US3313892A - Electromechanical transducers - Google Patents

Description

April 11, 1967 A. F. MOSTARDO, JR., ET Al.

ELECTROMECHANICAL TRANSDUCERS Filed July 29, 1963 United States Patent 3,313,892 ELECTROMECHANICAL TRANSDUCERS August F. Mostarrlo, In, Norridge, and Floyd W. Cross, Wheaton, lll., assignors to Industrial Research Products,

Inc., Franklin Park, 111, a corporation of Delaware Filed July 29, 1963, Ser. No. 298,332 6 Claims. (Cl. 179-115) The present invention relates to transducers, and more particularly to miniature. transducers of the type shown in copending US. patent application Ser. No. 27,006, filed May 5, 1960, by Elmer V. Carlson.

In both the present invention and in the Carlson invention, there is provided an E-shaped armature in which the outer arms of the E are held fixedly within a magnetic stack. The magnetic stack includes two permanent magnets spaced apart with their opposite poles confronting one another across a gap area. At the outer arms of the armature, non-magnetic spacers are fitted on either side of the armature arms between the magnets to secure the outer armature arms in place. These spacers end a short distance inwardly of the outer arms leaving a gap on either side of the intermediate arm of the armature in the space between the opposed pole faces. This gap is called the working gap and the intermediate armature arm is vibratable within this gap, as will be explained more fully.

To complete the magnetic circuit between the permanent magnets, the armature and magnetic stack are fitted in a rectangular magnetic case with the lower of the magnets directly resting on and engaging the bottom wall of the case. Above the magnetic stack, a magnetic bulkhead is fitted into the case and contacts the case side walls. In this way, the case and bulkhead complete the steady flux path of the fields generated by the permanent magnets.

The intermediate arm of the armature has positioned thereabout a signal coil whose generated magnetic field is completed through the armature. This field path may be traced from the armature intermediate arm through the base or spine of the armature to the outer armature arms and finally through individual magnetic pole pieces in the magnetic stack internally of the permanent magnets.

A drive pin extends normally from a connection to the intermediate or vibratable armature arm through an opening in the upper magnetic bulkhead to a connection to a diaphragm. The diaphragm is mounted parallel to the bulkhead and spaced therefrom. When the transducer is used as a microphone, the diaphragm is positioned to vibrate in response to sound waves impinging against it. As the diaphragm vibrates, it in turn vibrates the intermediate armature arm. The arm, on vibration, is moved successively adjacent the permanent magnet poles to change the magnetic potential of the armature. This change in the armature magnetic potential generates a corresponding varying voltage in the coil, the coil voltage variations being transmitted from the coil to the external circuit.

In use as a receiver, changes in voltage are fed to the coil. These coil changes generate a varying flux field which acts on the armature vibratable arm and which in turn vibrates the diaphragm to efiect an acoustic output.

Miniature transducers of the type described are known from the Carlson application, and are of particular advantage in hearing aids and especially in hearing aids fitted into spectacle and behind-the-ear frames. In these hearing aids, the tendency has been to develop smaller and yet smaller transducers for making the hearing aids less bulky and less noticeable. With these size reductions, the quality of reception must not be diminished. In addition, this industry is highly competitive, leading to extensive research into designs of minimal size, ease and minimum assembly cost without lessening the quality of the finished transducer.

It is, therefore, an object of the invention to provide an improved miniature transducer which may be assembled readily and inexpensively.

It is a further object of the invention to provide an improved transducer construction which is more compact than prior transducers and utilizes its compact size to effect a high quality transducer output.

To effect these and other objects, the present invention utilizes the magnetic stack structure, bulkhead, and E- armature shown by Carlson. The armature of Carlson is modified by bending the connecting base or spine of the armature to a position normal to the armature arms and extending parallel to the magnetic stack structure. The bulkhead of Carlson is modified to allow this E- armature with flange to move without interference. At the corners adjacent the armature base, the bulkhead has extensions designed to fit the magnetic structure and armature tightly within the enclosing case or envelope. The bulkhead also has an opening through which a drive pin extends for joining the armature vibratable arm to the diaphragm.

The diaphragm member is constructed with an outer frame disposed to fit tightly within the case side walls. The frame may be laminated or slit to contain an ovalshaped layer of plastic within its sheet members, and this plastic has affixed at the center thereof a diaphragm of aluminum or the like. The completed diaphragm member is essentially contained in a plane with a peripheral mounting or spacing flange at its edges, as heretofore used in Knowles Patent No. 3,002,058, Sept. 26, 1961. In the diaphragm plane, the plastic oval acts as a hinge about the entire edge of the diaphragm allowing the diaphragm to vibrate in a direction normal to the diaphragm plane.

To complete the assembly, a housing cover is fitted over the diaphragm to enclose the transducer within the case. The housing cover has a centrally positioned sound opening spaced above the diaphragm. This housing cover butts against the top of the case side wall and is cemented or otherwise adhered in place, as are many of the internal components of the transducer.

The invention both as to its organization and principle of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings in which:

FIGURE 1 is an exploded view of a transducer of the present invention;

FIGURE 2 is a perspective view of the transducer of FIGURE 1 with the outer case and other components broken away in part to show the interior construction;

FIGURE 3 is a sectional view taken along line 33 of FIGURE 2; and,

FIGURE 4 is a perspective view of the armature as used herein.

Turning to the drawings in detail, there is shown the transducer internal assembly 10 within an enclosing housing including a bottom case 12 and a housing cover 14. The internal assembly 10 includes the magnetic stack structure 15, the armature 16, the signal coil 18, and

the diaphragm member 20.

The magnetic structure includes a sandwich-like stack which includes respectively a bar permanent magnet 24 extending transversely across the structure. Above the magnet and coextensive therewith is a lower pole piece 26 of magnetically permeable material. Above the pole piece 26, adjacent both ends thereof, are fitted spacers 28 of non-magnetic material. These end spacers are mounted above the pole piece 26 and are used to rest thereon the outside arms and 32 of the E-shaped armature 16. These outer arms are mounted on the spacers, and there is a second pair of like spacers 34 mounted permanently above each of the armature outer arms. Above the upper spacers 34 is positioned a second transverse pole piece 36 coextensive with the lower pole piece 26 and lower magnet 24. A final member of the stack 15 is a second permanent bar magnet 38 which is magnetized transversely as is the lower magnet 24. The stack is secured as a single unit by suitable adhesives, rivets, or the like.

The magnets, as mentioned previously, are magnetized transversely so that the upper surface 40 of the lower magnet 24 may present a single pole such as a north pole. Assuming a north pole for the upper surface 49 of the lower magnet 24, the confronting or bottom face of magnet 38 would be a south pole (the pole opposed to that at surface 40).

The armature 16, as mentioned, is E-shaped, and has its outer arms 30 and 32 secured in the magnetic stack 15 and has its intermediate arm 42 extending through the stack in a working gap 44 provided by the absence of spacers in the mid-transverse stack portion. By this construction, the magnetic stack extends vertically and transversely with the armature 16 cantilevered therefrom at the midlevel height of the stack.

About the vibratable armature arm 42 between the stack and the base or spine of the armature, there is mounted a signal coil 18. This coil is connected by suitable leads 52 through openings 53 in the magnetic case to a source of power. The coil 18, when energized, generates a magnetic field which is concentrated in strength through its axis. The armature vibratable arm 42 extends through the coil 18 along the coil axis in the at-rest condition, and serves to complete the field generated by the coil through the armature.

Secured to the top surface of upper magnet 38 by suitable means is the bulkhead 54 which is made of magnetic material, and is of width sufficient to fit tightly Within case 12. This bulkhead may also be suitably connected to the exterior of coil 18 by the use of adhesives. The bulkhead is cantilevered from its connection to the magnetic stack and extends in superimposed spaced relationship parallel to the armature arms. At the corners most remote from its connection to the magnetic stack, the bulkhead 54 terminates in two parallel, spaced-apart tips 56 which are designed to abut against the adjacent wall of case 12 and hold the magnetic structure tightly within the case. Between these tips, the bulkhead includes a cutout 60 which uncovers a portion of the vibratable arm 42. The cutout 60 adjacent its innermost end passes therethrough drive pin 62 which connects the vibratable arm 42 to the diaphragm 2%). Drive pin 62 is secured by any suitable method such as welding or adhesion to the vibratable arm. The drive pin extends through the cutout 60 for connection by suitable method to the diaphragm. At the cutout end 64, remote from the stack, the cutout is sufficiently wide to allow the armature spine 50 to move easily without being impeded.

At the end remote from the stack, the armature arms 30, 32 and 42 are joined by the armature spine 59 (back surface of the armature E) which is bent to form substantially a right angle with the plane of the armature arms 30, 32 and 42. This base or spine 50 extends upwardly within the area of cutout 66 at the end 64 inwardly of bulkhead tips 56. This armature bend 66 serves a number of purposes. First, to a limited degree, it stitfens the armature structurally and by this bend impedes some of the tendency of the outer arms 36 and 32 to vibrate. This vibration inhibition aids in setting the vibrational node of the intermediate arm 42 adjacent the bend 66 in the armature spine 50. This setting of the armature vibrational node results in a greater efliciency for the unit in that the vibrational forces imparted to the vibratable arm are utilized to a greater degree in causing motion of the armature intermediate arm alone. In addition, this amature bend 66 lessens the linear length of the case allowing a more compact, and generally smaller structure than has been possible heretofore. Where the armature spine extends in the same plane as the armature arms, space must be left above and below the spine to allow free armature movement, this space adding but little to the efficiency of the unit. By bending the arma ture spine normal to the armature arms, this space is cut to a minimum allowing an even shorter transducer case to be used.

The diaphragm member 20 includes a rectangular frame 70 sized to fit tightly Within the case side walls. The frame has a flange '72 which is offset in configuration to space the diaphragm member from the bulkhead 54. The diaphragm frame rests on the bulkhead 54 in assembly to assure the proper alignment of the member in the case. The diaphragm frame has an oval layer 74 of plastic affixed to it inwardly of flange 72. Inwardly of this open plastic layer area called the surround 74, there is afiixed to the plastic an oval-shaped diaphragm 76 of aluminum or the like. This diaphragm is oval in shape, and light in weight so that it is allowed a limited amount of movement in a plane normal to the diaphragm member plane by the compliance of plastic surround 74. At its center, the diaphragm 76 is afiixed to the drive pin 62 for movement therewith. By this construction, the diaphragm member 2%) is fabricated as an integral unit substantially planar and including a support frame 70 with its flange '72, the complaint rnovernent-allowing-surround '74 and the actual diaphragm '76 in the center.

An inertance tube 80 is affixed to the internal assembly adjacent the magnetic stack and outwardly thereof. This tube 84) is L-shaped with a horizontal section 82 paralleling the lower magnet 24 and adjacent thereto. The tube bends to a vertical section 84 which extends through a suitable circular opening %6 in one corner of the diaphragm frame 70 to terminate slightly above the diaphragm. The functioning of an inertance tube is Well known and will not be explained fully herein.

To complete the assembly, a lid or housing cover 14, the bottom edge of which butts against the top edge of case 12, encloses the assembly 19. The lid may be cemented or otherwise adhered to the case to unite the structure in an assembly Which cannot readily be disassembled to tinker with the interior. The case itself includes suitable small openings for the coil leads, and an adjusting port adjacent the back end of one armature outer arm to allow adjustment of the armature. In addition, the lid 14 has a single, small, circular opening 94 at its center to allow sound to enter the sound cavity between the lid 14 and the diaphgram 76.

To provide improved performance characteristics, the base or spine 50 of the armature may be secured relative to the case by an optional bracket 96 extending from the armature spine St to a connection to the base. This bracket would be a stepped rigid bracket 96 firmly connected by adhesive or welding to both the armature spine 5t) and case 12. The use of such a bracket would further reduce the tendency of the armature spine 50 to vibrate with the armature vibratable arm 42. Clearly with such a bracket in use, the vibrational node of the armature would be slightly past the rear end of the coil adjacent to the armature spine. Instead of being mounted on the case, the bracket may be mounted on the bulkhead 54 or the coil 18.

The ramifications or alternative relative sizes of the magnets and the spacers is set out clearly in the previously cited Carlson application and need not be repeated herein.

As in the cited Carlson application, the signal flux or field generated by coil 18 is completed through the armature 16 and the pole pieces 26 and 3-6, wholly within the internal assembly. The steady flux circuit generated by the permanent magnets is completed through the stack structure, and magnetic case 12, and the upper bulkhead 54. As mentioned, the magnets 24 and 38 are respectively in contact with the case 12 and bulkhead 54 to complete the magnetic path. In this way, the signal flux circuit and steady flux circuit are isolated from one another with the steady fiux circuit by its use of the case and bulkhead surrounding the signal flux circuit. The steady flux circuit magnetically shields the internal assembly from stray magnetic fields. Any such stray magnetic fields which are received by the case will in no way afiect the operation of the armature vibratable arm and the signal flux circuit of which it is a part.

The use of the upper bulkhead 54 is manifold. First, it serves the purpose of completing the steady flux circuit about the coil and armature. Further, its shape allows the drive pin to pass freely there-through for connection to the diaphragm. Its shape further provides or allows movement of the armature with its angled spine or flange 50 without interference. head act to space and fit the internal assembly tightly within the case. Also, the bulkhead serves as a solid member on which the diaphragm frame may be rested. The construction shown allows for ready assembly with the component parts sized and shaped to fit snugly within the case and abutting against the adjoining components.

While there has been shown what is at present thought to be a preferred embodiment of the invention, it may be understood that many modifications may be made therein, and it is intended to cover in the appended claims all modifications which fall within the true spirit and scope of the invention.

What is claimed is:

1. In that type of electromagnetic transducer wherein the three ends of the arms of an E-shaped armature are positioned between spaced poles of opposite polarity of a steady flux circuit, the plane of the base of the E-shaped armature lying normal to the plane of the three arms, and a case surrounding the operable parts with one wall lying parallel to the plane of the base of the E-shaped armature.

2. An E-shaped armature for use in a transducer comprising a flat plate of flux-permeable, flexible material having the plan configuration of an E, with all three arms of the E flexible at right angles to the fiat surface of the flat plate, and with the base of the E positioned at right angles to the fiat surface of the plate.

3. An electromagnetic transducer comprising a steady flux circuit including spaced permanent magnets confronting one another with the opposite poles of the magnets opposing one another, an armature having a plurality of arms in a plane extending into the space between said magnets, one or more of the arms of said armature affixed in the space between said magnets and another of said arms vibratable in the space between the magnets, a back end of said armature connecting said arms, said armature back end forming substantially a right angle with the plane of the armature arms, a signal fiux circuit including said armature, and a magnetic case for completing the steady flux circuit and enveloping said signal flux circuit, with one wall of said case closely adjacent the back end of said armature.

4. An electromagnetic transducer comprising a steady flux circuit including two spaced permanent magnets with their opposite poles confronting across the space therebetween, an E-shaped armature positioned with its arms extending between the magnets of said circuit, a central arm of said armature vibratable in the steady flux circuit,

The corner tips 56 of the bulkouter arms of said armature afiixed in the space between the magnets in the same plane as said central armature arm, the portion of said armature connecting said arms comprising a stiffening spine for said armature arms, said spine substantially forming a right angle with the plane of said armature, a signal flux circuit including said armature arms and completed therethrough, a magnetic case enveloping said steady flux circuit, said case in magnetic engagement with said permanent magnets to complete said steady flux circuit from said magnets wherein said signal flux circuit is isolated from the steady flux circuit.

5. An electromagnetic transducer comprising a magnetic stack including spaced permanent bar magnets extending transversely of said transducer, said magnets confronting one another with opposite poles confronting across the space therebetween, an armature with a plurality of arms extending in the space between said magnets, means aflixing one or more of said arms in said stack, another of said armature arms extending between said magnets and vibratable therebetween, the back of said armature connecting said arms together, said armature back forming substantially a right angle with the plane of said arms, a coil surrounding said vibratable arm, said armature arms and back comprising a path for signal flux from said coil, a magnetic case enclosing said stack and in contact with the lower of said magnets, a magnetic bulkhead mounted on the upper of said magnets and engaging said upper magnet, said bulkhead contacting said case walls whereby to complete a steady flux circuit from said magnets through said case and said bulkhead to isolate said signal flux circuit therein.

6. An electroacoustic transducer comprising a magnetic stack including spaced permanent bar magnets extending transversely of said transducer, said magnets confronting one another with opposite poles confronting across the space therebetween, an armature with a plurality of arms extending in the space between said magnets, means afiixing one or more of said arms in said stack, another of said armature arms extending between said magnets and vibratable therebetween, the back of said armature connecting said arms together, said armature back forming substantially a right angle with the plane of said arms, a coil surrounding said vibratable arm, said armature comprising a path for signal flux from said coil, a magnetic case enclosing said stack and in contact with a lower of said magnets, a bulkhead mounted on the upper of said magnets and engaging said upper magnet, said bulkhead contacting said case walls whereby to complete a steady flux circuit from said magnets through said case and said bulkhead to isolate said signal fiux circuit therein, a diaphragm, a drive pin extending through said bulkhead, said drive pin connecting said diaphragm to said armature vibratable arm for movement therewith, a diaphragm frame, a compliant member joining said diaphragm to said frame to position said diaphragm centrally within said case, and a cover butted against said case to fully enclose said transducer.

References Cited by the Examiner UNITED STATES PATENTS 3,076,062 1/1963 Fener 179-114 3,111,563 11/1963 Carlson 179-114 KATHLEEN H. CLAFFY, Primary Examiner.

F. N. CARTEN, A MCGILL, Assistant Examiners,

Claims (1)

1. 2. AN E-SHAPED ARMATURE FOR USE IN A TRANSDUCER COMPRISING A FLAT PLATE OF FLUX-PERMEABLE, FLEXIBLE MATERIAL HAVING THE PLAN CONFIGURATION OF AN E, WITH ALL THREE ARMS OF THE E FLEXIBLE AT RIGHT ANGLES TO THE FLAT SURFACE OF THE

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