JPH0481752B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention sends out a pulsed laser, detects the pulsed laser light reflected by a target, and detects the intensity of the reflected laser light and the time delay from the pulse sending. This invention relates to a laser warning device that recognizes the approach of a target and issues a warning.

(Prior Art) A conventional laser alarm device employs a threshold determination method in which a single pulsed laser beam is sent out, and when the intensity of the reflected pulse is stronger than a certain level, the device outputs an alarm signal. Such a conventional laser warning device will be explained with reference to FIGS. 3 to 5. Figure 3 shows
1 is a diagram illustrating the optical arrangement of a laser warning device, in which a laser beam 12 is sent out from a transmitter 11. FIG. The light receiving field of the receiving section 13 is indicated by reference numeral 14. As shown in the figure, the transmitting laser beam 12 and the receiving field of view 14 overlap in the range from distance R ₁ to R ₂ , and when a target object 15 is placed between them, the laser reflected light is detected by the receiver 13 and an alarm is issued. Output a signal.

Figure 4 shows the waveforms of transmitted light and received light,
Reference numeral 12 indicates a transmitted light waveform, and 113 indicates a received light waveform. In this figure, the horizontal axis represents time, and the vertical axis represents amplitude. The received optical pulse 113a is received with a delay from the transmitted optical pulse 112a by a time proportional to the distance R, and its peak value V _S changes in relation to the reflectance of the target object 5 and the distance R.

The relationship between distance R and peak value V _S is shown in FIG. In FIG. 5, the horizontal axis is the distance R between the alarm device and the target object, and the vertical axis is the peak value V _S of the received light on a logarithmic scale. The transmitted laser beam 12 is within the receiving field of view 14 between distances R ₁ and R ₂ , and V _S is inversely proportional to the distance from the square to the fourth power according to the radar equation. 2 if the target completely covers the field of view
If the target is smaller than the field of view, it is inversely proportional to the fourth power, as in normal radar. However, it is undesirable in the design of the equipment for V _S to vary significantly with distance, so it is common practice to adjust the way the transmitting and receiving beams overlap so that they are as flat as possible. (The characteristic line a'-b'-c' is preferable to the characteristic line a-b-c, and the ideal characteristic line
a″−b″−c″).

(Problems to be solved by the invention) The biggest drawback of such conventional alarm devices is that
If there is a so-called imperfect reflector that exists uniformly between R ₁ and R ₂ and transmits most of it and reflects only a part of it, for example, clouds, fog, smoke, etc., if the reflectance is large, it will work erroneously. It's something you end up doing. (Separate measures are required for objects other than imperfect reflectors). An object of the present invention is to provide a laser warning device that operates correctly even in such situations.

(Means for Solving the Problems) Means provided by the present invention to solve the above-mentioned problems includes a transmitter that sends out a pulsed laser beam,
A laser alarm device includes a receiving section that receives reflected laser light from which the pulsed laser light is reflected by a target, generates a received signal, processes the received signal, and outputs an alarm signal, wherein the pulsed laser light has two When the time width of the nuclear pulse is τ, the time interval between the two pulses is 2τ, and the receiving unit sequentially receives the received signals, which are sequentially different from each other by τ. delay means for generating first to fifth signals with time delays; first, second and third phase inversion means for inverting the phases of the first, third and fifth signals, respectively; addition means for adding the outputs of the first, second and third phase inversion means and the second and fourth signals; and outputting the alarm signal when the output of the addition means exceeds a predetermined level. The method is characterized by comprising a determination means.

(Example) Next, the present invention will be explained in more detail with reference to Examples.

The optical arrangement of this embodiment is the same as that in FIG.
However, in this embodiment, double pulse laser light with an interval of 2τ is used as the transmission laser light. A block diagram of the receiving section of this embodiment is shown in FIG. In this figure, 1 is an optical sensor, 2 is an amplifier, 3 is a comparator, 6 is a delay element, 7 is an inverting amplifier, 8 is a non-inverting amplifier, and 9 is a summing amplifier. Comparator 3 connects the threshold voltage V _th with the output 109 of summing amplifier 9
When the received optical pulse is larger than a certain value, an alarm signal 103 is output. The dashed line in Figure 1 is
This is a newly added part to the conventional configuration in this embodiment, and the delay time of the delay element 6 is τ.

2A to 2D are diagrams showing waveforms of transmitted light and received light in the embodiment of FIG. 1. Figure a shows a double pulse transmission light waveform, and as shown in the figure, the interval between the first pulse 100a and the second pulse 100b is 2τ. When such a laser beam is reflected by an opaque target (for example, a person or a car) at a distance R, the pulse waveform is preserved and has a similar shape, but is shifted by the distance by time, as shown in Figure b. Received. On the other hand, in the case of an imperfect reflector (cloud, fog, smoke, etc.) that exists uniformly and transmits most of the signal, the pulse width is widened and received as shown in d of the figure. When an opaque target object and an incomplete reflector coexist, received light having a waveform as shown in c in the figure is obtained. If the signal processing is performed in the receiving section shown in FIG. 1 for the three cases shown in FIG. 2 b, c, and d, the reflected light from the target will be doubled in the case shown in FIG. 2 b. In case b of the same figure, the signal levels at time positions t2 and t4 are added, and the reflected light is doubled. In the case of figure d, the signal levels at time positions t1, 2, 3, 4, and 5 are almost the same, and the value obtained by subtracting the sum of the signal levels at t1, t3, and 5 from the sum of the signal levels at t2 and t4 is becomes below zero. In the case of c in the figure, when the sum of signal levels at time positions t1, t3, and t5 is subtracted from the sum of signal levels at time positions t2 and t4, the reflected component from the incomplete reflector is removed. As a result, the influence of uniformly distributed imperfect reflectors is eliminated. However, in this example, the wave value V _S of the received light shown in FIG. 4 is sufficiently uniform with respect to the distance, and the interval 2τ is set to be shorter than the time the laser takes to reach from R ₁ to R ₂ . .

(Effect of the invention) As explained above, according to the present invention, clouds,
It is possible to provide an alarm device that does not issue an alarm for incomplete reflectors such as fog and smoke, but issues an alarm for non-transparent targets such as people and vehicles.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a receiving section of an embodiment of the present invention, Figs. 2 a to d are diagrams showing waveforms of transmitted light and received light in the embodiment, and Fig. 3 is a general laser alarm device. Figure 4 is a diagram showing the waveforms of the transmitted light and received light of a conventional laser warning device, and Figure 5 is a diagram showing the relationship between the distance to the target and the peak value of the received light. be. DESCRIPTION OF SYMBOLS 1... Optical sensor, 2... Amplifier, 3... Comparator, 4... Threshold voltage input terminal, 5... Alarm signal output terminal, 6... Delay element, 7... Inverting amplifier, 8... Non-inverting amplifier , 9...Summing amplifier, 1
1... Transmission unit, 12... Transmission laser beam, 13
... Receiving section, 14... Light receiving field of view.

Claims (1)

[Claims] 1. A transmitter that sends out a pulsed laser beam, and a receiver that generates a received signal by receiving the reflected laser beam reflected from the pulsed laser beam at a target, processes the received signal, and outputs an alarm signal. In the laser alarm device, the pulsed laser light is a pair of pulses consisting of two pulses, and when the time width of the pulse is τ, the time interval between the two pulses is 2τ, The receiving section includes a delay means for generating first to fifth signals which are sequentially delayed by τ to the received signals, and the first, third and fifth signals.
first, second and third phase inverting means for respectively inverting the phase of the signals; the outputs of these first, second and third phase inverting means and the second and fourth phase inverting means;
What is claimed is: 1. A laser warning device comprising: adding means for adding the signals of the adding means; and determining means for outputting the alarm signal when the output of the adding means exceeds a predetermined level.