CA2106815C - Encapsulation of high voltage mechanism to prevent fracture thereof - Google Patents
Encapsulation of high voltage mechanism to prevent fracture thereof Download PDFInfo
- Publication number
- CA2106815C CA2106815C CA 2106815 CA2106815A CA2106815C CA 2106815 C CA2106815 C CA 2106815C CA 2106815 CA2106815 CA 2106815 CA 2106815 A CA2106815 A CA 2106815A CA 2106815 C CA2106815 C CA 2106815C
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- CA
- Canada
- Prior art keywords
- piezoelectric element
- tape
- fracture
- element means
- housing
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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- Piezo-Electric Transducers For Audible Bands (AREA)
Abstract
Structure is disclosed for a piezoelectric high voltage impact device which prevents fracture of the piezoelectric element contained therein. A tape is applied to the surface of the piezoelectric element and wrapped therearound. If the piezoelectric element becomes fractured as a result of actuation thereof, the tape provides support to the element permitting continued use of the device. A viscid encapsulating material can be used within the device so as to act in conjunction with the tape to further support the piezoelectric element permitting continued use of the impact device after fracture of the element has occurred.
Description
2106~1~
ENCAPSULATION OF PIEZOELECTRIC HIGH VOLTAGE ELEMENT
TO PREVENT FRACTURE THEREOF
TECHNICAL FIELD
The present invention relates, in general, to piezoelectric high voltage impact devices and, more particularly, to an impact device structure which prevents or minimizes fracturing of the piezoelectric element contained therein.
BACKGROUND ART
High voltage impact devices of the piezoelectric type typically include a piezoelectric element, an anvil member on which the piezoelectric element is seated, an impact member oppositely disposed to the anvil member and contacting the piezoelectric element, and a hammer member for striking the impact member causing the piezoelectric element to produce a voltage. All of the foregoing elements are contained within a housing. The piezoelectric element can be molded within the housing or can be loosely assembled therein. A portion of the space between the piezoelectric element and the housing is usually filled with an encapsulating material such as silicone oil, epoxy resin, silicone grease or rubber. Numerous instances of piezoelectric element fracturing have occurred with this structure. The frequency of such fracturing has been reduced by replacing the foregoing encapsulating material with a viscid encapsulating material, such as that disclosed in U.S. Patent No. 4,051,396 (Berlincourt). In addition to reducing the frequency of piezoelectric element fracturing, the utilization of such a viscid encapsulat-ing material minimizes dielectric breakdown across the surface of the piezoelectric element and the terminals of the impact device, and permits utilization of a piezoelectric element that does not have smooth and/or parallel impact surfaces.
Even though fracturing of the piezoelectric element occurs less frequently as a result of using the viscid encapsulating material, fracturing of the piezoelectric element is still a problem particularly at temperatures in excess of about 150°
F at which point the viscid encapsulating material becomes essentially non-viscid. In view of the foregoing, it has become desirable to develop an impact device structure wherein the ~
frequency of piezoelectric element fracturing is further reduced thus increasing the life expectancy of the device particularly at elevated temperatures.
r.
SUMMARY OF THE INVENTION
The present invention solves the problems associated with the prior art and other problems by providing an impact device structure which further reduces the frequency of piezoelectric element fracturing and which provides support to the element if fracturing has occurred, thus permitting continued use of the piezoelectric high voltage impact device. The foregoing is accomplished by the use of tape which is applied to the surface of the piezoelectric element and wrapped therearound. The opposite ends of the piezoelectric element which are adjacent the impact member and the anvil member remain uncovered ensuring firm electrical contact between the piezoelectric element and these members. By the proper selection of the tape material and the adhesive applied to the surface thereof that grippingly engages the piezoelectric element, the frequency of piezoelectric element fracturing is significantly reduced. In addition, if the piezoelectric element becomes fractured during use, the tape provides support to the element . permitting continued use of the impact device. If a viscid encapsulating material, such as that disclosed in U.S. Patent No. 4,051,296, is used to fill a significant portion of the space between the surface defining the bore in which the piezoelectric element is received and the outer surface of the tape, the incidence of piezoelectric element fracturing is further reduced. The viscid material also provides a very thin cushioning film between the ends of the piezoelectric element and the impact and anvil members. The encapsulat-ing material acts in conjunction with the tape to further prevent fracturing of the . " ., ,.; y:. :. : ;.; ; ,,. ., ;. ,: ,:. , ;;:. ,;, ,.:, ;..;, ;
: .
r . . . ;, : ; , .:J . . ~
;, ':., ~ ~;:. . -';: ,"'~~... ':. ' ~~~.; :;.::. v..~..:; ', ....:-;
~.. w~..y~ : .'. ',; .',~. ' ,. ,.... ; ..~.., .. . .'~..':~
: .
.,~ ~:' ~ ' -:' ..' :
, . ' 1 ."; .. .,'..~ ':. ; " .;:.. . '~ ~'.. '.
210G~15 piezoelectric element and to support same permitting the continued use of the high voltage impact device after the element has fractured.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross-sectional view of a prior art high voltage piezoelectric impact S device.
Figure 2 is an enlarged partial cross-sectional view of a piezoelectric impact device that incorporates the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings where the illustrations are for the purpose of describing the preferred embodiment of the present invention and are not intended to limit the invention described herein, Figure 1 is a cross-sectional view of a prior art piezoelectric high voltage impact device 10. The impact device 10 is of the axially actuated type and includes a body member 12 having a plurality of stepped bores therein.
A piezoelectric element 14 is received in one of the stepped bores and is interposed , , between an anvil member 16 and an impact member 18. A spring 20 holds a hammer member 22 in a spaced apart relationship with respect to the impact member 18.
An oppositely disposed spring 24, having a spring constant substantially greater than the spring constant of spring 20, contacts the hammer member 22 and is positioned such that its free end is received within a bore 26 provided within an actuating member 28. A cap 30 is received over a flange portion 32 provided on body member 12 and grippingly engages same to maintain the foregoing elements in an assembled relationship.
The electrical output of the impact device 10 is provided across an electrical contact 34 which is attached to impact member 18 and tip 36 on the end of anvil member 16.
210~8~.~
ENCAPSULATION OF PIEZOELECTRIC HIGH VOLTAGE ELEMENT
TO PREVENT FRACTURE THEREOF
TECHNICAL FIELD
The present invention relates, in general, to piezoelectric high voltage impact devices and, more particularly, to an impact device structure which prevents or minimizes fracturing of the piezoelectric element contained therein.
BACKGROUND ART
High voltage impact devices of the piezoelectric type typically include a piezoelectric element, an anvil member on which the piezoelectric element is seated, an impact member oppositely disposed to the anvil member and contacting the piezoelectric element, and a hammer member for striking the impact member causing the piezoelectric element to produce a voltage. All of the foregoing elements are contained within a housing. The piezoelectric element can be molded within the housing or can be loosely assembled therein. A portion of the space between the piezoelectric element and the housing is usually filled with an encapsulating material such as silicone oil, epoxy resin, silicone grease or rubber. Numerous instances of piezoelectric element fracturing have occurred with this structure. The frequency of such fracturing has been reduced by replacing the foregoing encapsulating material with a viscid encapsulating material, such as that disclosed in U.S. Patent No. 4,051,396 (Berlincourt). In addition to reducing the frequency of piezoelectric element fracturing, the utilization of such a viscid encapsulat-ing material minimizes dielectric breakdown across the surface of the piezoelectric element and the terminals of the impact device, and permits utilization of a piezoelectric element that does not have smooth and/or parallel impact surfaces.
Even though fracturing of the piezoelectric element occurs less frequently as a result of using the viscid encapsulating material, fracturing of the piezoelectric element is still a problem particularly at temperatures in excess of about 150°
F at which point the viscid encapsulating material becomes essentially non-viscid. In view of the foregoing, it has become desirable to develop an impact device structure wherein the ~
frequency of piezoelectric element fracturing is further reduced thus increasing the life expectancy of the device particularly at elevated temperatures.
r.
SUMMARY OF THE INVENTION
The present invention solves the problems associated with the prior art and other problems by providing an impact device structure which further reduces the frequency of piezoelectric element fracturing and which provides support to the element if fracturing has occurred, thus permitting continued use of the piezoelectric high voltage impact device. The foregoing is accomplished by the use of tape which is applied to the surface of the piezoelectric element and wrapped therearound. The opposite ends of the piezoelectric element which are adjacent the impact member and the anvil member remain uncovered ensuring firm electrical contact between the piezoelectric element and these members. By the proper selection of the tape material and the adhesive applied to the surface thereof that grippingly engages the piezoelectric element, the frequency of piezoelectric element fracturing is significantly reduced. In addition, if the piezoelectric element becomes fractured during use, the tape provides support to the element . permitting continued use of the impact device. If a viscid encapsulating material, such as that disclosed in U.S. Patent No. 4,051,296, is used to fill a significant portion of the space between the surface defining the bore in which the piezoelectric element is received and the outer surface of the tape, the incidence of piezoelectric element fracturing is further reduced. The viscid material also provides a very thin cushioning film between the ends of the piezoelectric element and the impact and anvil members. The encapsulat-ing material acts in conjunction with the tape to further prevent fracturing of the . " ., ,.; y:. :. : ;.; ; ,,. ., ;. ,: ,:. , ;;:. ,;, ,.:, ;..;, ;
: .
r . . . ;, : ; , .:J . . ~
;, ':., ~ ~;:. . -';: ,"'~~... ':. ' ~~~.; :;.::. v..~..:; ', ....:-;
~.. w~..y~ : .'. ',; .',~. ' ,. ,.... ; ..~.., .. . .'~..':~
: .
.,~ ~:' ~ ' -:' ..' :
, . ' 1 ."; .. .,'..~ ':. ; " .;:.. . '~ ~'.. '.
210G~15 piezoelectric element and to support same permitting the continued use of the high voltage impact device after the element has fractured.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross-sectional view of a prior art high voltage piezoelectric impact S device.
Figure 2 is an enlarged partial cross-sectional view of a piezoelectric impact device that incorporates the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings where the illustrations are for the purpose of describing the preferred embodiment of the present invention and are not intended to limit the invention described herein, Figure 1 is a cross-sectional view of a prior art piezoelectric high voltage impact device 10. The impact device 10 is of the axially actuated type and includes a body member 12 having a plurality of stepped bores therein.
A piezoelectric element 14 is received in one of the stepped bores and is interposed , , between an anvil member 16 and an impact member 18. A spring 20 holds a hammer member 22 in a spaced apart relationship with respect to the impact member 18.
An oppositely disposed spring 24, having a spring constant substantially greater than the spring constant of spring 20, contacts the hammer member 22 and is positioned such that its free end is received within a bore 26 provided within an actuating member 28. A cap 30 is received over a flange portion 32 provided on body member 12 and grippingly engages same to maintain the foregoing elements in an assembled relationship.
The electrical output of the impact device 10 is provided across an electrical contact 34 which is attached to impact member 18 and tip 36 on the end of anvil member 16.
210~8~.~
Operationally, the length of spring 20 and its spring constant are such so as to position hammer member 22 above a ledge 40 formed within body member 12 and in a spaced-apart relationship therewith. As the actuating member 28 is depressed, a circumferential flange surface 42 on hammer member 22 comes into contact with ledge 40. Further depression of actuating member 28 causes surface 44 defining the entrance to bore 26 within actuating member 28 to engage a conical surface 46 on hammer member 22 causing the circumferential flange surface 42 thereon to become disengaged from ledge 40 permitting hammer member 22 to move rapidly toward impact member 18. Inasmuch as spring 24 has a substantially larger spring constant than spring 20, spring 24 causes hammer member 22 to strike impact member 18 which, in turn, results in piezoelectric element 14 producing a voltage across electrical contact 34 and tip 36 of anvil member 16. Repeated striking of impact member 18 by hammer member 22 causes piezoelectric element 14 to eventually fracture resulting in the reduction or extinction of a voltage across electrical contact 34 and tip 36 of anvil member 16 when the hammer member 22 strikes the impact member 18.
The present invention is directed to structure for an impact device which minimizes the incidence of fracturing of the piezoelectric element and, if fracturing occurs, for supporting the piezoelectric element permitting the continued use of the impact device. Referring now to Figure 2, a partial cross-sectional view of a portion of an impact device 50, which can be one of any number of types of impact devices, such as an axially or a rotary actuated device, is illustrated. Impact device 50 includes a body portion S2 having a blind bore 54 therein which receives a piezoelectric element 56. An anvil member 58 and an impact member 60 are received within the body portion 52 and are disposed on opposite sides of piezoelectric element 56. The piezoelectric element 56 .
is cylindrical in configuration and its diameter is such so that an annular space 62 exists between its cylindrical surface and the surface defining the blind bore 54. It has been . CA 02106815 1999-10-20 found that the use of a strip of tape 64 having an adhesive on one side thereof for attachment to the cylindrical surface of the piezoelectric element 56 substantially reduces the incidence of fracturing of the element 56 resulting from repeated strikes by 5 a hammer member (not shown) on impact member 60. The tape 64 is usually 0.5 to 2.0 mils thick and the backing material for same can be paper, Mylar*, polyester film, Kapton*, etc. The tape 64 should have a sticky adhesive coating applied to the side that grippingly engages the cylindrical surface of the piezoelectric element 56, and the properties of the adhesive coating should remain substantially constant over the operating temperature range of the impact device 50. Alternatively, the surface of the tape that grippingly engages the cylindrical surface of the piezoelectric element 56 can be coated within an adhesive that hardens as a catalyzed epoxy resin. Regardless of the type of tape employed and/or the adhesive utilized for same, the width of the tape 64 in the longitudinal direction should be slightly less than the longitudinal width of the piezoelectric element 56 so that the edges of the strip of tape 64 do not enter the spaces between the piezoelectric element 56 and the impact member 60 and anvil member 58. Ideally, the piezoelectric element 56 should be wrapped with 1.2 to 1.9 turns of tape 64, with the optimum number of turns being approximately 1.33 turns, however, satisfactory test results have been obtained even when the piezoelectric element 56 has been wrapped with less than one full turn of tape .
From the foregoing, it is apparent that even if the entire cylindrical surface of the piezoelectric element 56 is not covered by the tape 64, the tape provides support to the portion of the piezoelectric element 56 that is covered which, in turn, provides support to the entire piezoelectric element 56.
Test conducted with the piezoelectric element 14 wrapped with 1.3 turns of polyester film tape in combination with a viscid encapsulating material within the annular space 62 indicate that the impact device can be operated at an elevated temperature of 300°F. for several thousand actuations without fracturing the piezoelectric element. The *trade~mark 21~68~~
The present invention is directed to structure for an impact device which minimizes the incidence of fracturing of the piezoelectric element and, if fracturing occurs, for supporting the piezoelectric element permitting the continued use of the impact device. Referring now to Figure 2, a partial cross-sectional view of a portion of an impact device 50, which can be one of any number of types of impact devices, such as an axially or a rotary actuated device, is illustrated. Impact device 50 includes a body portion S2 having a blind bore 54 therein which receives a piezoelectric element 56. An anvil member 58 and an impact member 60 are received within the body portion 52 and are disposed on opposite sides of piezoelectric element 56. The piezoelectric element 56 .
is cylindrical in configuration and its diameter is such so that an annular space 62 exists between its cylindrical surface and the surface defining the blind bore 54. It has been . CA 02106815 1999-10-20 found that the use of a strip of tape 64 having an adhesive on one side thereof for attachment to the cylindrical surface of the piezoelectric element 56 substantially reduces the incidence of fracturing of the element 56 resulting from repeated strikes by 5 a hammer member (not shown) on impact member 60. The tape 64 is usually 0.5 to 2.0 mils thick and the backing material for same can be paper, Mylar*, polyester film, Kapton*, etc. The tape 64 should have a sticky adhesive coating applied to the side that grippingly engages the cylindrical surface of the piezoelectric element 56, and the properties of the adhesive coating should remain substantially constant over the operating temperature range of the impact device 50. Alternatively, the surface of the tape that grippingly engages the cylindrical surface of the piezoelectric element 56 can be coated within an adhesive that hardens as a catalyzed epoxy resin. Regardless of the type of tape employed and/or the adhesive utilized for same, the width of the tape 64 in the longitudinal direction should be slightly less than the longitudinal width of the piezoelectric element 56 so that the edges of the strip of tape 64 do not enter the spaces between the piezoelectric element 56 and the impact member 60 and anvil member 58. Ideally, the piezoelectric element 56 should be wrapped with 1.2 to 1.9 turns of tape 64, with the optimum number of turns being approximately 1.33 turns, however, satisfactory test results have been obtained even when the piezoelectric element 56 has been wrapped with less than one full turn of tape .
From the foregoing, it is apparent that even if the entire cylindrical surface of the piezoelectric element 56 is not covered by the tape 64, the tape provides support to the portion of the piezoelectric element 56 that is covered which, in turn, provides support to the entire piezoelectric element 56.
Test conducted with the piezoelectric element 14 wrapped with 1.3 turns of polyester film tape in combination with a viscid encapsulating material within the annular space 62 indicate that the impact device can be operated at an elevated temperature of 300°F. for several thousand actuations without fracturing the piezoelectric element. The *trade~mark 21~68~~
foregoing was accomplished with polyester film tape (4113 tape) obtained from the Great Tape Company of Newburyport, Massachusetts. The polyester film tape utilized had a total thickness of 2.5 mils comprised of a 1.0 mil polyester film used as a backing material and an acrylic thermosetting adhesive applied to one side thereof.
The foregoing polyester film tape is typically used as an outer wrapping on capacitors and coils and for holding transformer construction and wire harness bundling. In contrast, tests in which only viscid encapsulating material was.utilized within the annular space 62 resulted in the piezoelectric element fracturing after only 50 to 100 impacts at an elevated temperature of 300° F. and fracturing after several thousand impacts at 200°
F.
Certain modifications and improvements will occur to those skilled in the art upon reading the foregoing. It should be understood that all such modifications and improvements have been deleted herein for the sake of conciseness and readability, but are properly within the scope of the following claims.
The foregoing polyester film tape is typically used as an outer wrapping on capacitors and coils and for holding transformer construction and wire harness bundling. In contrast, tests in which only viscid encapsulating material was.utilized within the annular space 62 resulted in the piezoelectric element fracturing after only 50 to 100 impacts at an elevated temperature of 300° F. and fracturing after several thousand impacts at 200°
F.
Certain modifications and improvements will occur to those skilled in the art upon reading the foregoing. It should be understood that all such modifications and improvements have been deleted herein for the sake of conciseness and readability, but are properly within the scope of the following claims.
Claims (15)
1. A piezoelectric device for converting a mechanical impact into a high electrical voltage comprising:
a housing;
actuating means positioned within said housing piezoelectric element means positioned within said housing and responsive to the actuation thereof by said actuating means to produce a voltage; and means for preventing fracture of said piezoelectric element means as a result of actuation thereof by said actuating means, said fracture preventing means being wrapped on said piezoelectric element means and covering at least a portion of the outer periphery of said piezoelectric element means in the direction of wrapping and having a width slightly less than the width of said piezoelectric element means along its longitudinal axis resulting in a portion of said piezoelectric element means on either side of said fracture preventing means remaining uncovered.
a housing;
actuating means positioned within said housing piezoelectric element means positioned within said housing and responsive to the actuation thereof by said actuating means to produce a voltage; and means for preventing fracture of said piezoelectric element means as a result of actuation thereof by said actuating means, said fracture preventing means being wrapped on said piezoelectric element means and covering at least a portion of the outer periphery of said piezoelectric element means in the direction of wrapping and having a width slightly less than the width of said piezoelectric element means along its longitudinal axis resulting in a portion of said piezoelectric element means on either side of said fracture preventing means remaining uncovered.
2. The device as defined in claim 1 wherein said fracture preventing means comprises tape.
3. The device as defined in claim 2 wherein said tape comprises a backing material and an adhesive composition applied thereto.
4. The device as defined in claim 3 wherein said adhesive composition is applied to one surface of said backing material.
5. The device as defined in claim 3 wherein said backing material is selected from a group consisting of Mylar, polyester film, paper and Kapton.
6. The device as defined in claim 5 wherein said backing material is a polyester film.
7. The device as defined in claim 3 wherein said adhesive composition is selected from a group consisting of acrylic adhesives and adhesives that form a catalyzed epoxy resin when hardened.
8. The device as defined in claim 7 wherein said adhesive composition is an acrylic adhesive.
9. The device as defined in claim 3 wherein said backing material has a thickness of about 1.0 mil.
10. The device as defined in claim 3 wherein said backing material and said adhesive composition have a combined thickness of about 0.5 to 2.5 mils.
11. The device as defined in claim 1 further including encapsulating material received within said housing and substantially covering said fracture preventing means and said portion of said peizoelectric element means on either side of said fracture preventing means.
12. The device as defined in claim 11 wherein said encapsulating material is a viscid material.
13. The device as defined in claim 1 wherein said piezoelectric element means is substantially cylindrical in configuration and said fracture preventing means substantially covers the cylindrical surface defining said piezoelectric element means.
14. The device as defined in claim 3 further including encapsulating material received within said housing and substantially covering said tape.
15. the device as defined in claim 14 wherein said encapsulating material is a viscid material.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US95476092A | 1992-09-30 | 1992-09-30 | |
| US954,760 | 1992-09-30 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2106815A1 CA2106815A1 (en) | 1994-03-31 |
| CA2106815C true CA2106815C (en) | 2000-06-27 |
Family
ID=25495891
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2106815 Expired - Fee Related CA2106815C (en) | 1992-09-30 | 1993-09-23 | Encapsulation of high voltage mechanism to prevent fracture thereof |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2106815C (en) |
-
1993
- 1993-09-23 CA CA 2106815 patent/CA2106815C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2106815A1 (en) | 1994-03-31 |
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| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |