JPH0714949Y2 - Light-blocking detector - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention is to detect and steal two beams of infrared-modulated light from a projector in which a high frequency is double-modulated by a low frequency, by receiving the separated light with a light receiver. The present invention relates to a light-blocking detector that detects abnormalities in the above.

[Prior Art] Conventionally, as a light-blocking detector using this type of double-modulated infrared-modulated light, for example, a high-sensitivity receiver of Japanese Examined Patent Publication No. 59-21132 is known, and a two-beam detector is also known. As a light-blocking detector of, the crime prevention alarm device of Japanese Utility Model Publication No. 57-479 is known.

First, in a high-sensitivity receiver that uses double-modulated infrared-modulated light, a 20KHz high-frequency light is received from a projector by driving the infrared light-emitting element to emit light by a modulation signal that is double-amplitude modulated at a low frequency of 500Hz. Infrared modulated light is emitted toward the detector, and at the receiver side 500Hz by synchronous detection of the received light signal.
The low frequency component of is detected, the low frequency detection signal of 500Hz is given to the PLL circuit, the oscillation frequency and phase of the PLL loop are made to follow the low frequency detection signal, and the state that the PLL loop is locked to the low frequency signal of 500Hz is determined. Then, the coincidence signal is output, and since it is a light-blocking detector, it is determined to be abnormal when the coincidence signal from the PLL circuit is cut off.

On the other hand, in the two-beam type detector, the projector is provided with a pair of light emitting parts to emit two infrared beams, and the pair of light receiving parts provided in the light receiver receive the respective light beams. One of the beam interruptions does not give a warning as a malfunction, and the warning is given only after two beams are blocked.

[Problems to be Solved by the Invention] However, when such a conventional high-sensitivity receiver is applied to the two-beam system, the response is low as a light-blocking detector that detects light blocking due to passage of a person. There was a problem too.

That is, in the conventional device, 500 Hz included in the received light signal
Since the low frequency component of is detected and applied to the PLL circuit,
It usually takes about 100 ms for the circuit to follow the input frequency of 500 Hz and enter the locked state.

Looking at the response time of this PLL circuit from the detection operation as a light-blocking detector, the light beam is normally received in the steady monitoring state, so the PLL circuit is locked to the low-frequency signal of 500 Hz. In order to release the PLL circuit from the locked state to detect an abnormality, a low frequency signal of 500Hz is 100
It is necessary to cut off the beam so that no more than ms can be obtained.

Here, the cutoff time of the light beam with respect to the passage of a person is said to be about 50 ms in the case of the fastest running, which is shorter than the follow-up time of 100 ms for the PLL circuit at 500 Hz.

As a result, the conventional device with a long response time of 100 ms cannot detect the interruption of the light beam due to the passage of a person in the range of 50 to 100 ms, and there is a problem that there is an undetectable area for intruder monitoring. .

The present invention has been made in view of the above conventional problems, and in the two-beam system, a high-sensitivity light-blocking type capable of detecting an abnormality by responding quickly even to light-blocking for a short time. An object is to provide a detector of the formula.

[Means for Solving the Problem] First, the present invention is directed to a light-blocking detector in which a light emitter and a light receiver are separately arranged in a facing state.

In the present invention, regarding such a light-blocking detector,
The projector is provided with a pair of light emitting units that alternately emit infrared-modulated light whose high frequency is double amplitude-modulated by low frequency.

As for the light receiver, a pair of light receivers that commonly receive the infrared-modulated light alternately emitted from the pair of light emitters provided in the projector and convert it into a continuous high-frequency electrical signal, and a pair of the light receivers A narrow band amplifier for extracting and amplifying only a narrow band frequency component centered on the frequency of the modulated high frequency from the received light signal, and the oscillation frequency in the loop for the frequency and phase of the high frequency signal extracted and amplified by the narrow band amplifier. And a PLL tone decoder that includes a PLL loop that follows the phase and that detects a lock state of the PLL loop and outputs a determination signal,
And a signal processing circuit for outputting an abnormality detection signal when the discrimination output of the PLL tone decoder is cut off for a predetermined time or longer.

[Operation] In the light-blocking detector of the present invention having such a configuration, the high-frequency signal of, for example, 20 KHz is continuously received by receiving the combined modulated light from the double-modulated projector. Since the oscillation frequency and phase of the PLL loop of the PLL tone decoder are made to follow the obtained high frequency signal, the tracking response of the PLL loop to the input frequency can be made sufficiently high.

Therefore, the PLL loop that is locked to a high frequency of 20 KHz in the steady monitoring state immediately leaves the locked state when the light beam is blocked, and the discrimination signal cannot be obtained. Corresponding to almost one-to-one
It is possible to obtain a change in the discrimination output of the PLL tone decoder, and it is possible to reliably detect an abnormality even with the shortest beam cutoff time of 50 ms due to the passage of a person.

Further, since the narrow band amplifier and the PLL tone decoder process a continuous high frequency signal of 20 KHz, compared with a case of processing a high frequency signal of 20 KHz intermittently at 500 Hz, that is, a case where a single beam light is received and processed, Since there is no generation of harmonic components due to intermittent 500Hz, it is possible to improve the frequency selection of the narrow band amplifier and PLL tone decoder for high frequency signals.

[Embodiment] FIG. 1 is a block diagram of an embodiment showing one embodiment of the present invention.

In FIG. 1, 10 is a projector and 12 is a photoreceiver. The projector 10 and the photoreceiver 12 are separately arranged in a facing state with a desired monitoring distance, for example, several hundred meters.

The light projector 10 is provided with a pulse generator 14 that generates a clock a of low frequency, for example, 500 Hz, and a carrier pulse oscillator 16 that oscillates a carrier signal b of high frequency, for example, 20 KHz. The carrier signal b from the pulse oscillator 16 is given to the gate circuit 18, and the carrier signal c1 of 20 KHz from the carrier pulse oscillator 16 is output at the H level of the clock a of 500 Hz, and the carrier pulse oscillator 16 at the L level of the clock a. Similarly, the carrier signal c2 of 20 KHz from is output. That is,
The gate circuit 18 alternately outputs the carrier burst type modulation signals c1 and c2 which are double-modulated every half cycle of the clock a.

Following the gate circuit 18, the first and second light emitting units 20-1, 20-
Two are provided. Each of the light emitting units 20-1 and 20-2 is provided with a light emitting element that emits infrared rays, and the optical system is driven from the light emitting units 20-1 and 20-2 by light emission drive by the modulation signals c1 and c2 from the gate circuit 18. The double-modulated infrared-modulated lights d1 and d2 are alternately emitted toward the light receiver 12 via the light-receiving device.

On the other hand, the light receiver 12 has a pair of light emitting units 20-
First and second light receiving units 22-1, 22-2 are provided corresponding to 1, 20-2. Each of the light receiving sections 22-1 and 22-2 receives the combined infrared modulated light d1 and d2 in common through an optical system, converts the infrared modulated light d1 and d2 into a continuous high frequency electric signal of 20 KHz, and supplies the narrow band amplifier 24 with the electric signal.

The narrowband amplifier 24 is provided with a bandpass filter having a narrowband pass characteristic of ± 100 Hz centered around the oscillation frequency of the carrier pulse oscillator 16 provided in the projector 10, that is, a high frequency of 20 KHz. The signal e which amplified the extracted high frequency component of 20 KHz was added to the PLL of the next stage.
Output to the tone decoder 26.

The PLL tone decoder 26 forms a PLL loop with a phase comparator, a low-pass filter, and a voltage controlled oscillator (VCO), inputs the oscillation output of the voltage controlled oscillator to the phase comparator, and receives the received light signal e from the narrow band amplifier 24, that is, A high-frequency signal of 20 KHz is input, and the PLL operation is performed to make the oscillation frequency and phase in the loop follow the high-frequency signal input of 20 KHz.
Further, a lock detector is provided following the PLL loop provided in the PLL tone decoder 26, and this lock detector is provided with a high frequency signal 20 generated by the carrier pulse oscillator 16 of the projector 10.
It has a KHz discrimination function, and when the PLL loop follows the input frequency of 20 KHz and enters the locked state, the discrimination output f which becomes the logic level 1 is obtained from the lock detector. PLL tone decoder 2
The output f of 6 is given to the signal processing circuit 28, and the signal processing circuit 2
Reference numeral 8 produces an abnormality detection output g when the discrimination output f from the PLL tone decoder 26 is cut off for a predetermined time. Specifically, the signal processing circuit 28 is provided with a timer circuit, and the timer circuit is set to a time exceeding half the cycle of the clock a of the pulse generator 14 provided in the projector 10. If the discrimination output f is cut off, the timer operation is started. If the discrimination output f is not obtained within the set time, a timer output is generated, and an abnormality detection output g is generated based on the timer output to give an alarm.

In this case, when either one of the infrared modulated lights d1 and d2 from the projector 10 is blocked near the projector side, the generation and stop of the discrimination output f from the PLL tone decoder 26 are repeated every clock half cycle, and the timer is stopped. Since the circuit receives the discrimination output f again and is reset before the set time after starting by stopping the discrimination output f, the abnormality detection output g based on the timer output is not output.

Further, when either one of the modulated lights d1 and d2 is cut off near the light receiver side, the output level of the narrow band amplifier 24 is lowered and the discrimination output f from the PLL tone decoder 26 is reduced.
Is continuously obtained, the abnormality detection output g is not output.

FIG. 2 shows the transmission / reception state of the modulated lights d1 and d2 between the pair of light emitting units 20-1 and 20-2 and light receiving units 22-1 and 22-2 shown in FIG. When the distance becomes long, such as several hundred meters, the light beams of the modulated lights d1 and d2 from the light emitting units 20-1 and 20-2 spread according to the distance, and the light receiving units 22-1 and 22-2 modulate the light beams. Both the lights d1 and d2 are incident, the combined light receiving signals of the two modulated lights d1 and d2 are obtained by the light receiving units 22-1 and 22-2 themselves, and the combined light receiving signals are further combined by the narrow band amplifier 24. Therefore, the light receiving sensitivity is improved.

Next, the operation of the embodiment of FIG. 1 will be described with reference to the signal waveform diagram of FIG.

First, the pulse generator 14 provided in the projector 10 has a low frequency.
The clock a is generated at 500 Hz and given to the gate circuit 18, and for the gate circuit 18, a carrier pulse oscillator is used.
A carrier signal b of 20 KHz having a higher frequency than 16 is given. Therefore, the gate circuit 18 opens one gate at the timing when the clock a becomes H level, passes the carrier signal b from the carrier clock oscillator 16, and passes through the light emitting section 20.
The modulated signal c1 is output to -1, the other gate is opened at the timing when the next clock a becomes the L level, the carrier signal b from the carrier clock oscillator 16 is passed, and the light emitting unit 20
The operation of outputting the modulated signal c2 to -2 is repeated. That is, the gate circuit 18 alternately obtains carrier burst type modulation signals c1 and c2 in which the carrier signal b is modulated with the clock signal a every half cycle of the clock. The modulated signals c1 and c2 from the gate circuit 18 are given to the light emitting units 20-1 and 20-2,
Based on the modulation signals c1 and c2, the modulated lights d1 and d2 having the modulation frequency of the carrier b are generated every half cycle of the clock a.
Are fired alternately toward.

In the light receiver 12, as shown in FIG.
Infrared modulated lights d1 and d2 from the projector 10 are commonly received by 1 and 22-2 and converted into electric signals.

The light receiving signals from the light receiving units 22-1 and 22-2 are combined by the narrow band amplifier 24, and then only the high frequency component of 20 KHz included in the combined light receiving signal is extracted and amplified. For example, as shown in FIG.
A combined light receiving signal e having a high frequency component of 20 KHz is obtained.

The PLL tone decoder 26 enters the PLL lock state with a high-speed follow-up property which almost coincides with the rising edge of the light receiving signal of 20 KHz, and the light receiving signal of 20 KHz is cut off with respect to the combined light receiving signal e from the narrow band amplifier 24. Immediately P when struck
It is possible to shift from the LL locked state to the released state.

As a result, in the steady monitoring state, since the continuous combined light receiving signal e is given to the PLL tone decoder 26, the output f of the PLL tone decoder 26, that is, the discrimination output f maintains the H level state, The timer provided in the processing circuit 28 is in a stopped state, and the timer output g is also kept at H level.

On the other hand, at time t1, the infrared modulated light d from the projector 10
If 1, d2 is blocked by the passage of a person, then PL
20 KHz from narrowband amplifier 24 to L tone decoder 26
The combined light receiving signal of is cut off, the PLL tone decoder 26 releases the PLL lock state, and the discrimination output f becomes L level and stops.

When the discrimination output f cannot be obtained from the PLL tone decoder 26, the timer is started, the timer output is inverted to the L level at time t2 when the set time To has passed, and the signal processing circuit 28 outputs the abnormality detection output g to the outside. Like

Here, as the set time To of the timer, a predetermined time of 2 ms or more, which is a burst cycle of 500 Hz, may be set, and for example, the shortest beam blocking time when a person runs and passes may be set to 50 ms.

[Advantages of the Invention] As described above, according to the present invention, a pair of light emitting portions alternately emit infrared-modulated light in which a high frequency is double amplitude-modulated by a low frequency, and the pair of light receiving portions commonly receive light. And combine them to extract continuous high frequency signals
Since the oscillation frequency and phase of the PLL loop of the tone decoder are tracked, the tracking response of the PLL loop with respect to the input frequency can be made sufficiently high, and even if the beam is cut off for a short time, the beam cutoff is almost 1: 1. A change in the discrimination output of the corresponding PLL tone decoder can be obtained, and an abnormality can be reliably detected even if the shortest beam cutoff time due to the passage of a person is 50 ms.

Further, since a continuous high frequency signal is obtained on the light receiving side, harmonics due to the intermittent high frequency signal are not generated, and the frequency selectivity of the narrow band amplifier and the PLL tone decoder can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention; FIG. 2 is an explanatory view showing how the light beam spreads between the light emitting portion and the light receiving portion of the present invention; and FIG. 3 is a signal showing the operation of FIG. It is a waveform diagram. 10: Emitter 12: Light receiver 14: Pulse generator 16: Carrier pulse oscillator 18: Gate circuit 20-1, 20-2: Light emitting part 22-1, 22-2: Light receiving part 24: Narrow band amplifier 26: PLL tone Decoder 28: Signal processing circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Bibliographic references Sho 55-174669 (JP, U) Japanese public official Sho 59-21132 (JP, B2) Official public Sho 50-15157 (JP, Y2)

Claims (1)

[Scope of utility model registration request] 1. A light-blocking detector in which a light emitter and a light receiver are separately arranged so as to face each other, and a pair of infrared-modulated light whose high frequency is double amplitude-modulated by a low frequency is alternately emitted to the light emitter. A pair of light receiving portions for receiving in common the infrared modulated light alternately emitted from the pair of light emitting elements of the projector and converting the infrared modulated light into continuous high frequency electric signals, and the pair of light emitting elements. A narrow band amplifier that extracts and amplifies only a narrow band frequency component centered on the frequency of the modulated high frequency from the received light signal of the light receiving unit of the loop, and loops to the frequency and phase of the high frequency signal extracted and amplified by the narrow band amplifier. A PLL tone decoder that includes a PLL loop that follows the oscillation frequency and phase of the internal loop and that detects a lock state of the PLL loop and outputs a determination signal, and the determination output of the PLL tone decoder is interrupted for a predetermined time or longer. Light blocking detectors, characterized in that a signal processing circuit for outputting at abnormality detection signal.