Optics: measuring and testing – By polarized light examination – With light attenuation
Reexamination Certificate
1999-09-20
2001-07-24
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By polarized light examination
With light attenuation
C701S028000, C250S559140
Reexamination Certificate
active
06266142
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates in general to the field of position and orientation measurement and, more particularly, to a noncontact position and orientation measurement system and method.
BACKGROUND OF THE INVENTION
Positioning of mechanical systems, robots, aircraft, and spacecraft may be accomplished by a variety of means, including mechanical or optical encoders, video cameras, radar, ultrasonic, and laser ranging systems. To measure the position and orientation of a rigid object, or a sensor attached to the rigid object, a direction to four or more optical targets fixed to a reference object must generally be measured. Sensors such as charge coupled devices, video camera or position sensing detectors may be used to detect the optical targets.
Position sensing detectors are analog devices that centroid incoming light energy sources to determine the direction and position of the optical targets. One example of a position measurement system utilizing position sensing detectors includes placing three or more reflective targets on a target object whose position and orientation is to be measured. Light beams are directed toward the optical targets and produce reflected beams. Each reflected beam is received by a position sensing detector, such as a lateral-effect photodiode. The signals generated by the position sensing detectors are used to determine measurements of translation along and rotation about three non-parallel axes which define the space in which the target object moves.
Prior position measurement systems and methods suffer several disadvantages. For example, the applications of the position measurement systems are generally restricted due to the necessity that retro-reflectors be positioned on an object which is essentially non-reflective. Additionally, any other objects in the measurement system environment must also be essentially non-reflecting.
Additionally, charge coupled devices and video cameras generally require post-processing of a relatively large quantity of digitized image data, in the form of digitized pixel response, to recognize and numerically centroid the optical target images. This process is generally computationally expensive and difficult in the presence of geometrical and environmental variations.
SUMMARY OF THE INVENTION
Accordingly, a need has arisen for an improved technique having greater flexibility and applications for position measurement than prior systems. In accordance with the present invention, a noncontact position and orientation measurement system and method is provided that substantially eliminates or reduces disadvantages and problems associated with previously developed systems and methods.
According to one embodiment of the present invention, a noncontact position and orientation measurement system includes at least four beacons disposed on a first object. Each beacon is operable to generate an optical signal. The system also includes a beacon controller operable to sequentially activate and deactivate each of the beacons. The system also includes an electro-optical sensor disposed on a second object. The electro-optical sensor is operable to generate an output signal for each optical signal received from the beacons. The system further includes a signal controller coupled to the electro-optical sensor. The signal controller is operable to determine a position and an orientation of the second object relative to the first object using the output signals generated by the electro-optical sensor.
According to another embodiment of the present invention, a method for noncontact position and orientation measurement includes sequentially activating and deactivating each of at least four beacons disposed on a first object. Each beacon is operable to generate an optical signal. The method also includes receiving the optical signals generated by each of the beacons at an electro-optical sensor disposed on a second object. The method also includes generating an output signal corresponding to each optical signal received from each beacon using the electro-optical sensor. The method further includes determining a position and an orientation of the second object relative to the first object using the output signals generated by the electro-optical sensor.
The technical advantages of the present invention include a system for noncontact position and orientation measurement that provides increased flexibility of applications. For example, according to one aspect of the present invention, a single electro-optical sensor is used to measure the position of four beacons disposed on an object to determine the position and orientation of the object relative to the electro-optical sensor. The beacons are sequentially activated and deactivated such that an output signal is generated by the electro-optical sensor for each optical signal received from a beacon. Thus, restrictions associated with retro-reflector location and attachment and other reflective objects in the measurement system environment are substantially eliminated.
Another technical advantage of the present invention includes a system for noncontact position and orientation measurement that provides increased efficiency. For example, position sensing detectors are analog devices and generally require less post-processing of image data. Additionally, according to one aspect of the present invention, a single beacon is activated at any given time, thereby resulting in less energy consumption and supply requirements.
Another technical advantage of the present invention includes a system for noncontact position measurement and orientation that automatically compensates for distance and environmental variations. For example, according to one aspect of the present invention, the amplitude and frequency of the optical signals generated by the beacons may be automatically modulated to compensate for distance and environmental variations based on prior optical signals received from the beacons.
Other technical advantages of the present invention will be readily apparent to one skilled in the art from the following figures, descriptions, and claims.
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Hughes Delcan
Junkins John L.
Schaub Hanspeter
Baker & Botts L.L.P.
Font Frank G.
Nguyen Sang H.
The Texas A&M University System
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