Patent ID: 8109008

Claim:
A device for measuring the length of an object, the device comprising: a first member; a second member movable relative to the first member; a uniform marking row including uniform markers, each uniform marker having a first length; a non-uniform marking row divided into equal sections, each section including a unique marker and a unique spacing, a length of the unique marker and a length of the unique spacing of each section each uniquely identifying the section; a first sensor positioned to detect the uniform markers as the first member and the second member are relatively moved, the first sensor generating a first output indicative of whether a uniform marker is detected; a second sensor positioned to detect the uniform markers as the first member and the second member are relatively moved, the second sensor generating a second output indicative of whether a uniform marker is detected; an absolute sensor positioned to detect the unique markers and unique spacings as the first member and the second member are relatively moved, the absolute sensor generating an absolute output, the absolute output indicating transitions between the unique markers and unique spacings; and a controller coupled to the first sensor, the second sensor, and the absolute sensor, the controller determining a location of the movable member based the first output, the second output, and the absolute output to thereby determine the length of the object.