| 摘要 |
The present invention is a method and apparatus which solves the problem of rapidly calibrating to a uniform value, the ion current (i) associated with each modulation electrode (50) of a print array (40) in an ionographic printing head (10). The calibration data may then be used during printing to produce high quality images of uniform density. The present invention employs a calibration array (30) positioned to sense the ion current (i) associated with each opposing modulation electrode (50) as a voltage (V(i)) across a calibration electrode (70) load resistance (R). When the instantaneous value of ion current (i) and the desired calibrated ion current (iF) differ when presented to a comparator, a feedback circuit (62) feeds back an error voltage (VINT) to a driver (100) coupled to the modulation electrode (50). The modulation voltage (Vm(i)) and the error voltage (VINT) are combined at the driver (100) input, producing a calibrated modulation voltage (Vm(i)') which adjusts the ion current (i) to the calibrated value. Calibrated modulation voltage (Vm(i)') is read and stored for later use during the printing, or used in real time depending on the time constants of the feedback circuit (62) and the speed of printing desired. Voltage (V(i)) indicative of calibrated ion current (iF) may also be read if desired.
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