Principle of Laser Ranging

Principle and method of laser ranging

The laser ranging coarse divided into two kinds, the first principle is roughly half the product of the speed of light and round-trip time, is the distance between the rangefinder and the measured object, taking the laser rangefinder as an example; the second is a method based on the principle of laser displacement sensor.

There are roughly three methods of laser measurement, pulse method (laser Echo method), phase method and triangular reflection method. The accuracy of the pulse method for measuring distances is usually around +/-1 meters. In addition, the measuring blind area of this kind of distance meter is generally about about four meters. Triangulation is used to measure distances up to 2000mm (the industry calls displacement) with a precision of up to 1um. Phase laser ranging is generally used in precision ranging, the precision is generally millimeter-level. The principle of laser echo analysis is used for long distance measurement.

1 First class ranging

If light c spread in the air in the Span style= "font-family: ' Times New Roman ';" >a b The time required for a round trip between two points is t a , b distance between two points d Span style= "font-family: the song Body;" The following representations are available.

D=CT/2 type 1.1

In the formula:

D--measuring the distance between site AandB two points;

C-the speed at which light travels in the atmosphere;

T-the time it takes totravel round aandB at once.

It is known from the above that to measure aandB distances is actually to measure the time Tof light propagation,depending on the measuring time method, Laser rangefinder can be divided into two kinds of measurement form, pulse type and phase type.

2 Type II ranging

Laser displacement sensors can be used to achieve contactless long distance measurement with high directivity, high monochrome and high brightness. Laser displacement sensor (magnetostrictive displacement sensor) is a new type of measuring instrument made by using these advantages of laser, which makes the accuracy and reliability of displacement measurement greatly improved, and provides an effective measurement method for non-contact displacement measurement.

According to the principle of measurement, laser displacement sensor principle is divided into laser triangulation method and laser Echo analysis method, laser triangulation method is generally suitable for high-precision, short-distance measurement, and the principle of laser echo analysis is used for long-distance measurement.

3 Measurement Method One: phase-type Laser ranging

Phase Laser rangefinder is the frequency of radio waves, the amplitude modulation of the laser beam and determination of the modulation of the light-to-round measurement of the phase delay, and then according to the wavelength of the modulated light to convert the distance represented by this phase delay. Indirect method is used to determine the time required for the light to travel through the line.

If the modulated light angle frequency is Ω, the phase delay of a round trip to the measured distance D is φ, then the corresponding time T can be expressed as:

t=φ/Omega type 3.1

Substituting this relationship (1.1) distance D can be expressed as

D=1/2 ct=1/2 C• φ/ω=c/(4πf) (Nπ+δφ ) = c/4f (n+ ΔN) =u (n+) type 3.2

In the formula:

The total phase delay generated by the φ--signal to and from the measurement line.

ω--the angular frequency of the modulated signal, ω=2πf.

U--unit length, value equal to the band modulation wavelength

N--The number of modulated half-wavelengths contained in the measuring line.

The δφ--signal is produced at one time to produce phase delay less than the π part.

ΔN--The measured line contains a small part of the modulation wave less than half a wavelength.

Δn=φ/ω

In the given modulation and standard atmospheric conditions, the frequency c/(4πf) is a constant, at which time the measurement of the distance becomes the measurement of the number of half-wavelengths contained in the measuring line and the measurement of the smaller part of the half-wavelength . or φ, due to the development of modern precision machining technology and radio phase measurement technology, the measurement of φ has achieved high precision.

In order to measure the phase angle φ of π, can be measured by different methods, usually the most used is the delay phase measurement and digital phase detection, the current short-range laser range Finder using the digital phase detection principle to obtain φ.

As described in the general case of the phase laser rangefinder using a continuous transmission band modulated signal laser beam, in order to obtain a high accuracy of distance measurement also need to configure cooperation objectives, and the current handheld laser rangefinder is a pulse laser rangefinder is another new rangefinder, it is not only small size, light weight, but also the use of digital phase pulse broadening subdivision technology, Millimeter-level accuracy is achieved without the need for a co-operative goal, and the range is already over 100mandcan be displayed quickly and accurately. is a short-range precision precision engineering measurement, building area measurement of the most new length measurement standard equipment. The most widely used is the disto series handheld laser rangefinder produced by Leica Corporation .

4 Measurement Method Two: pulsed laser ranging

The Pulse laser ranging is simply for the laser flight time difference to ranging, it is the use of laser pulse duration is very short, energy in time relative concentration, instantaneous power is very large characteristics of ranging. When there is a cooperative goal, can reach a very long distance, in the near-distance measurement (thousands of meters) even if there is no cooperative goal, in the case of high accuracy requirements can also be measured. This method is mainly used for topographic surveying, tactical frontier ranging, missile track tracking, lidar ranging, and satellite, Earth-Moon distance measurement.

Figure 4.1 pulsed laser ranging schematic diagram

The principle of pulsed laser ranging is shown in 4.1 . A pulsed laser with a very short duration is emitted by the laser transmitting system, which is reflected by the target object after the distance L is measured, and the transmitting pulse laser signal is received by the photoelectric detector in the laser receiving system, and the time interval circuit calculates the time between the laser emission and the echo signal arrival. T, the target object is reached with the emitted distance L.

The accuracy depends on the rising edge of the laser pulse, the bandwidth of the receiving channel, the detector signal-to-noise ratio and the time interval accuracy.

5 Measurement method 3:3 Angle Method Laser Ranging

The measurement method of the

Laser displacement sensor is called laser triangulation, and the accuracy of the laser rangefinder is certain, and the same distance measuring instrument 10 M with 100 M precision is the same. And the laser triangulation measurement accuracy is related to the range, the larger the range, the lower the accuracy.

Another principle of laser ranging is the principle of laser triangulation: the Semiconductor laser 1 is focused by the lens 2 on the object being measured 6. The reflected light is collected by the lens 3 and projected onto the CCD array 4 ; signal processor 5 The distance from the object is obtained by calculating the position of the light point on the array 4 through trigonometric functions.

Figure 5.1 Laser Triangulation Method

Laser emitter through the lens to the visible red laser beam to the surface, the object reflected by the laser through the receiver lens, the internal CCD Linear camera accepted, according to different distances,CCD Linear camera can be at different angles See "This light point." Based on this angle, the distance between the laser and the camera is known, and the digital signal processor can calculate the distance between the sensor and the analyte.

At the same time, the position of the beam in the receiving element is processed by analog and digital circuit, and the corresponding output value is calculated by microprocessor analysis, and the standard data signal is output proportionally in the user-set analog window. If the switching output is used, it is in the set window and is outside the window. In addition, the analog and switching outputs can be set independently of the detection window.

Commonly used in rails, product thickness, flatness, size and so on.

6 Measurement method Four: Laser Echo method

The laser displacement sensor uses the principle of echo analysis to measure the distance to a certain degree of accuracy. The inside of the sensor is composed of the processor unit, the Echo processing unit, the laser emitter, the laser receiver and so on. The laser displacement sensor emits 1 million pulses per second from the laser emitter to the detector and returns to the receiver, which calculates the time required for the laser pulse to meet the detector and return the receiver, which is the average output of thousands of measurements.

Figure 6.1 laser Echo Method

The principle is similar to the pulsed laser ranging, also called pulse echo method, and is used for laser displacement sensor.

7 "Safe" and "unsafe"

At present, the market of hand-held laser rangefinder working substances are mainly the following: working wavelength of 905 1540 NM semiconductor lasers, Working wavelength is 1064 Nano yag laser. 1064 1064 1064 Nano Laser. At home, some manufacturers also have the production of 1064

For 905 nano-and 1540 -nanometer laser rangefinder, we call it "safe". For the 1064 Nano Laser rangefinder, because it is potentially harmful to the human body, so we call it "unsafe".

Reference Links:

Http://www.chinabaike.com/t/9675/2013/1104/1701968.html

Http://www.docin.com/p-620029816.html

Http://baike.baidu.com/link?url=i4xMw2_QYjk-dArerDA5x_a_AgxQz0V8hGyJAs5uTw3VHOenPEShY2ihDAJMYxcM0O3aVbwj3Yy7egoyLiwrl_

Principle of Laser Ranging