Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
2002-04-30
2004-04-06
Wong, Don (Department: 2821)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C362S800000
Reexamination Certificate
active
06717604
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a circuit for driving an array of elements such as light-emitting diodes used as light sources in an electrophotographic printer or resistive heat-emitting elements used as heat sources in a thermal printer, and to an array head incorporating this circuit.
2. Description of the Related Art
As an example of a conventional circuit for driving an array of elements, Japanese Unexamined Patent Application Publication No. 9-174918 discloses a circuit for driving an array of light-emitting diodes (hereinafter, LEDs) in an electrophotographic printer. This circuit and printer will be described below with reference to
FIGS. 16
to
24
.
In the printer, the LED array selectively illuminates a charged photosensitive drum to form a latent image, which is developed by application of toner to form a toner image, and the toner image is transferred to and fused onto a sheet of paper. The control system of the printer is shown in FIG.
16
. The printing control unit
1
is a computing device comprising a microprocessor, read-only memory (ROM), random-access memory (RAM), input-output ports, timers, and other facilities. Upon receiving signals SG
1
, SG
2
, etc. from a higher-order controller (not visible), the printing control unit
1
generates signals that control a sequence of operations for printing dot-mapped data. The data are provided in signal SG
2
, which is sometimes referred to as a video signal because it supplies the dot-mapped data one-dimensionally.
The printing sequence starts when the printing control unit
1
receives a printing command from the higher-order controller by means of control signal SG
1
. First, a temperature (Temp.) sensor
23
is checked to determine whether a fuser
22
is at the necessary temperature for printing. If it is not, current is fed to a heater
22
a
to raise the temperature of the fuser
22
.
When the fuser
22
is ready, the printing control unit
1
commands a motor driver
2
to drive a develop-transfer process motor (PM)
3
, activates a charge signal SGC to turn on a high-voltage (HV) charging power source
25
, and thereby charges the developing unit (D)
27
.
In addition, a paper sensor
8
is checked to confirm that paper is present in a cassette (not visible), and a size sensor
9
is checked to determine the size of the paper. If paper is present, another motor driver
4
drives a paper transport motor (PM)
5
according to the size of the paper, first in one direction to transport the paper to a starting position sensed by a pick-up sensor
6
, then in the opposite direction to transport the paper into the printing mechanism.
When the paper is in position for printing, the printing control unit
1
sends the higher-order controller a timing signal SG
3
(including a main scanning synchronization signal and a sub-scanning synchronization signal) as shown in FIG.
17
. The higher-order controller responds by sending the dot data for one page in the video signal SG
2
. The printing control unit
1
sends corresponding dot data (HD-DATA) to an LED head
19
in synchronization with a clock signal (HD-CLK). The LED head
19
comprises a linear array of LEDs for printing respective dots (also referred to as picture elements or pixels).
After receiving data for one line of dots in the video signal SG
2
and sending the data to the LED head
19
, the printing control unit
1
sends the LED head
19
a latch signal (HD-LOAD), causing the LED head
19
to store the print data (HD-DATA). The print data stored in the LED head
19
can then be printed while the printing control unit
1
is receiving the next print data from the higher-order controller in the video signal SG
2
.
The video signal SG
2
is transmitted and received one printing line at a time.
FIG. 17
illustrates the printing of three consecutive dot lines N−1, N, and N+1. For each line, the LED head
19
forms a latent image of dots with a comparatively high electric potential on the negatively charged photosensitive drum (not visible). In the developing unit
27
, negatively charged toner is electrically attracted to the dots, forming a toner image.
The toner image is then transported to a transfer unit (T)
28
. The printing control unit
1
activates a high-voltage transfer power source
26
by sending it a transfer signal SG
4
, and the toner image is transferred to a sheet of paper passing between the photosensitive drum and transfer unit
28
. The sheet of paper carrying the transferred toner image is transported to the fuser
22
, where the toner image is fused onto the paper by heat generated by the heater
22
a
. Finally, the sheet of paper carrying the fused toner image is transported out of the printing mechanism, passing an exit sensor
7
, and ejected from the printer.
The printing control unit
1
controls the high-voltage transfer power source
26
according to the information detected by the pick-up sensor
6
and size sensor
9
so that voltage is applied to the transfer unit
28
only while paper is passing through the transfer unit
28
. When the paper passes the exit sensor
7
, the printing control unit
1
stops the supply of voltage from the high-voltage charging power source
25
to the developing unit
27
, and halts the develop/transfer process motor
3
. The above operations are repeated to print a series of pages.
FIG. 18
is a simplified schematic drawing showing the circuit structure of the LED head
19
. The print data signal HD-DATA and clock signal HD-CLK are used to shift bit data for two thousand four hundred ninety-six dots, a number suitable for printing on A4-size paper at a resolution of three hundred dots per inch, into a shift register comprising flip-flops FF
1
, FF
2
, . . . , FF
2496
. The latch signal HD-LOAD causes latches LT
1
, LT
2
, . . . , LT
2496
to latch the bit data. The strobe signal HD-STB-N activates a circuit comprising an inverter G
0
, pre-buffers G
1
, G
2
, . . . , G
2496
, and switching elements Tr
1
, Tr
2
, . . . , Tr
2496
that drive a linear array of light-emitting elements LD
1
, LD
2
, . . . , LD
2496
according to the latched bit data. The switching elements are p-channel metal-oxide-semiconductor (MOS) transistors; the light-emitting elements are LEDs.
The LED head
19
is supplied with power at a voltage denoted VDD in this drawing and the next. Some of this power is supplied as current to drive the LEDs. The notation VDDH will be used later to denote the voltage of the LED driving power supply.
As shown in
FIG. 19
, the LED head
19
comprises a plurality of LED array chips
101
driven by corresponding driver integrated circuits (ICs)
100
. In this example, there are twenty-six LED array chips and twenty-six driver ICs. The driver ICs
100
are connected in cascade. Each LED array chip
101
includes ninety-six LEDs. The LED head
19
also has a reference voltage generator
102
for supplying a reference voltage Vref to the driver ICs
100
.
Each driver IC
100
has the same internal circuit configuration, comprising: a shift register
100
a
with ninety-six flip-flops that receive the printing data (HD-DATA) in synchronization with the clock signal (HD-CLK); a latch circuit
100
b
that latches the output signals from the shift register
100
a
in response to the latch signal (HD-LOAD); an inverter
100
e
that inverts the strobe signal (HD-STB-N) from negative to positive logic; an AND logic circuit
100
c
that gates the output signals from the latch circuit
100
b
according to the output of the inverter
100
e
; an LED driving circuit
100
d
that supplies driving current to the LEDs in the corresponding LED array chip
101
in response to the output signals of the AND circuit
100
c
; and a control voltage generator
100
f
that supplies a control voltage to the LED driving circuit
100
d.
In the printing process, when the HD-DATA, HD-CLK, HD-LOAD, and HD-STB-N signals are sent from the printing control unit
1
to the LED head
19
, the LEDs that are driven are driven simultaneously for the same length
Minh D. A.
Oki Data Corporation
Rabin & Berdo P.C.
Wong Don
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