JPS63311191A - Ultrasonic range finder - Google Patents

Abstract

PURPOSE:To improve the ability for detecting a near object by providing plural- level detecting circuits having respective different thresholds of waveform shaping means. CONSTITUTION:The output of a wave receiving circuit 4 is compared with respective thresholds Va-Vd by the use of a level detecting circuit 5, and the waveform exceeding a threshold is shaped into a high level digital signal. The output of the level detecting circuit 5 is differentiated in a differentiating circuit 6 into resultant output. A negative pulse indicating the fall of the output of the level detecting circuit 5 is removed by depriving the logical sum of the output of the differentiating circuit 6 by the use of an OR circuit 7, and the output is obtained on the basis of only a positive pulse indicating the rise of the level detecting circuit 5. When the last output of an OR circuit 12 is input in a latch circuit 12, the distance of count value up to an object is computed. In this case the distance of a near object can also be detected unless the output is completely covered by a reverberating signal, and the ability for detecting the near object is improved.

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. 4 shows a received signal waveform of a conventional ultrasonic distance meter. 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 wave application period shown by T in the figure. A sonic 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. In this ultrasonic range finder, the ultrasonic transducer continues to vibrate even after a transmission signal is applied to it.
A so-called reverberation signal is generated as indicated by A in the figure. This reverberation signal I attenuates with the passage of time, so if this reverberation signal I attenuates below the threshold value vth, which is the object detection level,
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 in E in the figure, if a reflected wave from a nearby object is received by the ultrasonic transducer at a time when the reverberation signal A has not yet attenuated below the threshold value Vtb, the reverberation signal I The distance to the object cannot be measured because it cannot be distinguished from the received signal due to the reflected wave from the object. In other words, conventional ultrasonic rangefinders have a problem of poor detection ability for objects at close range.

[Objective of the Invention 1 The present invention has been made in view of the above-mentioned points, and its object is to provide an ultrasonic range finder with improved detection ability for objects at close range.

, [Disclosure of the Invention 1 (Structure) The present invention provides a pulse-type ultrasonic distance meter that detects the distance to an object by transmitting ultrasonic pulses and passing reflected waves from the object. When the level of the output obtained by amplifying and detecting the signal passed by the child is detected by a plurality of level detection circuits, each having a different level of threshold, and the output exceeds the threshold? ) A waveform shaping means that shapes the waveform into a digital signal that becomes a high level; The waveform shaping means is equipped with a plurality of level detection circuits each having a threshold value of a different level, so that the received signal cannot be detected unless it is completely hidden by the reverberant signal. The distance to the object is determined by the distance detection means based on the time delay from the time of transmission of the ultrasonic pulse when the slowest rise occurs after transmission of the ultrasonic pulse among the outputs of the waveform shaping means. By detecting this, it is possible to detect the distance of a nearby object as long as it is not completely hidden by the reverberant signal.

(Example) An embodiment of the present invention is shown in FIGS. 1 to 3.

The present invention replaces the conventionally one threshold value vth as shown in FIG. 4 with a plurality of threshold values Va to Ve of different levels as shown in FIG. We focused on the fact that if the presence or absence of ~2 is detected, the received signal E can also be detected as long as the transfer signal is not completely hidden in the reverberant signal A, and this makes it possible to measure the distance to a nearby object. This made it possible.

The ultrasonic distance meter of this embodiment also uses an ultrasonic transducer 1 for both transmitting and receiving waves, as shown in FIG. The transmitting means for driving the ultrasonic transducer 1 to transmit ultrasonic pulses includes a transmitting signal generating circuit 2 that generates a transmitting signal, and a transmitting signal generating circuit 2 that outputs the output of the transmitting signal generating circuit 2 from the ultrasonic vibrator 1. The transmitting amplification circuit 3 is configured to amplify the output of the ultrasonic vibrator 1 to a driving level, and the transmitting means is configured to amplify and detect the output of the ultrasonic vibrator 1. It consists of a wave receiving circuit 4. A plurality of level detection circuits each having a threshold value of a different level are used as a waveform shaping means to shape the output of the four transfer circuits into a digital signal that becomes high level when the level is higher than the threshold value. , in this embodiment, a plurality of level detection circuits are shown as one block) 5.

The distance detecting means 8 detects the distance to the object based on the time delay from the time of transmission of the ultrasonic pulse when the slowest rise occurs after transmitting the ultrasonic pulse among the outputs of the level detecting means 5. 5. A differentiating circuit 6 that differentiates the outputs of each of the differentiating circuits (this differentiating circuit also has a number of layers corresponding to the number of level detection circuits 5), an OR circuit 7 that calculates the logical sum of the outputs of the differentiating circuits 6, and the distance An oscillation circuit 9 that generates a clock signal for measurement, a counter 10 that counts the clock signal that is the output of this oscillation circuit 9, and the transmission signal generation circuit 2.
Start signal generation circuit 1 that generates a start signal indicating the timing to start counting of the counter 10 in synchronization with the output
1, and an arithmetic circuit 12 that latches the count value of the counter 10 when the output of the OR circuit 7 is input and calculates the distance to the object based on this count value, and the distance detection means 8 The distance to the object, which is the output, is displayed on the display 13.

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 the transmitting signal, which is the output of the transmitting signal generating circuit 2, by the transmitting amplifier circuit 3, and the ultrasonic transducer 1 transmits an ultrasonic pulse. When the output of the transmission signal generation circuit 2 is generated, the start signal generation circuit 8 outputs a start signal which is a negative pulse shown in FIG. Start counting a certain clock signal. When an object exists in the detection area, the amplified output of the wave receiving circuit 4 has a waveform shown in FIG. 2(a). Note that the amplified output of the wave receiving circuit 4 includes the output signal of the ultrasonic transducer 1 and the reverberation signal A when transmitting ultrasonic pulses from the ultrasonic transducer 1, as well as the transfer signal. ing. The output of the wave receiving circuit 4 is compared with each of the threshold values Va to Vd by the level detection circuit 5, and is waveform-shaped into a digital signal that becomes high level when it is equal to or higher than the threshold value. FIGS. 2(b) to 2(e) show the outputs of the level detection circuit 5 which performed level detection at the respective threshold values Va to Vd. The output of this level detection circuit 5 is differentiated by a differentiation circuit 6,
The outputs of the differentiating circuit 6 shown in FIGS. 2(f) to (i) are obtained. By taking the logical sum of the outputs of the differentiating circuit 6 using the OR circuit 7, the negative pulse indicating the fall of the output of the level detection circuit 5 is removed, and the output is based on the positive pulse indicating the rise of the output of the level detection circuit 5. get only The output of this OR circuit 7 is shown in FIG. 2(j). Every time the OR circuit 7 output is input to the arithmetic circuit 12, the count value of the counter 10 is latched, and the latched count value is updated every time a new OR circuit 7 output occurs. Then, the distance to the object is calculated from the count value when the last output of the OR circuit 12 is input to the latch circuit 12. This arithmetic circuit 12
The distance to the object, which is the output, is displayed on the display 13. In other words, the higher the threshold values Va to Vd, the closer the rise of the output of the level detection circuit 5 is to the peak value of the transfer signal, and the time delay from the time delay to the latest rise of these rises to the object. Even if the distance is calculated, the error from the actual distance to the object is small and does not pose any problem in practice. As described above, according to the present 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 is included in the reverberant signal A. As long as the object is not completely hidden, it is possible to detect the received signal as well, and therefore, the distance detection means 8 can detect the object by the time delay from the time of transmission until the latest rising point of the output of the level detection circuit 5. distance can be detected. In the above embodiment, the case where there are four thresholds has been described, but if the distance measurement accuracy is to be further increased, more level detection circuits 5 may be used. If this is desirable, it is also possible to reduce the number of level detection circuits 5.

[Effects of the Invention 1] As described above, 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. A waveform in which the level of the output obtained by amplifying and detecting the signal passed by the oscillator is detected by multiple level detection circuits each having a different threshold level, and the waveform is shaped into a digital signal that becomes high level when the threshold value is exceeded. comprising: a shaping means; and a distance detecting means for detecting the distance to the object based on the time delay from the time of transmission of the ultrasonic pulse when the slowest rise occurs after transmission of the ultrasonic pulse among the outputs of the waveform shaping means. Since the waveform shaping means is equipped with a plurality of level detection circuits each having a threshold value of a different level, it is possible to detect the passing signal as long as it is not completely hidden by the reverberation signal. By detecting the distance to the object using the distance detection means from the time delay from the time of transmission of the ultrasonic pulse at the time when the slowest rise after transmission of the ultrasonic pulse among the outputs of the shaping means, the reverberant signal can be completely detected. As long as it is not hidden, it is possible to detect the distance of objects at short distances, thus improving the detection ability of the ultrasonic range finder for objects at short distances.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the circuit configuration of an embodiment of the present invention, Fig. 2 is an explanatory diagram of the same operation as above, Fig. 3 is an explanatory diagram of the same principle as above, and Fig. 4 is an explanation showing the problems of the conventional example. It is a diagram. 1 is an ultrasonic transducer, 5 is a level detection circuit, and 8 is a distance detection means. Figure 2 Figure 3 Figure 4

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. and a distance detecting means for detecting the distance to the object from the time delay from the time of transmission of the ultrasonic pulse at the time when the slowest rise occurs after transmission of the ultrasonic pulse. Total.