Ink jet printer with droplet throw distance correction

An improved, continuous stream type ink jet printer of the type having a grounded, pressurized droplet generator with a plurality of nozzles in a linear array which emit streams of ink therefrom that are directed towards a moving recording medium, a charging electrode for each stream of ink located at the location where ink droplets are formed, whereat each droplet is encoded with a voltage representative of digitized information, a deflection electrode pair for each stream of droplets to direct the passing droplets to a specific location on the recording medium or to a gutter in accordance with the voltage the droplets received from the charging electrodes, a calibration sensor for calibrating the droplets so that they are properly stitched together at a predetermined printing plane, and a controller for operating the printer wherein the improvement comprises:

• a linear array of distance sensing sensors mounted in a support member that is located below the droplet trajectories, the distance sensing sensors being parallel to the surface of the recording medium and perpendicular to direction of movement thereof, each distance sensor being adapted to produce a signal representative of the actual droplet throw distance from one or more nozzles to the surface of the recording medium at predetermined time periods;
• means for comparing the signal representative of the actual droplet throw distance with a signal representative of a predetermined droplet throw distance;
• means for generating a comparison signal in response to the comparison of the actual and predetermined throw distance signals, said comparison signal indicating any increase or decrease in the actual throw distance relative to the predetermined throw distance;
• and
• means for adjusting the droplet trajectories in response to said comparison signals to correct the droplet trajectories for variations in the droplet throw distance relative to the predetermined printing plane and maintain the droplet placement accuracies in spite of said throw distance variations.