Ink jet head having an outer wall of ink cavity of piezoelectric material

An ink jet head has coaxially disposed inner and outer cylindrical tubes with the outer cylindrical surface of the inner cylindrical tube spaced from the inner cylindrical surface of the outer cylindrical tube to form an ink cavity therebetween from which ink is supplied through one or more arrays of ink jet nozzles. Only the outer tube is a piezoelectric material so that the outer tube vibrates radially when electrically excited to produce vibrations in the ink in the ink cavity whereby a stream of ink droplets is supplied from each of the ink jet nozzles. In embodiments having only multiple arrays of ink jet nozzles, if desired, only the inner cylindrical tube or both the inner and outer cylindrical tubes can be formed of a piezoelectric material. If both of the tubes are formed of a piezoelectric material, the operating frequencies, which are preferably resonant, of the two tubes must then be matched.

Cross reference is made to the copending patent application of Gary L. 
Fillmore et al for "Ink Jet Head," Ser. No. 958,916, filed Nov. 8, 1978, 
and assigned to the same assignee as the assignee of this application. 
When a plurality of ink jet nozzles is connected to an ink cavity, it is 
desired that the ink droplets produced from the streams passing through 
each of the nozzles have substantially the same break-off point, be 
substantially uniform in size, have substantially uniform spacing between 
the droplets, and be satellite free. This insures that the quality of the 
print from each of the nozzles will be substantially the same. 
To obtain this uniformity between the droplets of the various streams, it 
is necessary that the perturbations applied to each of the ink streams of 
the nozzles be substantially uniform and that the nozzles be of uniform 
quality. Furthermore, for the production of the droplets to be satellite 
free, the parturbations must be sufficiently large. It also is a requisite 
for the perturbations to not only be substantially uniform but to be 
reproducible throughout the time that the droplets are being produced. 
It also is necessary that the transducer or driver, which produces the 
vibrations to create the perturbations in the ink streams, be capable of 
producing the droplets at the desired frequency. This is determined by the 
overall requirements of the ink jet system including the size of the 
droplets, the spacing between the droplets on the medium on which the 
droplets are impinged, the rate at which the droplets can be charged, and 
the rate of relative movement between the medium and the nozzles. Thus, 
the transducer or driver must be capable of operating at a specific 
frequency. 
The present invention accomplishes this through providing a pair of 
elements with one of the elements preferably surrounding the other and the 
elements having their longitudinal axes preferably coaxial and at least 
parallel. With multiple arrays of ink jet nozzles, at least one of the 
inner and outer elements, which are preferably right circular cylindrical 
tubes, is formed of a piezoelectric material and is polarized to vibrate 
substantially perpendicular to its longitudinal axis when electrically 
excited so that nozzles, which have their axes disposed substantially 
perpendicular to the longitudinal axis of the inner element, will have the 
streams of ink droplets supplied therefrom uniformly. With only a single 
array or a single nozzle, only the outer element is formed of a 
piezoelectric material. 
With the ink jet head of the present invention capable of having a 
plurality of arrays of ink jet nozzles supplying streams of ink droplets 
therefrom at the same time, a plurality of separate recording mediums can 
have ink droplets supplied thereto from a single ink jet head. Thus, a 
relatively low cost print head for a plurality of separate recording 
mediums is provided. 
An object of this invention is to provide an ink jet head having a 
plurality of arrays of ink jet nozzles. 
Another object of this invention is to provide a unique ink jet head. 
A further object of this invention is to provide a method for forming an 
ink jet head having a plurality of arrays of ink jet nozzles. 
Still another object of this invention is to provide a method for forming a 
unique ink jet head. 
The foregoing and other objects, features, and advantages of the invention 
will be apparent from the following more particular description of 
preferred embodiments of the invention as illustrated in the accompanying 
drawings.

Referring to the drawings and particularly FIGS. 1-3, there is shown an ink 
jet head 10 of the present invention. The ink jet head 10 includes an 
inner cylindrical element 11, which is formed of metal, for example, and 
an outer cylindrical tube 12, which is formed of a piezoelectric material, 
disposed in surrounding relation to the inner cylindrical element 11 and 
spaced therefrom. 
One end of the element 11 is disposed within a circular recess 14 in an 
entry end plate 15, which is circular. A mounting screw 16 secures the 
entry end plate 15 to the adjacent end of the inner cylindrical element 
11. 
The other end of the element 11 is disposed within a circular recess 17 in 
an exit end plate 18, which is circular. A mounting screw 19 secures the 
exit end plate 18 to the adjacent end of the inner cylindrical element 11. 
The outer cylindrical tube 12 has one end disposed within an annular groove 
20 in the entry end plate 15 and its other end disposed within an annular 
groove 21 in the exit end plate 18. Thus, the outer cylindrical tube 12 is 
retained between the end plates 15 and 18 when they are secured to the 
inner cylindrical element 11. 
Accordingly, the outer cylindrical tube 12 has its inner cylindrical 
surface 22 spaced the same distance from outer cylindrical surface 23 of 
the inner cylindrical element 11 throughout the length and around the 
entire circumference. Thus, an annular ink cavity 24 is formed between the 
inner cylindrical surface 22 of the outer cylindrical tube 12 and the 
outer cylindrical surface 23 of the inner cylindrical element 11. 
The circular recess 14 in the entry end plate 15 has an annular groove 25 
adjacent its circumference to receive an O-ring 26 to form a seal between 
one end of the inner cylindrical element 11 and the entry end plate 15. 
The entry end plate 15 has a second O-ring 27, which is disposed within 
the annular groove 20, engaging the end of the outer cylindrical tube 12 
in the annular groove 20 to form a seal therebetween. Accordingly, the 
O-rings 26 and 27 cooperate to seal the ink cavity 24 relative to the 
entry end plate 15. 
The circular recess 17 in the exit end plate 18 has an annular groove 28 
adjacent its circumference to receive an O-ring 29 to form a seal between 
the end of the inner cylindrical element 11 and the exit end plate 18. The 
exit end plate 18 has a second O-ring 30, which is disposed within the 
annular groove 21, bearing against the end of the outer cylindrical tube 
12 disposed therein to form a seal therebetween. Accordingly, the O-rings 
29 and 30 cooperate to seal the ink cavity 24 relative to the exit end 
plate 18. 
The ink cavity 24 has pressurized, conductive ink supplied thereto from a 
pressurized source such as a pump, for example, through a passage 31 in 
the entry end plate 15. Whenever it is desired to flush the ink cavity 24, 
the pressurized ink flows from the ink cavity 24 through a passage 32 in 
the exit end plate 18 to an ink reservoir or the like connected to the 
suction side of the pump. This flow path from the ink cavity 24 is 
normally blocked. 
The ink is grounded in any suitable manner. If the entry end plate 15 is 
formed of metal, it could be grounded to ground the ink in the cavity 24. 
If the entry end plate 15 is formed of a plastic such as an acetal plastic 
sold under the trademark Delrin, for example, then the ink must be 
grounded in some other suitable manner. 
The outer cylindrical tube 12 has a plurality of longitudinally spaced flat 
portions 33 in its outer surface 34. Each of the flat portions 33 has an 
orifice 35, which functions as a nozzle, formed therein and extending 
through the outer cylindrical tube 12 to provide communication from the 
ink cavity 24 to the exterior of the outer cylindrical tube 12. Thus, the 
row of the orifices 35 forms an array of nozzles. 
The axis of each of the orifices 35 is disposed substantially perpendicular 
to the longitudinal axis of the inner cylindrical element 11 and the 
longitudinal axis of the outer cylindrical tube 12. The longitudinal axis 
of the outer cylindrical tube 12 is preferably coaxial with the 
longitudinal axis of the inner cylindrical element 11 although they could 
be parallel. 
As previously mentioned, the outer cylindrical tube 12 is formed of a 
piezoelectric material. It is polarized so that it vibrates in a radial 
direction when a voltage is applied thereto. The operating frequency at 
which the outer cylindrical tube 12 is electrically excited is preferably 
at or below its resonant frequency but it could be electrically excited 
above its resonant frequency in certain instances. 
The outer cylindrical tube 12 has its outer surface 34 metallized so that 
the outer cylindrical tube 12 can be electrically connected through a lead 
36 to an AC source 37 of power. Accordingly, when the AC source 37 of 
power is energized at a frequency, which is preferably equal to or below 
the resonant frequency of the outer cylindrical tube 12, the outer 
cylindrical tube 12 vibrates radially. This causes each ink stream 38 
passing through one of the orifices 35 to be broken up into droplets 39 at 
a uniform break-off point with the droplets 39 being of substantially 
uniform size and having substantially uniform spacing therebetween. 
Referring to FIG. 4, there is shown another form of the ink jet head 10 in 
which the outer cylindrical tube 12 is replaced by an outer cylindrical 
tube 45, which is formed of a piezoelectric material. The remainder of the 
structure of the ink jet head 10 of FIG. 4 is the same as shown in FIGS. 
1-3. 
The outer cylindrical tube 45 is similar to the outer cylindrical tube 12 
except that it has a single continuous flat portion 46 formed in its outer 
surface 47 so as to have a nozzle plate 48, which is preferably silicon, 
mounted thereon. It should be understood that the flat portion 46 extends 
for substantially the same length as the distance between the extreme 
edges of the outermost of the flat portions 33 in the outer surface 34 of 
the outer cylindrical tube 12 as shown in FIG. 1. 
The nozzle plate 48 has two offset arrays of ink jet nozzles 49 and 50. 
Each of the longitudinally spaced nozzles 49 is aligned with an orifice 51 
extending through the outer cylindrical tube 45 to the ink cavity 24 to 
provide communication therewith. Each of the longitudinally spaced nozzles 
50 is aligned with an orifice 52, which extends through the outer 
cylindrical tube 45 to communication with the ink cavity 24. 
Accordingly, when the outer cylindrical tube 45 is vibrated in the same 
manner as the outer cylindrical tube 12, the droplets 39 are produced in 
the same manner as discussed with respect to FIG. 1. Thus, a first 
plurality of the streams 38 passes through the nozzles 49 in the nozzle 
plate 48 with each of the streams 38 being broken up into the droplets 39. 
Similarly, a second plurality of the streams 38 passes through the nozzles 
50 with each of the streams being broken up into the droplets 39. 
Accordingly, two offset rows of the droplets 39 are produced. 
Referring to FIG. 5, there is shown an outer cylindrical tube 55, which is 
formed of a piezoelectric material, used in place of the outer cylindrical 
tube 12. The remainder of the structure of the ink jet head 10 of FIG. 5 
is the same as shown in FIGS. 1-3. 
The outer cylindrical tube 55 has a plurality of longitudinally spaced flat 
portions 56 formed in its outer surface 57 in the same manner as the flat 
portions 33 are formed in the outer surface 34 of the outer cylindrical 
tube 12. The outer cylindrical tube 55 has longitudinally spaced flat 
portions 58, which are diametrically disposed to the flat portions 56, 
formed in the same manner as the flat portions 33 are formed in the outer 
surface 34 of the outer cylindrical tube 12. 
Each of the flat portions 56 has an orifice 59 formed therein and extending 
through the outer cylindrical tube 55 to provide communication from the 
ink cavity 24 to the exterior of the outer cylindrical tube 55. Similarly, 
each of the flat portions 58 has an orifice 60 formed therein and 
extending through the outer cylindrical tube 55 to communicate with the 
ink cavity 24. 
Accordingly, when the outer cylindrical tube 55 is vibrated in the same 
manner as the outer cylindrical tube 12, the ink stream 38 flows from each 
of the orifices 59 and each of the orifices 60 and breaks up into the 
droplets 39. Thus, the droplets 39 from each of the orifices 59 can be 
utilized with a first recording medium and the droplets 39 from each of 
the orifices 60 can be employed with a second recording medium so that the 
ink jet head 10 functions as a double print head. 
Referring to FIG. 6, there is shown an outer cylindrical tube 65, which is 
formed of a piezoelectric material, being used in the ink jet head 10 in 
place of the outer cylindrical tube 12. The remainder of the structure is 
the same as that shown in FIG. 1. 
The outer cylindrical tube 65 has a first flat portion 66 formed in its 
outer surface 67 and a second flat portion 68, which is diametrically 
disposed to the first flat portion 66, formed in its outer surface 67. 
Each of the flat portions 66 and 68 extends for the same distance, which 
is preferably the same as that from the extreme edges of the outermost 
flat portions 33 in the outer surface 34 of the outer cylindrical tube 12 
as shown in FIG. 1. 
The flat portions 66 and 68 have nozzle plates 69 and 70, respectively, 
mounted thereon. The nozzle plate 69, which is preferably silicon, has a 
first array of longitudinally spaced nozzles 71 and a second array of 
longitudinally spaced nozzles 72 offset from the array of nozzles 71. The 
nozzles 71 communicate with the ink cavity 24 through orifices 73, which 
extend through the outer cylindrical tube 65 to the ink cavity 24. The 
nozzles 72 communicate with the ink cavity 24 through orifices 74, which 
extend through the outer cylindrical tube 65 to the ink cavity 24. The 
nozzle plate 70 is similarly formed as the nozzle plate 69. 
Accordingly, when the outer cylindrical tube 65 vibrates in the manner 
previously described for the outer cylindrical tube 12, the droplets 39 
are produced in two rows from each of the opposite sides of the outer 
cylindrical tube 65. Thus, two separate recording mediums may be utilized 
with each receiving two rows of the droplets 39. 
It should be understood that the outer cylindrical tube 12 of FIGS. 1-3 
could be formed in a manner similar to the outer cylindrical tube 45 of 
FIG. 4 so as to have a single row of the nozzles formed in a nozzle plate. 
Similarly, the outer cylindrical tube 55 of FIG. 5 could have each of the 
flat portions 56 and 58 continuous with a nozzle plate mounted thereon in 
the same manner as shown in FIG. 6. 
It also should be understood that the outer cylindrical tube 45 of FIG. 4 
could have a plurality of longitudinally spaced flat portions rather than 
the single flat portion 46 in the same manner as the flat portions 33 of 
FIG. 1 are formed in the outer cylindrical tube 12 and be utilized without 
the nozzle plate 48. Likewise, the nozzle plates 69 and 70 of FIG. 6 could 
be omitted from the outer cylindrical tube 65 and each of the flat 
portions 66 and 68 be a plurality of separate, longitudinally spaced flat 
portions like the flat portions 33 of FIG. 1 rather than a single 
continuous flat portion. 
Referring to FIGS. 7-9, there is shown as ink jet head 80, which includes 
an inner cylindrical tube 81 and an outer cylindrical tube 82. Each of the 
inner cylindrical tube 81 and the outer cylindrical tube 82 is formed of a 
piezoelectric material. The outer cylindrical tube 82 is disposed in 
surrounding relation to the inner cylindrical tube 81 and spaced therefrom 
to form an ink cavity 83 therebetween. 
The inner cylindrical tube 81 has one end disposed within an annular groove 
84 in an entry end plate 85 and its other end disposed in an annular 
groove 86 in an exit end plate 87. The outer cylindrical tube 82 has one 
end disposed in an annular groove 88 in the entry end plate 85 and its 
other end disposed in an annular groove 89 in the exit end plate 87. 
A cylindrical connecting element 90 extends between the inner surfaces of 
the entry end plate 85 and the exit end plate 87 and abuts against each. A 
mounting screw 91 secures the entry end plate 85 to one end of the 
connecting element 90, and a mounting screw 92 attaches the exit end plate 
87 to the other end of the connecting element 90. 
Accordingly, the outer cylindrical tube 82 has its inner cylindrical 
surface 93 spaced the same distance from outer cylindrical surface 94 of 
the inner cylindrical tube 81 throughout the length and around the entire 
circumference. Thus, the annular ink cavity 83 has the same spacing 
between its walls at any point. 
The entry end plate 85 has a first O-ring 95, which is disposed within the 
annular groove 84, engaging the end of the inner cylindrical tube 81 in 
the annular groove 84 to form a seal therebetween. The entry end plate 85 
has a second O-ring 96, which is disposed within the annular groove 88, 
abutting the end of the outer cylindrical tube 82 in the annular groove 88 
to form a seal therebetween. Accordingly, the O-rings 95 and 96 cooperate 
to seal the ink cavity 83 relative to the entry end plate 85. 
The exit end plate 87 has a first O-ring 97, which is disposed within the 
annular groove 86, engaging the end of the inner cylindrical tube 81 in 
the annular groove 86 to form a seal therebetween. The exit end plate 87 
has a second O-ring 98, which is disposed within the annular groove 89, 
abutting the end of the outer cylindrical tube 82 in the annular groove 89 
to form a seal therebetween. Accordingly, the O-rings 97 and 98 cooperte 
to seal the ink cavity 83 relative to the exit end plate 87. 
The ink cavity 83 has pressurized, conductive ink supplied thereto through 
a passage 99 in the entry end plate 85 in the same manner as described for 
the ink jet head 10 of FIG. 1. Flushing can occur in the same manner as 
described for the ink jet head 10 through utilization of a passage 100 in 
the exit end plate 87. The ink is grounded in any suitable manner. 
The outer cylindrical tube 82 has a plurality of longitudinally spaced flat 
portions 101 in its outer surface 102. Each of the flat portions 101 has a 
first orifice 103 and a second orifice 104 formed therein. Each of the 
orifices 103 and 104 extends through the outer cylindrical tube 82 to 
provide communication from the ink cavity 83 to the exterior of the outer 
cylindrical tube 82 and functions as a nozzle. Thus, there are two offset 
arrays of nozzles formed in the outer cylindrical tube 82 with the row of 
the orifices 103 forming one of the arrays of nozzles and the row of the 
orifices 104 forming the other of the arrays of nozzles. 
The axis of each of the orifices 103 and of each of the orifices 104 is 
disposed substantially perpendicular to the longitudinal axis of the inner 
cylindrical tube 81 and the longitudinal axis of the outer cylindrical 
tube 82. The longitudinal axis of the outer cylindrical tube 82 is 
preferably coaxial with the longitudinal axis of the inner cylindrical 
tube 81 although they could be parallel. 
As previously mentioned, each of the inner cylindrical tube 81 and the 
outer cylindrical tube 82 is formed of a piezoelectric material. In order 
for the resonant operating frequencies of the inner cylindrical tube 81 
and the outer cylindrical tube 82 to be matched, it is necessary that they 
be formed of different piezoelectric materials. 
Each of the inner cylindrical tube 81 and the outer cylindrical tube 82 is 
polarized to vibrate in a radial direction when a voltage is applied 
thereto. The operating frequency at which the inner cylindrical tube 81 
and the outer cylindrical tube 82 is electrically excited is preferably 
the matched resonant frequency but any matched operating frequency below 
the matched resonant frequency also could be employed. It should be 
understood that one of the tubes 81 and 82 could be electrically excited 
at its resonant frequency and the other of the tubes 81 and 82 having its 
operating frequency matched therewith. 
The outer cylindrical tube 82 has its outer surface 102 metallized so that 
the outer cylindrical tube 82 can be electrically connected through a lead 
105 to an AC source 106 of power. The inner cylindrical tube 81 has its 
inner cylindrical surface 107 metallized so that the inner cylindrical 
tube 81 can be electrically connected through a lead 108 and a phase 
inverter 109 to the AC source 106 of power. The lead 108 passes through a 
passage 110 in the entry end plate 85. 
Accordingly, when the AC source 106 of power is energized at a frequency, 
which is preferably equal to or below the matched resonant frequency of 
the inner cylindrical tube 81 and the outer cylindrical tube 82, each of 
the inner cylindrical tube 81 and the outer cylindrical tube 82 vibrates 
radially with one expanding while the other is contracting. This causes 
the ink streams 38 passing through each of the orifices 103 and each of 
the orifices 104 to be broken up into the droplets 39. 
Referring to FIG. 10, there is shown another form of the ink jet head 80 in 
which the outer cylindrical tube 82 is replaced by an outer cylindrical 
tube 115, which is formed of a piezoelectric material. The remainder of 
the structure of the ink jet head 80 of FIG. 10 is the same as shown in 
FIGS. 7-9. 
The outer cylindrical tube 115 has a first flat portion 116 formed in its 
outer cylindrical surface 117 and extending for substantially the same 
length as the distance between the extreme edges of the outermost flat 
portions 101 of FIG. 7. The outer cylindrical tube 115 has a second flat 
portion 118, which is diametrically disposed to the first flat portion 
116, formed in its outer cylindrical surface 117. The second flat portion 
118 extends for the same length as the first flat portion 116. 
A nozzle plate 119, which is preferably silicon, is mounted on the first 
flat portion 116, and a nozzle plate 120, which is preferably silicon, is 
mounted on the second flat portion 118. The nozzle plate 119 has a 
plurality of longitudinally spaced nozzles 121 therein with each of the 
nozzles 121 communicating with the ink cavity 83 through an orifice 122 in 
the outer cylindrical tube 115. Each of the orifices 122 extends through 
the outer cylindrical tube 115 to the ink cavity 83. 
The nozzle plate 120 has a plurality of longitudinally spaced nozzles 123 
therein with each of the nozzles 123 communicating with the ink cavity 83 
through an orifice 124 in the outer cylindrical tube 115. Each of the 
orifices 124 extends through the outer cylindrical tube 115 to the ink 
cavity 83. 
Accordingly, each of the nozzles 121 has one of the streams 38 pass 
therethrough, and each of the nozzles 123 has one of the streams 38 pass 
therethrough. Therefore, when the inner cylindrical tube 81 and the outer 
cylindrical tube 115 vibrate radially in the same manner as described for 
the inner cylindrical tube 81 and the outer cylindrical tube 82 of FIG. 7, 
the streams 38 are broken up into the droplets 39 and applied to two 
separate recording mediums. 
Referring to FIG. 11, there is shown another form of the ink jet head 80 in 
which the outer cylindrical tube 82 is replaced by an outer cylindrical 
tube 125, which is formed of a piezoelectric material. The remainder of 
the structure of the ink jet head 80 of FIG. 11 is the same as shown in 
FIGS. 7-9. 
The outer cylindrical tube 125 has a plurality of first flat portions 126 
formed in its outer surface 127 in the same manner as the flat portions 
101 on the outer cylindrical tube 82 of FIG. 7. A plurality of second flat 
portions 128 is formed in the outer cylindrical surface 127 of the outer 
cylindrical tube 125 and diametrically opposite to the first flat portions 
126. Each of the second flat portions 128 is formed at the same 
longitudinal position as one of the diametrically disposed first flat 
portions 126. 
Each of the first flat portions 126 has a first orifice 129 and a second 
orifice 130 formed therein with each of the orifices 129 and 130 providing 
communication from the ink cavity 83 to the exterior of the outer 
cylindrical tube 125. Thus, the orifices 129 form a first array of 
nozzles, and the orifices 130 form a second array of nozzles. 
Each of the second flat portions 128 has a first orifice 131 and a second 
orifice 132 formed therein with each of the orifices 131 and 132 extending 
through the outer cylindrical tube 125 to provide communication from the 
ink cavity 83 to the exterior of the outer cylindrical tube 125. The 
orifices 131 forms a first array of nozzles on the opposite side of the 
outer cylindrical tube 125 from the orifices 129 and 130. The orifices 132 
form a second array of nozzles, which is offset from the first array of 
nozzles formed by the orifices 131. Accordingly, this arrangement can be 
utilized with two separate recording mediums with two rows of the ink 
droplets 39 being applied to each of the recording mediums. 
It should be understood that the outer cylindrical tube 82 of FIGS. 7-9 
could be formed with the flat portions 101 as a continuous flat portion in 
a manner similar to the formation of the first flat portion 116 on the 
outer cylindrical tube 115 of FIG. 10 so as to have a nozzle plate with a 
single row of nozzles mounted thereon. Similarly, the outer cylindrical 
tube 125 of FIG. 11 could have each of the longitudinally spaced flat 
portions 126 and 128 continuous so as to have a nozzle plate mounted on 
each in the same manner as shown in FIG. 10. It also should be understood 
that the outer cylindrical tube 115 of FIG. 10 could have a plurality of 
longitudinally spaced flat portions rather than the single flat portion 
116 and a plurality of longitudinally spaced flat portions rather than the 
single flat portion 118 in the same manner as the flat portions 101 are 
formed in the outer cylindrical tube 82 of FIGS. 7-9 and be utilized 
without the nozzle plates 119 and 120. 
Referring to FIGS. 12 and 13, there is shown an ink jet head 140, which has 
a similar construction to that of the ink jet head 80 except that the 
outer cylindrical tube 82 of piezoelectric material is replaced by an 
outer cylindrical tube 141, which is not formed of piezoelectric material 
but of metal, for example. The outer cylindrical tube 141 has a nozzle 
plate 142, which is preferably silicon, mounted thereon through forming a 
flat portion 143 in outer cylindrical surface 144 of the outer cylindrical 
tube 141. 
The nozzle plate 142 has a first row of longitudinally spaced nozzles 145 
forming a first array of nozzles and a second row of longitudinally spaced 
nozzles 146 forming a second array of nozzles. Thus, the two arrays of the 
nozzles in the nozzle plate 142 are offset from each other. 
Each of the nozzles 145 in the nozzle plate 142 communicates through an 
orifice 147, which extends through the outer cylindrical tube 141, with 
the ink cavity 83. Each of the nozzles 146 communicates through an orifice 
148, which extends through the outer cylindrical tube 141, with the ink 
cavity 83. 
In the same manner as in FIG. 7, the inner cylindrical tube 81 has its 
inner surface 107 metallized and connected by the lead 106 to an AC source 
149 of power. Accordingly, when the AC source 149 of power is energized at 
a frequency, which is preferably equal to or below the resonant frequency 
of the inner cylindrical tube 81, the inner cylindrical tube 81 vibrates 
radially. This causes each of the ink streams 38 passing through the 
nozzles 145 and 146 to be broken up into the droplets 39 to provide two 
rows of the droplets 39 for application to a recording medium. 
Referring to FIG. 14, there is shown another arrangement of the ink jet 
head 140 in which the outer cylindrical tube 141 is replaced by an outer 
cylindrical tube 150, which is formed of metal. The remainder of the 
structure of the ink jet head 140 of FIG. 14 is the same as shown in FIGS. 
12 and 13. 
The outer cylindrical tube 150 has a first row of longitudinally spaced 
orifices 151, which function as nozzles, extending therethrough to provide 
communication from the ink cavity 83 to the exterior of the outer 
cylindrical tube 150. The outer cylindrical tube 150 has a second row of 
longitudinally spaced orifices 152, which are diametrically disposed to 
the orifices 151 and function as nozzles, extending through the outer 
cylindrical tube 150 to provide communication from the ink cavity 83 to 
the exterior of the outer cylindrical tube 150. 
When the inner cylindrical tube 81 is electrically excited from the AC 
source 149 of power, the streams 38 passing through the orifices 151 break 
up into the droplets 39 and the streams 38 exiting through the orifices 
152 break up into the droplets 39. Thus, the ink jet head 140 of FIG. 14 
can be utilized with two separate recording mediums with one of the 
recording mediums receiving the droplets 39 from the orifices 151 and the 
other of the recording mediums receiving the droplets 39 from the orifices 
152. 
Referring to FIG. 15, there is shown another arrangement of the ink jet 
head 140 in which an outer cylindrical tube 155 of metal is utilized in 
place of the outer cylindrical tube 141. The remainder of the structure of 
the ink jet head 140 of FIG. 15 is the same as shown in FIGS. 12 and 13. 
The outer cylindrical tube 155 has a plurality of first flat portions 156, 
which are longitudinally spaced, formed in its outer cylindrical surface 
157 in the same manner as the flat portions 101 are formed in the outer 
cylindrical tube 82 in FIG. 7. Each of the first flat portions 156 has a 
first orifice 158, which extends through the outer cylindrical tube 155 to 
the ink cavity 83, providing communication from the ink cavity 83 to the 
exterior of the outer cylindrical tube 155. Each of the first flat 
portions 156 has a second orifice 159, which extends through the outer 
cylindrical tube 155 to the ink cavity 83, to provide communication from 
the ink cavity 83 to the exterior of the outer cylindrical tube 155. Thus, 
the first orifices 158 form a first array of nozzles and the second 
orifices 159 form a second array of nozzles with the two arrays of nozzles 
being offset from each other. 
The outer cylindrical tube 155 has a plurality of second flat portions 160, 
which are longitudinally spaced, formed therein and diametrically disposed 
to the first flat portions 156. Each of the second flat portions 160 has a 
first orifice 161, which extends through the outer cylindrical tube 155 to 
provide communication from the ink cavity 83 to the exterior of the outer 
cylindrical tube 155, and a second orifice 162, which extends through the 
outer cylindrical tube 155 to provide communication from the ink cavity 83 
to the exterior of the outer cylindrical tube 155. Thus, the row of the 
first orifices 161 forms a first array of nozzles and the row of the 
second orifices 162 forms a second array of nozzles with the two arrays 
being offset from each other. 
Furthermore, the two arrays of nozzles in the first flat portions 156 are 
used with a first recording medium and the two arrays of nozzles in the 
second flat portions 160 are used with a second recording medium. Thus, 
each of the recording mediums has two offset rows of the droplets 39 
directed thereto when the inner cylindrical tube 81 is vibrated radially. 
It should be understood that the outer cylindrical tube 141 of FIGS. 12 and 
13 could have a plurality of longitudinally spaced flat portions rather 
than the single continuous flat portion 143 in the same manner as the flat 
portions 156 are longitudinally spaced in the outer cylindrical tube 155 
and be utilized without the nozzle plate 142. It also should be understood 
that the outer cylindrical tube 150 of FIG. 14 could be formed with a 
continuous flat portion on each side so as to have a nozzle plate mounted 
on each flat portion in the same manner as shown in FIG. 13. Likewise, 
each of the longitudinally spaced flat portions 156 and 160 in the outer 
cylindrical tube 155 of FIG. 15 could be continuous so as to have a nozzle 
plate mounted thereon in the same manner as shown in FIG. 13. 
Referring to FIGS. 16 and 17, there is shown an ink jet head 170, which 
includes a semi-cylindrical element 171 of a piezoelectric material. The 
element 171 has its inner semi-cylindrical surface 172 resting on a 
semi-cylindrical portion 173 of a support 174, which is formed of a 
suitable electrically insulating material such as plastic, for example. 
A body 175, which is formed of metal or plastic, for example, is supported 
on the support 174 and secured thereto by mounting screws 176. The body 
175 has a semi-cylindrical recess 177 to receive the semi-cylindrical 
element 171 and the semi-cylindrical portion 173 of the support 174 
therein with the element 171 having its outer surface 178 spaced from the 
wall of the recess 177 when the body 175 is secured to the support 174 by 
the mounting screws 176. Accordingly, the spacing of the outer surface 178 
of the semi-cylindrical element 171 the same distance from the wall of the 
recess 177 provides an ink cavity 179 therebetween with the ink cavity 179 
having the same thickness at any position. 
The body 175 has an O-ring 180 mounted in a groove 181 therein. The groove 
181 surrounds the recess 177 of the body 175 and forms a seal with the 
support 174 to seal the ink cavity 179. 
The ink cavity 179 has pressurized, conductive ink supplied thereto through 
a passage 182 in a plug 183 and a passage 184 in the support 174 from a 
pressurized source in the manner previously described relative to the ink 
jet head 10 of FIG. 1. When flushing is desired, the ink flows from the 
ink cavity 179 through a passage (not shown) in the support 174 and a 
passage (not shown) in a connecting plug 187 in the manner described 
relative to the ink jet head 10. The ink is grounded in any suitable 
manner. 
The body 175 has a nozzle plate 188, which is preferably formed of silicon, 
bonded thereto. The nozzle plate 188 has a first row of longitudinally 
spaced nozzles 189 therein to form a first array of nozzles and a second 
row of longitudinally spaced nozzles 190 therein to form a second array of 
nozzles offset from the first array of nozzles. 
Each of the nozzles 189 communicates with the ink cavity 179 through an 
orifice 191, which extends through the body 175 to the ink cavity 179, in 
the body 175. Each of the nozzles 190 communicates with the ink cavity 179 
through an orifice 192, which extends through the body 175 to the ink 
cavity 179. The axis of each of the orifices 191 and 192 is disposed 
substantially perpendicular to the longitudinal axis of the 
semi-cylindrical element 171. 
As previously mentioned, the semi-cylindrical element 171 is formed of a 
piezoelectric material. It is polarized so that it vibrates in a radial 
direction when a voltage is applied thereto. The operating frequency at 
which the semi-cylindrical element 171 is electrically excited is 
preferably below its resonant frequency but it could be at its resonant 
frequency. 
The semi-cylindrical element 171 has the inner semi-cylindrical surface 172 
metallized so that the semi-cylindrical element 171 can be connected 
through a lead 193, which extends through a passage 194 in the support 
174, to an AC source 195 of power. Accordingly, when the AC source 195 of 
power is energized at a frequency, which is preferably equal to or below 
the resonant frequency of the semi-cylindrical element 171, the 
semi-cylindrical element 171 vibrates radially. This causes each of the 
streams 38 passing through one of the nozzles 189 and 190 to be broken up 
into the droplets 39. 
Referring to FIG. 18, there is shown an ink jet head 200. The ink jet head 
200 includes an outer planar element 201, which is formed of a 
piezoelectric material, and an inner block 202, which can be formed of 
metal, for example. The outer element 201 is secured to the inner block 
202 by any suitable means such as bonding, for example. 
An ink cavity 203 is formed between the outer element 201 and the inner 
block 202 within the inner block 202. The distance between an inner 
surface 204 of the outer element 201 and an inner surface 205 of the inner 
block 202 is substantially constant throughout the length of the ink 
cavity 203. 
The ink cavity 203 has pressurized, conductive ink supplied thereto through 
a passage 206 in the inner block 202 from a suitable pressurized source in 
the same manner as discussed with respect to the ink jet head 10. Whenever 
it is desired to flush the ink cavity 203, the ink flows from the ink 
cavity 203 through a passage 207 in the inner block 202 to an ink 
reservoir or the like as discussed with respect to the ink jet head 10. 
The ink is grounded in any suitable manner. 
The outer element 201 has a plurality of longitudinally spaced flat 
portions 210 in its outer surface 211. Each of the flat portions 210 has 
an orifice 212, which functions as a nozzle, formed therein and extending 
through the outer element 201 to provide communication from the ink cavity 
203 to the exterior of the outer element 201. The axis of each of the 
orifices 212 is substantially perpendicular to the longitudinal axis of 
the outer element 201. 
As previously mentioned, the outer element 201 is formed of a piezoelectric 
material. It is polarized so that it vibrates in a direction substantially 
parallel to the axis of each of the orifices 212 when a voltage is applied 
thereto. The operating frequency at which the outer element 201 is 
electrically excited is preferably below its resonant frequency but it 
could be at its resonant frequency. 
The outer element 201 has its outer surface 211 metallized so that the 
outer element 201 can be connected through a lead 213 to an AC source 214 
of power. Accordingly, when the Ac source 214 of power is energized at a 
frequency, which is preferably equal to or below the resonant frequency of 
the outer element 201, the outer element 201 vibrates in and out relative 
to its thickness and substantially parallel to the axes of the orifices 
212. This causes each of the ink streams 38 passing through the orifices 
212 to break up into the droplets 39 in the manner previously described 
relative to the ink jet head 10. 
While the present invention has shown and described the surfaces of each of 
the ink cavities of FIGS. 1-17 as being cylindrical and each of the tubes, 
which form the cavity, as being cylindrical, it should be understood that 
such is not necessary for satisfactory operation. It is only necessary 
that the outer surface of the inner element and the cooperating inner 
surface of the outer means have substantially the same shape with the 
piezoelectric members, when electrically excited, vibrating in a direction 
substantially perpendicular to the longitudinal axes of the surfaces of 
the ink cavity. 
An advantage of this invention is that ink droplets can be supplied to more 
than one recording medium from a single ink jet head. Another advantage of 
this invention is that an efficient ink jet head is produced. A further 
advantage of this invention is that droplets are uniformly generated from 
each of a plurality of arrays of ink jet nozzles at the same time. 
While the invention has been particularly shown and described with 
reference to preferred embodiments thereof, it will be understood by those 
skilled in the art that the foregoing and other changes in form and 
details may be made therein without departing from the spirit and scope of 
the invention.