JPS6341008B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises a vibrating diaphragm member mounted at its edges and a piezoelectric ceramic disk on at least one of its sides for detecting or deflecting the diaphragm. relates to a piezoelectric vibration transducer mounted coaxially.

When such a diaphragm assembly is deflected in a direction perpendicular to its plane, the ceramic disk expands and contracts radially. The stress thus generated creates polar potentials on each disk surface, corresponding to the piezoelectric properties of the material. Electrodes in contact with both sides of such a disk transmit electrical signals between the transducer and the required type of external circuitry.

The invention particularly relates to a piezoelectric transducer in which the diaphragm and the ceramic disk carried thereon are free to flex in the fundamental mode at their natural or natural frequency.
Under such conditions, the transducer is a very sensitive vibration sensing device at its resonant frequency and generates vibrations with good efficiency in response to periodic input electrical signals. You can also do that.

To ensure optimal sensitivity of selective response at a severely limited target frequency, whether for vibration detection or vibration generation, the resonant frequency of the transducer should be as close to that target frequency as possible. It is important to match.

Such a selectively responsive transducer is
Difficulties in manufacturing economical transducers with well-defined resonant frequencies that are sufficiently uniform from unit to unit have limited their use in the past. Under conditions of mass production, the resonant frequencies of individual transducers differ from each other over a range that is too wide for many applications, especially if manufacturing costs are to be kept to a minimum. There is a tendency.

One important object of the present invention is to provide a structure and method for improving the resonant frequency uniformity of a piezoelectric ceramic resonant transducer of the type described above without significantly increasing manufacturing costs.

More specifically, it is an object of the present invention to reduce differences in resonance frequency between units due to differences in the dimensions of ceramic sensors.

The inventors have determined that the frequency differences between individual transducers are often due to slight differences in the diameter of the piezoelectric sensors that form an effective integral part of the vibrating element. I discovered something. The production of piezoelectric ceramic sensors requires
It includes a firing process (contracting the vibrating element) that is difficult to accurately control at low cost. Therefore, the diameter of the finished ceramic disk typically has a much larger tolerance than the dimensions produced by conventional metal manufacturing methods. For example, the inner diameter of the clamp structure is considered to be much more accurate than the disk diameter.

Furthermore, we have discovered that changing the diameter of the sensing disk by only a few percent can result in relatively large changes in the resonant frequency of the completed transducer. This is believed to be due to the fact that the effective spring constant of the vibrating system tends to be highly dependent on the part of maximum flexibility. In the construction according to the invention, the peripheral annular zone of the diaphragm, which is exposed with only the diaphragm between the outer diameter of the detection disc and the surrounding rigid support structure, is increased in rigidity by the ceramic sensor. It is much more flexible than the sandwich-like portion of the diaphragm assembly.
The resonant frequency is therefore primarily determined by the radial width of the exposed annular zone of this diaphragm.

Also, the width of such a sensitive annular band is typically only a small fraction of the disk diameter, so that relatively small changes in disk size can provide wide tuning of the resonant frequency. For example, in the case of a disk that is only 2% larger than the specified size, the width of the annular band can be reduced by as much as 20%. The resulting change in the effective spring constant changes the resonant frequency much more than the associated approximately 4% increase in the mass of the ceramic disc (particularly in the vicinity of the outer diameter, where such excess mass has a relatively small amplitude). (This is because it is located in

The present invention allows the diameter of the ceramic disk to vary due to errors in the normal manufacturing process as described above, and such a change in the diameter of the ceramic disk significantly changes the resonant frequency of the transducer. This is to eliminate the cause. This is achieved by introducing a structure that defines a zone of high flexibility so that it is nearly independent of the disk diameter. From a different perspective, the present invention clarifies the outer peripheral edge of the central region of the diaphragm, which has increased rigidity by mounting a ceramic disk. To provide such a boundary, the metal diaphragm is artificially stiffened, at least within a precisely defined zone that includes the entire area where the periphery of the ceramic disk varies as a result of manufacturing tolerances.

This is achieved, for example, by fixing or soldering an annular stiffening member to the side of the diaphragm opposite the sensor. One preferred method is to provide a plurality of circumferentially spaced ribs extending radially across the zone where the stiffness of the diaphragm is to be increased. Such ribs are usually formed integrally with the diaphragm. Increasing the rigidity to a required degree can be easily achieved, for example, by appropriately selecting the number and cross-sectional shape of the rigidity-increasing ribs.

The most desirable degree of stiffness increase will depend on many factors in the individual situation. It is preferable to increase the rigidity of the diaphragm alone by at least twice the increase in rigidity due to the lamination of ceramic discs, and a factor of 5 or more will stabilize the resonance frequency. The degree of this will further improve. In practice, it is often convenient to make the structure substantially more rigid than the flat diaphragm material within a fairly narrow band at the edge of the sensor. Increasing the stiffness at a sufficient rate can be achieved by, for example, using eight ribs (each approximately rectangular U-shaped and having a depth of the order of five times the thickness of the diaphragm sheet material). This is accomplished by providing uniformly circumferentially spaced locations.

The ribs are shaped in such a way that their height gradually decreases at least at their inner ends, so that the stiffening effect gradually decreases with decreasing radius and the position of the minimum radius due to disc manufacturing tolerances. becomes zero at a radial position sufficiently inside,
Preferably, the main part of the two-layer region which is to act as a vibrating body remains unaffected by the stiffening effect of the ribs.

The rib structure described above has the further advantage that the excess adhesive required to fully bond the ceramic disk and diaphragm member may flow into the hollow ribs. Such action reduces the tendency for the adhesive to spread onto the diaphragm surface surrounding the sensor (which would significantly change the effective elastic constant). Since the ribs are themselves rigid, the excessive stiffening effect of such excess adhesive in the rib channel has little effect on the elastic constants of the device.

The invention will now be described in detail with reference to preferred embodiments thereof, with reference to the accompanying drawings.

In FIGS. 1 and 2, a diaphragm assembly designated by the reference numeral 10 includes a circular metal diaphragm member 12 and a piezoelectric sensing element 20 assembled coaxially with respect to an axis of symmetry 11. Contains.
The diaphragm member 12 has a central diaphragm portion 14
and a substantially annular outer mounting portion 16.
Each of these diaphragm parts is numbered 1
5, 17 are axially offset in parallel planes and are connected by a generally cylindrical coupling structure 18. The coupling structure 18 is preferably an integral part of the diaphragm member and may be formed by forging or drawing a circular piece of sheet metal in a conventional manner. The cylindrical coupling structure 18 improves radial flexibility and stabilizes the resonant frequency against thermal and other effects due to clamping of the diaphragm edge 16.

Sensing element 20 typically includes a disk of piezoelectric ceramic material treated in well-known manner to create a potential difference between the two planes when curved from its plane. Both surfaces of the ceramic disk are made electrically conductive by, for example, applying a suitable electrode material. One disk surface is coaxially attached to one surface of the diaphragm portion 14 on the side within the cylindrical coupling structure 18, such as by a thin layer of epoxy adhesive allowing electrical contact between the two surfaces. is joined to.
A wire conductor 24 is soldered to the other disk surface near the periphery of the disk at a location indicated at 25. The electrical signal from the detection element 20 is taken out as a potential difference between the electrical conductor 24 as an actuation terminal and the detection element 20 as a ground terminal.

Central diaphragm portion 1 of diaphragm member 12
4 and sensing element 20 constitute a diaphragm assembly 22 that acts as an effective integral vibrating element. The fundamental mode of vibration of such a diaphragm assembly involves its central region curving up and down, the resonant frequency of which is the combined mass of these components in a modified state due to the presence of the coupling structure 18. , dimensions, and elastic modulus.

If it is desired that such a transducer be sensitive to a particular frequency, the dimensions of the diaphragm assembly are selected such that its fundamental resonance occurs near that frequency, and the diaphragm assembly is The assembly is mounted and stored in a manner that allows it to resonate freely without external interference. When vibrations of such a specific frequency are present in the surrounding atmosphere or when vibrations are applied externally to the entire housing, the diaphragm and sensing element vibrate with increased amplitude due to resonance. The transducer thus becomes a very sensitive instrument for detecting the presence of or generating vibrations of a particular frequency.

The dimensions and detailed form of the diaphragm member and sensing element may vary within wide limits selected in relation to the desired value of the resonant frequency. For example, the present invention may have a diaphragm member having an overall diameter of 1 inch (2.5
cm) and have been found to be very effective in conjunction with transducers whose members are formed of approximately 0.005 inch (0.13 mm) sheet material. Piezoelectric disc sensing elements used with such diaphragms typically have a thickness of
It is about 0.010 inch (0.25 mm) and the diameter is 0.60 ~
It is 0.75 inches (15.2 to 19.1 mm) and has a resonant frequency around 6kHz.

The invention particularly concerns the different resonant frequencies of individual transducers of the same design. As shown by reference numeral 28 in FIG. 4, which is exaggerated to some extent for clarity of explanation,
It has been found that relatively large manufacturing tolerances in the radius of the sensor can cause the position of the sensor's periphery 26 to vary within the error region 28, resulting in significant instability of the resonant frequency as discussed above.

The present invention substantially increases manufacturing costs by providing a means for stiffening its diaphragm member within a relatively precise annular zone extending at least between the maximum and minimum diameters of sensor 20. This method overcomes the above-mentioned difficulties without causing problems. That is, the zone of increased stiffness includes at least the error region 28 of the entire sensor.

In the illustrated embodiment of the invention, the stiffening means includes a radial rib 70 projecting from the face of the diaphragm opposite the sensor and extending across an annular region 72. This annular area includes an error area 28 that may or may not be covered by the ceramic disk. Rib 70 is typically formed integrally with the diaphragm member by conventional stamping means.

Preferably, the ribs 70 are sheared at their outer ends 74 to precisely define the outer periphery of the area where stiffness is increased. Preferably, such outer diameter is equal to or only slightly exceeds the maximum diameter area of the sensor, so that the exposed portion of the diaphragm is kept as undisturbed as possible. The inner ends of ribs 70 may be similarly treated if desired. However, it is generally preferred that the ribs be smoothly connected to a flat sheet (diaphragm member) at their inner ends, as indicated at 76. Thus, the stiffness increasing effect becomes zero at the inner boundary of the region 72, so that the stiffened outer region smoothly connects to the untreated inner region,
It is also believed that the tendency of the ribs to disrupt normal mode vibrations is reduced. Preferably, however, the taper of the ribs is steep enough to leave a relatively large central area of the sanderch arch, allowing that portion to bend freely in a conventional manner.

As shown, the rib 70 has a U-shaped cross section,
It has a constant width and a depth that decreases uniformly from a maximum at the outer end 74 to zero at the inner end 70. Such a linear configuration somewhat facilitates the manufacture of the rib 70 by conventional machining methods, and also allows for negligible vibration of the rib section across a relatively narrow range of error 28 at the sensor's outer periphery. It is something.

The increased depth of the ribs at their outer ends indicates that the adhesive used to secure the sensor to the diaphragm surface, as shown somewhat diagrammatically at 23, It is useful to provide a large volume for accommodating excess amounts of water. Changes in the amount of adhesive thus absorbed may change the stiffness of the ribs, but the effect is relatively small since such stiffness is already sufficiently large. The resulting change in resonant frequency is therefore also small, and in fact has a much greater effect than the same amount of excess adhesive would have, especially if extruded onto the exposed diaphragm surface. It is understood that this is negligible compared to the above.

The basic effect of the ribs 70 described above is to provide the diaphragm member with an increased stiffness section that extends over the error region of the sensor dimensions with respect to normal modes of vibration. The overall effective elastic behavior of the diaphragm assembly is thus rendered largely independent of the exact position of the sensor outer periphery. Normal variations in sensor diameter and slight deviations from exact concentricity in position on the diaphragm will result in very little difference in the resonant frequency from one unit to another. Therefore, the normal variations in sensor diameter, which would result in large differences in resonant frequency from unit to unit, are reduced by the rib stiffness and have a negligible effect.

An exemplary mounting and housing structure for detecting mechanical vibrations in a machine frame or other test member is shown at 30 in FIG. 3 with its axis of symmetry 31 vertical. The housing base 32 has at its lower end a stable mounting structure, illustrated as a coaxial thread 34, which rigidly fixes the measuring instrument on the test member 35 whose resonant frequency is to be detected. It is now possible to attach it to The upper end of the housing base 32 is formed with a hollow portion coaxial with itself, and has an upwardly directed annular mounting surface 38 and a relatively thin outer retaining flange 39 (curved from an initial position extending in the axial direction to a clamping position as shown). A recess 36 is formed, which is surrounded by a recess 36 (which is possible).

The cover member 40 has a substantially cup shape,
It has a morning glory-shaped mounting rim 42. A generally circular aperture 43 is formed in the flat cup base of the cover member and a hemmed flap is curved upwardly to define a conventional plow-shaped terminal.
A second terminal 46 having a similar shape and having an annular integral conductor guide 47 is insulated within the hole 43 of the cover, such as by a sealing wall 48 made of a plugging compound and defining a chamber 58. It is installed at. The conductor guide 47 forms a secure passage through the sealing wall 48 through which the conductor 42 can be inserted.

The edge 16 of the diaphragm member is spaced from the mounting surface 38 by a spacing and centering ring 50 formed of an electrically insulating material such as glass-reinforced epoxy resin. is preferred. The conductor 24 is soldered to the terminal 46 at a location indicated at 49 sealing the passageway formed in the guide 47.
The base flange 39 is curved onto an O-ring 54 and a second spacing/insulating ring 52 firmly clamps the diaphragm assembly and seals the housing from external contamination.

The housing structure of FIG. 3 is merely illustrative and may be modified as necessary to suit particular requirements, so long as the diaphragm assembly 22 is free to vibrate at its resonant frequency without interference. It's okay to be. For example, it may be desirable to detect or generate vibrations at a particular frequency in a gaseous medium, such as air, rather than within a mechanical member, such as test member 35. For this purpose, the base 32 may be provided with any suitable type of mounting structure around its periphery in place of mounting studs 34 in a manner well known in the art, and the lower portion of the base may be provided with an atmospheric vent. Sufficient holes connecting between chamber 56 and the outside may be provided in a known manner to allow vibrations to pass through.

Ribs 74 or equivalent structures for locally imparting stiffness to the diaphragm according to the invention are preferably used in combination with the cylindrical structure shown at 18 and disclosed in detail in the aforementioned patent application. . However, the advantages provided by the invention are independent of other frequency stabilization measures.

The accompanying FIG. 5 depicts an exemplary embodiment of the invention as a conventional flat diaphragm member having an edge 16a in the same plane as the diaphragm portion 14. Localized stiffening of such diaphragms is typically provided by a plurality of angularly spaced ribs 70 which are essentially similar to those described above and function in substantially the same manner. can get.

As described above, the present invention significantly improves the technology of resonant piezoelectric ceramic transducers by eliminating the normal error in the diameter of the ceramic sensing disk, which is the cause of differences in resonant frequency from unit to unit. It is.

Although the present invention has been described above in detail with respect to specific embodiments thereof, the present invention is not limited to such embodiments, and various modifications and omissions can be made within the scope of the present invention. This will be clear to those skilled in the art.

[Brief explanation of the drawing]

FIG. 1 is an illustrative plan view showing a diaphragm and sensor embodying the invention. FIG. 2 is an illustrative front view of the diaphragm and sensor of FIG. 1, partially cut away along a plane passing through the axis. FIG. 3 is an illustrative longitudinal cross-sectional view of a mounting/housing structure according to the present invention. FIG. 4 is an illustrative enlarged partial view showing a portion of the diaphragm and sensor shown in FIG. 2 on an enlarged scale. FIG. 5 is an illustrative enlarged partial sectional view showing one modification example. 10 - diaphragm assembly, 11 - axis of symmetry,
12 - diaphragm member, 14 - central diaphragm section, 16 - mounting section, 18 - connecting structure or cylindrical section, 20 - sensing element, 22 - diaphragm assembly, 23 - epoxy adhesive, 24 - conductor, 30 - Machine frame, 31 ~ axis of symmetry, 3
2 - Housing base, 34 - Threaded part, 35 - Test member, 36 - Recess, 38 - Mounting surface, 39 - Holding flange, 40 - Cover member, 42 - Mounting rim, 43 - Circular hole, 46 - Second terminal , 47~conductor guide, 48~seal wall, 49~terminal, 5
0,52~ring, 54~O ring, 56,58
- chamber, 70 - rib, 72 - annular region, 74 - outer end, 76 - inner end.

Claims (1)

[Scope of Claims] 1. A diaphragm member 12 having a diaphragm portion 14; a support structure 32 that supports the diaphragm member at its peripheral edge portion; A piezoelectric ceramic sensing element 20 in the form of a sheet piece is mounted on the diaphragm portion so as to be substantially aligned with its center so that its periphery is exposed, and is integrated with the diaphragm member to form a diaphragm. a piezoelectric sensing element adapted to provide an assembly; and an annular region of said diaphragm portion extending along a planar contour of said piezoelectric ceramic sensing element for adjusting the natural frequency of said diaphragm structure to a predetermined value. means 70,2 for selectively stiffening 72;
3. A piezoelectric transducer comprising: