Position tracking system

Details Position tracking system Position tracking system

2000-02-14

2001-07-24

Hellner, Mark (Department: 3662)

Optics: measuring and testing

Angle measuring or angular axial alignment

Relative attitude indication along 3 axes with photodetection

C356S152300

Reexamination Certificate

active

06266136

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates generally to optical emitters and detectors, and optical position tracking devices, in particular, optical devices having distinct radiation and detection properties that may be used to track position of objects, using a relatively small number of optical elements.
Position tracking is a growing technology with ever increasing applications. For example, in the entertainment arena, position tracking in three dimensions is used in virtual reality simulation. Position tracking is also used in the industrial arena, with applications in process control and robotics. The field of biomedics also uses position tracking devices for tracking portions of a human body to determine the body's motion patterns. Similarly in animation dynamics, the tracking of multiple body parts is used for controlling animated figures. Many other applications exist, for which position tracking is useful if not advantageous.
Conventional position tracking can be broken down into two broad technologies, i.e., active systems and passive systems. Active systems utilize active electronic elements on the objects being tracked. For example, the Polhemus' 3SPACE ISOTRACK II® system uses active magnetic elements to create a dynamic magnetic field that is representative of the body's position. By sensing changes in the magnetic field, the system delivers all six axes of the object's spatial location.
Active systems are generally high-performance, high-end products. However, they can have disadvantages, including limited range of motion, metal interference, complex operation and high cost. In particular, the range of the magnetic field is typically limited, and trailing connection wires are often a nuisance. Where the area of motion contains substantial metal, mapping of the entire field is usually part of the system's required initialization.
In contrast, passive systems track objects without physical links between the object and the system. Target points such as retro reflectors may be used, or image processing of a video image may be performed. While passive systems are often less complex and less expensive compared to active systems, they are often lacking in resolution. Thus, for object recognition, passive systems typically require extensive image processing, which can increase costs and the probability of errors. The use of reflectors avoids some of these problems, but not without introducing other problems, such as the need for critical alignment and extensive initialization.
Aside from the various system limitations discussed above, the sensing components of an optical detector, such as photodiodes or charge-coupled device (CCD), have their own limitations. While these components can be made directionally-sensitive (e.g., with the provision of a slit, or the use of Gray-coded multi-element arrays), the response is often limited. For example, they typically provide directional information or resolution about one axis only, and the sensor's accuracy is typically limited by the number of optical elements provided.
It should therefore be appreciated that there exists a definite need for a relatively simple and inexpensive position tracking system, which can track the position of an object along at least three axes, if not all six axes to include objection rotation, using minimal electrical and/or optical elements. It is desired that the system has low alignment and initialization requirements and low processing demands. In that regard, it is desired that the system be structurally and electronically simple, while remaining capable of providing at least directional indicative of the direction along which the object is positioned relative to the system. It is further desired that the system be able to provide locational data inclusive of range data, along with directional data, for tracking an object in three dimensional space. The present invention addresses all of these desires and more.
SUMMARY OF THE INVENTION
The present invention resides generally in an optical position tracking system that tracks the position of objects, using light intensity and/or frequency with the application of geometry and ratios of detector responses.
The present invention provides for the illumination of an area that may be defined by spherical or hemispherical coordinates with a tailored spatial intensity profile, and/or the detection of light associated with an object in the area, with the recognition that certain characteristics or properties of the light detected are indicative of the relative position or movement of the object in the area. Advantageously, the invention applies the concepts of constructed occlusion and diffuse reflection to accomplish its purpose with improved efficiency.
The positioning tracking system in one embodiment includes a retro reflector that is affixed to the object being tracked, and a head module that includes a light distributor and a light detector. Constructed occlusion as employed by the present invention includes the use of a mask that improves certain radiating characteristics of the distributor and certain response characteristics of the detector. For example, a mask in a predetermined position enables the distributor to provide a more uniform radiation profile, and the detector to provide a more uniform response profile, at least for elevations approaching the horizon. In general, changing the position and/or size of the mask changes the radiating and response profiles. The profiles may be further manipulated or enhanced with the use of a baffle, particular for the profile at angles at or near the horizon. The baffle can be conical or an intersecting structure. Where the electromagnetic radiation utilized by the present invention includes visible light, components including the mask and the baffle are formed of a Lambertian, polymeric material having a reflectance of approximately 99% for visible wavelengths.
In accordance with a feature of the present invention, the distribution profile of a constructively occluded distributor can be specifically tailored or made substantially uniform for over most, if not all, azimuths and elevations of a hemispheric area over the distributor. Correspondingly, the response profile of a constructively occluded detector can be specifically tailored or made substantially uniform for most, if not all, azimuths and elevations of a hemispheric area over the detector. In essence, constructed occlusion can render both the distributor and detector uniformly omnidirectional in the hemispheric area which the occluded device faces.
In order that the system track the position of a reflector (or point), or at least provide directional information for that reflector, the head module of the system includes a partitioned occluded device which may be either the distributor or the detector. In particular, the use of a partitioning baffle in a distributor renders a partitioned distributor having distinct emission sections where the sections can emit spectrally-different or distinguishable radiation. Correspondingly, the use of a partitioning baffle in the detector renders a partitioned detector having distinct detection sections where the sections can detect radiation from different directions.
The system may be variously configured, to use different combinations of partitioned and nonpartitioned devices, that is, a partitioned distributor with a nonpartitioned detector, or a nonpartitioned distributor with a partitioned detector. A partitioned distributor provides a plurality of radiation sections and a partitioned detector provides a plurality of detection sections. In most configurations, a single head module provides one set of directional data about two coordinates (e.g., &rgr; and &THgr;) for one reflector, using one of these combinations, wherein one of the devices is partitioned into four sections or quadrants.
An additional head module remotely positioned from the first head module can provide a second set of directional data for the reflector (e.g., &rgr;
2
and &THgr;
2
). By cr

Affiliated with

Also associated with

Rating

Position tracking system does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Position tracking system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Position tracking system will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2508361