| 摘要 |
Improved differential optical sensors are mounted at every intersection of the deflection planes of the ink droplets issued by a multi-nozzle printhead of a pagewidth ink jet printer. These sensors are located near the printing plane and gutters of the printer. They comprise first and second input apertures, each being coupled to a light source and fixedly located to direct beams of light to a confronting associated pair of output apertures. The input and output apertures are on opposite sides of the droplet deflection plane, and the input apertures are on opposite sides of a perpendicular line extending from the midpoint between the pair of output apertures. The light beams impinge the pair of output apertures thereby creating differentially detected zero-crossing optical axes at predetermined angles with respect to the perpendicular line therefrom. The output apertures are coupled to differential circuitry via photodetectors, so that horizontal droplet position may be determined relative to droplet charge voltage and vertical droplet position may be measured in absolute value above the output apertures.
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