Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2002-01-31
2003-11-25
Meier, Stephen D. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S009000, C347S017000
Reexamination Certificate
active
06652057
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a printing apparatus comprising a DC power source device, which drives a printhead (recording head) of an inkjet printer.
BACKGROUND OF THE INVENTION
An inkjet printing method is advantageous because it enables high-speed printing, makes almost no noise at the time of printing, enables direct printing on regular paper and does not require a fixing process so as to enable downsizing of a printer. Owing to these advantages, commercialization of the inkjet printing method is increasing. The inkjet printing method includes: a method which utilizes an electric/mechanical converter for jetting an ink droplet from a nozzle by making use of a motion caused by mechanical changes induced by input signals; and a so-called thermal inkjet method employing electrothermal transducers (heating resistances) for discharging an ink droplet by a pressure of bubbles generated on the heating resistances which generate heat upon application of a voltage pulse.
A known ink discharge method of an inkjet printer is to heat resistances or resistors by electric power applied to a printhead and discharge ink from a micro-nozzle by utilizing bubbles generated within the nozzle serving as an ink channel. In this case, to drive a printhead for discharging ink, a constant DC voltage is applied to the resistances to turn on/off switch devices connected in series to the resistances, thereby supplying the amount of power necessary for ink ejection to the heater resistances.
The printhead of an inkjet printer, which has a removable configuration, is held in a carriage unit moving in accordance with a width of a print medium, e.g., paper, at the time of printing. Therefore, a printhead set in a printer is not always the same. For instance, a printhead for printing black and white images, a printhead for printing color images, and so on, may be used for its purpose.
Since an arbitrary printhead is mounted as described above, the amount of head driving power necessary for discharging ink in a single discharge operation is controlled in order to stabilize the printing operation regardless of a variation in resistance values of the heater resistances in the printhead. Conventionally, the amount of electric power is controlled by detecting a variation of the heater resistance values based on a resistance value of a detection resistance, provided within the printhead that includes the heater resistances, then inputting the variation data to a control circuit provided on a main board fixed to a printer main body, and adjusting a head driving pulsewidth transmitted from the main board to the printhead.
Furthermore, an amount of heater driving power is also controlled by detecting a temperature rise in a printhead with the use of a thermometer, provided within the printhead that includes the heater resistances, and adjusting a head driving pulsewidth transmitted from the main board to the printhead.
Note that the DC voltage applied to the heater resistances is supplied as a constant voltage from an AC adapter or a DC power source device provided within a printer.
FIG. 7
is a block diagram showing a brief construction of an example of a conventional inkjet printer. In
FIG. 7
, reference numeral
51
denotes an inkjet printhead;
52
, a head carriage circuit board;
53
, a head carriage;
54
, a flexible cable;
55
, a main board of the printer main body;
56
, a driving pulse control circuit included in the main board
55
;
57
, a power source; and
58
, a host apparatus.
The inkjet printhead
51
, having a plurality of heating resistances, performs printing by discharging an ink droplet from a nozzle by making use of a pressure of bubbles, generated by converting energy to heat, the energy being supplied from the power source
57
in accordance with controlling of the driving pulse control circuit
56
in the main board
55
.
The main board
55
converts an image signal, transmitted from the external host apparatus
58
, to a bit signal which turns on/off each of the heating resistances in accordance with, for instance, a print mode or the like, and transmits the bit signal to the driving pulse control circuit
56
for generating a driving pulse. The driving pulse consists of, e.g., a heat source selection signal, printing serial signal, and so forth. The pulsewidth of the driving pulse is changed in accordance with information, such as a temperature of the inkjet printhead
51
, so as to perform most appropriate ink droplet discharge.
The generated driving pulse is transmitted to the head carriage
53
through a movable cable such as the flexible cable
54
, and transmitted to the inkjet printhead
51
through the head carriage circuit board
52
. The inkjet printhead
51
is constructed with one or more removable head units. The head carriage
53
is structured such that it is movable. The head carriage circuit board
52
mainly serves as a relay for electrically connecting the flexible cable
54
with the inkjet printhead
51
.
The power source
57
adopts an AC/DC converter having plural outputs for supplying a power source voltage to logical circuits such as the main board
55
, motors (not shown), and inkjet printhead
51
. Voltage precision is required particularly for the voltage supplied to the inkjet printhead
51
, in view of an influence of a voltage drop caused by wiring resistances generated as a result of passing through the long flexible cable
54
and also for stable ink droplet discharge.
FIG. 8
is an explanatory view of connection between heating resistances and driving switches in the example of the conventional inkjet printhead.
In
FIG. 8
, reference numeral
16
denotes a heating resistance;
17
, a driving switch; and
18
, a power source line connected to a power source. Reference numeral
19
denotes a heating resistance driving circuit connector. One end of the heating resistance
16
is connected to the power source line
18
which receives voltage supplies from the power source, and the other end is connected to the driving switch
17
.
Assume herein that the inkjet printhead has 64 nozzles. One end of the heating resistance
16
, corresponding to each of the 64 nozzles, is connected to the power source line
18
which supplies a driving voltage, while the other end of the heating resistance
16
is connected to the driving switch
17
. The heating resistance driving circuit connector
19
is connected to a heating resistance driving circuit (not shown) for being controlled such that a current is sent only to the heating resistances
16
selected in accordance with the heat source selection signal or printing serial signal transmitted from the main board. Note in
FIG. 8
, nozzles are numbered (N#
1
to N#
64
) from the left.
FIG. 8
shows an example in which the 64 nozzles are divided into 8 blocks each having 8 nozzles, and nozzles are driven in block unit. In
FIG. 8
, nozzles N#
1
to N#
8
are included in block
1
, N#
9
to N#
16
are in block
2
, . . . , and N#
57
to N#
64
are in block
8
.
Depending on an image to be printed, 8 nozzles in each block may be driven simultaneously. Among the signals outputted from the driving pulse control circuit
56
, the heat source selection signal is used for determining a block to be driven in the 8 blocks, and the printing serial signal is used for selecting a nozzle discharging ink from the 64 nozzles. The amount of current sent through the power source line differs in accordance with the number of nozzles driven simultaneously. Therefore, even in a case of driving one block, a voltage drop level caused by wiring resistances is different depending on the number of nozzles driven in the block. Also, a sudden variation in the amount of current affects the voltage drop level.
As mentioned above, a voltage drop level differs in accordance with the number of nozzles driven in each block. Conventionally, the voltage drop level is corrected by controlling a driving pulsewidth so as to supply uniform heating energy (power) to the heating resistances of the nozzl
Masuda Kazunori
Sekiguchi Kiyoshi
Meier Stephen D.
Nguyen Lam
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