Knowledge of laser scanning bar code is read implement because its are area of particular big depth of field, tall,the outstanding advantage such as scanning speed, wide sweep range got be used extensively. Additional, knowledge of scanning of laser whole point of view is read implement as a result of can the bar code sign that knowledge of high speed scanning reads aleatoric direction to pass, be used in great quantities in all sorts of automation degree tall, content sheds generous domain. Knowledge of laser scanning bar code is read implement receive by laser source, optical scanning, optics, enlarge of photoelectricity changeover, signal, plastics, quantify and the partial composition such as coding. Below bat around these component.
(one) laser source
Use MOVPE (metallic oxide gas phase is denotative) the laser of visible light semiconductor that the technology makes has low power comsumption, but direct modulation, bulk small, weight light, solidification, dependability tall, efficiency is advanced advantage. It appeared to replace the He that uses so quickly namely - Ne laser. The beam of light that semiconductor laser gives out is the elliptical beam of light that is not axial symmetry. Piece shoot beam of light perpendicular at P - the 30 ° of ≈ of ⊥ of V of horn of disperse the internal heat with sudorifics of direction of W knot extent, parallel the 10 ° of ≈ of ‖ of V of horn of disperse the internal heat with sudorifics at knot extent direction. If use technology of conventional collimation of beam of light, direction of the length of the elliptical facula of both sides of dot of assemble of beam of light, short axis will produce exchange. Apparent this will make the scanner has small scanning depth of field only. Jay M.Eastman put forward to use the technology of collimation of beam of light that the graph shows 3 times, overcame phenomenon of this kind of exchange, increased scope of scanning depth of field greatly. This kind of elliptical beam of light can apply on single-track laser scanner only. When arranging smooth route, the elliptical way length an axis that should allow facula and radial scanning direction are perpendicular. Read to single-track scanning knowledge implement, because this kind of elliptical facula is right presswork of noise not sensitivity, will compare below says circular facula character is better. To bar code of whole point of view scanning knowledge is read implement, when because beam of light is in,scanning knowledge reads bar code, had swept bar code with bigger banking angle sometimes. Accordingly, facula of beam of light is unfavorable make it is elliptic. Become its plastics the circle normally. At present commonly used plastic plan is diaphragm of one roundlet aperture is added before collimation lens. Character comes the diffraction of phenanthrene Nie ear that character of this kind of beam of light can use alveolus well approximate. Adopt this kind of plan, to bar code of standard measure UPC, depth of field can be accomplished about 250mm arrives 300mm. This is already enough to system of general business POS. But the circumstance of big to carrying the requirement such as the line like airport baggage depth of field, appear insufficient. At present commonly used plan is to increase the dimension of bar code symbol or the assemble of different scanning light that make constitute scanning pattern to be formed at different area " much more scorched area " . But more charming plan is to use special optical collimation cell, the smooth field that makes pass it has the part of diverge of beam of light that distributings specially to have minimum thereby, get bigger depth of field.
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