METHOD AND APPARATUS FOR DETERMINING POSITION AND ROTATIONAL ORIENTATION OF AN OBJECT

• US 20110121068A1
• Filed: 12/06/2010
• Published: 05/26/2011
• Est. Priority Date: 12/14/2004
• Status: Active Grant

• Current Assignee: Shenzhen Invention Discovery Company Limited
• Original Assignee: Sky-Trax Incorporated (TotalTrax, Inc.)
• Inventors: UNGERBUEHLER, Richard H., MAHAN, Larry G., EMANUEL, David C.
• Granted Patent: US 8,196,835 B2
• Time in Patent Office: Days
• US Class Current: 235/375
• CPC Class Codes: B66F 9/0755 Position control; Position detectors
• CPC Class Codes: B66F 9/24 Electrical devices or systems
• CPC Class Codes: G01S 5/16 using electromagnetic waves other than radio waves
• CPC Class Codes: G05D 1/0234 using optical markers or beacons optical beacons per se G01S1/70

Abstract

A method and apparatus for determining position and rotational orientation of an object within a predetermined area is disclosed. Position markers, encoded with their identity, are viewed with a camera, images are captured and processed, and the position and rotational orientation of the object are calculated. Three embodiments are disclosed; the first having a camera mounted on the movable object while position markers bearing linear bar codes are fixed in location, the second having a camera mounted on the movable object while position markers bearing two-dimensional bar codes are fixed in location, and the third having a position marker of either type affixed to the object while the camera is fixed in location.

Claims

1. A method of determining a coordinate position and rotational orientation of an object within a predefined coordinate space, the method comprising:

providing a plurality of unique position markers having identifying indicia and positional reference indicia thereupon, the markers being arranged at predetermined known X, Y, and Z coordinate positional locations within the coordinate space so that at least one position marker is within view of the object;

maintaining a look-up-table comprising actual X, Y, and Z coordinates and rotational orientation of all position markers within the coordinate space;

using an image acquisition system comprising a camera mounted on the object, acquiring an image of the at least one position marker within view;

processing the image to determine the identity, the coordinate position relative to the object, and the rotational orientation relative to the object of each position marker within view;

determining and selecting the position marker nearest to the center of the image;

determining an approximate position of the object by retrieving the actual X, Y, and Z coordinates and rotational orientation of the selected position marker from said look-up-table; and

using the selected position marker, calculating the coordinate position of the object and the rotational orientation of the object in the coordinate space and storing the position and the rotational orientation information in a memory.

2. The method of claim 1, wherein the step of calculating the position of the object and the rotational orientation of the object in the coordinate space further comprises:

identifying two key points in the position marker;

defining a line between the two key points;

calculating the length of the line;

determining the center of the line to define the center of the position marker;

determining a vector from the center of the image to the center of the position marker;

determining a length and angle of this vector relative to the field of view by plane geometry; and

calculating an actual position of the object by correcting the approximate position of the object by using the length and angle of the vector to calculate a position offset,

wherein the Z coordinate position of the object is determined from the length of the line between the two key points and the Z coordinate of the position marker, by calculating the proportional distance between the camera and the position marker by scaling the line length into units of actual space.

3. The method of claim 2, wherein the position markers are arranged substantially in a plane defined by the Z coordinate of the coordinate space.

4. The method of claim 2, wherein the position markers are arranged at different Z coordinate positions.

5. An apparatus useful for determining a coordinate position and rotational orientation of an object within a predefined coordinate space, the apparatus comprising:

a plurality of unique position markers arranged in at predetermined positional locations within the coordinate space such that at least one position marker is within view of the object, wherein each position marker comprises a substantially planar material imprinted with an asymmetric pattern which encodes the identity and angular orientation of the position marker;

an image acquisition system mounted on the object, for acquiring an image of at least one position marker within view;

an image processing system for processing pixels in the acquired image to determine the identity of each position marker within view, the position of each position marker relative to the object, the rotational orientation of each position marker relative to the object; and

a post processing system for calculating the position of the object and the rotational orientation of the object in the coordinate space.

6. The apparatus of claim 5, wherein the image acquisition system comprises a machine vision system, the machine vision system comprising a camera, a light source, and image capture electronics wherein the light source of the machine vision system is located adjacent to the camera.

7. The apparatus of claim 6, wherein the light source is pulsed.

8. The apparatus of claim 6, wherein the light source is continuous.

9. The apparatus of claim 6, wherein the light source emits a narrow wavelength band of illumination.

10. The apparatus of claim 6 wherein the light source comprises one or more light emitting diodes (LEDs).