Wireless position and orientation detecting system

Details Wireless position and orientation detecting system Wireless position and orientation detecting system

1999-11-16

2002-05-14

Font, Frank G. (Department: 2877)

Optics: measuring and testing

Position or displacement

Reexamination Certificate

active

06388755

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to remote control and remote target tracking, in particular to wireless direct pointing input devices in human-computer interfaces, or an optical device that directly determines the position and orientation of an object in six dimensions through wireless data acquisition.
2. The Prior Art
An optical direct pointing device is an optical system that has a moveable object called a direct pointer, held by an operator in front of a computer screen. At any instant t, the system provides crossing point coordinate data CXP(x
cxp
(t),y
cxp
(t),z
cxp
=0) in the computer display screen coordinate system (x,y,z). The crossing point CXP is the location on the screen surface intersected by the axis of the direct pointer. To provide the data for the crossing point CXP, the system must conduct measurements to determine a set of six independent geometric parameters of the pointer, including three displacement parameters, T(x
T
,y
T
,z
T
), and three rotation parameters, (&agr;, &bgr;, &ggr;). In accordance with the crossing point coordinate data, the computer displays an indicator, known as a cursor, on the screen at coordinate position CXP(x(t),y(t),z=0) so that at any instant t, the user knows where the direct pointer is pointing.
There are several challenges to providing such a six-dimensional direct pointing system so that the position and orientation of the pointer is viewable in real time. First, the data acquisition and processing must be fast. If the minimum time interval between consecutive data points is less than, for example, approximately 1 millisecond, the user would feel satisfactory control over the pointer. On the other hand, as the interval increases beyond, for example, approximately 20 milliseconds, the user would feel an increasingly large drag and discontinuity that eventually becomes unacceptable.
Computation of the crossing point CXP from the measured raw data must be performed in real time. Six-dimensional computation is essentially different from three-dimensional and other simpler cases in that it involves solving a group of nonlinear simultaneous equations, while simpler cases with fewer dimensions merely use straightforward triangle formulas. Thus, for fewer than five dimensions, there is always a solution that can be obtained relatively easily.
On the other hand, with six dimensions, three linear and three angular dimensions, quite often a great many fictitious solutions are produced, which then must be sorted through to find the correct solution. This would not be a critically important problem if there were no time constraints. But since there is a limit to the amount of time that can be taken to find a solution, a new method for finding the correct solution is needed. None of the relevant prior art systems for position and orientation measurement can provide such a capability. For example, U.S. Pat. No. 4,225,226, issued to Davidson et al., discloses the use of a light source, a number of retroreflectors, and a photodetection system to measure the position of an airplane over a crop field. The system is essentially limited to two dimensions because the airplane is assumed to be maintained in a plane parallel to that of the retroreflectors and the ground. Thus, the techniques disclosed are not applicable to six-dimensional measurements.
Second, the moveable object must be compact, light in weight, and draw little electrical power. It must be no larger than hand-held, and preferably smaller. Many six-dimensional measurement systems of the prior art developed for robot systems and target-tracking systems in industry and weaponry are not applicable to the present case largely because they are not sized to be hand held.
U.S. Pat. No. 5,059,789, issued to Salcudean, discloses the use of three mutually perpendicular light sources mounted on an object to illuminate a large resistive two-dimensional position-sensitive detector sheet to determine the position and orientation of the object in six dimensions. The technique requires a large resistive two-dimensional position-sensitive detector sheet with a dimensions comparable to the distance between the object and the detector, making it rely on an essentially different principle than that of the present invention.
U.S. Pat. No. 4,649,504, issued to Krouglicof et al., discloses the use of three light sources mounted at different fixed locations on a moveable object and a pair of 2D photodetectors to provide position and orientation of the object. The technique looks having some superficial similarity to the techniques of the present invention. However, the techniques need a reasonable amount of separation between the light sources or between the detectors to obtain meaningful data. So if the light sources are too close together on the moveable object, the detection system cannot distinguish between them with enough accuracy to be useful. Thus, the moveable object must be relatively large in order to have enough separation between the three light sources, meaning that the moveable object would be too large to be used as a light-weight handheld device.
Reversing the components, that is, fixing the location of the three light sources and mounting the photodetectors on the moveable object, does not solve the problem because the photodetectors would still need to be a reasonable distance apart.
SUMMARY OF THE INVENTION
The primary objective of the present invention is to provide an optical system for wirelessly determining the position and orientation of an object in six dimensions relative to another object.
The present invention offers an apparatus and method for wirelessly determining position and orientation of an object in six dimensions and at the same time substantially eliminates the problems and disadvantages associated with the relevant devices of the prior art.
A preferred embodiment of the present invention includes a movable orientation-coded optical transponder and two recording assemblies. Each recording assembly comprises a light source, a photodetector assembly, and optionally, a beam splitter. In the preferred embodiment, the light source, photodetector assembly, and beam splitter are installed rigidly together. The transponder is attached to the object whose position and orientation is desired.
In operation, each light source emits source light into the space that the transponder will potentially traverse. The source light is received, optionally modulated, retransmitted back to the photodetector. The light source is preferably a light emitting diode (LED) or semiconductor laser that emits light at an infrared wavelength.
An orientation-coded optical transponder is described in U.S. patent application Ser. No. 09/181,761, entitled INTEGRATED OPTICAL RETROREFLECTING MODULATOR, incorporated herein by reference. The orientation-coded optical transponder modulates the retransmitted light depending upon the direction of the incident light. In other preferred embodiments, identification-coded (ID-coded) transponders can be used or a combination of ID-coded transponders and an orientation-coded transponder can be used. Specific system configurations are described below.
Preferably the photodetector assembly includes a lens assembly and a photodetector. In one embodiment, the lens assembly includes a two-dimensional lens that focuses the retransmitted light onto a focal plane coincident with a two-dimensional photodetector to provide an image from the transponder. In another embodiment, the lens assembly includes two cylindrical lens that focus the retransmitted light onto two perpendicular focal lines coincident with two linear photodetectors to provide an image from the transponder. Both embodiments provide a two-dimensional Cartesian location for the image relative to a reference point on the photodetector assembly. A third embodiment of the photodetector uses a single cylindrical lens and a single linear photodetector. This embodiment is used to determine only a single coordinate of an image.
The transponders and r

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