Recording device functioning with fluid droplets

An improved recording device, which has a row of nozzles with each nozzle having an inlet opening and an outlet opening and a piezoelectric transducer arranged adjacent the inlet opening for forcing a drop of recording fluid from the outlet opening onto a recording medium in response to a voltage change on the transducer, characterized by the individual transducers being formed as teeth of a comb-like piezoplate that is a bilaminar plate formed of a piezoceramic layer and a carrier layer and has a reinforcing layer in the area of a spine of the comb which is shared by all teeth of the plate.

BACKGROUND OF THE INVENTION 
The present invention is directed to a recording device functioning with 
fluid droplets for point-by-point recording of analog progressions and/or 
alphanumerical characters as well as images. The device includes a 
plurality of nozzles, which have inlet openings and outlet openings and 
which are arranged in a row with a recording medium being disposed in 
front of the discharge openings of the nozzles to enable writing 
individual points on the medium. A piezoelectric transducer is provided in 
front of the intake openings of the nozzles and each of the transducers 
are provided with means for applying an electrical voltage so that with a 
given electrical voltage change the writing fluid is ejected from the 
particular nozzle. The individual transducers are formed by teeth of a 
comb-like piezoelectric plate which plate is a bilaminar plate of a 
piezoelectric ceramic layer and a carrier layer. 
A recording device, wherein the plate material consists of a layer of 
piezoceramic material and a metal layer is disclosed in U.S. Pat. No. 
4,072,959, which was based on German No. OS 2,527,647 and whose disclosure 
is incorporated by reference thereto. In this patent, a piezoplate 
comprising a layer of piezoceramic material and a carrier layer is 
disclosed which plate has a comb-like structure with parallelly extending 
teeth forming the individual transducers. In one embodiment, a spacer 
piece is provided between a nozzle plate and the comb-like piezoelectric 
plate. The comb is held in position by means of a clamp that extends over 
the entire length of the spine of the comb. The problem with this design 
is that the clamping of the comb in the clamp must occur with extreme 
precision. Since the thickness of the comb only amounts to a few tenths of 
a millimeter, a displacement between the spacer piece and the clamp of the 
same order of magnitude will lead to considerable changes in the flexural 
forces. The flexural lengths of the transducers in the two twist 
directions become different as a consequence and this will lead to 
imprecise writing. 
Given the traditional comb fixing, it must also be taken into consideration 
that the clamp comes into contact with all of the transducers of the comb 
precisely and with identical force insofar as possible. This is required 
so that the flexural length of all the transducers will remain identical. 
This is particularly difficult to achieve in the case of the central 
transducers of the comb which therefore tend to bend below the clamp. 
SUMMARY OF THE INVENTION 
The present invention is directed to providing a recording device utilizing 
a comb-shaped transducer wherein the lengths of the oscillatory parts of 
the individual transducers are precisely fixed in a simple manner and 
strain is avoided. 
This object is inventively achieved in an improvement for a recording 
device which utilizes fluid droplets for punctiform recording of analog 
curves of alphanumerical characters as well as images on a recording 
medium, said device having nozzles with intake openings and discharge 
openings disposed in a row for writing the individual points, a 
piezoelectric transducer being disposed in front of each intake opening of 
the nozzle and having means for applying electrical voltage so that with 
an electrical voltage change to a transducer, a writing fluid is ejected 
from the nozzle and applied to the recording being disposed in front of 
the discharge opening of the nozzles, said individual transducers being 
formed by teeth of a comb-like piezoplate which is a bilaminar plate of a 
layer of piezoceramic material and a carrier layer. The improvements 
comprise the piezoceramic layer being provided with a reinforcing layer in 
the area of a spine of the comb which spine is shared by all teeth. Thus, 
both surfaces of the spine of the piezoceramic plate is provided with a 
layer which is either a carrier layer or reinforcing layer. The dimension 
and material of the carrier layer should be selected so that they oppose 
forces of expansion of the piezoceramic layer upon application of voltage 
with equal resistance on both surfaces. Thus, the piezoceramic layer will 
expand in a straight-line fashion in the region of the reinforcing layer 
and undesirable warping will not occur. Another advantage is that a far 
simpler arrangement can be utilized as a clamp for the comb without making 
demands on the tolerances. The precise length of the oscillatory parts of 
the transducer is defined by the front edge of the reinforcement layer. 
Further advantages and details include the fact that the elasticity of the 
reinforcing layer corresponds to the elasticity of the carrier layer, that 
the carrier layer and the reinforcing layer are composed of the same 
material which may be a metal, for example, nickel. In addition, the 
reinforcing layer and the carrier layer may be composed of non-conductive 
materials selected from a group consisting of ceramic and glass and, for 
example, from a group consisting of aluminum oxide and silicon.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The principles of the present invention are particularly useful in a 
recording device generally indicated at 50 in FIG. 3. The recording device 
50 has a pair of conveyor rolls 1 and 2 which convey a recording medium 3, 
for example, a standard registration paper in a direction 4. As 
illustrated, the recording medium 3 is drawn over a distancer 5 along a 
side 6 of a housing 7. The housing 7 has a connecting line 8 which extends 
to a plug 9 at its free end for connection to a control device (not 
illustrated) that supplies the control signals for recording desired 
curves, characters and images on the recording medium 3. 
As best illustrated in FIG. 4, the surface or side 6 of the housing 7 
extends parallel to the medium 3. The side 6 is the side of a carrier 
member or plate 10 that exhibits a plurality of nozzles 11 disposed next 
to one another in a row (best illustrated in FIG. 1). As illustrated in 
FIG. 4, each of the nozzles 11 has an exit or discharge opening lla and an 
entrance or intake opening 11b. The housing 7 in addition to containing 
writing fluid also has bar-shaped transducers 12 of piezoelectric material 
that are electrically contacted and arranged so that they will spray 
writing fluid in the form of a droplet from the exit opening 11a of a 
nozzle 11 when a selected change in the electrical drive voltage occurs. 
The transducers 12 are designed as teeth of a comb (FIG. 1) and function as 
flexure resonators. The piezocomb 14, which consists of the transducers 12 
and the comb spine 13, is thereby disposed parallel to the plane of the 
carrier 10. It is shown in FIG. 4 that the piezoplate is a bilaminar plate 
and is formed with a piezoceramic layer 16 and a metal layer 17. The 
piezoceramic layer 16 is provided with a reinforcing layer 19 (FIG. 1) in 
the area of the comb spine 13 which is shared with all of the teeth. The 
position of an edge 20 of the reinforcing layer 19 defines the length of 
the oscillatory part of the transducers 12. The same material as employed 
for the carrier layer 17, for example, nickel, is preferably used for the 
reinforcing layer 19 so that the elasticity of the reinforcing layer 
corresponds to that of the carrier layer 17. The free end region of the 
individual transducers 12 is situated in front of the individual nozzle 11 
of the row of nozzles. The comb spine 13 is clamped on the carrier 10 by 
threaded fasteners such as nut and bolt arrangement 15. Given the 
application of electrical voltage to the connecting means for each of the 
transducers 12, the transducer will move to a position indicated in broken 
lines in FIG. 4. Given a short circuit of the transducer 12, it will 
spring back into its non-bent position indicated with solid lines and 
thereby forces a droplet of writing fluid through the nozzle 11 and out 
the opening 11a. 
As best illustrated in FIGS. 1 and 2, the ceramic layer 16 in the extension 
of the tooth interstices 18 is also removed on the comb transverse between 
the teeth or, respectively, the transducer 12 over the comb traverse 13 
shared by all of the teeth 12. FIGS. 1 and 4 are illustrated to scale. The 
spacing between, for example, each nozzle 11 or respectively between each 
tooth 12 amounts to approximately 250 um. 
Ceramic or glass can be provided instead of metal for the carrier layer 17 
as well as for the reinforcing layer 19. Examples of ceramic or glass 
materials utilized are aluminum oxide and silicon. 
Although various minor modifications may be suggested by those versed in 
the art, it should be understood that we wish to embody within the scope 
of the patent granted hereon, all such modifications as reasonably and 
properly come within the scope of our contribution to the art.