Importance

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Abstract

An apparatus and method are disclosed for determining the position and angular velocity of a print drum. The apparatus includes a detector that is positioned proximate to the drum, and a processor coupled to the detector. The drum has a cylindrical body with a plurality of alphanumeric characters and a sequence of marks, including an index mark and a plurality of timing marks uniformly disposed about the circumference of the body, the timing marks being in relative alignment with the characters such that each character is associated with a pair of timing marks. The index mark is used to designate a start or reference location on the body. The detector includes a magnetic field generating source such as a magnet, a magnetic lens for directing the field toward the marks, and a hall effect sensor for detecting (through changes in magnetic field caused by the marks when the drum is rotated) the index mark and respective pairs of the timing marks, and producing a digital signal representative of the detected marks. In response to the digital signal, the processor detects a pair of timing marks and determines the position on the drum of the character associated with the detected pair. The processor also determines the angular velocity of the drum based on frequency of detection of the timing marks.

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First Claim