Oki IP-6620 Maintenance Manual page 536

(2) Head drive voltage control
- Setting of the head drive voltage rank
The drive voltage for the print heads is set for each color to maintain the specified density
and for stability of ink discharge. Since the drive voltage varies depending on manufacturing
conditions of the head (lot, material properties, processing), the voltage is labeled on each
head during production and stored in the non-volatile memory of the head. The voltage rank
is set automatically when the head is installed to the printer.
- Temperature control
Ink viscosity increases as the temperature becomes lower, and decreases as the
temperature becomes higher. The energy for ink discharge must be increased when
viscosity increases, and conversely, the energy can be smaller as the viscosity decreases.
To control this discharge energy, the voltage is changed. The control method is digital control.
The temperature of the PZT element in the head is detected by the thermistor, and the head
is operated with the specified drive voltage for the detected temperature with control of the
engine controller firmware. The parameters for this temperature control have been provided
in a table, and values in the table are corrected for each head voltage rank.
(3) Head position adjustment
A function in the control firmware to adjust the dot spotting position in the main scanning
direction.
It corrects the shift in the dot spotting positions between the six or seven heads caused by
fluctuation in head installation positions and ink discharge speed.
Correction is executed by using the dot spotting position for color K head as the reference and
delaying (or advancing) the ink discharge timing for heads of other colors.
(4) Bidirectional adjustment
A function in the control firmware to correct the dot spotting position in the main scanning
direction. In bidirectional printing, the dot spotting position is matched for the forward and
backward directions for each head. Adjustment is performed by using the dot spotting position of
the forward direction as reference and delaying (or advancing) the ink discharge timing for the
backward direction.
(5) Nozzle position adjustment
A function in the control firmware to correct the dot spotting position in the subscanning direction.
It corrects the shift in dot spotting positions between the six or seven heads caused by fluctuation
in the head installation positions and the head sizes. Correction is performed by changing the
nozzles to be used for printing.
OKI Data Infotech Corporation CONFIDENTIAL
Chapter 8 Operation Mechanism
8-15