Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2001-10-16
2003-02-04
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C340S146200
Reexamination Certificate
active
06513893
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a head drive unit for ink-jet recorder and the like, and a method of driving the same.
BACKGROUND OF THE INVENTION
In ink-jet recording, thermal method and piezoelectric method are the two methods now in use widely. Between these two, the piezoelectric method has a feature that is capable of controlling precisely amount of ink mist and an ejecting spot since it uses a piezoelectric element as an actuator to eject ink mist.
Referring now to the accompanying figures, driving waveforms for an ink-jet head of the piezoelectric method will be described hereinafter.
FIGS. 5A through 5C
show head driving waveforms and injecting operation of ink mist.
FIG. 5A
is a diagrammatic illustration depicting an example of head driving wave as a voltage waveform,
FIG. 5B
is another diagrammatic illustration depicting the example of head driving wave as a current waveform, and
FIG. 5C
a diagrammatic illustration depicting changes of an actuator and a meniscus of a head, and appearance of ejected ink mist. Points of time at which driving waveform changes are represented as t
1
, t
2
, t
3
, t
4
, t
5
, t
6
, t
7
and t
8
, voltage values that cause deformation of the actuator as Va, Vb, Vc and Vd, and current values that cause the deformation of the actuator as Ia, Ib, Ic and Id.
Because the actuator consisting of a piezoelectric element is a capacitive load, the waveform shown in
FIG. 5B
has such a relation to
FIG. 5A
in that the waveform of
FIG. 5A
is differentiated.
With reference to the current waveform, described hereinafter pertains to an example of how an ink-jet head is driven.
At the time
0
, actuator
82
and meniscus
83
provided in one part
81
of the head are in a flat steady state
91
. When the actuator
82
is charged with electric current
1
b at the time t
1
, the actuator
82
begins to deform gradually in a direction of pushing out the meniscus
83
. At the time t
2
, it deforms up to a state marked
92
. After this state is maintained until the time t
3
, the actuator
82
is discharged by electric current Ic until the time t
4
, to cause the actuator
82
to pull the meniscus
83
back to a state marked
93
. After this state is maintained until the time t
5
, the actuator
82
is charged rapidly by a larger electric current Id than the current Ib until the time t
6
, so as to cause the actuator
82
to push the meniscus
83
abruptly out to a state marked
94
, and to make it eject ink mist
84
. This state is held until the time t
7
thereafter, and the meniscus
83
is gradually pulled back, and returned to the flat steady state
91
by discharging the actuator
82
by a smaller electric current la than the current Ic until the time t
8
.
One printing cycle (T) consisting of the above operations is repeated for a number of ties necessary to produce an image.
Described next pertains to the conventional head driving waveform generator circuit which performs the above operations.
FIG. 3
is an example of driving current waveform for the head actuator, as is shown in FIG.
5
B. In this example, reference characters t
1
through t
8
represent the time at which the electric current changes, and numerical values within parentheses under them are time data representing the time (shown in hex number; all data will be shown hereinafter using the hexadecimal number system). Reference characters Ia, Ib, Ic, and Id represent values of the electric current, and numerical values in parentheses next to them are electric current data. Here, a direction in which the electric current flows toward the head actuator is given as positive, another direction where the current flows out of the head actuator as negative, and electric current data when its value is
0
is assigned to be
7
F.
In
FIG. 3
, assuming that the printing cycle (T) is 25.6 microseconds, and time resolution is 0.1 microsecond, the driving current waveform for one printing cycle, when expressed in “electric current data/time data” is shown as follows. That is,
7
F/
00
,
7
F/
01
,
7
F/
02
, . . . ,
7
F/
20
, A
3
/
21
, A
3
/
22
, . . . , A
3
/
49
,
7
F/
4
A, . . . ,
7
F/
57
,
19
/
58
,
19
/
60
,
7
F/
61
, . . . ,
7
F/
6
B, F
4
/
6
C, . . . , F
4
/
70
,
7
F/
71
, . . . ,
7
F/
86
,
42
/
87
, . . . ,
42
/
9
E,
7
F/
9
F, . . . and
7
F/FF. It becomes data of 256 Bytes.
Two examples of generating the above-described head driving current waveform will be described next.
FIG. 6
is an example of block diagram of a head drive unit constructed with a memory.
In
FIG. 6
, a CPU (not shown in the figure), which controls a system of the ink-jet recorder, writes electric current data
16
in memory
121
using a time as an address, prior to initiating the head drive operation. Counter
1
repeats clearing operation and counting operation for every printing cycle according to the printing operation of the ink-jet recorder. Count data
11
is supplied to the memory
121
as an address, and the electric current data
16
is output from the memory
121
. This electric current data
16
is converted into an analog value by DAC
7
. An output of the DAC
7
is amplified by the amplifier circuit
8
, supplied to head
9
, and deforms the actuator
82
. Deformation of the actuator causes ejection of ink mist.
Referring now to a block diagram of
FIG. 7
, another example of head drive unit constructed with a shift register is described.
In
FIG. 7
, a CPU (not shown in the figure), which controls a system of the ink-jet recorder, writes electric current data
16
for one printing cycle in time-sequential order into shift register
141
, prior to initiating the head drive operation. The shift register
141
outputs the electric current data
16
in synchronization with clock according to the printing operation of the ink-jet recorder. A number of registers contained in the shift register
141
is equal to a number of the data for one printing cycle. In addition, since the output is fed back to input, it repeats outputting the head driving waveform in synchronism with the printing cycle.
Using FIG.
8
through
FIG. 15
, a process of generating the 256 Bytes of head driving current data is described next.
The ink-jet head receives a great influence of an ambient temperature, rise and fall in temperature of ink in particular, upon its performance of ejecting ink mist, i.e., ejecting amount and ejection velocity. It is therefore necessary to make correction of the head driving waveform according to the temperature, in order to maintain the ejecting performance for stable ink mist. The correction can be made in one case by varying only value of the electric current while keeping its timing unchanged, or in another case, by varying both timing and value of the electric current.
Referring to FIG.
8
through
FIG. 10
, described first pertains to the case of making correction by varying only the current value while not changing the timing.
FIG. 8
shows an example of head driving waveforms (waveform
161
in solid line and waveform
162
in dotted line) at different temperatures.
FIG. 9
shows an example of driving current value to temperature characteristic necessary to keep constant the ejecting performance of ink mist. Ink requires greater driving energy at lower temperature since its viscosity generally increases. Therefore, value of the electric current increases at low temperature, and decreases at high temperature. This temperature characteristic is non-linear relative to temperature. In a correction data table, 10 points or so of reference data are maintained in general as shown with dark dots in the figure in order to reduce an amount of the data. A value of electric current corresponding to any actual operating temperature is obtained by linear interpolation according to the reference data at both sides adjacent to that temperature.
A flow chart for this process is shown in FIG.
10
. Upon start of making a data table for the head driving current, an environmental temperature (operating ambient temperature/ink temperature) is checked (S
101
), and a dat
Asoh Toshihiro
Esaki Takahiro
Ikeda Hirokazu
Kajikawa Takanobu
Kimori Kenichi
Barlow John
Dudding Alfred E.
Matsushita Electrc Industrial Co., Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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