Abstract: Various edge detection arrangements are disclosed, including an edge detection method and arrangement that utilizes outputs of commonly illuminated reference and edge sensors as the inputs for a comparator. The reference sensor is configured to have a wide field of view and the edge sensor is configured to have a narrow, high gain, field of view. Therefore, the reference sensor has a broad signal response to an edge passage and the edge sensor a steep and narrow signal response. When the two signals are biased to cross each other, the comparator output changes state, indicating passage of an edge. Because the reference sensor provides a base signal level directly related to the real time illumination level that the edge sensor also receives, the reference sensor provides a switch point along the transition ramp of the edge sensor that integrates a majority of the random error sources.

Abstract: A timing and control circuit for a wide spanning impact hammer used in a digital printer can be fabricated by using a phase lock loop oscillator driven by a character pulse clock to output a plurality of timing pulses during the character pulse width. Appropriate intervals are selected from the timing pulses to generate a plurality of shifted timing pulses to be used as inputs to logic circuitry. Combination of the shifted timing pulses and logic circuitry together with control commands from a printer controller, can be used to generate a hammer trigger and hammer reset pulse. The hammer trigger and reset pulses are used in a conventional hammer matrix to fire the multiple spanning hammers at the appropriate times.