laser sensor

Lasers can be divided into four types according to the working substance. 1 Solid-state laser: Its working substance is solid. Commonly used are ruby ​​lasers, ytterbium-doped yttrium aluminum garnet lasers (ie, YAG lasers), and neodymium glass lasers. Their structure is roughly the same, characterized by small and sturdy, high power, and the neodymium glass laser is the device with the highest pulse output power, which has reached tens of megawatts. 2 gas laser: its working substance is gas. Various gas atoms, ions, metal vapors, and gas molecular lasers are available. Commonly used are carbon dioxide lasers, helium neon lasers and carbon monoxide lasers, which are shaped like ordinary discharge tubes and are characterized by stable output, good monochromaticity and long life, but low power and low conversion efficiency. 3 liquid laser: It can be divided into chelate laser, inorganic liquid laser and organic dye laser. The most important one is organic dye laser. Its biggest feature is that the wavelength is continuously adjustable. 4 semiconductor laser: It is a younger type of laser, of which the more mature is a gallium arsenide laser. It is characterized by high efficiency, small size, light weight and simple structure. It is suitable for carrying on airplanes, warships, tanks and infantry. It can be made into a range finder and a sight. However, the output power is small, the orientation is poor, and the ambient temperature is greatly affected. [1]

532nm green solid laser - (Model: mw|408x306 [2]

When the laser sensor is working,

Laser PM2.5 Sensor - TF-LP01

A laser emitting diode is first directed at the target to emit a laser pulse. The laser scatters in all directions after being reflected by the target. Part of the scattered light is returned to the sensor receiver, which is received by the optical system and imaged onto the avalanche photodiode. An avalanche photodiode is an optical sensor with an internal amplification function, so it can detect extremely weak optical signals and convert them into corresponding electrical signals. Common is the laser ranging sensor, which measures the target distance by recording and processing the time elapsed from the time the light pulse is emitted until the return is received. The laser sensor must measure the transmission time extremely accurately because the speed of light is too fast.

For example, the speed of light is about 3*10^8m/s. To achieve a resolution of 1mm, the electronic circuit of the transmission time-distance sensor must be able to distinguish the following extremely short time:

0.001m/(3*10^8m/s)=3ps

To distinguish the time of 3 ps, this is an excessive demand for electronic technology, and the implementation cost is too high. But today's laser ranging sensors cleverly avoid this obstacle, using a simple statistical principle, that is, the average law achieves a resolution of 1mm, and can guarantee the response speed. [1]

Non-contact long-distance measurement can be achieved by using the high directivity, high monochromaticity and high brightness of the laser. Laser sensors are often used for measuring physical quantities such as length, distance, vibration, speed, and azimuth. They can also be used for flaw detection and monitoring of atmospheric pollutants. [3]

Precision measuring length is one of the key technologies in the precision machinery manufacturing industry and optical processing industry.

Modern length measurement is mostly carried out by using the interference phenomenon of light waves, and the accuracy mainly depends on the monochromaticity of light. The laser is the ideal light source, which is 100,000 times purer than the best single-color light source (氪-86 lamp). Therefore, the laser length measuring range is large and the precision is high. It is known from the optical principle that the relationship between the maximum measurable length L of the monochromatic light and the wavelength λ and the line width δ is L = λ / δ. With a 氪-86 lamp, the maximum length can be measured to be 38.5 cm. For longer objects, segmentation measurement is required to reduce the accuracy. If a helium gas laser is used, it can measure up to several tens of kilometers. It is generally measured within a few meters and has an accuracy of 0.1 micron.

Its principle is the same as that of radio radar. After the laser is aimed at the target, it is measured by its round-trip time, and then multiplied by the speed of light to get the round-trip distance. by

Radar sensor ranging

The laser has the advantages of high directivity, high monochromaticity and high power. These are critical for measuring the distance, determining the target orientation, improving the signal-to-noise ratio of the receiving system, and ensuring the measurement accuracy. Therefore, the laser range finder More and more attention is being paid. The laser radar developed on the basis of laser range finder can not only measure distance, but also measure target azimuth, transport speed and acceleration. It has been successfully used for satellite ranging and tracking, such as laser using ruby ​​laser. Radar, the range of ranging is 500-2000 km, and the error is only a few meters. Not long ago, the LDM series of distance measuring sensors developed by the R&D center can reach the micrometer level within the measurement range of several kilometers. Ruby lasers, neodymium glass lasers, carbon dioxide lasers, and gallium arsenide lasers are often used as light sources for laser range finder.

It measures the vibration velocity of an object based on the Doppler principle. The Doppler principle means:

If the wave source or the observer of the received wave moves relative to the medium of the propagating wave, then the frequency measured by the observer depends not only on the frequency of the vibration emitted by the source but also on the magnitude and direction of the velocity of the wave source or observer. The difference between the measured frequency and the frequency of the wave source is called the Doppler shift. When the vibration direction is consistent with the direction, the frequency is fd=v/λ, where v is the vibration speed and λ is the wavelength. In the laser Doppler vibration velocity measuring instrument, fd = 2v / λ due to the round trip of light. The vibrometer converts the vibration of the object into a corresponding Doppler shift by the optical part during measurement, and the frequency shift is converted into an electrical signal by the photodetector, and then processed by the circuit part and sent to the appropriate The Puller signal processor converts the Doppler shift signal into an electrical signal corresponding to the vibration speed and finally records it on the magnetic tape. This vibrometer uses a HeNe laser with a wavelength of 6328 angstroms (┱), optical frequency modulation with an acousto-optic modulator, and a quartz crystal oscillator plus a power amplifier circuit as a driving source for the acousto-optic modulator, using a photomultiplier tube. Photoelectric detection is performed, and the frequency tracker is used to process the Doppler signal. The utility model has the advantages of convenient use, no need of a fixed reference frame, no influence on the vibration of the object itself, wide measurement frequency range, high precision and large dynamic range. The disadvantage is that the measurement process is greatly affected by other stray light.

It is also a laser speed measurement method based on the principle of Quitople. The laser Doppler flow meter (see laser flow meter) can be used to measure wind tunnel air velocity, rocket fuel flow velocity, aircraft jet flow velocity, Atmospheric wind speed and particle size and convergence rate in chemical reactions. [4]

Over-limit detection of vehicle width and height

The laser sensor is used for rapid measurement. The network core and sensor of the PC industrial computer and the visual programming software VB are used for real-time data transmission and processing. At the same time, the interface-friendly PC control software is designed. The field test data shows that the system has good real-time performance and high measurement accuracy, and has certain practical value.

Highway toll stations

Used for highway toll stations for vehicle counting and security protection. Teras Malaysia has applied hundreds of BEA laser sensors to its manual and automatic toll station systems. The laser sensor uses the time-of-flight (TOF) measurement principle to form four planes in the detection area to detect the vehicle. At the same time, the product also has functions such as anti-tailing and vehicle safety protection. Compared with traditional light curtains, laser sensors have the advantages of high sensitivity, high precision, convenient installation, high cost performance and strong stability. [5]

Google's second generation of unmanned vehicles: equipped with laser sensors

Google second generation driverless car prototype in addition to

The top laser sensor is still quite noticeable, and the other sensors are very concealed.

Significant Google Unmanned Vehicles logos are placed on the front and rear of the vehicle. The control principle of Google's unmanned vehicles is to continuously collect various accurate data of the vehicle itself and the surrounding area through the sensors installed around the car. The analysis and calculation are carried out by the processor inside the vehicle, and then the car is controlled according to the calculation result. . Unmanned vehicles use GPS equipment and sensors to accurately locate the vehicle and travel speed to determine pedestrians, vehicles, bicycles, lights and many other objects.

On the roof of this Lexus, a 360° rotating laser holographic sensor can sense the front, side and rear of the car almost simultaneously. The data collected by the sensor is input to the processor located on the right rear side of the vehicle through the green data line. This laser sensor also allows unmanned vehicles to be accurately positioned globally. The L-type Lexus logo in front of the car was also removed, replaced by a radar sensor; used to measure the distance in front and the speed of the vehicle to determine the front of the vehicle and control the vehicle's safety acceleration and deceleration.

The tire hub also has a position sensor for detecting wheel rotation and helping the vehicle to position. The heart of Google's unmanned vehicles - the processor is located on the right rear side of the vehicle. Data from each sensor is transmitted to the data line through the data and analyzed and processed by software to accurately sense and judge the difference between the unmanned vehicles. object. In addition to analyzing and judging the current position of the objects around the unmanned vehicle, the unmanned vehicle needs to be calculated by software to accurately predict the possible next position of each object. Finally, the unmanned vehicle will make safe driving decisions based on all collected data, including controlling the speed of the car and the surrounding distance. [6]

In 2008, the global sensor market capacity was 50.6 billion US dollars. Eastern Europe, Asia Pacific and Canada became the fastest growing regions in the sensor market, while the United States, Germany and Japan were still the regions with the largest sensor market. Real world companies and other high-end sensor manufacturers have begun to enter the Chinese mainland, and set up a technology development department. As far as the world is concerned, the fastest growing market in the sensor market is still the automotive market, and the second is the process control market, optimistic about the prospects of the communications market.

Some sensor markets such as pressure sensors, temperature sensors, flow sensors, and level sensors have been characterized by mature markets. Flow sensors, pressure sensors, and temperature sensors have the largest market size, accounting for 21%, 19%, and 14% of the total sensor market, respectively. The main growth in the sensor market comes from emerging sensors such as wireless sensors, MEMS (Micro-Electro-Mechanical Systems) sensors, and biosensors. Among them, the annual growth rate of wireless sensors in 2007-2010 is expected to exceed 25%.

The global sensor market is showing a rapid growth trend in the midst of ever-changing innovations. Experts pointed out that the main technologies in the field of sensors will be extended and improved on the existing basis, and countries will compete to accelerate the development and industrialization of next-generation sensors, and the competition will become increasingly fierce. In the field of high-end technology sensors, there are still international sensor giants that have already entered the domestic market and set up technology research and development departments directly in China. The development of new technologies will redefine the future sensor market, such as the emergence of new sensors such as wireless sensors, fiber sensors, smart sensors and metal oxide sensors, and the expansion of market share. [4]