Articulated light guide

An articulated light guide having internal mirrors and rotatable joints, vides a transmission path to a helmet mounted projector wherefrom light is transmitted onto a retroreflective screen to produce images utilized in simulation training. Located at the screen are photodiodes which detect the orientation of said images with respect to a reference and provide alignment signals to a servo-controlled image rotation device.

FIELD OF THE INVENTION 
The present invention relates to visual display apparatus and particularly 
to head coupled apparatus for providing a visual display to an observer 
such as seen from a moving perspective point. More particularly, the 
present device relates to apparatus for sensing the orientation of the 
images generated by such a visual display apparatus, when they are 
projected on a screen, and then orienting the images with respect to a 
known reference. 
DESCRIPTION OF THE PRIOR ART 
There have been devised a number of visual display apparatuses for use in 
training personnel such as pilots and aircrew members. A number of these 
incorporate axial rotation sensors to determine head position and thus 
image orientation. These are best suited for applications wherein the 
image plane is fixed with respect to the observer's head, such as in U.S. 
Pat. No. 3,205,303 to Bradley. Additionally, such sensors mounted on the 
observer's head can cause mechanical and electromechanical complications 
in operation and calibration. 
SUMMARY OF THE INVENTION 
The present invention represents an improvement in the field of visual 
display apparatus, in that it provides a means for sensing the orientation 
of the image directly on the image screen and then orienting the image in 
accordance with a predetermined reference, such as the horizon. The 
invention is to be used in conjunction with a computer image generating 
means which utilizes a plurality of scan lines to form the image at the 
image screen. The computer generated image is communicated to a helmet 
mounted projector which positions the image on an image screen. Imbedded 
in the screen is an array of photodiodes which sense the orientation of 
the scan lines and output electrical signals which are used to determine 
the degree of correction or compensation required to align the scan lines 
with the chosen reference. An image rotating means is utilized to 
accomplish the desired correction.

DESCRIPTION OF A PREFERRED EMBODIMENT 
FIG. 1 discloses the present invention in an embodiment wherein a computer 
image generator serves as light source 11 which generates an image 
utilizing a plurality of scan lines. An articulated light guide 12 is 
employed as a communicating means for conveying said image to a projector 
apparatus 13 mounted atop a helmet 15 to be worn by an observer 16. 
Projector apparatus 13 is a wide angle lens suitably selected to project 
said light data across the desired field of view onto a retroreflective 
screen 21. 
Articulated light guide 12 employs a plurality of link elements 25 through 
31, which are constructed of a light weight material such as plastic, each 
link element being connected to an adjacent element by a joint element 33. 
Each joint element 33 forms a fixed predetermined angle, the light data 
being deflected through this angle by an internal mirror 39. Optimally, 
mirror 39 will be set at a 45.degree. angle to the incident light data. 
Mirror 39 can be adjusted by three screws 42, 43, and 44. 
Referring to FIG. 2, there is shown a typical joint element 33 having 
coupled thereto link elements 28 and 29. Link element 28 is fixedly 
coupled to joint element 33, while link element 29 is rotatably coupled to 
joint element 33. A bearing element 41 is attached to link element 29 so 
as to allow the rotation of link element 29 within joint element 33. 
Transmission of light data through communicating means 12 distorts the data 
such that a visual image appearing on screen 21 will not be properly 
oriented. 
To compensate for this distortion problem, each scan line output by light 
source 11 is monitored by a sensor apparatus 50 utilizing a plurality of 
photodetectors 52 embedded in screen 21. Sensor apparatus 50 determines 
the orientation of each scan line relevant to the horizontal plane. A 
number of commercial systems are available which have this capability, one 
such apparatus being the UDT 131A non-contact optical displacement system, 
manufactured by United Detector Technology, Inc. 
The orientation information thus provided is utilized as an input to a 
servo control electronics circuit 54 which directs a servo motor 56 to 
rotate a dove prism 47 located at the output of light source 11. Prism 47 
is rotated to orient the scan lines provided by light source 11 in the 
horizontal direction at image surface 21. This novel combination provides 
a closed loop feedback system dependent on the actual orientation of the 
scan lines as output by the light guide, rather than on positional 
estimates as heretofore used. 
Operationally, lightweight articulated light guide 12 provides a minimally 
restrictive transmission path for light data from light source 11 through 
prism 47 to projector apparatus 13, which broadcasts the light data onto 
retroreflective screen 21 where sensor apparatus 50 determines the 
orientation of said data with respect to the horizon. This orientation 
information is used to rotate prism 47 to align the light data in the 
preferred direction. 
While a preferred embodiment has been shown and described, various 
modifications and substitutions may be made thereto without departing from 
the spirit and scope of the invention. Accordingly, it will be understood 
that the present invention has been described by way of illustration and 
not limitation.