JPH03135697A - Ultrasonic object sensing device - Google Patents

Abstract

PURPOSE:To prevent erroneous detection due to irregular reflection at a floor surface, etc., within a short distance, and to stabilize a detection characteristic at a long distance by raising the gain of a receiving amplification circuit with the lapse of time from the emission of an ultrasonic pulse. CONSTITUTION:A gain control circuit 15 is constituted as being connected to a tone burst generation circuit 11 and the receiving amplification circuit 17. Thus, as circuit constitution capable of changing the gain of the receiving amplification circuit 17, the circuit 15 lowers the gain of the receiving amplification circuit immediately after the emission of the ultrasonic pulse, i.e., in the case a detection distance is short. Accordingly, the influence of the irregular reflection from the floor surface is reduced, and the errorneous detection is prevented, and simultaneously, by raising the gain of the receiving amplification circuit 17 in stages or continuously from the emission of the ultrasonic pulse, the detection rate of an object at a long distance is improved. Thus, detection performance stable continuously from the short distance to the long distance can be secured.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an ultrasonic object sensing device that detects the presence of a human body, vehicle, etc. by utilizing reflection of ultrasonic waves.

Prior Art FIG. 5 shows a block diagram of a conventional ultrasonic object sensing device. In FIG. 5, an oscillator 1 is connected to a tone burst generating circuit 2 and a gate pulse circuit 3. The tone burst generation circuit 2 is connected to an ultrasonic transmitter 5 via a transmission amplifier circuit 4 to constitute a transmission circuit. Similarly, an ultrasonic wave receiver 6, a reception amplification circuit 7, a detector 8, and a detection section 9 are coupled as shown in the figure to form a reception circuit.

The oscillator 1 generates a reference timing signal, the tone burst generation circuit 2 generates ultrasonic pulses with a width of about 10 m5 at intervals of 200 m5, and the ultrasonic wave is transmitted from the ultrasonic transmitter 5 via the transmission amplifier circuit 4. Fire a pulse. When an object exists in front of the ultrasonic transmitter 5, the reflected wave from the object is received and amplified by the ultrasonic receiver 6 and the reception amplification circuit 7,
The wave detector 8 converts it to a DC level. In addition, the pulse of the tone burst generation circuit 2 and the reflected wave shifted by a fixed time are converted into a DC level by the detector 8 within the gate pulse time outputted from the gate pulse circuit 3 which generates a gate pulse which is a time period signal in which the reflected wave can be received. When the reflected wave is received, the detection unit 9 outputs a detection signal.

Problems to be Solved by the Invention However, the above conventional example having such a configuration had the following drawbacks. In other words, as shown in Figure 6, in an ultrasonic object sensing device, the level of reflected waves changes greatly depending on the distance to the object, so if you want to detect a distant object, the gain of the receiving amplifier circuit must be adjusted. However, if you make it carelessly large, it will cause erroneous detection due to reflected waves from nearby floors, walls, etc. that exist outside the original sensing area. This method has the disadvantage that it is difficult to stably detect the presence of an object within a continuous area over a certain distance.

The present invention eliminates the drawbacks of the above-mentioned conventional examples, and aims to provide an excellent ultrasonic object sensing device that can stably detect objects from short distances to long distances.

Means for Solving the Problems In order to achieve the above object, the present invention adds a gain control circuit to the receiving amplifier circuit, lowers the gain at the timing of receiving reflected waves from a nearby object, and lowers the gain when receiving a reflected wave from a nearby object. The gain is increased at the timing of receiving the reflected wave from the object, so that objects from short distances to long distances can be stably detected.

Effect: Therefore, the diffusely reflected waves from nearby floors, walls, etc. that exist outside the original sensing area have a lower level than the reflected waves from objects within the sensing area, so the gain of the receiving amplifier circuit is reduced. This can be eliminated by On the other hand, reflected waves from a long distance can be reliably detected by increasing the gain of the receiving amplifier circuit, and the detection limit can be extended.

Example FIG. 1 shows an embodiment of the present invention.

In Fig. 1, 10 is an oscillator, 11 is a tone burst generation circuit, 12 is a gate pulse circuit, 13 is a transmission amplifier circuit, 14 is an ultrasonic transmitter, 16 is an ultrasonic receiver, and 17 is a reception amplifier. circuit, 15 is a gain control circuit, 18 is a detector, 1
9 is a detection section.

Next, the operation of the above embodiment will be explained. In FIG. 1, an oscillator 10 is connected to a tone burst generation circuit 11, a gate pulse circuit 12, and a gain control circuit 15. The oscillator 10 is connected to an ultrasonic transmitter 14 via a tone burst generation circuit 11 and a transmission amplifier circuit 13 to constitute a transmission circuit. Similarly, an ultrasonic receiving circuit, a receiving amplifier circuit 17,
The gain control circuit 15, the detector 18, and the detection section 19 are combined as shown in the figure to constitute an ultrasonic receiving circuit.

The gain control circuit 15, which is a feature of this embodiment, is connected to the tone burst generation circuit 11 and the reception amplifier circuit 17 as shown in FIG. FIG. 2 shows an embodiment of the gain control circuit. In FIG. 2, 20 is an operational amplifier, 21 is a fixed resistor, 22, 23, 24 is a harmonic stable multivibrator, and 25, 26, 27 is an analog switch. The gain control circuit 15 is constructed by connecting an analog switch for switching the negative feedback voltage of a non-inverting amplifier constituted by an operational amplifier and a monostable multivibrator for producing the switching timing as shown in FIG. Gain switching timing is created by monostable multivibrators 22, 23, and 24 based on the ultrasonic emission timing pulse generated by the tone burst generation circuit 11. The output of the monostable multivibrator 22, 23, 24 is connected to the switching terminal of the analog switch 25, 26, 27 to control ON/OFF of the analog switch. The analog switch is connected between a fixed resistor that divides the output voltage of the operational amplifier and the inverting input terminal of the operational amplifier, and the gain of the operational amplifier is changed by switching the negative feedback voltage by turning the analog switch ON and OFF. It's in control.

In this embodiment, the gain of the amplifier is switched in three stages as shown in FIG. When an ultrasonic emission timing pulse is input to the monostable multi-high flake 22, it outputs a pulse with a constant width. The pulse is analog switch 25
While the pulse from the monostable multivibrator 22 is being input to the switching terminal of the monostable multivibrator 22, the analog switch 25 is in the ON state. The output terminal of the monostable multivibrator 22 is still connected to the input terminal of the monostable multivibrator 23 via a differentiation circuit, and the monostable multivibrator 24 is triggered when the output of the monostable multivibrator 22 falls. outputs a pulse with a constant width. The pulse is input to the switching terminal of the analog switch 26,
While the pulse from the monostate multipipulator 23 is being input, the analog switch 26 is in the ON state. The monostable multivibrator 24 and analog switch 27 operate in the same manner.

The gain is 1 when the analog switch 25 is ON, and the gain is R when the analog switch 26 is ON.
3/ (R2+R1), analog switch 27 is ON
Since the gain is (R3+R2)/R1 when the
．． When I KΩ, they are 1 times, 10 times, and 100 times, respectively. In this way, by setting the pulse width of the three monostate multipipulators and the value of the fixed resistor to appropriate values, as time passes after transmitting the ultrasonic pulse,
Gain control can be performed to increase the gain of the reception amplifier circuit.

As in this embodiment, as shown in FIG. By reducing the influence of diffuse reflection from the floor and preventing false detection, the gain of the receiving amplifier circuit is increased stepwise or continuously from the ultrasonic pulse emission, thereby increasing the detection rate of distant objects. This has the excellent effect of increasing the detection performance and ensuring continuous and stable detection performance from short to long distances.

Effects of the Invention The present invention has the above-mentioned configuration and provides the following effects. In other words, by increasing the gain of the receiving amplifier circuit over time after the ultrasonic pulse is emitted, false detections due to diffuse reflection from nearby surfaces such as floors are prevented, and detection performance at long distances is stabilized. This makes it possible to construct an ultrasonic object sensing device with extremely high performance.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an ultrasonic object sensing device according to an embodiment of the present invention, FIG. 2 is a gain control circuit diagram of this embodiment,
FIG. 3 is a timing chart of the gain control circuit, FIG. 4 is a signal waveform diagram of this embodiment, and FIG. 5 is a block diagram of the conventional example.
FIG. 6 is a signal waveform diagram of a conventional example. 1... Oscillator, 2... Tone burst generation circuit, 3
...gate pulse circuit, 4...transmission amplifier circuit, 5.
...Ultrasonic wave transmitter, 6... Ultrasonic wave receiver, 7... Receiving amplifier circuit, 8... Detector, 9... Detection unit, 10...
・Oscillator, 11...Tone burst generation circuit, 12・
・・Gate pulse circuit, 13・・Transmission amplifier circuit, 14・
...Ultrasonic transmitter, 15... Gain control section, 16...
Ultrasonic wave receiver, 17... Reception amplifier circuit, 18... Detector, 19... Detection unit, 20... Operational amplifier, 21...
・Fixed resistor, 22 ・ Monostable multivibrator, 23 ・ Monostable multivibrator, 24 ・ Monostable multivibrator, 25 ・
・Analog switch, 26...Analog switch, 2
7. Analog switch. Go III

Claims (1)

[Claims] a transmitter that emits ultrasonic tone bursts at a predetermined period; a receiver that receives reflected waves of the ultrasonic tone bursts from an object to be detected to detect the presence of the object; and emit the ultrasonic tone bursts. and a gain control section that sequentially increases the amplification degree of the receiver as time passes.