Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2002-12-05
2004-05-11
Brooke, Michael (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S010000, C310S317000, C341S148000
Reexamination Certificate
active
06733099
ABSTRACT:
TECHNICAL FIELD
The present invention belongs to the technical fields relating to waveform generating circuits generating voltage waveforms, inkjet head driving circuits driving actuators for ink ejection provided on an inkjet head, and inkjet recording devices provided with an inkjet head having actuators that are driven by such an inkjet head driving circuit.
BACKGROUND ART
Conventionally, inkjet heads having actuators for ink ejection are well known, and examples of such actuators of inkjet heads are piezoelectric actuators provided with electrodes on both sides of a piezoelectric element, which constitute a portion of a pressure chamber accommodating the ink. When a pulse-shaped voltage is applied to the electrodes of such an actuator, the actuator is deformed such that the volume of the pressure chamber is reduced, thus creating a pressure in the pressure chamber, which ejects ink drops from a nozzle that is in communication with the pressure chamber.
As shown for example in
FIG. 4
, the voltage waveform applied to the actuators is made of a first waveform P
1
(voltage-falling waveform), at which the potential falls from ground potential to the minimum potential (−Vf), a second waveform P
2
continuing the first waveform P
1
and maintaining this minimum potential, a third waveform P
3
(voltage-rising waveform) continuing the second waveform P
2
and rising from the minimum potential to the maximum potential (Vf), a fourth waveform P
4
continuing the third waveform P
3
and maintaining this maximum potential, and a fifth waveform P
5
(voltage falling waveform) continuing the fourth waveform P
4
and returning from the maximum potential to ground potential. This series of first to fifth waveforms P
1
to P
5
constitutes one driving pulse P for ejecting one ink drop from the nozzle, and the driving pulse P is given out repeatedly with a predetermined period.
An example of a waveform generating circuit (inkjet head driving circuit) generating the voltage waveform (driving pulse P) for driving the actuator is shown in FIG.
6
. In this drawing, numeral
101
is a CPU, which has two terminals outputting digital signals (for example of 8 bits) for generating the voltage waveform. A first D/A converter
102
for converting a digital signal into a positive analog signal and giving it out and a second D/A converter
103
for converting a digital signal into a negative analog signal and giving it out are connected to the digital signal output terminals of this CPU
101
. The first and second D/A converters
102
and
103
receive from the CPU
101
a data set signal together with the digital signals but from a different terminal than the digital signals, and when this data set signal has been input and a predetermined time (data settling time) has elapsed after its input (after the output of the D/A converter
102
(or
103
) has settled), the analog voltage is given out. The first D/A converter
102
is connected to a first power source
106
giving out a positive voltage, whereas the second D/A converter
103
is connected to a second power source
107
giving out a negative voltage.
A first and a second voltage/current converter
109
and
110
are respectively connected to the output terminals of the first and the second D/A converter
102
and
103
, and these first and second voltage/current converters
109
and
110
convert the positive and the negative analog voltage into currents. The output terminals of the first and second voltage/current converters
109
and
110
are connected to a current/voltage converter amplifier
111
, which amplifies the currents into which the voltages have been converted by the first and second voltage/current converters
109
and
110
, and converts the amplified currents into a voltage. It should be noted that the first voltage/current converter
109
, which is connected to the output terminal of the first D/A converter
102
, is connected to the first power source
106
, whereas the second voltage/current converter
110
, which is connected to the output terminal of the second D/A converter
103
, is connected to the second power source
107
, and the current/voltage converter amplifier
111
is connected to both the first power source
106
and the second power source
107
.
Based on the output voltage from the first and second D/A converters
102
and
103
, the first and second voltage/current converters
109
and
110
and the current/voltage converter amplifier
111
generate voltage waveforms like the first to fifth waveforms P
1
to P
5
. More specifically, when the first D/A converter
102
outputs a positive analog voltage and the second D/A converter
103
outputs ground potential, the voltage rising waveform (third waveform P
3
) is generated, whereas when the second D/A converter
103
outputs a negative analog voltage and the first D/A converter
102
outputs ground potential, the voltage falling waveforms (first and fifth waveforms P
1
and P
5
) are generated. Furthermore, when both D/A converters
102
and
103
output ground potential, waveforms maintaining the potential directly before the output of those ground potentials (second and fourth waveforms P
2
and P
4
) are generated, and the potential between neighboring driving pulses P is maintained at ground potential.
Then, the generated voltage waveform is applied to a multitude of actuators of the inkjet head, through a current amplifier
113
, which is made of two transistors
113
a
, and a driver IC
114
. The driver IC
114
includes for example switching transistors that are provided in accordance with the actuators, and, receiving print signals from the CPU
101
, selects the actuators corresponding to the nozzles through which ink drops are to be ejected, thus applying the voltage waveform only to the selected actuators.
With a conventional waveform generating circuit as described above, when for example a voltage rising waveform is generated, a digital signal is input into the first D/A converter
102
, which outputs a positive analog signal, whereas when the voltage rising waveform is not generated, it is necessary to output a voltage equal to ground potential (depending on the voltage waveform to be generated, there is no limitation to ground potential, and it can be a constant predetermined voltage that is midway between the maximum value and the minimum value of the output voltage of the first D/A converter
102
). Furthermore, when the voltage falling waveform is not generated, the output voltage of the second D/A converter
103
needs to be set to ground potential (depending on the voltage waveform to be generated, there is no limitation to ground potential, but can be a constant predetermined voltage that is midway between the maximum value and the minimum value of the output voltage of the second D/A converter
103
).
However, due to variations in the characteristics of the D/A converters
102
and
103
, it may happen that a voltage that is slightly different from ground potential (or the predetermined voltage) is output, and in the case of such variations in the characteristics, malfunctioning occurs in the current/voltage converter amplifier
111
, and a precise voltage waveform cannot be generated anymore.
In view of these facts, it is an object of the present invention to prevent malfunctioning due to variations in the characteristics of the D/A converters with a simple configuration, by improving the configuration of the above-described waveform generating circuit.
DISCLOSURE OF THE INVENTION
In order to attain these objects, the present invention is provided with a switching means whose input can be switched between the output voltage of a D/A converter and a predetermined voltage that is held constant, and which outputs one of those two output voltages to a waveform generating portion, wherein the input into the switching means is switched as necessary.
More specifically, according to a first invention, a waveform generating circuit includes at least one D/A converter that converts a digital signal into an analog voltage and outputs t
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