Electrode array for a print head

An electrode array is disclosed for a print head of an electrooptical facsimile recording device for recording spots line by line. The recording spots are exposed on a recording medium through light gates (35). These light gates (35) are arranged in rows and are defined by high field strength edge portions (switching areas) of spot electrodes (22, 22') and main electrodes (23, 24, 25, 26). Each spot electrode (22, 22') is associated with n light gates (35, 19), each spot-electrode row (27, 28) being associated with n main electrodes, so that n(N-n) light gates are formed by N electrodes. The electrode array in designed so that each spot-electrode row (27, 28) is between at least wo elongated main electrodes; each spot electrode 22 has n switching areas (20, 21) which are located adjacent n respective main electrodes.

TECHNICAL FIELD 
The present invention relates to an electrode array for a print head of an 
electrooptical facsimile recording device. 
BACKGROUND ART 
An electrode array for a print head of a facsimile recording device for 
recording a line of spots is disclosed in published German patent 
application DE-OS No. 34 40 406. A print head of this kind is intended for 
use as part of an optical printer where it is located between a light 
source and a recording medium. The recording medium is exposed one line at 
a time through the print head. 
DISCLOSURE OF INVENTION 
It is one object of the invention to provide an improved electrode array 
for a linear array print head for a facsimile machine or the like which 
permits shorter printing times. It is another object to provide an 
improved electrode array for a print head which does not require any 
insulating layer between the electrodes in simple electrode arrays. 
In accordance with one aspect of the present invention, there is provided 
on the surface of the electrooptical substrate of the print head electrode 
array a row of spot electrodes, with adjacent portions of a first 
elongated main electrode on a first side thereof defining a first row of 
light-gate areas, and a second main elongated electrode on the other side 
of the row of spot electrodes similarly defining a second row of 
light-gate areas. Thus no insulating layer is required for a simple array 
of two rows of light-gate areas located between two main electrodes. 
Furthermore, undesirable "crosstalk" is eliminated and switch times are 
reduced. 
In accordance with another aspect of the present invention, in order to 
expose a single recorded line there are provided a total of N/M rows (6, 
6') of said spot electrodes and at least N-1 of said elongated electrodes 
where N is an integer greater than 2, and M is the number of outputs of a 
1-of-M demultiplexer used for energizing purposes. 
In accordance with yet another aspect of the present invention, there are 
provided N rows of light-gates (7, 8) each having a height d, with the 
distance between the light-gate rows (15, 16, 17, 18) to be energized 
directly one after the other is d(m.+-.1/M), where m is an integer greater 
than or equal to 0. 
In accordance with still another aspect of the present invention, the light 
gates are rectangular and are arranged so that their sides and the line 
connecting the light-gate row include an angle of 45.degree..

BEST MODE FOR CARRYING OUT THE INVENTION 
FIG. 1 shows part of a first embodiment of an electrode array in accordance 
with the invention. The electrode array is of a periodic design which may 
be repeated for the remainder of the array (not shown). The electrodes are 
disposed on the one side of a PLZT substrate 1. To the other side of the 
substrate, an aperture plate is attached which has window-like openings in 
those areas where light is to pass (not shown). The PLZT substrate 1 is a 
known electrooptically active ceramic consisting of lead, lanthanum, 
zirconate and titanate. The electrode array consists of three elongated 
main electrodes 2, 3, 4 and of a plurality of individual spot electrodes 
5, 5'. The spot electrodes 5, 5' are arranged in two spot-electrode rows 
6, 6'. The main electrodes 2, 3, 4 and the spot-electrode rows 6, 6' are 
parallel to each other, two main electrodes 2, 3; 2, 4 being located on 
opposite sides of each spot-electrode row 6, 6'. 
The specific design details of the spot electrodes 5, 5' will now be 
described using the spot electrode 5a as an example. The spot electrode 5a 
has two border areas 9, 10 from which a homogeneous electric field emerges 
with a higher field strength than from the other areas of the spot 
electrode. In the following, also in the description of the other 
embodiments, these higher field strength border areas will be referred to 
as switching areas. The spot electrode 5a consists of a central rectangle 
5b and of two projecting portions 47, 48 located on two opposite sides of 
the rectangle. Those sides of the projecting portions 47, 48 which are 
parallel to the long sides 5c of the rectangle form the switching areas 9, 
10. An area 12 of the main electrode 2 acts as a counterelectrode to the 
switching area 9 of the spot electrode 5a and will be referred to as 
switching area 12. Between the switching area 9 and the switching area 12, 
an electric field is applied which causes the electrooptical effect; this 
area is referred to as light gate 8. Correspondingly, a light gate 7 is 
present between the switching area 10 and a switching area 11. 
Furthermore, the spot electrodes have an area 13 for a bonding wire 14 to 
be attached. When attaching the latter, care should be taken that it will 
not be located above the light gate 7. In FIG. 1, the bonding wire 14 is 
shown only at the spot electrode 5a, but it should be understood that 
similar bonding wires are provided to the other spot electrodes 5, 5'. The 
location of the two switching areas 9, 10 is so chosen that two directly 
adjacent recording spots on one recorded line are exposed through the 
corresponding light gates 7 and 8. 
The electrode array of FIG. 1 is energized by a 1-of-2 demultiplexer using 
time-division multiplexing. More particularly, in a first time interval, 
main electrode 2 is energized and in a second time interval, main 
electrodes 3 and 4 are jointly energized. Since the recording medium is 
then moving in a direction perpendicular to the linear electrode array, 
the light-gate rows 15 and 16 and the light-gate rows 17 and 18 are 
separated by distances of d(m+1/2), where d is the distance between two 
opposite switching areas forming the height of one light-gate row, and m 
an integer greater than or equal to 0. The distances between the 
light-gate rows 15 and 17 and between the light-gate rows 16 and 18 are 
dm', where m' is a positive integer. To reproduce a complete recorded 
line, not only the light-gate rows 15 and 16 formed by the spot electrodes 
5 and the main electrodes 2 and 3, but also the light-gate rows 17 and 18 
formed by the spot electrodes 5' of the spot-electrode row 6' and the main 
electrodes 2 and 4 are needed. The recording spots of a recorded line are 
exposed through four light-gate rows, recording spots adjacent on the 
recorded line being exposed through successive light-gate rows. 
The second embodiment, shown in FIG. 2, differs from the first embodiment 
in two aspects. First of all, instead of the single central electrode 2 of 
FIG. 1, there are two adjacent central electrodes 24, 25, and secondly, 
the two switching areas 20, 21 of the spot electrodes 22 are arranged 
differently. The electrode array of the second embodiment has four 
strip-shaped main electrodes 23, 24, 25 and 26, and two spot-electrode 
rows 27 and 28. This results in two sections 36, 37 which can be energized 
separately and which each have two light-gate rows 29, 30 and 29', 30'. 
The first row of light gates 35 formed by the upper switching areas 20 of 
the upper row of spot electrodes 22 and the switching areas 33 of the top 
main electrode 23 result in the first upper light-gate row 29. The second 
row of light gates 19 formed by the lower switching areas 21 of the spot 
electrodes 22 and the switching areas 34 of the upper central main 
electrode 24 result in the second upper light-gate row 30. Similarly, the 
third row of light gates 35' formed by the upper switching areas 20' of 
the lower row of spot electrodes 22' and the switching areas 33' of the 
lower central main electrode 25 result in the first lower light-gate row 
29' and the fourth row of light gates 19' formed by the lower switching 
areas 21' of spot electrodes 22' and the switching areas 34' of the bottom 
main electrode 26 result in the second lower light-gate row 30'. This 
electrode array is energized with a 1-of-2 demultiplexer using 
time-division multiplexing. In other words, in alternating fashion, either 
the upper section 36 the light-gate row 29 is energized via the main 
electrode 23 or else the light-gate row 30 is energized via the main 
electrode 24 in turn. The same is true in analogous fashion for the lower 
section 37. Compared to the first embodiment, this embodiment has the 
advantage of permitting simpler data conditioning. Since the recording 
medium is moving during the switching period, the light-gate rows 29 and 
30 and the light-gate rows 29' and 30' are separated by distances of 
d(m+1/2), where d is the height of one light gate and m an integer. The 
switching period and the feed rate of the recording medium are so chosen 
that the recording medium is moved on by the distance 1/2 in one switching 
operation. The distances between the light-gate rows 29 and 29' and the 
light-gate rows 20 and 30' are m'd where m' is a positive integer. 
The switching areas 20, 21 of the spot electrodes 22, 22' are arranged so 
that two recording spots which are exposed through two light gates 
associated with a common spot electrode 22 are printed on the recorded 
line separated by a third recording spot. This permits the bonding pad 38 
on each of the spot electrodes 22, 22' to be formed at the center of the 
electrode area. 
The electrode array of FIG. 3 is the third embodiment and is also suitable 
for energization with a 1-of-2 demultiplexer using time-division 
multiplexing. It has also two spot-electrode rows 40, 41 and four main 
electrodes 42, 43, 44, 45. The spot electrodes 46 have a structure similar 
to that of the first embodiment. Each spot electrode 46 also consists of a 
rectangle 46a and of two projecting portions 49, 50 located on two 
opposite sides of the rectangle, the latter having a recess 51 at one 
corner. Those sides of the projecting portions 49, 50 which are parallel 
to the long sides 46b of the rectangle form the switching areas 56, 57. On 
their sides facing the spot electrodes 46, each of the four main 
electrodes 42, 43, 44, 55 has projecting portions with the switching areas 
58, 59 each located so as to be opposite a switching area 56, 57 of the 
spot electrodes. The areas between the switching areas 56, 58 and between 
the switching areas 57, 59 form the light gates 60 and, thus, the 
light-gate rows 52, 53, 52', 53'. Furthermore, the size of the spot 
electrodes 46 is so chosen that the distances between the light-gate rows 
52 and 53 and the light-gate rows 52' and 53' equal d(m+1/2) and the 
distances between the light-gate rows 52 and 52' and the light-gate rows 
53 and 53' are m'd, where m and m' are positive integers and d is the 
distance between two opposite switching areas. The assignment of the light 
gates to the recording spots on one recorded line corresponds to that of 
the first embodiment. 
The electrode array of FIG. 4 is the fourth embodiment and, as the two 
preceding embodiments, is suitable for energization using time-division 
multiplexing. It also has two spot-electrode rows 61, 62 and four main 
electrodes 63, 64, 65, 66. The light gates 71 are also defined by two 
opposite switching areas 67, 69 and 68, 70 and are designed as light-gate 
rows 77, 78, 77', 78'. The light gates 71 are hatched in FIG. 4. The main 
electrodes 63, 64, 65, 66 are strip-shaped and have narrow, elongate 
projecting portions 75. Those sides of the projecting portions parallel to 
the strip-shaped main electrodes are oriented at an angle of 45.degree. in 
relation to the longitudinal axis of the strip. The ends of the angled 
portions form the switching areas 69,70 of the main electrodes 63, 64, 65, 
66. The projecting portions of the main electrodes 63 and 66 are longer 
than those of the main electrodes 64 and 65. Each spot electrode 72 is 
interposed between the main electrodes 63, 64 and 65, 66 as spot-electrode 
rows 61 and 62. Each of them is formed by a two-leg area, the two legs 73, 
74 including an angle of 135.degree.. The one leg 73 is parallel to the 
projecting portions 75 and interposed between two narrow projecting 
portions 75 of a main electrode. The other leg 74 is parallel to the sides 
of the narrow projecting portions 75 forming the switching areas 69, 70 
and interposed between two of these sides of projecting portions 75 of 
adjacent continuous electrodes. The sides of the leg 74 opposite the 
switching areas 69, 70 form the switching areas 67, 68 of the spot 
electrode 72. The distance between two opposite switching areas 67, 69 and 
68, 70 is equal to the length of the switching areas 69, 70. The light 
gates 71 thus are square, with the sides of the light gates making an 
angle of 45.degree. with the longitudinal axis of each of the light-gate 
rows 77, 78 77', 78'. Thus, if a recording medium is exposed, the 
recording spots are also rotated by 45.degree.. Compared to the electrode 
arrays of the preceding embodiments, this electrode array permits a 
different dot pattern on the recording medium with which, for example, 
diagonals can be reproduced more clearly. Furthermore, the narrow 
projecting portions 75 reduce the cross-coupling behavior between the spot 
electrodes 72. 
The electrode array of FIG. 5 is the fifth embodiment and is particularly 
suitable for energization with a 1-of-3 demultiplexer using time-division 
multiplexing. To this end, the electrode array has two spot-electrode rows 
81, 82 and five main electrodes 83, 84, 84', 85, 85'. Each spot electrode 
consists of a rectangle 87 and of three projecting portions 88, 89, 90 
whose end faces form the switching areas 91, 92, 93. The five main 
electrodes 83, 84, 84', 85, 85' are parallel to the spot-electrode rows 
and also have projecting portions with switching areas 94, 95, 96. The 
main electrode 83 is located between the two spot-electrode rows 81, 82, 
and the main electrodes 84, 85 and 84', 85' are arranged in pairs at the 
outer long sides of the spot-electrode rows 81, 82. The projecting areas 
of the main electrode 84 intersect the main electrode 85, and the 
projecting areas of the main electrode 85' intersect the main electrode 
84'. The main electrodes at these intersections 97 are separated by an 
insulating layer (not shown). The switching areas 91, 92, 93 of the spot 
electrodes 86 and the switching areas 94, 95, 96 of the main electrodes 
83, 84, 84', 85, 85' all have the same width d. The spot electrodes and 
the main electrodes are associated with each other so that the switching 
areas 91, 94; the switching areas 92, 95, and the switching areas 93, 96 
are located opposite each other at the distance d. The areas between the 
switching areas form the light gates 98, 99, 100. To this end, the 
switching areas 91, 92 are located on the same side of each spot electrode 
86, and the switching areas 93 are located on the opposite side of the 
switching areas 91, 92 of each spot electrode 86. The recording spots 
exposed through the associated light gates are each reproduced side by 
side on the recorded line, the recording spot exposed through the light 
gate 100 being located between the two others. The light gates are square, 
their sides have the length d. The light gates 98 form the light-gate rows 
101 and 101', the light gates 99 form the light-gate rows 102 and I02', 
the light gates 100 form the light-gates rows 103 and 103'. The electrode 
array is designed so that it can be energized using time-division 
multiplexing. To switch the light gates, each of the corresponding spot 
electrodes is energized and the main electrodes 83, 84, 84' and 85, 85' 
are energized one after the other. The main electrodes 84, 85, 85' are 
energized in pairs. 
To compensate for the advance of the recording medium during the switching 
period between the main electrodes, the light-gate rows 101, 101' are 
staggered in relation to the light-gate rows 102, 102' by the distance 
d(m.sub.1 .+-.1/3) and the latter are staggered in relation to the 
light-gate rows 103, 103' by the distance d(m.sub.2 .+-.1/3) in the 
direction of movement of the recording medium. Since each spot electrode 
contributes to form three light gates, and since only one bond is needed 
for each spot electrode, this electrode array permits a high resolution, 
since the resolution typically is limited by the closeness of the bonds. 
Therefore, this electrode array is suitable also for reproducing a 
three-color print. 
The electrode array of FIG. 6 is the sixth embodiment and is particularly 
suitable for energization with a 1-of-4 demultiplexer using time-division 
multiplexing. To this end, the electrode array has two-spot electrode rows 
104, 104' and six main electrodes 106, 107, 108, 108', 109 and 109'. Each 
spot electrode 105 consists of a rectangle 110 and of four projecting 
portions 111, 112, 113, 114 whose end faces form the switching areas 115, 
116, 117, 118. The spot electrodes and the six main electrodes, which also 
have projecting portions, are arranged similarly to the electrodes of the 
fifth embodiment. The difference is that instead of the main electrode 83 
(FIG. 5), there are two main electrodes 106 and 107 (FIG. 6). The 
projecting portions 119 of the main electrode 106 intersect the main 
electrode 107, and the projecting portions 120 of the main electrode 107 
intersect the main electrode 106. At these intersections, the electrodes 
are separated by an insulating layer (not shown). The end faces of the 
projecting portions of the main electrodes 106, 107, 108, 108', 109, 109' 
form the switching areas 122, 123, 124, 125 of the main electrodes 109, 
108, 106, and 107, respectively. The switching areas 115, 116, 117, 118 of 
the spot electrodes 105 and the switching areas 122, 123, 124, 125 all 
have the same width d. The spot electrodes and the main electrodes are 
associated with each other so that the switching areas 115, 122; the 
switching areas 116, 123; the switching areas 117, 124, and the switching 
areas 118, 125 are located opposite each other at distances d. To this 
end, two switching areas 115, 116 and 117, 118 each are located on one 
side of each spot electrode, but in pairs on opposite sides. The areas 
between opposite switching areas form the light gates 126, 127, 128, 129 
which are square. Their sides have the length d. The light gates 126 form 
the light-gate rows 130 and 130', the light gates 127 form the light gate 
rows 131 and 131', the light gates 128 form the light-gate rows 132 and 
132', and the light gates 129 form the light-gate rows 133 and 133'. To 
switch the light gates, the main electrodes 106, 107, 108, 108', 109 and 
109' are sequentially energized, with the main electrodes 108, 108' and 
109, 109' being energized in pairs. To compensate for the advance of the 
recording medium during the switching operation between the main 
electrodes, the light-gate rows are staggered in relation to each other by 
the distances d(m.sub.i .+-.1/4) in the direction of movement of the 
recording medium. By increasing the number of the light gates which are 
energized via a bonding wire, an extremely high resolution of 32 recording 
spots per mm can be achieved. 
Alternatively, the electrode array of the sixth embodiment may be modified 
for energization with a 1-of-3 demultiplexer using time-division 
multiplexing. To this end, the main electrodes 109 and 109' and the 
corresponding projecting portions 111 with the switching areas 115 are 
omitted and the other projecting portions with their switching areas are 
arranged so that a complete recorded line can again be exposed. The 
advantage of this electrode array as compared to that of the fifth 
embodiment is that the intersecting areas 119, 120 are limited to two main 
electrodes. 
The present invention has been described above with regard to the 
structure, function and use of a several presently contemplated specific 
embodiments of the invention. It should be appreciated by those skilled in 
the art that many modifications and variations are possible. Accordingly 
the exclusive rights afforded hereby should be broadly construed, limited 
only by the spirit and scope of the appended claims.