Fluorescent printer head

A fluorescent printer head capable of being subject to dynamic driving to reduce the number of ICs required. A shield electrode is provided between anode arrays having anode dots arranged in an offset manner and control electrodes are respectively arranged for the anode arrays. The anode arrays are subject to dynamic driving and selected by the control electrodes. Such construction of the fluorescent printer head ensures smooth selection of the anode arrays during the dynamic driving. Also, it eliminates non-uniformity in luminance of the anode dots of the anode arrays and accomplishes downsizing of the printer head and a reduction in manufacturing cost thereof due to a reduction in the number of ICs required.

BACKGROUND OF THE INVENTION 
This invention relates to a fluorescent printer head for optical writing to 
which a luminous principle of a fluorescent display device is applied, and 
more particularly to a fluorescent printer head adapted to be applied to 
various optical printers used for writing on a photosensitive drum, 
writing on a photosensitive film and the like. 
A conventional fluorescent printer head of the static drive type is 
typically constructed in such a manner as shown in FIG. 6. The 
conventional fluorescent printer head which is generally designated by 
reference numeral 100 in FIG. 6 includes a light-permeable anode substrate 
101, side plates 102 and a rear substrate 103, which are jointed to each 
other by means of sealing glass to provide an envelope 104. The envelope 
104 thus formed is then evacuated to a high vacuum. The anode substrate 
101 is provided on an inner surface thereof with two rows of anodes or two 
anode arrays 105, each of which is constructed of a plurality of anode 
dots arranged at predetermined intervals. The two anode arrays 105 are 
arranged so as to be parallel to each other and spaced from each other at 
a predetermined interval in a direction perpendicular to a longitudinal 
direction of the anode arrays 105. Also, the anode arrays 105 are so 
arranged that the anode dots of one of the anode arrays 105 and those of 
the other anode array 105 are kept from being aligned with each other with 
a space being interposed between the anode arrays 105. In other words, the 
anodes dots of the anode arrays 105 opposite to each other are arranged in 
an offset manner. 
The fluorescent printer head 100 thus constructed is of the static drive 
type, wherein a ratio of the number of anode dots of each of the anode 
arrays 105 to the number of output bits of each of ICs 106 corresponding 
thereto is set to be 1:1. More particularly, the anode dots are 
electrically separated from each other and led out of the arrays by means 
of wiring conductors arranged on the anode substrate 101. The ICs 106 each 
acting as a driver for anode driving are arranged on the anode substrate 
101 in a manner to be positioned outside the anode arrays 105 
corresponding thereto. The wiring conductors led out of the anode dots are 
connected to terminals of the ICs 106 corresponding thereto, respectively. 
The envelope 104 has two filamentary cathodes 107 stretchedly arranged 
therein in a manner to extend along the anode arrays 105 above the anode 
arrays, respectively. Also, the envelope 104 is provided therein with 
shield electrodes 108, which are respectively positioned outside the anode 
arrays 105, to thereby prevent electrons discharged from the cathodes 107 
toward the anode arrays from being impinged on the ICs 106. 
Driving of the fluorescent printer head 100 thus constructed is carried out 
by driving the ICs 106 to feed each of the anode dots of the anode arrays 
105 with a display signal. Luminescence of the anode dots is forwardly 
guided through the light-permeable anode substrate 101. 
In the conventional fluorescent printer head shown in FIG. 6, the ICs 106 
are arranged in the envelope 104. Alternatively, the fluorescent display 
device may be often constructed so that the anode substrate 101 
constituting a part of the envelope 104 is formed into a size somewhat 
larger than an outer configuration of the envelope 104 and the ICs 106 are 
arranged on a portion of the anode substrate 101 outwardly extending from 
the envelope 104. Also, the driver ICs 106 and connection terminals may be 
arranged on a resin tape and then connected through anisotropic conductive 
members to anode wirings led out to both sides of the envelope of the 
fluorescent printer head, resulting in the fluorescent printer head being 
constructed into a module structure. 
As will be noted from the above, in the fluorescent printer head 100 of the 
static drive type, not only the number of ICs required is increased but 
each of the ICs 106 acting as the driver for anode driving is increased in 
the number of output bits. The driver IC 106 accounts for a large part of 
a manufacturing cost of the fluorescent printer head 100. Thus, the 
conventional fluorescent printer head fails to be reduced in manufacturing 
cost or price. 
Also, employment of either the structure wherein the driver ICs 106 are 
arranged in the envelope 104 or the structure wherein the ICs are arranged 
on the portion of the anode substrate 101 outside the envelope renders 
downsizing of the fluorescent printer head highly difficult. Further, the 
structure wherein the tape having the ICs arranged thereon is connected to 
the anode wirings led out to both sides of the envelope substantially 
hinders downsizing of the fluorescent printer head which is constructed 
into a module. 
In order to avoid such disadvantages of the prior art described above, the 
inventors considered dynamic driving of the fluorescent printer head and, 
as a result, it was found that there exists a problem to be solved. More 
particularly, when the fluorescent printer head including two anode arrays 
wherein the anode dots are arranged in an offset manner is so constructed 
that each adjacent two anode dots between the anode arrays opposite to 
each other are connected to each other to reduce the number of bits of the 
anode driver to half, resulting in the anodes being driven while reducing 
a duty ratio to half, the number of bits required for the IC may be 
reduced to half. Unfortunately, this requires to arrange an electrode 
structure which permits any one of the two anode arrays to be selected in 
synchronism with driving of the anodes. 
For the purpose of selection of any one of the anode arrays, it would be 
considered to arrange a control electrode between each of the cathodes and 
each of the anode arrays. For example, a control electrode which has been 
conventionally commonly used for a fluorescent display device is 
constructed into a mesh-like structure, a wire-like structure or the like. 
The mesh-like control electrode has a disadvantage of causing a shade to be 
formed on a luminous section, leading to a variation in light quantity of 
the fluorescent printer head. Also, the conventional fluorescent printer 
head causes an interval between the anode arrays to be reduced, so that it 
is highly difficult to arrange two mesh-like control electrodes in a 
manner to keep the electrodes from being contacted with each other. 
Further, application of a cut-off voltage to one of the anode arrays while 
selecting the other anode array tends to hinder flowing of electrons into 
the anodes to be selected. The wire-like control electrode encounters, in 
addition to the above-described disadvantages of the mesh-like control 
electrode, a further disadvantage that it is required to increase 
positional accuracy in alignment between the anode dots and the wire-like 
control electrode. 
SUMMARY OF THE INVENTION 
The present invention has been made in view of the foregoing disadvantages 
of the prior art. 
Accordingly, it is an object of the present invention to provide a 
fluorescent printer head which is capable of realizing dynamic driving 
thereof. 
It is another object of the present invention to provide a fluorescent 
printer head which is capable of reducing the number of ICs required, to 
thereby accomplish downsizing of the fluorescent printer head and a 
reduction in manufacturing cost thereof. 
In accordance with the present invention, a fluorescent printer head is 
provided. The fluorescent printer head includes an anode substrate and 
first and second anode arrays arranged in a manner to extend in a 
longitudinal direction of the anode substrate and be spaced from each 
other at a predetermined interval in a direction perpendicular to the 
longitudinal direction. The first and second anode arrays each are formed 
of a plurality of anode dots and arranged so that the anode dots of the 
first anode array and the anode dots of the second anode array are not 
oppositely aligned with each other in the longitudinal direction of the 
anode substrate. Each one of the anode dots of the first anode array and 
each one of the anode dots of the second anode array which are adjacent to 
each other are commonly connected together. The fluorescent printer head 
also includes a drive means for driving each of the anode dots of the 
anode arrays, a first filamentary cathode arranged above the first anode 
array, a second filamentary cathode arranged above the second anode array, 
a shield electrode which is arranged between the first cathode and the 
second cathode so as to separate a space above the first anode array and a 
space above the second anode array from each other and to which a zero 
potential or a positive potential is applied, a first control electrode 
which is arranged on a side of arrangement of the first cathode based on 
the shield electrode and to which a selection voltage for selecting the 
first anode array is applied, and a second control electrode which is 
arranged on a side of arrangement of the second cathode based on the 
shield electrode and to which a selection voltage for selecting the second 
anode array is applied. 
In a preferred embodiment of the present invention, the shield electrode is 
constructed of a plate-like electrode member arranged above the anode 
substrate so as to be substantially vertical with respect to the anode 
substrate. 
In a preferred embodiment of the present invention, the shield electrode is 
positioned at an upper end thereof above the first and second cathodes. 
In a preferred embodiment of the present invention, the first and second 
control electrodes are so arranged that the first cathode is interposed 
between at least a part of the first control electrode and the shield 
electrode and the second cathode is interposed between at least a part of 
the second control electrode and the shield electrode. 
In a preferred embodiment of the present invention, the first and second 
control electrodes are arranged at least a part thereof above the first 
and second cathodes. 
In a preferred embodiment of the present invention, the fluorescent printer 
head further includes a second insulating substrate arranged opposite to 
the anode substrate, wherein the first and second control electrodes are 
mounted on an inner surface of the insulating layer through an insulating 
layer.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT 
Now, a fluorescent printer head according to the present invention will be 
described hereinafter with reference to FIGS. 1 to 5(e). 
Referring first to FIGS. 1 to 4, an embodiment of a fluorescent printer 
head according to the present invention is illustrated. 
A fluorescent printer head of the illustrated embodiment which is generally 
designated at reference numeral 1 includes an envelope 5 of a box-like 
shape which is formed by sealedly joining an anode substrate 2, side 
plates 3 and a rear substrate 4 to each other by means of sealing glass 
and then evacuated to a high vacuum. 
The anode substrate 2 is formed on an inner or upper surface thereof with 
first and second anode arrays 7 and 8 in a manner to extend in a 
longitudinal direction of the anode substrate 2 or a first direction. The 
first and second anode arrays 7 and 8 each are constituted by a plurality 
of anode dots 6. The anode dots 6 each include a frame-like conductive 
film and a phosphor layer deposited on the frame-like conductive film. The 
first and second anode arrays 7 and 8 are arranged so as to be spaced from 
each other at a predetermined interval in a direction perpendicular to the 
longitudinal direction of the anode substrate 2 or the first direction. 
The anode dots 6 of the first anode array 7 and those of the second anode 
array 8 are arranged so as to be kept from being oppositely aligned with 
each other in the direction perpendicular to the longitudinal direction of 
the substrate or the first direction. In other words, the anode dots of 
the first and second anode arrays 7 and 8 are generally arranged in a 
zigzag or offset manner in the first direction. Also, each one of the 
anode dots 6 of the first anode array 7 and each one of the anode dots 6 
of the second anode array 8 which are adjacent to each other are commonly 
connected together and led out to one side of each of the anode arrays 7 
and 8 by means of anode wirings 9 arranged on the anode substrate 2. 
The fluorescent printer head 1 is constructed into a dynamic drive 
structure. As described above, each one of the anode dots 6 of the first 
anode array 7 and each one of the anode dots 6 of the second anode array 8 
which are adjacent to each other are commonly connected together and led 
out to one side of each of the anode arrays 7 and 8 by means of the anode 
wirings 9 on the anode substrate 2. The envelope 5 is provided therein 
with ICs 10 each acting as an anode drive means in a manner to be arranged 
outside one of the anode arrays 7 and 8. The wiring conductors led out of 
the anode dots are connected to terminals of the ICs 10 corresponding 
thereto, respectively. Such construction permits the number of ICs 10 
required to be reduced to half as compared with the conventional 
fluorescent printer head of the static drive type described above. 
The anode substrate 2 is provided on the inner or upper surface thereof 
with a flat control electrode 11. The flat control electrode 11 is made of 
a conductive film of aluminum or the like and arranged on the same plane 
as the anode dots 6 while surrounding the anode dots 6 and anode wirings 
9. During driving of the fluorescent printer head 1, a positive voltage is 
kept applied to the flat control electrode 11, to thereby render an 
electric field therearound constant. 
The envelope 5 is also provided therein with first and second filamentary 
cathodes 12 and 13, which are stretchedly arranged above the first and 
second anode arrays 7 and 8 so as to extend along the anode arrays 7 and 8 
or in the above-described first direction, respectively. Also, the rear 
substrate 4 is formed on an inner surface thereof with a light-permeable 
conductive film or NESA film 14 acting as an antistatic means. The NESA 
film 14 is formed thereon with an anti-reflection layer which functions to 
absorb light emitted from the anode arrays 7 and 8 to prevent reflection 
of the light toward the anode arrays. 
The fluorescent printer head 1 also includes a shield electrode 20 arranged 
between the first anode array 7 and the second anode array 8. The shield 
electrode 20 is made in the form of a flat electrode member and arranged 
so as to be substantially perpendicular to the anode substrate 2. Also, 
the shield electrode 20 is positioned at a lower end thereof above the 
anode substrate 2 with a micro-interval being defined therebetween. In the 
illustrated embodiment, the micro-interval may be set to be as small as 
about 0.3 mm. An insulating layer may be interposedly arranged between the 
lower end of the shield electrode 20 and the anode substrate 2. Further, 
the shield electrode 20 is so arranged that an upper end thereof is 
positioned above the first and second cathodes 12 and 13, resulting in 
electrons emitted from the cathodes 12 and 13 from traveling beyond the 
shield electrode 20. 
The fluorescent printer head 1 of the illustrated embodiment also includes 
a first control electrode 30 arranged in a space defined on a side of the 
first cathode 12 based on the shield electrode 20, as well as a second 
control electrode 31 arranged in a space defined on a side of the second 
cathode 13 based on the shield electrode 20, as shown in FIGS. 1 to 3. The 
first and second control electrodes 30 and 31, as shown in FIG. 1, each 
are formed into a substantially L-shape in section taken in a direction 
perpendicular to the above-described first direction, resulting in 
including a vertical plate portion and a horizontal flange plate portion. 
The first and second control electrodes 30 and 31 each are so arranged 
that the flange plate portion is rendered parallel to the inner surface of 
the anode substrate 2 while defining a micro-interval between the flange 
plate portion of each of the control electrodes 30 and 31 and the anode 
substrate 2. In the illustrated embodiment, the microinterval may be set 
to be as small as about 0.5 mm. The first and second control electrodes 30 
and 31 each are arranged at an upper end thereof above the cathodes 12 and 
13. Thus, the cathodes 12 and 13 are surrounded by the shield electrode 20 
and both control electrodes 30 and 31. In the illustrated embodiment, the 
cathodes 12 and 13 are arranged between the shield electrode 20 and the 
control electrode 30 and between the shield electrode 20 and the control 
electrode 31, respectively. 
Now, the manner of driving of the fluorescent printer head 1 of the 
illustrated embodiment thus constructed will be described hereinafter. 
The first and second cathodes 12 and 13 are kept fed with electric power, 
resulting in emission of electrons therefrom being continued. Also, a zero 
voltage or a positive voltage is kept applied to the shield electrode 20 
and a positive voltage is kept applied to the flat control electrode 11. 
Pairs of dots each consisting of each one of the anode dots 6 of the first 
anode array 7 and each one of the anode dots 6 of the second anode array 8 
which are adjacent to each other are driven in order by the ICs 10. Then, 
a selection signal is fed to the first control electrode 30 or second 
control electrode 31 in synchronism with scanning of the anode dots. For 
example, a positive voltage is applied to the first control electrode 30 
in synchronism with a scanning timing of the anode arrays, during which a 
negative voltage is applied to the second control electrode 31. This 
permits electrons to enter between the first control electrode 30 having 
the positive voltage applied thereto and the shield electrode 20, 
resulting in impinging on the anode dots 6 of the first anode array 7 
which have fed with the drive signal. The electrons are kept from entering 
between the second control electrode 31 having the negative voltage 
applied thereto and the shield electrode 20, because the electrons are 
obstructed by the electric field. 
The shield electrode 20 is arranged so as to upwardly extend at the upper 
end thereof from the cathodes 12 and 13, to thereby prevent electrons from 
flowing into the anode array of which luminescence is not intended or 
desired. The shield electrode 20 having the positive voltage applied 
thereto prevents a potential of the control electrode having the negative 
voltage applied thereto from affecting the anode array of which 
luminescence is intended or desired and which is positioned on the side of 
the control electrode having the positive voltage applied thereto, so that 
the anode dots 6 on the side of the control electrode having the positive 
voltage applied thereto may be selectively excited for luminescence. 
A decrease in width of a space between the upper end of the shield 
electrode 20 and each of the control electrodes 30 and 31 permits a 
reduction in reactive current flowing to the anode arrays 7 and 8 between 
the shield electrode 20 and the control electrodes 30 and 31 and to the 
control electrodes 30 and 31. 
Luminescence of the anode dots 6 is guided forwardly of the anode substrate 
2 through the light-permeable anode conductor and anode substrate 2. The 
anti-reflection layer arranged on the inner surface of the rear substrate 
4 absorbs light emitted from the anode dots 6 to prevent reflection of 
light toward the anode dots. Absence of the anti-reflection layer causes 
light returning to the anode side to leak from between the anode dots 6 
and the flat control electrode 11 toward the anode substrate 2, resulting 
in deterioration in display contrast of the luminous dots or anode dots 6. 
In the fluorescent printer head 1 of the illustrated embodiment, as 
described above, the shield electrode 20 is provided between the anode 
arrays 7 and 8 having the anode dots 6 arranged in an offset manner and 
the control electrodes 30 and 31 are respectively arranged for the anode 
arrays 7 and 8, wherein the anode arrays 7 and 8 are subject to dynamic 
driving and selected by the control electrodes 30 and 31. Such 
construction of the fluorescent printer head 1 ensures smooth selection of 
the anode arrays 7 and 8 during the dynamic driving, eliminates 
nonuniformity in luminance of the anode dots 6 of the anode arrays 7 and 
8, and accomplishes downsizing of the fluorescent printer head 1 and a 
reduction in manufacturing cost thereof due to a reduction in the number 
of ICs required. 
In the illustrated embodiment, the shield electrode 20 and first and second 
control electrodes 30 and 31 each may be provided on a surface thereof 
with an anti-reflection film. This further enhances absorption of light 
emitted from the anode dots 6, to thereby further improve the display 
contrast. 
Application of a positive potential to the first control electrode 30 and 
application of a negative potential to the second control electrode 31 
permit such an electric field and a locus of electrons as shown in FIG. 4 
to be formed in the envelope 5. As will be noted from FIG. 4, electrons 
emitted from the cathode 12 on the side of the first control electrode 30 
are substantially caused to impinge on the anode array 7 on the side of 
the control electrode 30 while being kept from impinging on the adjacent 
anode array 8 beyond the shield electrode 20. More particularly, electrons 
emitted from the cathode on the side of the anode array of which 
luminescence is desired is prevented from going over the shield electrode 
20 by an electric field due to a negative potential applied to the 
opposite control electrode. Also, the cathode 13 on the side of the second 
control electrode 31 is surrounded by a negative electric field of the 
second control electrode 31, to thereby be kept from emitting electrons. 
Thus, the illustrated embodiment substantially fully prevents any 
unnecessary luminescence, to thereby ensure luminescence of only the anode 
dots 6 selected. 
Referring now to FIGS. 5(a) to 5(e), modifications of the control 
electrodes are illustrated. Control electrodes 40 and 41 shown in FIG. 
5(a) are formed into the same shape as the control electrodes 30 and 31 
described above and arranged in an inverted manner. Control electrodes 50 
and 51 shown in FIG. 5(b) each are formed of a flat electrode material 
into the same shape and size as the shield electrode 20. Control 
electrodes 60 and 61 shown in FIG. 5(c) each are formed into a flat shape 
and mounted on the inner surface of the rear substrate 4 through an 
insulating layer 62. Thus, it will be noted that the illustrated 
embodiment is not limited to mounting of the control electrodes on the 
side of the anode substrate 2. Control electrodes 70 and 71 shown in FIG. 
5(d) each are formed into a semi-cylindrical shape and the cathodes 12 and 
13 are positioned at a center of the control electrodes 70 and 71, 
respectively. Control electrodes 80 and 81 shown in FIG. 5(e) each are 
formed into a substantially U-shape and so arranged that an opening 
thereof inwardly faces. 
It was found that the control electrodes 30 and 31 described above and the 
control electrodes 40 and 41 shown in FIG. 5(a) exhibit increased 
mechanical strength as compared with the control electrodes 50 and 51 of a 
shape like a flat plate shown in FIG. 5(b). Also, the control electrodes 
80 and 81 of a U-shape shown in FIG. 5(e) exhibit mechanical strength 
larger-than the control electrodes 40 and 41 shown in FIG. 5(a). 
In the illustrated embodiment, the control electrodes so function that a 
positive electric field generated by the control electrode on the 
luminescence side surrounds the cathode to derive electrons from the 
cathode, to thereby impinge the electrons on the anode dots and a negative 
electric field generated by the control electrode on the non-luminescence 
side prevents the cathode from emitting electrons. Such a function of the 
control electrodes depends on an area of the control electrodes, an 
interval between the control electrodes and the cathode, and the like. The 
control electrodes may be formed into a shape which does not interfere 
impingement of electrons on the anode dots and permits a negative electric 
field to be produced around the cathodes. 
The fluorescent printer head of the illustrated embodiment constructed as 
described above may be suitably used as an optical printer head for 
forming an optical latent image on a photosensitive drum of any printing 
equipment, an optical printer head for transferring a video image on a 
developing paper or a film, an optical printer head for an optical 
recording equipment and the like. 
As can be seen from the foregoing, the fluorescent printer head of the 
present invention is so constructed that the shield electrode is provided 
between the anode arrays having the anode dots arranged in an offset 
manner and the control electrodes are respectively arranged for the anode 
arrays, wherein the anode arrays are subject to dynamic driving and 
selected by the control electrodes. Such construction of the fluorescent 
printer head ensures smooth selection of the anode arrays during the 
dynamic driving. Also, it eliminates non-uniformity in luminance of the 
anode dots of the anode arrays and accomplishes downsizing of the printer 
head and a reduction in manufacturing cost thereof due to a reduction in 
the number of ICs required. 
While a preferred embodiment of the invention has been described with a 
certain degree of particularity with reference to the drawings, obvious 
modifications and variations are possible in light of the above teachings. 
It is therefore to be understood that within the scope of the appended 
claims, the invention may be practiced otherwise than as specifically 
described.