Patent ID: 6092727
Filing Date: 2000-07-25
Classification: G06K

Abstract:
A data reading device for reading digital data encoded in a surface of a generally planar data-carrying stratum of a data carrier, where said digital data is encoded in said surface as either positive-going or negative-going surface irregularities in said surface, with respect to a predetermined datum plane, said data reading device comprising:a single wavelength laser diode, having a light output at a single frequency;a direct current power supply having a regulated voltage output for said single wavelength laser diode;a precision shunt connected in series with said single wavelength laser diode, across the output of said power supply;an operational amplifier having said precision shunt connected across an input thereto, and having an output connected to a data decoding circuit;a focusing objective lens having a short focal length;a support for a data carrier to be placed thereon, whereby the surface of said data carrier will be in a prescribed plane; anda pinhole diaphragm having a pinhole therein, interposed between said single wavelength laser diode and said focusing objective lens;wherein the pinhole, the center of said single wavelength laser diode, and the center of said focusing objective lens, are all substantially in linear alignment one with another;wherein said pinhole diaphragm is spaced linearly away from said prescribed plane at a distance substantially equal to twice the focal length of said focusing objective lens;wherein said pinhole, when illuminated by said single wavelength laser diode, will act substantially as a point source of light, with respect to said focusing objective lens, and will permit light reflected from said data carrier surface back through said focusing objective lens to be re-transmitted back to and impinge upon said single wavelength laser diode;wherein said single wavelength laser diode is such that reflected light at said single wavelength which impinges thereon will cause interference at a pn junction within said single wavelength laser diode and will thereby cause an anomaly in the current flowing through said single wavelength laser diode and through said series connected precision shunt, and variations in said reflected light will likewise cause varying anomalies in said current;wherein the mounting arrangement of said laser, pinhole diaphragm, focusing objective lens, and data carrier support is such that when there is relative motion of said data carrier on said support with respect to said focusing objective lens, light from said lens is focused on said surface and impinges thereon, and reflections and changes in said reflections due to said irregularities in said surface are at least partially re-transmitted back through said focusing objective lens and through said pinhole, so as to impinge on said single wavelength laser diode;whereby anomalies in the current flowing through said single wavelength laser diode and said series connected precision shunt are caused by said changes in said reflections due to said data carrier surface irregularities, and occur in real time;wherein said anomalies are manifested by variations in voltage across said precision shunt, which are detected by said operational amplifier, and result in a signal which is fed from said operational amplifier to said decoding circuits, said signal thereby being a direct function of said data carrier surface irregularities, in real time; andwhereby decoding of said signal by said decoding circuits results in an output therefrom of said digital data.