Abstract:
A movement sensor has a spherical body freely movable within a chamber. Radiation is passed through the chamber from at least two different sources. Detectors opposite the radiation sources produce signals responsive to the amount of detected radiation which is dependent on the position of the spherical body relative to the chamber.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a movement sensor and relates particularly to a device for detecting movement or variations of movement of a body. 
     Movement sensors are used in a variety of applications. In some applications, the movement sensors are designed to detect movement in a predetermined direction. In other applications, the movement sensors are designed to detect movement in more than one direction. The present invention is directed particularly at omni-directional movement sensors and will be described with particular reference to the use of such a sensor in a motor vehicle security and alarm system. 
     DESCRIPTION OF THE PRIOR ART 
     Various forms of movement sensors are available. For example, a mercury switch is a form of movement sensor commonly used in motor vehicle alarm systems and which operates when mercury moves from an at-rest position due either to acceleration of the switch, resulting from vehicle movement, or tilting of the switch. However, the known movement sensors suffer a number of inherent disadvantages. 
     The mercury switch, for example, can be set to detect acceleration and movement from a horizontal plane. However, as the switch is reliant on the gravitational effect on the mercury, the switch will not necessarily function as designed if its operating attitude is not substantially horizontal. 
     Another type of movement sensor works on the pendulum principal, where movement causes a suspended magnet to swing above a “Hall Effect” device thereby generating a signal in response to detected movement. A restriction with this sensor is that it only works on a horizontal plane. 
     Another known sensor uses a piezoelectric transducer wherein an acceleration or a sharp movement causes a piezoelectric material to generate an electrical signal. Even though this type of sensor is unaffected by its orientation, it is very susceptible to vibration but is not sensitive enough to detect small accelerations or slow variations in movement. 
     U.S. Pat. No 4,648,273 discloses a device for detecting the influence of gravitational forces on a flowable body contained within a cavity. The device is designed particularly for use in rocketry and space flight programming and instrumentation. However, the device is designed particularly to not only measure acceleration but to determine the state of zero gravity at which time the flowable material forms a sphere due to the surface tension of the medium. 
     Japanese Patent Abstract No 59-202067 (Mitsubishi Denki KK) discloses a three-axial direction acceleration detecting apparatus which includes a sphere supported by springs within a hollow container. Acceleration of the container causes the sphere to move relative thereto and that movement is detected by a light source on each of the yawing, rolling and pitching axes. 
     Japanese Patent Abstract No JP 6-258336 relates to an acceleration sensor which uses a liquid metal ball within a sphere. Shadows of the liquid ball are projected onto multi-element photo detectors. Acceleration causes the ball to deform in shape and the change in the shape of the shadow is measured as a function of the acceleration. 
     Japanese Patent Abstract No JP 6-258337 shows a sensor in which movement is detected by sensing changes to the size of the shadow of a ball within a sphere and detecting the shadow position using a multi-element photo detector. 
     SUMMARY OF THE INVENTION 
     It is therefore desirable to provide an improved movement sensor which has a number of applications but is particularly useful in motor vehicle security and alarm systems. 
     It is also desirable to provide a movement sensor which is able to detect movement in or variations in the motion of a body. 
     It is also desirable to provide a movement sensor which is relatively simple and economic to manufacture. 
     It is also desirable to provide a movement sensor which is reliable in operation. 
     According to one aspect of the invention there is provided a movement sensor including a chamber containing a spherical body freely movable within the chamber, radiation emitting means located relative to the chamber so that emitted radiation passes through the chamber, radiation detecting means to detect emitted radiation passing through the chamber, and signal generating means to generate a signal in response to detected radiation. 
     Preferably, the chamber is a spherical shape and has a relatively smooth inner surface which offers minimal resistance to movement of the spherical body within the chamber. If desired, the chamber may be evacuated, or partially evacuated, to further reduce resistance to movement of the body within the chamber. 
     The radiation emitting means may comprise a light source or a source of infra-red or any other suitable form of radiation including ultrasound. For simplicity, however, the invention will be described with reference to the radiation emitting means as a source of visible light. 
     The radiation detecting means preferably comprises a light detector which incorporates signal generating means so as to generate a signal proportional to the amount of detected light. Electrical circuitry is used to compare the output signal from the light detector with the input to the light source and detect any variation produced by movement of the body within the chamber which changes the amount of radiation passing through the chamber. 
     In one form of the invention, the chamber wall is formed of a material through which the radiation passes. Thus, the chamber may be formed of a synthetic plastics material which is transparent to the radiation. In a particular embodiment, the wall is formed of a material which is translucent to visible light but transparent to infra-red radiation. 
     In another form of the invention the chamber is provided with windows in the wall on opposite sides of the chamber which windows are transparent to the radiation. The radiation emitting means is located at one window and the radiation detecting means is located at the other window. In one preferred form, four windows are provided in the chamber wall with two radiation detecting means and two radiation emitting means so located at the windows that the radiation beams extend across the chamber, preferably at right angles to each other. 
     In a most preferred embodiment, six windows are provided in the chamber wall equally spaced from each other. Three radiation emitting devices are located at three of the windows and three radiation detecting devices are located at the other windows. The emitting and detecting devices are so located that the radiation beams extend at right angles to each other. 
     A movement detector having the two or more emitting and detecting means can be associated with electrical circuitry to firstly detect relative movement between the chamber and the body and secondly determine the extent and direction of acceleration of the chamber. The electrical circuitry receives signals from the detecting devices and compares the signals with the input to the emitting devices. The results of the comparison and then compared with each other and the circuitry is then able to determine whether or not there has been any change from an existing state and, if so, the rate and direction of change. The detector of the invention is therefore able to provide precise determination and calculation of movement of the body relative to the chamber. 
    
    
     In order that the invention is more readily understood, one embodiment thereof will now be described with reference to the accompanying drawing. 
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of a movement detector in accordance with an embodiment and 
     FIG. 2 is side view of the movement detector of FIG.  1 . 
     FIG. 3 is a block diagram of an electrical circuit associated with the detector of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings, the movement detector of this embodiment comprises a hollow, spherical chamber  12  containing a spherical ball  14 . The chamber  12 , which may be formed of any suitable material such as metal or synthetic plastics material, may be evacuated or partly evacuated. The spherical ball may also be formed of any suitable material including metal, synthetic plastics material, wood or any other relatively rigid material which is able to block radiation emitted from a radiation emitter. 
     A radiation emitter  16 , which, in this embodiment, is a light source, is located on one side of the chamber  12  and a second emitter  19  is located at 90° to the emitter  16 . A radiation detector  18 , which may be a photosensor, is located on the opposite side of the chamber  12  from the emitter  16  and a second detector  17  is located opposite the emitter  19 . 
     The chamber wall is provided with windows  15  which are transparent to the emitted radiation, i.e. visible light, so that the radiation beams  21  and  22 , which are preferably parallel beams, can pass through the chamber  12 . 
     When the chamber  12  is at rest, or is moving horizontally with uniform velocity in a normal gravitational field, the ball  14  will remain in the position shown in FIG.  1 . In that “at-rest” position, the ball  14  blocks all the light emitted by the emitter  19  so that the detector  17  will not receive any light. The ball will also block a proportion of the light emitted by the emitter  16  so that the detector  18  will detect only a portion of the total light emitted. 
     On movement or acceleration of the chamber  12 , the ball  14  moves within the chamber. The amount of relative movement between the ball  14  and the chamber  12  depends on the acceleration of the chamber  12  and the inertia of the ball  14 . The direction of the acceleration of the chamber  12  will also determined in which direction the ball moves relative to the chamber. Such relative movement of the ball  14  and chamber  12  will cause a variation in the amount of light blocked by the ball  14  and, therefore, in the amount of light received by the two detectors  17  and  18 . If the ball  14 , for example, moves to the left as viewed in FIG. 1, the amount of light received by the detector  18  will be reduced, as the ball moves relatively upwardly across the light beam  21 , while the amount of light received by the detector  17  will increase as the light beam  22  becomes exposed. 
     As shown in dotted outline in FIG. 2, a third light emitter  20  and a third detector  25  may be provided to improve detection and measurement in three dimensions of acceleration of the chamber as determined by movement of the ball  14 . With three emitters and detectors, the acceleration of the ball  14  within the chamber  12  is more easily calculated and the relative location of the ball  14  may be determined by simple calculation. 
     Referring to FIG. 3, the outputs from the detectors  17  and  18  and  25  (if present) are received at a comparator  23  which compares the respective outputs with the inputs as determined by the input circuit  24  in relation to the emitters  16 ,  19  and  20  (if present). A calculator  26  is able to determine the relative position of the ball  14  by the compared results and is also able to determine a direction of relative movement of the ball  14  by timed comparisons to thereby signal an alarm circuit  28 , or any other output circuit, when predetermined thresholds have been reached or exceeded. 
     While the invention has been described with reference to a spherical chamber having transparent windows in the wall thereof, it will be appreciated that the chamber may be of other shapes, such as ellipsoidal or non-regular shapes. Also, the wall of the chamber may be of a material through which the radiation passes thus obviating the need for radiation transparent windows. Thus, a translucent synthetic plastics material may be used for the chamber wall and which allows the transmission of infra-red radiation. 
     To avoid errors arising from radiation reflected from the ball  14  and impinging on a detector other than that towards which the radiation was directed, the radiation emitted from the emitters may be of different frequencies, or have other characteristics whereby the specific radiation from each emitter can be identified. In addition, or as an alternative, the surface of the ball  14  may be formed of a material or in such a manner as to prevent or minimize reflection of emitted radiation. Similarly, the internal surface of the wall of the chamber  12  may also be formed of a material or in a manner so as to minimize or prevent reflection of radiation which impinges thereon. 
     The movement sensor of the invention may be used for any movement detecting purpose, such as in an alarm system for a motor vehicle, such as an automobile or motorbike. The sensor of the invention is particularly suitable for vehicle movement detectors as the security system can be actuated with the vehicle in any orientation relative to the horizontal and, on actuation, the system will sense the relative position of the ball  14  within the chamber  12  at the time of actuation. This will be the “at-rest” position of the ball  14 . Any subsequent movement of the chamber which causes relative movement of the ball therein will then be detected by the variation in detected radiation at the two detectors  17  and  18 . 
     It will be appreciated that a movement sensor in accordance with the invention may be constructed using a single pair of emitter and detector. An alarm system operated by a movement detector of the invention may be calibrated to allow for varying degrees of sensitivity to take account of vibrations and the like which might otherwise cause relatively minor acceleration of the ball  14  within the chamber  12 . 
     Any form of radiation may be used in the -performance of the invention, including microwave radiation and the like. 
     The electrical circuitry associated with the detector of the invention may also compute the angle, direction or distance travelled by a chamber  12  by determining the acceleration of the chamber over a given period of time.