JPH0431781A - Pulse type ultrasonic sensor - Google Patents

Abstract

PURPOSE:To detect the presence of an object without fail even when a reflected wave of a level very near to a threshold value is received due to fluctuation of attenuation of an ultrasonic pulse, by providing a plurality of pulse type ultrasonic sensors in parallel and by determining the logical sum of detection outputs by an arithmetic circuit. CONSTITUTION:It is determined by an ultrasonic transmission-reception circuit 1a, for instance, whether a received reflected wave exceeds a prescribed threshold value or not, and an object is determined not to be present when the wave does not exceed the threshold value, while a time delay caused from transmission of an ultrasonic pulse to reception of the reflected wave is measured when the wave exceeds the threshold value. When the time delay is within a prescribed time, the object is determined to be present within a prescribed range of distance and an object detection signal is outputted. Besides, a distance to the object is also measured on the basis of the aforesaid time delay and outputted. Other ultrasonic sensors Sb,... Sn are constructed likewise and the sensors are provided in parallel toward the same object 4 of detection. Detection outputs are inputted to an arithmetic circuit 3, and by determining the logical sum thereof, the object detection signal is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pulse type ultrasonic sensor that detects the presence of an object by transmitting and receiving ultrasonic pulses.

[Conventional technology] Conventionally, pulsed ultrasonic waves transmit ultrasonic pulses, receive reflected waves from a sensing object, and measure the presence of the sensing object and the distance to the sensing object from the time required for transmission and reception. sensor is known. A sensor using such ultrasonic waves is
Compared to sensors using light or radio waves, the propagation speed of ultrasonic waves is slow, so it is known that distances can be measured relatively easily. A threshold value is set, and the presence or absence of a reflected wave is determined based on whether the delivered signal exceeds the threshold value.

[Problems to be Solved by the Invention] However, although ultrasonic signals are attenuated while propagating through the air, the amount of attenuation is not constant over time but fluctuates. Therefore, as shown in Figure 3, if a reflected wave is received at a level that either exceeds or does not exceed the threshold value, the object may or may not be detected, resulting in unstable operation. There was a problem. In Figure 3,
P is a transmitted ultrasonic pulse, R is a received reflected wave, and ■ is a threshold value. Since the first and third reflected waves R exceed the threshold value ■, an object detection signal is output, but the second reflected wave R does not exceed the threshold value V, so no object detection signal is output. in this way,
When the object detection signal is output or not output, the operation of equipment connected to the output of the ultrasonic sensor becomes unstable.

Therefore, the object detection signal is output for the first time when the reflected wave from the object is received consecutively for a predetermined number of times or more, and the object detection signal is output only when there is no received signal for the set number of consecutive times. Stopping method (Patent application 1987-2287)
No. 63 and No. 228764) have been proposed. However, this method has a problem in that the presence of an object cannot be detected if the reflected wave is at a level where the delivery signal exceeds or does not exceed a threshold value.

The present invention has been made in view of these points, and its purpose is to provide a pulse type ultra-high speed sensor that can detect objects more reliably than conventional methods even when the transfer signal fluctuates and the transfer level is unstable. Our goal is to provide sonic sensors.

[Means for solving the problem] In the present invention, in order to solve the above problem, the first
As shown in the figure, the receiver receives the reflected waves of the ultrasonic pulses transmitted from the transmitter by the object, and detects the received reflected waves of the transmitted ultrasonic pulses. Pulse type ultrasonic sensors S a, S b that detect the presence of
,..., multiple Sn are installed in parallel, and each sensor S a,
The present invention is characterized in that it is provided with an arithmetic circuit 3 that calculates the logical sum of the outputs detected by S b, . . . , Sn.

[Function] In the ultrasonic sensor of the present invention, multiple pulsed ultrasonic sensors are used to respond to reflected waves at a level that either exceeds or does not exceed the threshold value, which would result in unstable output with a single pulsed ultrasonic sensor. Sa.

The arithmetic circuit 3 calculates the logical sum of the detection outputs of Sb, ..., Sn, and detects the object if at least one pulsed ultrasonic sensor receives a reflected wave from the object that exceeds the threshold value. It is determined that it has been detected.

[Example] FIG. 1 shows the configuration of an embodiment of the present invention.

The ultrasonic sensor Sa includes an ultrasonic transducer 2a that serves as a transmitter and a delivery device, and an ultrasonic transducer that excites the ultrasonic transducer 2a to transmit ultrasonic pulses and receive vibrations caused by reflected waves. It consists of a sound wave transmitting/receiving circuit 1a. The ultrasonic wave transmitting/receiving circuit 1a determines whether or not the received reflected wave exceeds a predetermined threshold value, and if it does not exceed the threshold value, it determines that the object does not exist. In addition, if the threshold value is exceeded, the time delay between sending the ultrasonic pulse and receiving the reflected wave is measured, and if the time delay is within a predetermined time, the time delay is measured. It determines that an object exists within the distance range and outputs an object detection signal. Also,
Based on the above time delay, the distance to the object is also measured and output. Other ultrasonic sensors Sb, . . . , Sn also have similar configurations.

These ultrasonic sensors S a, S b, ..., S
n are arranged in parallel facing the same detection object 4, and the detection outputs of each sensor S a, S b, ..., Sn are input to the arithmetic circuit 3, and by calculating the logical sum,
Outputs object detection signal.

FIG. 2 is a diagram schematically explaining the operation of this embodiment.

The ultrasonic transceiver circuit 1a sends a transmission pulse to the ultrasonic transducer 2a, and the detected object 4 returns to the same ultrasonic transducer 2a.
The presence of the sensing object 4 and the distance to the sensing object 4 are determined by signal processing. The other ultrasonic wave transmitting/receiving circuits 1b, . . . 1n operate similarly. For example, the following interference prevention measures are taken to prevent the transmitted pulses P of each of the transducers 2 a, 2 b, . . . , 2n from being received by other ultrasonic transducers.

■By changing the oscillation frequencies of the transmitted pulses P, a bandpass filter is provided in each ultrasonic transmitter/receiver circuit 1a, 1b, ..., ln to detect objects for the transmitted pulses P other than itself. The reflected wave R from 4 is selected so as not to be received.

■All ultrasonic transceiver circuits 1a, 1b,...
Synchronous wiring is performed to match the timing of the In transmission pulse P.

■ Sharpen the directivity of each vibrator 2m, 2b,..., 2r+ so that their directional lobes do not overlap.

Further, the ultrasonic transducers 2a, . . . , 2n are installed as close to each other as possible so that the distance from the detection object 4 does not change. Note that in this embodiment, the ultrasonic transducers 2a, .
..., 2n used for both transmitting and receiving waves, but there is no problem in using two ultrasonic transducers, one for transmitting and the other for receiving, instead of the respective ultrasonic transducers for transmitting and receiving.

In FIG. 2, all ultrasonic wave transmitting/receiving circuits 1a.

For example, even if the level of the received signal of the reflected wave R exceeds the threshold value V in only one ultrasonic transceiver circuit 1b among lb, ..., 1n, the arithmetic circuit 3 calculates the logical sum of each detection output. Therefore, an object detection signal is output. Of course, even if reflected waves exceeding the threshold value are received by two or more ultrasonic transceiver circuits, the arithmetic circuit 3 calculates the logical sum, so it goes without saying that an object detection signal will be output. .

In addition, a flip-flop is set using the logical product of detection outputs from multiple ultrasonic sensors to output an object detection signal.
The object detection signal may be stopped by resetting the flip-flop using a logical sum.

[Effects of the Invention] As described above, in the present invention, a plurality of pulse type ultrasonic sensors are installed in parallel, and the logical sum of the detection outputs of each sensor is determined by an arithmetic circuit. Due to the fluctuation of the attenuation, the presence of an object can be reliably detected even when a reflected wave is received at a level that may or may not exceed a threshold value.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention, FIG. 2 is an explanatory diagram of the same operation as above, and FIG. 3 is an explanatory diagram of the operation of a conventional example. la, lb, -, In are ultrasonic transceiver circuits, 2 m,
2 b. ..., 2n is an ultrasonic transducer, 3 is an arithmetic circuit, 4 is a sensing object, P is a transmitted pulse, R is a reflected wave, Sa, Sb, ...
・Sn is an ultrasonic sensor, ■ is a threshold value.

Claims (1)

[Claims] (1) The receiver receives the reflected wave of the ultrasonic pulse transmitted from the transmitter by the object, and detects the received reflected wave of the transmitted ultrasonic pulse and detects the presence of the object. A pulse-type ultrasonic sensor is characterized in that a plurality of pulse-type ultrasonic sensors are arranged in parallel to detect , and an arithmetic circuit is provided to calculate the logical sum of the outputs detected by each sensor.