Laser scanning based bar code symbol reading system for producing a 3-D scanning volume substantially free of spatially and temporally coincident laser scanning planes
A holographic laser scanner of ultra-compact design capable of reading bar and other types of graphical indicia within a large scanning volume using holographic optical elements and visible laser diodes. The holographic optical elements are arranged on the scanning disc in such a manner so that none of the laser scanning planes generated within the 3-D scanning volume of the system are spatially and temporally coincident with any other laser scanning plane within the 3-D scanning volume. This novel feature of the present invention ensures that there is substantially zero cross-talk at the plurality of photodetectors provided within the system, significantly improving the performance of the system.
1. A laser scanning based bar code symbol reading system for producing a 3-D scanning volume substantially free of spatially and temporally coincident laser scanning planes, said laser scanning based bar code symbol reading system comprising:
a housing;
a plurality of laser sources disposed within said housing, for producing a plurality of laser beams;
a plurality of photodetectors disposed within said housing, wherein each said photodetector is assigned to only one of said plurality of laser sources for detecting laser light produced by said laser source; and
a laser beam scanning mechanism disposed within said housing, for scanning said plurality of laser beams and producing a plurality of laser scanning planes within a 3-D scanning volume, for scanning a code symbol on a object as the object is moved through said 3D scanning volume;
wherein substantially none of said laser scanning planes within said 3-D scanning volume are spatially and temporally coincident with any other laser scanning plane in order to ensure that laser light produced by each said laser source is only detected by its assigned photodetector to ensure that substantially zero cross-talk is generated at said plurality of photodetectors.
2. The laser scanning based bar code reading system of claim 1 , wherein each said laser scanning plane has predefined beam characteristics; and
said plurality of laser scanning planes intersect within said 3-D scanning volume and said predefined beam characteristics of said scanning planes cooperate within said 3-D scanning volume so as to produce an omnidirectional laser scanning pattern within said 3-D scanning volume for omnidirectional scanning of bar code symbols therewithin.
3. The laser scanning based bar code reading system of claim 2 , wherein said 3-D scanning volume has at least three focal zones, a depth of field of at least 10 inches.
4. The laser scanning based bar code reading system of claim 2 , wherein said 3-D scanning volume is in the shape of a 3-D polygonal shaped object.
5. The laser scanning based bar code reading system of claim 4 , wherein said 3-D polygonal shaped object has at least four substantially rectangular shaped side surfaces.
6. The laser scanning based bar code reading system of claim 1 , wherein each said laser source comprises a laser diode for producing a visible laser beam.
7. The laser scanning based bar code reading system of claim 1 , wherein said laser beam scanning mechanism comprises a holographic scanning disc, disposed in said housing, supporting a plurality of holographic optical elements, for scanning said plurality of laser beams as said holographic scanning disc rotates about an axis of rotation.
8. The laser scanning based bar code reading system of claim 7 , wherein said laser diodes are symmetrically arranged about said holographic scanning disc.
9. The laser scanning based bar code reading system of claim 7 , wherein said plurality of laser sources comprises at least three laser diodes, and wherein said plurality of holographic optical elements comprises at least sixteen volume transmission holograms, and said plurality of laser scanning planes comprises at least forty-eight laser scanning planes, none of which are spatially and temporally coincident with any other laser scanning plane.
10. The laser scanning based bar code reading system of claim 1 , wherein each said holographic optical element is a volume hologram.
11. The laser scanning based bar code reading system of claim 10 , wherein each said volume hologram is a transmission-type volume hologram.