JPH05215850A - Ultrasonic range finder - Google Patents

Abstract

PURPOSE:To enable the correct measurement of distance to a target even with the level fluctuation of reflected waves from the target in a range finder utilizing ultrasonic waves. CONSTITUTION:A receiving part 1 receives reflected waves from a target based on ultrasonic transmit waves sent out synchronously with transmit timing pulses. A comparing part 14 generates a detection signal when the level of an input signal exceeds the threshold value, and a time difference signal generating part 15 generates a signal of time difference between the detection signal and transmit timing pulse. The distance to the target is measured by this time difference. In this case, a low-pass filter 16 is provided to convert the waveform of the input signal into envelope waveform, and this envelope waveform is used as the threshold value. As a result, even if the level of a reflection signal is fluctuated, the detection threshold value is changed accordingly so as to allow the distance to the target to be measured always correctly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring device using ultrasonic waves, and more particularly, it can accurately measure the distance to a target even when the level of a reflected wave from the target changes. The present invention relates to a sound wave distance measuring device.

[0002] An ultrasonic distance measuring device is a device that uses ultrasonic waves to measure the distance to a target, and is widely used because it can easily measure the distance to a target without contact. It is what has been.

In such an ultrasonic distance measuring device, it is possible to accurately measure the distance to the object to be measured even if the level of the reflected wave fluctuates due to changes in the distance and posture between the ultrasonic sensor and the object. is necessary.

[0004]

2. Description of the Related Art FIG. 5 shows an example of a circuit configuration on the receiving side in a conventional ultrasonic distance measuring apparatus, which is designated by reference numeral 1.
Reference numeral 1 is a reception sensor for receiving a reflected wave, reference numeral 12 is an amplifying section for amplifying an input signal, reference numeral 13 is a low-pass filter for selectively passing a low frequency component, and reference numeral 14 is for comparing the input signal with a detection threshold value. A comparator, reference numeral 15, is a time difference gate generation circuit for generating a time difference gate signal indicating the distance from the target.

FIG. 6 shows the timings of signals at various parts in the circuit of FIG. 5. The upper part shows the case where the level of the reflected wave is high, and the lower part shows the case where the level of the reflected wave is low. ..

The receiving sensor 11 receives the reflected wave from the target with a certain time difference from the transmission timing pulse,
The amplification unit 12 amplifies this and generates an output. The low-pass filter 13 converts the output waveform of the amplification section 12 into an envelope waveform and generates a comparator input. Comparator 14
Generates an output when the input level from the low-pass filter 13 exceeds the detection threshold value, and the time difference gate generation circuit 15
Is set by the transmission timing pulse at the set input S and reset by the comparator output at the reset input R, corresponding to the time from the transmission timing pulse to the rise of the comparator output,
A time difference gate signal is generated at the output Q. The time difference gate signal represents the round trip time of the ultrasonic signal, and the distance from this to the target can be obtained.

As described above, in the conventional ultrasonic distance measuring apparatus shown in FIG. 5, the arrival time is detected by comparing the envelope wave conversion of the reflected wave with the detection threshold value set arbitrarily. I am trying.

FIG. 7 shows another circuit configuration example on the receiving side in the conventional ultrasonic distance measuring apparatus.
It lacks a low-pass filter as compared to. In this case, the arrival time is detected by comparing the reflected wave with the detection threshold value without converting the envelope waveform.

FIG. 8 shows the timing of each signal in the circuit of FIG. 7. The upper part shows the case where the level of the reflected wave is high, and the lower part shows the case where the level of the reflected wave is low. ..

The receiving sensor 11 receives the reflected wave from the target with a certain time difference from the transmission timing pulse, and the amplifying section 12 amplifies it and generates an output. Comparator 14
Produces an output when the amplifier output exceeds the detection threshold,
The time difference gate generation circuit 15 is set by the transmission timing pulse at the set input S and reset by the comparator output at the reset input R, so that the time difference gate generation circuit 15 outputs an output corresponding to the time from the transmission timing pulse to the rise of the comparator output. Generate a time difference gate signal on Q.

As described above, in the ultrasonic distance measuring apparatus shown in FIG. 7, the arrival time is detected by directly comparing the reflected wave with an arbitrarily set detection threshold without converting the envelope waveform. I am trying.

[0012]

In the conventional ultrasonic distance measuring apparatus, the arrival of the reflected wave can be achieved by performing envelope waveform conversion on the reflected wave or by directly comparing the reflected wave with an arbitrarily set detection threshold value without envelope waveform conversion. I try to detect the time.

The reflected signal in the ultrasonic distance measuring device is
As shown in FIG. 6 or 8, the leading edge has a constant slope. Also, when the reflected wave is converted into an envelope waveform, its leading edge also has a constant inclination.

The signal strength of the reflected wave changes if the distance or posture between the target and the ultrasonic sensor changes, so that the level of the received signal changes. Therefore, as shown in FIG. 6 or FIG. 8, even the reflection signal from the same target changes the inclination state of its leading edge.

On the other hand, as the detection threshold value, a DC voltage or a value having a curve corresponding to the arrival time of the reflected signal is generally used. Therefore, once the detection threshold is determined, the detection threshold is always constant when the arrival time is determined.

As described above, since a constant detection threshold value is used and the point exceeding the threshold value is detected as the arrival time of the reflection signal, when the level of the reflection signal changes and the inclination of the leading edge changes, the time difference gate The arrival time of the reflected wave indicated by the signal changes. FIG. 6 and FIG. 8 show that the fluctuation portion shown in the figure occurs in the time difference gate signal indicating the time of the ultrasonic wave because the level of the reflected wave changes.

The present invention is intended to solve such a problem of the prior art, and in an ultrasonic distance measuring device, a reflected signal of a reflected signal is generated based on a change in the distance or posture between a target and an ultrasonic sensor. The purpose is to enable accurate distance measurement even if the level changes.

[0018]

According to the present invention, a receiving section 1 for receiving a reflected wave from a target, which is based on an ultrasonic transmission wave transmitted in synchronization with a transmission timing pulse, and a level of the reception signal have a threshold value. A comparison unit 2 that generates a detection signal when the value exceeds
An ultrasonic distance measuring device that includes a time difference signal generating unit 3 that generates a signal of a time difference between a detection signal and a transmission timing pulse, and an ultrasonic distance measuring device that measures a distance to a target by this time difference, and includes a low-pass filter 4 to receive a received signal. Is converted into an envelope waveform, and this envelope waveform is used as a threshold value.

A detection signal is generated when the level of the signal received by the reflected wave from the target, which is based on the ultrasonic wave transmitted in synchronization with the transmission timing pulse, exceeds a threshold value. The time difference between the target and the target is measured by this time difference.
The low-pass filter 4 converts the waveform of the received signal into an envelope waveform and uses this envelope waveform as a threshold.

Therefore, according to the present invention, even if the level of the reflected signal changes depending on the distance and the posture between the target and the ultrasonic sensor, the detection threshold value changes accordingly, so that the time difference is prevented from changing. The distance to the target can be measured correctly.

[0021]

1 shows a circuit configuration of an embodiment of the present invention, in which the same components as those in FIG. 5 are designated by the same reference numerals, and the reference numeral 16 indicates that the offset value of the output signal can be changed. It is a low-pass filter that is made possible.

FIG. 2 shows the timings of signals at various parts in the embodiment of FIG. 1. The upper part shows the case where the level of the reflected wave is high, and the lower part shows the case where the level of the reflected wave is low. .. The operation of the embodiment of the present invention will be described below with reference to FIGS.

The reception sensor 11 receives the reflected wave from the target with a certain time difference from the transmission timing pulse, and the amplification section 12 amplifies the received wave to generate an output. The low-pass filter 16 converts the output waveform of the amplification section 12 into an envelope waveform and generates a comparator input. The comparator 14 is
The output of the amplifier 12 is compared with the output of the low pass filter 16, and when the output of the amplifier 12 exceeds the output of the low pass filter 16, an output is generated.

The time difference gate generation circuit 15 is set by the transmission timing pulse at the set input S,
Resetting by the comparator output at reset input R produces a time difference gate signal at output Q corresponding to the time from the transmission timing pulse to the rise of the comparator output. The time difference gate signal represents the round trip time of the ultrasonic signal, and the distance from this to the target can be obtained.

At this time, by changing the magnitude of the offset signal given to the low-pass filter 16, it is possible to prevent detection of signal components below a predetermined level and prevent erroneous detection in the comparator 14. it can.

As shown in FIG. 2, when the level of the reflected signal changes, the envelope waveform converted signal also changes accordingly. In the present invention, this is given as a detection threshold to one input of the comparator, and the reflected signal is given to the other input of the comparator. Therefore, the detection threshold value also changes according to the change in the level of the reflected signal, and the arrival time can be detected with a fixed relationship, so that the fluctuation of the time difference gate signal due to the change in the magnitude of the reflected signal can be reduced. it can.

FIG. 3 shows an example of the configuration of the low-pass filter portion according to the present invention. The same parts as those in FIG. 1 are indicated by the same numbers, D1 and D2 are detection diodes, C is a smoothing capacitor, and VR is a variable resistor for level adjustment, OPA is an operational amplifier, and R1 to R4 are operational amplifiers OP.
It is a fixed resistor that determines the gain of A.

FIG. 4 shows the signal waveform of each part in the circuit of FIG. 3, and illustrates the operation of the circuit of FIG. In the figure, (a) is the output of the amplifier 12, (b)
Is the output of the operational amplifier OPA, and these are the comparator 1
4 inputs. Also, (c) is a variable resistor V for level adjustment.
Input of R, showing envelope waveform. (d) is
Shows the value of the offset signal V _OS of the low-pass filter,
(e) represents noise and the like.

The positive side (a) of the output of the amplifying section 12 is added to the smoothing capacitor C via the detection diode D1. If the time constant of the low-pass filter composed of the capacitor C and the variable resistor VR is sufficiently larger than the time constant of the reflected wave waveform, the waveform of the voltage V _E across the capacitor C becomes
A smoothed envelope waveform (c) corresponding to the amplitude of the output of the amplification unit 12 on the positive polarity side is obtained.

The portion composed of the operational amplifier OPA and the resistors R1 to R4 constitutes a threshold value adjusting portion and operates as an adder circuit, and the voltage given through the output V _E 'of the variable resistor VR and the resistor R2. In FIG. 4, the sum of V _OS and (b)
Produces an output V _O. That is, " _VO = _VE '+
V _OS ".

Therefore, by appropriately adjusting the voltage V _OS applied via the resistor R2, the comparator 14 is controlled by a small amplifier output below the offset voltage V _OS and noise (e) shown in FIG. 4 (d). Can be prevented from operating, which can prevent erroneous detection of distance due to noise or the like.

When the voltage V _OS is adjusted in the circuit of FIG. 3, the output V _O from the operational amplifier OPA moves in parallel as a whole, so that the detection threshold becomes larger than the output of the amplifier and the reflected signal cannot be detected in some cases. In this case, the level adjusting variable resistor VR may be adjusted to adjust the amplitude of the output voltage V _E ′.

[0033]

As described above, according to the present invention, in the ultrasonic distance measuring device, even if the level of the reflection signal fluctuates based on the change in the distance between the target and the ultrasonic sensor or the change in posture, It becomes possible to measure the distance.

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing timings of signals of respective parts in the embodiment of FIG.

FIG. 3 is a diagram showing a configuration example of a low-pass filter unit in the present invention.

FIG. 4 is a diagram showing signal waveforms of respective parts in the circuit of FIG.

FIG. 5 is a diagram showing a circuit configuration example on the receiving side in a conventional ultrasonic distance measuring apparatus.

FIG. 6 is a diagram showing timings of signals in respective parts in the circuit of FIG.

FIG. 7 is a diagram showing another circuit configuration example on the receiving side in the conventional ultrasonic distance measuring apparatus.

8 is a diagram showing timings of signals in respective parts in the circuit of FIG.

[Explanation of symbols]

 1: Receiving unit 14: Comparator as a comparing unit 15: Time difference gate generating circuit as a time difference signal generating unit 16: Low pass filter

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuaki Hishinuma 2-16-46 Minami Kamata, Ota-ku, Tokyo Within Tokimec Co., Ltd.

Claims (1)

[Claims] 1. A comparison between a receiving unit that receives a reflected wave from a target based on an ultrasonic transmission wave transmitted in synchronization with a transmission timing pulse, and a detection signal that is generated when the level of the received signal exceeds a threshold value. And a time difference signal generation unit that generates a signal of a time difference between the detection signal and the transmission timing pulse, and in the ultrasonic distance measuring device that measures the distance to the target by the time difference, the waveform of the received signal Is provided with a low-pass filter for converting into an envelope waveform, and the envelope waveform is used as the threshold value.