JPH067169B2 - Infrared detector - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to an infrared type detection device including a light projector and a light receiver.

[Prior art]

Conventionally, in this type of infrared detection device used for crime prevention or for notifying visitors, an infrared LE is generally used as a light projecting element.
D, a phototransistor is used as a light receiving element, and a lens or a parabolic reflector whose surface is aluminum-deposited is used as an optical system. Infrared light emitted from the projector is emitted as pulsed light in order to distinguish it from ordinary sunlight and other light such as illumination light at night that is a disturbance for the detection device. The frequency of the pulsed light varies from several hundreds of hertz to several tens of kilohertz, and double-modulation with two kinds of frequencies. The intensity of the pulsed light emitted from the projector and the ability of the receiver to receive the pulsed light define a standard installation interval (a warning distance in the case of crime prevention) of each detection device. In this case, consider the attenuation of light between the sender and the receiver, and the attenuation of light due to contamination of the optical system used for the sender and the receiver, and the amplitude of the pulsed light after being amplified by the receiver. The corresponding pulse signal is normally set to be large during standby. For example, the pulsed light that reaches the light receiving element of the light receiver is
It may be set such that the light receiving state is maintained and the detection signal is not issued even if the light is attenuated to about one-hundredth as compared with the state where the attenuation rate is low such as outdoors under normal fine weather. When used outdoors, it is necessary to have such a margin considering various weather conditions. For this reason, the pulsed light emitted from the light projector has a large amplitude while the pulse occupancy rate (duty ratio) is reduced to reduce power consumption and consider the life of the LED. In the light receiver, the selective light receiving ability of this pulsed light is increased to increase the sensitivity. Also, since the elements of the light emitting and receiving elements are not perfect points, the divergence angle and light receiving range of the pulsed light created by the optical system (convex lens or parabolic mirror) depend on the element area and the focal length of the optical system. It will have a certain range to be determined. This spread makes it easier to adjust the optical axis during installation,
There is an advantage that it is less affected by the deviation of the direction due to vibration after installation.

[Problems to be Solved by the Invention]

If one set of emitter and receiver should be watched for the longest possible distance, and if there is a sufficient margin for the attenuation of the amplitude of the pulsed light reaching the light receiving element, the intensity of the emitted pulsed light will be increased and the light receiving sensitivity will be increased. . This means that the amplitude of the pulsed light reaching the light receiving element increases more than necessary during normal caution (when there are few factors that attenuate light), which may cause a problem on the contrary. As described above, the light emitted from the light projector has a certain spread, and the light receiver also has a light receiving range of the same extent. Therefore, depending on the setting state, even if the reflected light from the ground surface or the wall surface of the guard area is received and the light near the central axis is blocked, the reflected state may be maintained only by this reflected amount. Such a phenomenon occurs only in a special case in which the installation height of the light emitter / receiver is low, the ground is a flat place like asphalt, and the surface is wet. However, in the case of a detection device used for crime prevention, it must be prevented under any condition that a person passing near the reflection surface cannot detect it.

[Means for solving the problem]

As a method for solving this problem, a method of narrowing the divergence angle of the light of the projector can be considered, but the narrowing thereof makes it difficult to adjust the optical axis and causes a problem that malfunctions due to vibration increase. Therefore, in order to solve these problems, the conventional light emitting / receiving element and the optical system are used, and in the present invention, as the pulsed light, a pulsed light including pulses having different amplitudes is emitted from the light projector, and To provide a detection device which is selected according to the amount of light received by a light receiver, receives and processes only pulsed light having a specific amplitude, and does not accept pulsed light having an amplitude larger than necessary during normal standby. Is.

【Example】

As the pulsed light emitted from the projector, a pulse having the maximum amplitude is used as a reference pulse, and a pulsed light having different amplitudes is delayed from the reference pulse by times t1 and t2, as shown in FIG. 2 (a). FIG. 1 shows a block diagram of a projector that emits this pulsed light and a light receiver that forms a pair. The light projector is provided with a light projecting element for projecting the pulsed light and an oscillating unit. A signal photoelectrically converted by a light receiving element such as a phototransistor on the light receiver side is amplified by an amplifier 1. In the pulse signal amplified by the amplifier 1, a reference pulse is detected by the maximum pulse detector and is input to the synchronous pulse controller. The synchronous pulse control unit first generates a pulse synchronized with the pulse having the smallest amplitude, which is delayed by the time t2 from the generation timing of the detected reference pulse. The amplifier 2 selects and amplifies only the pulse of the timing that coincides with the pulse output from the synchronous pulse control unit among the outputs of the amplifier 1. The output of the amplifier 2 is connected to the window comparator and the alarm comparator. The threshold level of the alarm comparator and the lower threshold level of the void comparator are set to the same value, Th1. The higher threshold level of the window comparator is Th2. Now, when the output of the amplifier 2 is at a level exceeding Th2, no output is output from these two comparators. Therefore, the one shot for alarm does not work and no alarm is output. This state is shown in part (a) of FIG. (A) is a waveform of pulsed light emitted from the projector, (b) is an output waveform of the amplifier 1, (c) is an output waveform of the maximum pulse detector, (d)
Shows the output waveform of the synchronous pulse control unit, and (e) shows the output waveform of the output of the amplifier 2. Next, the operation when the output of the amplifier 2 is reduced, that is, when the environment of the light receiving time of the projector is deteriorated and the light transmittance is reduced will be described. It is assumed that the output of the amplifier 2 is between the levels Th1 and Th2 that produce the output of the window comparator. At this time, an output is output from the window comparator and is input to the sync pulse control unit via the delay circuit. Then, the sync pulse control unit changes the timing of sync pulse generation after the time t1 of the reference pulse. That is, it is changed so as to generate a synchronization pulse synchronized with a pulse having a larger amplitude than the pulse that has been received and amplified by the amplifier 2 until then. With this synchronizing pulse, the amplifier 2 amplifies the pulse delayed by the time t1 from the reference pulse, and becomes larger than the output of the amplifier 2 up to that point. Therefore, the output of the window comparator disappears. Depending on the state of the environment, the same operation is repeated to adjust the output level of the amplifier 2. This allows Th2 and amplifier 2
Output difference (margin until alarm action) does not become larger than necessary. If the output of the window comparator is sent to the synchronous pulse control unit as it is, the output of the amplifier 2 will be changed regardless of the time required to attenuate the received pulsed light. When the pulsed light is gradually attenuated due to fog or the like, it cannot be distinguished. Therefore, a delay circuit is provided between the output of the window comparator and the sync pulse control unit,
Make this distinction possible. Then, after a lapse of a time longer than the delay time set by the delay circuit, the original sync pulse is restored and it is confirmed that the environmental condition is not recovered. The part (b) of FIG. 2 shows a state after the output is output from the window comparator and the output of the amplifier 2 is adjusted. In this way, the alarm comparator produces an output when the output of the amplifier 2 is constantly lower than Th1 while maintaining the output always higher than the rush level Th2, and the alarm signal is output from the alarm one-shot section and the alarm circuit. Will be issued. When the pulsed light showing the maximum amplitude is used as the reference pulsed light, it is possible that the output of the amplifier 1 in the light receiver is saturated and the pulse with the maximum amplitude cannot be detected when the set distance between the light emitter and the light receiver becomes short. To be In order to avoid this state, the pulse width of the reference pulse may be set to a value different from that of the other pulses, and the maximum pulse detection unit may be provided with a function of detecting this difference in pulse width. The more pulses having different amplitudes generated between the reference pulses, the more precise the level can be adjusted. It goes without saying that the present invention can also be applied to an infrared detection device that uses double-modulated infrared pulsed light in which high-frequency modulated light is amplitude-modulated at low frequency.

【The invention's effect】

By making the pulsed light emitted from the projector as in the present invention, the current consumption can be reduced as compared with the conventional method that always emits the maximum pulse. Further, since the amplitude of the pulse signal of the amplifier 2 which is the target when the alarm level is finally determined by the light receiver can be automatically adjusted to the optimum value according to the level of the pulsed light reaching the light receiving element, While maintaining the function of detecting light shields, it is possible to prevent malfunctions due to excessively strong pulsed light during standby. Further, according to the present invention, the reference pulse is selected from the pulsed light reaching the light receiving element, and the pulse signal to be amplified is specified based on the pulse generation timing. Wiring is required for this purpose, and a complicated structure such as using a storage device is not required, and the device can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention. FIG. 2 shows a part of the waveforms of the block diagram of FIG. 1 for explanation.

Claims (2)

[Claims] 1. A light projector that emits infrared pulsed light that spreads at a fixed angle and a light receiver that receives infrared pulsed light from a fixed range of directions are installed with a warning zone in between. In an infrared detection device that outputs a detection signal when interrupted, one or more pulsed lights having a lower amplitude and a different amplitude than the reference pulsed light between the pulses of the reference pulsed light of a constant period,
Each of the projectors emits light with a certain time delay from the reference pulse, a light receiving element for converting the infrared pulsed light emitted from the projector into a pulse signal, an amplifier 1 for amplifying the pulse signal, and an output from the amplifier 1. A maximum pulse detector that detects the reference pulse from the signal, and a synchronization that generates a pulse signal that is synchronized with the pulse signal with the smallest amplitude from one or more pulse signals that are generated after a certain time delay from the reference pulse. A pulse control unit, an amplifier 2 that selectively amplifies a pulse at a timing that matches a pulse signal output from the synchronous pulse control unit, and an amplifier 2
And a delay circuit that sends a signal to the synchronous pulse control unit after a predetermined time has elapsed since the output from the amplifier 2 decreased and the output from the amplifier 2 fell between the two reference values of the window comparator, The synchronization pulse control unit switches the synchronization signal sent to the amplifier 2 for a predetermined time immediately after the signal from the delay circuit is input, to a pulse signal synchronized with a pulse signal having the next largest amplitude of the amplitude of the pulse signal until then, An infrared detection device comprising a light receiver configured such that the amplitude of a signal output from the amplifier 2 has a substantially constant value. 2. The reference pulsed light having a pulse width different from the pulse widths of other pulsed lights is adopted, and a maximum pulse detector has a function of detecting whether or not it is the same as the pulsed width of the reference pulsed light. The infrared detection device according to claim 1, wherein the infrared detection device is provided.