TRANSDUCER

FIELD OF THE INVENTION

This invention relates to motion detectors.

BACKGROUND OF THE INVENTION

Motion detectors are used in security devices that sound an alarm when there is unauthorized movement of an object, such as occurs during theft of the object. Such antitheft devices include an alarm that is sounded when the motion detector detects movement of the object.

For example, US Patent 5,027,105 to Bailey et al, discloses a security device for the prevention of theft. It comprises an alarm and a motion detector that provides a signal, effective through an electrical circuit for actuation of the alarm. The motion detector includes a tubular cylinder, a sphere, and a tether which are conductive and connected in series across an electrical potential. Movement of the detector, from any initial orientation and in any direction results in an increase in contact resistance between the sphere and cylinder. This generates a motion signal that sounds the alarm.

SUMMARY OF THE INVENTION

The present invention provides a motion detector. In a preferred embodiment, the detector of the invention comprises a housing made from a non-conducting material. The housing contains a particle that is preferably a sphere or cylinder and is formed from an electrically conducting material such as iron or copper. The particle has two states inside the housing. In one state, the particle forms an electrical connection between two electrical contacts. In a second state the particle does not form an electrical connection between the two electrical contacts. The particle assumes an initial position when the particle is not undergoing an acceleration or deceleration, in which the particle

is in either the first or second state. When the particle undergoes an acceleration or a deceleration, it moves to a final position in which it is in the other state. In one embodiment of the invention, the particle moves from the final position to its initial position under the influence of gravity. In a second embodiment, the motion detector is provided with a magnet, and the particle moves from its final position to its initial position under the influence of the magnet. In a third embodiment, the motion detector is provided with an elastic element, such as a spring, and the particle moves from its final position to its initial position under the influence of the elastic element.

The motion detector of the invention may be used in a motion detecting device comprising the motion detector of the invention and an alarm producing a sensible signal when the particle moves from its initial position to its final position. The motion detecting device may be configured, for example, as an anti-theft device adapted to be affixed to an object whose theft or movement is to be monitored or prevented, a device for detecting motion of a fence to detect intruders attempting to cross the fence, or a device for detecting motion of a wall to detect a break-in through the wall.

Thus in its first aspect, the invention provides a motion detector comprising a particle having a first state in which the particle creates an electrical connection between two electrical contacts and a second state in which it does not create an electrical connection between the two electrical contacts, the particle moving from an initial position to a final position when the particle is accelerated or decelerated, and the particle moving from the final position to the initial position when the particle ceases to undergo the acceleration or deceleration, the initial position being the first position and the final position being the second position, or the initial position being the second position and the final position being the first position. In its second aspect the invention provides a motion detecting device comprising:

(a) a motion detector comprising a particle having a first state in which the particle creates an electrical connection between two electrical contacts and a second state in which it does not create an electrical connection between the two electrical contacts, the particle moving from an initial position to a final position when the particle is accelerated or decelerated, and the particle moving from the final position to the initial position when the particle ceases to undergo the acceleration or deceleration, the initial position being the first position and the final position being the second position,

or the initial position being the second position and the final position being the first position.

(b) . a current monitor monitoring electrical current in an electrical circuit comprising the first contact and the second contact; and (c) an alarm, the alarm being sounded when the monitor detects a change in current in the electrical circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Fig. 1 shows a motion detector in accordance with one embodiment of the invention;

Fig. 2 shows the motion detector of Fig. 1 in cross section; Fig. 3 shows a motion detecting device comprising the motion detector of Fig. 1; and

Fig. 4 shows a motion detector according to a second embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 shows a movement detector 1 in accordance with one embodiment of the invention. The detector 1 comprises a housing 2 shown in broken lines in Fig. 1.

The housing 2 is made from a non-conducting material, such as rubber or plastic, and has in its interior a cylindrical channel 4. The channel 4 has a first opening 11 and a second opening 13 at opposite ends of the housing 2. The channel 4 contains a cylinder

10 formed from an electrically conducting material such as iron or copper. After the cylinder 10 has been inserted into the channel 4, the cylinder 10 is preventing from escaping from the channel 4 by a first screw 12 and a second screw 14. The screws 12 and 14 are screwed through threaded holes 16 and 18 respectively in the upper surface

20 of the housing 2. In the orientation shown in Fig. 1 , the cylinder 10 rests on a first wire 6 and a second wire 8 extending longitudinally along the bottom of the channel 4. The wire 6 has a first end 22 near the screw 14, although the wire 6 does not contact the screw 14. The wire 6 has a second end 15 extending beyond Use first opening 11. The

first wire 6 is immobilized in the position shown in Fig. 1 by the screw 12 which is screwed into the channel 4 to firmly press the wire 6 against the wall of the channel 4. Similarly, the wire 8 has a first end 26 near the screw 12, although the wire 8 does not contact the screw 12. The wire 8 has a second end 28 extending beyond the second opening 13. The second wire 8 is immobilized in the position shown in Fig. 1 by the screw 14 which is screwed into the channel 4 to firmly press the wire 8 onto the wall of the channel 4. The holes 16 and 18 in the openings of surface 20 are surrounded by rims 21 and 23, respectively, so as to prevent inadvertent handling of the screws 12 and 34, so as to prevent an electric shock when an electric current passes through the wires 6 and 8, as explained below. For further protection against electric shock, caps 25 and 27 may be provided that snap onto the rims 21 and 23 respectively to completely hide the heads of the screws 12 and 14.

Fig. 2 shows the detector 1 in a cross sectional view passing through the center 34 of the cylinder 10. When the detector 1 is held in the orientation shown in Fig. 2a, the cylinder 10 contacts the first wire 6 and the second wire 8 at a first contact point 32 and a second contact point 34 respectively. A gravitational force indicated by the vector 32 acts on the center 34 of the cylinder 10 and bisects a line joining the first and second contact points 32 and 34. The position of the cylinder 10 shown in Fig. 2a in which the cylinder 10 is hi contact with both wires 6 and 8, is referred to herein as the "equilibrium position" of the cylinder 10. When the detector 1 is caused to accelerate in a direction not parallel to the longitudinal axis of the channel 4, the cylinder 10 leaves its equilibrium position. For example, when the detector 1 is caused to accelerate in the direction of the arrow 40 shown in Fig. 2a, the cylinder 10 rolls clockwise over the first wire 8 and arrives at the non-equilibrium position shown in Fig. 2b in which the cylinder 10 is in contact with the wire 6, at a new contact point 35 but is not in contact with the wire 8. The diameters of the cylindrical channel 4 and the cylinderlO are selected so as to limit the movement of the cylinder 10 inside the cylindrical channel 4. As shown in Fig. 2b, the cylinder 10 may contact the wall of the channel 4 at a point 37 and thus prevents loss of contact between the cylinder 10 and the wire 6. This ensures that the cylinder 10 returns to its equilibrium position shown in Fig. 2a under the influence of gravity when the detector 1 ceases to accelerate and the detector is in the orientation shown hi Fig. 2a with respect to the gravitational vector 36. The detector 1 thus functions as an acceleronieter or decelerometer. In this context, it should be noted

that the cylinder 10 will leave its equilibrium position during prolonged acceleration or when subject to a brief jolt.

Fig. 4 shows a motion detector 60 in accordance with a second embodiment of the invention. The motion detector 60 has several components in common with the motion detector 1 shown in Fig. 1, and the same reference numeral is used to indicate similar components in both embodiments without further comment. The motion detector 60 is provided with a magnet 62 located on a bottom surface 64 of the housing. The strength of the magnet 62 is selected so that it is, on the one hand, sufficiently weak so as to allow the cylinder 10 to rotate from its first position to its second position during acceleration or deceleration of the device 60, and an the other hand, sufficiently strong to cause the cylinder 10 to move from its second position to its first position under the influence of the magnet 62, and to maintain the cylinder 10 in its first position when the detector 60 is not experiencing an acceleration or deceleration, irrespective of the orientation of the detector with respect to the gravitational field. In this way the particle will return to its first position regardless of the orientation of the device 60 with respect to the gravitational field.

The motion detector of the invention, for example, the motion detector 1 or 60, may be used in a motion detecting device comprising the motion detector of the invention and an alarm producing a sensible signal when the particle moves from its initial position to its final position. The motion detecting device may configured, for example, as an anti-theft device adapted to be affixed to an object whose theft or movement is to be monitored or prevented, a device for detecting motion of a fence to detect intruders attempting to cross the fence, or a device for detecting motion of a wall to detect a break in through the wall. Fig. 3 shows schematically a motion detecting device 40 in accordance with this aspect to the invention. The device 40 may be affixed onto an object (not shown) whose theft or movement is to be monitored or prevented. The device 40 includes a manually operated on-off switch 44 that is actuated when desired to prevent movement of the object. After being activated, subsequent movement of the object, as in an attempted theft, will result in sounding of the alarm 62. The switch 44 is de- actuated to prevent sounding of the alarm 46 when the object is moved.

Activating the switch 44 results in a signal input to a delay circuit 46, so that after a predetermined amount of time, such as 10 seconds, a monitoring circuit 48 is

activated. Activation of the monitoring circuit 48 applies a voltage across the wires 6 and 8. When the cylinder 10 is in its equilibrium position (Fig. 2a), the cylinder 10 electrically connects the wires 6 and 19, and current flows in the circuit including the wires 6 and 8 and the cylinder 10. The monitoring circuit monitors the current in the circuit. When the object, and hence the motion detector 1, is moved, the cylinder 10 moves from its equilibrium position (Fig. 2a) to a non-equilibrium position (Fig. 2b). In the non-equilibrium position, the cylinder 10 does not electrically connect the wires 6 and 8 so that current does not flow in the circuit including the wires 6 and 8 and the cylinder 10. movement of the object is thus detected by the monitoring circuit 48 as a cessation of current in the circuit including the wires 6 and 8 and the cylinder 10. The cessation of current may be transient or sustained. When movement has been detected by the monitoring circuit 48, a second delay circuit 50 is activated, and after a predetermined second delay such as 10 seconds, the alarm 52 is sounded.

The first delay circuit 46 introduces a delay between the time the on-off switch 44 is activated and the time that the monitoring circuit 46 is activated. This allows the object whose motion is to be detected to be conveniently positioned after activating the switch 44. Similarly, the second delay circuit 50 introduces a delay between the time that motion of the object is detected by the monitoring circuit 48 and the time that the alarm 52 is activated. This allows the object to be retrieved without sounding the alarm.