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Abstract

An optical scanning system operates asynchronously by electro-optically detecting movement of a scanning unit directly from the data being scanned. A first embodiment of the system includes two sets of optical sensors in a handheld unit. One set extends transversely of a scanning direction for detecting the optical pattern, and a second set is approximately aligned with the scanning direction for detecting relative movement between the pattern and the scanning unit. Relative movement is detected by detecting a pattern in a first subset of the second set of sensors and then sensing a shift of the detected pattern to a second subset of the second set of sensors. In response to detecting a unit movement, the optical states of the first set of sensor elements are polled to record a portion of the pattern along the line. This response is preferably triggered indirectly by calculating an average time interval between relative movements and periodically polling the first set of sensors at a rate set by this average interval. Upon detecting a uniform optical state of the second set of sensors, such as when scanning across a blank region in the pattern, sensing of the optical state of the first sensors continues at periodic intervals so long as the uniform state continues to be detected. The optical information is thus obtained in a succession of steps, and is assembled by the host computer. A second embodiment of the system differs from the first embodiment in that the former uses a rectangular array of imaging elements arranged in rows and columns and calculates an estimate of the instantaneous rate of relative movement. Each of the rows of imaging elements is aligned generally parallel to the scanning direction and changes optical states in a manner analogous to that of the line of second imaging elements described above. The second embodiment promotes increased accuracy during collection of optical information for situations in which the scanning direction is misaligned from the optical information and the scanning velocity is nonuniform.

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