JPS63311192A - Ultrasonic range finder - Google Patents

Abstract

PURPOSE:To improve the ability for detecting a near object by detecting the fall of the output of a level detecting circuit in which the most rapid rise is produced and seeking the middle point between the rise and the fall. CONSTITUTION:When a latch signal O1 is input in a signal selecting circuit 8, an arithmetic circuit 11 latches the value of count 10 at the time of the fall of a level detecting circuit 5 of the most rapid rise and computes the distance of the count value up to an object. In this case the value of the counter 10 is the middle point between the rise and the fall of the most rapid rise level detecting circuit 5 in regard to a clock signal f1, the time lag till the time at which the peak for a wave receiving signal is detected after ultrasonic wave pulse is transmitted is found, and so the distance up to the object can be computed by the use of the arithmetic circuit 11 and the output of the arithmetic circuit 11 is shown in a display 14. Therefore, the distance up to a near object can be detected unless the output is completely covered by a reverberated signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field 1] The present invention relates to a pulse-type ultrasonic distance meter that detects the distance to an object using ultrasonic pulses.

[Background Art] FIG. 5 shows a voltage waveform between the terminals of an ultrasonic transducer of a conventional ultrasonic pulse. This ultrasonic distance meter uses an ultrasonic transducer for both transmitting and receiving waves, and a transmitting signal is applied to this ultrasonic transducer during the transmitting period indicated by T in the figure. An ultrasonic pulse is transmitted, and the distance to the object is detected from the time delay from the time the ultrasonic pulse is transmitted until the reflected wave from the object is received. This ultrasound y
In the giant distance meter, the ultrasonic transducer continues to vibrate even after a transmission signal is applied to the ultrasonic transducer, and a so-called reverberation signal is generated as indicated by A in the figure. Since this reverberation signal I attenuates with the passage of time, this reverberation signal I is a threshold value vt at which the object detection level is
If the attenuation is equal to or less than h, the distance to the object can be detected by the received signal from the reflected wave from the object shown in the figure. However, as shown by water in the figure, if the reflected wave from a nearby object is received by the ultrasonic transducer at a time when the reverberant signal A has not attenuated below the threshold value vth, the reverberant signal It is impossible to distinguish between the received signal and the received signal due to the reflected wave from the object, and the distance to the object cannot be measured. In other words, conventional ultrasonic rangefinders have a problem of poor detection ability for objects at close range.

1. OBJECT OF THE INVENTION] The present invention has been made in view of the above-mentioned points, and its purpose is to provide an ultrasonic range finder with improved ability to detect objects at close range.

[Disclosure of the Invention] (Structure) The present invention provides a pulse-type ultrasonic distance meter that detects the distance to an object by transmitting ultrasonic pulses and receiving reflected waves from the object. The level of the output obtained by amplifying and detecting the signal received by the sensor is detected by a plurality of level detection circuits, each having a different threshold level, and the waveform is shaped into a digital signal that has a 7% level when it exceeds the threshold value. A waveform shaping means detects the earliest rising edge of the output of the waveform shaping means after transmitting the ultrasonic pulse, and detects the falling edge of the output of the level detection circuit where the earliest rising edge occurs, and detects the falling edge of the output of the level detection circuit where the earliest rising edge occurs, and The device is equipped with a distance detecting means for determining the intermediate point between the falling edge and the falling edge, and detecting the distance to the object by the time delay from the transmitting point up to this intermediate point, and the waveform shaping means each have a different level of precision. By providing a plurality of level detection circuits having threshold values,
The received signal can be detected as long as it is not completely hidden by the reverberant signal, and the rising and falling edges of the level detection circuit which rises earliest after transmitting the ultrasonic pulse among the outputs of this waveform shaping means are detected. , by using the distance detecting means to find the intermediate point between the rising edge and the falling edge, and detecting the distance to the object based on the time delay from the time of wave transmission up to this intermediate point, as long as it is not completely hidden by the reverberant signal. The system is designed to be able to detect the distance of objects that are close to each other.

(Example) An embodiment of the present invention is shown in FIGS. 1 to 4.

The present invention replaces the conventionally one threshold value vth as shown in FIG. 5 with a plurality of threshold values Va to Ve of different levels as shown in FIG. We focused on the fact that if we detect the presence or absence of ~2, it is also possible to detect the received signal E as long as the received signal is not completely hidden in the reverberant signal A. This made measurement possible.

The ultrasonic distance meter of this embodiment also uses an ultrasonic transducer 1 for both transmitting and receiving waves, as shown in FIG. A transmitting means for driving the ultrasonic transducer 1 to transmit ultrasonic pulses is connected to a transmitting signal generating circuit 2 that generates a transmitting signal, and an output of the transmitting signal generating circuit 2 to the ultrasonic vibrator 1. The transmitting amplification circuit 3 amplifies the output of the ultrasonic transducer 1 to a driving level, and the transmitting means receives the reflected wave of the ultrasonic pulse transmitted from the ultrasonic transducer 1 by an object. It consists of a wave receiving circuit 4 for detecting waves. As a waveform shaping means for shaping the output of the wave receiving circuit 4 into a digital signal that becomes high level when the output is higher than the threshold value of each different level,
It is composed of a plurality of level detection circuits 5 (in this embodiment, a plurality of level detection circuits are shown as one block) each having a threshold value of a different level. Among the outputs of the level detection circuit 5, the earliest rise after the transmission of the ultrasonic pulse is detected, and the fall of the output of the level detection circuit 5 where the earliest rise has occurred is detected, and the above-mentioned rise and fall are detected. A distance detecting means for determining the intermediate point in time and detecting the distance to the object by the time delay from the transmitting point up to this intermediate point is set by the rise of each output of the level detection circuit 5, and
7-lip 70-tub circuit that is reset by falling edge (
(hereinafter referred to as F/F, the number of F/Fs corresponding to the number of level detection circuits) 71 to 7. and a clock signal with two high and low frequencies for distance measurement, fz (however,
f, = 2 f2), and the above-mentioned F/Fs 7, to 7. after transmitting the ultrasonic pulse. The first clock signal f1 with a higher frequency is output until the earliest rise occurs, and the second clock signal with a lower frequency is output until the fall of the output of the level detection circuit 5 at which the earliest rise occurs. a signal selection circuit 8 that outputs a signal f2;
The clock signal f generated at the output of this signal selection circuit 8,
The count value of the counter 10 is determined by a counter 10 that counts f2 and a latch signal 0° that is output when the signal selection circuit 8 detects a falling edge of the output of the level detection circuit 5, which causes the above-mentioned early rise. Along with latching,
A calculation circuit 11 calculates the distance to the object by calculating this count value based on the clock signal f1 of @1, and a start signal i indicating the count start timing of the counter 10 synchronized with the output of the transmission signal generation circuit 2. , and inputs it to the counter 10 and the signal selection circuit 8, and a level detection circuit in which the above amount also rises quickly in the signal selection circuit 8 after transmitting the output of the level detection circuit 5. 5, and a gate circuit 6 that allows the signal to pass until the falling edge of the output occurs.
The distance to the object, which is three outputs, is displayed on the display 14. FIG. 2 shows a concrete circuit of the signal selection circuit 8, and the configuration of this concrete circuit will be explained together with the explanation of the operation described later.

The operation of this embodiment will be explained below with reference to FIG. The ultrasonic transducer 1 is driven by a drive signal obtained by amplifying a transmission signal, which is an output of the transmission signal generation circuit 2, by a transmission amplifier circuit 3, and transmits an ultrasonic pulse. When an object exists in the detection area, the output after amplification of the wave receiving circuit 4 is as shown in Fig. 13 (a
) is the waveform shown. Note that the output after amplification of the 20 delivery circuit 4 includes the received signal as well as the output signal of the ultrasonic transducer 1 and the reverberation signal A when the ultrasonic pulse is being transmitted from the ultrasonic transducer 1. It is. The output of the wave receiving circuit 4 is compared with the respective threshold values ①a to Vd by the level detection circuit 5, and is waveform-shaped into a gage digital signal that becomes high level when the output is equal to or higher than the threshold values Va to Vd. Each threshold value V
The outputs of the level detection circuit 6 which performed level detection at a to Vd are shown in FIGS. 3(b) to 3(e). Note that when the transmission signal is output from the transmission signal generation circuit 2, the start signal generation circuit 12 outputs a start signal i having a pulse width equal to the transmission wave application period T shown in FIG. 3(f). . This start signal i sets the 7-lip, 70-tub circuit 15 inside the signal selection circuit 8 shown in FIG. The output of this 7-lip 70-tube circuit 15 is used as the date signal o3 of the date circuit 6, and when the 7-lip 70-tube circuit 15 is set, the date signal o3 goes high as shown in FIG. 3(1). level. Therefore, the date circuit 6 is opened and the output of the level detection circuit 5 is output from F/F 7, to 7. is input. This F/F7. ~74 is @1 When the output of the level detection circuit 5 whose threshold level is higher in the upper part of the diagram is input, and the output of the transfer circuit 4 once falls below the threshold value Va~Vd and then exceeds it again, that is, this time. Threshold value Va~
When a transfer signal of Vd or higher is detected, F/F7, ~
7. is reset when the output of each level detection circuit 5 further falls below the threshold values Va to Vd. In other words, this F/F 7, ~7. As a result, only the output corresponding to the transmission signal and the reverberation signal of the output of the wave receiving circuit 4 are extracted. Regarding the threshold value Vd in FIG. 3, since the output of the wave receiving circuit 4 once falls below and does not exceed it again, F/F7. ~74 is neither set nor reset and produces no output. This F/F
71-7. The signal selection circuit 8 performs signal processing according to the output, and after transmitting the ultrasonic pulse, the above F/Fs 7, - 7
．． The oscillation circuit 9
0, a first clock signal r1 with a high frequency is output, and a second clock signal f2 with a low frequency is output until the fall of the output of the level detection circuit 5 where the earliest rise occurs. Further, this operation will be explained in detail. The signal selection circuit 8 includes F/F7. ~7. In order to detect the rise and fall of the fastest rise among the outputs 12 to i,
Among the threshold values Va to Vd, the one with the lowest threshold level is prioritized and used for signal processing, and this is composed of AND circuits 16 to 18, inverters 19 to 21, and OR circuit 22. . For example, in the case of FIG. 3, the OR circuit 22 outputs a signal obtained by removing the transmission signal G and the reverberation signal A from FIG. Therefore, the output of this OR circuit 22 is shown in FIG. 3(h). This OR circuit 22
The output is the clock signal f+, f2 which is the output of the oscillation circuit 9.
This selection circuit is input to the AND circuit 23.
25, an OR circuit 26, and an inverter 29. The output obtained by inverting the output of the OR circuit 22 by the inverter 29 (Fig. 3 (g)) and the clock signal f of the oscillation circuit 9
, are ANDed in the AND circuit 24, and ANDed between the output of the AND circuit 24 via the OR circuit 26 and the 7-lip 70-tub circuit 15 in the AND circuit 25. Until the earliest rising edge of the detection circuit 5 occurs, the clock signal f is outputted to the counter 10 as shown in FIG. 3(i).

In addition, the OR circuit 22 output (Fig. 3 (h)) and the oscillation circuit 9
The AND circuit 23 performs AND processing on the clock signal f2 of From the time when the early level detection circuit 5 output rises until it falls, the clock signal f2 is output to the counter 10 as shown in FIG. 3(i). The 7-rip, 70-tube circuit 15 is reset by the output of the OR circuit 22, that is, by the fall of the level detection circuit 5, which has the earliest rise (FIG. 3 (1)). In addition, the output of the OR circuit 22, which is the level detection circuit 5 that rises fastest, is differentiated by the differentiating circuit 27 (as shown in FIG. 3 (j)).
, by inverting at the inverter 28.

A latch signal O7 for latching the count value of the counter 10 is created in the arithmetic circuit 11 shown in FIG. 3(k). The counter 10 is reset by the start signal i, which is the output of the start signal generation circuit 12, and starts counting the clock signal f+yf2, which is the output of the signal selection circuit 8, 0°. The arithmetic circuit 11 latches the count value of the counter 10 when the latch signal 01 is inputted to the signal selection circuit 8, that is, at the falling edge of the level detection circuit 5 which has the earliest rise, and calculates the distance to the object from this count value. Calculate. Since the counter 10 of this embodiment counts the clock signal f and the clock signal f2 having half the frequency of the clock signal f1, the count value of the counter 10 is determined by the level detection circuit that has the earliest rising edge for the clock signal f. 5, the time delay between when the ultrasonic pulse is transmitted and when the peak of the received signal is detected is known, and therefore the arithmetic circuit 1
1, the distance to the object can be calculated, and this calculation circuit 1
1 output is displayed on the display 14. As described above, according to this embodiment, the level detection circuit 5 detects the level of the output of the ultrasonic transducer 1 using a plurality of threshold values having different levels, so that the received signal can be detected within the reverberant signal A. As long as it is not completely hidden, it is possible to detect the received signal, and therefore, among the outputs of the level detection circuit 5, the rise and fall of the level detection circuit 5, which rises the earliest after transmitting the ultrasonic pulse, can be detected. The distance detection means 13 determines the intermediate point between the rising edge and the falling edge, and detects the distance to the object based on the time delay from the transmitting point up to this intermediate point, so that the distance to the object is not completely hidden by the reverberant signal. To this extent, it is also possible to detect the distance of nearby objects. In addition, in the above-mentioned embodiment, the case where there are four threshold values was explained, but
It goes without saying that the number of level detection circuits 5 is not limited as described above.

[Effects of the Invention] As described above, the present invention provides an ultrasonic distance meter that detects the distance to an object by transmitting ultrasonic pulses and receiving reflected waves from the object. The output of the amplified and detected signal received by the sonic transducer is level-detected by multiple level detection circuits, each having a different level of threshold. A waveform shaping means for shaping, detecting the earliest rising edge after transmission of the ultrasonic pulse among the outputs of the waveform shaping means, and detecting the falling edge of the level detection circuit output at which the earliest rising edge has occurred, Distance detecting means for determining the intermediate point between the rising point and the falling point and detecting the distance to the object by the time delay from the transmitting point up to this intermediate point, and the waveform shaping means respectively By providing a plurality of level detection circuits with thresholds of different levels, it is possible to detect the received signal as long as it is not completely hidden by the reverberation signal, and the ultrasonic pulse is detected within the output of this waveform shaping means. The rise and fall of the level detection circuit that rises earliest after the wave is transmitted is detected, and the intermediate point between the rise and fall is determined by the distance detection means, and the object is detected by the time delay from the time of wave transmission up to this intermediate point. By detecting the distance to the object, it is also possible to detect the distance of a nearby object as long as it is not completely hidden by the reverberant signal, thus improving the ability of the ultrasonic pulse to detect objects at a short distance.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the circuit configuration of an embodiment of the present invention, Fig. 2 is a specific circuit diagram of the signal selection circuit of the above, Fig. 3 is an explanatory diagram of the operation of the same, and Fig. 4 is an explanation of the principle of the same. FIG. 5 is an explanatory diagram showing problems in the conventional example. 1 is an ultrasonic transducer, 5 is a level detection circuit, and 13 is a distance detection means. Agent Patent Attorney Shi 1) Chief Qiji $ Yanyan Caifu + + Province σ County

Claims (1)

[Claims] (1) In a pulse-type ultrasonic distance meter that detects the distance to an object by transmitting ultrasonic pulses and receiving reflected waves from the object, the received signal by the ultrasonic transducer is amplified and detected. A waveform shaping means that detects the level of the output using a plurality of level detection circuits each having a different level of threshold, and shapes the waveform into a digital signal that becomes high level when the level exceeds the threshold, and an output of this waveform shaping means. Detecting the earliest rising edge after transmitting the ultrasonic pulse, detecting the falling edge of the output of the level detection circuit at which the earliest rising edge occurs, and finding the intermediate point between the rising edge and the falling edge; An ultrasonic distance meter characterized by comprising distance detection means for detecting the distance to an object by a time delay from the time of transmitting the wave up to this intermediate point.