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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.
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