Note: Descriptions are shown in the official language in which they were submitted.
CA 02284085 2002-04-08
TITLE: TOPOLOGICAL AND MOTION MEASURING TOOL
FIELD OF THE INVENTION
This invention relates to sensor technology. In
particular, the invention relates to measuring the
geometric location and configurations of objects in
space. The invention is suited to robotic applications
and to extracting human geometry and motion.
A preferred application 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 series of rigid, linked
elements in space by measuring the angular degree of
rotation existing at the various joints joining such
linked elements, cf U.S. Patent No. 5,576,727 to
Rosenberg et al.
In the field of interfaces between humans and
mechanisms, goniometers based upon rotary potentiometers
or strain gauges are used to measure the angular
relationships between parts of the human body, cf, U.S.
Patent No. 5,163,228 to Edwards et al.
U.S. Patent 4,988,981 (Thomas Zimmerman et al)
reveals means for sensing body position using flex
sensors; including the use of flex sensors carried by a
1
CA 02284085 2002-04-08
d. ~1
glove. Such gloves have been. widely used and reported on.
Reported problems include ambiguity of response due to
finger motion occurring in multiple degrees of freedom,
and other inaccuracies due to fit of the glove to the
hand. Similar methods of providing flex sensing in a
glove are reported in U.S. Patent 5,097,252 (Y. L. Harvill
et al ) .
Slidable linkage flex sensors designed to sense
two degrees of freedom of finger joint motion have been
described in U.S. Patent No. 5,316,017 (Glenn Edwards et
al). The slidable linkage permits the sensor to
accommodate for the changing distance between attachment
points during flexure.
U.S. Patent 5,533,531 (Glenn Edwards et al)
addresses separating and identifying motions having
multiple degrees of freedom (DOFs) using a mufti DOF
contacting sensor: the DOFs are exercised separately in a
calibration routine, which provides a mathematical
relationship between the outputs of the sensors
responding to detected motions which can be used to
provide separate DOF signals. A similar method is
advanced in U.S. Patent 5,531,257 (Danisch), in which
three fiber optic sensors mounted in parallel with their
sensing surfaces splayed in separate directions are used
for resolving bends in multiple DOFs in a flexing
structure. However, neither reference suggests methods of
dealing with twist, which would cause ambiguity or be
undetectable in the readings of either of the patented
sensor methods. Nor does either patent deal with the
problem of determining the complete position and
2
CA 02284085 2002-04-08
b
orientation of a longitudinally extended structure based
only on measurement of flexure.
Rotations in a flexure include bending that is
transverse to the longitudinal extent of the substrate;
and twisting that occurs about an axis which is
coincident with the longitudinal extent of the substrate.
Both types of bending 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 flat, ribbon-like flexures. Such flexures are very
convenient for incorporation in garments.
Virtual Technologies Inc. of Palo Alto
California markets an instrumented fabric glove, which
incorporates bend sensors at the finger joints and other
sensors for measuring thumb cross-over, palm arch, wrist
flexion and wrist abduction. The position of the glove
and its sensors in space is also measurable by coupling
the glove wristband to a degrees-of-freedom space-
position tracking mechanism.
An instrumented glove marketed by General
Reality Company of San Jose California relies upon fiber
optic bend sensors to sense bending at various points on
the glove.
In the field of animation motion capture
procedures are used to record the positions and movements
of the human body. One method has involved visually
capturing the locations in space of "target" markers
carried on the lambs and bodies of human actors. Another
3
CA 02284085 2002-04-08
method has been to provide an "exoskeleton" mechanical
structure which acts as a mechanism in following, and
providing signals for recording, the motions and
positions assumed by the human body. Accuracy is then
limited by the ability of the exoskeleton to maintain a
stable mounting to the body. The penalty of such systems
is the constricting and cumbersome nature of mechanical
exoskeletons. Also, it is very difficult, if not
impossible, to build exoskeletons that permit full limb
movement or that can account for all limb rotations and
other subtle multiple degree of freedom limb movements.
Further, exoskeletons are generally removed a significant
distance from the measured surface, leading to their
inaccuracy and increased bulk.
Both of the target marker and exoskeleton
methods as presently conceived are complex and entail
inconveniences in their implementation. A need exists for
a light weight, unencumbering, position and motion
sensing device that can conveniently track and identify
the location and geometric configuration of objects in
space. The invention herein addresses such an objective.
More particularly an. object of the present
invention is to provide a flexural reference platform
equipped with distributed sensors wherein changes in the
shape of the platform are sensed by the sensors in such a
way that the complete shape of the platform 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
4
CA 02284085 2003-03-06
curved obj ect and act. a;~ a :sensor to provide
electronically proccsssable d<~ta a:; i~c~ the shape of that
surf ace .
Prior art patent and patent application
referE>_nces of relevance to the techniques or measurement
of the invention herein inc~Lude:
(1) GB-A-2, 23~, 11.2 for an instrumented glo,Je
(2) DE-C-42 40 53:L foxy a metkaocl of shaping a shell
(3) EP-A-344 322 for the measurement of deformation
in large objects.
A variety of technologies exist for measuring
the state of f lexurf=_ - bend and twist - in an obj ect . A
convenient class of technology pax:t:icularlv suited to
this objective relies on fiber opt:i.c-~:.
U. S. Patent 5, 321, 2~ 7 tc.~ t:)anisch describes a
modified optical fiber tYxat is proqaided with a light
absorbent region on a portion of the outer fiber surface
whereby the curvature at such modified region may be
remotely detected by the chance :in the overall light
transmission capacity of the fiber . 'this patent depicts
the deployment of c:Lusters of modi.f~.ed fibers capable of
detecting a bend in threE: dimensional space (reference is
made to figure 12 of US patent 5,32:1,257).
Patent Co-operation 'T:reaty application
PCT/CA94/00314 (published December 22, 1.994 as WO
94/2971) discloses the use of looper~ fiber optic light
wave guides to measure curvature . The fiber is looped to
provide outgoing and return wave paths that. pass through
a looped end that e:~fect~~~ a 180 degree bend. The surface
3 0 of the f fiber i s t:r eate>.d adj acent to and within the
curvature of the looped portion to render it. absorbent of
5
CA 02284085 2002-04-08
Y
light. In one configuration it is the side of the fiber
surface lying along the top plane of the looped end that
is treated. Once the looped end is so treated, it is
sensitive to its state of curvature when deflected out of
or through the normally flat plane of the loop. Such
flexure can be detected remotely by the change of
intensity in returning light carried by the fiber. This
provides a measure of localized curvature in the region
of the loop.
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.
Looped optical fiber sensors can measure bend
and, in accordance with the invention hereafter
described, twist based on the disposition of the loop and
the location of the treated; light absorbing region of
the fiber surface adjacent to or within the loop. The
sensitive region at the looped end of the fiber can be
contained within a running length of on the order of
three millimeters to a few centimetres depending on
desired sensitivity and the diameter of the fibers. This
provides a corresponding span for the sampling of the
average state of curvature of the sensing looped end of
the optic fiber.
Fiber optic technology is convenient for use in
sensors because it is robust, benign and inexpensive. A
need exists for a fiber-optic based sensor system that
can provide remote information on the locations of
objects in space, the shape of surfaces and changes in
CA 02284085 2002-04-08
T
the shape of surfaces. The present invention addresses
such a need.
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. The invention in
its broadest and more specific forms will then be further
described, and defined, in each of the individual claims
which conclude this Specification.
SUMMARY OF THE INVENTION
In one broad aspect, the invention is a shape
and configuration measuring tool which comprises:
(a) a flexible substrate capable of bending in at
least two degrees of freedom;
(b) spaced bend sensor means and twist sensor
means, coupled to and positioned at known respective
bend sensor and twist sensor spacing intervals along
the substrate to provide signals indicating the
local state of bend and twist present in the
substrate a the respective locations where the bend
sensor means and twist sensor means are attached to
the substrate; and
(c) sensor data processing means coupled to the
bend sensor means and twist sensor means for
receiving flexure signals therefrom and for
7
CA 02284085 2002-04-08
presenting data on the geometric configuration 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
provided by the bend sensor means and twist sensor
means and from the spacing intervals for such
sensors.
This invention works by sampling curvature at
multiple, spaced intervals along a supporting substrate
which is flexible, and preferably substantially
continuous, incompressible and inextensible. This
substrate acts as a carrier for the sensors. The
invention relies upon inter-referencing the position of
bend and twist sensor means located at known intervals
along the supporting substrate with the location of
adjacent sensors so that the location of all sensors with
respect to each other is known. The bend sensors and
twist sensors may be distinct. Or paired sensors may
produce signals that are a measure of both bend and
twist. In this latter case the paired sensors, as with
distinct sensors, may be said to comprise a bend sensor
moans and a twist sensor means.
The flexure conditions being measured to
determine the geometric configuratiorz of the substrate is
based on measuring both bending and the state of twist
present in the substrate.
Flexure may be measured by twist sensors and
bend sensors attached to and positioned at known twist
and bend sensor spacing intervals along the length of the
8
CA 02284085 2002-04-08
z- r
substrate. These provide signals indicating the local
state of twist and bending present in the substrate at
the locations where such sensors are attached to the
substrate.
Bend can be measured about either one or two
axes that are orthogonal to the longitudinal dimension of
the substrate, depending on the nature of the substrate.
Thus a rope-like substrate would require that bending be
sensed about two such axes, either directly or
indirectly.
By providing a substrate which is deformable
only in restricted degrees of freedom, the number of
sensors required can be reduced. As a preferred
configuration, bend and twist sensors may be bonded to a
substrate which is in the form of a ribbon. In such case
bend sensors are only required for measuring flexure of
the ribbon in its permitted bending mode. This reduces
the number of bend sensors needed per unit of length.
A ribbon is an article which is substantially
limited to bending along its length about axes which are
transverse to the longitudinal dimension of the ribbon
while the ribbon remains free to twist about such
longitudinal dimension. Thus a single bend sensor will
suffice to measure bend at a location along a ribbon. To
complete the definition of the geometric configuration of
a ribbon-like substrate, twist as well must be measured
by twist sensors located at known intervals along the
longitudinal extent of the length of the ribbon. Such
bend and twist sensors may be interspersed with each
other or co-located along the ribbon.
9
CA 02284085 2002-04-08
T
When the substrate is of a ribbon-like
configuration employing both bend and twist sensors
freedom of movement and tracking of the geometric
configuration of the ribbon in three dimensional space is
nevertheless available. This is because the ability of a
ribbon to twist allows portions of the ribbon to be re-
oriented in any direction in space.
As an alternate configuration, bend and twist
sensors may be coupled along a pliable core or substrate
that has two degrees of bending freedom, akin to a rope .
In such applications, two bend sensors may be provided
for each twist sensor to provide balanced sensing of bend
and twist.
This configuration for the invention can also
be equivalently implemented by applying, an instrumented
planar tape of the ribbon-type format to the outside, or
inside, of a cylindrical flexure such as a hose. When a
hose-like carrier is employed, sensor communications may
pass through the core.
The invention will perform with greater
precision if the flexure sensors are mounted along the
neutral axis of a carrier substrate. This can be achieved
in the case of a ribbon substrate by assembling two
substrate portions as a lamination with the sensors
contained between the layers. By using ribbon layers of
similar flexibility, the sensors will be positioned
essentially along the neutral axis.
Bend sensors based on optical fiber technology,
and particularly looped-end fibers, are suitable for
sampling curvatures at multiple locations, the associated
CA 02284085 2002-04-08
i
fiber ends all being connectable to a multi-fiber light
source, light sensing and signal processing unit. The
bend and twist sensors may be based an optical fibers
that have been rendered sensitive to their state of
curvature by having appropriate, local portions or
regions of their outer surfaces rendered absorbent to
light passing through such fibers.
In the case of a ribbon substrate, the sensors
may be based on optical fibers with curvature-sensitized
portions that are aligned parallel to the plane of the
ribbon at the locations where the treated portions are
attached to the substrate.
To measure bend the sensitized portions of a
treated fiber optic sensor may be generally aligned to
lie across the axis about which bending is to occur, e.g.
the axes extending transversely to the length of a ribbon
substrate.
When looped-ends are employed, the treated,
light-absorbing portions of the surfaces of each of the
loops maybe located either on one half of the loop only,
or, if optionally.on both halves of the loop; then on the
same face of the loop in order to measure bend. By
treating both sides, two treated portions of the fiber
will be modulating the light transmitted by the fiber
based on the same local condition of curvature that each
treated portion is experiencing. This will raise the
ratio of the "signal" to the background "carrier" of
light within the fiber guide.
To measure twist a looped sensor whose loop
straddles the central longitudinal median line of a
11
CA 02284085 2002-04-08
u.
ribbon substrate may be conveniently employed: The
surface of the optical fiber is treated on half portions,
on opposite faces of the loop, the treatment being
applied on opposite sides of the median line. The
portions of loops so treated and positioned respond
inversely to bending, but cumulatively to twisting and
therefore measure twist exclusively.
For looped-end sensors it is not essential that
the central, most curved, portion of the loop be treated
to render it non-transmissive of light. It is sufficient
for the treated portion to be proximate to the looped end
to benefit from the mode filtering effect of the looped
end.
For convenience of signal processing, when a
ribbon substrate is employed, both twist and bend at a
single location can be measured using ,two bend sensors
which may or may not be looped optical fibers. The
directions of the treated portions of the respective
sensors of the pair are preferably oriented at
substantially the same angle off of the longitudinal
median line of the ribbon substrate and preferably at 45
degrees to the longitudinal dimension of the substrate.
This permits two fibers to be used to measure both bend
and twist at a single location by processing their
outputs to extract their sum and difference signals as a
measure of bend and twist. The referenced angular
orientations simplify signal processing. With
computational adjustments other angles would still be
able to provide both twist and bend values from a splayed
pair of sensors. Since the sensors will normally be
12
CA 02284085 2002-04-08
} ,
operated in their linear ranges, the computations
normally involve sums and differences of linear equations
very amenable to high speed automatic computation.
Although this description concentrates on
inexten~ible ribbon-like flexures with longitudinally
distributed sensors, the invention includes structures
based on flexures that are not inextensible, not narrow
and not planar.
By assembling distributed sets of sensors,
flexure sensing regions may be formed not only linearly,
as along a supporting rope or ribbon-like substrate, but
also over an area using a flexible carrier sheet as the
substrate. For instance, a wide planar form can be a
lamination in the form of a flexible, planar ,carrier,
such as a rubber and fiber sheet, with sensor groups
distributed across its area. The groups can consist of
bend and twist sensors, or dual--direction bend sensors,
which are able to completely describe the shape of the
sheet. Using data on the state of curvature at each
sensing region, and knowing the separation between
sensors, the signal detection system can construct a
depiction of the shape of the carrier. With the carrier
sheet placed in contact with a geometric surface of
unknown form, the shape of such surface can be measured,
at least where the sheet and surface are in contact.
As another instance of non planar forms,
conventional measuring tapes (e. g. for measuring linear
distances in carpentry) are of quasiplanar shape, having
a continuous transverse bend when axially flat. This
gives them greater stiffness, and concentrates axial
13
CA 02284085 2002-04-08
R.
bends at discrete axial locations unless the tape is
constrained on a spool (as when the' tape is rewound into
its holder). In this latter case transverse bends are
eliminated, being transformed into bends along the
central axis of the tape. The transversely bent
conventional form would be a possible form for the
invention as well.
As another instance of non-planar forms, a
cylindrical form of substrate or carrier that resists
torsion because of embedded wires or helical ribs may be
employed. Such a substrate will bend in 2DOF, without
permitting twist. This form could only be used to
determine constrained three dimensional locations and
2DOF orientation information.
In all forms, the sensors for bend need not be
co-located with the sensors for twist, and bend sensors
need not be co-located with their differently oriented
bend sensing mates (unless both bend and twist are being
measured, as described above). It is sufficient for them
to be distributed along the substrate at known intervals
that allow the configuration of the substrate to be
determined.
Although most references herein have been made
to inextensible flexures, extensibility can be allowed to
eXist in the substrate. Thus,' a possible form of the
invention could be a stretches-ble flexure wherein not only
bend and possibly torsion are measured but also
extension. The degree of extension must be detected to
ensure that the spacings between the flexure sensors will
be known. Extension sensors could include conductive
14
CA 02284085 2002-04-08
r s
elastomers sensitive to extension. For convenience and to
improve compliance, extension could be limited to a small
increase in length beyond which the flexure becomes
functionally inextensibTe.
While reference is made herein to a "substrate"
as a carrier for the flexure sensors, the word
"substrate" is not restricted in its meaning to a strict
positional relationship with the sensors. While the
sensors may be located on an outer surface of the
substrate, they may also be embedded or contained within
the body of the substrate. It is sufficient for the
substrate to serve as a carrier for the sensors,
preserving their inter-sensor spacings and their
orientations with respect to the body of the substrate.
This shape or profile measuring tool may be
coupled over all or part of its extent by constraining
means to a portion of a body or object the location,
shape or orientation in space of which is to be measured.
It is thereby able to provide information indicating the
position, shape, orientation and motion of the coupled
portion. Such information is obtained from all parts of
the sensor including uncoupled portions even though the
objective is to acquire data only in respect of the
coupled portions.
Because the invention provides locational
information along and for its entire length, it is
permissible for a portion of the substrate to be
uncoupled from the body being measured over parts of its
extent. It is sufficient for at least one portion of the
sensor to be attached to a body for the location and
CA 02284085 2002-04-08
t r
orientation of that portion of the body to be determined
with respect to a reference point elsewhere on the
sensor. "Signature" characteristics of the coupled
portions, such as invariant proportional signals between
specific sensors, can be used to identify and track the
coupled portions.
The invention performs in the same sense that a
snake is able to be aware kinaesthetically of the
location of its head, and its entire body, with respect
to the position of its tail. Every sensor's location, and
orientation, can be determined with respect to other
sensors by inter-referencing the positions of the
intervening sensors.
This capacity to permit portions of this
position, orientation and shape measuring tool to be
uncoupled along portions of its length from the body or
object being measured is especially advantageous when
this invention is used to effect motion capture of the
human form.
Because of the capacity of the shape measuring
tool of the invention to equally track surface segments
anywhere: along its length; the invention does not require
precision location of the instrumented tool with respect
to the joints whose angular positions are to be measured.
Thus, for example, a loose-fitting, shape measurement
glove whose position shifts over a human hand during
movement is, if implemented in accordance with the
invention, nevertheless able to provide accurate output
signals as to the location and orientations of the
various joints of the wearer's hand.
16
CA 02284085 2002-04-08
r r
Another potential application of the invention
is as a "keyboard" or device for inputting signals based
upon contact and applied pressure. Mounted on a
compressible under-support, a ribbon sensor can provide
outputs that are indicative of the location of contact,
the degree of applied pressure, and provide a third
signal according to the amount of twist created. An
instrumented planar array positioned over a compressible
under-support can provide positional information as to a
point of contact in two dimensions. The degree of
pressure being applied at a point can provide a further
dimension for expression by a user of such "key board".
The foregoing summarizes the principal features
of the invention and some of its optional aspects. The
invention may be further understood by the description of
the preferred embodiments, in conjunction with the
drawings, which now follow.
SUM~!'ARY OF THE FTGURES
Figure 1 is a schematic of a planar mechanism
composed of rotary bending joints and links provided with
joint sensors whereby the location in space of the distal
end with respect to the base end can be determined;
Figure 2 is the mechanism of Figure 1 with an
additional rotary-twisting joint present;
Figure 3 is the mechanism of Figure 1 with
rotary twisting joints associated' with each rotary-
bending joint;
17
CA 02284085 2002-04-08
Figure 4 is the mechanism of Figure 3 with the
twisting and bending joints separately disposed within
the mechanism;
Figure 5 is a pictorial depiction of a ribbon
carrying bend and twist sensors;
Figure 6 is a side view of the ribbon of Figure
5 bent into a curve;
Figure 7 is a depiction of a "rope" substrate
carrying bend and twist sensors;
Figure 8 is a pictorial depiction of a ribbon
in space depicting bend and twist;
Figure 9 is a side view of a straight optical
fiber with an upper surface treated to absorb light;
Figure 10 is the fiber of Figure 9 in a bent
1S condition;
Figure 11 is a plan view of a looped optical
fiber with an upper surface treated to absorb light and
in planar configuration;
Figure 12 is a side view of Figure 11;
Figures 13 and l4 correspond to Figures 11 and
l2 with the looped end in a-curved configuration;
Figures 15 and 16 are similar to Figures 11 and
12 but with the treated surface present only on half of
the loop;
Figure 17 is a right end view of the looped
fiber of Figures 15 and 16;
Figures 18, 19 and 21 depict the looped .fiber
of Figures 15, 16 and 17 with treatment of the loops on
opposite, opposed sides;
18
CA 02284085 2002-04-08
r ,
Figure 20 is the looped fiber of Figures 18, 19
and 21 in right end view, in a twisted configuration;
Figure 22A illustrates in side view a ribbon in
a corrugated formation, resting on a rigid body;
Figure 22B is similar to Figure 22A, but with a
second body applying a pressure from above;
Figure 22C illustrates a modified form of the
ribbon in Figures 22A and 22B, the ribbon of crenulated
form;
Figure 22D illustrates, in plan view, a ribbon
sensor cut from a flat sheet;
Figure 22E illustrates a serpentine form with
thinner hinge sections;
Figure 22F is a cross-section through a hinge
section, such as on lines A A or B-B of Figure 22E;
Figure 22G illustrates a sensory ribbon
installed in a flexible conduit;
Figure 22H is an end view of the arrangement of
Figure 22G;
Figure 23 depicts a single, nested pair of
looped sensors on a tape connected to signal processing
operational amplifiers to feed a data processing computer
and video display;
Figure 24 is a cross-sectional end view through
the tape of Figure 23 in the untreated carrier length;
Figure 25 is a cross-sectional end view through
the tape of Figure 23 at the treated looped sensor end;
Figure 26 is a pictorial depiction of the
sensor of Figure 23 supported by a semi rigid conduit;
19
CA 02284085 2002-04-08
r r
Figure 27 is a plan view of a ribbon format
sensor with crossed, reflexively operating bend sensors;
Figure 28 is a cross-sectional side view of
Figure 27;
Figures 29 and 29A are plan views of half
arrays of distributed sensors on ribbon substrates to be
placed one over the other to form a laminated sensor;
Figure 30 is a cross-sectional side view of the
arrays of Figures 29 and 29a assembled as a laminated
sensor;
Figure 31 is a plan view of a ribbon-format
sensor with pairs of twin, nested looped sensors deployed
in a "Y" configuration;
Figure 32 is a cross-sectional side view of
Figure 31;
Figure 33 is a plan view of a ribbon format
sensor with pairs of twin, nested looped sensors deployed
in an "X" configuration;
Figure 34 is a plan view of a ribbon format
sensor with a linear array of twin nested loop sensors;'
Figure 35 is a plan view of an assembly of the
sensor of Figure 34 to form a planar array;
Figure 36 is a side view of Figure 35;
Figure 37 is a plan view of an assembly of the
sensor of Figure 33 to: form a planar array;
Figure 38 is a pictorial depiction of a person
wearing a ribbon-type sensor to capture motion on a video
display; and
CA 02284085 2002-04-08
Figure 39 is a pictorial depiction, similar to
that of Figure 38, with a flexible sensory ribbon wrapped
around the arm; and
Figure 40 is a side view of a joystick
application of a ribbon-type sensor.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure 1 represents a mechanism 1 in the form
of rigid links 2 that are coupled at joints 3 that have
parallel axes. This mechanism 1 is therefore free to move
or bend in a single plane. It is anchored to a reference
point 4 at one end and may have an end effector 5 at its
other end. All of the joints 3 are instrumented to have
sensors (not shown) which provide information as to the
angular orientation of the joints 3.
It is possible by processing the signals from
the sensors and knowing the lengths of each of the links
2 to determine by calculation the distance to and
position of the end effector 5 in space with respect to
the reference point 4.
In fact, the positions of all joints 3, and
locations therebetween on specific links 2, can be
calculated by interpolation.
With rigid links and mechanical joints it has
not been possible in the past to multiply such elements
to a number which is large enough to provide a shape or
position measuring tool which has a high capacity for
compliance with an irregularly curved surface. Further,
21
CA 02284085 2002-04-08
the mechanism of Figure 1 is limited to motion in a
single plane.
Figure 2 depicts a modified mechanism 22 to
that of Figure 1 that contains an additional "twist"
joint 6 that also carries a sensor to indicate its
rotational position. This twist joint 6 enables the end
effector 5 to rotate out of the plane to which the
mechanism 1 of Figure 1 is confined, giving it access to
a volume of three dimensional space.
Figure 3 shows a generalized expansion of the
mechanism 22 of Figure 2 wherein multiple twist joints 6
are provided, shown co-located with bending joints 3,
along the length of the modified mechanism 23. Figure 4
shows a similar generalized expansion to provide a
mechanism 24 wherein the bend 3 and twist 6 joints are
distributed along the length of the mechanism 24 without
necessarily being co-located.
The mechanisms of Figures 3 and 4 have the
mechanical capability of conforming to some degree to a
surface that is curved in three dimensions. However, with
the use of rigid links and mechanical joints, such
elements could not in the past be multiplied to provide a
measuring tool with a high capacity for compliance with a
curved surface.
Referring again to Figure 1, it is possible to
calculate the location in two dimensions of the end
effector 5 and each joint 3 with respect to the reference
point 4 using simple geometry based upon the length of
each link 2 and the angular setting 26 of each joint 3.
Similarly, such parameters can be calculated in three
22
CA 02284085 2002-04-08
i l
dimensi4nal space for the mechanisms 22, 2:3, 24 of
Figures 2, 3 and 4. To indicate this the symbols for x, y
and z coordinates are provided opposite the end effector
in each of these Figures.
5 The invention carries this methodology into
effect by providing a flexible substrate 8, 21 to serve
as a carrier for a series of flexure-detecting sensors
10, 11 distributed along its length. This substrate, as
shown in Figures 5~, 6 may have a reference surface 28
which may be applied against the outer surface of an
object to extract a profile therefrom based on signals
received from the sensors indicating their angular
orientations.
This technique of measuring shape by sampling
curvature and twist using a flexible substrate 8 with a
reference surface 28 can be applied if the curvatures and
twists being measured are not permitted to take on sharp
gradients, or if the sensor spacing is sufficiently small
to adequately sample the gradients. The spacing and
individual range of sensors determines the permissible
range of operation for the sensor array.
In Figure 5, a shape and position measuring
tool 7 is shown that relies upon a flexible substrate 8
shaped in the form of a ribbon 8. A "ribbon" describes
herein a body of flexible material that is essentially
inextensible, has a longitudinal dimension 12 of
considerable length compared to its width 13 and depth 14
and whose width 13 is so much greater than its depth that
bending of the body is limited substantially to bending
about axes 15, 15a which are transverse to the
23
CA 02284085 2002-04-08
s !
longitudinal dimension 12 of the ribbon. A ribbon is,
however, free to twist. For this reason the transverse
bending axes 15, 15a are not necessarily parallel.
Figure 8 depicts a ribbon 8 with arrows
indicating both bending and twisting.
The Figure 5 a ribbon substrate 8 has
distributed along and attached to its exposed surface 9 a
series of separatelyy distributed bend 10 and twist 11
sensors. These are schematically depicted as essentially
point objects. In fact, all such sensors 10, 11 are
coupled to a signal processing unit (not shown in Figure
5) that receives signals from such sensors 10, 11.
In Figure 6, the ribbon 8 of Figure 5 is shown
in a side view when bent within a single plane, without
twist being present. The curvature between two points 16,
17 proximate to bend sensors 10 may be approximated as a
circular arc 18 about a center 19. This approximation
will be sufficient to provide reasonable accuracy if the
ribbon 8 bends in a well-behaved manner e.g. if the
ribbon 8 has relatively constant thickness 14 and flexing
characteristic, and if the sensors 10 are sufficiently
dense in their distribution along the substrate 8:
The curvature between points 16 and 17 can be
estimated by the state of measured curvature at points
16, 17 as measured by the bend sensors 10, 11 located at
those positions. If these curvatures differ; an average
curvature, or a curvature value based upon further
adjacent curvature measurements, may be taken: as the
approximated curvature for the arc 18.
24
CA 02284085 2002-04-08
Knowing the value of the curvature of the arc
18 and the arc length, being essentially the separation
of the sensors 10 distributed along the ribbon 8, the
position of a consecutive point 17 can be calculated with
reference to an adjacent point 16. This type of inter
referencing calculation can proceed from a base end of a
ribbon 8 to a terminal end. Such a calculation will
provide geometric values for the positions of all of the
sensors 10, 11 in space, plus by extrapolation for any
intermediate locations on the ribbon 8.
The above explanation has been made for
simplicity by reference.°to the bend sensors 10 only.
Similar calculations can incorporate data received from
the twist sensors 11 to provide geometric data in three
dimensional space.
If a flat untwisted section of substrate 8 has
two parallel ends, then twist is defined as the angular
difference between the ends when a twist is applied. When
the substrate 8 is also bent, the twist is interpreted to
be the same as that present in; say; a thin cylindrical
driveshaft along its long axis, i.e. the twist remains
invariant as the shaft is bent. When this happens, the
end lines are no longer in parallel planes.
If twist alone is applied to a straight section
of the substrate 8, then the twist will not affect the
position of the longitudinal axis line l2 until a section
is reached which has a bend.
A model of the substrate's shape may be
constructed in a computer, based on the above calculus. A
convenient means of presenting the model visually is to
CA 02284085 2002-04-08
draw the arcs in sequence, using small flat sub-arc
segments; so that twist is also visible ever for straight
arc segments. Refinements may be added by use of
interpolation, averaging, and other conventional curve
fitting techniques.
Figure 6 has demonstrated the invention for
simplicity by reference to a ribbon substrate 8, as
defined above. Figure 7 depicts, for visual impact, a
"rope" 20 provided with bend and twist sensors 10, 11
separately distributed along its entire length. Again,
similar calculations based on the signals received from
such sensors can calculate the geometric orientation of
such a fully flexible substrate in space. While a "rope"
is pictorially depicted, in practice the fully
15 flexible substrate 21 could be a length of extruded
rubber or flexible polymeric material within which the
sensors may be embedded. If this flexure has a hollow
core, such core may be used to route the leads carrying
signals from the flexure sensors.
20 Another alternative is to "cage" a ribbon
format substrate in a cylindrical tube, such as a
longitudinally split corrugated tube used to shield
electrical wire. This. constrains the substrate to be more
manageable or "well behaved" when being bent around an
2 5 obj ect .
A further alternative is to employ a substrate
with limited bending freedom as by using a rod with a
square cross-section that is treated with transverse
grooves to permit bending while retaining a resistance to
26
CA 02284085 2003-03-06
twisting. With such "mechanical f:ilt:ering" present, only
bend sensors need beg employed.
Tn figure 7, tws.~ bend sensors 10 for every
single 10 twist. sensor 11 are depict~eca, Thi:~ is to ensure
that bend in two directi<:ms rattier than only in a single
plane can be detected. While the bend sensors 10 are
depicted as being ~~o-located, this is not a necessary
requirement. It is suffi~:~ient fo:r a:11. sensors 10, 11 to
be distributed along trae substrate 21 so that their
signal. values can b~~ combined with the signal value: of
other sensors to 1>ermit: <~a.lc:ulatiorb of the geometric
disposition o~ the s~abstrat.e 21..
Sensors suitable for bend and twist
measurements include fiber optic bead and strain sensors;
1'p conductive elastomer sensors of bend and extension
generally referred to ass force sensitive resistors
(FSRs) , bend sensitive resistors (BSR5) and
piezoresistive ser_sors; elecvtri.cal strain gauges
including bonded wire ar:~d semi.c:onc actor forms; and any
other sensors capable of measuring bending, extension,
and torsion, inc:Ludin<3 capacitive, magnetic, and
piezoelectric methods.
Fiber optic sensors such as those described in
U.S. patent 5,321,257 arid PCT pub7.ication WO 94/29671
(application PCT/94C'_A/00314) are well suited for this
application because these sensors are immune to
electromagnetic interference and will function in the
neutral axis of a flexure, where there is no strain. The
type of fiber optic :aerasors referred to in these
publications can be ~~lass:~.fied a~ "Bend Enhanced Fibers" .
2 '7
CA 02284085 2002-04-08
Bend Enhanced Fiber sensors (BEF) are based on
the loss of light from a light guide in a zone where the
core/cladding interface has been treated and modified
such that light striking the modified zone is lost from
the core and does not return. In BEF sensors, a nominally
straight fiber is treated on one side so that light loss
increases as the light guide bends to make the straight
treated zone more convex and decreases as the guide bends
the other way.
Straight 30 and bent 31 BEF sensors are
respectively shown in Figures 9 and 10. The treated
portions 32 on the top surface are shown in black. The
geometry is such that the modulation. of the intensity of
light traveling through the fiber 30, 31 is linear with
curvature of the fiber. Output is bipolar about the
straight shape. Modulation by curvature in the treated
zone has been measured to be 3000 times that produced by
curvature of untreated light guides.
In loop sensors, the treatment is on one face
of the light guide loop 33 (see Figures 11 and 12), and
modulation occurs when the loop 33 is bent out of its
plane 34 (see Figures 13 and 14) . The treated surface 32
in Figures 11 and 13 is shown as shaded. In Figures l2
and l4 it is shown as a darkened line.
Figures 15, 16 and 17 show a looped sensor 35
wherein the treated zone 32 occurs on the portion of the
loop 33 leading up to the region of reversing curvature
36. It is not necessary for this reversing region 36 to
be treated, although this is optional. As well,' the
opposite half of the loop 33 may remain untreated:
28
CA 02284085 2002-04-08
Throughput and modulation efficiencies are
particularly high for loop sensors. The combination of
treated zones 32 on the light guide surface and the tight
loops is synergistic. A treated zone 32 on top of the
light guide emphasizes loss of light in modes that would
not pass freely by the nearby tight loop when the loop is
straight, so there is little penalty for introducing a
tightly curved (and therefore lossy) loop 33 in the light
guide. However; when the loop 33 is bent aut of its
plane, the loss zones interact strongly with modes that
would otherwise travel freely around the loop 33,
resulting in efficient modulation.
As a further variant on looped sensors, a twist
sensor as shown in Figures 18-21 may be formed in a loop
33 having a bisecting, median line 46 by treating loop 33
on only half of each outwardly facing surface portion and
doing so on opposite faces 47, on opposite halves of the
loop 33. A loop 33 so treated is shown in Figures 19 to
21 with the treated portion 32 shown as being raised for
clarity. For Figure 21 the loop 33 is flat. If bent
upwardly or downwardly transversely to the median line
46, the treated surfaces 32 will have opposite effects
that cancel. Accordingly, bending is not sensed. However,
as shown in Figure 20 the loop 33 is twisted about its
median line 46, the modulating effects of the treated
surface portions 32 are additive, providing an enhanced
measurement of twist.
Figure 22A shows a side view of a ribbon 8 in
"corrugated" configuration. It has been made so that at.
rest, with no forces applied, it is bent out of its plane
29
CA 02284085 2002-04-08
in one degree of freedom, with sinuations that repeat at
multiples of the sensor spacing. In this case, the
sinuations have the same spatial frequency as the sensor
pairs 50, indicated by boxes 51 on opposite sides of the
ribbon. The ribbon is resting on a rigid body 52, such
that its mean locus, indicated in the side view by the
dashed line 53, takes on the shape of the rigid body. The
computer image of the ribbon will look like the figure;
i.e. a surface that sinuates in space but whose mean
position and orientation can be found by an averaging or
spatial filtering process that eliminates the ~sinuations,
leaving the mean surface.
Figure 22B shows the same corrugated ribbon 8
but now with a second body 54, applying a pressure from
above. The computer image will now show a diminution of
the sinuation amplitude in the region of applied
pressure, yet still contains information on the shape of
the underlying surface, both in the area of applied
pressure and beyond the area of applied pressure. For a
combined, pressure and shape sensor, the sensor spacing
implies a minimum spatial-frequency that either body may
have without its pressure field or shape field causing an
error in the measured shape or pressure data. The spatial
features of the bodies must have no spatial frequency
components greater in frequency than those of the sensor
spacing, and the sinuations must be in phase with the
sensor spacings. This rule is analogous to the principles
of photography, whereby it is not valid to photograph
features in the image plane smaller than the grain size
of the photographic emulsion.
CA 02284085 2002-04-08
This demonstrates a method of measuring both
pressure and shape using a pre-sinuated sensory ribbon.
It should be obvious that sinuation as shown in the
figure is not the only means of obtaining shape and
pressure information simultaneously. For instance, the
ribbon could have regular variations in twist, or could
be crenulated, with stiff 90 degree bends 55 between
sensors locations, as shown in Figure 22C in an elevation
with height exaggerated. In the case of Figure 22C,
pressure will cause an increase in the bending signal
from affected sensors, but the mean shape will be
unaffected if the spatial frequency restriction is
satisfied.
Figure 22D shows a plan view of a ribbon sensor
8 cut from a flat sheet, such that at rest it lies in a
plane but is sinuated from side to side in a "serpentine"
conf iguration. The X' s 56 show the locations of bend and
twist sensing pairs positioned at common, shared spacing
intervals. In acme cases it will be sufficient to locate
these pairs only at the center of each straight leg,
thereby reducing the number of sensors required.
Variations on the serpentine form include zigzags and 90
degree turns, resembling triangle and square waveforms
respectively. Such forms may be fitted to fabrics or
other substrates which may then be curved or bent to make
garments, seat covers, or other conformable surfaces.
When twisted, the form of Figure 22D will produce bend
signals only. When bent along its long axis, twist
31
CA 02284085 2002-04-08
signals will result. In this respect, it acts as a
converse case of a straight ribbon.
Figure 22E shows a serpentine form that is
stiff everywhere but at thinner hinge sections 58
designed to permit bending only, without twist. The hinge
sections are produced by thinning the substrate as shown
in cross section 22F. At the hinge sections are located
bend sensors indicated schematically by the box forms 60.
The serpentine form of Figure 22E is a sensor array that
uses bend only sensors, yet is capable of transmitting
full 3 dimensional information to a computer.
Figure 22G shows a side view of a flexible
plastic conduit 61 having corrugations in its wall and a
slit at the top. A sensory device 62 is installed
extending along the conduit, in the slit, extending out
of the conduit. The end view of Figure 22H shows the
sensory ribbon 63 to the left and a stiffening band 64 of
spring steel to the right, both projecting out of the
slit in the top of the conduit. Not shown are "0" rings
spaced at regular intervals to keep the ribbon and steel
band from working out of the conduit when it is bent. The
advantage of adding conduit is twofold: it helps to
distribute curvature between sensor locations, thus
acting as a low pass mechanical filter that minimizes
errors due to sharp bending, while allowing overall
freedom of bending and twisting; and it allows an easy
means of adding or removing stiffening to the ribbon. The
ribbon and any stiffener band are held at the slit and at
the opposite inner surface of the conduit . They are thus
at the neutral axis of the conduit with respect to bends
32
CA 02284085 2002-04-08
out of the plane of the ribbon, so the force required to
bend them is minimal and slippage between the ribbon,
band, and conduit are minimized. The conduit also
provides a means of adding wires or hoses to the
construction.
Intensity based sensors are attractive for low
cost applications because signal processing can be very
simple. However, intensity in a light guide can be a
function of many things other than the measurand
(curvature). Unwanted intensity modulators include:
- Variations in optical connections
- Bending of leads
Aging of light source
- Aging of light guides
- Effect of temperature on light sources and
detectors.
One technique to reduce balancing requirements
between fibers is to form a "lossie" zone, as by abrading
or heating a local point in order to adjust the
throughput of individual leads.
Looped fiber optic technology overcomes these
obstacles by using an optical and electronic bridging
technique involving two opposed laminated loops. A
standard balanced loop sensor configuration is shown in
Figure 23, wherein two "nested" loops 37 are employed.
The four leads 38 are kept parallel and
contiguous, arranged in a plane inside sealed
laminations, as seen in Figure 24. This reduces the
predominant degrees of freedom for lead bending from two
to one. One LED light source 40 is used to illuminate
33
CA 02284085 2002-04-08
both loops, and is controlled through an integrator 43 to
keep the sum of the loop throughputs constant. The
controlled throughputs include optical and electronic
signals (i.e. LED, light guides, photodiodes, and
amplifiers). The constant sum technique for controlling
the LED 40 simultaneously overcomes common mode
modulations due to aging or temperature effects on
optoelectronic devices and light guides, and bending of
the leads.
However, the measurand (curvature) is not in
common mode because the two loops 37 are treated on
opposite, outwardly directed, faces 40, 41, as seen in
Figure 25, so that a given bend causes throughput to
increase in one and decrease in the other. The signals
are linear so they may be subtracted in an operational
amplifier 42 to yield an output signal linear with
curvature and unaffected by common mode errors. Because
of the substraction, the resulting signal is also twice
as large'as that from a single loop 33.
The resulting complete sensing system amounts
to an aptoelectronic balanced bridge which produces a
high level electrical output using one quad operational
amplifier 42. The circuit functions to produce a high
level output signal that rejects common mode errors.
A practical low cost sensor may be manufactured
by forming nested loops 37 around pins on 1 cm centers,
in situ treatment to create loss zones, and in situ
application of laminations 39 which hold the loops 37 and
leads 38 in plane. The leads 38 may be laid-out in a
slightly sinuous or 'wavy" pattern to protect them from
34
CA 02284085 2002-04-08
tensional stress. Present lead length capacity has been
demonstrated at 5.5 meters, but can be expanded. Standard
laminations with outer layers of latex rubber, and two
part polyurethane core filler 44 between, are 1.2 mm
thick x 7 mm wide, and contain 0.5 mm diameter fibers 38
with a polymethylmethacrylate core. Smaller laminations
are possible using 0.25 mm diameter fiber 38. The
standard, treated, sensitive zone 33 is 12 mm long for
0.5mm fibers and 6 mm long for 0.25 mm fibers. A typical
sensor is shown in Figure 26.
Twist and bend sensors of the looped type may
be nested so that they axe intimately co-located along
the substrate.
While looped sensors have been described in
detail,. certain advantageous deployment of sensors along
a substrate will be depicted in Figures 27-30 using
simplified symbols-. These "hockey stick" images 50 may be
taken as Treated Bend Enhanced Fiber Sensors 51 with
reflective ends 52 that act in reflexive mode in the
known manner. The "blade" portions 53 of each image SO,
are treated and positioned to be sensitive to bending
about axes 15 that are at an angle to the blade's length.
In Figure 27 the sensors are laid-out in
crossed formats with the sensing portians 53 overlying
the median line 54 of the substrate at splayed angles.
For clarity the depiction of the leads 55 is broken with
the intervening carrier portions omitted. The' signals
from each pair of sensors, however, may be fed to
operational amplifiers as described above to extract
their sums and differences. If the sensing portions are
CA 02284085 2002-04-08
located on the same faces (outwardly or inwardly
directed) then the sums of the signals will measure
bending and the differences will measure twist.
While Figures 27 and 28 depict crossed sensor
pairs on a single substrate 8, Figures 29 to 30 show two
partially instrumented substrates 8, 8a which, when
assembled as a lamination 56 with the sensors in the
center,' from a sensor assembly 56 with the sensors
effectively embedded within a collective "substrate",
positioned conveniently along the neutral axes of the
assembly 5&.
Instead of mounting the sensor blades 53
together in pairs on the substrate 8, half of each pair
may be laid-down initially as shown in Figure 29 and a
second nearly identical substrate with loops as iii
Figure 29a may be laid over the first. The treated
surfaces 53 of Figures 29, 29a must be on opposite faces
to achieve the same configuration as Figure 27. If
treated on the same faces in Figures 29, 29a the outputs
from the operational amplifier 42 will be reversed in
measuring bend and twist. To add stiffness and prevent
one sensor of a pair from bending the other, a ribbon of
rubber, plastic or metal may be placed between the two
substrates.
Once the two substrates are assembled, the two
may be laminated together to provide dual sets of sensors
with all leads exiting at the same end. A side view of
the resulting lamination 56 is shown in Figure 30. As an
alternative to having the optical fibers directly
adjacent to each other the substrates 8, 8a may be
36
CA 02284085 2002-04-08
connected so that the fibers are on the outside of a
common core substrate.
If identical half-substrates are built, when
assembled the treated surface portions face in opposite,
outward directions. Nevertheless, by taking sums and
differences of the outputs of respective members of each
pair of sensors, twist and bend values are still
provided.
By bonding the two outer substrates 8 along
their edges 57 only, an interior space 58 is formed
wherein the leads 55 for each sensor 51 may be routed in
a loose form. This provides a tool which is flexible and
avoids placing unnecessary stresses on the leads 55 of
the sensors.
In the same manner as depicted for the
reflexive fiber sensor 51, looped sensors 33 may be
distributed along a substrate 8. Figures 31 and 33 show
two modes for co-locating nested twin looped sensors in
pairs that measure bend and twist simultaneously. Figure
32 is a cross--sectional view through Figure 3l showing
raised surfaces 32 where the loops 33 carry treated
surface portions 32.
In Figure 31 the loops 33 are separated in a
splayed "Y" configuration; in Figure 33 they overlap in
an "X" configuration with their median lines still
splayed in their angular orientation. In both Figures 31
and 33 the median lines 46 of the loops 33 are angled
outwardly from the median line 54 of the substrate 8.
This angle 59 is preferably equal for sensors 33 'on both
sides of the substrate 8. This allows both bend and twist
37
CA 02284085 2002-04-08
values to be obtained by summing and adding outputs: If
the angle 59 is 45 degrees, maximum, direct signal
strengths corresponding to bend and twist are obtained.
In Figure 34 a string of nested looped sensors
37 are shown linearly deployed on a ribbon substrate 8.
Either the nested loops may alternate as bend and. twist
sensors, or within each nested pair, one sensor may
measure bending and the other twist:
Planar arrays 60 of sensors may be assembled by
bonding the edges of ribbon substrates 8 together to form
a carrier sheet 8a. This is depicted in two different
formats corresponding to prior Figures 34 and 33 in the
planar arrays 60 of Figures 35 and 37. Alternately, in a
manner analogous to that depicted in Figures 29 and 30,
sensors may be bonded to two flexible sheets which serve
as carriers, and these sheets may be over-laid and bonded
to form an instrumented planar shape sensing foal.
This invention has been built and demonstrated
in planar tape form with 8 sensor pairs, each pair
collectively measuring bend and twist. Loops in fibers of
0.25 mm diameter were formed and treated for bend
sensitivity according to the procedures of U.S: patent
5,531,257, Patent Cooperation Treaty application
PCTjCA94/ø0314, and the SPIE Article SPIE Vol. 2839, pp.
311-322, 1996). These were affixed in pairs every 5 cm at
45 degrees to the long axis of a latex substrate 0.32 mm
thick, 12 mm wide. The light loss portions of the fibers
faced way, i.e. were outwardly directed; from the
substrate; the apexes of the loops were approximately 1
mm inside 'the edge of the substrate. Sensors were in
38
CA 02284085 2002-04-08
pairs, in crossed form, with facing light loss zones so
that the sensitized portion of each loop crossed the
axial center of the substrate. The leads of the loops
were bent and led axially to beyond the end of each
substrate with the leads being no closer than 1 mm to the
edge.
During the process, fiber leads (38 in Figure 25)
were kept in order in pairs on organizer cards. A fiber
from each pair was connected to a light emitting diode
(LED) 40. Generally 8 or more fibers 38 can be
illuminated by the same LED. The other fiber from each
pair was connected to a photodiode 61, one fiber per
photodiode. Conventional transimpedance amplifiers 62
converted photodiode current to voltage. These voltages
were fed to sum and difference amplifiers 42 (or may be
digitized immediately). Analog sums and differences were
digitized and fed to a computer 61 for further
processing.
Calibration Procedure
The preferred embodiment of the invention
consists of pairs of fiber optic sensors operating within
ranges for which light intensity throughput of each
individual sensor changes linearly with curvature. When
the invention is flat (no curvatures are applied) , it is
desirable to have all of the intensities equal, so that
when pair wise sums and differences are taken, all the
differences will be the zero, and all the sums will be
the same positive value. This reduces computational
39
CA 02284085 2002-04-08
overhead and ensures minimal interaction between bend and
twist outputs.
As a convenient method for adjusting the light
intensities use of micro-bend fiber optic "resistors" may
be made by sandwiching untreated sections of the fibers
between layers of metal and blackened elastomer which are
resilient but stiff enough to retain an applied bend. For
example, a sandwich is made of the following 4 x 20 mm
layers: black vinyl tape, black double sided adhesive
tape; fiber along the 20 mm dimension at the center,
black vinyl tape, 0.010" brass. Optical signals may be
routed through fibers contained within these sandwiches
and bent to adjust the signals to all take on the lowest
value, so that all are equal. This adjustment method
allows repeated reduction and restitution within broad
limits, so that adjustment can be quite precise and
forgiving of initial errors.
Once the individual sensor values are equal,
then the digitized outputs from the light sensors may be
conveyed to a computer. An alternative is to first take
sums and differences in analog form, and then send these
to a computer. For either case, we may now address the
calibration of the values representing bends and twists
(or bends, bends and twist), in the computer.
Since the preferred embodiment sensors are
linear, the sums and differences will be linear also. In
order to calibrate the invention, we need only calibrate
at two points of each of the bend and twit ranges. A
preferred method of calibrating the invention for bend in
its ribbon or tape format is to first lay the tape flat
CA 02284085 2002-04-08
and set all the bend values in the computer to zero. Then
the invention can be formed into a hoop on a cylindrical
mandrel, and gains (multiplicative positive or negative
numbers) can be applied to each bend value until all
computer bend values are equal to a constant that
corresponds to the uniform curvature seen at the
circumference of the mandrel. Since no offsets (added or
subtracted values) have been applied, the computer
"image" of the tape will contain all zeroes when the tape
is again laid flat.
In similar fashion, the twist values may first
be set to zero with the tape flat, then gains may be
applied when the tape is held straight but has a uniform
twist applied over its full length by means of a fixture
holding the ends at different angles of rotation about
the long axis. An example would be mounting the tape
axially in a lathe and rotating the lathe head a known
amount.
A preferred method of calibrating both twist
and bend simultaneously is to first set bend and twist
values to zero while the tape is held flat, then to form
the tape in a uniform helix around a cylindrical mandrel.
Since a helix has a constant curvature and a constant,
distributed twist, gains may be applied to all the bends
and separately to all the twists to obtain a computer
image of the helix.
The above mandrel-based calibration procedures
may be automated in the computer, since a11. desired bend
and twist values are known a priori from the mandrel
information, and do not interact. The procedure is simply
41
CA 02284085 2002-04-08
one of creating a look-up table of gains such that for
each bend signal, the bend signal times its assigned gain
equals a constant, and a similar procedure for twists.
For sensors that are not linear, a similar
procedure may be used, but more than two points will have
to be calibrated, requiring more mandrels and more steps.
Accuracy and Precision
Precision (resolution) is defined as what can
be resolved over noise, not counting long term drift.
Accuracy is defined as what can be measured to
an absolute scale, even in the presence of long term
drift .
Precision determined from empirical measurement
based on prototype versions of the invention has been
established as being about 1-3 mm per meter of ribbon
substrate length. A precision calculation based on 0.02
deg of resolution for each bend sensor and using 20 pairs
of sensors at 5 cm spacing on 1 meter of tape provides a
worst case value of 0.35mm, rms - 0.09 mm per meter of
tape.
Absolute accuracy, influenced mainly by long
term drift, was calculated based on an assumption of 1%
drift over 2 months, of a standard sensor. For a 1 meter,
20 pair tape, a worst case error of 0.5 cm/month, and rms
value of 1.1 mm/month is obtained. In general, the errors
will not add. The error contribution to end point
position is greater for segments of tape closer to the
fixed reference point.
42
CA 02284085 2002-04-08
The invention is depicted in use in a human
motion capture application in Figures 38 and 39. In
Figure 38 a ribbon-type, tape substrate is mounted along
the upper arm 63, forearm 64, and hand 65 of a wearer.
The sensor leads 66 terminate in a terminal box 67
mounted conveniently on outer clothing which feeds
signals 68 to a computer 69. The instrumented tape is
affixed to desired body portions by adhesive tape 70. No
critical attachment points are dictated by the tape,
although computational efficiency may be associated with
preferred locations.
While the tape is capable of actually measuring
the shape of the surface to which it conforms, e.g: the
forearm 64, it may suffice to extract only orientations
of the limbs for certain segments of the routing of the
tape. At the hands 65, data as to shape as well as
orientation may be extracted.
Conveniently, loops 71 may be formed at the
elbow and wrists from which no data need be collected,
other than the locations of the bounding ends of the
shape and orientation measuring portions. These
disconnected segments 71 may extend freely into space,
fully unconstrained: Advantageously, they provide comfort
and mobility to the wearer.
Figure 39 shows a sensory ribbon in a conduit,
of f fixed to a person's arm . The conf igurat ion and purpose
are the same as Figure 38, except that the ribbon and
conduit are arranged in a helix form around the arm. The
sensing ribbon 8 is flexible, wrapped around the arm, and
also having a sensing portion 73 which is attached to at
43
CA 02284085 2002-04-08
least one finger. Sensor portion 73 de ects and provides
measurement of the finger movement, for example when
actuating a switch. This produces a computer image that
follows the surface of the arm, such that the image has
some of the elements of a closed volume. The conduit is
not necessary to this configuration, but can reduce the
number of sensors required, by smoothing the curves. Not
only can a central surface or line representing hinged
links to model a "stick figure" of the arm, be derived
from the image, but the image can be used to model
bulging muscles or other changes linked to volume or
shape of the surface. In a similar manner, the helix or
other sinuated or serpentine shape could be used to
create a volumetric model of other human or animal parts,
or of any other physical body. For instance, sensory
ribbons .can be used to image changes to the torso volume
or shape during breathing:
While the terminal box 67 may serve as a
reference point for defining position, orientation and
shape of measured surfaces in space, any poW t on the
tape can equally serve as the reference point. This may
include a bony protrusion on the collar bone or the nape
of the neck over which the tape passes. This provides
exceptional convenience in motion capture technology
since the tape is then referenced to a defined location
on the human skeleton.
The output from the computer 69, as with all
applications of the invention, can provide a video
display 72 of the geometric configuration of the shape
44
CA 02284085 2002-04-08
x a
measuring tool in space, and of the surface to which it
is attached.
As a further example of the use of the
invention, Figure 40 depicts a planar axial flexure 78
arranged in an arch or sinuous form, supported by a
reference 74 surface at one end and terminating at the
free end with a body 75 capable of Cartesian positioning
and orientation x, y, z location and roll, pitch; and yaw
orientations . The terminating body 75 may be a knob with
a switch or button that serves as an actuated joy-stick
to send positional signals 76 in 6 degrees of freedom to
a controlled system, e.g. a robot.
CONCLUSION
The foregoing has constituted a description of
specific embodiments showing how the invention may be
applied and put into use. These embodiments are only
exemplary: The invention in its broadest, and more
specific aspects, is further described and defined in the
claims which now follow.
These claims, and the language used therein,
are to be understood in terms of the variants of the
invention which have been described. They are not to be
restricted to such variants, but are to be read as
covering the full scope of the invention as is implicit
within the invention and the disclosure that has been
provided herein.
45
