At present, there are four main technologies that can be used for non-contact obstacle detection: laser ranging technology, infrared technology, ultrasonic technology and microwave technology, of which the application of laser scanning and multi-probe infrared photoelectric technology in AGV has matured , And the other two methods are still in the stage of engineering product verification.
1 Laser scanning detection
As shown in the above figure, laser detection is usually photoelectric modulation. The laser diode emits a modulated pulsed laser beam (Laser Beam) S. When the laser beam reflects back from an object, it is received by the laser detector For the same pulse signal E, the distance between the laser emission point and the measured object can be obtained by calculating the small time difference between the S signal and the E signal. Rotating on the laser transmitter can detect objects within a certain fan-shaped range, thereby realizing laser scanning obstacle detection.
The principle of this technology is simple, but it is not easy to realize. The precision of its optical devices, real-time calculation accuracy and control accuracy are very high.
The laser scanning obstacle detection product currently used in AGV is S3000 produced by German SICK company. Its advantages are: high precision and good anti-interference. The detection area can be set by programming and has certain self-determination. Learning function. The disadvantages are: due to the characteristics of the laser, no matter whether a cylindrical lens or a prismatic lens is used, the scanning range can only be on a horizontal fan-shaped plane, which is very limited in the vertical direction; when suddenly entering a dark environment from a bright environment , There is a short-term "day blindness" phenomenon; due to the use of high-precision devices and control devices, its price is very high; general users do not have the ability to program them, they can not adjust their detection range, and require professional and technical personnel on-site service, so Its maintenance costs will increase accordingly.
2 Multi-probe infrared photocell detection
This is the earliest method used in AGVs and is by far the most common method.
By modulating the infrared light with a wavelength of 0.76 ~ 1000um, receiving the reflected light, and estimating the distance of the detected object through the reflected light intensity, due to the wide wavelength range of infrared light, a certain wavelength of light is easily specified The absorption of the object, the attenuation of the reflected light intensity must be different, based on this principle, the detection distance is mostly an approximate value.
At present, there are many multi-probe infrared photoelectric tube detector products that can be used on AGVs. Among them, the P2 series products produced by SUNX of Japan are the most mature and have been recognized by most AGV manufacturers. The advantages of this product are: the infrared emission is cone-shaped scattering, the detection range is large; its structure is simple, the volume is small; the use and maintenance are simple and convenient, the user can adjust the detection distance by himself; there are many kinds of alternative products, and the price Lower. The disadvantage is that different objects absorb infrared light differently, which can lead to great differences in the detection distance; most of them are analog circuits, and the detection accuracy is not high.
3 Multi-probe ultrasonic detection
In life, we have seen the application of ultrasonic detectors-car reversing radar! But it is not so easy to use it for AGV. First, the detector on the AGV is always in working condition, which has requirements on the service life of the device; second, the detection range of the ultrasonic detector used on the AGV requires more Far; third, the ultrasonic detector used on the AGV must avoid the mutual interference of ultrasonic waves when multiple vehicles meet.
Although ultrasonic technology may be used for AGVs in the future, due to its own characteristic limitations, such as the audio frequency range of 20kHz to 100kHz, although the wavelength is short and the directivity is good, its modulation characteristics are poor and it is easily interfered by external noise , Especially in factory applications; like infrared technology, sound waves are also easily absorbed by a particular material, which affects the accuracy of ranging.
4 Microwave detection
This technology uses the Doppler effect of microwave (0.8 ~ 3GHz) to detect the measured object with the principle of radar. At present, there is no application example on AGV. With this technology, the detection area of the AGV can be increased, and the detector can be hidden and installed. However, the accuracy of its detection is related to the speed of object movement and the size of the object, so it is generally not suitable for sports equipment.
5 Notes on the selection of AGV obstacle detector
For the selection of detectors, under normal circumstances, we decide according to the user's order price, because the price difference between laser and infrared products is huge. If the user has special needs, or the user has some knowledge about this type of product, the user can specify it and pay the corresponding price.
6 Other instructions
The general use environment of AGV is unmanned work area. Although safety protection is very necessary, it only works in emergencies. Generally, no one should intentionally trigger the safety protection system. It is very unfavorable, it will greatly shorten its service life and affect the guidance and navigation accuracy!
