Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to an electro-pneumatic
signal converter comprising a piezoelectric bending element
which is elastically pretensioned against at least three
bearing supports, of which at least one is adjustable to
permit setting of the bending element relative to the port.
A signal converter of this type is known, for example,
from EP-B1 191011. In this converter, the piezoelectric
bending element is held by a guide spring that is anchored
in the sender housing, pressed against the bearing supports,
and lies on the supply-air port, for example, under spring
tension. As soon as a voltage is applied to the bending
element, this lifts away from the supply-air port and closes
the exhaust-air port. The signal output of the signal
converter, which was evacuated through the exhaust-air port,
is thus connected to the supply-air port, so that pressure
medium supplied through the supply-air port is present at
the signal output as a pneumatic pressure signal. As soon
as the voltage at the piezoelectric bending element is
switched off, or its polarity is reversed, the bending
element moves back into the starting position, when the air
is once again removed from the signal output. This electro-
pneumatic signal converter is distinguished by a low power
requirement and operates without any notable energy
consumption, so that it can advantageously be used to
replace conventional solenoid valves for the electrical
activation of pneumatic circuits and apparatuses.
The three point suspension of the piezoelectric on the
support bearings permits initial setting or adjustment of
the position of the bending element between the ports that
are to be controlled. In addition to an adjustment by axial
displacement of the ports that are to be controlled, this
initial adjustment can be effected, in particular, by
setting at least one of the three support bearings, when the
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CA 02093257 2002-05-31
effect of the pneumatic output signal can be very easily
observed.
During the installation of the known signal converter
described heretofore, it is usually difficult to avoid the
piezoelectric bending element from being mechanically warped,
at least briefly. As a result of the so-called mechanical
relaxation (this is a familiar characteristic, in particular
of piezo-ceramic), this bending only reverts in part
l0 immediately after mechanical relief. Because of the fact
that the relief of the bending element is effected by the
adjustment of the support bearings, which are then preferably
secured by adhesive, mechanical relaxation can still take
place even after this initial adjustment. Signal converters
that react in this way drift in the course of a few hours
after installation or adjustment out of the usable and
adjusted range of the bending element position; because of
the adjustable support bearings that have already been
permanently secured (and in particular cemented) this leads
to the fact that the complete signal converter has to be
considered as scrap.
It is an object of the present invention to so improve a
signal converter of the type described in the introduction
hereto that the disadvantages addressed heretofore are
alleviated, and in that, in particular, the production
wastage rate is not increased as a result of additional
mechanical relaxation of the piezoelectric bending element or
by adjustment errors only noted subsequently.
According to the present invention there is provided an
electro-pneumatic signal converter, for controlling at least
one pneumatic port, comprising a housing and a piezoelectric
bending element mounted in that housing and resiliently
biased against at least three supports. At least one of the
supports is adjustable to permit setting of the bending
element relative to the at least one port. The at least one
adjustable support comprises a sleeve insert fixedly-mounted
in the housing and a supporting pin axially-movable in that
sleeve.
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CA 02093257 2002-05-31
More specifically, there is provided a signal converter
wherein the adjustable support bearing has a supporting pin
arranged in a concentric sleeve insert, the position of which
relative to the other support bearings is fixed after
adjustment, and which can be adjusted axially relative to the
sleeve insert. The adjustable support bearing is thus made
essentially so as to be divided into two parts. The outer part,
which is configured as a concentric sleeve insert, can be
secured relative to the housing or to the other support bearings
during the initial setting adjustment or after this has been
done, for example, by adhesion, by compression or the like. The
second part, which is configured as a supporting pin, is also
adjustable after the initial setting or fixing of the first part
in an axial direction relative to the insert sleeve, whereby
corrections, for example, to counteract the continuing
mechanical relaxation that has already been described, are
possible after initial adjustment of the signal converter. The
supporting pin itself needs only very small adjustment travel,
for the positional errors of the bending element that occur
after the initial adjustment are usually very small, relatively
speaking. If the adjustable support pin is not to be
additionally secured relative to the sleeve insert, the
supporting pin can naturally be such as to be difficult to move
within the sleeve insert so that any unintended maladjustment is
precluded.
In a signal converter of the type described heretofore, in
which the support bearing that can be moved to provide
adjustment is also configured as an electrical contact for the
bending element, in a preferred additional embodiment of the
present invention provision is made such that the adjustable
support pin serves directly as a contact pin. This permits a
simple configuration of the signal converter, for both the
support pin and the contact pin require direct contact with the
surface of the piezoelectric bending element or the electrodes
that are installed there.
According to another configuration of the present
invention, the supporting pin can have a fine pitch thread that
works in conjunction with the sleeve insert, which ensures
precise adjustability and at the same time provides
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a simple method of ensuring that loss of adjustment will be
difficult; this is achieved by the dimensions of the threads
that work in conjunction with each other.
According to another embodiment of the present
invention, the supporting pin can also have a sloping front
end that lies against a support that projects eccentrically
to the supporting pin on the bending element. This also
provides for simple and precise subsequent adjustability of
the supporting pin relative to the sleeve insert.
The invention will now be described in more detail, by
way of example only, with reference to the accompanying
drawings, in which:
Figure 1 is an axial cross-section through a signal
converter configured according to the present invention, on
the line I-I in figure 2;
Figure 2 is a cross-section on the line II-II in figure
1; and
Figure 3 is a cross-section on the line III-IIT in
figure 2.
The electric-pneumatic signal converter shown in
figures 1 to 3 consists of a pick-up housing 1 forming a
tightly sealed chamber 2, within which a piezoelectric
bending element 3 is arranged. A pneumatic signal output 4
leads out of the chamber 2. In addition, a supply-air port
5 and an exhaust-air port 6 are installed in drilled holes
in the housing 1 that are aligned with each other. The
piezoelectric bending element 3 is secured and guided in the
chamber 2 by means of a guide spring 7. This controls the
supply-air port 5 and the exhaust-air part 6. Contact pins 8
and 9 are installed in the pick-up housing 1 in order to
deliver electric power to the piezoelectric bending element
3.
The pick-up housing Z consists of two solid plates 10
and 11, which are preferably of rigid and preferably
electrically insulating material, e.g., ceramic or glass.
The chamber 2 is formed by flat recesses 12 and 13 in the
plates 10 and 11. It can be seen, in particular from
figures 1 and 3, that the recesses 12, 13 in the plates 10
and 11 fit tightly around the piezoelectric bending element
3 and the associated guide spring 7, so that only the
required tree play and the over-dimension that is required
for manufacturing tolerances remain. The two plates 10 and
11 are an air-tight fit around the recesses 12, 13, and they
are preferably cemented to each other.
Z5 The piezoelectric bending element 3 is essentially
supported on three support bearings within the chamber 2,
these being spaced apart from each other. In the exemplary
embodiment that is shown, one support bearing 14 is formed
on the lower end of a supporting pin that simultaneously
serves as a contact pin 8. This is installed with a sleeve
insert 15 in a drilled hole in the plate 11 of the pick-up
housing 1. In contrast to this, the other supporting
bearings are in the form of pivot bearings 16 that project
from the plate 11 into the chamber 2 like knobs. The two
supporting or pivot bearings 16 are indicated by dashed
lines in figure 2.
The guide spring 7, which is shown in plan view in
figure 2, presses the piezoelectric bending element 3
against the support bearings 14 and 16. This acts on the
piezoelectric bending element 3 with a point-like supporting
point 17 that is formed from a hemispherical bead, in an
area that lies in an axial direction between the support
bearing 14, at one end, and the bearings 16, at the other.
5
It can be seen from figure 2 that the point of support 17 is
on a tongue 18 that is formed by lateral cuts 19. The guide
spring 17 is secured to the pick-up housing 1 by tabs 20
that project from the sides over the piezoelectric bending
element 3 and which are clamped securely between the two
plates 10 and 11 of the pick-up housing 1. The contact pins
9 that are anchored in the pick-up housing 1 engage in
drillings in the tabs 20 to provide a centering effect.
This also ensures the supply of electrical power through the
contact spring 7 to the piezoelectric bending element 3. A
bead 21 that runs transversely to the guide spring 7 between
the tabs 20 provides a stiffening effect. The bent-over
edge 22 of the guide spring 7 also serves the same purpose
and provides an additional centering effect; this edge
extends into a groove 23 in the plate 10 of the pick-up
housing 1.~ The guide spring has similar retaining tabs 24
that extend from the side in the area of the tongue 18;
these are bent around the piezoelectric bending element 3
and secure this.
It can be seen from the drawings that the piezoelectric
bending element 3 is held securely in the pick-up housing 1
by the guide spring 7 and is guided precisely. It presses
the piezoelectric bending element 3 against the support
bearings 14 and 16 that are so arranged relative to each
other that the end of the piezoelectric bending element 3 is
pressed onto the supply-air part 5 and closes this tightly.
In this position, which is shown in figure 1, the signal
output 4 is connected through the chamber 2 with the
exhaust-air port 6 and is thereby relieved. When an
electric voltage is supplied through the contact pins 8 and
9, the piezoelectric bending element flexes, whereupon it
lifts away from the supply-air port 5 and closes the
exhaust-air port 6. The pressure medium that is delivered
through the supply-air port 5 can then move into the chamber
2, and out of this to the signal output 4, which means that
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the electrical signal is converted into a pneumatic pressure
signal. As soon as the supply of electrical power is cut
oft, the piezoelectric bending element 3 moves back into its
starting position, whereupon the signal output 4 is once
again relieved.
The three-point suspension of the piezoelectric bending
element 3 on the plate 11 of the pick-up housing 1, or on
the supporting bearings 14 and 16, respectively, permits
precise adjustment of the position of the bending element 3
between the supply-air port 5 and the exhaust-air port 6.
Initial adjustment or setting is possible by axial
adjustment of the supply-air port 5 and of the exhaust-air
port 6, as well as of the sleeve insert 15 together with the
support or contact pin 8, the lower end of which forms the
support bearing 14. After this initial adjustment of the
correct position of the bending element relative to the two
ports 5 and 6, the sleeve insert 15 is fixed in its position
relative to the pick-up housing 1, to which end, for
example, the sleeve insert can be cemented into the
drilling.
In order to permit another subsequent correction to
this setting even after this initial adjustment or after the
final establishment of the position of the sleeve insert 15
relative to the housing 1, the supporting or contact pin 8
is adjustable in the axial direction by way of a thread 25
with a. fine pitch that acts in conjunction with the sleeve
insert 15, by rotation relative to the sleeve insert 1'S,
when the supporting bearing 14 also remains additionally
adjustable. Despite the small deflection of the
piezoelectric bending element 3, this also makes precise
subsequent adjustment of the signal converter.
Quite apart from the arrangement of three supporting
bearings that is shown and which has been discussed, of
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which the one that simultaneously serves as an electrical
contact is adjustable both initially and subsequently, a
plurality of supporting bearings could also be provided and
of these, once again, several could be adjustable either
initially and/or subsequently, when this could also be done
independently o~ the electrical contact that they provide.
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