Abstract:
There is disclosed a device and method for providing signals representative of the positional altitude of a user. The device is responsive to hand or head movements to move a dampened substance contained within a confined tube past one or more sensors. Light passing through the tube is interrupted by the movement of the dampened substance which can be a liquid or a solid object within a viscous liquid.

Description:
TECHNICAL FIELD OF THE INVENTION 
     This invention relates to motion sensors and more particularly to a method and apparatus for a sensor which is portable, light weight and adaptable to be worn or hand held by a user. 
     CROSS REFERENCE TO RELATED APPLICATIONS 
     The following patent applications are cross-referenced to one another, and all have been assigned to Texas Instruments Incorporated. These applications have been concurrently filed and are hereby incorporated in this patent application by reference. 
     
         ______________________________________Ser. No.   Filed     Title______________________________________593,190 10/05/90  Method and Apparatus for Providing a             Portable Visual Display593,823 10/05/90  Method and Apparatus for Monitoring             Physical Positioning of a User593,702 10/05/90  Method and Apparatus for Presentation             of On-Line Directional Sound______________________________________ 
    
     BACKGROUND OF THE INVENTION 
     The relative position and altitude of a person or object is important to monitor for many reasons. For example, in an artificial reality system, such as that disclosed in the above-identified copending patent application entitled &#34;Method and Apparatus for Providing a Portable Visual Display,&#34; it is necessary to continually determine the direction a viewer is facing, the viewer&#39;s motion and the speed of the viewer&#39;s movements. 
     In the past, such measurements have been made using expensive, typically bulky, equipment. 
     In portable artificial reality systems, light weight and economy are mandatory since, in one embodiment, the viewer wears the directional sensor on a helmet, and in other embodiments carries the directional sensors in his/her hand. 
     Typically, such sensors are flux gate compasses, cameras, radio wave detectors and sensors, spring loaded acceleration devices, and other sophisticated devices, usually relying on magnetic flux detection or visual imaging. Also, usually such sensors require calibration each time a user begins a session using the device. 
     Thus, there is a need in the art for a positional sensor which is self contained, light weight and economical to manufacture. 
     There is a further need in the art for such a sensor which allows for positional determination and velocity calculations while still remaining portable and reliable. 
     There is still a further need in the art for such a sensor which requires no calibration upon initial use and which is without mechanical moving parts. 
     SUMMARY OF THE INVENTION 
     A method and device have been devised which allows for the monitoring of a tube containing a liquid, or alternatively, a solid object, by a light sensing device such as a CCD. In operation, a linear CCD array is positioned to detect light passing through the tube. As the tube is tilted from the horizontal, gravity will cause the surface of the liquid (or solid object) to move (rise or fall) with respect to the CCD sensor array, blocking the light and causing signals to be generated dependent upon the relative position of the liquid within the tube. 
     In one embodiment, it is a trapped air bubble within the liquid which causes a light change to occur with respect to each CCD mounted to the tube. The number of CCDs &#34;on&#34; or &#34;off&#34; at any given instant of time is integrated over a period of time to provide an indication of motion direction and speed. The CCD array can be integrally packaged with the tube or could be detachably mounted. This device is economical to manufacture, light in weight and without mechanical moving parts. 
     The processing, based upon the speed with which the signals from the individual CCD sensors change, calculates the positional movement of the user. There can be one such sensor for each plane of possible movement so that a system can have three, or more, such sensors for precise motion and speed determination over a wide range of possible motion. 
     In one embodiment, two such devices can be used to define three planes of motion. This is accomplished by measuring the highest point of the liquid and the lowest point and then calculating the angle or tilt between these points. Thus, one device can provide two dimensions. 
     It is thus one technical advantage of this invention to provide a level measuring device which is portable, light weight, economical, and without mechanical moving parts and which is capable of use without initial calibration. 
     It is a further technical advantage of this invention that the fluid level within a confined enclosure can be monitored to determine the direction of change and the rate of change. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the present invention may be acquired by referring to the detailed description and claims when considered in connection with the accompanying drawings in which like reference numbers indicate like features wherein: 
     FIG. 1 is a helmet mounted virtual reality device with the speaker elements exposed; 
     FIG. 2 is also a helmet mounted virtual reality device; 
     FIG. 3 is a schematic representation of a simulated reality system; 
     FIGS. 4a, 4b and 4c depict a CCD position-orientation sensor in various orientations; and 
     FIG. 5 shows a three-dimensional position-orientation sensor. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 depicts a portable virtual reality system 10 worn by an individual on his or her head. System 10 consists of a color liquid display screen 101, an array of piezoelectric film elements 102, a position-orientation sensor 12 and a processor 13. 
     Processor 13 generates a visual picture according to helmet 10 orientation information from position-orientation sensor 12 and on board software. Processor 13 creates a three dimensional environment and projects a view of it on screen 101. As the user moves his/her head and, hence, helmet 10, processor 13 changes the image on screen 13 to mimic the view the user would perceive if he/she were actually in the three dimensional environment. Similarly, if the user walks or runs to a new location, processor 13 changes the image on screen 101 as if the user walked or ran the same distance and direction in the three dimensional environment. 
     Note that while screen 101 is a color liquid crystal display, it can be any type of display and can, for example, be positioned close to a user&#39;s eyes with a short focal length. 
     Processor 13 also generates a sound field through piezoelectric elements 102 of sound band 11. Individual elements 102 are separately driven by processor 13. The processor selectively powers piezoelectric film elements 102 on an individual basis to create a directional sound field. By doing so, the processor can create the illusion of a moving sound source and of a stationary sound source when the user&#39;s head or body moves. The sound source would be stationary, i.e., the same sound would continue to come from the same elements when the user stops moving. The sound elements can be small chips or elongated bands, each driven by a separate signal from the processor. 
     FIG. 2 shows a system in which the user, using control 21, manually changes the presented image or manually creates a change in direction or speed with respect to the created environment. Band 22 contains elements 102 and can be adjusted via tightening mechanism 20, which can also be a volume control for the elements. 
     FIG. 3 schematically depicts processor 13, screen 101, speaker elements 11, joystick 21, position-orientation sensor 12 and direction control module 306. Processor 13 takes graphic information stored in a data base and generates images that are displayed on screen 101. Processor 13 also generates sound projected from piezoelectric film segments 102. Processor 13 could be a single processor or multiple processors such as a graphics processor from the TMS340 series and a digital signal processor from the TMS320 series, all available from Texas Instruments Incorporated. The &#39;340 generates images shown on screen 101 and the &#39;320 generates sound on element band 11. Connected to processor 13 is a position-orientation sensor 12. Position-orientation sensor 12 senses the direction that the user is looking. A flux gate compass (not shown) may also be linked to processor 13 to provide absolute north-south orientation information. Direction control block 306 provides processor 13 with information indicating the user&#39;s location and view within the three dimensional environment. Direction control block 306 receives user orientation information from position sensor 12 through processor 13 and from the user directly through joystick 21. Direction control block 306 can determine the user&#39;s position within the three dimensional environment by mathematically integrating the instantaneous orientation information from position-orientation sensor 12. 
     FIGS. 4a, b and c depict an element in an embodiment of a position and orientation sensor 12. Container 40 is fluid filled and has light source 43 (or other source of electronic signals such as infrared or microwave) on one side and CCD 44 (&#34;charge coupled device&#34;) or other electronic signal detectors on the other. CCD 44 is able to sense where light 401 impinges on it from source 43 and when light is blocked by fluid 42. FIGS. 4b and 4c depict different orientations of assembly 40 and hence depict different levels of fluid in device 40. 
     In FIG. 4b as assembly 40 is tilted down, a larger area of CCD 44 is blocked by fluid 42, allowing less light 401 to strike CCD 44. The amount of light impacting CCD 44 can be detected, for example, by using an array of individual CCD (or other detectors) devices, and monitoring, perhaps on a digital basis, the light level. When horizontal, no light gets through to CCD 44. In FIG. 4c fluid completely covers CCD 44. 
     In FIG. 5 a number of CCD assemblies 40 can be combined to indicate the tilt in different axes. Three assemblies, 40a, 40b and 40c are aligned along mutually orthogonal axes and encapsulated in direction sensor 12 to detect motion in three dimensions. The orientation information from assemblies 40a, 40b and 40c is transmitted through cable 301 to processor 13. The CCD assemblies can also provide information on the motion and position of sensor 12 by examining the output of CCD device over time. 
     It is possible to use only two devices to obtain all three orientations by taking into account the slope of liquid within each device 40. 
     Although this description describes the invention with reference to the above specified embodiments, it is but one example, and the claims, not this description, limit the scope of the invention. Various modifications of the disclosed embodiment, as well as alternative embodiments of the invention, will become apparent to persons skilled in the art upon reference to the above description. Therefore, the appended claims will cover such modifications that fall within the true scope of the invention.