Buzzer having spring blade vibrating at natural frequency

BACKGROUND OF THE INVENTION

Field of the invention

This invention relates to buzzers and, more particularly, to buzzers in which the sounds are produced by a membrane that an elongated spring blade set and entertained in vibration at a natural frequency by an electrodynamic transducer mechanically causes to vibrate.

Description of the prior art

In the known buzzers of this type the vibrating blade causing the membrane to vibrate is itself fixed to a supporting member at one of its ends. The other blade end strikes against the membrane.

These known buzzers, however, operate satisfactorily only if delicate and time expensive setting operations have previously been carried out. The vibrating blade or the armature secured thereto must be at an exact distance from the electromagnet of the transducer. This result is not easy to obtain with a blade fixed only at one of its ends. The sound intensity, indeed, decreases quickly if that distance is somewhat increased. If that distance is, on the contrary, decreased the armature remains in contact with the core of the electromagnet. Moreover, the distance between the blade and the membrane must also be set with a great precision. As soon as the membrane is somewhat too faraway from the blade, it is no longer satisfactorily excited by the latter and the sounds are substantially weaker. On the contrary, if the membrane is set too near to the blade, it impedes the latter by causing it to remain in contact with the core of the electromagnet.

Moreover, the material of the blade must be of a very high quality. In particular, the blade should not be subjected to altering. The smallest weariness would have as a consequence a modification of the distances between the armature and the electromagnet and between the blade and the membrane and would cause a perturbation of the alarm.

Since it is one end of the spring blade which strikes against the membrane in the known buzzers, the latter have the further drawback that they are cumbersome, because the blade cannot be arranged within the boundaries of the membrane unless the latter is made with excessively large sizes.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a buzzer which can be set easier during the manufacture and which does not risk to be put out of order in use while being less cumbersome than the known buzzers of the same type.

A more specific object of the invention consists in providing a buzzer in which the vibrating spring blade is rigidly fixed at its two ends to a supporting member of the buzzer.

By fixing the vibrating spring blade at its two ends so as to cause the middle portion thereof to vibrate, it is possible to keep the distance from that blade to the electromagnet core within very narrow tolerances. The membrane need then only be set at the proper distance of the vibrating blade in order to obtain a buzzer producing a satisfactory sound and keeping its qualities in use.

In some buzzers, in particular in the small ones, it has, however, been observed that upon mounting the same in an apparatus or instrument, the mere fact to fix the buzzer therein could produce disturbing deformations of the blade support with respect to the membrane.

That drawback can, however, be removed by securing the membrane to an own supporting member and by providing adjusting means permitting one of the supports of the membrane and of the vibrating blade to be set with respect to the envelope enclosing the buzzer parts.

Still further objects of the invention will become apparent in the course of the following description.

BRIEF DESCRIPTION OF THE DRAWING

One embodiment and a modification of the buzzer according to the invention are represented diagrammatically and by way of example in the accompanying drawing in which:

FIG. 1 is a diametrical cross-section of that embodiment;

FIG. 2 is a plan view thereof, some parts having been removed and other ones having been partly broken away;

FIG. 3 is a cross-section of the modification along a diametrical plane perpendicular to that of the cross-section of FIG. 1, and

FIG. 4 is a wiring diagram of the electronic control device of the buzzer.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The buzzer represented in FIGS. 1 and 2 is mounted in a support 1. The support 1 is provided with a first cylindrical recess 2 and with a second elongated recess 3 in the bottom of recess 2. FIG. 2 shows that recess 3 extends along a diameter of recess 2.

The buzzer itself firstly comprises a fixed armature including: a ferromagnetic plate 4 (FIG. 1) set on the bottom of the elongated recess 3; a core 5 also made out of a ferromagnetic material and secured to plate 4, and two permanent magnets 6 having a parallelepipedic shape and being set on a plate 4 near the ends thereof within recess 3. The height of magnets 6 is equal to that of the part of core 5 which extends above plate 4. The buzzer, moreover, comprises a plastic body member 7 which is accommodated in a recess 8 extending in parallel to recess 3 so that body member 7 is located on the side of plate 4. Furthermore, body member 7 is flush with the bottom of the cylindrical recess 2. Body member 7 carries the electrical parts which ensure the operation of the buzzer. These members comprise a transistor 9 and a resistor 10 both embedded in body member 7. They also comprise two coils 11, 12, which are rigidly secured to body member 7 for instance by gluing, and extend around core 5 between magnets 6. As shown in FIG. 4

3,530,463 the energizing coil 11 and the motor coil 12 are connected to an input circuit and an output circuit, respectively, of transistor 9 which starts oscillating when its input and output leads 13, 14 are set to an electrical potential.

Tests made with a transistor 9 of the type AC 129, a resistor 10 of 400 ohms, a coil 11 of 420 windings and a core 12 of 840 windings had a satisfactory result.

In a modification (not shown) the transistor and the resistor of the amplifier could be replaced according to the integrating technic by a single solid member. The coils 11 and 12 are wound up simultaneously; their windings are glued together so as to form a rigid body member which can itself be glued on body member 7 in which the other circuit means are embedded. The extremely thin electrical conductors (the diameter of which is about ^s/ioo mm.), which come out of coils 11 and 12 and which are connected to transistor 9 and to resistor 10, are also embedded in the mass of body member 7 and are, consequently, protected.

The input and output leads 13, 14 of the oscillator described can be connected to terminals 15, 16 (FIG. 3) of the supporting member of the buzzer by passing through the wall of that support. If the latter consists, for instance, of a plastic, the leads 13, 14 can easily be embedded in the mass constituting the walls of the support.

To retain the magnets 6 as well as body member 7 in place within recess 2, a magnetic frame member 17 extending in part above magnets 6 and coils 11, 12 and in part beyond the space occupied by those elements, is secured at its two ends to supporting member 1 by means of two screws 18. The latter, moreover, serve to fix the ends of an elongated spring blade 19 on the parts of member 17 extending beyond the boundaries of recess 3. In that way, spring blade 19 is rigidly fixed at its two ends and it extends above magnets 6, coils 11, 12 and core 5 which cause blade 19 to vibrate and constitute an electrodynamic transducer. A movable ferromagnetic armature 20 is secured to the center of blade 19 so as to extend within a central opening 17« of frame member 17, however, without coming in contact either with magnets 6 or with core 5. The movable armature 20 nevertheless closes the magnetic circuit of the fixed armature. The thickness of frame member 17 is chosen with respect to that of the movable armature 20 so that the latter which extends within frame member 17 does not come in contact with magnets 6 when blade 19 is vibrating, the air-gap between the fixed and the movable armatures being, however, as small as possible.

Since blade 19 is rigidly fixed at its two ends, it holds armature 20 at rest in a relatively stable position. When the transistorized amplifier is energized, blade 19 vibrates at a natural frequency, the amplitude of which is, however, small.

As soon as the leads 13 and 14 are set to an electrical' potential, the current oscillations produced by the transistor 9 in the coils 11, 12 cause the magnetic field through the air-gap between the movable armature 20 and the fixed armature (4 to 6) to be modified thus periodically attracting armature 20 and causing blade 19 to vibrate at a natural frequency which can range between 600 and 900 Hz.

The blade 19 is provided in its center with a projection 21 striking against the apex of a conical plastic membrane 22 which produces an audible sound when the transistorized oscillator is energized. Membrane 22 is made with a peripheral flat flange 23 seceured for instance by gluing to a ring 24 serving as a supporting member for the membrane. Ring 24 is threaded and screwed into a tapped opening 25 of supporting member 1 which, in combination with membrane 22, forms an envelope enclosing the buzzer parts mounted within recesses 3 and 8. The outer surface of ring 24 is provided with at least one pair of holes 26 which can be engaged by an appropriate tool for screwing and unscrewing ring 24 in opening 25. A perforated cover member 27 provided with a threaded peripheral rim, is screwed in opening 25 above ring 24. Cover member 27 protects membrane 22 by preventing foreign bodies from coming in contact with the membrane and tearing the same. The perforations of cover member 27 set the membrane in communication with the atmosphere thus ensuring a free propagation of the sounds produced by membrane 22.

To excite membrane 22 under the best possible conditions, projection 21 of blade 19 advantageously strikes against the membrane in a point located as near as possible to the apex of the membrane, i.e. to the center thereof. Due to the fact that blade 19 is rigidly fixed at its two ends, it is also its center point which has the largest amplitude when the transistorized oscillator is energized and which strikes against the membrane 22. Using a blade 19 rigidly fixed at its two ends has the advantage to permit the buzzer to be manufactured compactly. It is in particular possible to locate the blade 19 within the boundaries of membrane 22 since this blade is arranged along a diameter of the membrane. The space at disposal under the membrane is, moreover, exploited more judiciously than with the known buzzers in which the blade is accommodated along a radius of the membrane thus leaving unoccupied an important sector of the space covered by the membrane.

In order that projection 21 of blade 19 conveniently strikes against membrane 22, the apex of the latter must be set in a very, precise position with respect to blade 19. If membrane 22 is too far away from blade 19 the latter does not reach the membrane when it vibrates. On the contrary, if membrane 22 is too near to blade 19, it impedes the latter. Upon making the tests it can easily be observed that the distance between membrane 22 and blade 19 must be set with a precision of some hundredths of mm.

That setting operation is carried out at last in the embodiment described, i.e. after having assembled the buzzer. That setting operation is possible because membrane 22 is not rigidly fixed to supporting member 1 in a definite position. Upon screwing more or less ring 24 carrying membrane 22, the latter is moved relative to blade .19. The distance between blade 19 and membrane 22 obviously need not be measured. It suffices to cause blade 19 to vibrate by energizing the transistorized oscillator. The workman entrusted with that adjusting operation can then easily displace membrane 22 by screwing more or less ring 24 since the latter is accessible as soon as cover member 27 has been removed. To set membrane 22 in the convenient position that workman will only have to energize the transistorized amplifier so as to cause blade 19 to vibrate. He will then be guided by the quality of the sounds produced by the membrane. Once the optimum quality of the sound has been reached, cover member 27 is set in place where it serves as a lock-nut.

Instead of the adjusting means described, the membrane could also, in a modification not represented, be rigidly fixed to the envelope of the buzzer, the supporting member of the vibrating blade then being made adjustable relative to that envelope; said support would only need be made adjustable from outside said envelope. For that purpose, an adjusting screw accessible from outside the opening could advantageously be provided.

If the distance between the membrane and the blade striking thereagainst were incidentally put out of order during the use of the buzzer, it could easily be readjusted without having to disassemble the buzzer.

To prevent the perspiration from entering the buzzer by passing through the threads of opening 25 and ring 24, a watertight gasket 28 having a circular cross-section is located under ring 24 which, according to the position in which the membrane 22 has finally been set, more or less compresses gasket 28 on a shoulder 29 of supporting member 1. In order that gasket 28 ensures the tightness of the closure of the envelope of the buzzer, which

3,530,463 ever the position of membrane 22 may be, it is chosen with a cross-section enabling relatively large deformations of the gasket.

Tests have shown that in submitting the buzzer to overpressures of about one atmosphere, the membrane 22 was not stressed beyond its limit of elasticity. As regards gasket 28 it still ensures the tightness of the passage between ring 24 and supporting member 1.

During all the time the lines 13, 14 remain connected to the electrical potential, membrane 22 produces a continuous sound.

To feed the circuit represented in FIG. 4, lines 13, 14 need only be connected to a battery. The miniature batteries which can be found on the market are perfectly convenient. A switch will have to be connected to the circuit in order to permit the buzzer to be excited at will. An electronic interrupter comprising a transistor, the base of which is biased by a flip-flop, can also be used at that place. By means of an appropriate choice of the time constants of the flip-flop it is possible to adjust, on the one hand, the frequency of the current interruptions produced in the buzzer circuit, and, on the other hand, the relative length of said interruptions with respect to the flowing time of the electrical current.

Such an interrupter consequently produces an interrupted sound. Due to that interrupter the manufacturer can at will produce short sound interruptions following each other at more or less short time intervals, or, on the contrary, cause membrane 22 to vibrate only during very short time periods at more or less spaced time intervals.

The sizes of the buzzer described can be reduced to such an extent that the buzzer can be mounted either in the casing of a wrist-watch or in the cap of a stylograph. In the first event supporting member 1 could be constituted by the bottom of the watch case and, in the second event, by the cap of the stylograph, cover member 27 forming part of the outer surface of said bottom or of said cap. The last use more particularly interests the persons seeking installations and permits a substantial reduction of the sizes of the devices usually carried in the pockets and which have hitherto been equipped with a buzzer comprising a membrane caused to vibrate by a transformer and a battery having relatively large sizes. Due to its small sizes and to its economic consumption the described buzzer can also advantageously be used in telephonic installations instead of the buzzers used hitherto.

In order to ensure a fully independent manufacture of the buzzer, it is finally possible to assemble the parts thereof in a capsule 30, as shown in the modification represented in FIG. 3. That capsule can then be set into a recess 31 of supporting member la. To establish necessary electrical contact between leads 13, 14 and the remaining circuit elements (battery, interrupter), the supporting member la is provided with male connecting members 32, 33 corresponding to the terminals 15, 16 of capsule 30 and entering the latter when the capsule is introduced into recess 31. In this modification supporting member la and capsule 30 are preferably moulded cut of a plastic.