Bar Code Scan Head for Reading Etched Marks on Metallic Surfaces
Original Publication Date: 1986-Feb-01
Included in the Prior Art Database: 2005-Mar-08
A considerable improvement in signal-to-noise ratio can be achieved by using the system shown in the figure. A HeNe laser is used as the light source (alternative lasers or LEDs (light-emitting diodes) at other wavelengths could be used). A focusing lens is used to produce a focused spot size which is smaller than the bar width on the edge of the metal surface. Due to machined turning marks on the edge of the metal surface, light is diffracted along a line parallel to the axis of rotation of the metal surface. A cylindrical lens is then used to collect the diffracted light and image it onto the photodetector. A mask may be placed in front of the lens to restrict the collection solid angle to only that of the diffracted light from the turning marks.