Patent Publication Number: US-2015077547-A1

Title: Attitude measurement between optical devices

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims rights under 35 U.S.C. 119(e) from U.S. Application No. 61/909,855 filed Nov. 27, 2013, entitled ATTITUDE MEASUREMENT ATTITUDE SUBSYSTEM (AMCS) HUB and also this application claims rights under 35 U.S.C. 120 from U.S. application Ser. No. 13/904,046 filed May 29, 2013, entitled “OPTICAL AUTOMATIC ATTITUDE MEASUREMENT FOR LIGHTWEIGHT PORTABLE OPTICAL SYSTEMS”, and the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to optical devices and more particularly to an attitude measurement between the optical devices. 
     2. Brief Description of Related Art 
     In a typical optical system (e.g., a lightweight laser designator rangefinder), multiple optical devices need to be aligned to reduce error in target computations. Existing approach may use large and heavy mechanical interfaces (couplings) between the optical devices to hold the optical devices tightly and to ensure good alignment from tolerance perspective. However, such large and heavy mechanical interfaces may be sensitive and result in misalignment and unexpected errors when the interfaces get fouled, dirty, and/or banged. 
     SUMMARY OF THE INVENTION 
     A system for measuring an attitude between optical devices is disclosed. According to an aspect of the present subject matter, the system includes a plurality of optical devices and a hub. Further, the hub includes a plurality of attitude measurement and control subsystems (AMCSs) that are aligned with a predetermined angle during factory calibration. Each AMCS is connected to one of the optical devices and each AMCS measures an attitude between an AMCS and a corresponding optical device connected to the AMCS. Furthermore, the hub includes an attitude measurement unit to measure the attitude between the optical devices based on the measured attitude between each AMCS and a corresponding connected optical device and the predetermined angle between the AMCSs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages and features of the present disclosure will become better understood with reference to the following detailed description and claims taken in conjunction with the accompanying drawings, wherein like elements are identified with like symbols, and in which: 
         FIG. 1  is a block diagram of a system for measuring an attitude between optical devices, according to an example embodiment of the present subject matter. 
         FIG. 2  is a block diagram of a system for measuring an attitude between an attitude measurement and control subsystem (AMCS) and an optical device connected to the AMCS, according to an example embodiment of the present subject matter. 
         FIG. 3  is a schematic illustrating a captured image including two dots associated with a reference beam and an attitude beam, according to an example embodiment of the present subject matter. 
         FIG. 4  is a schematic illustrating effects of yaw movement between the AMCS and the optical device, such as those shown in  FIG. 2 , on the captured image including the two dots, according to an example embodiment of the present subject matter. 
         FIG. 5  is a schematic illustrating effects of pitch movement between the AMCS and the optical device, such as those shown in  FIG. 2 , on the captured image including the two dots, according to an example embodiment of the present subject matter. 
         FIG. 6  is a schematic illustrating effects of roll movement between the AMCS and the optical device, such as those shown in  FIG. 2 , on the captured image including the two dots, according to an example embodiment of the present subject matter. 
         FIG. 7  is a schematic illustrating effects of roll movement between a light source and a camera, such as those shown in  FIG. 2 , on the captured image including the two dots, according to an example embodiment of the present subject matter. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The exemplary embodiments described herein in detail for illustrative purposes are subject to many variations in structure and design. The present technique proposes a hub approach that allows connecting multiple optical devices to a hub that includes multiple attitude measurement and control subsystems (AMCSs) aligned with a predetermined angle during factory calibration. Further, each AMCS establishes communication and measures an attitude between an AMCS and a corresponding optical device connected to the AMCS. For example, the attitude is an offset angle, such as a pitch angle, a yaw angle and/or a roll angle. Furthermore, an attitude measurement unit in the hub measures an attitude between the optical devices by summing the offset angle between each AMCS and the corresponding connected optical device and the predetermined angle between the AMCSs. The optical devices can then be aligned based on the measured attitude. 
       FIG. 1  is a block diagram of a system  100  for measuring an attitude between optical devices  104 A-N, according to an example embodiment of the present subject matter. As shown in  FIG. 1 , the system  100  includes a hub  102  and the optical devices  104 A-N connected to the hub  102 . Example optical devices include designators, sights, inertial measurement units (IMUs), vehicle optics and the like. Further, the hub  102  includes AMCSs  106 A-N aligned with a predetermined angle during factory calibration and an attitude measurement unit  108  connected to the AMCSs  106 A-N. For example, the predetermined angle between the AMCSs  106 A-N include a predetermined angle between the AMCSs  106 A and  106 B, the AMCSs  106 A and  106 N and the AMCSs  106 B and  106 N. In the example illustrated in  FIG. 1 , the AMCSs  106 A-N are connected to the optical devices  104 A-N, respectively. In this example, the AMCS  106 A is connected to the optical device  104 A, the AMCS  106 B is connected to the optical device  104 B and the AMCS  106 N is connected to the optical device  104 N. 
     In operation, the AMCS  106 A measures an attitude between the AMCS  106 A and the optical device  104 A, the AMCS  106 B measures an attitude between the AMCS  106 B and the optical device  104 B and the AMCS  106 N measures an attitude between the AMCS  106 N and the optical device  104 N. This is explained in more detailed with reference to  FIG. 2 . For example, the attitude is an offset angle, such as a pitch angle, a yaw angle and/or a roll angle. 
     Further, the attitude measurement unit  108  measures the attitude between the optical devices  104 A-N based on the offset angle between the AMCS  106 A and the optical device  104 A, the offset angle between the AMCS  106 B and the optical device  104 B, the offset angle between the AMCS  106 N and the optical device  104 N and the predetermined angle between the AMCSs  106 A-N. For example, the attitude measurement unit  108  can be a processor programmed to co-ordinate information from the AMCSs  106 A-N and measure the attitude between the optical devices  104 A-N. In one embodiment, the attitude measurement unit  108  measures the attitude between the optical devices  104 A-N by summing the offset angle between the AMCS  106 A and the optical device  104 A, the offset angle between the AMCS  106 B and the optical device  104 B, the offset angle between the AMCS  106 N and the optical device  104 N and the predetermined angle between the AMCSs  106 A-N. In another embodiment, the attitude measurement unit  108  measures the attitude between the optical devices  104 A-N by summing an offset angle of each of the AMCS  106 A-N to a standard normal mirror in the factory calibration, an offset angle between the mirror normal to components within each of the optical devices  104 A-N in the factory calibration, the measured offset angle between the AMCS  106 A and the optical device  104 A, the measured offset angle between the AMCS  106 B and the optical device  104 B, and the measured offset angle between the AMCS  106 N and the optical device  104 N. 
       FIG. 2  is a block diagram of a system  200  for measuring an attitude between an AMCS  202  (e.g., any of the AMCSs  106 A-N shown in  FIG. 1 ) and an optical device  204  connected to the AMCS  202  (e.g., a corresponding optical device  104 A-N connected to one of the AMCSs  106 A-N as shown in  FIG. 1 ), according to an example embodiment of the present subject matter. As shown in  FIG. 2 , the AMCS  202  includes a power source  206 , a light emitting diode (LED) control  208 , a light source  210 , a first collimating optic device  212 , a beam splitter cube  214 , a second collimating optic device  216 , a camera  218  and an image processing unit  220  coupled to the camera  218 . Further as shown in  FIG. 2 , the optical device  204  includes a sight mirror  226 . 
     In operation, the light source  210  generates a beam. Exemplary light source  210  is a LED and the like. In the example illustrated in  FIG. 2 , the power source  206  provides needed power to the light source  210  to generate the beam. In this example, the light source  210  is controlled by the LED control  208 . The beam is then passed through the first collimating optic device  212  that collimates the generated beam and directs the collimated beam towards the beam splitter cube  214 . The beam splitter cube  214  then receives the collimated beam from the first collimating optic device  212  and splits the collimated beam into a reference beam  222  and an attitude beam  224 . In an example, the beam splitter cube  214  is configured so that the reference beam  222  goes through the beam splitter cube  214  and reflects back as shown in  FIG. 2 . The beam splitter cube  214  is also configured to reflect the attitude beam  224  and direct the reflected attitude beam  224  towards the sight minor  226  in the optical device  204 . Upon receiving the attitude beam  224  from the beam splitter cube  214 , the sight mirror  226  reflects the attitude beam  224  back to the beam splitter cube  214  as shown in  FIG. 2 . The beam splitter cube  214  then receives attitude beam  224 , from the sight minor  226 , and directs the attitude beam  224  along with the reflected reference beam  222  towards the camera  218 . In some embodiments, the beam splitter cube  214  directs the attitude beam  224  along with the reference beam  222  towards the camera  218  via the second collimating optic device  216  that further collimates the attitude beam  224  and the reference beam  222 . The camera  218  then receives the reference beam  222  and the attitude beam  224  from the beam splitter cube  214  or second collimating optic device  216 . The received reference beam  222  and attitude beam  224  illuminate the camera  218  and generate associated two dots  310  and  320  on a captured image as shown in  FIG. 3 . 
     In addition, the image processing unit  220  measures the attitude between the AMCS  202  and the optical device  204  by computing a differential measurement between the reference beam  222  and the attitude beam  224  in x and y planes using the associated two dots  310  and  320 , formed on the captured image by the camera  218 . In an example implementation, the image processing unit  220  determines a center of each of the two dots  310  and  320  and computes a pixel distance between the centers of the two dots  310  and  320  in the x and y planes. In this example implementation, the reference beam  222  and the attitude beam  224  are configured to produce the two dots  310  and  320 , on the captured image, having a predetermined size that is suitable for the image processing unit  220  to determine the centers of the two dots  310  and  320  to single pixel accuracy. The image processing unit  220  uses well known centroiding algorithms to determine the centers of the two dots  310  and  320 . The image processing unit  220  then measures the attitude between the AMCS  202  and the optical device  204  based on the computed pixel distance between the centers of the two dots  310  and  320  in the x and y planes. 
     In some embodiments, based on the orientation of the sight mirror  226 , the beam splitter cube  214  and the camera  218 , the attitude between the AMCS  202  and the optical device  204  is determined. For example, as shown in a schematic  400  of  FIG. 4 , if the sight mirror  226  is rotated about its vertical axis and the beam splitter cube  214  is rotated within the plane of a paper (yaw movement), then the attitude manifests itself into an x-movement about the center of the dot  320 . Similarly, as shown in a schematic  500  of  FIG. 5 , if the sight mirror  226  is rotated about its horizontal axis and the beam splitter cube  214  is rotated within the plane of the paper (pitch movement), then the attitude manifests itself into a y-movement about the center of the dot  320 , while the front surface continues to act as a mirror providing both pitch and yaw measurements. Further as shown in a schematic  600  of  FIG. 6 , if the sight mirror  226  is configured as a dove prism and is rotated about its central axis and the beam splitter cube  214  is rotated within the plane of the paper (roll movement), then the dove prism  226  rotation does not manifest itself in any attitude change between the AMCS  202  and the optical device  204 . Furthermore as shown in a schematic  700  of  FIG. 7 , any movement (roll movement) in the light source  210  and the camera  218  results in both the dots  310  and  320  moving together by a same amount resulting in no attitude manifestation. 
     The above proposed technique reduces weight and significantly improves tolerance to fouling in battlefield. Further, the above technique provides environmentally sensitive interfaces while maintaining high accuracy between optical devices in an optical system or a vehicle. Furthermore, the above technique is an active feedback system that dynamically provides the needed attitude measurement while the optical system is in operation. Moreover, the above technique significantly loosens up tolerance requirements to be maintained between the optical devices in the optical system. Also, the above technique is based on differential measurement and all components, which can move with environmental impacts that affect both the reference and attitude beams, thereby the final attitude measurement between the optical devices is differential in nature resulting in being impervious to the environmental conditions, such as temperature, shock, vibration and the like. 
     The foregoing descriptions of specific embodiments of the present disclosure have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present disclosure to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present disclosure and its practical application, to thereby enable others skilled in the art to best utilize the present disclosure and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the claims of the present disclosure.