Technical Field
[0001] The present invention relates to ink jet drop generators and, more particularly,
to an improved structure for an ink jet drop generator.
Background Art
[0002] In continuous ink jet printing, ink is supplied under pressure to a manifold region
that distributes the ink to a plurality of orifices, typically arranged in a linear
array(s). The ink discharges from the orifices in filaments which break into droplet
streams. The approach for printing with these droplet streams is to selectively charge
and deflect certain drops from their normal trajectories.
[0003] In the field of ink jet printers, it is desirable from the standpoint of throughput
to utilize long arrays of ink jets. For example, U.S. Patent No. 4,999,647 discloses
a drop generator for use with a long array of holes such that the length is larger
than the height. A plurality of slots were employed to insure uniform vibration amplitude
of the longitudinal mode (height direction) across the orifice plate face. Co-pending,
commonly assigned U.S. Patent Application Serial No. 07/891,492, filed May 29, 1992,
incorporated herein by reference, defines an improved drop generator in which the
fluid cavity length is established to suppress pressure waves in the fluid cavity.
Such pressure waves in the fluid can interfere with stimulation produced by the resonator-induced
motion of the orifice plate.
[0004] With longer array devices or higher frequencies, it becomes more difficult to excite
the desired vibration mode without exciting other modes which can adversely affect
stimulation uniformity. For example, in the equation

A
n is the vibration amplitude of mode n, B
n is a constant depending on the mode shape, f
n is the resonant frequency of node n, f is the driving frequency, and c is a small
value related to attenuation. To drive the n
th mode while trying to avoid driving the n+1
th mode, the resonator is driven at a frequency of f = f
n. The amplitude A
n would reach its maximum value of B
n/c. The amplitude of A
n+1 would be B
n₊₁/((f
n₊₁² - f
n²) + c). As the desired frequency or the resonator length increase, the separation
between the resonant modes, f
n+1 - f
n, decreases. As the mode separation, f
n+1 - f
n, decreases, the ratio of their amplitudes A
n/A
n+1 decreases. It is therefore harder to excite the mode n without also exciting the
n+1 mode.
[0005] Even with judicious design of the drop generator to insure that the desired mode
is uniform, the undesirable excitation of an adjacent resonant mode can produce unacceptable
stimulation uniformity across the array. Furthermore, the degree to which the undesirable
modes are excited and subsequently the level of vibration uniformity across the array
may be unacceptably sensitive to the operating frequency and manufacturing tolerances.
[0006] It is seen then that there is a need for an improved structure for an ink jet drop
generator which can provide mode uniformity and which overcomes the problems and disadvantages
of prior procedures.
Summary of the Invention
[0008] This need is met by the print head device of the present invention wherein mode uniformity
is provided. One important object of the present invention is to provide an improved
structure for an ink jet drop generator which can utilize long arrays of ink jets.
This is accomplished by an approach wherein the system is designed to include damping
means for suppression of undesired vibration modes.
[0009] In accordance with one aspect of the present invention, a print head device is used
in continuous ink jet printing systems. The print head device comprises a resonator
means with an ink supply body formed of a solid high acoustic Q material. Piezoelectric
transducer means are attached to the resonator means. The print head device further
includes means for energizing the transducer means at a desired drop frequency. Finally,
damping means are provided for suppression of undesired vibration modes.
[0010] Accordingly, it is an advantage of the present invention that it provides mode suppression
in relatively long orifice arrays. Other objects and advantages of the invention will
be apparent from the following description, the accompanying drawing and the appended
claims.
Brief Description of the Drawing
[0011]
Fig. 1 illustrates a prior art drop generator;
Fig. 2 illustrates a vibrating fluid fitting;
Fig. 3 illustrates a fluid fitting with the damping material, according to the present
invention;
Fig. 4 illustrates prior art fluid cavity walls having undesired flexure mode;
Fig. 5 illustrates a drop generator according to the present invention wherein damping
suppresses the fluid cavity wall mode; and
Fig. 6 illustrates the drop generator of Fig. 5 mounted in a frame.
Detailed Description of the Preferred Embodiments
[0012] Referring to the drawings, Fig. 1 schematically illustrates the components that cooperate
to comprise a prior art embodiment of a drop ejection device. It will be understood
that such drop ejection device, generally referred to as 10, cooperates with other
known components used in ink jet printers. The device 10 functions to produce the
desired streams of uniformly sized and spaced drops in a highly synchronous condition.
Other continuous ink jet printer components, such as charge and deflection electrodes,
drop catcher, media feed system and data input and machine control electronics (not
shown) cooperate with the drop streams, produced by device 10 to effect continuous
ink jet printing.
[0013] The drop generator 10 is constructed to provide synchronous drop streams in a long
array printer, and comprises a resonator/manifold body 12. The resonator/manifold
body 12 is constructed of a high acoustic Q material, e.g. stainless steel, and in
the form of a predeterminedly dimensioned rectangular solid, the length (1) of which
is substantially greater than its height (h), which body height (h) is substantially
greater than the body thickness.
[0014] Continuing with Fig. 1, an orifice plate 14 having a plurality of orifices, is bonded
onto the resonator body 12. The resonator body 12 also includes an ink supply body
or fluid cavity 16, having fluid cavity side walls for containing the ink. It is understood
that the resonator/manifold body 12 further includes fluid ports, or fluid fittings
20, for supplying ink from a fluid supply means to the ink supply cavity. The fluid
inlet and outlet fittings 20 may comprise thin wall tubing bent to form an elbow 24,
over which flexible ink conduit lines 22 may be attached. Pins 26, protruding outward
from the front and back faces of the resonator body 12 can be used to mount the drop
generator 10 in a support frame, such as frame 34 in Fig. 6.
[0015] A plurality of piezoelectric elements 18 are used to induce the vibration of the
resonator/manifold body 12. In such a drop generator 10, the desired vibration mode
for good stimulation is typically the longitudinal mode in the h direction. In this
mode, the resonator/manifold body 12 expands and contracts in the h direction. The
slots 28 ensure that the uniformity of this longitudinal mode is sufficient for proper
drop generation operation. In addition to this longitudinal mode, it is possible to
excite other vibration modes even when the drop generator has been carefully designed
to provide uniform vibration in the desired vibrational mode. These other vibrational
modes, which typically vary in amplitude and/or phase across the array, can seriously
degrade the vibrational uniformity across the jet array.
[0016] In accordance with the present invention, to suppress these undesirable vibrational
modes, damping means may be utilized. Although any suitable damping means may be used,
a typical damping means comprises a damping material such as viscoelastic materials.
As these materials undergo periodic stress or strain, they convert some of the vibrational
energy into heat, attenuating the vibration amplitude. Since these materials must
undergo periodic stress to attenuate the vibration amplitude, they are most effective
when they are attached to the high stress regions of the resonating system. Suppression
of the undesirable vibration mode therefore involves attaching damping materials to
those areas of drop generator 10 where the stresses are concentrated for such undesired
modes. Conversely, the damping materials should not be attached to those areas of
the drop generator 10 having high stress in the longitudinal mode.
[0017] Use of damping materials, in accordance with the present invention, can suppress
undesirable modes. The following three types of undesirable modes are exemplary of
the modes which can be suppressed using the damping concept of the present invention.
One undesirable mode involves a resonance of the fitting 20. Fig. 2 illustrates one
possible vibration mode of the fittings. In this mode, the elbow 24 can be seen to
flex in and out. Of course, it will be obvious to those skilled in the art that Fig.
2 is representative of only one of many possible modes. The resonant mode of Fig.
2 can couple into the resonator body 12 affecting the vibration uniformity at the
orifice plate 14, or it can drive a pressure wave in the fluid cavity 16. In accordance
with the present invention, the placement of a damping rubber sleeve 30 around the
elbow 24 as shown in Fig. 3 can strongly attenuate this mode while having little effect
on the resonator body longitudinal mode.
[0018] A second type of interfering vibrational mode involves flexure modes of the sides
of the cavity. As illustrated in Fig. 4, the side walls 32 around the fluid cavity
can undergo flexure modes in the form of standing waves down the array. Again, it
will be obvious to those skilled in the art that Fig. 4 is representative of only
one of many possible cavity wall flexure modes. Such modes can produce large variations
in the stimulation amplitude down the array. In accordance with the present invention,
cavity flexure modes can be suppressed by attaching damping material 36, such as E-A-R/SC
SD-40PSA material to the side walls 32 of the fluid cavity 16 as shown in Fig. 5.
As the stresses are low near the end of the resonator in the longitudinal mode, the
longitudinal mode is not strongly attenuated by the damping material.
[0019] The third type of interfering resonance involves the drop generator mounting frame.
As shown in Fig. 6, the drop generator is mounted in a frame 34 by means of pins 26.
Although the pins 26 are located near the nodal plane of the drop generator 10, they
are able to couple some vibrational energy from the drop generator 10 to the frame
34. If the frame has a resonance near the operating frequency of the drop generator
this can result in the frame 34 resonating. The vibration of the frame 34 can then
be coupled back into the drop generator 10 through the pins 26, affecting the stimulation
uniformity. In accordance with the present invention, applying damping material 38
to the frame can suppress the frame resonance so that the stimulation uniformity is
not degraded, without adversely affecting the longitudinal mode of the resonator.
[0020] The damping rubber sleeve 30, the damping material 36 and the damping material 38
being used for mode suppression may be used singularly or cooperatively, depending
on the presence or absence of the interfering modes for a particular drop generator.
[0021] The interfering resonant modes illustrated herein are examples of some of the many
interfering resonant modes which may be present in drop generator designs, and are
not to be considered as limiting the scope of the invention. In accordance with the
present invention, the desired suppression of the interfering mode can be produced
by placement of the damping material in regions having relatively high stress in the
interfering modes and relatively low stress in the desired mode.
Industrial Applicability and Advantages
[0022] The present invention is useful in the field of ink jet printing, and has the advantage
of suppressing undesired vibration and interfering resonant modes. The present invention
has the further advantage of providing such suppression without adversely affecting
the longitudinal mode of the resonator.
[0023] The invention has been described in detail with particular reference to certain preferred
embodiments thereof, but it will be understood that modifications and variations can
be effected within the spirit and scope of the invention.
1. A print head device for use in continuous ink jet printing, the device comprising:
a. a resonator means having an ink supply body formed of a solid high acoustic Q material;
b. transducer means attached to the resonator means;
c. a means for energizing the transducer means at a desired drop frequency; and
d. damping means for suppression of undesired interfering vibration modes of the resonator
means, to achieve a desired mode.
2. A print head device as claimed in claim 1 wherein the damping means are placed in
regions having relatively high stress in the interfering modes and relatively low
stress in the desired mode.
3. A print head device as claimed in claim 1 wherein the damping means comprises a viscoelastic
material.
4. A print head device for use in continuous ink jet printing, the device comprising:
a. a resonator means having an ink supply body formed of a solid high acoustic Q material
and further having fluid ports for supplying ink from a fluid supply means to the
ink supply body;
b. transducer means attached to the resonator means;
c. a means for energizing the transducer means at a desired drop frequency; and
d. means for applying a damping means to the fluid ports for suppression of undesired
interfering vibration modes, to achieve a desired mode.
5. A print head device as claimed in claim 4 wherein the damping means comprises a viscoelastic
material.
6. A print head device for use in continuous ink jet printing, the device comprising:
a. a resonator means having an ink supply body formed of a solid high acoustic Q material,
the ink supply body including fluid cavity side walls for containing the ink;
b. transducer means attached to the resonator means;
c. a means for energizing the transducer means at a desired drop frequency; and
d. means for attaching a damping means to the fluid cavity side walls for suppression
of undesired interfering vibration modes, to achieve a desired mode.
7. A print head device as claimed in claim 6 wherein the damping means comprises a viscoelastic
material.
8. A print head device for use in continuous ink jet printing, the device comprising:
a. a resonator means having an ink supply body formed of a solid high acoustic Q material,
the resonator means mounted in a support frame;
b. transducer means attached to the resonator means;
c. a means for energizing the transducer means at a desired drop frequency; and
d. means for applying a damping means to the support frame for suppression of undesired
interfering vibration modes, to achieve a desired mode.
9. A print head device as claimed in claim 8 wherein the damping means comprises a viscoelastic
material.
10. A print head device as claimed in claim 8 wherein the resonator means is mounted in
a support frame using a plurality of pins.