Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-09-20
2002-05-07
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S019000, C347S060000
Reexamination Certificate
active
06382755
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a printhead and a printing apparatus using the printhead, and more particularly, to a printhead which performs printing in accordance with an ink-jet method and a printing apparatus using the printhead.
In ink-jet printing, noise upon printing is very small and negligible, and printing speed is high, further, a print image can be fixed onto a so-called normal paper without special processing. Recently, attention is focused on the ink-jet printing method having these advantages.
Among ink-jet printing methods, a printing method disclosed in Japanese Patent Publication Laid-open No. 54-51837 and DOLS No. 2843064, for example, has a feature different from other ink-jet printing methods in that thermal energy is applied to liquid such as ink so as to obtain a driving force for discharging the liquid.
That is, according to the above printing method disclosed in these publications, printing is performed by causing a state change with sudden volume increase in the liquid acted upon by the thermal energy, then discharging the liquid from an orifice at the end of a printhead by the action based on the state change, as liquid droplets, and attaching the liquid droplets to a print medium.
Especially, according to DOLS No. 2843064, the method is very effectively applied to so-called drop-on-demand printing. Further, the method easily realizes a full-line type printhead having a printing width corresponding to the entire width of a print medium and orifices in a high density. Accordingly, high-resolution and high quality image can be printed at a high speed.
The printhead to which the printing method is applied has orifices to discharge liquid, liquid channels, connected to the orifices, each including a heat action portion to supply thermal energy to liquid, and a substrate having electrothermal transducers (heat generators) to generate the thermal energy.
Recently, the substrate not only holds the plurality of heat generators but also integrates a plurality of drivers to drive the respective heat generators, a logic circuit including a shift register for temporarily storing image data of number of bits corresponding to the number of heat generators, to transfer the image data serially inputted from a printing apparatus to the respective drivers in parallel, a latch circuit which temporarily latches data outputted from the shift register, and the like.
FIG. 16
is a block diagram showing the arrangement of a logic circuit in a conventional printhead having N heat generators (printing elements).
In
FIG. 16
, reference numeral
400
denotes a circuit board;
401
, heat generators;
402
, power transistors;
403
, an N-bit latch circuit; and
404
, an N-bit shift register. Numeral
415
denotes a sensor for monitoring resistance values of the heat generators
401
and the temperature of the circuit board
400
and a heater to maintain the temperature of the circuit board
400
. The sensor may be integrated with the heater, or a plurality of sensors and heaters may be packaged. Numerals
405
to
414
and
416
denote input/output pads. Among these input/output pads, the pad
405
is a clock input pad for inputting a clock (CLK) to operate the shift register
404
; the pad
406
, an image data input pad for serially inputting image data (DATA); the pad
407
, a latch input pad for inputting a latch clock (LTCLK) to hold image data in the latch circuit
403
; the pad
408
, a drive signal input pad for inputting a heat pulse (HEAT) to externally control driving period by turning the power transistors
402
ON to energize the heat generators
401
; the pad
409
, a drive power input pad for inputting a driving power (3-8V; generally 5V) for the logic circuit; the pad
410
, a GND terminal; the pad
411
, a heat generator power input pad for inputting power to drive the heat generators
401
; the pad
412
, a reset input pad for inputting a reset signal (RST) to initialize the latch circuit
403
and the shift register
404
; and the pad
413
, an HGND terminal for heat generator drive power source.
Further, numerals
414
a
and
414
b
denote an output pad for outputting a monitor signal and an input pad for inputting control signals for sensor drive and drive of the temperature maintaining heater. Further, numerals
416
-(
1
) to
416
(n) denote block-selection signal input pads for inputting block selection signals (BLK
1
to BLKn) for block selection in time-division drive. In time-division drive, the N heat generators are divided into n blocks, and driven in block units. Numeral
417
a
denotes AND circuits which calculate the logical products of the outputs from the latch circuit
403
and the block selection signals (BLK
1
to BLKn); and
417
b
, AND circuits which calculate the logical products of outputs from the AND circuit
417
a
and the heat signal (HEAT).
Numerals
418
a
and
418
b
denote parasitic resistances which occur on the wiring used for driving the heat generators
401
.
The drive sequence of the printhead having the above construction is as follows. In the following description, image data (DATA) is binary data where 1 bit corresponds to 1 pixel.
First, the image data (DATA) is serially outputted from a printing apparatus main body to which the printhead is attached, in synchronization with a clock (CLK), then the data is inputted into the shift register
404
. Next, the image data (DATA) is temporarily stored in the latch circuit
403
, and ON/OFF outputs in correspondence with image data value (“0” or “1”) are made from the latch circuit
403
.
In this state, when a heat pulse (HEAT) and a block selection signal are inputted, power transistors supplied with ON outputs from the latch circuit
403
, corresponding to heat generators in a block selected by the block selection signal, are driven for “ON” period of the input heat pulse (HEAT). Then, an electric current flows through the corresponding heat generators. Thus, the print operation is performed.
Next, the parasitic resistances
418
a
and
418
b
will be described.
It is preferable that the parasitic resistance does not exist, however, actually it cannot be ignored. The example of
FIG. 16
shows the parasitic resistances in the logic circuit of the printhead, however, parasitic resistance also exists on a PCB (printed circuit board) within the printhead or a flexible printer cable (FPC) connecting the printhead and the printing apparatus.
In
FIG. 16
, as the resistances are common to the plurality of heat generators
401
, the ratio between the parasitic resistances and the resistance of all the driven heat generators differs dependent on the number of time-divisionally driven heat generators. As a result, the value of a voltage applied to the heat generators (in other words, the value of voltage drop by the parasitic resistances) changes. Accordingly, the voltage applied to both ends of the heat generators changes due to the duty of a pattern to drive the heat generators, which causes variation in energy to the heat generators.
On the other hand, in accordance with the recent tendency of increase in printing speed, a growing number of heat generators are provided in a printhead, and the drive frequency is increasing. In time division drive, the number of simultaneously-driven heat generators is increasing, therefore, the change of voltage drop due to parasitic resistance is not negligible.
Conventionally, some methods to prevent voltage drop have been proposed. One of these methods is to feed-back control a heat pulse (HEAT) to drive heat generators, on the printing apparatus side, so as to change the pulse width based on a pattern for driving the heat generators of the printhead.
More specifically, as shown in
FIG. 17A
, on the printing apparatus side, a counter
801
counts the number of simultaneously-driven heat generators based on generated image data, then the counted number is stored into a memory
802
. A drive pulse generator
803
modulates the pulse width based on the number. Otherwise, as shown in
FIG. 17B
, the counter
801
provided in the
Imanaka Yoshiyuki
Mochizuki Muga
Ozaki Teruo
Barlow John
Canon Kabushiki Kaisha
Dudding Alfred
Fitzpatrick ,Cella, Harper & Scinto
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