US 3692264 A
Description (OCR text may contain errors)
United States Patent Burkhard et al.
[451 Sept. 19, 1972 SHOCK ISOLATION MOUNTS FOR FRAGILE DEVICES  Inventors: Mahlon D. Burkhard, Hinsdale; Russell J. Maxwell, West Dundee, both of III.
 Assignee: Industrial Research Products, Inc.,
Elk Grove Village, Ill.
 Filed: July 13, 1970  Appl. No.: 54,461
 US. Cl. ..248/15, 179/146 R, 179/179, 248/358 R  Int. Cl. ..G04c 3/00  Field of Search ....248/358 R, 358 A, 15, 22, 26; 179/179, 146,180
 References Cited UNITED STATES PATENTS 1,704,570 3/1929 Lee et a1. ..248/358 R 2,404,799 7/1946 Harry et al ..179/179 X 2,415,983 2/1947 Yerzley ..248/ 18 X 3,048,668 8/1962 Weiss ..179/ 179 3,257,516 6/1966 Knowles ..248/358 R X Primary ExaminerJ. Franklin Foss AttorneyKinzer, Dorn and Zickert  ABSTRACT Shock isolation mounts for miniature microphones, sound reproducers, and other fragile devices, in which the device is suspended between thin film support members mounted on a rigid frame in a configuration such that shock stresses of substantial magnitude occurring in either direction along a given path are absorbed almost entirely by tensional stress of one or more of the film support members. Vibration isolation is also provided, separately from the shock isolation, by means of one or more vibration absorption elements, formed of rubber or other material of high resilience and high compliance in compression, interposed between the fragile device and support members or between the support members and the frame or between the frame and an external support structure. The support members are usually made of plastic, such as a polyester film, and may be preformed to fit the external configuration of the transducer or other device or may be flat strips with no pre-forming required.
20 Claims, 21 Drawing Figures PATENTEDSEP I 9 I972 FIG] SHEET 1 BF 2 W I 0 I a) B I 8 I a I n: I n: cc I STRAIN Q STRAIN g STRAIN Q F164 FI(5.5 INVENTORS MAHLON D. BURKHARD RUSSELL J. MAXWELL 1 6%? M ZW ATTORNEYS PATENTED E 3.692264 sum 2 8F 2 INVENTO RS MAHLON D4 BURKHARD AT TOR NEYb RUSSELL J. MAXWELL SHOCK ISOLATION MOUNTS FOR FRAGILE DEVICES BACKGROUND OF THE INVENTION This invention relates to new and improved devices for minimizing the shock forces applied to a miniature transducer or other relatively fragile device when subject to high acceleration, as may occur when the device is dropped onto a hard surface or is abruptly set into motion from a static or rest condition. The invention is particularly applicable to the protection of the microphones and sound reproducing units in hearing aids, which may frequently be subject to relatively high shock stresses; it is also applicable to the protection of a variety of other electrical, mechanical, electromechanical, and electronic devices and instruments.
In many applications requiring shock protection for miniature fragile devices, and particularlyin hearing aids, it has been common practice to surround the devices with rubber, foamed plastic, or other viscoelastic material. The protective material is frequently molded into a specific shape to fit the device requiring protection, or may be assembled from flat stock or bulk material. The rubber is intended to serve two protective functions. The first function is to provide vibration isolation for the device with respect to external structures or with respect to other devices in a common assembly (e.g., vibration isolation between the microphone and the sound reproducer in a hearing aid). The second function is to reduce the shock force applied to the device when the assembly in which it is incorporated is subject to a severe mechanical shock. But the conventional rubber or other viscoelastic shock protection provided for hearing aid transducers and similar devices is not particularly effective.
The space available for shock isolation elements in modern hearing aids and like apparatus is quite limited because the apparatus is by its nature extremely small. Furthermore, the transducers and other devices requiring protection are usually of miniature construction and of light weight so that many known types of shock isolators cannot be used. Moreover, the reduction of shock forces by compression of rubber or similar viscoelastic material is quite ineffective as compared to other mechanisms because of the inherent nature of the stress-strain characteristics'of the material itself. The attempted use of rubber compression elements for simultaneous shock protection and vibration damping does neither job well the resulting structure is usually too stiff for good vibration suppression and too soft for effective shock protection.
Other compression devices for shock isolation have been proposed, as, for example, in Weiss US. Pat. No. 3,048,668 in which a hearing aid transducer is suspended within a rigid housing by means of a plurality of tubular compression members. This type of compression shock absorber is operationally generally similar to the rubber shock absorption and vibration suppression elements that have seen more general use.
There have also been other proposals for vibration isolation and shock isolation mountings, as few of which have used mounting members that are stressed at least partly in tension when subjected to external vibration or shock forces. One such device is shown in l-Ioekstra US. Pat. No. 2,910,263, in which the shock and vibration isolation mount for an electronic chassis comprises a suspension member of braided wire ribbon. Tension stressing of the suspension ribbon is apparently incidental and flexure of the ribbon is relied upon for the principal isolation functions. Another device of this general kind is shown in Lawrence et al. US. Pat. No. 3,204,911 in which vibration damping is effected by a combination of flexure, compression, and tension of semicircular loops of stranded wire cable.
Other arrangements in which some tension of the mounting members has been employed for vibration or shock isolation have utilized helical springs, as, for example, in Wells US. Pat. No. 3,028,138. But most of these constructions are not readily adaptable to miniature devices such as hearing aid transducers, requiring excessive space or exhibiting unduly complex structural requirements that cannot be readily duplicated on the small scale required.
SUMMARY OF THE INVENTION It is an object of the present invention, therefore, to provide superior shock energy absorbing capabilities in an extremely limited space in a shock isolation mount for small and relatively fragile devices.
A further object of the invention is to afford a shock isolation mount for miniature transducers and the like that not only provides superior shock protection but which also affords effective vibration isolation of the device from its surrounding structure. A specific object of the invention is to provide vibration isolation in a negligible amount of space in comparison to the space required for shock protection while at the same time maintaining effective shock protection.
A particular feature of the invention is the utilization of thin film support members in a shock isolation mount for miniature transducers or like fragile devices in which shock stresses are absorbed by tension of the film to provide the most efficient and effective use of available space in the overall structure in which the device is mounted.
Accordingly, the invention is directed to a shock isolation mount for mounting a miniature transducer or like small, relatively fragile device within a given limited space and for protecting that device against shock damage from sudden acceleration in either direction along a given path. A shock isolation mount constructed in accordance with the invention comprises a first thin film support member extending across one side of the device approximately normal to the path of potential damaging acceleration and a second thin film support member extending across the opposite side of the device with the device being wholly supported by the film support members. Preferably, the support members are formed of a thin tough plastic film having a high modulus of elasticity. The film members may be performed to conform to the configuration of the device to be protected or may be fabricated from flat flexible strips. The shock isolation mount further comprises rigid frame means engaging the support members beyond the periphery of the protected device to complete an assembly, the configuration of the frame means, the support members, and the device being such that the energy of shock stresses of substantial magnitude in either direction along the aforesaid path is absorbed primarily by tensional stress of at least one of the support members. Energy absorbed during tensional stress in general includes energy storage by elastic deformation and energy dissipation by internal loss mechanisms and by external frictional losses as the support member slides in response to the tensional stress. In the preferred forms of the invention, separate vibration isolation is provided by one or more small vibration absorption elements of rubber or other material having high resilience and high compliance in compression, interposed between the fragile device and the support members, between the support members and the frame means, or between the frame means and external support structure.
Other and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which, by way of illustration, show preferred embodiments of the present invention and the principles thereof and what is now considered to be the best mode contemplated for applying these principles. Other embodiments of the invention embodying the same or equivalent principles may be made as desired by those skilled in the art without departing from the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded perspective view of a shock isolation mount constructed in accordance with one embodiment of the present invention;
FIG. 2 is a perspective view of the shock isolation mount of FIG. 1 as assembled;
FIG. 3 is a sectional elevation view showing the shock isolation mount of FIGS. 1 and 2 mounted in an external support structure;
FIGS. 4, 5 and 6 are stress-strain plots showing the operating characteristics of different forms of shock isolation mounts;
FIG. 7 is a detail sectional view, similar to FIG. 3, illustrating a modification of the mount construction;
FIG. 8 is a sectional elevation view, similar to FIG. 3, illustrating another modification of the invention;
FIG. 9 is an exploded perspective view of another form of shock isolation mount constructed in accordance with the invention;
FIG. 10 is a plan view of the shock isolation mount of FIG. 9 in assembled condition;
FIG. 11 is a bottom view of the shock isolation mount of FIG. 9 as assembled;
FIG. 12 is a sectional elevation view taken approximately along line l2-l2 in FIG. 10;
FIG. 13 illustrates a modification of the assembly of FIGS. 9-12 in a sectional elevation view;
FIG. 14 is a plan view of a further modification of the invention;
FIG. 15 is a sectional elevation view taken approximately along line 15-15 in FIG. 14;
FIGS. l6, l7 and 18 are detail sectional views of different forms of vibration isolators that may be incorporated in shock protection mounts constructed in ac corclance with the invention;
' FIGS. 19 and 20 are detail views of an alternate construction for the shock mount of FIGS. 10-12; and FIG. 21 is a perspective view of another embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates, in an exploded perspective view, a shock isolation mount 10 constructed in accordance with the present invention. The shock isolation mount 10 is utilized for mounting a miniature microphone, sound reproducer, or other small, relatively fragile device 11 within a limited space and is employed to protect the device 11 against shock damage from sudden acceleration in either direction along a given path generally indicated by the phantom line X. If it is assumed that device 11 is a miniature microphone or other transducer, it will be recognized that the device is primarily susceptible to damage as the result of shocks occurring along the path X, considered as a path perpendicular to the transducer diaphragm. Shock forces applied to the device in directions transverse to path X are much less likely to damage the device. As shown in FIG. 1, the transducer or other miniature device 11 may be provided with suitable electrical leads 12. The device is shown as being of rectangular configuration, but the shock mount 10 can be equally well applied to a device of square, circular, elliptical or other configuration, as will be apparent from the detailed description hereinafter.
The shock isolation mount 10 of FIG. 1 comprises a first thin film support member 13 that extends across one side of the device 11 transversely of the critical shock path X. Member 13 may be formed from a wide variety of materials but preferably is fabricated from a thin tough plastic film having a high modulus of elasticity. A particularly suitable material is polyester film. Member 13 is preformed to afford a central cuplike portion 14 that conforms to the configuration of the upper half of transducer 11. That is, when support member 13 is mounted on transducer 11, the cup-like portion 14 fits closely around the exterior of the upper half of the transducer. The cup portion 14 of member 13 may be provided with appropriate apertures 15 for the electrical leads 12 of the transducer. Moreover, a central aperture 16 may be formed in member 13 to provide access to the transducer 11 for entry or egress of sound waves.
The shock isolation mount 10 of FIG. 1 further includes a second thin film support member 17 that is essentially similar in construction to member 13 and is pre-formed to afford a central cup-like depression 18 for receiving the bottom half of transducer 11. The shock mount further comprises a rigid frame means that includes an upper mounting member I9 and a lower mounting member 21. Mounting member 19 is of generally ring-like configuration. That is, the mounting member is provided with a central aperture 22 that fits around the cup portion 14 of support member 13 when the mount is assembled (see FIG. 2). Similarly, mounting member 21 has a central opening 23 for receiving central cup portion 18 of support member 17.
When the shock isolation mount 10 of FIGS. l-3 is assembled, the transducer or other delicate device 1 l is deposited in the lower cup portion 18 of support member 17 and the upper support member 13 is brought down over the transducer with its cup portion 14 encompassing the upper part of the transducer. The two rigid ring-like mounting members 19 and 21 fit closely around the projecting cup portions of the support members so that the peripheral portions of the two support members 13 and 17 are clamped between the mounting members 19 and 21. This completes the assembly shown in FIG. 2 and also shown in cross-section in FIG. 3. It should be noted that the engagement of the rigid frame means comprising the mounting members 19 and 21 with the periphery of the support members 13 and 17, and the overall configuration of the frame means, the support members, and the device 11 are such that any stresses of substantial magnitude produced by acceleration of device 11 in either of the opposed directions A and B along the path X (FIG. 3) can be absorbed only by tensional strain on the part of one of the support members 13 and 17. It should be emphasized that the walls of the film cup portions 14 and 18 serve for tension shock absorption as much as or more than the bases of the cups. Absorption of such shock stresses by flexure or by compression of the film support members is minimal. I
In order to reach a full realization of the operational advantages of the shock isolation mount 10, when mounted in a confining external structure as shown in FIG. 3, some analysis of different forms of shock isolators is desirable. The fundamental concept upon which any shock isolator is based is that the energy absorbed by the compression or extension of the shock isolating elements, plus the energy lost due to friction forces, must equal energy lost or gained by the supported device, as the result of stopping of the device abruptly after dropping some specified height or as the result of the device being set in motion by an abrupt applied force of some kind. The energy lost or gained is equal to the area under the force versus displacement curve of the protected device moving against the spring system represented by the shock isolation elements. Mathematically, for the case of a dropped structure, that energy is d E=f Pda: 0
where P is the force created by the abrupt deceleration of the device, d is the distance the device travels while under the influence or restraint of the shock isolation mount, and x is the integration variable; It is evident that a low force P acting over a long distance d is preferable to a large force acting over a short distance if low acceleration forces are to be generated and if a low rate of energy transfer to the protected device is required. The maximum available distance d (e.g., the rattle space dimensions D, FIG. 3) is likely to be rather small. Thus, the basic problem is to produce maximum protection for a fragile device in a given limited amount of available rattle space D for an anticipated shockproducing condition by keeping the force generated by the shock to a minimum level. Some motion of the protected device relative to the surrounding structure must be provided, but that motion should be made to occur at reaction force levels critically designed in relation to the shock resistance characteristics of the protected device. As the available range of motion is increased, the reaction force can be made smaller.
For conventional compression shock absorption elements, the stress-strain or force displacement curve is a tangent curve of the form generally illustrated in FIG. 4. Rubber and most other spring elements which compress between the protected device and the encompassing structure follow tangent elasticity laws. For tangent elastic elements of this kind, a part of the rattle space D must be used to contain the compressed elastic material, with the result that not all of the rattle space can be used for motion of the protected device.
Furthermore, compression spring members and other tangent elasticity protectors produce a force increasing with compression deformation of the spring material. Typically, a rubber compression material may permit 50 to 60 percent compression at very low force levels, absorbing only small amounts of energy. If the device is dropped from a large height, most of the energy must be absorbed at very high force levels after the rubber is substantially fully compressed, resulting in large peak accelerations with respect to the protected device. Thus, tangent elasticity shock protection elements are inefficient with respect to use of a given amount of rattle space and in many instances cannot provide the required protection within existing dimensional limitations.
Improved efficiency in the shock absorption elements is achieved by utilization of elements which afford linear or generally hyperbolic deformation characteristics as shown in FIGS. 5 and 6 respectively. Characteristics of this kind are more readily obtainable using shock absorption elements that are deformed in tension rather than in compression. Furthermore, the tension-deforming support members employed in the present invention make it possible to utilize virtually all of the available rattle space in motion of the protected device. That is, tension members such as the support members 13 and 17, because they usually occupy 5 percent or less of the total available rattle space, afford substantial advantages in comparison with compression shock absorption elements because the latter inevitably require a substantial portion of the available space for storage of the material when it is compressed. Preferably, in the shock isolation mount 10 and in the other embodiments of the invention discussed herein, the dimensions of the film are selected in proportion to the mass and dimensions of the protected device and the anticipated maximum shock so that all of the film is stretched to its elastic limit under maximum shock conditions.
Referring again to FIGS. 1-3 and the shock isolation mount 10 illustrated therein, it is seen that there are a plurality of vibration absorption elements 24 on the surface of mounting member 19 opposite that surface of the mounting member which engages support member 13. The vibration absorption elements 24 may comprise minute dots of a material having high resilience and high compliance in compression. A good example is the thixotropic mixture of silicon rubber known as RTV, which may be applied to the surface of mounting member 19 by means of a hypodermic syringe or by transfer techniques such as those used in the printing of various materials onto metal surfaces. A similar series of minute vibration absorption elements 25 is applied to the lower surface of the other mounting member 21, as seen in FIG. 3.
In FIG. 3, the shock absorption mount 10 is shown mounted in an external structure that forms an external frame for the assembly and that also defines the maximum available rattle space D. This external frame, forming a part of a housing for the shock absorption mount, comprises wall members 26, 27 and 28 (one wall has been cut away) affording a continuous slot 29 for receiving the edge portions of the shock mount assembly. The film members 13 and 17 project a short distance outwardly of the edges of the mounting members l9 and 21 into engagement with the side walls of the slot 29 and serve to isolate the rigid mounting members 19 and 21 from the external frame 26-28. The projection of the film members into engagement with the walls of the external frame also serves to center the assembly within the external frame. The vibration absorption elements 24 and 25, on the other hand, engage the upper and lower surface of slot 29 to afford vibration isolation for device 11 with respect to the encompassing structure. The external frame or housing may be completed by appropriate face plates 31 and 32 which define the limit of maximum displacement of the device 11 along path X and thus determine the maximum available rattle space D at each side of the device.
If the structure encompassing transducer 11 (e.g., the frame means 19, 21 and housing 26-28 and 31-32 is subject to a high shock force in the direction indicated by the arrow A, (FIG. 3), transducer 11 tends to remain at rest and the shock force is absorbed almost entirely by tensional strain or stretching of the side walls of the cup portion 18 of film support member 17. Conversely, a shock force in the opposite direction, accelerating the encompassing structure in the direction of the arrow B, is absorbed by tensional stress of the side walls of the cup portion 14 of film support member 13.
It is feasible to utilize only the linear range of elongation of the film support members 13 and 17, as delineated in FIG. 5. On the other hand, it is equally possible to construct the shock isolation mount for operation in the non-linear range FIG. illustrated in Fig. 6, with the film support members absorbing additional energy of drop or other shock at an approximately constant force level. It is characteristic of the shock isolation mount that the stresses on the support members may exceed the range normally considered permissible for linear springs.
It has been found that polyester films are manufactured and available in a range of film thickness and with mechanical constants quite suitable for fabrication of shock isolation mounts in accordance with the invention. The basic requirements are that the film have a high modulus of elasticity, that the film be readily formable, and that the film be capable of a reasonable but not excessive elongation before exceeding its elastic limit. In this regard, it should be noted that such highly compliant compression isolators 24 and 25 and by the flexible extension portions at the edges of the film support members 13 and 17. Because vibration forces are of much lower magnitude than the shock forces produced by dropping or other sudden movement of the device, they can be effectively damped by the compression elements 24 and 25. Moreover, it is practical to provide vibration isolation in all directions, though not necessary in all instances.
FIG. 7 illustrates a modification of the shock mount of FIGS. 1-3. As in the previous construction, the miniature transducer or other relatively fragile device 11 is wholly supported between two pre-formed cuplike film support members 43 and 47 with the edge portions of the support members clamped between two rigid ring-like mounting members 49 and 51. Mounting members 49 and 51 correspond in all respects to the mounting members 19 and 21 of the previous embodiment except that they are not provided with the vibration isolation elements employed in the previous embodiment. As before, the shock mount assembly is mounted in an external frame or housing illustrated by the wall members 27 and 28 and the cover members 31 and 32, projecting into the slot 29 in the external frame.
In the construction shown in FIG. 7, however, the peripheral portion 44 of the film support member 43 is looped back over the adjacent mounting member 49. Similarly, the outer portion 52 of support member 47 is looped back to the outer surface of mounting member 51. The two looped portions 44 and 52 of support members 43 and 47 each afford a vibration absorption element of relatively high compliance effectively interposed between the external frame and the mounting member with which the support member is associated. Thus, the looped portions 44 and 52 of the film support members provide vibration isolation for device 1 1; they also serve to center device 11 in the overall construction, including the external frame.
FIG. 8 illustrated another form of shock isolation mount constructed in accordance with the present invention. In the construction shown in FIG. 8, a miniature transducer or similar fragile device 11 is wholly supported between two film support members 61 and 62. Support member 61 and 62, like the support members of the previous embodiments, are pre-formed to afford cup-like receptacles for the opposite sides of device 11. In this instance, however, the sides of the cup portions of the support members flare outwardly away from device 11 instead of conforming closely to the sides of the device.
The frame means for the construction illustrated in FIG. 8 comprise a pair of rigid ring-like mounting members 63 and 64 between which the peripheral portions of support member 61 and 62 are clamped. Furthermore, the edge portion of support member 61 is bent around the external surface of mounting member 63. Similarly, the periphery of support member 62 extends around the outer edge of mounting ring 64. An external clamp ring 65 fits tightly over the resulting assembly to afford a strong mechanical connection between the two film support members and the mounting members 63 and 64.
In the construction shown in FIG. 8, minute individual protruding spikes or spires 66 of RTV silicon rubber or like material are spaced around the upper surface of mounting member 63. Similar elements 67 of the same material are disposed around the lower surface of mounting member 64. These vibration isolation elements 66 and 67 are interposed between the mounting members and an external frame or housing generally illustrated in FIG. 8 by the upper frame member 68 and the lower frame member 69.
The operation of the construction illustrated in FIG. 8 is generally similar to that discussed above in connection with the embodiments of FIGS. 1-3 and 7. Low amplitude relatively high frequency vibrations are effectively absorbed by compression of the vibration isolation elements 66 and 67. Shock forces along the path X, on the other hand, are absorbed almost entirely by tension deformation of either the film support member 61 or the film support member 62, depending upon the direction in which device 11 is accelerated by the shock. There is some flexure of the film support members, due to the inclination of the walls of the cup portions of those members, but this is relatively insignificant and the principal absorption of shock forces is accomplished, as before, by tensional strain of the film support members.
FIGS. 9 through 12 illustrate a shock isolation mount 100 constructed in accordance with another embodiment of the invention; used in conjunction with a rectangular miniature transducer or other delicate device 111. The device shown has a sound pressure opening 112 and appropriate electrical leads 113 and 114. The shock isolation mount 100 includes a rigid frame means comprising two rigid mounting members 115 and 116. The shock isolation mount further includes a first thin flat strip film support member 117 and a second film support member that is divided into two segments 118A and 1188.
When assembled, shock isolator mount 100 has the film strip support member 117 extended upwardly over the outer surface of mounting member 115, across the top of the mounting member, downwardly along the inner surface of the mounting member 115, across the space between the two mounting members, upwardly along the inner surface of mounting member 116, across the top of member 116, and downwardly in engagement with the outer surface of mounting member 116, as best shown in FIG. 12.
A similar configuration is employed for the two strips of film 118A and 118B forming the other support member for this construction except that these two strips are reversed with respect to strip 117. Thus, strips 118A and 1188 each extend across the top surface 121 of device 111 and strip 117 extends across the bottom surface 122 of the device, device 111 being wholly supported by the strip film support members. The lapped-over portions of the film strip support members are cemented or otherwise secured to the outer surface of mounting members 115 and 116. The inner portions of the film strips are left free of the mounting members so that they can stretch, in tension, whenever the device 111 is subject to substantial shock forces along the path X. The space between strips 118A and 1188 affords working access to the transducer 111, as shown by the location of opening 112. It should be noted that the ends of the transducer are also exposed and readily accessible.
Shock isolation mount 100 functions in essentially the same manner as described above with respect to the other embodiments of the invention. Because any shock forces of substantial magnitude are absorbed almost entirely by tensional strain of the film strip support members, it is readily possible to achieve a linear or even hyperbolic stress-strain characteristic as shown in FIGS; 5 and 6. It will be recognized that mounting members 1 15 and l 16 may comprise opposed walls of a rectangular cylindrical frame. Furthermore, although no vibration isolation means or external housing have been shown for the construction of FIGS. 9-12, it should be understood that a vibration isolation arrangement like that shown in the preceding figures can be employed.
FIG. 13 illustrates a slight modification of the shock isolation mount mounted in an external frame. In the construction shown in FIG. 13, an external clamping ring 124 is added to assembly 100, clamping the film strip support members firmly against the outer walls of the frame members and 116. The edges of clamping rings 124 carry a multiplicity of small vibration absorption elements of a material having high compliance and resilience in compression. These elements 122 are engaged by an external frame or housing 123. It is thus seen that the construction shown in FIG. 13 provides both vibration isolation and shock isolation for the transducer or other miniature fragile device 1 l 1.
An alternative method of assembly, to afford the same basic construction as illustrated in FIGS. 9-12, but with the added advantage of elimination of any need to cement the film support members to the mounting members, is illustrated in FIGS. 19 and 20. The shock isolation mount, in this instance, is constructed from a tube 161 of thin polyester film. The tube is cut at two locations intermediate its length as indicated by the cuts 162 and 163 in FIG. 19. The transducer 111 is then threaded into space 166 between the segments of the film tube, arranged as shown in FIG. 20, and mounting plates 115 and 116 are inserted into spaces 167 and 168. The end result is a construction essentially similar to that shown in FIGS. 1 l and 12, with surplus film members 164 and 165 (FIG. 20) extending directly across the construction. The presence of the additional film loops 164 and 165 has no detrimental effect. Indeed, the additional film loops can afford some small vibration isolation is used to support the transducer along a central line or at a central portion so that the rigid mounting members 115 and 116 do not contact encompassing structures.
The principal advantage of the construction illustrated in FIGS. 19 and .20 is the elimination of any need for cement or other fastening of the film supports to the rigid mounting members or to the protected device. In actual assembly, the mounting members 115 and 116 are inserted first into the tube 161, in spaces 167 and 168, and then mounted in a jig, following which device 111 is forced into the central portion 166 of the film tube. A long conical needle" is utilized as a guide for threading the transducer or other device 111 into the desired position. Needless to say, the dimensions for the elements of the assembly should be selected to afford a tight fit, tensioning the film slightly, when assembled.
FIG. 21 illustrates a further modification of the invention that is essentially similar to the construction discussed above in connection with FIGS. 19 and 20.
The shock protection mount shown in FIG. 21 utilizes three tubular film support members 171, 172 and 173. The film loops or tubes 171-173 conform to the configuration realized if the slits 162 and 163 shown in FIG. 19 are extended completely through the tube 161 of thin polyester film or other like material. As shown in FIG. 21, each of the tubular film support members 171-173 is looped around each of the two rigid mounting members 1 and 1 l6, and the fragile transducer or other device 111 is mounted between the support members, the tubular support member 172 being located on the opposite side of device 1 l 1 from support members 171 and 173. The overall effect, therefore, is the positioning of the rigid mounting members 115 and 1 16 in successive pockets in the loops corresponding to the pockets 167 and 168 of FIG. 20. The difference is that in the construction of FIG. 21, the film support members 171-173 may be spaced from each other, whereas in the construction shown in FIGS. 19 and 20 the tubular strip segments are contiguous.
FIGS. 14 and 15 illustrate another modification of the present invention, again using strip film support members that have not been preformed to the configuration of the transducer or other device 111 requiring shock protection. In this instance, there are only two film strip support members 131 and 132, engaging opposite sides of the device 1 1 1.
In the embodiment of FIGS. 14 and 15, the frame means for the isolation mount comprises a rectangular frame including four mounting members 133, 134, 135 and 136. The mounting members may constitute the walls of a rectangular tube. The film strip support member 131 extends upwardly along the outer surface of mounting member 136, over the top of the mounting member, downwardly along the inner surface of mounting member 136, across the bottom surface of transducer 111, up the inner surface of mounting member 134, over the top of the mounting member, and downwardly along the outer surface of mounting member 134. The mounting arrangement for support member 132 is similar except that it is oriented at an angle of 90 relative to strip 131, passes over the opposite side of transducer 11 1 from strip 131, and is supported from mounting members 133 and 135. The resulting structure functions in essentially the same manner for shock absorption as the embodiments of the invention described above. It will be recognized that an additional clamp ring (not shown) can be mounted upon the shock mount of FIGS. 14 and 15, in the manner generally illustrated in FIG. 13, and that appropriate vibration absorption elements can be utilized as in the embodiments of the earlier figures.
In all of the embodiments of the shock isolation mount of the present invention discussed above there is some tendency toward the development of relatively high stresses at the points at which the film support members make the transition from one surface to another in engagement with the mounting members. Referring to FIG. 3, such points of relatively high potential stress are indicated at the corners 39. In all of the various views, the corresponding points of potential high stress on the film are shown as having definite radii; in most instances, the use of a definite radius at the transition point is sufficient to preserve the integrity of the film support member.
On the other hand, it may be desirable to form a bead of plastic or other like material at each such transition point in order to reduce the concentration of stress as applied to the film support members. Furthermore, if such a bead is formed from viscoelastic material affording high compliance for small-amplitude vibrations, the bead serves a dual purpose, reducing stress concentrations in the film for shock absorption while at the same time providing vibration isolation for the transducer or other protected device.
One construction of this general nature is illustrated in FIG. 16, in which a mounting member 141 is provided with an edge bead 142 over which a film strip support member 143 extends. A similar construction, in which a relatively thin layer or pad of highly compliant vibration isolation material 145 is interposed between a film strip support member 146 and a mounting member 147 is illustrated in FIG. 17. FIG. 18, on the other hand, shows the mounting member 147 and vibration isolation strip 145 used in conjunction with a film support member 149 of a somewhat different configuration, allowing a fiexure portion 151 in the form of an overhang over the rim of mounting member 147. These and similar constructions may be utilized to afford both vibration isolation and reduction of stress concentration in the shock protection mount. In any of these constructions, and in the other shock protection mounts of the invention, vibration isolation can be aided or even accomplished entirely by interposing resilient compression isolators between the transducer or other protected device and the film supports instead of in the external frame or between the frame and the film supports. Thus, vibration isolation can be effected by one or more small, compressible, resilient rubber inserts such as the insert 150 (FIG. 17) between the device 1 1 1 and the support strip 146.
1. A shock isolation mount for mounting a miniature transducer or like small, relatively fragile device within a housing, and for protecting that device against shock damage from excessive acceleration in either-direction along a given path, the minimum spacing from the device to the housing along that path being a distance D, comprising:
a first thin, fiat film support member, formed of a low-compliance material having a high modulus of elasticity, extending across one side of said device approximately normal to said path;
a second thin, flat film support member, formed of a low-compliance material having a high modulus of elasticity extending across the other side of said device, said device being wholly supported by said support members;
each of said support members having a width many times greater than its thickness;
and rigid frame means, connected to said housing and engaging said support members in broad area contact, beyond the periphery of said device, to complete an assembly, the configuration of said frame means, said support members, and said device being such that stresses of substantial magnitude produced by acceleration of said housing and said frame means in either direction along said path are absorbed primarily by tensional strain, of limited amplitude less than said distance D, of one of said film support members.
2. A shock isolation mount for a fragile miniature device, according to claim 1, in which each of said support members is a flat, flexible strip of plastic film stretched tautly across said frame means.
3. A shock isolation mount for a fragile miniature device, according to claim 1, in which said frame means, at the point of engagement with said film support members, is padded with a material having high resilience and high compliance in compression to afford vibration isolation for said device and to preclude excessive localized stressing of the film under shock conditions.
4. A shock isolation mount for a fragile miniature device, according to claim 1, in which at least one vibration absorption element, of high resilience and high compliance in compression, is interposed between each of said support members and said device.
5. A shock isolation mount for a fragile miniature device, according to claim 1, in which at least one vibration absorption element of high resilience and high compliance in compression, is interposed between each of said support members and said frame means.
6. A shock isolation mount for a fragile miniature device, according to claim 1, in which each of said thin film support members is a plastic film having a high modulus of elasticity pre-formed into a cup-like configuration conforming to one-half of said device and having a projecting flange engaged by said frame means.
7. A shock isolation mount for a fragile miniature device, according to claim 6, in which the outer rim of the cup portion of each film support member is spaced inwardly of the point of engagement of that support member with said frame means to allow limited flexure of that rim and thereby afford vibration isolation for said device.
8. A shock isolation mount for a fragile miniature device, according to claim 1, in which said frame means comprises a pair of rigid mounting members located on opposite sides of said device and in which the end portions of each of said support members are at least partially wrapped around said mounting members.
9. A shock isolation mount for a fragile miniature device, according to claim 8, in which said housing comprises an external frame for supporting said assembly, and in which at least one vibration absorption element, of high resilience and high compliance in compression, is interposed between said external frame and each of said mounting members to afford vibration isolation as well as shock isolation for said device.
10. A shock isolation mount for a fragile miniature device, according to claim 8, in which said housing comprises an external frame for supporting said assembly, and in which a plurality of individual rubber vibration absorption elements are interposed between each of said mounting members and said external frame to afford vibration isolation as well as shock isolation for said device.
11. A shock isolation mount for a fragile miniature device, according to claim 8, in which there are at least three thin film support members, all of tubular configuration, with said rigidity mounting members and said device threaded thereinto.
12. A shock isolation mount for a fragile miniature device, according to claim 1 1, in which the tubular thin film su port members are separate from each other.
13. shock isolation mount for a fragile miniature device, according to claim 11, in which the tubular thin film support members are all part of a single unitary tube, slit transversely at spaced points.
14. A shock isolation mount for a fragile miniature device, according to claim 1, in which said frame means comprises a pair of rigid ring-like mounting members and in which the peripheral portions of said support members are clamped between said mounting members.
15. A shock isolation mount for a fragile miniature device, according to claim 14, in which said housing comprises an external frame for supporting said assembly, and in which at least one vibration absorption element, of high resilience and high compliance in compression, is interposed between said external frame and each of said mounting members to afford vibration isolation as well as shock isolation for said device.
16. A shock isolation mount for a fragile miniature device, according to claim 14, in which said housing comprises an external frame for supporting said assembly, and in which a plurality of individual rubber vibration absorption elements are interposed between each of said mounting members and said external frame to afford vibration isolation as well as shock isolation for said device.
17. A shock isolation mountfor a fragile miniature device, according to claim 14, in which said housing comprises an external frame slotted to receive said as sembly, and in which said support members project outwardly of said mounting members to isolate said mounting members from said external frame and to center said assembly within said external frame.
18. A shock isolation mount for a fragile miniature device, according to claim 17, in which the outwardly projecting portion of each of said support members is looped back to afford a high-compliance vibration absorption element interposed between one of said mounting members and said external frame to afford vibration isolation therebetween.
19. A shock isolation mount for a fragile miniature device, according to claim 14, in which each of said film support members is bonded to the surfaces of a respective one of said mounting members.
20. A shock isolation mount for a fragile miniature device, according to claim 19, in which said film support members are each bent over a respective mounting member, and further comprising an external band clamping each support member to its mounting member.