Patent ID: 7201321

Claim:
A reader for electro-optically reading a direct part marking (DPM) in a reflective surface of a workpiece part, the DPM having different elements that reflect light with minimal contrast, comprising: a) a solid-state imager for capturing the light in a reading mode over a field of view from the DPM elements located in a range of working distances relative to the reader; b) a first light projector for projecting a first light pattern in a ranging mode in the field of view throughout the range; c) a second light projector for projecting a second light pattern in a ranging mode in the field of view throughout the range in superimposition with the first light pattern, the light patterns having a predetermined visual relationship at a target plane within the range, the projectors being inoperative during the reading mode to prevent the DPM elements from reflecting the light from the patterns and saturating the imager, wherein the imager stores coordinates of the locations of the light patterns at multiple working distances throughout the range to self calibrate the reader; and d) a handheld housing for supporting the imager and the projectors, the housing being movable to a reading position in which the predetermined visual relationship is obtained to enable the imager to capture light from the DPM elements located in a vicinity of the target plane.