Abstract:
A head tracking system combines a plurality of sources of radiant energy, a plurality of sensors and at least one reflective element. As the reflective element moves, various radiant energy beams become incident thereon. The incident beams are reflected to respective sensors thereby providing head position signals.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention pertains to head trackers. More particularly, the invention pertains to optical head trackers which are relatively inexpensive and have relatively minimal set-up time.  
       BACKGROUND OF THE INVENTION  
       [0002]     It has been known to use head trackers in simulators which are used in various types of equipment, such as flight simulators, vehicular simulators such as armored units or other types of land vehicles as well as water born vehicles. Many of the known types of head trackers provide multiple degrees of information, such as six degree of freedom in position and orientation information so that appropriate views or displays can be activated only as needed. Known multiple degree of head trackers have been based on various different technologies. These have included ultrasound, optical, inertial, or magnetic.  
         [0003]     While known head trackers are effective for their intended purpose, they are often expensive and require extensive set-up times. Additionally, known head trackers often require substantial software interaction to address the various signals coming therefrom. This can include dedicating resources to carry out extensive plotting.  
         [0004]     Certain types of simulations require information for only a single degree of freedom, for example, in the azimuthal direction. For example, armoured simulators, such as armored wheeled or tracked vehicles present to the vehicle commander a plurality of spaced-apart displays simulating cupola or tank turret periscopes which face different directions. In these instances, the vehicle commander would only need to rotate his or her head about a substantially fixed vertical axis to view displays presented at several different angles. Viewing directions could include, for example, straight ahead, 20 to 22 degrees to the right, 45 degrees to the right, and similar angles to the left.  
         [0005]     Thus, there continues to be a need for head trackers which provide more limited amounts of information, corresponding to fewer degrees of freedom, than heretofore known. Preferably, such head trackers could be implemented more cost effectively than multiple degree of freedom head trackers of known types. Additionally, it would be preferable if set-up times could be reduced so that the speed of training or conducting exercises can be increased. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a top plan view of an apparatus in accordance with the present invention;  
         [0007]      FIG. 2  is a side elevational view of the apparatus of  FIG. 1 ; and  
         [0008]      FIG. 3  is a block diagram of a system in accordance with the invention. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0009]     While embodiments of this invention can take many different forms, specific embodiments thereof are shown in the drawings and will be described herein in detail with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiment illustrated.  
         [0010]     This invention provides a simple, low-cost means for determining a single-plane angular orientation of an object, such as a person&#39;s helmet in a simulator. This is accomplished in a disclosed embodiment by the use of fixed infra-red (IR) light sources spaced circumferentially around the helmet, pointing at the helmet. Reflective material placed at one point on the helmet. A detector is located near each light source to detect the reflected infra-red beam.  
         [0011]     Some of the advantages of this embodiment of this invention are that they do not require complex equipment configurations. They are very low cost. Data processing does not require detailed plotting as many trackers do. They do not cause electromagnetic interference in displays and electronics as magnetic trackers sometimes do. Conventional head trackers cost several thousand dollars for the hardware. Embodiments of this invention can be implemented for no more than a few hundred dollars. Set-up time for conventional head trackers can be several man months. For embodiments of this invention it is a matter of a few man days.  
         [0012]     One embodiment of this invention uses several similar infra-red (IR) sources angularly displaced around the helmet position and directed toward the geometric center of the cupola, where the helmet is normally centered. The helmet has a retroreflective material, which could be a retro-reflective tape, attached to it so that each IR source illuminates the retro-reflector, in turn, as the head is rotated about a vertical axis.  
         [0013]     IR detectors, each placed close to a respective IR source, detect the retro-reflected light only from the respective IR source, and only when the retro-reflective material is within the IR beam. In this way the angular position of the helmet is determined, well enough to determine which of the several discrete displays is being viewed by an operator. In this way display generating capacity can be conserved by only providing imagery to those displays viewable by the operator or trainee.  
         [0014]      FIGS. 1 and 2  are a top plan view and a side elevational view, respectively, of an exemplary vehicular simulator, such as a simulator for an armored vehicle which might have a turret or a cupola. Periphery views in the turret or cupola are in part simulated by a plurality of displays or display units  14 - 1 , - 2 , - 3 , - 4 , - 5 . The displays  14 - 1  . . . - 5  are dispersed around an axis of rotation A.  
         [0015]     The axis of rotation A corresponds to an axis of rotation about which a human operator H with a nose N rotates his/her head from a straight ahead rotation to the right or left, depending on the requirements of the training exercise or the simulation. A display generator, best seen in  FIG. 3 , energizes some, but not necessarily all, of the displays  14 - 1  . . . - n  depending on the position of the nose N of the operator H.  
         [0016]     A head positioning system in accordance with the invention is in part indicated generally at  20  and can be incorporated into the simulator  10  as described subsequently. The system  20  incorporates a plurality of sources  22 - 1 ,  22 - 2  . . .  22 - 5  of beams of radiant energy, of a selected frequency, such as infra-red or visible red. The sources, such as  22 - 1  transmit a respective beam of radiant energy  24 - 1  . . .  24 - 5  toward the axis A. The operator or trainee H might be wearing a helmet which carries a reflective material indicated generally at  30  thereon. The material  30  is selected such that it will reflect radiant energy at the frequency of the respective source or sources  22 - 1  . . . - n.    
         [0017]     A respective sensor,  26 - 1  . . . - 5  is associated with each of the sources  22 - i.  Each of the sensors  26 - i  is responsive to incoming or sensed radiant energy, such as radiant energy  24 - 3 R which has been reflected off of surface  30  and as result, is incident on sensor  26 - 3 .  
         [0018]     As the trainee or operator H rotates his/her head about the axis A, the reflective surface  30  is arcuately moved about the axis A and can reflect a different beam of incident radiant energy, for example, beam  24 - 1  which would then be reflected back to sensor  26 - 1  in the event that the nose N of the trainee or operator has been rotated so as to be directed toward the display  14 - 5 . The source/sensor combinations  22 - 1 ,  26 - 1  provide signals to a related control system, which could include a programmable processor, best seen in  FIG. 3 , indicative of an azimuthal parameter indicated in phantom on  FIG. 1  by angle A 1 .  
         [0019]     It will be understood that neither the exact number or type of sources of radiant energy or sensors are limitations of the present invention. The number to be used would be determined by the type of simulator as would be understood by those of skill in the art. Similarly, the frequency of the transmitted beams of radiant energy is not a limitation of the present invention.  
         [0020]     The exact configuration of a source/sensor combination is not a limitation of the present invention. Sources and respective sensors can be carried in a common housing. Alternately, separate housings can be used. The configuration of source and sensor can be coaxial if desired. Other combinations and orientations are possible and all come within the spirit and scope of the present invention.  
         [0021]      FIG. 3  illustrates system  34  in accordance with the invention. The plurality of sources  22 - 1  . . . - n  is driven from control circuitry, which could include a programmed processor,  36 . The control circuitry  36  provides overall control functionality to carry out the desired simulation or training exercise.  
         [0022]     Sensors  26 - 1  . . . - n  are coupled to control circuitry  36 . The sources  22 - 1  generate respective beams of radiant energy  24 - 1 . As indicated above, the beams of radiant energy can be of various frequencies, infra-red or visible. Alternately, it should be understood that the sources  22 - 1  . . . - n  need not emit the same frequencies. The sources  22 - 1  . . . - n  could in fact emit different respective frequencies, as would be understood by those of skill in the art.  
         [0023]     The sensors  26 - 1  . . . - n  respond to received incident energy of the appropriate frequency, such as respective incident energy  24 - i R. In accordance with the embodiment of  FIGS. 1 and 2 , only one of the sensors will receive reflected signal depending on the position of reflective element  30 . It will be understood that other embodiments of the invention are possible. These include a plurality of reflective elements spaced around the helmet of the trainee or operator H. The plurality of reflective elements would generate a plurality of reflected beams, similar to  24 - i R, but a multiplicity thereof, directed toward respective sensors such as sensors  26 - 1 , - 2 , . . . - n.  In such instances, the control computer  36  will received a plurality of signals from the sensors  26 - 1  . . . - n  indicative of position of the head of the operator H. All such variations come within the spirit and scope of the present invention.  
         [0024]     Control circuitry  36  also provides feedback azimuthal signals to image generator  38 . Generator  38  in turn drives respective members of the plurality displays  14 - 1  . . .  14 - n  with signals to present an appropriate image on those display units which are individual fields of vision of the trainee or operator H. For example, if the operator or trainee H is looking straight ahead, as in  FIG. 1 , displays  14 - 2 , - 3  and - 4  could be activated with the appropriate display as those would be within the expected field of vision of the operator or trainee H. Displays  14 - 1 , - 5  could be displaying an image if desired but the image would not necessarily be the current imagery as seen in displays  14 - 2 , - 3  and - 4 . With other orientations of the nose N of the trainee or operator H, other combinations of display units could be energized with the current appropriate display segment  
         [0025]     From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.