator 7.

The amplifying / detecting section 4 amplifies the signal received from the ultrasonic microphone 3 (reflected wave from an obstacle), performs integral conversion, and performs the same detection waveform (FIG. 6B) as shown in FIG. (Detection output). When the ultrasonic wave is transmitted, the output wave of the ultrasonic microphone 3 is also input to the amplification / detection unit 4 as a reception signal. The functions of the oscillator 1, the microphone drive unit 2, and the amplification / detection unit 4 are the same as those of the conventional general ultrasonic sensor device, and therefore, the details are omitted.

The level state detector 5 compares a predetermined threshold level with the detection output of the amplifier / detector 4 and shapes the waveform to generate a high (H) -low (L) pulse waveform.
Here, in the present embodiment, sampling of the detection output is started at a predetermined interval in response to the pulse signal from the oscillator 1, and the comparison is performed by changing the threshold value in a plurality of steps for each sampling.

That is, the principle is schematically explained. While the detection output of the received signal is input to the input terminal of the comparator 10 from the amplifying / detecting section 4, a resistor 12 is connected between the reference terminal and the power supply VE. , And resistors 13a, 13b,.
Are switchably connected by the switch 14 so that the potential of the threshold can be changed. As described above, by changing the threshold value at the time of one sampling, a set of a plurality of comparator outputs, that is, a level state of the received signal, is obtained corresponding to the threshold value.

The reflected wave detector 6 identifies the reflected wave from the transition of the level state for each sampling, and calculates the distance calculation unit 7
Finds the time from the transmission of the ultrasonic wave to the reception of the reflected wave,
Based on this elapsed time, the distance to a reflective object such as an obstacle is calculated. The warning unit 8 issues a warning in a predetermined manner according to the distance calculated by the distance calculation unit 7. For example, in the case of warning of approaching an obstacle in a garage or the like, an alarm is started with an intermittent buzzer sound when approaching a preset distance, and the intermittent time can be shortened as the distance becomes narrower. Among the above, at least the oscillator 1, the level state detector 5, the reflected wave detector 6, and the distance calculator 7 can be constituted by a microcomputer.

Next, the processing procedure in the level state detecting section 5, the reflected wave detecting section 6, and the distance calculating section 7 will be described. FIG. 2 is a flowchart showing the processing procedure. First, at step 101, the level state detector 5 samples the detection output of the received signal at intervals of about 100 μs as described above, and at step 102, obtains the level of the received signal.

Here, A, B,
As four stages of C and D, the level of the detection output is obtained by changing the threshold value in the order of D, C, B and A for each sampling. In this case, the level state of the received signal is one of the five levels shown in FIG. Here, the lower the level state number, the lower the level state, and the higher the number, the higher the level state.

In step 103, the reflected wave detector 6 checks for each sampling whether the level state has changed to a lower level than the level state in the previous sampling. If the level state has changed to the lower side, the process proceeds to step 104, and if not, the process returns to step 101.

In steps 104 and 105, step 1
Sampling is continued similarly to steps 01 and 102, and the level of the received signal is obtained. Then, in step 106, it is checked whether or not the level state has changed to a higher level than the level state in the previous sampling. If the level state has changed to the upper side, the process proceeds to step 107 on the assumption that the rise of the reflected wave has been detected, and if not, the process proceeds to step 112.

FIG. 4 shows an example of a change in the level state of the received signal. FIG. 4A shows a level change of a received signal in which the output wave Wo and the reflected wave Wh are sufficiently separated. Sampling is started in response to a pulse from the oscillator 1 for transmitting ultrasonic waves. For example, at the sampling time t2, the value of the received signal is high with respect to any of the threshold values D, C, B, and A. The level corresponding to the threshold value is “H, H, H, H” in the order of the threshold value.

Similarly, at times t3, t4, t5, and t6,
For the threshold values D, C, B, and A, the levels of the received signals are “L, H, H, H”, “L, L, L, L”, “L, L,
L, L "and" H, H, H, H ". Hereinafter, if sampling is continued, the level of the received signal at each time changes as shown in the figure. In this figure, the sampling times t1 to t4 detect the level of the output wave Wo, and the sampling times t5 to t8 detect the level of the reflected wave Wh. However, as will be described later, sampling is not necessary after the level state first changes to the upper side at the rise of the reflected wave Wh.

As is apparent from the figure, before the rise of the reflected wave Wh, the levels of the received signals with respect to the threshold values D, C, B, and A are "L, H,
H, H "(level state 4) to" L, L, L, L "(level state 1), and thereafter, at times t5 to t6," L,
L, L, L "(level state 1) to" H, H, H, H "
(Level state 5). This change in the level state can be schematically shown as in FIG. That is, a point (time t6) where the level state changes to the upper side for the first time after the level state changes to the lower side can be detected as the rise of the reflected wave Wh. In the figure, the width of the step portion is drawn large for easy understanding, but the time width is small enough to be ignored.

FIG. 4B shows a change in the level of the received signal in which the output wave Wo and the reflected wave Wh partially overlap each other when the distance to the obstacle is short. At sampling time t2,
As in (a), the levels for the thresholds D, C, B, and A are "H, H, H, H" in the order of the thresholds, but at times t3, t4, and t5, the thresholds are set. Values D, C,
The level of the received signal is "L, H, H,
H "," L, L, H, H "," H, H, H, H ".

That is, also in this case, the level state changes from "L, H, H, H" (level state 4) to "L, L, H, H" (level state 3) from time t3 to t4. Then, from time t4 to t5, the state changes from “L, L, H, H” (level state 3) to “H, H, H, H” (level state 5) to the upper side. As a result, as shown by the arrow in FIG. 5B, the point at which the level state changes to the higher side (time t)
5) can be detected as the rise of the reflected wave Wh.

Returning to the flowchart, step 107
Then, the elapsed time from the rising of the pulse of the oscillator 1 to the sampling time when the rising of the reflected wave Wh is detected by the distance calculation unit 7 is determined as the reflected wave detection time T0 (T0 '). In the next step 108, the above-mentioned step 106 is performed with respect to the reflected wave detection time T0 (T0 ').
At the rising edge of the reflected wave Wh detected in step (1), the maximum threshold value whose level state has been changed to the upper side is confirmed, and the correction time ΔT is set from FIG. 6 according to this threshold value. This is to correct the delay of the time at which the reflected wave crosses the threshold as the threshold increases.

In step 109, the reflected wave detection time T0
The correction time ΔT is added to (T0 ′) to obtain a reflected wave reception time T. For example, in the example of FIG. 4A, the change of the received signal to the upper side crosses the threshold D at time t6, and the threshold D closest to the received signal is the maximum level. Based on this threshold value D, the correction time ΔT = −0.3 ms is added to the reflected wave detection time from FIG. Thereby, for example, the time lag due to the rising slope is corrected with respect to the time when the rising of the same reflected wave is detected at time t5.

In step 110, the distance calculation unit 7
Is the reflected wave reception time T = T0 corrected in this way.
The distance to the obstacle is calculated using (T0 ′) + ΔT as the time when the ultrasonic wave reciprocates the distance to the obstacle, and the distance data is sent to the alarm unit 8. Thereafter, the process proceeds to step 111, where the sampling is terminated, and the next pulse oscillation,
That is, the transmission of the ultrasonic wave is waited.

On the other hand, in step 112 when the level state has not changed to the upper side, the level state detecting section 5
It is checked whether a predetermined time has elapsed from the rise of the pulse of the oscillator 1. If the predetermined time has not elapsed, the process returns to step 104;
Proceed to. That is, the sampling ends after a time corresponding to a preset detection distance has elapsed after the start, and the reception signal is not taken in until the next transmission of the ultrasonic wave.

In this embodiment, steps 101, 1
02, 104, 105 and 112 constitute the level detecting means of the invention, and steps 103 and 106 constitute the reflected wave detecting means. Steps 107 to 109
Represents a reflected wave reception time setting means, and step 110 constitutes a distance calculation means.

The embodiment is constructed as described above. In an ultrasonic sensor device for transmitting an ultrasonic wave, receiving its reflected wave, and detecting the presence of an obstacle or the like, and further detecting its distance, a received signal is transmitted at a predetermined interval. Sampling is performed, and the level of the received signal is obtained with a plurality of threshold values for each sampling,
Since the rise of the reflected wave is detected based on the change in the level state consisting of the combination of the levels for each threshold value,
Even if the transmitted output wave and the reflected wave approach each other and they partially overlap, the reflected wave can be detected by the change in the level with respect to the higher threshold value among the plurality of stages, and the reflected wave from a relatively long distance can be detected. Even if the signal strength is low, it is reliably detected by a low threshold value among a plurality of steps.

In particular, when detecting an obstacle or the like at a short distance, depending on which threshold the change in the level state at which the rising of the reflected wave is detected occurs,
Since a predetermined correction time is added in a direction to shorten the detection time of the reflected wave, a deviation of the detection time due to the difference in the threshold value is corrected, and the distance to an obstacle or the like can be measured with high accuracy.

In the above embodiment, the structure and operation of one ultrasonic microphone 3 relating to transmission and reception of ultrasonic waves have been described. However, even when a plurality of ultrasonic microphones are provided, the detection range is set according to the purpose. Other than that, it is common to each ultrasonic microphone. Although the embodiment has been described with respect to an example in which the invention is applied to an alarm device for a vehicle, the application target is not limited to this.

The numerical values such as the width of the pulse output from the oscillator 1, the sampling interval of the received signal, and the number of steps of the threshold value are merely examples, and appropriate values can be used as needed. Furthermore, in the embodiment, the ultrasonic microphone 3 is used also as a transmitter and a receiver, but independent transmitters and receivers may be used.

Further, in the embodiment, the rise of the reflected wave is detected to determine the detection time from the transmission of the ultrasonic wave (pulse output). Instead, the first rise of the output wave and the first rise of the reflected wave are used instead. It is also possible to detect the fall and determine the time between both fall as the detection time, or detect the peak of each of the output wave and the reflected wave from the transition of the level state change and determine the time between both peaks as the detection time Can also be sought.

[0038]

As described above, according to the present invention, in an ultrasonic sensor device, a reception signal is sampled at a predetermined interval,
Detecting the level of the received signal at a plurality of threshold values for each sampling, detecting that the level state comprising a combination of levels for each of the threshold values has changed in a predetermined direction, and detecting the reflected wave. Therefore, even if the output wave of the ultrasonic wave and the reflected wave are close to each other and partially overlap with each other, the reflected wave can be detected by identifying the two by the change in the level with respect to any one of the threshold values. This has the effect of expanding the detection range of obstacles and the like.

Then, the receiving time of the reflected wave from the transmission of the ultrasonic wave is determined based on the sampling time at which the level state has changed, and the distance to the reflecting object can be determined based on this.

In particular, in detecting the reflected wave, the first change point of the level state corresponding to the rising after the falling of the waveform of the received signal is detected as the rising of the reflected wave, so that the reflected wave is detected without error. be able to.

Then, the reflected wave detection time from the transmission of the ultrasonic wave to the sampling time when the rise of the reflected wave is detected can be easily obtained as the reception time of the reflected wave.
Furthermore, as the reception time, by correcting in a direction to shorten the reflected wave detection time according to the threshold value that has changed the level state, a slight shift due to the slope of the rise of the reflected wave is also corrected, The distance to the reflecting object is required with high accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of an embodiment in which the present invention is applied to an alarm device.

FIG. 2 is a flowchart illustrating a processing procedure in a level state detection unit and a distance calculation unit.

FIG. 3 is a diagram illustrating a level state of a reception signal.

FIG. 4 is a diagram showing a transition example of a change in a level state.

FIG. 5 is a diagram schematically showing a change in level state after waveform shaping.

FIG. 6 is a diagram illustrating a correction amount with respect to a reflected wave detection time.

FIG. 7 is an explanatory diagram showing a principle of detecting a distance to an object by the ultrasonic sensor device.

FIG. 8 is an explanatory diagram showing a problem in a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oscillator 2 Microphone drive part 3 Ultrasonic microphone 4 Amplification / detection part 5 Level state detection part 6 Reflection wave detection part 7 Distance calculation part 8 Alarm part 10 Comparator 12 Resistance 13a, 13b, ... Resistance 14 Switch VE power supply Wo output Wave Wh reflected wave

Claims (6)

[Claims] An ultrasonic reflected wave detection method for transmitting an ultrasonic wave and detecting a reflected object from a reflected wave included in a received signal, wherein the received signal is sampled at predetermined intervals, and a plurality of samples are provided for each sampling. Obtaining the level of the received signal with the threshold value of the step, detecting that the level state composed of a combination of the levels for each threshold value has changed in a predetermined direction, and judging the received signal at the time of the detection as a reflected wave. A method for detecting a reflected wave of an ultrasonic wave, comprising: 2. An ultrasonic sensor device for transmitting an ultrasonic wave and detecting a reflected object from a reflected wave included in a received signal,
The received signal is sampled at a predetermined interval, and a level state comprising a level detecting means for obtaining the level of the received signal at a plurality of threshold values for each sampling, and a combination of levels for each threshold value obtained by the level detecting means is provided. An ultrasonic sensor device comprising: a reflected wave detecting unit that detects a change in a predetermined direction and detects a reflected wave. 3. An ultrasonic sensor device for transmitting an ultrasonic wave and detecting a reflected object from a reflected wave included in a received signal,
The received signal is sampled at a predetermined interval, and a level state comprising a level detecting means for obtaining the level of the received signal at a plurality of threshold values for each sampling, and a combination of levels for each threshold value obtained by the level detecting means is provided. Reflected wave detecting means for detecting a change in a predetermined direction and detecting a reflected wave; and reflected wave reception time setting means for determining a reception time of a reflected wave from ultrasonic transmission based on the sampling time at which the change has occurred. And a distance calculating means for calculating a distance to a reflecting object based on the reflected wave receiving time. 4. The reflected wave detecting means detects a first change point of a level state corresponding to a rise after a fall of a waveform of a received signal as a rise of a reflected wave. The ultrasonic sensor device according to claim 1. 5. The reflected wave reception time setting means sets a reflected wave detection time from transmission of an ultrasonic wave to a sampling time at which the rise of the reflected wave is detected as a reception time of the reflected wave. The ultrasonic sensor device according to claim 4, wherein 6. The reflected wave reception time setting means for correcting the reflected wave detection time in a shortening direction in accordance with a threshold value that has changed the level state. The ultrasonic sensor device according to claim 1.