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Adaptable Power Control With Independent Full Power And Gray Scale Adjustability

IP.com Disclosure Number: IPCOM000099346D
Original Publication Date: 1990-Jan-01
Included in the Prior Art Database: 2005-Mar-14
Document File: 3 page(s) / 136K

Publishing Venue

IBM

Related People

Gibson, BD: AUTHOR [+2]

Abstract

Described is a programmable laser power control system for use in electrophotographic laser printers. This implementation supports control of the laser bias and full scale power levels and separate control of the intermediate power levels. This interface is applicable in discharge and charge area development (DAD, CAD) electrophotographic processes and is intended to support the gray scale requirements of the different processes.

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Adaptable Power Control With Independent Full Power And Gray Scale Adjustability

       Described is a programmable laser power control system for
use in electrophotographic laser printers.  This implementation
supports control of the laser bias and full scale power levels and
separate control of the intermediate power levels.  This interface is
applicable in discharge and charge area development (DAD, CAD)
electrophotographic processes and is intended to support the gray
scale requirements of the different processes.

      A block diagram illustrating this "Laser Data Control
Interface" between the printhead control card and laser driver card
is shown in the figure.  This interface provides the input to the
laser driver card, which drives a laser diode through an 8-bit, high
speed Digital-to-Analog Converter (DAC).  This laser driver control
interface also is used by the laser power control servo.

      Many EP processes require intermediate power levels to smooth
lines or match stroke width imbalances between horizontal and
vertical lines.  Also, power levels may change between a solid area
and a character in a DAD process.  Previously, the intermediate power
levels were proportional to the full scale power, i.e., a fixed
percentage of full scale.  This implementation illustrates a method
of selecting intermediate power levels which are not proportional to
the full scale power level.  The magnitudes of the intermediate
levels are independent of the solid area fill power level in a DAD
process, or the white discharge power level in a CAD process.

      This implementation illustrates a method of realizing a full
laser power (Solid Area Fill or White Discharge) level set by one
external reference, and the intermediate power levels set to a
different reference.  The magnitudes of the intermediate power levels
are controlled by the "full scale" reference of the DAC located on
the laser driver card.  This "full scale" reference sets the
magnitude of the full scale or full on power level.  In a
conventional system, this full scale level would be the solid area
fill or white discharge power level, and the intermediate levels
would be the only choices for stroke width matching, boldness
control, character smoothing and other gray scale functions. However,
the full scale power level is not used for solid area fill or white
discharge power level.  The "Laser Data Control Interface" will
select the output of an 8-bit, up/down counter to be transferred to
the Laser Driver Card, whenever the incoming data is decoded as a
solid area fill or white discharge power level (see the figure).  The
counter is incremented or decremented as required during the power
control cycle to obtain the referenced power level as determined by
the EP process.  In this way, both the magnitudes of the solid area
fill or white discharge power level, and the intermediate power
levels can be independently servoed.  The laser driver control
inte...