JPS6154184B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reflective ultrasonic switch.

Conventionally, so-called reflection-type ultrasonic switches, which detect the approach of a human body by emitting ultrasonic pulses intermittently and measuring the time it takes for the reflected waves to return, have been used as automatic door switches, etc. Widely used. Generally, such reflective ultrasonic switches are installed on the ceiling, and normally receive reflected waves from the floor, but when a human body approaches, the time for the reflected waves to return becomes shorter, so avoid approaching a human body. It is something that can be detected. By the way, in such a switch that uses ultrasonic waves, the gate of the receiving circuit is closed between the time when an ultrasonic pulse is emitted by an ultrasonic transducer and the time when the reverberant sound disappears. Although it is necessary to prevent the sound from being picked up, the reverberation time changes as the indoor temperature changes, and the reverberation time becomes longer at low temperatures, so the reverberation of the emitted ultrasonic waves has not yet completely disappeared. The gate of the receiving circuit sometimes opened, causing malfunction. On the other hand, if the timing of opening the gate is delayed by the length of the reverberation time, malfunctions due to reverberant sound will not occur, but reflected waves from a short distance will not be detected, which is a drawback. The present invention aims to eliminate such drawbacks of the conventional example.

The configuration of the present invention will be described below with reference to illustrated embodiments. FIG. 1 is a block diagram showing the circuit configuration of the present invention, the main parts of which are a transmitting circuit 1 that emits ultrasonic pulses intermittently, and a gate that opens an appropriate time after emitting ultrasonic waves to reflect them. A wave receiving circuit 2 that receives, amplifies and detects waves, a level detection circuit 3 whose output is turned on when the detected output of the wave reception circuit 2 exceeds a predetermined threshold level, and a level detection circuit 3.
The circuit comprises a pulse width detection circuit 4 whose output is turned on when the output width of the pulse width exceeds a predetermined detection width, a flip-flop 5 operated by the output of the detection circuit 4, a switching circuit 6, and a relay 7. Among these, the transmitter circuit 1 includes a time constant circuit 8 that determines the emission period of the ultrasonic pulse, a monostable multivibrator 9 that determines the pulse width of the ultrasonic pulse, and a monostable multivibrator 9 that operates. Oscillation circuit 1 that oscillates ultrasonic waves only during the period
0, which drives the ultrasonic transducer 11 to transmit ultrasonic pulses into the air. Next, the ultrasonic pulse reflected from the floor surface 12 is received by the wave receiving circuit 2 via the microphone 13. Here, the wave receiving circuit 2 includes an amplification circuit 14, a filter circuit 15, and a detection circuit 17 which is driven by a distance setting circuit 16 and also functions as a gate circuit.
It is composed of. The filter circuit 15 allows only the ultrasonic frequency component to pass through, and the distance setting circuit 16 opens a gate provided in the detection circuit 17 after an appropriate amount of time has elapsed after emitting the ultrasonic pulse to receive reflected waves. It is intended to do so. By the way, this gate was originally the ultrasonic vibrator 11.
The gate is set to open after the gate stops oscillating and the reverberant sound completely disappears, but the reverberation time is longer at low temperatures than at room temperature, so the reverberant sound remains even after the gate opens. In such cases, malfunctions may occur. Figure 2 is a time chart showing this situation.
When an ultrasonic pulse with a pulse width W _A is emitted as shown in Figure 2, the reverberation sound at room temperature attenuates relatively quickly as shown by the solid line in Figure b, and after the reverberation time T _A has elapsed, the reverberant sound decays relatively quickly as shown in the solid line in Figure b. As shown in Figure b, the output of the distance setting circuit 16 becomes H and the gate in the detection circuit 17 opens, but at low temperatures, the attenuation of reverberant sound becomes relatively slow, as shown by the dotted line in Figure b. Even if the gate is opened after the reverberation time T _A at room temperature has elapsed, the reverberant sound may not completely disappear. In such a case, there is a risk of malfunction, but as described above, delaying the timing of opening the gate is not desirable because reflected waves from a short distance cannot be detected. Therefore, in the present invention, in order to be able to automatically set the pulse width of the emitted ultrasonic waves and the detection width of the pulse width detection circuit to be short at low temperatures, a circuit configuration as shown in FIGS. 3a and 3b is used. It's getting better. That is, the CR time constant circuit 18 of the monostable multivibrator 9 for setting the pulse width of the ultrasonic pulse to be emitted.
and setting the detection width of the pulse width detection circuit 4.
A temperature sensing element 20 having a positive temperature resistance characteristic is used as a part of the resistor constituting the CR integration circuit 19, and the firing pulse width and pulse detection width are short at low temperatures.
It is constructed so that it becomes longer when the temperature is high.

The operation of the present invention will be explained below with respect to the embodiment shown in FIG. 3. First, in FIG. The output is normally L. In this state, when an impulse-like rising signal is output from the time constant circuit 8, the output of the NAND circuit Q becomes H, and therefore the output of the NAND circuit N becomes L.
Therefore, even if the output of the time constant circuit 8 becomes H again, the output of the NAND circuit Q remains in the H state and the output of the NAND circuit N remains in the L state. When the capacitor _C1 is charged through the temperature sensing element 20 in this state, the input of the NAND circuit N will eventually become a low potential, so the output of the NAND circuit N will return to the H state again, and the output of the NAND circuit Q will also become L. and return to the initial state. Therefore, the monostable multivibrator 9 is composed of the above circuit blocks, and the output pulse width of the monostable multivibrator 9 is determined by the CR time constant circuit 1.
8, and in the case of this embodiment, since the temperature sensing element 20 with positive temperature resistance characteristics is used as a part of this time constant circuit 18,
It operates so that the pulse width becomes short when the temperature is low and becomes long when the temperature is high. Next, the circuit diagram shown in FIG. 3b shows one embodiment of the pulse width detection circuit 4, and as shown in the same figure, a positive temperature resistance is used as a part of the resistance of the CR integration circuit 19 that determines the detection width. Since a temperature sensitive element 20 with a specific temperature is used, the pulse detection width is short when the temperature is low, and the pulse detection width is long when the temperature is high.

As described above, in the present invention, the pulse width and pulse detection width of the emitted ultrasonic waves can be automatically set short at low temperatures where the reverberation time becomes long, so that the ultrasonic waves emitted until after the gate opens The reverberant sound will not remain and cause malfunction. In addition, in the present invention, FIGS.
As shown in the example, one temperature sensing element with positive temperature resistance characteristics is installed in each of the monostable multivibrator circuit and the pulse width detection circuit, which can be easily configured using a CR time constant circuit and a logic circuit. The above purpose can be achieved just by connecting, the production cost is low, and the industrial value is great.

The reason why the pulse width setting circuit according to the present invention is configured so that the pulse width becomes longer as the temperature increases is that by using the longest pulse that can be used at that temperature, it is possible to prevent malfunctions due to external electrical noise, etc. This is to prevent it.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the circuit configuration of an embodiment of the present invention, FIGS. 2a to 2d are time charts showing the operation of the same, and FIGS. 3a and 3b are circuit diagrams of the main parts of the same. 1 is a transmitting circuit, 2 is a receiving circuit, 3 is a level detection circuit, 4 is a pulse width detection circuit, 9 is a monostable multivibrator, 18 is a CR time constant circuit, 19 is a CR
In the integrating circuit, 20 is a temperature sensing element.

Claims (1)

[Claims] 1. A transmitting circuit that emits ultrasonic pulses intermittently, a receiving circuit that opens a gate at an appropriate time after emitting ultrasonic waves to receive reflected waves, amplifies and detects them, and detects the detection output of the receiving circuit. Reflection type consisting of a level detection circuit that turns on the output when the output exceeds a predetermined threshold level, and a pulse width detection circuit that turns on the output when the output width of the level detection circuit exceeds the predetermined detection width. In an ultrasonic switch, a part of the resistor that makes up the CR time constant circuit of the monostable multivibrator, which sets the pulse width of the emitted ultrasonic pulse, and the CR integral circuit, which sets the detection width of the pulse width detection circuit, is A reflection type ultrasonic switch characterized in that it uses a temperature sensing element having temperature resistance characteristics and is configured such that the emitted pulse width and the pulse detection width are short when the temperature is low and long when the temperature is high.