LFNM 2008, October 2 - 4, Alushta, Crimea, Ukraine

LASER DISTANCE METER MODEL

V.S.Tyurin, Y.P.Machehin

Kharkov National University of Radio Electronics 61166, Kharkov, Ukraine, Lenin Avenue, 14,

Phone: 8 (057) 702-14-84, e-mail: tvs_volodya@mail.ru

Abstract- Models of the basic units for Laser Distance Meter are submitted. These models are developed on the basis of an applied package SIMULINK of program system MATLAB. Keywords: laser distance meter, units model, optical signal.

INTRODUCTION The actual problem of a modern laser measuring devices is precision measurements of

distances up to each point of an object surface in conditions of change of light exposure and parameters fluctuations of the reflected signals [1]. Process of creation of such devices represents a difficult scientific and technical task and demands from developers of use of non-standard approaches and effective methods of research of received results.

The traditional approach to develop the Laser Distance Meter usually consists in creation of the prototype. After that the prototype passes detailed testing and is exposed to respective changes. This approach demands the big time and financial expenses. Effective alternative is imitating modeling with the help of applied software package SIMULINK. It provides fast construction and testing of virtual prototypes and gives access to any level of detailed elaboration of the project with the minimal efforts [2]. Use of SIMULINK-model for iterative correction of the project before construction of the prototype allows the developer to optimize quickly characteristics of the device and much more effectively to execute the project.

The actuality of researches is defined by necessity of optimization of parameters and structure for Laser Distance Meter by results of testing their imitating models.

The purpose of research consists in development of Units models for Laser Distance Meter which adequately describes process of formation of a measuring signal and allows revealing quickly and evidently a degree of influence of various factors on main parameters of devices.

CONSTRUCTION OF UNIT’S MODELS

Construction of the Laser Distance Meter Model is based on the mathematical expressions which developed in [3]. The model will consist of 6 blocks. The first block refers to “Ranging signal”. The structure of the block is submitted on Fig. 1.

Fig.1. Ranging Signal Block

This block can form the Gaussian signals or rectangular pulses. Except for that it sets

starting time and allow to supervise signals with the help of an oscilloscope. Next block refers to “Returned signal”. A task of the given block is attenuation of the

signal due to influence of an atmosphere and of the optical modules, of the reflected

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LFNM 2008, October 2 - 4, Alushta, Crimea, Ukraine

surface and range up to object, and also realization of delay for the period of pulse propagation up to object and back. The internal structure of the block is shown in figure 2.

Fig.2. Returned signal Block

This block realizes mathematical transformations of a signal which are caused by

various factors. Thus, the output signal represents a copy of the probing signal, but shifted for the period of a delay and attenuated by influence of an atmosphere. Besides the attenuating factor is used in the next block for an estimation of a dispersion of noise.

Block " Noise " calculates the common noise which will consist of shot noise for dark current of the detector, shot noise of the most useful signal, shot noise of background radiation and thermal noise of an electronic circuits. Backscattering of the laser radiation in model is not taken into account. The structure of the block is submitted on Fig. 3.

Fig.3. Noise Block

On an output of the block it is formed Gaussian noise with a total dispersion which is

determined by separate components of noise. Addition of a useful signal and noise is carried out on the adder after which the signal

comes on an input of the block “Received Channel”. The structure of the block is shown on Fig.4.

Fig.4. Received Channel Block

The given block carries out transformation of an optical signal to an electric signal, its

amplification, a filtration and signal detection at excess of noise level. After that the signal us pulse "Stop" comes in block Interval Meter. The structure of the

block is submitted on Fig. 5.

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LFNM 2008, October 2 - 4, Alushta, Crimea, Ukraine

Fig.5. Interval meter Block

The given block carries out calculation of the periods of a signal of the basic quartz

generator under the two-contour method. The task of the first contour will consist in rough measurement of a time interval on an integer of the basic generator periods. The second contour makes precision measurement of a time interval within the limits of one period of basic frequency. Calculation of pulses of basic frequency comes to an end after arrival of a pulse "Stop".

The information on number of pulses for basic frequency comes in block “Microcontroller”. The structure of the block is submitted on Fig. 6.

Fig.6. Microcontroller Block

This block carries out calculation of distance up to object on the basis of results for time

interval measurements. To eliminate the distance errors it is used corrected table. It is under construction on dependence of an estimation of range on the current value of distance. In the elementary case such dependence can be approximated by a direct line.

CONCLUSION Scientific novelty of researches consists in development of imitating model for the Laser

Distance Meter which adequately describes process of signal formation. The practical importance of researches will be that the model allows to optimize parameters and structure of blocks on the basis of the account of a degree of influence of various factors on results of distance measurements. Besides the given model can represent itself as a ready subsystem by development of multipurpose laser devices of various purpose with use of program system MATLAB.

REFERENCES 1. A. Kilpela, R. Pennala, J. Kostamovaara. Precise pulsed time-of-flight laser range finder for industrial distance measurements. Review of Scientific Instruments, Vol. 72, No. 4, 2001, pp. 2197-2202.2. SIMULINK. Dynamic System Simulation for MATLAB. Version 2.2. MathWorks Inc., 1998.3. M. Bukov, V. Tyurin, S. Tyurin. Modeling of process for signal formation in a pulse semi-conductor Laser Rangefinder. Radio electronics and Computer Science, Kharkov National Radio electronic University, No. 4, 2006, pp. 11-15.

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