Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2001-11-09
2002-11-05
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S019000
Reexamination Certificate
active
06474764
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to a control circuit for driving a print head of a printing apparatus, and more particularly, to a control circuit for driving a print head of a printing apparatus to make temperature compensation and provide uniform ink spots.
2. Description of the Prior Art
Please refer to FIG.
1
.
FIG. 1
is a schematic diagram of a prior art print head
70
. The print head
70
comprises an ink reservoir
72
, a plurality of tubes
74
and a plurality of ink chambers
76
. The plurality of tubes
74
connects the ink reservoir
72
to the plurality of ink chambers
76
. Ink inside the ink reservoir
72
can flow through the tubes
74
to the ink chambers
76
. Inside each ink chamber
76
is a heating resistor
78
that heats up the ink, increasing the ink's thermal energy. When the thermal energy of the ink in the ink chamber
76
is above a predetermined threshold, the ink generates bubbles
80
to eject ink spots from a nozzle
82
for printing. When the nozzle
82
receives many instructions successively to eject ink spots, the heating resistor
78
of the nozzle
82
continually heats up, and ink inside the ink chamber
76
has a higher temperature and a lower viscosity. If, however, another nozzle
82
receives fewer instructions to eject ink spots, ink inside the ink chamber
76
has a lower temperature and a higher viscosity. If the same amount of energy is used to drive the heating resistors
78
of these two nozzles
82
, non-uniform ink spots are ejected and the printing quality is lowered. So, it is preferable that the energy provided by the heating resistor
78
in the print head
70
not only makes the thermal energy of ink in the ink chamber
76
higher than the predetermined threshold, but can also be adjusted to make the sizes of ejected ink spots uniform so as to optimize printing quality.
Please refer to FIG.
2
.
FIG. 2
is a schematic diagram of a prior art driving circuit of a print head. For example, a driving circuit
10
can receive an input of eight printing data
30
and produce eight controlling signals (D
1
, D
2
, D
3
, D
4
, D
5
, D
6
, D
7
, D
8
) to output to a print head
40
. The print head
40
has a heating circuit
42
and eight ink chambers (R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
, R
8
). The driving circuit
10
has a shift register
22
, a latching circuit
24
and a driving module
26
. The shift register
22
receives binary printing data
30
transmitted serially from the printing apparatus. Then, the latching circuit
24
latches the printing data
30
and stores the printing data
30
in the latching circuit
24
according to a latching signal
34
. The driving module
26
consists of a plurality of AND gates
28
and causes the heating circuit
42
in the print head
40
to heat up each predetermined ink chamber according to a driving signal
36
. The heating circuit
42
consists of a plurality of heating resistors
78
and transistor switches
44
. Each transistor switch
44
is linked from its corresponding control signal (D
1
, D
2
, D
3
, D
4
, D
5
, D
6
, D
7
, D
8
) to the AND gate it controls. When a specific control signal is turned on, the corresponding transistor switch
44
turns on, current flows through the corresponding heating resistor
78
, the corresponding ink chamber is heated up, and ink inside the ink chamber is ejected as ink spots to print.
Please refer to FIG.
3
.
FIG. 3
is a timing diagram for a first driving pattern of a prior art print head. The thermal energy of ink inside the ink chamber
76
is influenced by energy provided by the heating resistor
78
and other factors, such as the number of ink chambers to be driven in a printing process. When there are more ink chambers to be driven in a printing process, the heating resistor
78
provides less energy to these ink chambers. Between T
0
and T
1
, eight printing data
30
are input sequentially to the shift register
22
via the control of a pulse signal
32
. When the latching signal
34
produces a pulse, binary bits of eight printing data
30
are respectively latched in the latching circuit
24
. Between T
1
and T
2
, a pulse
37
is produced in the driving signal
36
. The AND gate
28
of the driving module
26
then decides whether or not to output the pulse of the corresponding driving signal
36
, depending on whether the latched printing data
30
in latching circuit
24
is a “1” or a “0.” For example, between T
0
and T
1
, the printing data
30
are (1, 1, 1, 1, 0, 0, 0, 0). When the pulse
37
of the driving signal
36
is produced between T
1
and T
2
, the corresponding transistor switch is on and a current flows through the corresponding heating resistors to heat up the corresponding ink chambers (R
1
, R
2
, R
3
, R
4
) to eject ink spots. Other transistors that are off do not conduct, so the corresponding heating resistors have no current and the corresponding ink chambers (R
5
, R
6
, R
7
, R
8
) are not heated. As a result, no ink spots are ejected from those chambers.
Between T
1
and T
2
, printing data is renewed to (1, 1, 1, 1, 1, 0, 0, 0). So, between T
2
and T
3
, a pulse
38
of the driving signal
36
is produced and corresponding ink chambers (R
1
, R
2
, R
3
, R
4
, R
5
) are heated to eject ink spots. Other ink chambers (R
6
, R
7
, R
8
) are not heated, so they do not eject ink spots. The duration of pulses
37
,
38
, and
39
is the same, but their voltages are different. The voltage of pulse
38
is lower than that of pulse
37
because five ink chambers are driven with less energy provided by heating resistor
78
in the second printing process compared to four ink chambers driven with more energy in the first printing process. For the same reason, six ink chambers are driven with even less energy in the third printing process, so the voltage of pulse
39
is lower than the voltages of both pulses
37
and
38
.
Please refer to FIG.
4
.
FIG. 4
is a timing diagram of a second driving pattern of a prior art print head.
FIG. 3
showed a case where the printing data
30
is concentrated (1, 1, 1, 1, 0, 0, 0, 0).
FIG. 4
is different in that the printing data
30
is more dispersed (0, 1, 1, 0, 0, 1, 1, 0), (1, 0, 0, 1, 0, 1, 0, 1). Because the prior art only considers the number of ink chambers to be driven to eject ink drops, the duration and voltages of pulses
47
,
48
,
49
of the driving signal
36
, and the energy provided to heating resistor
78
, are the same. In fact, the thermal energy of ink inside the ink chamber
76
is influenced by other factors, one being active ink chambers in proximity to reserved ink chambers. As shown in
FIG. 4
, the distribution of the active ink chambers in the first printing process is concentrated, so the thermal energy of ink inside these ink chambers is actually higher. However, the distribution of the active ink chambers in the third printing process is very dispersed, so the thermal energy of the ink inside these ink chambers is actually lower. This situation is not considered in the prior art as shown in FIG.
4
. Ejected ink spots are still not uniform in size and the printing quality is influenced.
SUMMARY OF INVENTION
It is therefore a primary objective of the claimed invention to provide a control circuit for driving a print head of a printing apparatus to make temperature compensation and provide uniform ink spots.
According to the claimed invention, a control circuit for driving a print head of a printing apparatus is provided. The print head comprises a plurality of heating elements and a plurality of corresponding ink chambers. Each ink chamber is used for storing ink and has a nozzle. The control circuit includes a thermometer for measuring a temperature of the ink chambers, and a processor for generating a heating signal according to printing data transmitted from the printing apparatus to drive heating elements to heat ink chambers corresponding to nozzles which will jet ink drops, so as to cause the nozzles to jet ink drops. The processor also includes a pre-heating signa
Fang Yu-Fan
Kao Chih-Hung
Barlow John
Benq Corporation
Hsu Winston
Stewart Jr. Charles W.
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