BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a sensor for sensing rotational movement, and in particular, a tilt sensor that can be adapted to indicate tilt in at least one direction in a plane.  
           [0003]    2. Problems in the Art  
           [0004]    Tilt sensors (sometimes called inclinometers) sense rotational movement of the sensor or the body to which they are attached. Many times they actuate or produce a signal in response to rotation in the plane. A variety of uses exist for such tilt sensors.  
           [0005]    Co-pending, co-owned U.S. Ser. No. 10/210,170, filed Aug. 1, 2002, discloses embodiments of tilt sensors of this type.  
           [0006]    Such tilt sensors can be used to create an alert or alarm perceivable by the user, or to initiate some action. The alarm or action can be autonomous.  
           [0007]    U.S. Ser. No. 10/210,170 illustrates a relatively small tilt sensor that can be placed inside or on an object (e.g. camera). It can actuate an alarm for the user if the camera is tilted beyond an angular amount in either direction generally a vertical plane. Gravity works on a member inside of a race. Depending on direction of tilt, the member occludes a photo detector. Appropriate circuitry interprets the state of the photo detector to interpret whether tilt necessitating an alarm has occurred.  
           [0008]    While the tilt sensor of Ser. No. 10/210,170 provides certain advantages, there is still room for improvement in the art. For example, cameras, and particularly digital cameras, are being made smaller and smaller. Miniaturization of the camera itself means there is less room for auxiliary components such as a tilt sensor.  
         BRIEF SUMMARY OF THE INVENTION  
         [0009]    It is therefore a principal object of the present invention to provide an apparatus and method which improves upon or solves problems and deficiencies in the art.  
           [0010]    Another object, feature, advantage or aspect of the present invention is to provide an apparatus and method which accurately senses rotation in a plane.  
           [0011]    Still other objects, features, advantages, and aspects of the present invention include an apparatus and method which:  
           [0012]    a) senses tilt in one or more directions in a plane;  
           [0013]    b) uses reflectivity principals with electro-optical principals;  
           [0014]    c) enables manufacturing to small sizes, even miniaturization and micro-sizes;  
           [0015]    d) is reliable;  
           [0016]    e) is durable; and  
           [0017]    f) is economical.  
           [0018]    According to one aspect of the invention, an apparatus includes a housing having a cavity. The cavity is adapted to form a race for a movable disk. The disk can move between at least a first default position and a second position. An electromagnetic radiation source is mountable on the housing and adapted to transmit light through an aperture coincident with the default position of the cavity. A photo detector is mountable to the housing and adapted to receive light energy through an aperture coincident with the second position in the cavity. When the body is in a reference or default position (generally horizontal in use), the disk by gravity is seated in the default position and blocks the aperture to the light source. When the body is rotated in generally vertical plane, gravity causes the disk to move away from the default position. Light energy from the light source is allowed to enter through the coincident aperture into the cavity. The interior of the cavity has least some reflectivity properties. A photo detector, appropriately positioned away from the second position for the disk, would then receive reflected light energy to indicate tilt from the default position.  
           [0019]    In another aspect of the invention, the cavity can have a third position, like the second position, away from the default position. The third position can indicate a different direction on state of tilt.  
           [0020]    In a still further aspect of the invention, the apparatus can be micro-sized where the disk is on the order of one or two millimeters diameter or less. The housing can be molded from plastic in two pieces.  
           [0021]    In a still further aspect of the invention, the disk cavity can be configured for a variety of sensing functions, including threshold amounts of tilt before the disk moves out of the default position. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIG. 1 is an enlarged sectional assembled view of a tilt sensor according to an exemplary embodiment of the present invention.  
         [0023]    [0023]FIG. 2 is an isolated front elevation view of a printed circuit board that can be assembled into one side of the tilt sensor of FIG. 1.  
         [0024]    [0024]FIG. 3 is a back elevation of the tilt sensor of FIG. 1 with the back housing lid removed and the sensor in a reference or default position relative to horizontal.  
         [0025]    [0025]FIG. 4A is an interior elevation of a housing lid for the tilt sensor of FIG. 1.  
         [0026]    [0026]FIG. 4B is a sectional view taken along FIG. 4B of FIG. 4A.  
         [0027]    [0027]FIG. 5A is a diagrammatic perspective view of the tilt sensor of FIG. 1 mounted to the interior side of the back wall of a digital camera and in the reference or default position relative to horizontal, indicated by the X axis.  
         [0028]    [0028]FIG. 5B is a top sectional diagrammatic view of FIG. 5A.  
         [0029]    [0029]FIGS. 6A and 6B are similar to FIGS. 5A and 5B except showing the tilt sensor rotated such that its left side is tilted below generally horizontal.  
         [0030]    [0030]FIGS. 7A and 7B are similar to FIGS. 5A and 5B except showing the right side of the tilt sensor rotated below horizontal.  
         [0031]    [0031]FIGS. 8A and 8B are perspective views relative to the coordinate system of FIGS. 5-7, but showing the tilt sensor tilted forwardly and downwardly around the X axis. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0032]    For a better understanding of the invention, one illustrative embodiment the invention can take will now be described in detail. Reference will be taken to the drawings. Reference numerals will be used to indicate certain parts and locations in the drawings. The same reference numerals will be used to indicate the same parts and locations throughout the drawings, unless otherwise indicated.  
         [0033]    A. Apparatus  
         [0034]    [0034]FIGS. 1-4A and  4 B illustrate the basic components of a tilt sensor  10  according to the exemplary embodiment. A main housing (injected molded plastic) has a center wall  113 . On one side of center wall  113  is disk cavity  114 . Housing lid  104  fits over this cavity  114  to enclose it. Housing lid  104  is injected molded plastic and can be ultrasonically welded to housing  102 . The other side of middle wall  113  includes cut-out  108  adapted to receive and seat printed circuit board  106 . Pins  112  extend outwardly in cut out  108  to align PCB  106 . The distal ends of pins  113  can be heated or expanded to lock PCB  106  in place.  
         [0035]    A pair of photo transistors  68 L and  68 R can be mounted by conventional means onto PCB  106 . Likewise, an electromagnetic radiation source or light source  62  (e.g. IR LED) can be mounted to PCB  106 . By appropriate circuitry, each of the photo transistors and LED can be electrically connected to electrical connections  32 , which are adapted for electrical connection to electrical power and inputs and outputs.  
         [0036]    Middle wall  113  of main housing  102  includes appetures in alignment with photo transistors  68 L and  68 R and LED  62 . As can be seen, when PCB  106  is installed into main housing  102 , LED  62  is aligned with aperture  64  through middle wall  113 . This provides an optical pathway from LED  62  into disk cavity  114 . Similarly, when PCB  106  is installed to housing  102 , photo transistors  68 L and  68 R are aligned with aperture  66 R and  66 L in middle wall  113  to allow an optical pathway between each photo transistor and disk cavity  114 .  
         [0037]    A secondary cut-out  108  can exist in middle wall  113  to provide adequate space around each photo transistor  68 L and  68 R when PCB  106  is installed to housing  102 .  
         [0038]    Sensor  10  therefore basically consists of a PCB  106 , with the electro-optical components discussed, heat staked to housing  102 , and a housing lid  104  ultrasonically welded to the other side of housing  102 . Before attaching lid  104 , a stamped bronze disk  60  is inserted into disk cavity  114 . The welding of lid  104  to housing  102  encloses and restrains disk  60  in disk cavity  114 .  
         [0039]    Cavity  114  is basically V-shaped (see, in particular, FIG. 3). In its default or reference position, disk  60  is seated in a semi-cylindrical trough or seat  115 . Cavity  114  has two branches extending angularly in opposite directions from that default position. Aperture  64  for LED  62  is essentially centered with the center of disk  60  when disk  60  is in the position shown in FIG. 3. As can be appreciated, in this default position, light energy from LED  62  would be substantially blocked from entering cavity  114 .  
         [0040]    As shown in FIGS. 4A and 4B, along with FIG. 1, lid  104  includes a cut out portion  118  that is generally coincident with disk  60  when it is in the default position. Note, though, cut out  118  is asymmetrical and includes a beveled edge  120 . This configuration prevents disk  60  from sliding forward.  
         [0041]    [0041]FIGS. 1-4A and  4 B illustrate exemplary dimensions for one embodiment of sensor  10 . As can be seen, the diameter of disk  60  in this example is on the order of two millimeters. The outer dimensions of housing  102  are on the order of five millimeters wide, four millimeters tall, and three millimeters deep. This shows how sensor  10  can be miniaturized or micronized (micro-sized). It should be understood, however, that this configuration can be made in many different sizes, including smaller or larger versions. These particular sizes are for example only and are on the order of which are possible with many commonly commercially available electro-optical components, such as photo transistors  68 L and  68 R and LED  62 .  
         [0042]    The embodiment of FIGS. 1 and 4A and  4 B, plastic of housing  102  and lid  104  can be of any of a variety of plastics.  
         [0043]    B. Operation  
         [0044]    The operation of sensor  10  is similar to that disclosed in Ser. No. 10/210,170. If housing  102  is rotated to sufficiently counterclockwise or clockwise (see FIG. 3), gravity will cause disk  60  to leave seat  115  in disk cavity  114  and move along branch of disk cavity  114  until it reaches the distal end of a branch cavity  114 . Doing so would unblock aperture  64  of LED  62  and allow light into disk cavity  114 . At the same time, disk  60  would block aperture  66 R or  66 L, as the case may be, and thus block any light from LED  62  of appreciable amount of entering the corresponding aperture to that photo transistor. But also, disk  60  would leave the other aperture  66  unblocked. Light from LED  62  entering cavity  114  would reflect off of the walls of cavity  114  and enter the aperture to the unblocked photo transistor  68 . By appropriate selection of components and calibration, this would cause the unblocked photo transistor to sense the light and, with appropriate circuitry, actuate an alarm (e.g. LED light and/or sound) to indicate a tilt of housing  102  in a direction. A tilt in the opposite direction of sufficient angular amount would cause disk  60  to move in the opposite leg of cavity  114 , unblock LED  62 , block the photo transistor in that leg of cavity  114 , and allow light from LED  62  to be detected by the photo transistor that is unblocked in the opposite leg of cavity  114 . The electronic circuitry can then sense a tilt in the other direction.  
         [0045]    The basic circuitry, and functional operation of such circuitry, is described in detail in Ser. No. 10/210,170, and therefore will not be repeated here as that disclosure is incorporated by reference herein. The major difference is utilization of disk  60  to block a single LED in the default position, and block a single photo-transistor if there is a tilt in one direction or the other, using reflectivity to trigger the other unblocked photo transistor. Therefore sensor  10  is a reflective sensor as opposed to an interrupter type described in Ser. No. 10/210,170.  
         [0046]    [0046]FIGS. 5A and 5B,  6 A and  6 B,  7 A and  7 B illustrate diagrammatically the three basic states of sensor  10 . FIGS. 5A and 5B show a default state where disk  60  blocks LED  62  from entering cavity  114 . Neither photo transistor  68 L or  68 R would detect light energy above a threshold to trigger them. The sensor  10  thus would indicate a default position.  
         [0047]    [0047]FIGS. 6A and 6B illustrate how rotation of housing  102  such that its left side rotates under horizontal a sufficient amount, causes disk  60  to roll or move to the end of leg  50 L of cavity  114  blocking photo transistor  68 L. Light from LED  62  entering cavity  114  would reflect from the near side of disk  60  and/or illuminate the remainder of cavity  114 . Photo transistor  68 R would detect this illumination and trigger.  
         [0048]    [0048]FIGS. 7A and 7B illustrate the third state, where the right side of housing  102  is rotated under horizontal, disk  60  blocks photo transistor  68 R, and photo transistor  68 L triggers.  
         [0049]    In this embodiment, some rotation around the X axis while housing  102  is generally horizontal along the X axis would not change the state of sensor  10 . Disk  60  would tip forward into a symmetrical cut out  118  in lid  104  and would be prevented from sliding forward or upwardly in disk cavity  114 . Disk  60  would thus be somewhat retained in its default position and thus be deterred from signaling any tilting relative to the X axis.  
         [0050]    C. Options and Alternatives  
         [0051]    The above described exemplary embodiment is but one form the invention can take. Variations obvious to those skilled in the art are included within the invention which is solely described by the claims.  
         [0052]    For example, the precise configuration and dimensions of sensor  10  can vary according to desire and need. Materials can vary. In this embodiment, the materials of disk  60  and housing  102  are such that there is a relatively low coefficient of friction, meaning that disk  60  can move relatively freely in cavity  114 . Like Ser. No. 10/210,170, the angular shape of cavity  114  is configured to spread approximately in either direction at 45° from the default position. Therefore, sensor  10  must be tilted at least close to 45° or more to get disk  60  to move out of its default position. However, other angular relationships are possible.  
         [0053]    The specific electrical optical components can be selected from commercially available products with specifications according to desire and need.  
         [0054]    The use of sensor  10  can be easily adapted to even the smaller digital cameras. Other uses and applications are, of course, possible.  
         [0055]    The circuitry for connecting the electrical-optical components to the electrical connections  32  can be designed according to need and desire. Such design is well within the skill of those skilled in the art. It should be understood that if sensor  10  is tilted near or over 90° forwardly or backwardly relative to the Y axis, it could cause disk  60  to leave the default position. However, sensor  10  would deter, and usually disallow, movement of disk  60  out of the default position for Y axis tilting up to on the order of 90°.  
         [0056]    The electro optical components can be die attached to a single PCB mounted to the plastic housing. Other methods of attachment of the components and the PCB are possible.  
         [0057]    Disk  60  can be made of other materials. It basically functions as a blocking paddle.  
         [0058]    As can be seen, in the default state (where the camera, for example, is level) disk  60  remains in its lower trough or seat  115  which is in direct alignment with the LED aperture  64 . With disk  60  in the default location, the light from LED  62  is blocked from entering the interior of housing  102 . At this point, no light is incident on either photo diode  68 L or  68 R so the output for both left and right channels are low. Once the sensor is tilted left or right, disk  60  will roll into the corresponding trough or leg  50 L or  50 R and block the aperture  66 R or  66 L centered in that leg and now occupied by disk  60 . Light from LED  62  is now free to flood the interior of disk cavity  114  and is reflected off the surface of lid  104  and into the unblocked photo transistor aperture.  
         [0059]    Whereas the invention has been shown and described in connection with the preferred embodiment thereof, it will be understood that any modifications, substitutions, and additions may be made which are within the intended broad scope of the following claims. From the foregoing, it can be seen that the present invention accomplishes at least all of the stated objectives.
A tilt sensor especially adapted for micro-size, which includes a micro-size housing with a cavity inside. An element, such as a disk, is movable in the cavity between a default position and a second position. A light source is aligned with an aperture which, in turn, is aligned with the default position of the disk in the cavity. In the default position the disk blocks the light source. If the housing is tipped sufficiently in a certain plane, the disk moves out of the default position allowing light from the light source to enter the cavity. A photo detector aperture is positioned to receive light from the unblocked light source to indicate tilt of the housing. The housing can be made of two pieces and plastic and receive a printed circuit board with all electrical optical components.