US3899784A

US3899784A - Glass breakage detector

Info

Publication number: US3899784A
Application number: US361207A
Authority: US
Inventors: Vincent J Mchenry
Original assignee: Omni Spectra Inc
Current assignee: SOUTHWEST MICROWAVE Inc A CORP OF
Priority date: 1973-05-17
Filing date: 1973-05-17
Publication date: 1975-08-12
Anticipated expiration: 1992-08-12

Abstract

A device attachable to a plane of glass to set off an alarm in response to its breakage but immune to other vibrations. The device comprises a base attachable to the glass by an adhesive, a member carried by the base and spring-urged from a set to an alarm position, and a sensing element holding the member in its set position and responsive only to glass breakage to release the member. The sensing element comprises a curved spring fixed at one end and responsive only to the shock wave of the shattering glass to trigger the device, the spring being immune from triggering excitation normal to the glass plane.

Description

United States Patent 1 1 McHenry 1 GLASS BREAKAGE DETECTOR [75] Inventor: Vincent J. Mcl-lenry, Farmington.

Mich.

[731 Assignee: Omni Spectra, Inc., Farmington,

Mich.

[22] Filed: May 17, 1973 21 Appl. No.: 361,207

[52] U.S. Cl 340/274 R; ZOO/61.84; ZOO/61.93;

200/6108 [51] Int. Cl. G08b 13/08 [58] Field of Search 340/276, 274 R, 273;

ZOO/61.76, 6178, 61.79, 61.8, 61.84, 61.93, 223, 61.08; 116/75, 77, 67 R, DlG. 18

[56] References Cited UNITED STATES PATENTS 3,706,090 12/1972 Callaghan 340/273 1 Aug. 12, 1975 Primary ExaminerJohn W. Caldwell Assistant Examiner-william M. Wannisky Attorney, Agent, or FirmHarness, Dickey & Pierce 1 ABSTRACT A device attachable to a plane of glass to set off an alarm in response to its breakage but immune to other vibrations. The device comprises a base attachable to the glass by an adhesive, a member carried by the base and spring-urged from a set to an alarm position, and a sensing element holding the member in its set position and responsive only to glass breakage to release the member. The sensing element comprises a curved spring fixed at one end and responsive only to the shock wave of the shattering glass to trigger the device, the spring being immune from triggering excitation nonnal to the glass plane.

20 Claims, 2 Drawing Figures CLASS BREAKAGE DETECTOR BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to devices for detecting glass breakage, particularly to mechanisms of the type which will set off an alarm when a pane of window glass is fractured or shattered.

2. Description of the Prior Art Various types of window sensors in intrusion detection systems include window foil, piezoelectric transducers, variable current bridges and mechanical vibrators. The window foil method uses thin metal foil mounted to the glass connected to a normally closed alarm circuit. When the glass is broken, the foil generally breaks to provide the alarm. While reliable, this equipment is costly to install and maintain, being subject for example to scars or cracks in the foil.

Piezoelectric devices work on the principle of an output voltage generated from a crystal by mechanical excitation. The devices generally require adjustment when installed and always require a power supply and electronic circuitry preceding the alarm circuit. The small output voltage of a piezoelectric device is usually insufficient to operate alarm contacts directly but must work through relay means.

Variable current bridge devices operate on the principle of current balance in a bridge circuit. Mechanical shock through a transducer changes the balance in the bridge, thus changing the current level in the alarm circuit. Such devices require a power supply, electronic circuitry and an alarm circuit current regulator.

Mechanical vibrators have seldom been used but work on the principle of a mechanical member being mounted to the glass surface and set into vibration by applied mechanical shock. Such devices in the past have been extremely difficult to adjust so that they will only respond to breaking glass.

Among the patents collected in a novelty search on the subject matter of this invention, the following were noted but are not believed to affect the patentability of the claims: Stelter U.S. Pat. No. 2,884,623; Swiss Pat. No. 277,847; Callaghan US. Pat. No. 3,706,090; Lupold et al. US. Pat. No. l,974,779; Traweek, Jr., US. Pat. No. 2,230,l70; White US. Pat. No. 3,441,925; and Colman US. Pat. No. 3,634,845.

BRIEF SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel and improved glass breakage detector which fulfills the need for a reliable, low cost sensor ideally suited for mass production and responsive only to glass breakage.

It is another object to provide an improved glass breakage detector of this type which is immune from excitation normal to the plane of the glass so that an object striking the glass but not breaking it will not set off the alarm, and which cannot be magnetically defeated.

It is another object to provide an improved glass breakage detector of this type which utilizes the principle of a mechanically resonant sensing element.

It is a further object to provide an improved glass breakage detector of this character which requires no power supply other than that normally provided in the alarm circuit and also no electronic circuitry to perform its function.

It is also an object to provide an improved glass breakage detector having these characteristics, which permits either a normally open or normally closed cir cuit operation. or both, in the same device, requires no changes in alarm circuitry to allow its use, and provides positive contact closure and opening.

It is a further object to provide an improved glass breakage detector of this nature which will operate satisfactorily in either extremely low or extremely high ambient temperatures.

It is another object to provide an improved glass breakage detector of this nature which may be visually inspected and tested to determine its setting and performance, and must be manually reset after it is triggered, thus permitting positive identification of the alarm location when used as part of a group of detectors.

The invention centers around the use of a resonant sensing element responsive only to the shock wave which accompanies glass breakage but immune to other vibrations. As illustrated, the invention comprises a switch actuating member securable to the glass and spring-urged from a set position to an alarm or triggered position, contact means controlled by the member in response to said movement and a spiral resonant sensing element holding the member in its set position and responsive only to the shock wave attendant upon shattering of the glass to release the member. More specifically, the illustrated embodiment comprises a base securable to the glass surface, switch means mounted on the base, switch actuating means rotatably mounted on the base and spring-urged from its set to its triggered position, and a curved spring fixed at one end and carrying a detent normally holding the member in its set position, the spring being so constructed as to be immune from excitation normal to the plane of the glass but responsive to the shock wave which accompanies glass shattering to release the member.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a side elevational view in cross section taken along the line 1-1 of FIG. 2 and showing the glass breakage detector of this invention mounted on a pane of glass, parts being broken away;

FIG. 2 is a front elevational view of the device with the cover removed, with the switch actuating rotor in its set position;

FIG. 3 is a plan cross-sectional view taken along the line 33 of FIG. 2; and

FIG. 4 is a front elevational view similar to FIG. 2 with parts being sectioned and showing the rotor in its triggered position.

DESCRIPTION OF THE PREFERRED EMBODIMENT The glass breakage detector is generally indicated at l I and is intended to detect the fracturing or shattering of a pane of window glass partially. indicated at I2. The device comprises a base 13 of circular shape having a substantially flat rear surface 14 securable to the inner surface IS of glass pane 12 by means of a bonding agent I6. The bonding agent is preferably of a nonresilient nature which will not dry out or otherwise alter characteristics with time in a manner which might affect the sensitivity of device II. The shear characteristics of bond 16 may be such that base I3 is removable from glass I2 is desired. Although the location of the device on the glass is not critical, it is so mounted as to be easily accessible for wiring. The number of devices needed for a given pane will depend on its size. It has been found that a single detector II is adequate to protect a pane of glass up to 32 square feet in area. A suitable location for the detector on a glass pane of typical size is about 6 inches from one side and 6 inches from the top or bottom.

Base 13 has a central post 17 extending therefrom, the outer end of which carries a cup-shaped cover 18 for the device. Cover 18 is secured to post 17 by a screw 19 and fits in a recess 21 around the edge of the base. The outer surface of cover 18 is flat, and a circular window 22 in the form of transparent cylindrical plastic member or the like is provided on the front of the cover for purposes which will hereinafter appear.

A contact support 23 is secured to post 17 immediately inwardly of cover 18. The support is of segmental shape, having four ribs 24 extending outwardly from a hub 25 secured to the post. Three

contacts

26, 27 and 28 are secured to support 23 between bridges 24 and extend toward base 13. The contacts are of cylindrical shape and secured in position. Wire attaching terminal screws 29 are provided for the contacts.

The lower portion of base 13 has an extension 30 of arcuate shape, the outer end of which interfits with the edge of contact support 23. This extension is for the purpose of supporting electrical conductor wires (not shown) which lead in past cover 18 by means of radial grooves 31 in the base and thence to axially extending grooves 32 which are formed in the underside of extension 30. Although there are only three contacts, four wire access channels are provided for convenience purposes. Base I3 is provided with a flattened portion 33 opposite extension 30 for orientation purposes during manufacture.

A switch actuating member in the form of a rotor 34 is rotatably mounted on post 17 inwardly of contact support 25. Both the rotor and contact support may be fabricated of an electrically insulative material. The diameter of rotor 34 is almost as great as the inside diameter of cover 18. The outer edge of the rotor is provided with an elongated recess 35 in the vicinity of base extension 30 which limits its rotating movement between the set and triggered positions. The outer edge of rotor 34 is notched as indicated at 36 to facilitate finger gripping. The rotor carries a contact engaging wiper element 37 of arcuate shape having curved end portions 38 supported by posts 39. This spring-like element will connect

contacts

26 and 27 when the rotor is in its set position as shown in FIG. 2, and

contacts

27 and 28 when the rotor is triggered (FIG. 4). Thus the device may be used with either a normally open or a normally closed alarm circuit, or both. In the latter arrangement, one alarm circuit will supervise the other. A notch 40 is provided along the edge of rotor 34 for orientation purposes during manufacture.

A helical coil spring 41 is provided which surrounds hub 42 of rotor 34 and has one end 43 fixed by insertion in an aperture of contact support 23. The other end 44 of spring 41 extends into an aperture on rotor 34. Spring 4] urges rotor 34 in a counterclockwise direction from its set position as shown in FIG. 2 to its triggered position of FIG. 4.

The means for holding rotor 34 in its set position comprises a pin 45 carried by the rotor and a detent 46 carried by a glass breakage sensing element generally indicated at 47. Pin 45 is eccentrically formed on a cylindrical member 48 rotatably mounted in rotor 34. The rotational position of member 48 may be frictionally adjusted by turning the member, which is provided with a screwdriver slot 49. As seen in FIG. 3, member 48 is provided with a shoulder 5| engaging the forward surface of rotor 34, and a cover 52 is mounted on pin 48. The purpose of this cover is to indicate the triggered position of the rotor through window 22, for which purpose it may be colored red as indicated in FIG. 2. The rotor 34 also carries a raised portion 53 which will be opposite window 22 when the rotor is in its set position and is colored green. Together, cover 52 and raised portion 53 comprise visual indicia for the condition of the device.

Preferably, the cross-sectional shape of pin 45 is semicircular as seen in FIG. 4 so as to present a sharp edge engaging detent 46. The detent has a surface 54 which extends substantially radially when the device is set. This arrangement, plus the ability to adjust eccentric pin 45 by rotation of member 48, provides satisfactory sensitivity and adjustment control.

Sensing element 47 is a spring of generally spiral shape. The inner end 55 of this spring extends radially inwardly and is wrapped around post 17 between rotor 34 and base 13. A bushing 56 is mounted on the post and has a slot 57 for receiving end 55 of the spring, the bushing holding the spring in fixed position. The crosssectional shape of spring 47 is seen in FIGS. 1 and 3 and is rectangular, with the long axis being parallel to the rotational axis of rotor 34 and the short axis perpendicular thereto. Thus, the spring is substantially more flexible in a plane parallel to the plane of glass 12 than it is normal to the glass plane. When a window glass is fractured or shattered, a high level shock wave is transmitted in the plane of the glass. Element 47 is so constructed as to be resonant to this shock wave, which will set the element into strong vibration principally parallel to the plane of the glass.

Although the shape of spring 47 may be varied to suit individual requirements, a suitable construction utilizes an Archimedes spiral extending from inner end 55 to detent 46 and an involute spiral outwardly therefrom, the outer end 58 of the spring being curled around itself and the total extent of the spring being approximately 270".

In use, device 11 will be set by removing cover 18 and rotating rotor 34 clockwise. Half-round pin 45 will engage a beveled edge 59 on detent 46, flexing spring 47 out of the way until pin 45 snaps behind shoulder 54 of detent 46. At the same time contact 37 will connect

contacts

26 and 27 and

disconnect contacts

27 and 28, and green indicator 53 will be visible through window 22 to show that the device is set. The setting of rotor 34 will also tension spring 41 so that the rotor is urged counterclockwise.

Any vibration of the glass 12 normal to its plane which is not accompanied by glass breakage will not affect the set position of the device. However, upon shattering or fracturing of the glass, the attendant shock wave and vibration in predominately low frequencies generated in the plane of the glass will be transmitted through base 13 and post 17 to sensing element 47. This will set it into strong vibration, principally parallel to the plane of the glass, retracting detent 46 from pin 45 and permitting spring 41 to rotate rotor 34 counterclockwise from its FIG. 2 to its FIG. 4 position. This will connect

contacts

27 and 28 and

disconnect contacts

26 and 27, setting off the alarm. It will also move red indicator 52 in front of window 22 so that the triggered condition of the device is visible.

I claim:

1. In a glass breakage detector, a sensing element. means securing said element to the inside surface of the glass, the element extending from said securing means, the shape of said element being such that movement of said securing means by the shock wave attendant only upon glass breakage will set said element into strong resonant vibration principally parallel to the plane of the glass, the shape of said element further being such that it is relatively immune to movement of said securing means by vibrations normal to the glass plane, and means connected to said sensing element and movable from a normal set position to a triggered position in which it initiates an alarm, said last-mentioned means being responsive to said vibrations of the sensing element parallel to the glass plane to move to its triggered position and thus initiate an alarm.

2. The combination according to claim 1, said sensing element being a spiral resonant element fixed only at its inner end.

3. The combination according to claim 1, said sensing element having a cross-sectional shape such that it is substantially more flexible in a plane parallel to the glass than normal to it.

4. The combination according to claim 1, said lastmentioned means comprising a member securable to the glass and spring-urged to move from a set position to a triggered position. and contact means controlled by the member in response to said movement, said sensing element holding the member in its set position and responsive only to said vibrations to release the member.

5. In a glass breakage detector, a base securable to the glass surface, switch means mounted on the base to initiate an alarm, switch actuating means rotatably mounted on the base and spring-urged from its set to its triggered position, and a curved spring fixed at one end and carrying a detent normally holding the member in its set position, the curved spring being so constructed as to be immune from excitation normal to the plane of the glass but responsive to the shock wave which accompanies glass shattering to release the member.

6. A glass breakage detector comprising a flat base secured to one surface of the glass, at least two spaced switch contacts carried by said base. a switch actuating member carried by said base to initiate an alarm, means constantly urging said member from a set position to a triggered position changing the conductive relation between said contacts, a detent normally holding said member in its set position, and an element secured to said base and connected to said detent, said element being so shaped as to be set into relatively strong resonant vibration principally in the plane of the glass in response to the shock wave transmitted to the base by the glass when it is fractured or shattered, whereby the detent will be moved to release the switch actuating member which is then permitted to move to its triggered position.

7. The combination according to claim 6, said sensing element comprising a spring of generally spiral shape having its inner end fixed to said base and its outer end free, the cross-sectional shape of this said spring being elongated in a direction normal to the glass plane.

8. The combination according to claim 7, said detent being carried by an intermediate portion of said spring.

9. The combination according to claim 8, the portion of said spring between its inner fixed end and said detent having the shape of an Archimedes spiral, the portion outwardly of the detent having the shape of an involute spiral.

10. The combination according to claim 8, the crosssectional shape of said spring being rectangular, its outer end being curled around itself.

11. The combination according to claim 6, there being three contacts, said member being rotatably mounted on said base, said urging means comprising a helical spring.

12. in a glass breakage detector, a substantially flat base securable to the surface of a plane of glass by a bonding agent, a central post carried by said base, a cover removably securable to the outer end of said post to enclose the elements of the device, a contact support fixed to said post and carrying a plurality of circumferentially arranged contacts, a switch actuating member to initiate an alarm comprising a rotor rotatably mounted on said post, said rotor being movable between a set position in which it creates a certain conductive relation between said contacts and a triggered position in which another conductive relation is created, spring means constantly urging said rotor from its set to its triggered position, a pin carried by said rotor, a detent engageable with said pin to hold the rotor in the set position, a sensing element comprising a spiral spring fixed at its inner end to said post and carrying said detent at an intennediate portion, said spring having a rectangular crosssectional shape with its long axis normal to the plane of the glass, whereby the spring will exhibit a high degree of immunity to vibrations normal to the plane of the glass but will be set into resonant vibration by the shock wave created by glass breakage sufficiently to cause said detent to release said pin.

13. The combination according to claim 12, there being three circumferentially spaced contacts, said rotor carrying a wiper contact connecting first and second fixed contacts when the rotor is in its set position and second and third fixed contacts when it is in its triggered position.

14. The combination according to claim 12, said pin being eccentrically carried by a rotatable member on said rotor, whereby the position of the pin may be adjusted with respect to the detent.

15. The combination according to claim 14, said pin being of half-round cross-sectional shape with a sharp edge engageable with a shoulder on the detent.

16. The combination according to claim 15, said detent having a beveled surface engageable by the rounded portion of the pin when rotated toward its set position.

17. The combination according to claim 12, said cover being provided with a window and visual indicia carried by the rotor and visible through said window to indicate the set and triggered rotor positions.

18. The combination according to claim 12, said base having an axial extension inside said cover, and electrical conductor recesses formed in said extension and leading to terminals on said contact support.

19. The combination according to claim 18, further provided with coacting means on said rotor and base limiting movement of the rotor in both directions.

20. The combination according to claim I9, said coacting means comprising an elongated recessed portion on the edge of said rotor adjacent said base extension.

Claims

1. In a glass breakage detector, a sensing element, means securing said element to the inside surface of the glass, the element extending from said securing means, the shape of said element being such that movement of said securing means by the shock wave attendant only upon glass breakage will set said element into strong resonant vibration principally parallel to the plane of the glass, the shape of said element further being such that it is relatively immune to movement of said securing means by vibrations normal to the glass plane, and means connected to said sensing element and movable from a normal set position to a triggered position in which it initiates an alarm, said last-mentioned means being responsive to said vibrations of the sensing element parallel to the glass plane to move to its triggered position and thus initiate an alarm.

4. The combination according to claim 1, said last-mentioned means comprising a member securable to the glass and spring-urged to move from a set position to a triggered position, and contact means controlled by the member in response to said movement, said sensing element holding the member in its set position and responsive only to said vibrations to release the member.

6. A glass breakage detector comprising a flat base secured to one surface of the glass, at least two spaced switch contacts carried by said base, a switch actuating member carried by said base to initiate an alarm, means constantly urging said member from a set position to a triggered position changing the conductive relation between said contacts, a detent normally holding said member in its set position, and an element secured to said base and connected to said detent, said element being so shaped as to be set into relatively strong resonant vibration principally in the plane of the glass in response to the shock wave transmitted to the base by the glass when it is fractured or shattered, whereby the detent will be moved to release the switch actuating member which is then permitted to move to its triggered position.

10. The combination according to claim 8, the cross-sectional shape of said spring being rectangular, its outer end being curled around itself.

12. In a glass breakage detector, a substantially flat base securable to the surface of a plane of glass by a bonding agent, a central post carried by said base, a cover removably securable to the outer end of said post to enclose the elements of the device, a contact support fixed to said post and carrying a plurality of circumferentially arranged contacts, a switch actuating member to initiate an alarm comprising a rotor rotatably mounted on said post, said rotor being movable between a set position in which it creates a certain conductive relation between said contacts and a triggered position in which another conductive relation is created, spring means constantly urging said rotor from its set to its triggered position, a pin carried by said rotor, a detent engageable with said pin to hold the rotor in the set position, a sensing element comprising a spiral spring fixed at its inner end to said post and carrying said detent at an intermediate portion, said spring having a rectangular cross-sectional shape with its long axis normal to the plane of the glass, whereby the spring will exhibit a high degree of immunity to vibrations normal to the plane of the glass but will be set into resonant vibration bY the shock wave created by glass breakage sufficiently to cause said detent to release said pin.

20. The combination according to claim 19, said coacting means comprising an elongated recessed portion on the edge of said rotor adjacent said base extension.