Note: Descriptions are shown in the official language in which they were submitted.
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1
Mechano-electrical Sensor
The present invention relates to sensing of force or vibration, delivering
electrical signals representative of the sensed force or a parameter of a
vibration
s state. More particularly, the invention relates to a mechano-electrical
sensor for
sensing force or vibration and delivering at least one electrical signal that
is a
function of the sensed force or vibration.
Force sensors, acceleration sensors and vibration sensors have many
uses, and exist in many embodiments. Usually, two or three separate sensors
are
to utilized e.g. to sense acceleration in three orthogonal directions, by
allowing mas-
sive bodies, suspended in spring systems, to move relative to respective
reference
frames. Rotation is usually sensed with a gyroscope device.
The present invention aims at providing a sensor that, better than previously
known solutions, is able to operate with a directional effect and provide good
mea-
~s surements regarding translation as well as rotation, by means of one
movable
body only.
Therefore, in accordance with the invention there is provided a mechano-
electrical sensor such as precisely defined in the appended claim 1.
Advantageous
embodiments of the invention appear from the attached dependent claims.
zo In the following, the invention shall be illuminated further by describing
exemplary embodiments of the invention, and in this connection it is also
referred
to the appended drawings, wherein
Fig. 1 shows a two-dimensional embodiment of the sensor in accordance
with the invention;
Zs Fig. 2 shows the same embodiment as Fig. 1, however suspended in an
outer frame;
Fig. 3 shows another two-dimensional embodiment of the sensor in accor-
dance with the invention;
Fig. 4 shows the same embodiment as Fig. 3, however suspended in an
so outer frame;
Fig. 5 shows a three-dimensional embodiment of the sensor in accordance
with the invention, with foil-shaped support structures, in a partially cut-
away view;
and
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Fig. 6 shows another three-dimensional embodiment with filament-shaped
support structures, this drawing also in a partially cut-away view.
In Fig. 1 appears a relatively simple, two-dimensional embodiment of the
sensor of the invention. An inner body 1 is supported by means of
piezoelectric
foils 3 in a framework 2, and non-appearing signal wires connected e.g. to
respec-
tive sides of a foil 3, are able to deliver electrical signals generated when
the foils
are subject to deformation due to shift of the inner body 1 relative to a
relaxed
centre position. The figure shows three foils tautened in a hexagonal opening,
however one single foil may be used, or a larger number of foils. The choice
of
inner body will depend on the use field of the sensor. The inner body may, in
uses
including recording from soft surfaces, consist of e.g. plastic or silicone
rubber with
various shore values. In other applications, for example industrial diamond
mate-
rial may be used. Combinations of material and geometrical shape of the inner
body is important. The inner body may also exhibit openings to provide a
possibi-
~s lity for air passage therethrough, for example in microphone applications.
The foils
may possibly be attached between two metallic frame parts that are insulated
from
each other and possibly from other frame parts along the periphery, so that
signals
can be collected from the metallic frame parts. When foils 3 are used such as
indi-
Gated in the figure, the stretch directions of the foils may be e.g. along the
longitu-
ao dinal direction for each foil strip, and this provides an opportunity to
collect a hig-
her, summed total signal compared to the case of only one single foil, either
as a
strip across the opening, or as a complete "diaphragm" covering the whole
opening.
Centering of the inner body 1 is not necessary, one may visualize embodi-
as ments with an inner body arranged in an eccentric position. Nor is the
shape of
framework 2 crucial, as long as the frame is rigid and suitable for attaching
the
piezoelectric foils.
Such a two-dimensional sensor will clearly be most sensitive with regard to
force or vibratory influence in a direction perpendicular to the plane spanned
by
so the sensor, but it will also be possible (when using several foils with
separate sig-
nal wires) to sense a force in the support plane, i.e. lateral movement of the
inner
body.
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In Fig. 2 appears the same embodiment as in Fig. 1, however the whole
basic sensor is suspended in an outside framework 5. The suspension is by
means of elastic elements 4, e.g. rubber elements, and such an embodiment of
the invention will be particularly favourable e.g. when using the sensor as a
sensor
s element in a microphone. The main purpose of the outside framework 5 is
noise
attenuation, i.e. attenuation of noise in the form of vibrations that may
bring the
piezo elements of the sensor into oscillation. When the sensor is attached to
an
outer frame 5, there will be two oscillatory systems, of which the inner
system is
the sensor itself. The design must then be so as to give the outer system a
reson-
ant frequency that is low relative to the resonant frequency of the system
compris-
ing inner frame/piezoelectric suspension structure/inner body. One will then
achi-
eve the effect that the frame works as a low pass filter. This relates
primarily to the
two-dimensional solution.
Further, it will be of great importance whether it is the framework 2 or the
~s inner body 1 that is supposed to oscillate in relation to the surroundings.
Ideally, it
is desirable to maintain the framework 2 at rest in relation to the
surroundings,
while the inner body oscillates relative to the framework. In practice, the
suspen-
sion of the sensor frame will normally provide "good" acoustic coupling
between
the surroundings and the sensor elements, and normally this is not desirable.
Gen-
ao erally, the mass of the inner body will influence the characteristic (the
frequency
response) most strongly, but design and material choice will also be of
importance
regarding the coupling between the "sensed medium" and the sensor. Due to the
coupled oscillatory systems, the characteristic must be optimized as a
function of
mass ratios, stiffnesses etc.
as In an application in a microphone that is supposed to be good at high fre-
quencies, the oscillations in the air will bring the suspension diaphragms
(see
Fig. 4) into oscillation, and the framework 2 will then oscillate around the
inner
body 1. In such a case, the vibrating part of the sensor must be as light as
possible.
3o In Fig. 3 appears an alternative embodiment of the sensor in accordance
with the invention, still in a two-dimensional version. Here appears an inner
body 1
suspended in a number of sector-shaped piezoelectric foils 3, and preferably
the
stretch direction for every foil sector is arranged in the same manner in
relation to
the radius in the respective position, e.g. pointing substantially in a radial
direction.
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There are small openings between foils in this case, which for example in
connec-
tion with use in a microphone, may be favourable regarding air passage through
the openings. Moreover, connection of signal leads is made in a similar manner
as
mentioned regarding Fig. 1, and it appears that it may be possible to achieve
high
s sum voltages with appropriate coupling of signal leads from each respective
foil
sector, if this is desirable. Alternatively, of course separate signals can be
collec-
ted from each respective sector.
Fig. 4 shows suspension in an outer frame 5 in the same manner as in
Fig. 2, however in this case the suspension structures are elastic, sector-
shaped
diaphragms made of e.g. rubber.
In Fig. 5 appears an embodiment of a three-dimensional type. The inner
body 1 is held suspended at the centre of a spherical frame 2, by means of
piezo-
electric foil pieces 3 arranged in such a manner that a relative shifting of
the inner
body 1, or a rotation for that matter, will be detectable by means of voltages
cre-
~s ated in the foils 3, and that can be collected by means of (not shown)
signal wires
connected to the two sides of the foil pieces projecting out through the
frame. Of
course, framework 2 does not have to be spherical, nor does it need to be
closed,
but it is important that it is rigid, in order to constitute a reference for
the position of
the inner body.
ao Fig. 6 shows a similar design, but the piezoelectric foils have been
replaced
by filaments, and the filaments are either of a piezoelectric type with
correspond-
ing function as the foil pieces in Fig. 5, or the filaments are taut and
substantially
inelastic, but attached to piezoelectric areas (not shown) of the framework,
so that
these areas generate voltages depending on the translation or rotation of the
inner
as body relative to framework 2.
Such a three-dimensional force/vibration sensor as shown in Fig. 5 and
Fig. 6, is based upon a rigid coupling between the framework and the body for
which force or possibly acceleration shall be measured, and thereby the
inertia of
the inner body will create the measurable voltages in the suspension
structures 3
30 or in their attachment areas. Hence, with signal leads coupled to suitable
process-
ing equipment, such an acceleration/vibration sensor may constitute a main ele-
ment in e.g. an inertia navigation system.
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Also the three-dimensional embodiments shown in Figs. 5 and 6 can be
suspended in an outer framework via an elastic material in two or three dimen-
sions.
The foil pieces shown in the embodiment of Fig. 5 may come in other sha-
s pes, for example more sector-like or possibly as approximations to full
circle areas,
and the planes to be spanned, do not necessarily have to be orthogonal like in
the
figure.
Besides, foil materials or filament materials are not the only possible materi-
als in this application, the suspension structures between inner body and
frame-
work may possibly be piezoelectric bimorph elements or similar elements.
The invention is also intended to accommodate the variant that has already
been mentioned, namely the variant with suspension structures that are not
piezo-
electric, but attached to piezoelectric areas of the framework.
