SENSING TRANSDUCER

• US 3,604,958 A
• Filed: 05/14/1970
• Issued: 09/14/1971
• Est. Priority Date: 05/14/1970
• Status: Expired due to Term

• Current Assignee: Oscar Palini
• Original Assignee: Oscar Palini
• Inventors: Palini, Oscar
• Primary Examiner(s): Hirshfield, Milton O.
• Assistant Examiner(s): Reynolds, B. A.
• Application Number:
  US05/037,111
• Time in Patent Office: 488 Days
• Field of Search: 310/8,8.3,8.5,9.1,8.2,9.2,9.7,8.1,8.7,8.6 340/278,279,280,261,274,272,258,213
• US Class Current: 310/319
• CPC Class Codes: G01L 1/16 using properties of piezoelectric devices
• CPC Class Codes: G08B 13/08 by opening, e.g. of door, of window, of drawer, of shutter, of curtain, of blind
• CPC Class Codes: G08B 13/1472 with force or weight detection

Abstract

An improved sensing transducer for use in a security device to protect objects from unauthorized removal is designed to sense both increases and decreases in pressure and to provide an output signal indicating that a pressure change has occurred. The sensing transducer includes a piezoelectric element and an actuator for transmitting pressure to the piezoelectric element to provide two different types of stress in the element. When an increase or decrease in pressure occurs, the piezoelectric element produces an output signal to indicate a change in pressure.

Claims

1. A transducer for sensing a change in mechanical pressure and providing an output signal in response to the change in pressure, which comprises:

a piezoelectric element for producing a voltage in response to a change in stress applied to said element;

a pair of electrodes positioned on opposite sides of said piezoelectric element for sending the voltage; and

actuator means for transmitting pressure to said piezoelectric element to produce two different types of stress in said element so that upon an increase or decrease in pressure said element is stressed to produce a voltage indicating a change in pressure.

2. The transducer of claim 1, wherein:

said piezoelectric element is elongated; and

which includes a resilient support extending the length of said piezoelectric element for supporting said element.

3. The transducer of claim 2, which includes:

restraining means for limiting movement of said piezoelectric element at a fixed position along said element; and

wherein said actuator means transmits pressure to said piezoelectric element on opposite sides of said fixed position to produce two different types of stress in said element.

4. The transducer of claim 3, which includes:

a housing, and wherein said restraining means includes a spring mounted on the interior of said housing at one end of said element.

5. The transducer of claim 1, which includes:

a housing; and

a unidirectional current device mounted within said housing and having a gate electrode for controlling the conduction of said current device, said gate electrode connected to one of said pair of electrodes so that the conduction of said current device is controlled by the voltage produced by a change in stress of said piezoelectric element.

6. A transducer for sensing a change in mechanical pressure and providing an output signal in response to the change in pressure, which comprises:

a housing;

an elongated piezoelectric element located within said housing for producing a voltage in response to a change in stress applied to said element;

a resilient support located within said housing for supporting said piezoelectric element;

a pair of electrodes positioned on opposite sides of said piezoelectric element for sensing the voltage produced upon a change in stress of said element;

restraining means for limiting movement of said piezoelectric element at a point intermediate between the ends of said element; and

actuator means for transmitting pressure to said piezoelectric element at points on opposite side of said intermediate point to stress said element in two directions so that when said pressure is increased or decreased said element produces a voltage to indicate a change in pressure.

7. The transducer of claim 6, wherein:

said resilient support comprises an elongated block of resilient material mounted within said housing and having an elongated slot formed therein for receiving said piezoelectric element; and

said restraining means includes a spring mounted on the interior of said housing beneath said block of resilient material.

8. The transducer of claim 7, wherein:

said spring is a flexible metal band having a convex center portion for providing support at said piezoelectric element at a position located over the approximate center of said convex portion.

9. The transducer of claim 6, wherein:

said resilient support comprises an elongated hollow block of resilient material located within said housing for receiving and supporting said piezoelectric element; and

said actuator means comprises a protuberance formed on said block of resilient material and protruding outward from said housing.

10. The transducer of claim 9, wherein:

said protuberance formed on said block of resilient material is elongated and extends in a direction parallel to piezoelectric element so that pressure applied to said protuberance is transmitted to said element at points on opposite sides of said intermediate point.

11. The transducer of claim 7, wherein:

said pair of electrodes are elongated and are inserted in said slot formed in said block of resilient material on opposite sides of said piezoelectric element.

12. The transducer of claim 6, which includes:

a unidirectional current device mounted within said housing and having (1) a set of output terminals and (2) a gate electrode for controlling the conduction of said current device through said output terminals, said gate electrode connected to one of said pair of electrodes to sense the voltage produced by a change in stress of said piezoelectric element; and

a set of conductors extending through said housing and connected to said output terminal of said current device for connection to a warning circuit to indicate that a change in pressure is sensed by the transducer.

13. The transducer of claim 12, wherein:

said unidirectional current device comprises a field effect transistor having gate, drain, and source electrodes, and said gate electrode connected to one of said pair of electrodes and said drain and source electrodes connected to said conductors extending through said housing.

14. The transducer of claim 13, which includes:

a diode connected between the gate and source electrodes of said field effect transistor for providing an alternative conducting path for the charge which appears on said pair of electrodes when a change in stress is applied to said piezoelectric element.

15. The transducer of claim 14, wherein:

said field effect transistor and said diode are combined as an integrated circuit.

16. A transducer for use in a security device to protect an object from unauthorized removal by sensing a change in pressure which occurs as a result of any disturbance of the object and providing an output signal to indicate the change in pressure, which comprises:

a piezoelectric element for producing a voltage in response to a change in stress applied to said element;

a pair of electrodes positioned on opposite sides of said piezoelectric element for sensing the voltage; and

actuator means for contacting the object to be protected and transmitting pressure from the object to said piezoelectric element to produce two different types of stress in said element so that upon an increase or decrease in pressure said element is stressed to produce a voltage indicating a change in pressure.

17. The transducer of claim 16, wherein:

said piezoelectric element is elongated; and

which includes a hollow block of resilient material having an elongated slot formed therein for receiving said piezoelectric element; and

restraining means for limiting movement of said piezoelectric element at a point intermediate between the ends of said element.

18. The transducer of claim 17, wherein:

said actuator means comprises a protuberance formed as an integral part of said block of resilient material for contacting the object to be protected and transmitting pressure from the object to said element at points on opposite sides of said intermediate point.