JPS6071974A - Laser range finder - Google Patents

Abstract

PURPOSE:To improve the distance measuring capacity by arranging an optical shutter between a receiving optical system and a photodetector and opening the shutter when a proper time corresponding to the distance to a target to be measured elapses after the generation time of a start pulse. CONSTITUTION:A part of the oscillation light from a laser oscillator 1 is made incident to a photo diode 3, and the start pulse which is its electric signal is led to a delay circuit 14. The delay circuit 14 drives a controller 16 controlling an optical shutter 15 when a proper time corresponding to the distance to the target to be measured elapses after the generation time of the start pulse, and the controller 16 opens the optical shutter 15.

Description

[Detailed description of the invention] (Technical field of invention).

The present invention relates to an improvement in a laser distance measuring device that measures distance by measuring the time it takes for a pulse of laser light to travel back and forth to a target.

[Prior art]

The received power of the laser ranging device is expressed by a linear equation when the size of the target object is smaller than the transmitted laser beam.

Here, Pr: Received power Prd Laser output peak value from the laser oscillator Kt: Transmitting optical system efficiency Kr: Receiving optical system efficiency r: Reflectance of target object D - Upper moving aperture of receiving optical system A: Target object Area 0: Transmitted laser beam spread at 9 angle μ: Atmospheric attenuation constant R: Distance to the target As shown in equation +11 above, the magnitude of the received power is related to the reflectance 1 area of the target and the distance to the target. 0 FIG. 1 shows an example of the configuration of a conventional laser distance measuring device. A laser oscillator 0) oscillates a gigantic pulsed laser beam, and most of this oscillated light is adjusted to a predetermined beam spread angle from a transmission source system (2)K and emitted toward a target. A part of the oscillated light also enters the photodiode (3), and the electrical signal serves as a start pulse (transmission time signal) to open the gate of the counter (4), which receives the clock from the clock pulse oscillator (5). Start counting pulses. The start pulse is also applied to the range gate control circuit (6). The range gate control circuit (6) controls the opening and closing of the gate of the range gate circuit (7), and after delaying the start pulse by an appropriate time corresponding to the distance of the target to be measured, the range gate is closed. Open the gate of circuit (7).

The delay time from this start pulse can be changed arbitrarily.

10,000, the light reflected by the target is the receiving source system (8)
and passed through a filter (9) to remove background optical noise and directed to the former detector member.

This received signal is amplified by a video amplifier (Iυ) and enters the range gate circuit (7). When the gate of the range gate circuit (7) is open, a stop pulse (reception time signal) is generated and the counter (4) is activated. The number of clock pulses counted during the opening/closing time of the gate by the start pulse and stop pulse is converted into a distance, and the distance 1IllIi value is displayed on the display α.

The sighting telescope O1 is used to aim at a target object.In the case of distance measurement, the sighting telescope O1 is used to irradiate a transmitted laser pulse light toward the target object to be measured.

A target object other than the object to be measured may be present in the transmitted laser beam at the same time. At this time, a plurality of received pulse signals will be generated. Figure 2 shows this situation. The giant laser pulse light oscillated by the laser oscillator (1) is adjusted to a predetermined beam spread angle by the transmission optical system (2), and is transmitted toward the target object A to be measured. In addition to the target object A to be measured, there is a target object B other than the target object to be measured in the transmitted laser beam L, and reception pulse signals a and b from these targets are generated simultaneously. Further, the received pulse signals d and e may be generated by back scattering from the atmosphere C at a short distance. In such a situation, a range gate method is normally used as a method for distance measurement by separating the received pulse signal from the target object to be measured and the received pulse signal from other objects. FIG. 3 shows the operation of the range gate in the situation of FIG. 2 of the apparatus shown in FIG. 1. The received pulse signals a, b, (1, θ correspond to the received pulse signals in Fig. 2. Fig. 3 (a) shows the photodetector a0
(hereinafter referred to as including atmospheric backscatter)
This figure shows the temporal appearance of the received light from the start pulse starting from the start pulse generation time. FIG. 3 υ) is the output signal of the video amplifier aυ. In order to separate the signal a from the target object to be measured from these multiple received pulse signals, a range gate as shown in FIG. 3(C) is generated by visual judgment or by obtaining information from other equipment. Thus, the delay time from the start pulse generation time of the range gate control circuit (6) to the time when the range gate is opened is adjusted. As a result, a strus pulse signal corresponding to the target object to be measured is obtained as shown in FIG. 3(a).

Incidentally, the magnitude of the received power of the laser distance measuring device depends on the size and reflectance of the target object, as can be seen from equation (1). Figure 4 shows that in the same situation as Figure 2, target object B, which is not the object of measurement, has a much larger size and reflectance than target object A, which is the object of measurement, and is approaching target object A. This figure shows the state of the conventional laser distance measuring device when it is located at a short distance side. Figure 4(a) is similar to Figure 3(a)
Similarly, this figure shows the state of the received light incident on the photodetector a. The intensity of the received light from the target object B is much larger than that from the target object A. In such a case, the strong reception signal from the target object B causes the original detector OI or the video amplifier aυ to become saturated, as shown in FIG. The output signal of the video amplifier corresponding to the received signal from the video amplifier will be lost. In this case, even if a range gate is applied as shown in FIG. 4(C), a stop pulse signal for the target object A to be measured cannot be obtained as shown in FIG. 4(0). In order to avoid saturation of the photodetector and the video amplifier I due to this strong reflected signal, a method has conventionally been used in which a light amount diaphragm device is installed in the receiving optical system (8). However, in the above situation, if the strong reflected light from the target object B is attenuated by the diaphragm 9 device and the saturation of the one-element detector or video amplifier is eliminated, the relatively strong reflected light from the target object A to be measured will be reduced. Weak reflected light is also attenuated in the same way, and may fall below the detectable level of the received signal, making it impossible to receive it.

[Summary of the invention]

This invention aims to improve these shortcomings.

An optical shutter that can control the passage and blocking of the received light is placed between the receiving optical system and the photodetector, and after delaying the start pulse by an appropriate amount of time corresponding to the distance of the target to be measured, the above It is equipped with means for opening the original shutter.

[Embodiments of the invention]

FIG. 5 shows an embodiment of the present invention.

In the figure, (1) to (51, f81 to OI are the same as in Fig. 1. A part of the oscillation light from the laser oscillator 111 enters the photodiode (3), and the electric signal is the start The pulse is guided to a delay circuit α4.The delay circuit I is a controller that controls the halo shutter a!9, which delays the start pulse from the time when the start pulse is generated by an appropriate time corresponding to the distance of the object to be measured. (I[9 is driven to open the optical shutter a!9'f. Note that the optical shutter t1
! 19 requires a fast response and good efficiency for the laser wavelength used, such as a method that utilizes changes in the polarization state due to electro-optic effects, a method that deflects the direction of the incident light to the photodetector a value, etc. There is.

FIG. 6 shows the operation of the apparatus according to the present invention in the situation shown in FIG. 2 above.

This corresponds to FIG. 4, which shows the operation of the conventional device. The received pulse signals a, b, d, and θ correspond to the received pulse signals shown in FIG.

The reflected light from the target object A to be measured, the reflected light from the target object B other than the measured object which is very strong compared to the target object A, and the backscattered light from the atmosphere at a short distance are received by the receiving optical system (8). The light passes through the filter T91'fr and enters the optical shutter al. This situation is shown in FIG. 6(a).

The optical shutter (l!9) can be used as shown in Fig. 6 (b
), the delay circuit I is adjusted so that it opens just before the time when the received pulse source from the target object A to be measured is received. ・This allows the delay circuit I to open from the multiple received pulse signals from the target object A to be measured. The received pulse signal a of the target object A to be measured can be separated, and the strong received signal 9 from the target object B does not enter the photodetector Ql and the video amplifier ai+. It is possible to eliminate the phenomenon of losing the received pulse signal, and it is possible to obtain a 7" pulse for the object to be measured as shown in FIG.
) Although the explanation has been made regarding the case where the change is made in a stepwise manner, it may also be controlled so that the open state is maintained only during appropriate time periods.
A shutter that can control passage and shielding of the receiving source is placed between the receiving source system and the photodetector, and after delaying the start pulse generation time by an appropriate time corresponding to the distance of the target to be measured, the above By providing a means for opening the shutter, it is possible to measure a distance to a target to be measured that is close to a target that generates strong reflected light, and has the effect of improving distance measurement performance.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional laser ranging device, Figure 2 is a diagram explaining the state of the received signal when multiple targets are simultaneously present in the transmitted laser beam, and Figures 3 and 4 are FIG. 5 is a diagram showing the time relationship between the intensity of light incident on the photodetector, the output of the video amplifier, the ranging signal, and the manual input signal of the counter, and explaining the operation of the conventional device (10). FIG. FIG. 6 shows the time relationship between the input light intensity to the optical shutter, the transmittance of the optical shutter, and the video amplifier output. FIG. 2 is a diagram illustrating the invention in detail. In the figure, fl) is a laser oscillator, and (2) is a transmission optical system. (4) is a counter, (8) is a receiving optical system, Ql is a photodetector, ao is a video amplifier, 1st is a display, (1waku is a sighting telescope. (I4 is a delay circuit, Qe is an optical shutter, ao is a controller O. Note that the same or corresponding parts in Figure 1 are indicated with the same reference numerals. Agent Masuo Oiwa (11) Figure 3 (0-) Time 14 Figure (0-) (tb clear time

Claims (1)

[Claims] A laser oscillator that oscillates a huge pulse, a transmission optical system that transmits laser light to a target object with a predetermined beam spread of 9 angles, a reception optical system that collects reflected light from the target object, and the reception optical system described above. a photodetector that converts the optical signal focused by the laser beam into an electrical signal; a video amplifier that amplifies the electrical signal from the photodetector; and a video amplifier that converts the transmission time signal of the laser beam into a reception time signal of the reflected light from the target object. In a laser range finder comprised of a counter that calculates the measured distance value, a display that displays the measured distance value, and a sighting telescope that aims at the target, there is a distance between the receiving optical system and the photodetector. An optical shutter capable of controlling passage and shielding of the received light is disposed in the area, and means is provided for opening the optical shutter after delaying the transmission time of the laser beam by an appropriate time corresponding to the distance of the target object. A laser distance measuring device characterized by 'fr.