Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2001-08-02
2004-01-06
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S011000, C347S017000, C347S185000
Reexamination Certificate
active
06672711
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to a driving circuit of an ink jet print head in a printing device, and more particularly, to a driving circuit that balances thermal energy among heating elements of ink jet print cells.
2. Description of the Prior Art
Please refer to FIG.
1
.
FIG. 1
is a diagram of a prior art ink jet print head
70
. The ink jet print head
70
comprises an ink tank
72
, a plurality of channels
74
, and a plurality of ink jet cells
76
. The ink tank
72
connects to the plurality of ink jet cells
76
through the plurality of channels
74
. Ink in the ink tank
72
can flow into the ink jet cells
76
through the channels
74
. A heating resistor
78
is installed alongside each inkjet cell
76
. The heating resistor
78
heats up ink in the ink jet cells
76
. The plurality of heating resistors
78
form a heating circuit
60
, as shown in FIG.
2
. When the heating resistor
78
has energy greater than a threshold, bubbles
80
are generated in the ink. The bubbles force ink drops to jet from the nozzles
82
onto the medium (such as paper) to perform printing. However, the amount of ink jetted out is related to the energy supplied by the heating resistors
78
. So, if higher energy is supplied, larger ink drops are jetted out and larger ink spots are formed on the medium. If lower energy is supplied, smaller ink drops are jetted out and smaller ink spots are formed on the medium. If the sizes of the ink drops are not uniform or within a limited range, the printing quality is low. Therefore, the energy generated by the heating resistors
78
should be higher than the threshold so as to jet ink drops, and should also be maintained within a limited range so as to form ink drops of substantially equal sizes.
FIG. 2
is a diagram of a prior art ink jet print head driving circuit
10
. The driving circuit
10
comprises a row driving module
20
and a column driving module
40
. The row driving module
20
receives row data
30
and passes four row control signals R
1
, R
2
, R
3
, R
4
to the heating circuit
60
in the ink jet print head. The column driving module
40
receives column data
50
and passes four column control signals C
1
, C
2
, C
3
, C
4
to the heating circuit
60
in the ink jet print head. The row driving module
20
comprises a shift register
22
, a latch circuit
24
, and a starter
27
. The column driving module
40
comprises a shift register
42
, a latch circuit
44
, and a starter
47
. The row driving module
20
and the column driving module
40
use a common clock signal
32
, a latch signal
34
, and a start signal
39
.
The shift registers
22
and
42
, controlled by the clock signal
32
, receiving binary printing data from the printing device. Then, the latch circuits
24
and
44
latch and store the printing data according to the latch signal
34
. The starters
27
and
47
are composed of a plurality of AND gates
37
. Each of the plurality of AND gates
37
is connected at one input to an output of a corresponding latch circuit
24
,
44
. Another input of the AND gate
37
is connected to the start signal
39
. According to the start signal
39
and content of the latch circuits
24
,
44
, the starters
27
and
47
cause the heating circuit
60
in the ink jet print head to start to heat the plurality of ink jet cells. The heating circuit
60
comprises a plurality of row and column data lines arranged in an array. Each row data line and column data line is connected by a heating resistor and a transistor switch, which are respectively controlled by row control signals R
1
, R
2
, R
3
, R
4
and column control signals C
1
, C
2
, C
3
, C
4
. The row control signals R
1
, R
2
, R
3
, R
4
are respectively connected to the drains of the transistor switches via resistors, and the column control signals C
1
, C
2
, C
3
, C
4
are respectively connected to the gates of the transistor switches. When a specific column and a specific row data line are activated at the same time, the transistor corresponding to the activated row and column data lines conducts, so that current flows through the corresponding heating resistor, and the corresponding ink jet cell jets ink drops.
FIG. 3
is a timing diagram of a prior art ink jet print head driving signal.
FIG. 3
illustrates the method of driving the prior art ink jet print head. Between times T
0
and T
1
, four row data
30
and four column data
50
are sequentially input to the shift registers
22
and
42
, according to the clock signal
32
. When a pulse is generated in the latch signal
34
, binary bits of the four row data
30
and the four column data
50
are respectively latched and stored in the latch circuits
24
and
44
. The row data
30
and the column data
50
now appear at one input of the AND gates
37
of the starter
27
. Between times T
1
and T
2
, a pulse is generated in the start signal
39
. Thus, according to the data appearing at the inputs of the AND gates
37
of the starter
27
, the outputs of the AND gates
37
go high. For example, if between times T
0
and T
1
, the row data
30
(R
1
,R
2
,R
3
,R
4
) equals to (1, 0, 0, 0), and the column data
50
(C
1
,C
2
,C
3
,C
4
) equals to (1, 0, 1, 0), then between times T
1
and T
2
, when the pulse of the start signal
39
generates, the row data line RI and the column data lines C
1
and C
3
are activated. Therefore, the transistors
62
and
64
conduct, causing current to pass through the heating resistors
66
and
68
, so that the corresponding ink jet cells are heated and jet ink. Please note that, because other un-activated transistors do not conduct, current does not pass through the corresponding heating resistances, and the corresponding ink jet cells are not heated.
The size of the ink spot jetted from the ink jet cell is an important factor influencing printing quality. The size of the ink spots is related not only to the energy supplied by the heating resistors, but is also related to whether the ink jet cells have been heated in a previous time. More specifically, if an ink jet cell has been heated to jet ink recently, energy accumulation results in jetting larger ink spots in a new ejection. In other words, if heating a previously unheated ink jet cell and a previously heated ink jet cell with a same energy, ink spots of the former are smaller, and ink spots of the latter are larger. Therefore, if heating the ink jet print head with the prior art driving circuit, the jetted ink drops may have varying sizes, which results in poorer printing quality.
SUMMARY OF INVENTION
It is therefore an objective of the present invention to provide a driving circuit in a printing device that drives heating resistors in a balanced way, so as to improve uniformity of ejected ink spots.
Briefly, the claimed invention provides a driving circuit of an inkjet print head in a printing device. The ink jet print head has a plurality of ink jet cells and corresponding heating elements. Each ink jet cell contains ink and has a nozzle. The driving circuit selectively drives the heating elements to provide energy to the corresponding ink jet cells and to heat the ink jet cells according to printing data from the printing device. The printing data determines whether or not the inkjet cells, and corresponding nozzles, should jet ink. When supplied energy is greater than a threshold, ink drops are jetted from the nozzles onto the medium. The driving circuit has a shift register, a latch circuit, and a driving signal generator. The driving signal generator provides a first driving signal to a first set of nozzles that are expected to jet ink. The first driving signal drives a corresponding first set of heating elements of the first set of nozzles with an energy greater than the threshold to heat a corresponding first set of printing cells, so that ink is jetted from the first set of nozzles. The driving signal generator provides a second driving signal to a second set of nozzles that are expected not to jet ink. The second driving signal drives a corresponding
Fang Yu-Fan
Kao Chih-Hung
Barlow John
BenQ Corporation
Hsu Winston
Nguyen Lam
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