Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-11-24
2002-09-10
Barlow, John (Department: 2861)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06447086
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to acoustic printing, and more particularly to controlling the on/off switching ratio between ejectors of an acoustic printhead.
The fundamentals of acoustically ejecting droplets from an ejector device such as a printhead has been widely described, and the present assignee has obtained patents on numerous concepts related to this subject matter. In acoustic printing, an array of ejectors forming a printhead is covered by a pool of liquid. Each ejector can direct a beam of sound energy against a free surface of the liquid. The impinging acoustic beam exerts radiation pressure against the surface of the liquid. When the radiation pressure is sufficiently high, individual droplets of liquid are ejected from the pool surface to impact upon a medium, such as paper, to complete the printing process. The ejectors may be arranged in a matrix or array of rows and columns, where the rows stretch across the width of the recording medium, and the columns of ejectors are approximately perpendicular.
Ideally, each ejector when activated ejects a droplet identical in size to the droplets of all the other ejectors in the array. Thus, each ejector should operate under identical conditions.
In acoustic printing, the general practice is to address individual ejectors by applying a common RF pulse to a segment of a row, and to control the current flow to each ejector using column switches. In some cases it is desirable to use one column switch for several rows in parallel in order to reduce the number of column driver chips and wire bonds, and hence cost, in the system. Unfortunately, this approach results in parasitic current paths which can cause undesired RF current to flow through ejectors that are not in an ON state.
In existing systems, the switching ratio is limited and will vary with the number of ejectors that are ON in a given row. A switching ratio is defined as the RF power in an OFF ejector to the RF power in an ON ejector (i.e. P
OFF
/P
ON
).
FIG. 1
illustrates an acoustic switching array with a desired current path for a selected row and selected column for an existing system. Switching matrix
10
is a 4-row
12
a,
12
b,
12
c,
12
d
by 64 column
14
a,
14
b,
14
zz
switching matrix. Rows are connected to the matrix via switching elements
16
a,
16
b,
16
c,
16
d,
and columns are connected through switching elements
18
a,
18
b,
18
zz.
At the intersection of the columns and rows are transducers
20
. Current paths of matrix
10
are terminated at RF ground
21
. It is to be appreciated that while the matrix of
FIG. 1
is a 4-row by 64-column matrix, the present invention may be used in other matrix designs.
Matrix
10
is supplied by a power source
22
which provides its output to an RF signal matching circuit or controller
24
. By proper switch sequencing, a desired current path for a selected row and selected column is obtained. For example in
FIG. 1
, by closing switch
16
a
and switch
18
a,
a current path is provided from RF matching network
24
to a transducer
20
a
via row
12
a
and column
14
a.
As the remaining rows and columns are unselected, only transducer
20
a
is intended to be activated to emit a droplet.
Unfortunately, the interconnect paths used to implement a low cost acoustic printhead include unavoidable, undesirable current paths, as shown and discussed for example, in connection with
FIGS. 2-4
.
FIG. 2
is a simplified depiction of an undesired current path through an unselected transducer in the same row as a selected transducer. In this example, switches
16
a
and
18
a
are maintained in a closed position while the remaining switches are unselected. Therefore current is provided to transducer
20
a
. However, undesired current will also flow through transducer
20
b
, which is in selected row
12
a
but unselected column
14
b.
Similarly,
FIG. 3
illustrates a situation where an undesired current flows through transducer
20
c
, which is in selected column
14
a and unselected row
12
c.
Column switches
18
a
-
18
zz
are, in one embodiment, implemented with a component such as a PIN diode, which has a reasonably high intrinsic switching ratio, i.e., in the range of −6 dB or greater. A high switching ratio of this type may insure that a particular column switch is securely turned OFF if it were the only device in the system. However, a net switching ratio of a selected column and a selected row ejector (relative to other ejectors which should be OFF) can vary between approximately −2.3 dB and −6 dB, depending upon the number of existing parasitic current paths through ejectors which are not selected.
Turning to
FIG. 4
, a more detailed discussion is provided regarding the parasitic current paths introduced in connection with
FIGS. 2 and 3
. The transducers are identified by the row and column numbers to which they are connected. For the case illustrated, all current paths start from the conductor of row
0
,
12
a
, and terminate at RF ground return
21
.
In the following example, transducer
20
b
is an unselected transducer. The undesired current through unselected transducer
20
b
consists of three components, all of which start from row
0
,
12
a
, and proceed down through transducer
20
b
. The first component flows from transducer
20
b
, down through the top segment of column
1
,
14
b
, up through transducer
20
d
, through a segment of row
1
,
12
b
, down through transducer
20
e
, down through column
0
,
14
a
, and finally through the selected column
0
switch,
18
a
, to RF ground return
21
.
The path of the second component is from row
0
,
12
a
, down through transducer
20
b
, and the top two segments of column
1
,
14
b
, up through transducer
20
f
, through a segment of row
2
,
12
c
, down through transducer
20
c
, down through column
0
,
14
a
, and finally through column
0
switch,
18
a
, to RF ground return
21
.
The path of the third component is from row
0
,
12
a
, down through transducer
20
b
, and the top three segments of column
1
,
14
b
, up through transducer
20
g,
through a segment of row
3
,
12
d
, down through transducer
20
h,
down through column
0
,
14
a
, and finally through column
0
switch
18
a
, to RF ground return
21
.
It is to be noted that no significant current is assumed to flow through any of the open (unselected) switches in columns
1
through
63
(
14
b
-
14
zz
), and rows
1
,
2
or
3
(
12
b
-
12
d
).
Unwanted current paths, similar to those just described, also exist through other unselected transducers located on row
0
,
12
a
, and columns
2
through
63
(
14
b
-
14
zz
).
Transducers
20
e
,
20
c
, and
20
h
have the largest magnitude of total unwanted current. For example, the current flowing through the unselected transducer
20
e
is the sum of the currents in all the other transducers in row
1
,
12
b
. All of this unwanted current flows through the conducting path of unselected row
1
,
12
b
. In this example, transducers
20
e
,
20
c
and
20
h
are on a selected column and unselected rows. The switching ratio is the poorest for this category when only one column is selected. This may also be seen in
FIGS. 6 and 7
.
In the following description it is to be noted that
FIGS. 5
,
6
,
9
,
10
,
15
,
16
and
18
are block diagrams representing four categories of transducer states used in calculations of relative RF currents to determine the switching ratios for different numbers of selected columns.
For example, in
FIG. 5
the block in the upper left part of the figure represents all of the transducers that are at Selected Row, Selected Column locations. Similarly, the block in the upper right part of the figure represents all of the transducers that are at Selected Row, Unselected Column locations. The block in the lower left part of the figure represents all of the transducers that are at Unselected Row, Selected column locations, and the block in the lower right part of the figure represents all of the transducers that are at Unselected Row, Unselected Column locatio
Baker Lamar T.
Buhler Steven A.
El Hatem Abdul M.
Elrod Scott
Gunning William F.
Barlow John
Fay Sharpe Fagan Minnich & McKee LLP
Feggins K.
LandOfFree
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