Olympus OEP-3, Service Manual

Page: 145 / 176

4-37
OEP-3 V1 (UC)
4-3-5. Head Control Block
The head control block corrects the parallel print data per line from the VPR-63 board and transfers it to
the thermal head for printing.
The head control block consists of the following five blocks.
.
γ
RAM that
γ
-corrects the parallel print data from VPR-63 board
.
Image processing circuit (picture quality control IC) that performs pattern recognition interpolation,
edge emphasis, and thermal storage correction
.
Head drive circuit that PWM-converts parallel data and transfers print data to the thermal head
.
Line number correction circuit (voltage drop control IC) that corrects the voltage drop due to the
common resistor of a thermal head
.
Head voltage correction circuit
.
PLD for color balance adjustment
Print data is received from the VPR-63 board as parallel data,
γ
-corrected, and processed by a PQC
circuit. After that, the print data is PWM-modulated using a head drive circuit and transferred to the
thermal head.
1. Blocks
γ
correction circuit
The print data sent from the VPR-63 board is
γ
-corrected using the data conversion table of
γ
RAM
(IC209). Before printing, the
γ
data of each YMC (L) color corresponding to the temperature correction,
media type, and paper feeding is written in the address of
γ
RAM.
PQC IC
.
Edge emphasis
Performs the edge emphasis that improves the sharpness of an image using a digital filter in the
horizontal and vertical directions.
.
Thermal storage correction
Corrects the dullness and unstableness of rising due to the defective thermal response of a head using a
digital filter.
Head drive circuit
.
PWM modulation
PWM-modulates eight-bit parallel data and converts it into serial print data.
.
Divided print processing
Divides one gradation into four for printing so that the clearance between print lines does not stand out
when the print dot area of a low-density image portion becomes smaller.
Line number correction circuit
The combined resistance of an element decreases when the number of heating resistor elements that
carries a current to the thermal head increases. In this case, the voltage drop due to the common
resistance of a harness cannot be ignored and the print density decreases. Therefore, this circuit controls
the current-carrying time of a head element and corrects the print density.