Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2001-01-11
2003-05-13
Pyo, Kevin (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S227160, C385S013000
Reexamination Certificate
active
06563107
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to sensor technology. In particular, the invention relates to a tool or device for measuring the geometric location and configurations of objects in space. The invention is suited to robotic applications and to monitoring or measuring human geometry and motion. This invention represents modifications and improvements in the inventions described in U.S. Pat. No. 6,127,672, issued Oct. 3, 2000 to Lee Danisch, and PCT Appln. No. PCT/CA98/00213, published as WO98/41815, which are both incorporated by reference.
A preferred application, amongst others, is in the field of animation effected by motion capture of movements by the human body.
BACKGROUND TO THE INVENTION
Various technologies have been applied to measure the location, orientation and surface shapes of objects in space.
In the field of robotics it is known to determine the location of a flexible member formed by a series of rigid, linked elements in space by measuring the angular degree of rotation existing at the various joints joining such linked elements.
Rotations in a flexible member include bending that is transverse to the longitudinal extent of the member; and twisting that occurs about an axis which is coincident with the longitudinal extent of the member. Both types of movement or distortions qualify as “flexures”.
Twist is usually negligible in sensor structures based on cylinders, rods, and other solids with significant cross-sectional dimensions. However, it can be very advantageous to measure the presence of twist in elongate, flexible members that are rope-like in their flexibility. Such members would be very convenient for incorporation in garments.
Thus one object of the present invention is to provide an improved flexible member or reference platform equipped with distributed sensors wherein changes in the shape of the member are sensed by the sensors in such a way that the complete shape of the member can be found by calculations from the outputs of the sensors.
Another object of this invention is to provide an instrumented flexible member that is sufficiently compliant to substantially conform to the surface of a curved object and act as a sensor to provide electronically processable data as to the shape of that surface.
A variety of sensors exists for measuring the state of flexure—bend and twist—in an object; these include optical fibers and conductive metal fibers, i.e. wires. A convenient class of sensors particularly suited to this objective relies on fiber optics.
U.S. Pat. No. 5,321,257 to Lee Danisch, describes modified optical fibers that are provided with a light absorbent region on a portion of the outer fiber surface, especially on one selected side of the outer fiber surface, such region providing a bend sensor whereby the curvature at such modified region may be remotely detected by the change in the overall light transmission capacity of the fiber. This prior patent depicts, in
FIG. 12
, the deployment of clusters of modified fibers capable of detecting a bend at a particular location in three dimensional space. The associated fiber ends are all connectable at one end to a multi-fiber light source, light sensing and signal processing unit. These modified fibers, or so-called “bend enhanced fibers”, are referenced in the aforesaid '672 patent.
The aforesaid U.S. Pat. No. 5,531,257 also discloses three optic fiber sensors mounted in parallel, with the sensors being sensitive to bending in separate directions, and which are used for resolving bends in multiple DOFs in a flexing structure. However, this prior patent does not suggest any method of dealing with twist, which would cause ambiguity or be undetectable in the readings of the patented sensor method of this '257 patent. Accordingly, this patent does not deal with the problem of determining the complete position and orientation of a longitudinally extended structure based only on measurement of flexure.
Another problem with this simple structure is that when three straight fibers are bent, some will be extended and some compressed, due to difference in radius of curvature, which leads to significant errors in measurement.
A further paper on this subject by the inventor herein entitled “Laminated Beam Loops” has been published in SPIE Vol. 2839, pp. 311-322, 1996. The contents of this paper, the above referenced United States patents and the published PCT application PCT/CA94/00314 are all incorporated by reference herein.
Optical fiber sensors can measure bend and, in accordance with the invention described in the aforesaid '672 patent, twist, based on the disposition of the fiber and the location of the treated, light absorbing region of the fiber surface along the fiber. The sensitive region of the fiber can be contained within a running length of on the order of three millimeters to many centimeters for example 30 cm, depending on desired sensitivity and the dimensions of the fibers. This provides a corresponding span for the sampling of the average state of curvature of the sensing region of the optic fiber. Fiber optic technology is convenient for use in sensors because it is robust, benign and inexpensive. The aforesaid '672 patent describes various forms of measuring tools which incorporate bend and twist sensors, of which the preferred forms are fiber optic based sensor systems that can provide remote information on the locations of objects in space, the shape of surfaces and changes in the shape of surfaces. However, the '672 patent is not limited to fiber optic based sensors. Similarly, while the present invention will also be described principally in relation to fiber optics sensors, it is not limited to systems using such sensors.
The invention of the U.S. '672 patent, according to one aspect, is a shape and position measuring tool which comprises the following features:
1. a longitudinally extending, flexible substrate having a compliant reference surface and being capable of bending in at least two degrees of freedom so as to be configurable in three dimensional space;
2. a plurality of spaced bend sensor means and a plurality of spaced twist sensor means each of said plurality of sensor means being respectively coupled to and positioned at specific discrete locations, on and at known respective bend sensor and twist sensor spacing intervals along the longitudinal extent of the substrate, to provide flexure signals indicating the respective local state of bend and twist present in the substrate at the respective locations where the respective bend sensor means and twist sensor means are coupled to the substrate;
3. sensor data processing means coupled to the bend sensor means and the twist sensor means for receiving signals therefrom and for presenting data on the geometric configuration of the reference surface of the substrate in three-dimensional space,
wherein the sensor data processing means operates by determining the geometric configuration of the substrate from the bend and twist signals derived from the flexure signals provided by the bend sensor means and twist sensor means at their specific locations and from the spacing intervals between such sensor means.
As indicated, the shape measuring tool of the '672 patent included a flexible substrate which carried the bend and twist sensors at specific locations on the substrate. The substrates included ribbons (
FIGS. 5
,
6
and
8
), and ropes (FIG.
7
). Substrates of sheet form were also contemplated, including a planar array with substantial width as well as length, for example a “keyboard” type of device.
The present invention is based on similar principles, but with the omission or minimization of the presence of a substrate for the support and positioning of flexure sensors.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. Th
Danisch Jonathan Freeman
Danisch Lee Allen
Lutes Jordan Patrick
Canadian Space Agency
French David J.
Pyo Kevin
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