RU2343413C1 - Laser range finder - Google Patents

Abstract

FIELD: physics; measurement.

SUBSTANCE: laser range finder contains the first pulsed solid state laser, forming optical system, clock pulse generator with output connected to input of pulse counter, gating circuit, receiving optical system, photodetector, reading device and indicator. Additionally mentioned range finder includes the second pulsed solid state laser, beam splitter, two delay lines and coincidence circuit.

EFFECT: higher reliability of range measurement to low-sized object.

3 dwg

Description

The invention relates to technical means for measuring the distance to various objects on the ground using laser radiation.

Known optical location devices in which the value of the distance from this device to an object on the ground (range) is determined by measuring the time interval between the emitted optical pulse and the reflected optical signal that has passed the measured distance [1, p. 51-55].

In the presence of reflections of optical radiation from objects located in front of the object to which the distance is measured (tree branches, shrubs, etc.), and also behind the object indicated above (hillside, forest, etc.), several reflected signals may occur, therefore, you must select the correct countdown.

The closest analogue to the claimed solution is the background exclusion scheme for measuring range presented in Figure 2.6, a [1, p. 55-56]. The circuit consists of a pulsed laser, a forming optical system, a mirror, a receiving optical system, two photodetectors, a clock generator, three key circuits, a pulse counter, an intermediate and terminal memory unit, a reader and an indicator.

The pulses of radiation from the optical output of the laser through the forming optical system are directed towards the object to which the distance is measured. Part of the laser radiation branched by the mirror passes to the first photodetector, the output of which is electrically connected to one of the inputs of the pulse counter. Counting pulses are generated by a clock pulse generator and fed to the counter through the first key circuit.

The reflected optical signals are transmitted through a receiving optical system to a second photodetector, the output of which is connected to the second input of the pulse counter via an intermediate memory unit and three key circuits. Each number of pulses between the moment the counter is started and the moments of signal formation from the output of the photodetector is transferred from the counter to the intermediate memory unit, and the counter continues to count. When the counter is full, the count stops, the last number received in the intermediate memory block is transferred to the terminal memory block and then it goes to the reader and indicator. As a result, the indicator displays the value of the maximum measured range and excludes all other results stored in the intermediate memory unit.

The presence of the mirror and the first photodetector in the considered circuit is not critical, since information on the laser pulse emission time can be obtained directly from the laser switching circuit.

In the presence of reflection of radiation from objects located behind the object to which the distance is measured, the result of measuring the distance to one of these objects, i.e. the countdown will be incorrect. To exclude such results, the linear dimensions of the radiation spot on the object in a plane perpendicular to the line of sight should not exceed the size of the object. For example, in order to measure the distance to a person (the minimum size is about 0.5 m) at a distance of 1000 m, it is necessary to ensure radiation divergence not exceeding 0.5 / 1000 = 0.0005 rad.

In the considered range finder, different types of lasers can be used, but for reasons of the highest efficiency, minimum dimensions and energy consumption, it is advisable to use pulsed semiconductor lasers. The emitting area of a pulsed semiconductor laser is the active region of the p-n junction and has a height of 1 ... 2 μm and a length of 0.1 ... 1.5 mm [2, p. 78]. For example, for the ILPN-112 semiconductor laser, the dimensions of the emitting area are 0.002 × 0.15 mm [3, p. 4].

As a forming optical system, a lens is used that projects the image of the laser emitting area into the plane of the object to which the distance is measured. To ensure the laser beam divergence of 0.0005 rad (at the output of the lens) and with respect to the ILPN-112 semiconductor laser, it is necessary that the focal length of the lens be at least 0.15 / 0.0005 = 300 mm. An optical system with such a focal length is large and unacceptable for use in small sights, binoculars, etc.

The task to which the claimed invention is directed is to create a small-sized laser range finder based on pulsed semiconductor lasers, in which the influence on the measurement result of interference from objects located in front of the object to which the distance is measured, and also behind the specified object, is eliminated.

The technical result consists in increasing the reliability of measuring ranges to a small subject.

The specified technical result is achieved using a laser rangefinder containing the first pulsed semiconductor laser; shaping optical system; a clock pulse generator, the output of which is connected to the input of the pulse counter through a key circuit; receiving optical system; photo detector; a reader, the input of which is connected to the output of the pulse counter, and an indicator; according to the invention, a second pulsed semiconductor laser, a beam splitter, two delay lines and a matching circuit are additionally introduced into the device; the emitting areas of the first and second pulsed semiconductor lasers are oriented in such a way that in the plane perpendicular to the line of sight, the cross section of the radiation beam is a plane figure symmetrical about the center, and the boundaries of this figure are formed by the intersection of two ovals, the large axis of symmetry of which are perpendicular; the electrical input of the first pulsed semiconductor laser is connected to the output of the first delay line and to the START input of the pulse counter, and the electrical input of the second pulsed semiconductor laser is connected to the output of the key circuit; the input of the first delay line is connected to the same output of the key circuit, while the electrical output of the photodetector is connected to the input of the second delay line and to the first input of the matching circuit; the second input of the matching circuit is connected to the output of the second delay line; the output of the matching circuit is connected to the STOP input of the pulse counter, and the delay time of the pulses in the first and second delay lines is the same.

Figure 1 shows the functional diagram of the device. Figure 2 illustrates the cross section of a laser beam in a plane perpendicular to the line of sight in the region of the object to which the distance is measured, as well as the location of objects located in front of the object to which the distance is measured, and behind the above object. Figure 3 shows the diagrams of the pulse sequences on the functional elements of the device.

The laser range finder (Fig. 1) contains the first 1 and second 2 pulsed semiconductor lasers installed on both sides of the beam splitter 3. A forming optical system 4 is placed in series with the beam splitter 3. The electrical input of the first laser 1 is connected to the output of the first delay line 5, it is also connected to it the “START” input of the pulse counter 6. In addition to the “START” input, the pulse counter 6 has three more inputs: “PULSE SEQUENCE”, “RESET”, “STOP”, as well as one output “NUMBER OF PULSE”.

The input of the pulse counter 6 “PULSE SEQUENCE” is connected to the output of the clock generator 7. The electrical input of the second laser 2 is connected to the output of the key circuit 8, to which the input of the first delay line 5 is connected. The range measurement signal is input to the key circuit 8. The same signal is fed to the input "RESET" of the pulse counter 6.

A photodetector 10 is installed in series with the receiving optical system 9, the electrical output of which is connected to the input of the second delay line 11 and to the first input of the matching circuit 12. The delay time of the pulses in the first delay line 5 and the second delay line 11 is the same. The second input of the matching circuit 12 is connected to the output of the second delay line 11. The output of the matching circuit 12 is connected to the “STOP” input of the pulse counter 6. The output of the pulse counter 6 “NUMBER OF PULSES” is connected to the input of the reader and indicator 13.

The emitting area of the first laser 1 is placed in the focal plane of the forming optical system 4 and the larger side of the area is parallel to the plane of the drawing in figure 1. The emitting area of the second laser 2 is also located in the focal plane of the forming optical system 4, the larger side of the area perpendicular to the plane of the drawing in figure 1.

In Fig. 2, in a plane perpendicular to the line of sight, in the region of the small-sized object 14 to which the distance is measured, the cross section of the radiation beam 15 from the first laser 1 (Fig. 1) is shown in the form of a flat figure, the boundaries of which generally represent an oval. For the second laser 2, the cross section of the radiation beam has the form indicated by 16. The cross section of the radiation beam from both lasers is a plane figure symmetrical about the center, and the boundaries of this figure are formed by the intersection of two ovals, the large axis of symmetry of which are perpendicular. Figure 2 also conditionally shows an object 17 located in front of the object to which the distance is measured, and an object 18 located behind the above object.

In the considered embodiment of the device, the linear size of the major axis of the oval, which determines the area of the presence of radiation, may exceed the linear size of the object. Therefore, as a forming optical system 4, you can use a lens having a significantly smaller focal length compared with the case discussed on page 2-3 of the present description. Almost the focal length of the lens can be reduced by 3-4 times or more. Thus, the laser range finder in question can be used in small-sized sights, binoculars and similar devices.

All elements included in the laser rangefinder are known. As pulsed semiconductor lasers 1 and 2, laser diodes, for example, type PGEW1S09 from Perkin Elmer, can be used, and as a photodetector 10, any highly sensitive photodiode, for example, C30724 photodiode from EG&G, Canada. As a beam splitter 3, gluing of two AR-90 ° prisms can be used, while one of the prisms has a beam splitting coating, for example, a multilayer polarizing one, on the hypotenuse face. In this case, the radiation beams from two lasers will be combined practically without loss. The forming optical system 4 and the receiving optical system 9 are lens lenses. The first delay line 5, the pulse counter 6, the clock 7, the key circuit 8, the second delay line 11, the match circuit 12, the reader and the indicator 13 are typical electronic components and can be implemented on a standard electronic element base.

The device operates as follows. The clock generator 7 (figure 1) generates a sequence of pulses 19, shown in figure 3. An external ranging signal from the control panel (not shown in FIG. 1) resets the previous reading of the pulse counter 6 and is supplied to the key circuit 8, at the output of which a pulse 20 is generated, which arrives at the first delay line 5 and the second laser 2. Time delayed τ ₁ pulse 21 from the first delay line 5 is supplied to the first laser 1 and starts the pulse counter 6, forming a sequence of pulses 22. Lasers 1 and 2 emit optical pulses that are spatially combined on the beam splitter 3, pass through the forming optical system 4. The radiation is directed towards the object 14, to which the distance is measured, and the center of the radiation beam (the geometric center of the superposition of two ovals in figure 2) is aligned with the center of the object 14.

The optical radiation of lasers 1 and 2 is diffusely reflected both from the object 14, to which the distance is measured, and from foreign objects 17 and 18. A part of the reflected radiation passes through the receiving optical system 9 and enters the optical input of the photodetector 10. Pulses 23 and 26 on the electric the output of the photodetector 10 is due respectively to reflections of the radiation of the second laser 2 (from a closer located object 17) and the first laser 1 (from a further located object 18). The pulses 24, 25 are due to reflections of the radiation of the second 2 and first 1 lasers, respectively, from the object 14, to which the distance is measured.

At the output of the second delay line 11, pulses 23a ... 26a will be generated, delayed relative to the pulses 23 ... 26 at a time τ ₁ . At the output of matching circuit 12, a pulse 27 will occur. This pulse will stop the pulse counter 6, at the output of which a number "n" is generated, which is proportional to the measured range and fed to the reader and indicator 13. As a result, the value of the measured range is displayed on the indicator.

As follows from the above description of the rangefinder, the presence of interference (reflections from foreign objects) will not lead to range measurement errors.

Thus, as a result of the proposed solution, it is possible to obtain a technical result - increasing the reliability of measuring ranges to a small item.

Information sources

1. Prayer V.V. Optical location systems. - M.: Mechanical Engineering, 1981. - 181 p., Ill.

2. Ishanin G.G., Pankov E.D., Radaykin B.C. Sources and receivers of radiation. - M.: Mechanical Engineering, 1982. - 222 p., Ill.

3. Emitters ILPN-112. Specifications ASHPK.433750.005 TU. 1989 .-- 73 p.

Claims (1)

A laser range finder comprising a first pulsed semiconductor laser forming an optical system, a clock generator whose output is connected to the input of the pulse counter, a key circuit, a receiving optical system, a photodetector, a reader, the input of which is connected to the output of the pulse counter, and an indicator, characterized in that it additionally introduced a second pulsed semiconductor laser, a beam splitter, two delay lines and a matching circuit emitting the areas of the first and second pulsed semiconductors conductor lasers are oriented in such a way that in the plane perpendicular to the line of sight, the cross section of the radiation beam is a plane figure symmetrical about the center, and the boundaries of this figure are formed by the intersection of two ovals, the large axis of symmetry of which are perpendicular, with the pulse counter input connected to the output clock pulse generator, an external range measurement signal, an electrical input of the first impulse, are input to the key circuit input and the RESET input of the pulse counter a pulsed semiconductor laser is connected to the output of the first delay line and to the START input of the pulse counter, and the electrical input of the second pulsed semiconductor laser is connected to the output of the key circuit; the input of the first delay line is connected to the same output of the key circuit, while the electrical output of the photodetector is connected to the input of the second delay line and to the first input of the matching circuit; the second input of the matching circuit is connected to the output of the second delay line; the output of the matching circuit is connected to the STOP input of the pulse counter, and the delay time of the pulses in the first and second delay lines is the same.

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