Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2001-08-30
2002-12-31
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S009000
Reexamination Certificate
active
06499820
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and a method of generating waveforms for driving a print head used for serial printers such as ink-jet printers and impact dot printers. Particularly, this invention relates to an apparatus and a method of generating driving waveforms for driving a print head, capable of programmably generating driving waveforms by retrieving driving waveforms per wave portion at a given timing from a memory, etc., in which the overall driving waveform data have been stored and converting the overall driving-waveform data into analog signals.
2. Related Background Art
Ink-jet printers have a print head with several nozzles in a sub-scanning (perpendicular) direction. The print head is moved in a main-scanning (horizontal) direction by a carriage mechanism while a paper is being fed, thus producing desired printouts.
The print head discharges ink drops through the nozzles at a given timing based on dot-pattern data developed from printing data entered by a host computer. The ink drops are sprayed onto a printing storage medium such as a printing paper.
Ink-jet printers, however, cannot produce printouts at an intermediate gradation such as gray due to the fact that they discharge ink drops or not, in other words, perform a dot-on/off control.
A known method of producing an intermediate gradation uses a dot matrix of 4×4 or 8×8 for one pixel. Another known technique for producing enhanced gradation is to discharge ink drops of various weights through the same nozzle per dot for dot control so that dots of various diameters are printed on a printing paper.
Variation in head-driving waveforms is required for discharging ink drops of various weights through the same nozzle. Such a known technique is described below.
FIG. 1
is a schematic illustration of an ink-jet printer hardware configuration.
An ink-jet printer
1
is equipped with a printing engine
3
for an actual printing operation and a printer controller
2
that controls the printing engine
3
.
The printer controller
2
includes a CPU
24
for executing a control program, etc., stored in a ROM (Read Only Memory)
22
, an EEPROM (Electrically Erasable and Programmable Read Only Memory)
21
that is a non-volatile memory for storing various setting-data, a RAM
23
acting as a main memory for the CPU
24
and also an image buffer memory for developing printing data into bit maps, and a custom-IC chip
25
such as an ASIC (Application-Specified Integrated Circuit).
All of these devices in the printer controller
2
are controlled by the CPU
24
via buses connected among the devices. The custom-IC chip
25
outputs signals for controlling several sections that constitute the printing engine
3
. The IC chip
25
also acts as an interface for receiving print-command data entered from the host computer
5
via an interface port
4
under IEEE (Institute of Electrical and electronics Engineers)—1284 standards.
The print engine
3
has a motor
31
for driving a carriage (not shown), a print head
32
mounted on the carriage, and a D/A (Digital-to-Analog)-converter IC chip
33
for applying analog driving-voltage waveforms to the print head
32
.
A transfer line
27
is a bus line with a bit width corresponding to the number of nozzles mounted on the print head
32
. An ink-discharging or -halting signal is sent to the print head
32
per nozzle along the transfer line
27
based on image buffer-data developed in the RAM
23
while a driving voltage to the print head
32
depends on an analog voltage waveform generated by the D/A-converter IC chip
33
.
FIG. 2
is a graph showing an example of a head driving-voltage waveform in which the abscissa and the ordinate are time and voltage variation applied on a piezoelectric vibrator of the print head. Several trapezoidal waveform patters such as shown in
FIG. 2
are prepared for discharging various sizes of ink drops. The trapezoidal waveform patters are combined for production of various sizes for ink drops.
Trapezoidal waveforms such as shown in
FIG. 2
are formed in combination of directed segments. In detail, each of periods from moments T
1
to T
8
is expressed as vector data with gradient and length.
The known ink-jet printer forms these trapezoidal waveforms as follows.
The D/A-converter IC chip
33
has a memory that stores data in address spaces such as a Table
30
in FIG.
3
. In the figure, 8-bit data is stored in each address space expressed by 5-bit data. Each 8-bit data is a value indicating a height in unit length of each directed segment, or segment gradient shown in FIG.
2
. There are 32 different gradient values (for 5 bits) in
FIG. 3
required for forming each segment of the trapezoidal waveform shown in FIG.
2
.
In
FIG. 1
, in accordance with data on ink-drop sizes carried by a print command sent from the host computer
5
, the custom-IC chip
25
designates a gradient address for forming each directed segment and sends the gradient address to the D/A-converter IC chip
33
. The transfer line
26
for this data transfer is constituted by 5-bit address buses, clock signal lines for synchronous communications and data-latch signal lines.
Shown in
FIG. 4
is a timing chart for each signal line of the transfer line
26
in data transfer. Data are latched at timing when they are fed on address-bus signal lines A
0
to A
4
.
Height values (right column in Table
30
) corresponding to the addresses are added by the number of clocks to obtain a height of one directed segment, as illustrated in FIG.
5
. It is understood from
FIG. 3
that accumulation of the height values (right column in Table
30
) like steps by the number of clocks produces one directed segment. The larger the height value, the steeper the gradient whereas the smaller the value, the more gentle the gradient. A value accumulated by an adder is rounded to an appropriate number of bits and converted into an analog voltage based on the number of bits.
The driving-waveform generation described above is, however, restricted in the number of waveform gradients, and hence disadvantageous in generation of complex waveforms.
Formation of further multilevel dots has been studied for further multiple gradation. However, the known driving-waveform generation described above could not be adapted for such multilevel dots due to requirement of more complex driving waveforms.
The known method requires height values corresponding to various gradients of segments in the memory of the D/A-converter IC chip in formation of directed segments. The memory must have a very large storage capacity for generation of further various waveforms, thus resulting in cost-up.
SUMMARY OF THE INVENTION
In view of the problems discussed above, a purpose of the present invention is to provide an apparatus and a method of appropriately generating desired waveforms for driving an ink-jet print head with a simple configuration.
Another purpose of the present invention is to provide an apparatus and a method of generating several and complex waveforms for driving an ink-jet print head for multiple gradation.
In order to attain the purposes, in an apparatus and a method of generating several and complex waveforms for driving an ink-jet print head, waveform data for overall head-driving waveforms is written per given unit in waveform buffers and then sequentially retrieved at a given timing for analog conversion to obtain an analog head-driving waveform signal per given unit.
Therefore, features of a driving-waveform generating apparatus according to claim
1
are writing waveform data for overall head-driving waveforms per given unit in waveform buffers and sequentially retrieving the waveform data at a given timing for analog conversion to obtain an analog head-driving waveform signal per given unit.
Features of a driving-waveform generating apparatus according to claim
2
that is an apparatus for generating at least one assumed waveform for driving an ink-jet print head in accordance with gradation data are a waveform-data writing sect
Barlow John
Dudding Alfred E
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Seiko Epson Corporation
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