Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-10-28
2001-10-09
Vo, Anh T. N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06299272
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to correcting non-uniformity of size or ejection velocity of each individual droplet of acoustic inkjet printheads and more particularly to an acoustic inkjet printhead where the RF signal delivered to each transducer is individually controlled to provide a desired droplet size or ejection velocity.
Referring to
FIG. 1
, there is shown a portion of a prior art acoustic inkjet printhead
10
. Printhead
10
has a liquid level control structure
12
which captures an ink layer
16
over a glass substrate
14
. Liquid level control structure
12
has a plurality of apertures
18
each of which is dedicated to a single acoustic ejector. Under the glass substrate, there is a plurality of piezo-electric transducers
20
. For the purpose of simplicity, hereinafter, the “piezo-electric transducer” is referred to as “transducer.” Each transducer
20
is dedicated to one aperture
18
and is located directly across its respective aperture
18
. Once each transducer
20
is activated, it will oscillate and generate acoustic waves
22
which travel within the glass substrate
14
toward the ink
16
.
Over the glass substrate
14
, there is a plurality of Fresnel lenses
24
, each of which corresponds to one of the transducers
20
and is located across from its respective transducer
20
. The Fresnel lenses
24
receive the acoustic waves
22
from the transducers
20
and focus the acoustic waves onto the liquid surface in their respective apertures
18
. The focused waves
22
cause the ink to be ejected from the apertures as droplets
26
.
Oscillator
30
generates a RF signal and sends it to a RF Amplifier
32
to be amplified. The amplified RF signal is sent to several RF power switches
34
. Each output of each power switch
34
is distributed between the plurality of transducers
20
where each transducer
20
is grounded through its individual switch Z. Switches Z control the time and duration of the RF signal applied to each transducer
20
. Once each switch Z is closed, the RF signal flows into the respective transducer
20
and once the switch is opened, the flow of the RF signal into the transducer
20
will be significantly reduced. The time each switch Z is closed determines the duration of the RF signal applied to the transducers. All switches Z receive the same control signal C from a switch driver circuit
36
. As a result, all switches Z, that are supposed to close, close at the same time and all the closed switches Z open at the same time. The electrical connection shown in
FIG. 1
is designed to deliver a RF signal with the same power to each transducer
20
. However, due to the variations in the focusing characteristics of different transducers
20
, droplets
26
ejected from different apertures
18
might have different sizes.
Non-uniformity of droplet size
18
creates different size pixels which can be observed as variation of the thickness of a line. However, non-uniformity of ejection velocity causes pixels not to align on a straight line. Since the paper is moving, in order to have a straight line, all the droplets have to be ejected at the same time to strike the paper at the same time. If a droplet is ejected before or after the intended time, the pixel on the paper will be above or below the intended line respectively. Non uniformity of the droplet size and velocity are two problems of the prior art acoustic ink jet printheads.
It is an object of this invention to provide a driver circuitry to control the size or ejection velocity of droplets of acoustic inkjet printheads.
SUMMARY OF THE INVENTION
In accordance with one aspect of this invention, a method of correcting non-uniformity of droplet size or ejection velocity by pulse width modulation comprises the steps of receiving a pulse with a first pulse edge and a second pulse edge and delaying the first pulse edge of said pulse according to a plurality of predetermined delay data to create a plurality of delayed first pulse edges. Subsequently, sending out each delayed first pulse edge with the received second pulse edge of the pulse as the first pulse edge and second pulse edge of a control pulse to create a plurality of control pulses with different pulse widths.
In accordance with another aspect of this invention, an apparatus for correcting non-uniformity of droplet size or ejection velocity by pulse width modulation comprises a delaying means. The delaying means receives a pulse and creates a plurality of control pulses. The received pulse has a first pulse edge and a second pulse edge. A lookup table stores an individual delay data for each of the plurality of control pulses. The delaying means is in communication with the lookup table to receive the plurality of delay data. The delaying means is responsive to the delay data from the lookup table to delay only the first pulse edge of the pulse according to each of the delay data to create a plurality of delayed first pulse edges. The delaying means sends out each of the plurality of delayed first pulse edges in combination with the received second pulse edge of the pulse as the first pulse and second pulse edges of a control pulse to create a plurality of control pulses with different pulse widths.
REFERENCES:
patent: 4087825 (1978-05-01), Chen et al.
patent: 4672398 (1987-06-01), Kuwabara et al.
patent: 4982199 (1991-01-01), Dunn
patent: 5107276 (1992-04-01), Kneezel et al.
Baker Lamar T.
Buhler Steven A.
ElHatem Abdul M.
Elrod Scott A.
Hadimioglu Babur B.
Pope William
Rad Fariba
Vo Anh T. N.
Xerox Corporation
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