SU1816967A1 - Method of distance measurement - Google Patents

Description

The invention relates to methods and means for measuring distances in special engineering and geodetic works and can be used to create high-precision distance meters in communication systems, optical location, Doppler speed meters, in Optoelectronic instrumentation, to build high-precision light-range meters for geodetic and special purposes.

The aim of the invention is to improve the accuracy of measurement.

This goal is achieved by the fact that by changing the power mode of the modulator of the light demodulator within the limits of -dr] 0.35 ... 0.65 (informational characteristics are obtained, maximum steepness points (special points) are detected, when the optimal power mode and fixed special points are selected demodulation characteristic, which determines the position of the modulator-demodulator of light corresponding to the minimum of the electric signal and the measured distance.

Consider the demodulation characteristic (DMX) of the process of modulation-demodulation of the Light flux in an electro-optical modulator-demodulator of light, bearing in mind that useful information is contained in the phase of the subcarrier.

The relative intensity of the light flux at the input of a photodetector (DMX) of the phase light range finder shown in Fig. 1 is

1816967 A1

Ι / Ι ₀ = | (ί-Ιο (2λ ^ cos ^) J (1) where -d ^ is the power mode of the light modulator-demodulator on the electro-optical element, which is understood as the normalized value of the modulating oscillation, i.e., its ratio amplitudes to half-wave voltage;

D is the measured distance;

Yam is the wavelength of the modulating oscillation;

! - Bessel function of the first kind of zero order.

Analyzing the overall course of the curves in FIG. 2, it can be noted that despite some differences between the maximum values of l / io, the differences in the region of the minimum characteristics are significant.

In any mode 1) ohm / ip, the repetition rate of the minima of the demodulated light flux at the output of the demodulator is equal to the modulation frequency (Um is preserved when I / Un changes. Moreover, the main requirement for choosing the Uom / ΙΙπ mode is reduced to the condition under which the initial operating point of the system The modulator-demodulator is stable and maintains its position on the modulation characteristic.

When photoelectric registration of the signal received at the output of the demodulator, a change in the intensity at the output of the analyzer causes corresponding changes in the photocurrent at the output of the FPU.

When working on a linear section of the amplitude characteristic of the FPU, the function la = f (D), up to a constant coefficient, will coincide with the DMX. In the prototype of the method, the indication is carried out at the extreme (zero) points of the DMX. In this case, the accuracy of the zero point function is limited by the interference caused by the intrinsic noise of the FPU. In the proposed method, the indication is carried out at the DMX points with the greatest steepness, and the fixation is performed at the points of the curve l _a = f (D) calculated at the sensitivity threshold level of the FPU.

Similar points are defined as singular.

The steepness of the change in the signal at the output of the FPU (determining the sensitivity of the light range finder, i.e., the range of values that determine the accuracy of fixation of the phase cycle dommer) is proportional to the steepness of the change in DMX. Therefore, the estimate of the steepness of the DMX at the minimum (threshold) values of the relative intensity 1/1 ₀ at the output of the system is equivalent to the estimate of the steepness at the singular ”point of the curve la = f (D). Obviously, the singular point has a coordinate depending on the power mode of the light modulator-demodulator and the intensity of the receiving light.

Thus, the maximum steepness of the DMX Smax for this mode is -jjj ^), determined at the special ”point Ln, can serve as a parameter characterizing the accuracy of the indication of the magnitude of the demodulated light flux.

Determined steepness DM3 for the circuit shown in figure 1, focusing on the relation (1) ¹⁵ ~ 'dD ^{/ d = 1} -m ^s ~

(2)

Fig. 3 shows the dependence of the slope S DMX on the power mode of the modulator-demodulator in the region of the point Ln, calculated according to formula (2) for the case f / lo = const, Uom = 0. As follows from the curve of Fig. 3 in the range of values and _О m / ip = = 0.3-0.65, the dependence of the slope S on the amplitude of the alternating voltage is linear.

So, to improve the accuracy of measuring distances, the recommended power mode of the modulator-demodulator of light should be selected in the interval and _About m / ip ₃₅ 0.35 - 0.65.

The implementation of the method of measuring distances is carried out by a light range finder, the functional block diagram of which is shown in FIG. The light-range finder contains 40 laser oscillators 1, the light of which through the block of the modulator-demodulator 2 is directed to the measured path. Reflected from the mirror reflector 3, the light flux is again received at the modulator-de45 modulator unit and sent to a photodetector (FPU) 4, which includes a light analyzer (not shown in the figure). The electric signal from the FPU 4 is amplified by the amplifier 5 and fed to the 5Q analog-to-digital converter 6. Information from the output of the analog-to-digital converter 6 is fed to the input of the microprocessor 7. The output of the high-frequency generator 8 is connected to block 3 for 55 modulation of the demodulation of the light beam. The block of the modulator-demodulator 2 is moved by a step motor 9. The outputs of the microprocessor 7 are connected to an indicator 10, a high frequency generator 8, and a step motor 9 to control them.

The light range finder works as follows. Modulating oscillations from the high-frequency generator 8 are fed to the modulator-demodulator 2 unit. The beam of the laser generator 1, passing through the modulating element of unit 2, is modulated and sent along the measured path to the reflector 3 and, returning, again enters block 2, where it is demodulated after transformation in the light analyzer, e amplitude-modulated is received at the FPU 4. The electric signal from the FPU is amplified by an amplifier 5.

Before the start of the distance measurement process, we carry out the alignment of the measuring path of the light range finder, in particular, we determine the power mode Uon / Un of the light modulator-demodulator corresponding to the maximum steepness of the DMX. To this end, the stepper motor 9 moves the block of the modulator-demodulator 2 from one extreme position to another. After each step of the stepper motor 9, the output voltage of the amplifier 5 is measured and converted into a digital code by an analog-to-digital converter 6. Information from the output of the analog-to-digital converter is recorded in the memory of the microprocessor 7.

As a result, discrete values are accumulated in the microprocessor memory (Si,

S ₂ .... Sn) of the family of curves of the average integral luminous flux. Next, the microprocessor 7, according to a given program, analyzes the incoming information, calculates the position of the singular points by the optimal power mode of the light demodulator modulator and the corresponding position of the demodulator-modulator 2. The completion of the operation means the readiness of the LED range finder to conduct distance measurement.

The distance measurement cycle includes taking one curve of the average integral luminous flux for the selected Tsom / Un power mode, calculating the position of the modulator-demodulator 2 with a minimum of an electric signal based on processing the measured values of the entire curve of the average integral luminous flux, displaying information about the measured distance on the digital indicator board 10 The operation of the nodes, namely the high-frequency generator 8, the stepper motor 9, the analog-to-digital converter 6 and the indicator 10 is controlled by a microprocessor p 7 for a given measurement program, which can be changed depending on the specific measurement task.

Claims (1)

Claim A method for measuring the distance with a light-range finder, including changing the optical path of the light flux by moving the light modulator-demodulator unit until a minimum electrical signal is obtained, sequentially fixing the light modulator-demodulator unit with measuring the positions of the fixation points and processing the measurement results, characterized in that, in order to increase accuracy , before moving the light modulator-demodulator unit set mode power Uom / Uii modulator-demodulator light within 0.35 - 0.65, and wherein m - amplitude of the modulating oscillation, Un - half-wave voltage, and fixed power mode corresponding to the maximum slope change Uom / Uh ratio. FIG. 1 FIG. I