Abstract:
A head worn display system (e.g., helmet mounted (HMD) display system, and an eye wear mounted display system,) can include a combiner, a head position sensor and a computer. The computer provides symbology in response to first sensor input values associated with the head position. The symbology can be conformal with a real world scene. A monitoring system includes a redundant head position sensor for providing second sensor input values associated with head position. The computer monitors for positional accuracy of the symbology by comparing symbology calculated using the first and second input sensor values or by using an inverse function to compare sensor values.

Description:
BACKGROUND OF THE INVENTION 
     The present specification relates generally to the field of displays. More specifically, the specification relates to integrity monitoring for head worn displays. 
     A head worn display (HWD) can be positioned in front of a user&#39;s eyes to provide operational capabilities similar to a fixed installation head up display (“HUD”). Head worn displays (e.g., helmet mounted displays, eyewear mounted displays, etc.) can provide information that is viewable in virtual space for the operation of equipment, such as aircraft, ships, boats, naval crafts, medical equipment, robotic equipment, remote vehicles, unmanned vehicle systems (“UVS”), training simulators, entertainment systems, military equipment, land vehicles, etc. The information can include navigation parameters, guidance parameters, equipment parameters, location information, video information, remote views, symbology, etc. 
     Head worn displays can be used to overlay display symbology (e.g., one or more symbols) onto scenes viewable out of a window or other port. The symbols are intended to represent or enhance features in the view of the user and are projected to a combiner. For the symbology to remain conformal with the view through the combiner on a head worn display, the head worn display generally tracks the head position. A head tracker sensor assembly is generally integrated with the head worn display and includes sensors that provide head position measurements for aligning the conformal symbology presented on the combiner with the view of the pilot based on the orientation of the user&#39;s head. Generally, head tracker sensor assembly can measure the following values: x (lateral) position, y (vertical) position, z (horizontal) position, roll (left/right tilt) angle, pitch (up/down tilt) angle and yaw (rotation) angle. 
     In aircraft applications, head worn displays generally include a computer (e.g., a HUD computer) that utilizes the values from the head tracker sensor assembly to determine the pilot&#39;s head position relative to an aircraft frame of reference (e.g., the bore sight) and the orientation of the aircraft relative to the ground provided by an attitude and heading reference system (“AHRS”) or inertial reference system (INS). Head position (e.g., x, y, z, roll, pitch, and yaw) measurement values are combined with associated parameters measured for the aircraft by the AHRS/IRS and transformed into earth (ground) frame. After this transformation to the ground frame, HWD symbology can be positioned on a combiner to overlay specific features of a real world scene as viewed through the combiner. For example, runway symbols can be displayed on the combiner that overlay the actual runway that the aircraft is approaching. 
     Assurance that information presented on a combiner correctly overlays the corresponding real world features is desirable prior to displaying that information to the user. For example, display functions can be monitored and redundant aircraft sensors can be utilized in fixed installation HUDs to ensure that symbols are properly positioned on the combiner. U.S. Pat. No. 4,698,785, incorporated herein by reference in its entirety, discloses a digital-based control data processing system for detecting during system operation the occurrence of data processing errors for HUDs. U.S. Pat. No. 7,212,175, incorporated herein by reference, also discloses a display presentation monitor for HUDs. An inverse algorithm can convert symbol position back to values of input parameters of aircraft orientation sensors which were used to position the symbol. The inverse values are compared to the actual input values associated with aircraft orientation sensors to determine if there is an unacceptable discrepancy. However, head tracking functions are currently not monitored for integrity in head worn display systems. 
     Thus, there is a need to determine head tracking errors in head worn displays. Further, there is a need to maintain a required level of integrity for aircraft applications in an head worn displays. Further still, there is a need for integrity monitoring of head worn displays that utilizes redundant head monitoring sensors. Further still, there is a need for a low cost integrity monitor and method for head worn displays. Yet further still, there is a need to determine symbology errors caused by head tracking sensors. 
     SUMMARY OF THE INVENTION 
     An exemplary embodiment relates to a monitoring system for use in a head worn display system. The head worn display system includes a combiner and a first head position sensor for providing first sensor input values. The head worn display system also includes a computer. The computer causes the combiner to provide symbology in response to the first sensor values associated with head position. The symbology is conformal with a real world scene. The monitoring system includes a redundant head position sensor for providing second sensor input values associated with the head position. The computer monitors positional accuracy of the symbology by comparing symbology calculated using first independent hardware components responding to the first input sensor values with symbology calculated using second independent hardware components responding to the second input sensor values. 
     Another exemplary embodiment relates to a method of monitoring integrity of symbology provided on a combiner. The symbology is conformal with a scene viewable through the combiner and is provided in response to first sensor input values. The symbology is conformal with the scene. The first sensor input values are associated with head position. The method includes calculating second sensor input values associated with the head position from data associated with the symbology using an inverse algorithm. The method also includes comparing the first sensor input values with the second sensor input values to determine if an integrity error exists. 
     Another exemplary embodiment relates to an error detection method for use in a head worn display system. The head worn display system provides symbology on a combiner in response to first sensor input values according to a first processing operation. The first sensor input values are associated with head position. The symbology is conformal with a scene viewable through the combiner. The method includes receiving second sensor input values associated with the head position. The second sensor values are from a source different than the first sensor input values. The method also includes receiving a symbol position associated with the symbology provided on the combiner, processing the symbol position in accordance with a second processing operation representing an inverse function of the first processing operation to provide calculated sensor values, and comparing the calculated sensor values to the first sensor values or to the second sensor values to determine a presence of an error. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The exemplary embodiments will become more fully understood from the following detailed description, appended claims and the accompany drawings, which are briefly described below and wherein like numerals denote like elements: 
         FIG. 1  is a schematic general block diagram of a head worn display system in accordance with an exemplary embodiment; 
         FIG. 2  is a schematic general block diagram of a head worn display system in accordance with another exemplary embodiment; 
         FIG. 3  is a schematic general block diagram of a head worn display system in accordance with yet another exemplary embodiment; 
         FIG. 4  is a schematic illustration of a head worn display in an aircraft in accordance with an exemplary embodiment; and 
         FIG. 5  is a schematic illustration of a view through the combiner illustrated in  FIG. 4  in accordance with an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before describing in detail the particular improved system and method, it should be observed that the invention includes, but is not limited to, a novel structural combination of components and not in the particular detailed configurations thereof. Accordingly, the structure, software, optics, methods, functions, control and arrangement of components have been illustrated in the drawings by readily understandable block representations and schematic drawings in order not to obscure the disclosure with structural details which will be readily available to those of ordinary skill in the art having the benefit of the description herein. Further, the invention is not limited to the particular embodiments depicted in the exemplary diagrams, but should be construed in accordance with the language of the claims. 
     With reference to  FIGS. 1, 4 and 5 , a head worn display system  100  provides conformal display symbology  90  associated with an environment  11 . System  100  can be embodied as a helmet mounted display (“HMD”) system, eyewear mounted display system or other worn display device. System  100  can be utilized in various applications including but not limited to aviation, medical, naval, targeting, ground-based vehicle, military, remote control, etc. In one embodiment, environment  11  can be a cockpit of an aircraft  91 , bridge, operating room, etc. and include a window  92  or a port to an external environment. In an aircraft application, environment  11  can be an aircraft cockpit and the real world can be viewable through the windshield of a cockpit. The aircraft  91  has a boresight  94  and an operator has an operator line of sight  96 . 
     Head worn display system  100  includes a display  102  including a combiner  104  for providing conformal symbology to a user. System  100  also includes a display generation processor or computer  108 , a set of vehicle state sensors  110 , and a set of head tracking sensors  112 . System  100  also includes a display monitor processor or computer  118 , a set of vehicle state sensors  120  and a set of head tracking sensors  122 . Sensors  120  and  122  can be redundant sensors to sensors  110  and  112 . 
     In one embodiment, head tracking sensors  120  and  122  can determine x, y and z positions  506   a - c  as well as pitch, tilt and rotation angles  506   d - f  associated with head position of a pilot. Vehicle state sensors  110  and  120  can provide sensor values associated with the vehicle attitude  526   a  and heading  526   b  in one embodiment. Computer  108  receives sensor values from sensors  110  and sensor values from sensors  112  and determines the operator&#39;s sight vector  96  relative to the aircraft bore sight  94 . Display monitor computer  118  receives sensor values from sensors  120  and sensor values from sensors  122  and determines the operator&#39;s sight vector  96  relative to the aircraft bore sight  94 . Computers  108  and  118  can utilize the same processing routine on independent hardware components in one embodiment. Although computers  108  and  118  are shown as separate computers in  FIG. 1 , computers  108  and  118  can be a single computer or be considered a single computer with separate processing elements. 
     Alternatively, a separate processing routine different than the processing routine used by computer  108  is used in computer  118 . With such a system, an error in one of the algorithms utilized to process sensor signals from sensors  110 ,  120  or sensors  120  and  122  will not result in a common fault that may go unmonitored according to one embodiment. In one embodiment, computers  108  and  118  is a single computer with separate processors for each processing path. In another embodiment, computer  108  can be a processing path in a HUD computer, and computer  118  can be a processing path in a head tracking computer or head tracking electronics. 
     Computer  108  utilizes an aircraft/ground coded transformation matrix, such as, an Euler matrix, to provide display content (e.g., symbology) to display  102  according to one embodiment. The display content preferably includes symbology provided at locations for conformal representation on combiner  104 . The display content can include enhanced vision images, synthetic vision images, text, pictograms, or other data useful when operating an aircraft according to various embodiments. 
     System  100  includes a comparator  130  which can be part of computers  108  and  118  or can be a separate computing or processing device. Comparator  130  receives the symbol position calculated by computer  118  and the symbol position provided to display  102  according to one embodiment. The symbol positions are compared to determine if they are within a tolerance according to one embodiment. If the symbol positions are not within a tolerance, comparator  130  can disable display  102  in one embodiment. Alternatively, a warning can be provided on display  102  if the symbol positions are not within a tolerance. The tolerance can be a fixed tolerance, a percentage, etc. 
     Comparator  130  can be a routine operating on one or both of computers  108  and  118 . Alternatively, an independent computer/processor can operate a compare routine as comparator  130 . In one embodiment, comparator  130  is a hardware or ASIC device. 
     Sensors  110  and  122  can be the same type sensors or can be sensors of different technology. According to one embodiment, sensors  112  can rely on inertial or other type sensing for head position while sensor  122  can utilize optical or other type of sensing. The types of sensors  112  and  122  are not disclosed in limiting any fashion. Sensors  112  and  122  can be inertial sensors manufactured by Intersense in one embodiment, magnetic sensors, or optical sensors in certain embodiments. In one embodiment, sensors  112  are part an optical system with sensors disposed on helmets for tracking markers in the cockpit, and sensors  122  are part of an optical system with sensors disposed in the cockpit for tracking markers on the helmet. Sensors  110  and  120  can be part of an attitude and heading reference system or an inertia navigation system in one embodiment. Alternatively, sensors  110  and  120  can include discrete yaw, pitch, and roll sensors. 
     Sensors  110  and  112  are used for display generation (e.g., symbology generation), and sensors  120  and  122  are used to monitor for errors in one embodiment. Computers  108  and  118  have independent hardware components to ensure the errors associated with hardware will be detected. In one embodiment, computers  108  and  118  include one or more processors and memories and can include the hardware associated with a HUD computer. 
     With reference to  FIG. 2 , a computing system such as a head worn display system  200  includes vehicle state sensors  210 , head tracker sensors  212 , vehicle state sensors  220 , head tracker sensors  222 , display generator processor or computer  208 , display monitor processor or computer  218 , display  202  and combiner  204  disposed in an environment  211 . System  200  also includes a comparator  230 . Sensors  210  and  212 , computer  208  and display  202  operate similarly to sensors  110  and  112 , computer  108  and display  102  discussed with reference to  FIG. 1 . 
     Computer  218  receives symbol positions associated with symbology provided on combiner  204  via computer  208  and uses a dissimilar processing operation to provide calculated sensor values to comparator  230 . Comparator  230  also receives sensor values from sensors  222  and  230  and disables display  202  when the sensor values are out of a tolerance. Accordingly, system  200  compares calculated sensor values generated from symbols determined from sensor values from sensors  210  and  212  with sensor values from different sensors (e.g., sensors  220  and  222 ) in one embodiment. The algorithm can be an inverse algorithm for transforming the symbol position to sensor values. An inverse Euler matrix can be utilized in one embodiment. The use of the inverse algorithm allows errors associated with the software executed by computer  108  to be detected because identical software is not used in each of computer  108  and  118 . 
     If the sensor values of sensors  210  and  212  and sensors  220  and  22  are not within a tolerance, comparator  230  can disable display  202  in one embodiment. Alternatively, a warning can be provided on display  202  if the sensor values are not within a tolerance. The tolerance can be a fixed tolerance, a percentage, etc. 
     Comparator  230  can be a routine operating on one or both of computers  208  and  218 . Alternatively, an independent computer/processor can operate a compare routine as comparator  230 . In one embodiment, comparator  230  is a hardware or ASIC device. 
     With reference to  FIG. 3 , a processing system such as head worn display system  300  includes a display generation processor or computer  308 , a display  302 , a combiner  304 , vehicle state sensors  310  and head tracking sensors  312 . Sensors  310 ,  312 , computer  308 , display  302  and combiner  304  can be similar to sensors  110  and  112 , computer  108 , display  102  and combiner  104  discussed with reference to  FIG. 1 . 
     System  300  also includes a display monitor processor or computer  318 , vehicle state sensors  320 , head tracking sensors  322 , and a comparator  330 . Computer  318 , sensors  320  and  322 , and comparator  330  can be similar to computer  218 , sensors  220  and  222 , and comparator  330  with reference to  FIG. 2 . In addition, system  300  can include a computer  418  coupled to sensors  320  and  322  and a comparator  430  according to one embodiment. Computer  418  and comparator  430  can provide a function similar to computer  118  and comparator  130  discussed above with reference to  FIG. 1 . 
     In one embodiment, system  300  can provide additional integrity by utilizing both an inverse algorithm monitoring approach and a symbol position comparison approach for symbol position monitoring. Symbol positions are compared via comparator  430 , which receives a symbol position calculated from sensor values from sensor  320  and  322  using computer  308  and a symbol position calculated from sensor values  310  and  312  using computer  418  in one embodiment. Sensor values calculated by an inverse algorithm using computer  318  are compared to sensor values  320  and  322  in comparator  330  to determine if an error exists. The use of both types of monitoring systems provides additional integrity. If errors are not within a tolerance as determined by comparators  330  and  430 , comparators  330  and  430  can disable display  302  in one embodiment. Alternatively, a warning can be provided on display  302  if the errors are not within a tolerance. The tolerance can be a fixed tolerance, a percentage, etc. 
     In one embodiment, sensors  322  can utilize different tracking technology from that used by sensor  112 . Such a system can guard against head tracking technology sensitivities due to certain vehicle constraints such as flight deck configurations, electromagnetic interference, etc. Comparator  330  can advantageously compare the sensor values calculated by computer  318  to one or both of sensor values from sensors  322  and  320  or  310  and  312  in one embodiment. 
     While detailed drawings, specific examples of particular configurations given describe preferred and exemplary embodiments, they are for the purpose of illustration only. The invention disclosed is not limited to the specific form shown. For example, the methods may be formed in any variety of sequential steps or according to any variety of mathematical formulas. Hardware and software configurations shown and described may differ depending on chosen performance characteristics and physical characteristics of the communication devices. Software can be stored on a non-transitory medium for operation on hardware associated with computers such as HUD computers. The systems and methods depicted and described are not limited to the precise details and conditions disclosed. Specific data types and operations are shown in a non-limiting fashion. Furthermore, other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of exemplary embodiments without departing from the scope of the invention is expressed in the independent claims.