Abstract:
The Orientation and Position Sensor is a compact, non-contact sensor that measures up to three orientations and up to three positions of an alignment target with respect to a camera. The alignment target has two distinct features, and a lens images those features into a camera. From the camera image, an operator or software can interpret the relative position and size of the features to determine the orientation and position of the alignment target with respect to the camera.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is related to application Ser. No. 09/777,962, filed Feb. 02, 2001 titled Orientation and Position Sensor 
     
    
     
       BACKGROUND  
         [0002]    1. Field of Invention  
           [0003]    This invention relates to multi-dimensional orientation and position sensors. This sensor detects up to three-dimensional position, i.e. the distance of an object relative to three orthogonal axes of a reference frame. Also, it measures orientation of that object about each of the three axes of that reference frame.  
         BACKGROUND  
         [0004]    2. Description of Prior Art  
           [0005]    Many types of sensors measure position or orientation on an object relative to a sensor. However, most measure only one position or one orientation of the possible six: three-dimensions of position and three-dimensions of orientations. A few sensors measure two or three dimensions, but cost and complexity increase greatly with an increase in the number measured. A typical three-dimensional position sensor commonly used for measuring accuracy of construction can cost as much as one quarter of a million dollars and provide no information on orientation. Of course, six or more one-dimensional position sensors can be located around an object such that an object&#39;s position and orientation can be determined. However, this also is a costly and complex approach with another disadvantage of a workspace that is large and highly susceptible to misalignment.  
           [0006]    There are some sensors that measure all three orientations and all three positions, such as the “Polhemus”. While it is a relatively compact sensor, it has a distinct disadvantage of requiring a metallic target and falters when any additional metal is in the workspace. Since there are usually many metal objects in the workplace, this sensor has very limited application. The most common type of tracking systems use multiple cameras such as the “ReActor”, observing an object from many different angles. While such a system can track all the orientations and positions of an object, it is computationally intensive and only applicable when a large space is available to mount cameras at different fields of view. Furthermore, multiple sensors are very vulnerable to misalignment, since motion of any of the sensors due to temperature, structural creep, or accidental disturbance will un-calibrate the system.  
         SUMMARY  
         [0007]    In accordance with the present invention, all orientations and positions are detected with a single sensor, simply and at low cost. The object is tagged with a small, inexpensive alignment target. Unlike the “Polhemus” sensor, this invention works in a metallic surrounding, and unlike “ReActor” it has only one camera.  
         OBJECTS AND ADVANTAGES  
         [0008]    Accordingly, several objects and advantages of my invention are:  
           [0009]    Reliably measures all three positions and three orientations with one sensor.  
           [0010]    Very small size, allows use in space-restricted places other sensors cannot.  
           [0011]    As an optical sensor, it does not contact or interfere with object it is sensing.  
           [0012]    High-speed operation of many detections/second, enabling it to track objects.  
           [0013]    Simple and low-cost, consisting of a camera, optics, target, and monitor.  
           [0014]    Capable of sub-millimeter position and sub-milliradian orientation accuracy.  
           [0015]    Further objects and advantages of my invention will become apparent from a consideration of the drawings and ensuing description. 
       
    
    
     DRAWING FIGURES  
       [0016]    Reference is now made to the embodiment of Orientation and Position Sensor illustrated in FIG. 1- 6  wherein like numerals are used to designate like parts throughout.  
         [0017]    [0017]FIG. 1 is an isometric view of first embodiment of sensor.  
         [0018]    [0018]FIG. 2 is a camera image of alignment target in reference position and orientation.  
         [0019]    [0019]FIG. 3 is a camera image of alignment target deviating from reference image.  
         [0020]    [0020]FIG. 4 is an isometric view of second embodiment of sensor.  
         [0021]    [0021]FIG. 5 is an isometric view of third embodiment of sensor.  
         [0022]    [0022]FIG. 6 is an isometric view of forth embodiment of sensor.  
     
    
     REFERENCE NUMERALS IN DRAWING  
       [0023]    [0023] 10  first embodiment  
         [0024]    [0024] 11  alignment target  
         [0025]    [0025] 12  camera  
         [0026]    [0026] 13  lens  
         [0027]    [0027] 14  optical axis of lens  
         [0028]    [0028] 15  camera cable  
         [0029]    [0029] 16  monitor  
         [0030]    [0030] 21  spot  
         [0031]    [0031] 22  base  
         [0032]    [0032] 23  transparent support  
         [0033]    [0033] 24  cross-hair  
         [0034]    [0034] 24   a - c  cross-hair strands  
         [0035]    [0035] 25  XYZ reference frame  
         [0036]    [0036] 30  camera image  
         [0037]    [0037] 31  center of camera image  
         [0038]    [0038] 40  second embodiment  
         [0039]    [0039] 41  posts  
         [0040]    [0040] 50  third embodiment  
         [0041]    [0041] 60  forth embodiment  
         [0042]    [0042] 61  computer  
       DESCRIPTION  
     First Embodiment  
       [0043]    [0043]FIG. 1 shows the first embodiment of Orientation and Position Sensor  10  including alignment target  11 , camera  12 , lens  13  with optical axis  14 , cable  15 , and monitor  16 . In a preferred arrangement, alignment target  11  includes a spot (first-feature)  21 , base  22 , transparent support  23 , and a cross-hair (second-feature)  24 . Spot  21  is circular, opaque, and mounted onto transparent support  23 . Transparent support  23  is mounted on base  22 . Base  22  is opaque and cross-hair  24  is drawn, attached, scribed or by other means highlighted on base  22 . Cross-hair  24  may consist of several strands, e.g.  24   a - c,  that in the preferred embodiment are placed in a non-symmetric arrangement to avoid orientation ambiguity.  
         [0044]    Also shown in FIG. 1 is a reference frame  25  with three orthogonal axes (XYZ) to describe translation (TX, Ty, Tz) and orientation (Rx, Ry, Rz) errors.  
         [0045]    [0045]FIG. 2 shows camera image  30  of alignment target  11 .  
       Operation  
       [0046]    Alignment target  11  is placed in the field of view of camera  12  such that camera image  30  contains first and second features  21 , 24 . The relative size and location of those features will be compared to the image  30  of a target  11  perfectly aligned to camera  12 .  
         [0047]    [0047]FIG. 2 shows camera image  30  when alignment target  11  is perfectly aligned with camera  12 . This image is referred to hereafter as reference image  30 , and the location of features  21 , 24  are described as right/left or up/down relative to image center  31  in the horizontal and vertical direction, respectively.  
         [0048]    In reference image  30 , features  21 , 24  are symmetric about camera center  31 , and strand  24   a  is parallel with horizontal of image  30 , and spot  21  is at the preset diameter as described below.  
         [0049]    In the preferred reference image  30 , cross-hair  24  is in focus, but spot  21  is not in focus. Out of focus, spot  21  is blurred, and the diameter of the blur varies linearly and sensitively to the distance between alignment target  11  and camera  12 , i.e. translation along the Z axis. Therefore, establishing a preset diameter of spot  21  defines a distance between alignment target  11  and camera  12  as the Z-axis reference position.  
         [0050]    [0050]FIG. 3 shows camera image  30  when alignment target  11  is not perfectly aligned with camera  12 , including an image  30  for each alignment error in translation (Tx, Ty, Tz) and an image  30  for each error in orientation (Rx, Ry, Rz). As shown, image  30  for each error is unique from the other images  30 , enabling an operator to easily distinguish one error from another or combinations of many errors.  
         [0051]    [0051]FIG. 3A shows camera image  30  when alignment target  11  has a positive X axes translation error (+Tx offset) with respect to image center  31 . Spot  21  and strands  24   b,c  are located right of camera center  31  while the location of strand  26   a  remains symmetric about camera center  31 , parallel to camera horizontal, and spot  21  is at the preset diameter.  
         [0052]    [0052]FIG. 3B shows camera image  30  when alignment target  11  has a positive Y axes translation error (+Ty offset) with respect to image center  31 . Spot  21  and strands  26   a  are located up from camera center  31  while the location of strand  24   b,c  remains symmetric about camera center  31 , and strand  26   a  remains parallel to camera horizontal, and spot  21  is at the preset diameter.  
         [0053]    [0053]FIG. 3C shows camera image  30  when alignment target  11  has a positive Z axes translation error (+Tz offset) with respect to image center  31 . The diameter of Spot  21  is larger. Strands  26   a - c  remain symmetric about camera center  31 , and strand  26   a  remains parallel to camera horizontal.  
         [0054]    [0054]FIG. 3D shows camera image  30  when alignment target  11  has a positive Z axes orientation error (+Rz offset) with respect to image center  31 . Strand  26   a  rotates from camera horizontal while spot  21  and strands  26   a - c  remain symmetric about camera center  31 , and spot  21  is at the preset diameter.  
         [0055]    [0055]FIG. 3E shows camera image  30  when alignment target  11  has a positive X axes orientation error (+Rx offset) with respect to image center  31 . Strand  26   a  is located up from camera center  31  while the location of spot  21  and strands  24   b,c  remain symmetric about camera center  31 , and strand  26   a  remains parallel to camera horizontal, and spot  21  is at the preset diameter.  
         [0056]    [0056]FIG. 3F shows camera image  30  when alignment target  11  has a positive Y axes orientation error (+Ry offset) with respect to image center  31 . Strand  24   c - d  are located right of camera center  31  while the locations of spot  21  and strands  26   a  remain symmetric about camera center  31 , and strand  26   a  remains parallel to camera horizontal and spot  21  is at the preset diameter.  
       Second Embodiment  
       [0057]    [0057]FIG. 4 shows the second embodiment  40  of Orientation and Position Sensor that includes all components of first embodiment  10  except alignment target  11  is modified such that spot  21  is mounted on base  22  and cross-hair  24  is mounted on posts  41 .  
       Third Embodiment  
       [0058]    [0058]FIG. 5 shows the third embodiment  50  of Orientation and Position Sensor that includes all components of first embodiment  10  except alignment target  11  is modified such that spot  21  is replaced with sphere  51  and many cross-hairs  24  form a spherical frame about sphere  51 . Transparent support  23  holds sphere  51  in the center of cross-hairs  24 .  
       Forth Embodiment  
       [0059]    [0059]FIG. 6 shows the forth embodiment  60  of Orientation and Position Sensor that includes all components of first embodiment  10  except monitor  16  is replaced with computer  61 . Software in computer  61  process images from camera  12  and interprets the position and orientation of alignment target  11  to camera  12 .  
       Advantages  
       [0060]    The Orientation and Position Sensor is a substantial advance in the state of the art of multi-dimensional measurement sensors. Because of the small size of cameras, this sensor is extremely small. Because of the large number of pixels in most cameras, the resolution is high. Its simple design and low cost make it practical for many applications. The sensor is ideally suited for providing feedback for medical and industrial robots with many degrees of freedom, even up to the maximum of six. The number of other applications is large because it is so adaptable, compact, inexpensive, and easy to use.  
       Conclusions, Ramifications, and Scope  
       [0061]    This invention is capable of measuring variations in all positions and all orientations. The sensor is compact, accurate yet simple and inexpensive. This sensor will be of major benefit to automated machines such as robots functioning in all positions and orientations. Presently there are no robot sensors that provide feedback for more than three axis of operation, leaving three and often more axes without feedback. This lack of feedback is a major source of error and inefficiency. The Orientation and Position Sensor will be a practical and effective solution to this problem.