Abstrict A flow meter includes a flow channel having walls and defining
a direction of flow. Stators are provided, having walls, disposed
at least partially within the flow channel. A rotor is included
for rotating with respect to the stator. A one piece retainer is
provided for assisting in limiting axial rotor movement comprising
a first pair of spaced apart wall portions for engaging the flow
channel walls wherein each wall portion in the first pair of wall
portions is located on a side of an axis opposite from the other.
A second wall portion is located on the axis for engaging the stator
wall wherein compression of each of the first pair of wall portions
toward the axis results in a component of force being applied to
the second wall portion along the axis.
Claims What is claimed is:
1. A flow meter comprising:
a flow channel having walls and defining a direction of flow;
stator means disposed at least partially within the flow channel;
rotor means, for rotating with respect to the stator; and
retaining means limiting axial rotor movement comprising means
exerting a squeezing force on the stator means and dilating force
against the walls of the flow channel wherein the retaining means
in cross section is substantially in an outline of a bowtie having
outer dimensions including ends and a center portion such that the
furthest ends are bowed outward into arcuate portions each having
a radius of curvature and the center portion is in the form of arcs
of a circle of radius less than the respective radii of curvature
of the arcuate portions.
2. A flow meter retaining element for use in a flow channel, having
walls and defining a direction of flow, for retaining a flow meter
in the flow channel having stator means disposed at least partially
within the flow channel and rotor means for rotating with respect
to the stator, the retaining element comprising means for exerting
a squeezing force on the stator means and a dilating force against
the walls of the flow channel wherein the retaining element in cross
section is substantially in an outline of a bowtie having outer
dimensions including ends and a center portion such that the furthest
ends are bowed outward into arcuate portions having a radius of
curvature and the center portion is in the form of arcs of a circle
of radius less than the respective radius of curvature of the arcuate
portions.
3. A retaining spring for retaining a flow meter within a flow
channel comprising a metal of one-piece construction having a uniform
thickness and wherein the metal comprises a first arcuate side defining
an angle of approximately 90.degree. for contacting one portion
of a wall of a flow channel, a second arcuate side defining an angle
of approximately 90.degree. for contacting a second portion of the
flow channel wall, wherein the first and second sides are substantially
oppositely facing along a first line, third and fourth arcuate portion
substantially oppositely facing with respect to each other along
a second line, a first flange portion coupling the first end of
the first arcuate side with a first end of the first arcuate portion,
a second flange portion for coupling a second end of the first arcuate
side with a first end of the second arcuate portion, a third flange
portion for coupling a first end of the second arcuate side to a
second end of the first arcuate portion and a fourth flange portion
for coupling a second end of the second arcuate side to a second
end of the second arcuate portion.
4. The retaining spring of claim 3 wherein separation of the first
and second arcuate portions produces an expansive force in one of
the first and second arcuate sides.
5. A flow meter comprising:
a flow channel having a flow-defining walls;
stator means having first and second longitudinally spaced apart
end lying in the channel;
a turbine rotatably supported between the ends of the stator means;
means for securing the first end in the channel against axial and
rotational motion with respect to the channel;
a retaining spring in a one-piece construction bearing outwardly
against the walls of the channel and inwardly against the second
end to secure the second end in the channel against axial and rotational
motion with respect to the channel and to couple the second end
with the walls, the retaining spring being the sole means of said
coupling of the second end; and
wherein the first end securing means comprises part of the retaining
spring bearing outwardly against the walls of the channel and inwardly
against the first end to secure the first end in the channel against
axial and rotational motion with respect to the channel and to coupled
the first end with the walls, the retaining spring being the sole
means of said coupling of the first end.
Description BACKGROUND OF THE INVENTION
This invention relates to in-line flow meters and more specifically
to retainer and support devices for in-line flow meters.
Flow meters have a range of applications such as in water meters
for houses, meters for medical diagnostic instruments, meters for
measuring fuel flow in airplanes and meters commonly known as anemometers.
The principles underlying these various meters are often the same,
though the structures are different. For example, the principle
underlying the anemometer and the aircraft fuel flow meter is a
rotor disposed in the fluid flow path turning on a stator mounted
on a stationary member. The rotational velocity of the rotor constitutes
a measure of the fluid flow parameter sought to be measured. Such
is the general principle disclosed in Potter, U.S. Pat. No. 2270141.
Potter teaches a rotor comprising a shaft split longitudinally
in the middle so that the split portions, when spread apart and
twisted slightly, form two spaced apart arcuate vanes, the rotor
being supported by a stator. The stator is held stationary at each
end about four sides of the stator by retaining means comprising
three or four resiliently deformable cylinders. The cylinders are
retained at their outer surfaces by the walls of the flow channel.
The vanes of the rotor contain a bar magnet which produces a varying
magnetic field when the flow of the fluid past the vanes causes
the rotor to spin. Disposed about the outside of the flow channel
walls at the point along the length of the channel where the vanes
are located is means for sensing the rate of change of the magnetic
field within the flow channel. The sensing means is then connected
by a conductor to a meter or dial calibrated to indicate the parameter
of fluid flow sought to be measured. The Potter flow meter is similar
in theory to the flow meter contemplated for use with the present
invention.
The retaining means of Potter are easy to manufacture but, because
of the number of cylinders used at each stator, the apparatus is
difficult to assemble. Furthermore, the type of bearings used to
support the rotor may dictate the use of a different retaining means.
Another prior art device is used in conjunction with a modified
form of the above-described flow meter. The modified flow meter
assembly comprises a flow meter housing to be placed in-line with
a longitudinal flow channel such as a pipe or tube, and a magnetic
field sensor housing attached to the outer surface of the housing
whereby a conductor can be attached to the housing for connecting
a remote meter or dial to a magnetic field sensor within the sensor
housing. Within the flow meter housing, a rotor is rotatably mounted
on longitudinally extending stator means parallel to the fluid flow
and within the flow channel. The stator means has oppositely facing
ends in the shape of nose cones. The prior art device employs a
spoked hub to retain and support the stator means, and thereby the
rotor, within the flow meter housing. The retainers are in turn
secured within the flow meter housing by annular retainer spring
clips, one at each end of the flow meter housing, preventing the
retaining and supporting means from being moved in a direction away
from the rotor and therefore out of the flow meter housing. This
form of the retainer is relatively difficult and costly to fabricate
because it must be machined. Because the support must be machined,
each support is inherently different from the previous one, to varying
degrees. Therefore, flow resistance varies from unit to unit.
SUMMARY OF THE INVENTION
The present invention includes a flow meter comprising a flow channel
with walls, stator means within the flow channel oriented such that
the major axis of the stator means is parallel to the direction
of fluid flow, rotor means for rotating on the stator means in response
to fluid flow, retaining means retaining and supporting the stator
means such that the rotor remains longitudinally stationary with
respect to the flow channel comprising resiliently deformable means
exerting a squeezing force on the stator means and a dilating force
against the walls of the flow channel.
In one embodiment of the invention, the retaining and supporting
means is formed from a sheet of spring steel i.e. sheet metal symmetrically
about a central longitudinal spine with various convolutions on
each side of the spine, the first convolution and the third convolution
substantially constituting the dilating means and the second convolution
substantially constituting the squeezing means. Such retaining and
supporting means is easily and economically manufactured because
it can be stamped from stock material and presents a minimal hindrance
to fluid flow. Additionally, the cross-sectional area presented
to oncoming fluid is less for the stamped support than for the machined
support, and is also more uniform along the length of the support.
Another benefit exists in the presence of vanes formed by the shape
of the support serving to straighten flow past the meter. Furthermore,
such retaining and supporting means is easily inserted together
with the stator and rotor into a fluid flow channel.
In a second feature of the invention, the retaining and supporting
means includes a retaining mechanism or clip at one end for engaging
a circular groove in the flow channel wall such that movement of
the retainer and thereby the stator and rotor is precluded. A further
feature of the invention is linearity control trim tabs adjacent
the rotor which can be adjusted toward or away from the central
axis of fluid flow to ensure maximum linearity of meter response
to fluid flow changes.
In another embodiment of the invention, the retaining and supporting
means comprises a pair of separate retainers, one for each end of
the stator. The shape of each retaining and supporting means is
substantially the same as the shape of the single retaining and
supporting means. However, having two supporting and retaining means
in such a fashion allows easier assembly of the flow meter. This
embodiment may also include the retaining mechanism and the flow
linearity control trim tabs as mentioned above.
BRIEF DESCRIPTION OF THE DRAWINGS
The features of the specific embodiments considered to be several
of the best arrangements of the device are illustrated in the drawings,
in which:
FIG. 1 is a perspective view of a flow meter embodying the devices
of the present invention;
FIG. 2 is a perspective view of the one-piece retaining and supporting
device embodying the present invention;
FIG. 3 is a cross-sectional view of the device of FIG. 2 taken
along line 3--3 of FIG. 2;
FIG. 4 is a perspective view of the retaining and supporting device
prior to formation into the form shown in FIG, 2;
FIG. 5 is an elevation view of the rotor and stator means used
with the devices embodying the present invention;
FIG. 6 is a perspective view of the two-piece retaining and supporting
device suspending the stator and rotor means;
FIG. 7 is, a perspective view of one of the retaining and supporting
means of FIG. 6; and
FIG. 8 is a graph of the relationship between flow pulse output
per unit volume as a function of flow rate in gallons per minute.
DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS
FIG. 1 shows a flow meter assembly 20 designed to be placed in
line with a flow channel, such as a pipe (not shown), and extending
longitudinally substantially parallel to the flow channel and to
the directional line of fluid flow 22. Flow meter assembly 20 includes
a longitudinal flow meter housing 24 of inside diameter D to be
placed in-line with the flow channel and a magnetic field sensor
housing 26 attached to the surface thereof to facilitate connection
of a remote meter, dial or other indicator to the meter housing
24. Contained within the cylindrical bore of flow meter housing
24 is a rotor 28 disposed to rotate, in response to longitudinal
fluid flow, about an axis parallel to the line of fluid flow 22.
Rotor 28 comprises vanes 30 made of a ferromagnetic material and
distributed about a hub 32 such that the fluid flow in the direction
indicated at 22 imparts rotation to rotor 28 creating a changing
magnetic field sensed by a magnetic field sensor (not shown) within
magnetic field sensor housing 26. The magnetic field sensor is connected
to a meter or dial (not shown) calibrated to indicate the desired
flow parameter.
Rotor 28 is rotatably mounted on stator means, generally depicted
in FIG. 1 at 34. Stator means 34 includes a longitudinal shaft 35
(FIG. 5) oriented parallel to the direction of fluid flow 22 and
about which rotor 28 rotates on bearings (not shown). Stator means
34 also includes a shaft support or cone 36 at each end of the rotor
28 and enclosing a respective end of the shaft. Each cone 36 extends
longitudinally away from each end of the rotor along line 22.
Flow meter assembly 20 also includes stator retaining and supporting
means 38 extending longitudinally within flow meter housing 24 for
supporting stator means 34 and rotor means 28 within meter housing
24. Retainer 38 includes a clip or retaining mechanism 40 for holding
retainer 38 within the bore of meter housing 24.
FIGS. 2 and 3 show in detail stator retaining and supporting means
in the form of retainer 38. Retainer 38 comprises a left end 42
substantially to the left of rotor 28 as seen in FIG. 1 a right
end 44 substantially to the right of rotor 28 as seen in FIG. 1
and an arcuate elongate spine 46 extending from end to end of retainer
38. In general, the specific embodiment of FIG. 2 has left end 42
and right end 44 as mirror images of each other about a plane through
a geometric center 48 of the retainer 38 transverse to the retainer
38. Similarly, a vertical plane parallel to fluid flow 22 and bisecting
retainer 38 would produce substantial mirror images. Furthermore
a horizontal plane extending parallel to fluid flow 22 and through
geometric center 48 would generally bisect retainer 38 into top
and bottom portions producing substantial mirror images except for
a scission 50 defined by first and second spaced apart ends 50a
and 50b extending the length of retainer 38 opposite spine 46 to
be described below.
The shape of retainer 38 can be more readily perceived by viewing
a transverse cross section of the retainer 38 in the direction shown
by line 3--3 of FIG. 2 and shown in FIG. 3. In cross section, retainer
38 has various convolutions and is substantially in the form of
a bowtie shown in FIG. 3 standing on end having top and bottom parts
in the form of a first side 46a for contacting one portion of the
flow channel wall and a second side 62a for contacting a second
portion of the flow channel walls. The top and bottom parts include
outer portions substantially arcuate with a radius of curvature
r, and have a center portion connecting the top part and the bottom
part comprising oppositely facing, substantially vertical semicircles
of radius r', where radius r' is less than radius r. To put it another
way, the cross section of retainer 38 is in the form of upper and
lower isosceles triangles 52 and 54 respectively, whose respective
angles formed by the two equal sides are oppositely facing, whose
respective third sides opposite the angles are arcuate and oppositely
facing having radius r (where D is approximately twice r) and where
a circle 56 of radius r' less than r is superimposed on the triangles
52 and 54 at their junction such that radius r and radius r' have
common origins on a geometric center 48. In such a form, retainer
38 is symmetric about vertical and horizontal planes passing through
the center or origin of the radii r and r'.
The structure of retainer 38 comprises for the most part upper
and lower triangular portions 52 and 54 respectively, and central
semicircular portions 56 constituting means for interconnecting
the first and second sides, all extending longitudinally the length
of retainer 38. Upper triangular portion 52 is integral with the
upper ends of central semicircular portions 56. The lower ends of
semicircular portions 56 are integral with lower triangular portion
54. The semicircular portions include a first arcuate portion 56a
and a second arcuate portion 56b.
Upper triangular portion 52 is composed of spine 46 formed from
the third side of the upper isosceles triangle and extending longitudinally
the length of the retainer 38 and upper radial wall portions 58
formed from the two equal sides of the upper isosceles triangle
and substantially perpendicular to spine 46 at their respective
points of intersection with spine 46. The wall portions comprise
means in the form of a flange portion 58a for joining the first
side to the first arcuate portion and means in the form of a flange
portion 58b for joining the first side to the second arcuate portion.
Wall portions 58 extend at their upper ends substantially radially
from spine 46 inwardly toward the common origin and preferably at
right angles to each other.
At a distance r' from the common origin of r and r', each of the
lower reaches of wall portions 58 substantially perpendicularly
intersect oppositely facing central semicircular portions 56 formed
from the portions of the circle of radius r' superimposed on the
upper and lower isosceles triangles at their junction with the latter.
Lower triangular portion 54 includes lower radial wall portions
60 formed from the two equal sides of the lower isosceles triangle
extending perpendicularly at their convergent ends from the lower
edges of the respective central semicircular portions 56 outward
at right angles to each other from the common origin to respective
lower arcuate portions 62 formed from the third side of the lower
isosceles triangle. The lower radial wall portions comprise means
in the form of a flange portion 60a for joining the second side
to the first arcuate portion 56a and means in the form of a flange
portion 60b to joining the second side to the second arcuate portion
56b. Upper and lower radial portions 58 and 60 respectively, would
intersect at right angles if extended inward to a common center
48. Lower arcuate portions 62 are substantially perpendicular to
respective lower perpendicular wall portions 60 at the respective
points of interaction with the latter and extend inward along an
arc of radius r toward each other. Lower arcuate portions 62 extend
longitudinally the length of retainer 38 and have radii of curvature
r. Lower arcuate portions 62 complement spine 46 but for a gap in
the form of scission 50 longitudinally bisecting the retainer 38
into two halves symmetric about a vertical plane through geometric
center 48 parallel to fluid flow. Each side of the semicircular
portions 56 of the retainer 38 extends in a convex arc from the
respective upper radial wall portions 58 to the lower radial wall
portions 60.
Retainer 38 of FIG. 2 preferably has two pairs of apertures comprising
left stator support locking slot pair 64 and right stator support
locking slot pair 66 for engaging outwardly extending flanges 63
(FIG. 5) on extensions of cones 36. Left locking slots 64 are located
approximately midway between the end of left end 42 and the geometric
center 48 and right locking slots 66 are located approximately midway
between the end of right end 44 and the geometric center 48. The
locking slots extend vertically downward from respective parts of
the upper radial wall portions 58 through central semicircular portions
56 and into the respective parts of lower radial wall portions 60.
In order to accommodate rotor means 28 retainer 38 has rotor openings
68 disposed about each side of spine 46 and separating left end
42 from right end 44. Rotor openings 68 extend from respective sides
of spine 46 to the lowest portion of lower radial wall portions
60. Therefore, if rotor means 28 and stator means 34 are to be inserted
within retainer 38 retainer 38 must be dimensioned to allow rotor
means 28 to extend from geometric center 48 to just within the underside
of spine 46 in one direction and to just within scission 50 in the
other direction. Therefore, the radius of the rotor is necessarily
less than radius r of FIG. 3. In final assembly, rotor means 28
is disposed about stator means 34 and retainer 38 is disposed within
flow meter housing 24 parallel to flow 22.
To optimize linearity of response of the meter or indicator during
various flow conditions, retainer 38 of FIGS. 2 and 3 has linearity
adjusting trim tabs 70 on the upper radial wall portions 58 and
lower radial wall portions 60 on the left end 42 adjacent rotor
openings 68. These are placed preferably upstream from rotor means
28 in order to affect the flow as the fluid passes rotor means 28.
These can be adjusted as desired to achieve optimum linearity.
As mentioned above, retainer 38 has an S-shaped retaining mechanism
in the form of a clip 40 in the upstream end of retainer 38 which
extends outwardly from spine 46 to fit into a perimetrical groove
72 (FIG. 1) on the inside of flow meter housing 24. Retaining mechanism
40 fits within groove 72 to maintain retainer 38 and rotor means
28 in a fixed axial position relative to flow meter housing 24.
Significantly, retainer 38 is preferably fabricated from a rectangular
sheet of spring material. Retainer 38 is stamped from a rectangular
sheet, as shown in FIG. 4 to obtain an inchoate retaining mechanism
40 left and right stator support locking slots 64 and 66 respectively,
a spine 46 and rotor openings 68. Subsequent to stamping, retainer
38 is rolled into the form shown in FIGS. 2 and 3. Clip 40 is formed
prior to insertion of the flow meter combination into the housing
24.
The rotor means 28 and stator means 34 to be used in conjunction
with the aforementioned embodiment of retainer 38 in FIG. 2 is shown
in FIG. 5. Rotor means 28 is mounted coaxially with respect to stator
means 34 and is mounted at the midpoint thereof. Rotor means 28
includes vanes 30 and rotor hub 32 the substantial portion of the
vanes 30 and hub 32 having a radius r.sub.1. Radius r.sub.1 is less
than radius r, the distance from the geometric center 48 to spine
46 of retainer 38 for example. Rotor means 28 rotates about a shaft
35 which in turn is supported on each end by cones 36. Preferably,
the outside diameter of the upstream edge of hub 32 is slightly
less than the maximum outside diameter of the adjacent cone. Each
cone 36 includes a right circular cylindrical portion 74 immediately
adjacent the rotor hub 32 and a nose cone portion 76 converging
from the cylindrical portion 74 to a more sharply convergent end
portion 78 further removed from rotor hub 32. The cones are preferably
shaped to ensure laminar flow at the rotor portion of the assembly,
and also to minimize the force of the fluid flow on the downstream
cone. The final convergent end portion 78 terminates in a cylindrical
portion 80 of radius r" slightly greater than r'. Cylindrical
portion 80 extends longitudinally from cone portion 76 to an end
flange portion 63 of radius r.sub.3 where r.sub.3 is greater than
r". Preferably, the length of each cone is in a 2:1 ratio to
the diameter of the cylindrical portion 80. Thus, stator means 34
includes a shaft 35 a cone section 36 and a flanged cylindrical
portion 80 retained by retainer 38. Therefore, when the cylindrical
portion 80 is inserted in retainer 38 it is enclosed and held via
spring compression by the central semicircular portions 56 of radius
r' and securely held thereby since r" is slightly greater than
r'.
As stator means 34 is inserted into retainer 38 the cylindrical
portions 80 of stator means 34 are held in retainer 38 by spring
compression forces and by the interlock of flanges 63 with locking
slot pairs 64 and 66. As a result, rotor means 28 and stator means
34 are rigidly suspended by retainer 38 within flowmeter housing
24 and axial movement of rotor means 28 is thereby precluded. Furthermore,
the diameter D is now slightly less than twice radius r because
radius r has increased upon insertion of the cones of radius r"
into retainer 38.
In final assembly, the rotor 28 stator 34 and retainer 38 combination
is held within flowmeter housing 24 by the combination of clip 40
engaging groove 72 in flowmeter housing 24 and by the spring expansion
forces created in retainer 38 when the combination is inserted into
the flowmeter housing 24. The expansion forces are created due to
the fact that the inside diameter D of flowmeter housing 24 is slightly
less than twice the radius r with the cones in place.
Another embodiment of flow meter assembly 20 shown in FIGS. 2 and
3 is the combination shown in FIG. 6 of rotor means 28 stator means
34 and a two-piece retainer 38. The shape of the two-piece retainer
38 is the same as for the one piece. However, in this embodiment,
the two-piece retainer comprises a left retaining mechanism 83 on
the upstream end of the left piece and a right retaining mechanism
84 on the downstream end of the right piece. Linearity adjusting
trim tabs 70 are placed on the downstream portion of the left piece.
Trim tabs 70 are placed on the upper radial wall portions 58 and
lower radial wall portions 60 (FIG. 7). This embodiment in FIG.
6 of the rotor means 28 stator means 40 and the retainer combination
is significant in that it also contributes to linearity of meter
response to changes in flow conditions.
The significance of the linearity adjusting trim tabs 70 is shown
in the graph of FIG. 8. The graph is an empirical plot of flow pulse
output per unit volume per unit time as a function of flow rate
in gallons per minute. The ideal response is represented by dashed
line 85 and shows a linear relationship between the flow pulses
produced at the magnetic field sensor and the actual flow conditions
to be measured. The lower curve 86 shows the relationship for a
retainer without trim tabs and the upper curve 88 shows the curve
for a retainer with trim tabs in position for optimum linearity.
Vertical lines 90 show the limits of the nominal flow range for
a given flow system. Curve 88 shows that the use of linearity adjusting
trim tabs 70 enhances the linear response of the meter to flow changes
by more closely approximating ideal conditions. The trim tabs are
bent in such a way that the flow impacts the rotor vanes in a direction
more nearly normal thereto.
The assembly of the flowmeter apparatus is accomplished first by
spreading scission 50 of retainer 38 and inserting stator means
34 comprising nose cone portions 76 and cylindrical portions 80.
Keeping the scission 50 separated, the assembled rotor 28 shaft
35 and appropriate bearings are then inserted between stator means
34. The shaft 35 must be twisted or walked into cone portions 76
because the length of shaft 35 is preferably slightly greater than
the distance between the inside surfaces of cone portions 76. Thereafter,
the rotor 28 stator 34 and bearings (not shown) are adjusted as
desired with an adjust screw (not shown) setting the bearing tolerances.
Retainer 38 is then allowed to return to a compressive configuration.
With the rotor 28 and stator means 34 inserted, the retainer 38
is in a slightly expanded configuration because the radius r"
is slightly greater than radius r'. Therefore, stator means 34 is
retained and supported by retainer 38 via the compressive spring
forces and preferably by the interlocking flanges 63 and the respective
locking slot pairs 64 and 66.
The meter and retainer 38 combination is then inserted into flowmeter
housing 24 by squeezing the lower triangular portion 54 and working
the combination into flowmeter housing 24. Upon squeezing, upper
and lower radial portions 58 and 60 respectively, flex so that
the combination may be inserted into housing 24. As a result, the
combination is retained in flowmeter housing 24 by a combination
of expansive spring forces created in retainer 38 and by clip 40.
The expansive forces in retainer 38 result from the fact that the
inside diameter D of flowmeter housing 24 is slightly less than
twice the radius r of retainer 38 with the cones in place. Therefore,
when the lower triangular portion 54 is squeezed, the combination
inserted into flowmeter housing 24 and the lower triangular portion
54 released, the expansive spring forces in retainer 38 force the
convolutions of retainer 38 out to the inside walls of flowmeter
housing 24. The several trim tabs 70 can be adjusted to optimize
linearity of response of the meter or indicator to flow changes.
Assembly and adjustment for the two-piece retainer is similar to
the process described above.
The retainer 38 in the above-described embodiments provides an
easily and inexpensively manufactured retainer and one that is easily
assembled. The resulting flow meter provides optimum results in
in-line flow measurements and represents a flow meter retainer which
is a significant improvement over previous retainers.
It should be noted that the above are preferred configurations
but others are foreseeable. The described embodiments of the invention
are only considered to be preferred and illustrative of the inventive
concept; the scope of the invention is not to be restricted to such
embodiment. Various and numerous other arrangements may be devised
by one skilled in the art without departing from the spirit and
scope of the invention. For example, other shapes are foreseeable
which would exert both a compressive force and a dilating force.
Similarly, linearity may be achieved by molding the retainer differently
without requiring trim tabs. The retaining mechanism or clips may
also be varied in structure and method of application. Furthermore,
the retainer need not be formed from a sheet but merely from a skeleton
frame. |