US20050280532A1 - Displacement sensing system - Google Patents

Abstract

A displacement sensing system including an oscillator circuit having a characteristic frequency which varies as a function of a magnetic field in the vicinity thereof, an element whose position relative to the oscillator circuit is varied by a displacement, the element being operative to vary the magnetic field in the vicinity of the oscillator circuit as a function of the displacement and circuitry for sensing a change of frequency of the oscillator circuit over time (delta f/delta t) and for providing an output indication when the change in frequency of the oscillator circuit over time exceeds a threshold.

Description

FIELD OF THE INVENTION
• The present invention relates to security systems and apparatus generally and more particularly to systems and apparatus for protecting against unauthorized displacement of objects.
BACKGROUND OF THE INVENTION
• Various types of protective apparatus and systems are known in the prior art. The following U.S. Patents are believed to represent the state of the art: U.S. Pat. Nos. 5,986,549; 5,767,672; 5,760,577; 5,731,785; 5,656,998; 5,519,317; 5,264,733; 5,241,297; 5,237,307; 5,191,314; 5,012,206; 4,897,531; 4,857,892; 4,587,486; 4,458,241; 4,391,203; 4,359,717; 4,274,088; 3,973,191; 3,579,222.
SUMMARY OF THE INVENTION
• The present invention seeks to provide improved protective apparatus and systems, particularly suitable for protection of works of art and the like.
• There is thus provided in accordance with a preferred embodiment of the present invention a displacement sensing system including an oscillator circuit having a characteristic frequency which varies as a function of a magnetic field in the vicinity thereof, an element whose position relative to the oscillator circuit is varied by a displacement to be sensed, the element being operative to vary the magnetic field in the vicinity of the oscillator circuit as a function of the displacement, and circuitry for sensing a change of frequency of the oscillator circuit over time (Δf/Δt) and for providing an output indication when the change in frequency of the oscillator circuit over time exceeds a threshold.
• Further in accordance with a preferred embodiment of the present invention the circuitry for sensing a change of frequency over time provides at least first and second different output indications when the change in frequency of the oscillator circuit over time exceeds respective at least first and second different thresholds.
• Further in accordance with a preferred embodiment of the present invention the threshold is variable. Preferably, the threshold varies as a function of a currently perceived threat.
• Additionally the currently perceived threat may be determined by a pattern of past outputs of the circuitry for sensing a change of frequency.
• Still further in accordance with a preferred embodiment of the present invention the oscillator circuit and the circuitry for sensing a change of frequency are operated in accordance with a duty cycle. Preferably, duty cycle is variable. Additionally or alternatively, the duty cycle is adaptive or the duty cycle may vary as a function of a currently perceived threat.
• Additionally in accordance with a preferred embodiment of the present invention the currently perceived threat is determined by a pattern of past outputs of the circuitry for sensing a change of frequency.
• Furthermore in accordance with a preferred embodiment of the present invention the threshold varies in accordance with long time scale changes in the characteristic frequency.
• Further in accordance with a preferred embodiment of the present invention the threshold includes first and second frequency thresholds, respectively above and below the characteristic frequency and which are normally generally equally separated therefrom in the frequency domain.
• Still further in accordance with a preferred embodiment of the present invention the displacement sensing system also includes wireless communication circuitry operative to transmit the output indication to a remote receiving location. Preferably, the wireless communication circuitry is operative to transmit the output indication for at least a predetermined time following sensing of the change in frequency.
• Furthermore in accordance with a preferred embodiment of the present invention the displacement sensing system also includes a locator operative for sensing the location of at least one of the oscillator, the element and the circuitry for sensing.
• Additionally in accordance with a preferred embodiment of the present invention the element is a magnet Preferably the element is an electromagnet Alternatively the element is a permanent magnet.
• Further in accordance with a preferred embodiment of the present invention the circuitry for sensing a change of frequency includes a microprocessor which receives an output of the oscillator circuit as a clock input.
• Furthermore in accordance with a preferred embodiment of the present invention the circuitry for sensing a change of frequency is operative to count oscillator pulses over variable time periods which represent variable sensitivity thresholds.
• There is thus also provided in accordance with a preferred embodiment of the present invention a displacement sensing system including an oscillator circuit having a characteristic frequency which varies as a function of a magnetic field in the vicinity thereof, an element whose position relative to the oscillator circuit is varied by a displacement to be sensed, the element being operative to vary the magnetic field in the vicinity of the oscillator circuit as a function of the displacement, and circuitry for sensing a time duration over which a change of frequency of at least a given amount takes place and for providing an output indication when the time duration exceeds a threshold.
• Further in accordance with a preferred embodiment of the present invention the circuitry for sensing a time duration provides at least first and second different output indications when the time duration exceeds respective at least first and second different thresholds. Preferably, the threshold is variable and varies as a function of a currently perceived threat.
• Additionally in accordance with a preferred embodiment of the present invention the currently perceived threat is determined by a pattern of past outputs of the circuitry for sensing a change of frequency.
• Still further in accordance with a preferred embodiment of the present invention the oscillator circuit and the circuitry for sensing a time duration are operated in accordance with a duty cycle. Preferably the duty cycle is variable and adaptive.
• Preferably the duty cycle varies as a function of a currently perceived threat.
• Still further in accordance with a preferred embodiment of the present invention the currently perceived threat is determined by a pattern of past outputs of the circuitry for sensing a change of frequency. Preferably the given amount remains generally constant notwithstanding long time scale changes in the characteristic frequency.
• Additionally in accordance with a preferred embodiment of the present invention the displacement sensing system also includes wireless communication circuitry operative to transmit the output indication to a remote receiving location. Preferably, the wireless communication circuitry is operative to transmit the output indication for at least a predetermined time following sensing of the change in frequency.
• Further in accordance with a preferred embodiment of the present invention the displacement sensing system also includes a locator operative for sensing the location of at least one of the oscillator, the element and the circuitry for sensing.
• Moreover in accordance with a preferred embodiment of the present invention the element is a magnet the element is an electromagnet. Alternatively the element is a permanent magnet.
• Additionally in accordance with a preferred embodiment of the present invention the circuitry for sensing a time duration includes a microprocessor which receives an output of the oscillator circuit as a clock input.
• Further in accordance with a preferred embodiment of the present invention the circuitry for sensing a time duration is operative to count oscillator pulses over variable time periods which represent variable sensitivity thresholds. Preferably the circuitry for sensing a time duration includes a microprocessor which provides the output indication.
• There is thus further provided in accordance with yet another preferred embodiment of the present invention a displacement sensing system including an oscillator circuit having a characteristic frequency which varies as a function of a magnetic field in the vicinity thereof an element whose position relative to the oscillator circuit is varied by a displacement to be sensed, the element being operative to vary the magnetic field in the vicinity of the oscillator circuit as a function of the displacement, circuitry for sensing a change of frequency of the oscillator circuit over time (Δf/Δt) and for providing an output indication when the change in frequency of the oscillator circuit over time exceeds a frequency threshold, and circuitry for sensing a time duration over which a change of frequency of at least a given amount takes place and for providing an output indication when the time duration exceeds a time threshold.
• Further in accordance with a preferred embodiment of the present invention the circuitry for sensing a change of frequency over time provides at least first and second different output indications when the change in frequency of the oscillator circuit over time exceeds respective at least first and second different thresholds.
• Still further in accordance with a preferred embodiment of the present invention the frequency threshold is variable. Preferably the frequency threshold varies as a function of a currently perceived threat Additionally the currently perceived threat is determined by a pattern of past outputs of the circuitry for sensing a change of frequency.
• Furthermore in accordance with a preferred embodiment of the present invention the frequency threshold varies in accordance with long time scale changes in the characteristic frequency. The frequency threshold includes first and second frequency thresholds, respectively above and below the characteristic frequency and which are normally generally equally separated therefrom in the frequency domain.
• Additionally in accordance with a preferred embodiment of the present invention the time threshold is variable. Preferably the time threshold varies as a function of a currently perceived threat and wherein the currently perceived threat is determined by a pattern of past outputs of the circuitry for sensing a change of frequency.
• Additionally in accordance with a preferred embodiment of the present invention the oscillator circuit and the circuitry for sensing a time duration are operated in accordance with a duty cycle. Preferably the duty cycle is variable and adaptive.
• Additionally in accordance with a preferred embodiment of the present invention the duty cycle varies as a function of a currently perceived threat and wherein the currently perceived threat is determined by a pattern of past outputs of the circuitry for sensing a change of frequency.
• Additionally in accordance with a preferred embodiment of the present invention the given amount remains generally constant notwithstanding long time scale changes in the characteristic frequency.
• Still further in accordance with a preferred embodiment of the present invention the circuitry for sensing a time duration provides at least first and second different output indications when the time duration exceeds respective at least first and second different thresholds.
• Further in accordance with a preferred embodiment of the present invention the displacement sensing system also includes wireless communication circuitry operative to transmit the output indication to a remote receiving location and is operative to transmit the output indication for at least a predetermined time following sensing of the change in frequency.
• Additionally in accordance with a preferred embodiment of the present invention the displacement sensing system also includes a locator operative for sensing the location of at least one of the oscillator, the element and the circuitry for sensing.
• Still further in accordance with a preferred embodiment of the present invention the element is a magnet. Alternatively the element may be an electromagnet or a permanent magnet.
• Additionally in accordance with a preferred embodiment of the present invention the circuitry for sensing a time duration and the circuitry for sensing a change of frequency includes a microprocessor which receives an output of the oscillator circuit as a clock input.
• Further in accordance with a preferred embodiment of the present invention the circuitry for sensing a time duration is operative to count oscillator pulses over variable time periods which represent variable sensitivity thresholds.
• There is thus provided in accordance with a further embodiment of the present invention a protected object including an object having associated therewith a displacement sensing system. The displacement sensing unit includes an oscillator circuit having a characteristic frequency which varies as a function of a magnetic field in the vicinity thereof, an element whose position relative to the oscillator circuit is varied by a displacement to be sensed, the element being operative to vary the magnetic field in the vicinity of the oscillator circuit as a function of the displacement and circuitry for sensing a change of frequency of the oscillator circuit over time (Δf/Δt) and for providing an output indication when the change in frequency of the oscillator circuit over time exceeds a threshold, wherein one but not both of the oscillator circuit and the element is fixedly mounted onto the object.
• Further in accordance with a preferred embodiment of the present invention the oscillator circuit is fixedly mounted onto the object.
• Still further in accordance with a preferred embodiment of the present invention the element is fixedly mounted onto the object.
• Additionally in accordance with a preferred embodiment of the present invention the threshold is variable. Preferably the threshold varies as a function of a currently perceived threat.
• Moreover in accordance with a preferred embodiment of the present invention the currently perceived threat is determined by a pattern of past outputs of the circuitry for sensing a change of frequency.
• Additionally in accordance with a preferred embodiment of the present invention the oscillator circuit and the circuitry for sensing a change of frequency are operated in accordance with a duty cycle. Preferably the duty cycle is variable or adaptive. The duty cycle may also vary as a function of a currently perceived threat.
• Furthermore in accordance with a preferred embodiment of the present invention the currently perceived threat is determined by a pattern of past outputs of the circuitry for sensing a change of frequency.
• Preferably the threshold varies in accordance with long time scale changes in the characteristic frequency. Additionally the threshold includes first and second frequency thresholds, respectively above and below the characteristic frequency and which are normally generally equally separated therefrom in the frequency domain.
• Additionally in accordance with a preferred embodiment of the present invention the circuitry for sensing a change of frequency over time provides at least first and second different output indications when the change in frequency of the oscillator circuit over time exceeds respective at least first and second different thresholds.
• Further in accordance with a preferred embodiment of the present invention the protected object also includes wireless communication circuitry operative to transmit the output indication to a remote receiving location.
• Additionally in accordance with a preferred embodiment of the present invention the wireless communication circuitry is operative to transmit the output indication for at least a predetermined time following sensing of the change in frequency.
• Still further in accordance with a preferred embodiment of the present invention the element is a magnet. The element is an electromagnet or a permanent magnet.
• Additionally in accordance with a preferred embodiment of the present invention the circuitry for sensing a change of frequency includes a microprocessor which receives an output of the oscillator circuit as a clock input.
• Moreover in accordance with a preferred embodiment of the present invention the circuitry for sensing a change of frequency includes operative to count oscillator pulses over variable time periods which represent variable sensitivity thresholds.
• Additionally in accordance with a preferred embodiment of the present invention the circuitry for sensing a change of frequency is a microprocessor which provides the output indication.
• There is thus provided in accordance with another preferred embodiment of the present invention a protected object including an object having associated therewith a displacement sensing system. The displacement sensing system includes an oscillator circuit having a characteristic frequency which varies as a function of a magnetic field in the vicinity thereof, an element whose position relative to the oscillator circuit is varied by a displacement to be sensed, the element being operative to vary the magnetic field in the vicinity of the oscillator circuit as a function of the displacement, and circuitry for sensing a time duration over which a change of frequency of at least a given amount takes place and for providing an output indication when the time duration exceeds a threshold, wherein one but not both of the oscillator circuit and the element is fixedly mounted onto the object.
• Further in accordance with a preferred embodiment of the present invention the circuitry for sensing a time duration provides at least first and second different output indications when the time duration exceeds respective at least first and second different thresholds.
• Still further in accordance with a preferred embodiment of the present invention the oscillator circuit is fixedly mounted onto the object.
• Additionally in accordance with a preferred embodiment of the present invention the element is fixedly mounted onto the object.
• Moreover in accordance with a preferred embodiment of the present invention the threshold is variable. Preferably the threshold varies as a function of a currently perceived threat and wherein the currently perceived threat is determined by a pattern of past outputs of the circuitry for sensing a change of frequency.
• Additionally in accordance with a preferred embodiment of the present invention the oscillator circuit and the circuitry for sensing a time duration are operated in accordance with a duty cycle. Preferably the duty cycle is variable or adaptive.
• Furthermore in accordance with a preferred embodiment of the present invention the duty cycle varies as a function of a currently perceived threat.
• Additionally in accordance with a preferred embodiment of the present invention the currently perceived threat is determined by a pattern of past outputs of the circuitry for sensing a change of frequency.
• Further in accordance with a preferred embodiment of the present invention the given amount remains generally constant notwithstanding long time scale changes in the characteristic frequency.
• Still further in accordance with a preferred embodiment of the present invention the circuitry for sensing a time duration provides at least first and second different output indications when the time duration exceeds respective at least first and second different thresholds.
• Additionally in accordance with a preferred embodiment of the present invention the protected object also includes wireless communication circuitry operative to transmit the output indication to a remote receiving location and is operative to transmit the output indication for at least a predetermined time following sensing of the change in frequency.
• Moreover in accordance with a preferred embodiment of the present invention the element is a magnet The element may be an electromagnet or a permanent magnet.
• Furthermore in accordance with a preferred embodiment of the present invention the circuitry for sensing a change of frequency includes a microprocessor which receives an output of the oscillator circuit as a clock input.
• Further in accordance with a preferred embodiment of the present invention the circuitry for sensing a change of frequency is operative to count oscillator pulses over variable time periods which represent variable sensitivity thresholds.
• There is also provided in accordance with yet another preferred embodiment of the present invention a protected object including an object having associated therewith a displacement sensing system. The displacement sensing system includes an oscillator circuit having a characteristic frequency which varies as a function of a magnetic field in the vicinity thereof, an element whose position relative to the oscillator circuit is varied by a displacement to be sensed, the element being operative to vary the magnetic field in the vicinity of the oscillator circuit as a function of the displacement, circuitry for sensing a change of frequency of the oscillator circuit over time (Δf/Δt) and for providing an output indication when the change in frequency of the oscillator circuit over time exceeds a frequency threshold, and circuitry for sensing a time duration over which a change of frequency of at least a given amount takes place and for providing an output indication when the time duration exceeds a time threshold, wherein one but not both of the oscillator circuit and the element is fixedly mounted onto the object.
• Further in accordance with a preferred embodiment of the present invention the oscillator circuit is fixedly mounted onto the object.
• Still further in accordance with a preferred embodiment of the present invention the element is fixedly mounted onto the object.
• Additionally in accordance with a preferred embodiment of the present invention the frequency threshold is variable. Preferably the frequency threshold varies as a function of a currently perceived treat and wherein the currently perceived threat is determined by a pattern of past outputs of the circuitry for sensing a change of frequency.
• Further in accordance with a preferred embodiment of the present invention the oscillator circuit and the circuitry for sensing a change of frequency are operated in accordance with a duty cycle.
• Still further in accordance with a preferred embodiment of the present invention the duty cycle is variable and adaptive.
• Further in accordance with a preferred embodiment of the present invention the duty cycle varies as a function of a currently perceived threat and wherein the currently perceived threat is determined by a pattern of past outputs of the circuitry for sensing a change of frequency.
• Moreover in accordance with a preferred embodiment of the present invention the frequency threshold varies in accordance with long time scale changes in the characteristic frequency. Preferably the frequency threshold includes first and second frequency thresholds, respectively above and below the characteristic frequency and which are normally generally equally separated therefrom in the frequency domain.
• Further in accordance with a preferred embodiment of the present invention the circuitry for sensing a change of frequency over the provides at least first and second different output indications when the change in frequency of the oscillator circuit over time exceeds respective at least first and second different thresholds.
• Still further in accordance with a preferred embodiment of the present invention the time threshold is variable and may vary as a function of a currently perceived threat Preferably the currently perceived threat is determined by a pattern of past outputs of the circuitry for sensing a change of frequency.
• Further in accordance with a preferred embodiment of the present invention the oscillator circuit and the circuitry for sensing a time duration are operated in accordance with a duty cycle. The duty cycle is variable and adaptive. The duty cycle may also vary as a function of a currently perceived threat.
• Still further in accordance with a preferred embodiment of the present invention the currently perceived threat is determined by a pattern of past outputs of the circuitry for sensing a change of frequency.
• Additionally in accordance with a preferred embodiment of the present invention the given amount remains generally constant notwithstanding long time scale changes in the characteristic frequency.
• Moreover in accordance with a preferred embodiment of the present invention the circuitry for sensing a time duration provides at least first and second different output indications when the time duration exceeds respective at least first and second different thresholds.
• Furthermore in accordance with a preferred embodiment of the present invention the element is a magnet. The element may be an electromagnet or a permanent magnet.
• Further in accordance with a preferred embodiment of the present invention the circuitry for sensing a change of frequency is a microprocessor which receives an output of the oscillator circuit as a clock input.
• Still further in accordance with a preferred embodiment of the present invention the circuitry for sensing a change of frequency is operative to count oscillator pulses over variable time periods which represent variable sensitivity thresholds.
• Additionally in accordance with a preferred embodiment of the present invention the circuitry for sensing a change of frequency is a microprocessor which provides the output indication.
• Preferably the protected object is an art object The art object may be a painting and wherein one but not both of the oscillator circuit and the element is fixedly mounted onto a frame of the painting.
• Further in accordance with a preferred embodiment of the present invention the art object may be a painting and wherein one but not both of the oscillator circuit and the element is fixedly mounted onto a canvas of the painting.
• Still further in accordance with a preferred embodiment of the present invention the protected object also includes wireless communication circuitry operative to transmit the output indication to a remote receiving location. Preferably the wireless communication circuitry is operative to transmit the output indication for at least a predetermined time following sensing of the change in frequency.
• Further in accordance with a preferred embodiment of the present invention the displacement is a vibrational displacement.
• Additionally in accordance with a preferred embodiment of the present invention the oscillator circuit and the element are physically attached to each other. Alternatively the oscillator circuit and the element are not physically attached to each other.
BRIEF DESCRIPTION OF THE DRAWINGS
• The present invention will be, understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:
• FIG. 1 is a simplified pictorial illustration of displacement sensing systems used in conjunction with protected objects in accordance with a preferred embodiment of the present invention;
• FIG. 2 is a simplified pictorial illustration of the operation of a location functionality in the environment ofFIG. 1;
• FIGS. 3A, 3B and3C are simplified sectional illustrations of a displacement sensing assembly in three different operative orientations;
• FIG. 4 is a simplified sectional illustration of an alternative embodiment of a displacement sensing assembly;
• FIG. 5 is a simplified sectional illustration of another alternative embodiment of a displacement sensing assembly;
• FIGS. 6A and 6B are simplified illustrations of two alternative embodiments of circuitry employed in displacement sensing systems constructed and operative in accordance with a preferred embodiment of the present invention;
• FIG. 7 is a simplified flowchart illustrating the operation of the sensing systems ofFIGS. 6A and 6B;
• FIGS. 8A-8F are illustrations useful in understanding the operation of the embodiments ofFIGS. 6A and 6B, respectively.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
• Reference is now made toFIG. 1, which is a simplified pictorial illustration of displacement sensing systems used in conjunction with protected objects in accordance with a preferred embodiment of the present invention.FIG. 1 illustrates a typical picture gallery, such as in a museum, wherein various displacement sensing devices are associated withpictures10 mounted on awall12. For the purposes of illustration, four different types of displacement sensing devices, constructed and operative in accordance with a preferred embodiment of the present invention, are shown, it being appreciated that a single type may be employed for all the pictures in a gallery or alternatively multiple types may be employed in accordance with the specific applications.
• A first arrangement of displacement sensing device is indicated atreference numeral20 and preferably includes an oscillator circuit, indicated generally byreference numeral22 and having a characteristic frequency which varies as a function of a magnetic field in the vicinity thereof. Anelement24, preferably a permanent magnet, is non-fixedly mounted relative to theoscillator circuit22, typically on aspring26.
• The spring mounting of theelement24 relative to theoscillator circuit22 is such that the position of theelement24 relative to theoscillator circuit22 varies by a displacement to be sensed. The change in the relative positions of theelement24 and theoscillator22 is operative to vary the magnetic field in the vicinity of the oscillator circuit as a function of thedisplacement Circuitry28 is also provided for sensing a change of frequency of the oscillator circuit over time (Δf/Δt) and for providing an output indication when the change in frequency of the oscillator circuit over time exceeds a threshold.
• In the arrangement illustrated atreference numeral20, the entire displacement sensing device described hereinabove is mounted onto apicture30 and the displacement sensing device preferably is operative to provide an output indication of touching, moving, or removal of thepicture30 fromwall12.
• A second arrangement of displacement sensing device is indicated atreference numeral40 and preferably includes an oscillator circuit, indicated generally byreference numeral42 and having a characteristic frequency which varies as a function of a magnetic field in the vicinity thereof. Anelement44, preferably a permanent magnet is non-fixedly mounted relative to theoscillator circuit42, typically on aspring46.
• The spring mounting of theelement44 relative to theoscillator circuit42 is such that the position of theelement44 relative to theoscillator circuit42 varies by a displacement to be sensed. The change in the relative positions of theelement44 and theoscillator42 is operative to vary the magnetic field in the vicinity of the oscillator circuit as a function of the displacement.Circuitry48 is also provided for sensing a change of frequency of the oscillator circuit over time (Δf/Δt) and for providing an output indication when the change in frequency of the oscillator circuit over time exceeds a threshold.
• In the arrangement illustrated atreference numeral40, the entire displacement sensing device described hereinabove is mounted onto awall12 behind and preferably touching apicture50. The displacement sensing device preferably is operative to provide an output indication of touching, moving, or removal of thepicture50 fromwall12.
• A third arrangement of displacement sensing device is indicated atreference numeral60 and preferably includes an oscillator circuit, indicated generally byreference numeral62 and having a characteristic frequency which varies as a function of a magnetic field in the vicinity thereof. Theoscillator circuit62 is preferably mounted onto the back of apicture63. Anelement64, preferably a permanent magnet, is fixedly mounted ontowall12, in close spatial relationship to theoscillator circuit62.
• The mounting of theelement64 relative to theoscillator circuit62 is such that the position of theelement64 relative to theoscillator circuit62 varies by a displacement to be sensed. The change in the relative positions of theelement64 and theoscillator62 is operative to vary the magnetic field in the vicinity of the oscillator circuit as a function of thedisplacement Circuitry68, typically also mounted on the back ofpicture63, is provided for sensing a change of frequency of the oscillator circuit over time (Δf/Δt) and for providing an output indication when the change in frequency of the oscillator circuit over time exceeds a threshold.
• In the arrangement illustrated atreference numeral60, the displacement sensing device described hereinabove is bifurcated, with theoscillating circuit62 mounted ontopicture63 and theelement64 being mounted ontowall12. As in the embodiments described hereinabove, the displacement sensing device preferably is operative to provide an output indication of touching, moving, or removal of thepicture63 fromwall12.
• A fourth arrangement of displacement sensing device is indicated atreference numeral80 and preferably includes an oscillator circuit, indicated generally byreference numeral82 and having a characteristic frequency which varies as a function of a magnetic field in the vicinity thereof. Theoscillator circuit82 is preferably mounted ontowall12, typically in arecess83. Anelement84, preferably a permanent magnet, is fixedly mounted onto the back of apicture85, in close spatial relationship to theoscillator circuit82.
• The mounting of theelement84 relative to theoscillator circuit82 is such that the position of theelement84 relative to theoscillator circuit82 varies by a displacement to be sensed. The change in the relative positions of theelement84 and theoscillator82 is operative to vary the magnetic field in the vicinity of the oscillator circuit as a function of thedisplacement Circuitry88, typically mounted inrecess83, is provided for sensing a change of frequency of the oscillator circuit over time (Δf/Δt) and for providing an output indication when the change in frequency of the oscillator circuit over time exceeds a threshold.
• In the arrangement illustrated atreference numeral80, the displacement sensing device described hereinabove is bifurcated, with theoscillating circuit82 mounted ontowall12 and theelement84 being mounted ontopicture85. As in the embodiments described hereinabove, the displacement sensing device preferably is operative to provide an output indication of touching, moving, or removal of thepicture85 fromwall12.
• Reference is now made toFIG. 2, which is a simplified pictorial illustration of the operation of a removed picture location functionality in the environment ofFIG. 1. In accordance with a preferred embodiment of the present invention, once an output indication of touching, moving or removal of apicture90 is provided, a tracking functionality is provided.
• In this embodiment of the invention, preferably when at least a part of the displacement sensing device is mounted onpicture90, such as in the arrangements indicated byreference numerals20,60 and80, atransmitter92 fixed to thepicture90, preferably associated with the displacement sensing device, provides a wireless output indication, typically viamultiple receivers94 distributed throughout the gallery, to acontrol unit96. Preferably,control unit96 includes adisplay98 which shows the path and current position of a picture in respect of which tracking functionality has been initiated.
• The tracking functionality itself may be entirely conventional, such as described in U.S. Pat. No. 5,731,785, the disclosure of which is hereby incorporated by reference.
• Reference is now made toFIGS. 3A, 3B and3C, which are simplified illustrations of a displacement sensing system constructed and operative in accordance with a preferred embodiment of the present invention in three operative orientations.
• As seen inFIGS. 3A, 3B and3C, in this embodiment, which corresponds to theembodiments20 and40, there is provided a displacement sensing assembly including ahousing100, typically formed of plastic, inside of which is preferably mounted a printedcircuit board102. Mounted on printedcircuit board102 is anoscillator coil104 and abattery106, as well asadditional circuitry108 which senses a change of frequency of said oscillator circuit over time (Δf/Δt) and provides an output indication when the change in frequency of said oscillator circuit over time exceeds a threshold. Additionally mounted on printedcircuit board102 there is preferably also providedRF transmitter circuitry110.
• Apermanent magnet112 is preferably mounted onto aspring114, which in turn is mounted onto the outside ofhousing100.
• FIG. 3A shows a situation wherein thespring114 is at rest, whileFIG. 3B shows a situation wherein thespring114 is somewhat compressed, as in a typical situation, such as that illustrated atreference numeral20 inFIG. 1.FIG. 3C shows a situation where thespring114 is further compressed, as might occur momentarily when a picture with which thedisplacement sensing assembly100 is associated, is touched. It is appreciated that a transition between the orientation shown inFIG. 31B and those of eitherFIGS. 3A and 3C normally causes an output indication of displacement to be transmitted by the displacement sensing assembly.
• FIG. 4 illustrates an alternative embodiment of the displacement sensing assembly shown inFIGS. 3A-3C. In this embodiment, anadditional magnet120, preferably a permanent magnet but possibly an electromagnet, is provided on acircuit board122. Otherwise, the embodiment ofFIG. 4 may be identical to that ofFIGS. 3A-3C. The provision ofmagnet120 is operative to enhance the sensitivity of the displacement sensing assembly, by maximizing the change in inductivity of thecoil104 as a function of the change in magnetic field in the vicinity of the coil.
• FIG. 5 illustrates a further alternative embodiment of the displacement sensing assembly shown inFIGS. 3A-3C. In this embodiment, which corresponds to the embodiments indicated byreference numerals60 and80 inFIG. 1, no spring is provided. Additionally, in this embodiment, anoscillator coil130 may be located at any suitable location on acircuit board132 within ahousing134 and need not be at the center thereof. Otherwise, the embodiment ofFIG. 5 may be identical to that ofFIGS. 3A -3C.
• Reference is now made toFIGS. 6A and 6B, which are simplified illustrations of two alternative embodiments of circuitry employed in displacement sensing systems constructed and operative in accordance with a preferred embodiment of the present invention. Turning toFIG. 6A, it is seen that anoscillating circuit150 includes acoil152 preferably having acore154. Thecoil152 preferably is coupled to ground at both ends thereof viarespective capacitors156.
• Circuitry158 includes aRC combination160, including acapacitor162 and aresistor164, which defines a time base ΔT.Circuitry158 also includes amicroprocessor166, incorporating acounter168, which receives the time base ΔT fromRC combination160 and receives at clock inputs thereof, oscillator outputs from oscillatingcircuit150. Counter168 counts pulses in theoscillator output Microprocessor166 preferably outputs to aconventional RF transmitter170.
• Amagnet172, such as the magnets described hereinabove which are displaceable relative to coils for varying the magnetic field in the vicinity thereof, is located in the vicinity ofcoil152, such that displacement thereof causes a change in the frequency of theoscillator150 output tomicroprocessor166. In response to such changes, themicroprocessor166 may provide an alarm output indication viaRF transmitter170.
• Turning toFIG. 6B, it is seen that anoscillating circuit180 includes acoil182 preferably having acore184. Thecoil182 preferably is coupled to ground at both ends thereof viarespective capacitors186.
• Circuitry188 includes atimer190 and acounter192, which are coupled to amicroprocessor196, which receives at clock inputs thereof, oscillator outputs from oscillatingcircuit180. Counter192 counts pulses in theoscillator output Microprocessor196 preferably outputs to aconventional RF transmitter198.
• Amagnet200, such as the magnets described hereinabove which are displaceable relative to coils for varying the magnetic field in the vicinity thereof, is located in the vicinity ofcoil182, such that displacement thereof causes a change in the frequency of the oscillator outputs tomicroprocessor196. In response to such changes, themicroprocessor196 may provide an alarm output indication viaRF transmitter198.
• It is appreciated that various additional functionalities ofmicroprocessors166 and196 may be provided. Some of these functionalities are described in Israel Patent Application 134,026 filed Jan. 13, 2000, entitled “Circuitry for Signal Measurement”, the disclosure of which is hereby incorporated by reference.
• Reference is now made toFIG. 7, which is a simplified flow chart illustrating operation of the circuitry ofFIGS. 6A and 6B. As described hereinabove, in response to touching, moving or removing a picture or other objects from its intended location, the displacement sensing assembly causes the distance between the magnet and the oscillator coil to change. This causes the magnetic field in the vicinity of the coil to change and results in a corresponding change in the inductance of the coil.
• The change in the inductance of the coil causes a corresponding change in the frequency of the oscillating circuit, which is supplied as a clock frequency to the microprocessor. The number of clock pulses in a given time period are counted by the microprocessor. Two different pulse counts N1 and N2 taken at different times over an identical time duration are illustrated graphically inFIG. 8A.
• Such counts over multiple time periods ΔT produce an indication of the frequency variation over time. Decisions as to whether and when an alarm indication is output depend on the nature of the changes in frequency, including inter alia, their time duration. Thresholds for alarm indications may change dynamically depending, inter alia on past history.
• Turning toFIG. 8B, it is seen that the clock frequency f, which is a direct function of the pulse count over time duration ΔT, varies up and down from a characteristic frequency f_oover time. These variations may exceed predetermined thresholds f₁and f₂. The time duration over which the clock frequency f exceeds either threshold is designated Δt.
• Referring now additionally toFIG. 8C, it is noted that depending on the programming of the microprocessor, an alarm indication may be provided each time that the clock frequency f exceeds either threshold. Alternatively, and preferably, an alarm indication is only provided when the clock frequency (Freq) exceeds either threshold for at least a predetermined time duration threshold T₁, such as when Δt>T₁. Alternatively or additionally, multiple frequency thresholds, in addition to thresholds f₁and f₂, such as threshold f₃may be defined and each may be associated with a different time duration threshold, such as T₁, T₂and T₃, respectively. It is appreciated that the greater the separation of the threshold f_nfrom the characteristic frequency f_o, the shorter is the corresponding time duration threshold T_nthereof.
• Reference is now made toFIG. 8D, which illustrates one manner in which the past history of frequency variation is taken into account in accordance with a preferred embodiment of the present invention. Here, the elapsed time et between exceedences of a given threshold, such as f₄is measured and compared with an elapsed time threshold T_et. If the elapsed time et between exceedences of a given threshold is less than the corresponding elapsed time threshold T_et, an alarm indication may be provided. Otherwise, in this embodiment, an alarm indication is not normally provided. It is appreciated that the functionalities ofFIGS. 8B, 8C and8D may, of course, be combined in various ways.
• Reference is now made toFIG. 8E, which illustrates the fact that the characteristic frequency f_omay vary slowly in time and that the various thresholds, such as f₁and f₂may vary accordingly. However, an event frequency change may vary rapidly. It is appreciated that this functionality may, of course, be combined with that ofFIGS. 5B, 8C and8D.
• Referring now toFIG. 8F, it is appreciated that the duty cycle DS of the occurrence of time durations ΔT during which the pulse counts are taken may also vary as a function of past history, such that when variations in the clock frequency meeting given criteria are detected, pulse counts are taken more often. This enables the circuitry ofFIGS. 6A and 6B to be operated in a sleep mode for energy savings, particularly when powered by batteries. It is also appreciated that this functionality may, of course, be combined with that ofFIGS. 8B, 8C,8D and8E.
• It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove as well as variations and modifications which would occur to persons skilled in the art upon reading the specification and which are not in the prior art.

Claims (52)

1-146. (canceled)

147. Security apparatus comprising:

at least one displacement sensor associated with an object, said at least one displacement sensor sensing a distance of displacement;

at least one time duration sensor for sensing a duration of time said distance of displacement exceeds at least a first predetermined distance, indicative of a possible security violation; and

at least one alarm actuator operative to provide a security violation alarm in response to said duration of time exceeding at least a first predetermined duration.

148. Security apparatus according toclaim 147 and wherein at least one of said first predetermined distance and said first predetermined duration is variable.

149. Security apparatus according toclaim 147 and wherein said at least one alarm actuator is operative to provide at least said first and a second security violation alarm when said distance of displacement exceeds said first predetermined distance and a second predetermined distance for at least said first predetermined duration, said second predetermined distance being different from said first predetermined distance.

150. Security apparatus according toclaim 147 and wherein:

said at least one alarm actuator is also operative to provide at least an additional security violation alarm when said duration of time exceeds a second predetermined duration, said second predetermined duration being different from said first predetermined duration.

151. Security apparatus according toclaim 147 and wherein:

said at least one time duration sensor is also operative to sense an additional duration of time said distance of displacement exceeds a second predetermined distance, said second predetermined distance being different from said first predetermined distance; and

said at least one alarm actuator is also operative to provide at least an additional security violation alarm when said additional duration of time exceeds a second predetermined duration, said second predetermined duration being different from said first predetermined duration.

152. Security apparatus according toclaim 149 and wherein at least one of said first and second predetermined distances and said predetermined duration is variable.

153. Security apparatus according toclaim 148 and wherein said first predetermined distance varies as a function of a currently perceived security violation threat.

154. Security apparatus according toclaim 153 and wherein said currently perceived security violation threat is determined by a pattern of past distances of displacement sensed by said at least one displacement sensor.

155. Security apparatus according toclaim 147 and wherein at least one of said at least one displacement sensor and said at least one duration sensor are operated in accordance with a duty cycle.

156. Security apparatus according toclaim 155 and wherein said duty cycle is variable.

157. Security apparatus according toclaim 156 and wherein said duty cycle is adaptive.

158. Security apparatus according toclaim 156 and wherein said duty cycle varies as a function of a currently perceived security violation threat.

159. Security apparatus according toclaim 158 and wherein said currently perceived security violation threat is determined by a pattern of past outputs of said at least one displacement sensor sensing said distance of displacement.

160. Security apparatus according toclaim 147 and wherein said first predetermined distance varies in accordance with long time scale changes in said distance of displacement.

161. Security apparatus according toclaim 147 and also comprising wireless communication circuitry operative to transmit said security violation alarm to a remote receiving location.

162. Security apparatus according toclaim 147 and also comprising a locator operative for sensing the location of at least one of said displacement sensor, said time duration sensor and said alarm actuator.

163. Security apparatus according toclaim 147 and wherein at least one of said displacement sensor, said time duration sensor and said alarm actuator are attached to said object.

164. Security apparatus according toclaim 147 and wherein said at least one displacement sensor is operative for sensing said distance of displacement by sensing changes in a magnetic field in the vicinity of said displacement sensor.

165. Security apparatus according toclaim 164 and wherein said magnetic field is generated by a magnet, which is associated with said displacement sensor.

166. Security apparatus according toclaim 165 and wherein said magnet is mounted onto said displacement sensor.

167. Security apparatus according toclaim 165 and wherein said magnet is physically separated from said displacement sensor.

168. Security apparatus according toclaim 165 and wherein said magnet is mounted onto said object.

169. Security apparatus according toclaim 165 and wherein at least one of said displacement sensor, said magnet, said time duration sensor and said alarm actuator is attached to said object.

170. Security apparatus according toclaim 164 and wherein said at least one displacement sensor is operative to sense changes in said magnetic field by sensing changes in the frequency of an oscillator for which the oscillating frequency changes in accordance with changes in said magnetic field.

171. Security apparatus comprising:

at least one displacement sensor associated with an object, said at least one displacement sensor sensing a distance of displacement;

at least one time duration sensor for sensing a duration of time said distance of displacement exceeds at least a first predetermined distance, indicative of a possible security violation; and

at least one alarm actuator operative to provide a security violation alarm when said distance of displacement exceeds said first predetermined distance for at least a first predetermined duration and is followed, within a predetermined time window, by another distance of displacement which exceeds at least a second predetermined distance for at least a second predetermined duration.

172. Security apparatus according toclaim 171 and wherein said first predetermined distance and said second predetermined distance are equal.

173. Security apparatus according toclaim 171 and wherein said first predetermined distance and said second predetermined distance are not equal.

174. Security apparatus according toclaim 171 and wherein said first predetermined duration and said second predetermined duration are equal.

175. Security apparatus according toclaim 171 and wherein said first predetermined duration and said second predetermined duration are not equal.

176. Security apparatus comprising:

at least one displacement sensor associated with an object, said at least one displacement sensor sensing a distance of displacement; and

at least one time duration sensor for sensing a duration of time said distance of displacement exceeds at least a predetermined distance, indicative of a possible security violation, and wherein said sensor provides an output indication.

177. Security apparatus according toclaim 176 and wherein said predetermined distance is variable.

178. Security apparatus according toclaim 177 and wherein said predetermined distance varies as a function of a currently perceived security violation threat.

179. Security apparatus according toclaim 178 and wherein said currently perceived security violation threat is determined by a pattern of past distances of displacement sensed by said at least one displacement sensor.

180. Security apparatus according toclaim 176 and wherein at least one of said at least one displacement sensor and said at least one time duration sensor are operated in accordance with a duty cycle.

181. Security apparatus according toclaim 180 and wherein said duty cycle is variable.

182. Security apparatus according toclaim 181 and wherein said duty cycle is adaptive.

183. Security apparatus according toclaim 181 and wherein said duty cycle varies as a function of a currently perceived security violation threat.

184. Security apparatus according toclaim 183 and wherein said currently perceived security violation threat is determined by a pattern of past outputs of said at least one displacement sensor sensing said distance of displacement.

185. Security apparatus according toclaim 176 and wherein said predetermined distance varies in accordance with long time scale changes in said distance of displacement.

186. Security apparatus according toclaim 176 and also comprising a locator operative for sensing the location of at least one of said displacement sensor and said time duration sensor.

187. Security apparatus according toclaim 176 and wherein at least one of said displacement sensor and said time duration sensor is attached to said object.

188. Security apparatus according toclaim 176 and wherein said at least one displacement sensor is operative for sensing said distance of displacement by sensing changes in a magnetic field in the vicinity of said displacement sensor.

189. Security apparatus according toclaim 188 and wherein said magnetic field is generated by a magnet, which is associated with said displacement sensor.

190. Security apparatus according toclaim 189 and wherein said magnet is mounted onto said displacement sensor.

191. Security apparatus according toclaim 189 and wherein said magnet is physically separated from said displacement sensor.

192. Security apparatus according toclaim 189 and wherein said magnet is mounted onto said object.

193. Security apparatus according toclaim 189 and wherein at least one of said displacement sensor, said magnet, and said time duration sensor is attached to said object.

194. Security apparatus according toclaim 188 and wherein said at least one displacement sensor is operative to sense changes in said magnetic field by sensing changes in the frequency of an oscillator for which the oscillating frequency changes in accordance with changes in said magnetic field.

195. Security apparatus comprising:

at least one displacement sensor associated with an object, said at least one displacement sensor sensing a distance of displacement;

at least one time duration sensor for sensing a plurality of time durations during which said distance of displacement exceeds a corresponding plurality of predetermined distances, each of said plurality of predetermined distances being associated with a respective one of a plurality of predetermined durations, indicative of a possible security violation; and

at least one alarm actuator operative to provide a security violation alarm when at least one of said plurality of time durations exceeds a corresponding one of said plurality of predetermined durations.

196. Security apparatus according toclaim 195 and wherein said plurality of predetermined durations are determined as inverse functions to corresponding ones of said plurality of predetermined distances.

197. Security apparatus according toclaim 195 and wherein said at least one alarm actuator provides at least said first and a second security violation alarm when said distance of displacement exceeds a first and a second of said plurality of predetermined distances for a first and a second of said respective predetermined duration.

Images