RU2756381C1 - Laser rangefinder - Google Patents

Abstract

FIELD: semiconductors.

SUBSTANCE: laser rangefinder containing the main and test emitters of different power with power circuits, a photodetector with a lens, a threshold device with a variable threshold adjuster connected at the output of the photodetector and connected at the output with a control circuit and a time interval meter, the threshold device is equipped with a constant threshold level adjuster U_o, variable threshold adjuster U(Z), where Z is the current value of the range, and the power supply circuit of the main emitter is connected to the output of the control circuit, the output energy Е₀ of the probe radiation is limited by the relation

where D_pd is the diameter of the photodetector lens, ψ is the angle of divergence of the probe emitter, R is the distance to the mirror reflector, E_min is the minimum radiation energy received by the photodetector, E_mpl is the maximum permissible level of illumination of the photodetector, and the variable threshold U (Z) is The scatter envelope is set above the backscatter envelope for all possible dissipation factors. The variable threshold can be inversely proportional to the third power of the current range Z.

EFFECT: ensuring a safe mode of operation of the photodetector while maintaining the required probability of reliable measurements in a wide range of ranges.

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Description

The invention relates to laser ranging, namely, to pulsed laser range finders and locators.

Known systems of pulsed laser ranging, containing a pulsed laser and a photodetector, as well as a circuit for measuring the delay of the reflected signal, designed to measure the distance to distant objects [1].

A feature of such systems is a wide amplitude range of signals reflected from objects at short and long distances. This leads to overloads of the receiving path and reduces its noise immunity in the near zone [2]. Protection against interference created by extraneous local objects and aerosols of the airway is carried out using temporary automatic gain control (VARC) and threshold (VARP) [2], however, these measures are ineffective when overloading the first stages of the receiving-amplifying path, causing deterioration of the resolution and accuracy time reference of the reflected signal [3]. In this case, there is a risk of damage to the photodetector by radiation reflected from the mirror object. Known photodetector laser rangefinder [4], in which this drawback is eliminated by introducing a controlled electro-optical attenuator in front of the sensitive area of the photodetector, however, this solution leads to a significant complication of the device and deterioration of the signal-to-noise ratio.

The closest in technical essence to the proposed invention is a laser rangefinder with a test emitter [5]. The specified device contains two emitters of different power with control circuits, a photodetector, a threshold device with a standard threshold adjuster connected at the output of the photodetector and connected at the output with a time interval meter and with a control circuit of a more powerful emitter.

This scheme highlights weak received signals, such as signals reflected by atmospheric aerosols. Therefore, in the presence of a backscatter signal [2] that exceeds the standard backscatter signal generated by the master, the system is blocked and loses the ability to receive information from distant objects.

The objective of the invention is to provide a safe mode of operation of the photodetector while maintaining the required probability of reliable measurements in a wide range of ranges.

где D_пр - диаметр объектива фотоприемника, ψ - угол расходимости излучения пробного излучателя, R - дальность до зеркального отражателя, E_min - минимальная принимаемая фотоприемником энергия излучения, Е_пду - предельно допустимый уровень засветки фотоприемника, а переменный порог U(Z) в области действия помехи обратного рассеяния установлен выше огибающей помех обратного рассеяния для всех возможных коэффициентов рассеяния.This problem is solved due to the fact that in the known laser rangefinder, containing the main and test emitters of different power with power circuits, a photodetector with a lens, a threshold device with a variable threshold adjuster connected at the output of the photodetector and connected at the output with a control circuit and a time interval meter , the threshold device is equipped with a constant threshold level U _o , a variable threshold U (Z), where Z is the current range value, and the power supply circuit of the main emitter is connected to the output of the control circuit, the output energy E _{0 of the} probe radiation is limited by the ratio

wherein D _ave - diameter photoreceiver lens, ψ - divergence angle probe emitter radiation, R - distance to a mirror reflector, E _min - minimum accepted photodetector radiation energy E _RC - maximum allowable level of illumination of the photodetector, and the variable threshold U (Z) in The backscatter interference action is set above the backscatter noise envelope for all possible dissipation factors.

The variable threshold can be inversely proportional to the third power of the current range Z.

In the drawing, FIG. 1 shows a functional diagram of a laser rangefinder. Fig. 2 illustrates the path of the rays along the path of the rangefinder. FIG. 3 shows an oscillogram of backscatter interference.

The laser rangefinder includes a main emitter 1, a test emitter 2, a photodetector with a lens 3, at the output of which a threshold device 4 is switched on with a constant threshold setpoint 5 and a timed automatic threshold control unit (VARP) 6. The output of the threshold device is connected to a time interval meter ( IVI) 7 and control circuit 8, the output of which is connected to the inputs of the VARP 6 setter and the "start" input of the main emitter. The "start" input of the test emitter 2 is also connected with the control circuit 8.

The device works as follows.

In the initial state, the main emitter 1 and the VARP regulator 6 are blocked. When the command "start" is given, the test emitter 2 is triggered, directing a pulse of probing radiation to the selected object. The moment of radiation t ₀ is fixed by the time interval meter, the photodetector 3 receives the pulse reflected by the object. The constant triggering threshold of the threshold device 4 determined by the control unit 5 corresponds to the minimum threshold energy of the received signal E _min (signal power P _min = E _min / t _and , where t _and is the pulse duration). These parameters are determined by the noise of the photodetector and the probabilities of false triggering and correct detection [1, 2].

If a mirror reflector (retroreflector, retroreflector, triple-prism) with an effective reflecting surface sufficient to generate energy on the photodetector exceeding the level E _min is present in the probe radiation alignment, then the threshold device 4 is triggered and generates a pulse, the temporal position of which t _{1 is} recorded by the meter time intervals 7, calculating the time interval T = t ₁ -t ₀ . The distance R to a specularly reflecting object is determined by the formula R = cT / 2, where c is the speed of light [1].

If there is no mirror reflector in the probe beam alignment, then the threshold device does not work, and the control circuit 8 generates signals to start the VARP 6 and the main emitter 1. Further, the range measurement procedure is carried out in the same order as in the trial sounding.

Thanks to the described order of operation of the device, a safe level of illumination of the photodetector by reflected radiation pulses is ensured.

With the current level of sensitivity of photodetectors E _min , close to the theoretically limiting one, and weight and size restrictions imposed on the optics of rangefinders, to ensure the maximum measured range of 5-25 km, the energy of probing radiation E ₀ should be at least 10-20 mJ [2]. Known range finders have just such an output energy of laser radiation [6]. With such energy ratios, the mirror reflector overlapping the radiation beam (Fig. 2) leads to irradiation of the photodetector with energy that significantly exceeds the maximum permissible level E _pdu .

For clarity, the diagram in FIG. 2, the path of the reflected beams is conditionally continued in the direction of the probe radiation. It is obvious that the current mirror reflector maximum diameter D _Neg half the diameter D of the receiving lens _{so on.} Based on this, it is easy to determine the energy of the photodetector illumination specularly reflected main laser radiation with the radar equation [1, 2].

where ψ is the angle of divergence of the probe radiation beam;

R is the distance to the reflector.

Example 1

D _pr = 40 mm; ψ = 10 ^-3 rad; E ₀ = 0.01 J; R = R _min = 100 m - the minimum distance to the reflector, at which the illumination of the photodetector is maximum. Do-rp = Dnp / 2 = 20 mm. With these data, in accordance with (1)

The maximum permissible energy level E _pdu = 10 ^-10 J is set for a standard FUO-119 photodetector based on a silicon avalanche photodiode [7].

It can be seen from inequality (2) that if there is a reflector on the path under the conditions of example 1 and at higher ranges R within the specified measurement range, the photodetector will be disabled by the back reflected radiation of the main emitter.

Formula (1) is also valid for assessing the level of illumination by specularly reflected radiation of the probe emitter.

Known miniature semiconductor laser emitter with a microcylindrical lens, in this technical solution does not require additional focusing optics [8]. Parameters of this emitter: output radiation power 60 W; radiation beam divergence 10 × 10 °; pulse duration 10 ^-8 s; pulse energy 60 W⋅10 ^-8 s = 6⋅10 ^-7 J; laser dimensions ∅5.8 × 4.6; dimensions of the microcylindrical lens ∅1 × 2.

According to (1), for a test emitter

E * pr = 7.88⋅10 ^-13 J.

отмеченному в формуле изобретения.Thus, during the operation of the test emitter, the received signal exceeds the minimum received energy E _min = 6⋅10 ^-16 J [7] and does not exceed the maximum permissible level E _pdu = 10 ^-10 J, which corresponds to the condition

noted in the claims.

The atmosphere has a significant impact on the operation of the rangefinder. Attenuation on the path above was not taken into account, since the worst case in terms of the level of harmful flares was considered. However, in the main mode of operation, the backscattered radiation from the laser transmitter of the rangefinder can cause interference.

The backscattered signal has the form [9]:

where Z is the distance to the elementary scattering volume;

Z '- variable of integration;

A (Z) - instrumental function that takes into account the energy potential and the geometric factor of the device, due to the incomplete overlap of the fields of the emitter and receiver in the near zone;

β _s (Z) and β _t (Z ') are the averaged profiles of the volumetric scattering and attenuation coefficients; for a rough estimate, β _s (Z) = β _t (Z ') = 3 / V;

V - meteorological visibility range;

g _π (Z) is the averaged profile of the lidar ratio (normalized backscattering coefficient determined by the scattering indicatrix); one can take g _π (Z) = 1 / 8π [9].

For the mean value β (Z) = β from (3) it follows:

where A * (Z) is the normalized function A (Z); A * (Z) ~ 1 at Z ~ 100 m;

E _o - the energy of the probing signal;

β is the average scattering coefficient;

c is the speed of light;

D is the diameter of the receiving lens;

τ _o is the transmittance of the receiving optics.

Derivative (4) with respect to β

Equality (5) implies the zero condition for the maximum P (Z) in each section of the sounding path.

where P and P * are constant coefficients determined by the energy potential of the equipment.

The effective length of the backscatter interference does not exceed 1 km. FIG. 3 shows an example of such interference (the horizontal division is 1 μs, which corresponds to 150 m on the Z scale. In the near zone, the backscatter interference is limited by the instrumental function of the rangefinder [2]. Therefore, in reality, dependence (6) should be implemented using the variable component of the threshold in the region the effects of backscatter interference in a relatively narrow range from 100 to 1000 m.

In accordance with the proposed invention, a prototype laser rangefinder was developed.

The studies carried out have confirmed the fulfillment of the specified technical requirements in all specified operating conditions.

Thus, the proposed technical solution provides a safe mode of operation of the photodetector while maintaining the required probability of reliable measurements in a wide range of ranges.

Sources of information

1.V.A. Volokhatyuk et al. "Questions of optical location". - M .: Soviet radio, M., 1971. - p. 213.

2. V.G. Vilner et al. Measurement reliability of a pulsed laser rangefinder. M .: Photonics. 2013, no. 3. - S. 42-60.

3. V.G. Vilner et al. Ways to achieve the ultimate accuracy of a laser speed meter. M: The world of measurements. 2010, no. 7. - P.17-21.

4. Radiation receiver with active optical protection system. US patent No. 6,548,807.

5. Laser measurement system. US pat. No. 4,657,382. - prototype.

6. Simrad LP7. Jane's Electro-Optic Systems 2003-2004, p. 355.

7. Single-element photodetector FUO-119-01 OS2.003.030TU.

8. V.G. Vilner et al. New methods for increasing the probe radiation energy of pulsed range finders-altimeters based on semiconductor lasers. Kazan: KSPEU, Izvestiya VUZov. Energy problems. Power engineering. No. 11-12, 2013. - S. 33-37.

9. Questions of laser sounding of the atmosphere. [Collection of articles / AN SSSR, Sib. department, Institute of Atmospheric Optics; Resp. ed. Corresponding Member USSR Academy of Sciences V.E. Zuev. - Novosibirsk: Science. Sib. department, 1976 .-- 189 p.

Claims (2)

1. A laser rangefinder containing the main and test emitters of different power with power circuits, a photodetector with a lens, a threshold device with a variable threshold adjuster connected at the output of the photodetector and connected at the output with a control circuit and a time interval meter, characterized in that the threshold device is equipped with setpoint constant threshold level U _o , setpoint variable threshold U (Z), where Z is the current value of the range, and the power circuit of the main emitter are connected to the output of the control circuit, the output energy E _{0 of the} probe radiation is limited by the ratio

wherein D _ave - diameter photoreceiver lens, ψ - divergence angle probe emitter radiation, R - distance to a mirror reflector, E _min - minimum accepted photodetector radiation energy E _RC - maximum allowable level of illumination of the photodetector, and the variable threshold U (Z) in The backscatter interference action is set above the backscatter noise envelope for all possible dissipation factors. 2. The laser rangefinder according to claim 1, characterized in that the variable threshold is inversely proportional to the third power of the current range Z.

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