U.S. patent application number 11/640052 was filed with the patent office on 2008-06-19 for optic spacing nubs.
This patent application is currently assigned to Sol Focus, Inc.. Invention is credited to Michael Milbourne.
Application Number | 20080142000 11/640052 |
Document ID | / |
Family ID | 39525649 |
Filed Date | 2008-06-19 |
United States Patent
Application |
20080142000 |
Kind Code |
A1 |
Milbourne; Michael |
June 19, 2008 |
Optic spacing nubs
Abstract
A solar energy system, including a front panel and at least two
mirrors, is provided. The mirrors are used to focus light onto a
photoconductive cell. In the preferred embodiment, three or more
nubs are an integral part of at least one of the mirrors. When the
system is assembled, these nubs are configured between the panel
and a mirror to provide a substantially uniform gap for an
adhesive. The mirror is secured to the panel by the adhesive. Thus,
the nubs assist with desired attachment and alignment of a mirror
to the panel in the solar energy system.
Inventors: |
Milbourne; Michael; (El
Granada, CA) |
Correspondence
Address: |
THE MUELLER LAW OFFICE, P.C.
12951 Harwick Lane
San Diego
CA
92130
US
|
Assignee: |
Sol Focus, Inc.
Palo Alto
CA
|
Family ID: |
39525649 |
Appl. No.: |
11/640052 |
Filed: |
December 15, 2006 |
Current U.S.
Class: |
126/688 |
Current CPC
Class: |
F24S 2025/601 20180501;
Y02E 10/52 20130101; F24S 23/72 20180501; F24S 23/79 20180501; Y02E
10/47 20130101; F24S 80/50 20180501; H01L 31/0547 20141201; H01L
31/0543 20141201; F24S 25/00 20180501 |
Class at
Publication: |
126/688 |
International
Class: |
F24J 2/10 20060101
F24J002/10 |
Claims
1. A solar power unit, comprising: a substantially planar surface;
a primary mirror radially symmetric about a first axis, said
primary mirror having a perimeter wherein at least a portion of
said perimeter is attached to said planar surface; a secondary
mirror radially symmetric about a second axis, said secondary
mirror having a mounting surface wherein at least a portion of said
mounting surface is attached to said planar surface; three nubs on
said mounting surface, said nubs having nub heights, wherein said
nub heights are substantially equal; and an adhesive substance;
wherein said secondary mirror is secured to said planar surface by
said adhesive substance, and wherein said nubs provide a
substantially uniform gap between said mounting surface and said
planar surface for said adhesive substance.
2. The solar power unit of claim 1, wherein said nubs are integral
to said secondary mirror.
3. The solar power unit of claim 1, wherein said primary mirror and
said secondary mirror focus light on a photovoltaic cell.
4. The solar power unit of claim 1, wherein said nub heights
determines the bond thickness of said adhesive.
5. The solar power unit of claim 1, wherein said first axis is
coaxial to said second axis.
6. A method of attaching and aligning a mirror with integral nubs
to a panel of a solar power unit, comprising: dispensing an
adhesive onto said panel; positioning said mirror over said panel;
placing said mirror with said integral nubs in contact with said
adhesive; distributing said adhesive; and confirming contact of
said nubs with said panel; wherein said integral nubs have nub
heights, and wherein said nub heights provide a substantially
uniform gap in which to distribute said adhesive substance.
7. The method of claim 6, wherein said mirror is a curved primary
mirror with a perimeter, wherein said nubs are configured on said
perimeter of said primary mirror, and wherein said nub heights are
substantially equal.
8. The method of claim 7, wherein four nubs are configured on said
perimeter of said curved primary mirror.
9. The method of claim 6, wherein said mirror is a curved secondary
mirror with a mounting surface, wherein said nubs are configured on
said mounting surface of said secondary mirror, and wherein said
nub heights are substantially equal.
10. The method of claim 9, wherein three nubs are configured on
said mounting surface of said curved secondary mirror.
11. The method of claim 6, wherein said distributing of said
adhesive comprises rotating said mirror.
12. The method of claim 6, wherein said distributing of said
adhesive comprises compression.
13. A solar energy system, comprising: a panel; a mirror having a
mounting surface; three nubs with nub heights, wherein said nubs
are integral to said mounting surface of said mirror; and an
adhesive substance, wherein said mirror is secured to said panel by
said adhesive substance, and wherein said nub heights provide a
substantially uniform gap between said panel and said mounting
surface of said mirror.
14. The solar energy system of claim 13, wherein said nub heights
determine the bond thickness of said adhesive substance.
15. The solar energy system of claim 13, wherein said mirror is a
curved primary mirror with a perimeter, wherein said nubs heights
are substantially equal, and wherein said nubs are configured on
said perimeter of said primary mirror.
16. The solar energy system of claim 13, wherein said mirror is a
curved secondary mirror with a mounting surface, wherein said nub
heights are substantially equal, and wherein said nubs are
configured on said mounting surface of said secondary mirror.
17. The solar energy system of claim 13, wherein said mirror
directs light to a photovoltaic cell.
18. The solar energy system of claim 13, wherein said mirror is
symmetric about a first axis; and further comprising a secondary
mirror symmetric about a second axis substantially coaxial to said
first axis, said secondary mirror having a mounting surface wherein
at least a portion of said mounting surface is attached to said
panel.
19. A solar energy system comprising; a panel; a pressed optic
having a mounting surface; multiple nubs with nub heights, wherein
said nubs are integrally formed on said mounting surface; an
adhesive substance, wherein said pressed optic is secured to said
panel by said adhesive substance, and wherein said nub heights
establish a spacing between said mounting surface and said
panel.
20. The solar energy system of claim 19, wherein said pressed optic
is a mirror.
21. The solar energy system of claim 19, wherein said pressed optic
is a lens.
22. The solar energy system of claim 19, wherein said nubs assist
in alignment of said pressed optic with said panel.
Description
BACKGROUND OF THE INVENTION
[0001] It is generally appreciated that one of the many known
technologies for generating electrical power involves the
harvesting of solar radiation and its conversion into direct
current (DC) electricity. Solar power generation has already proven
to be a very effective and "environmentally friendly" energy
option, and further advances related to this technology continue to
increase the appeal of such power generation systems. In addition
to achieving a design that is efficient in both performance and
size, it is also desirable to provide power units and corresponding
solar systems that are characterized by reduced cost and increased
levels of mechanical robustness.
[0002] Solar concentrators are solar energy generators which
increase the efficiency of conversion of solar energy to DC
electricity. Solar concentrators which are known in the art utilize
parabolic mirrors and Fresnel lenses for focusing the incoming
solar energy, and heliostats for tracking the sun's movements in
order to maximize light exposure. A new type of solar concentrator,
disclosed in U.S. patent application Ser. No. 11/138,666, entitled,
"Concentrator Solar Photovoltaic Array with Compact Tailored
Imaging Power Units" utilizes a front panel for allowing solar
energy to enter the assembly, with a primary mirror and a secondary
mirror to reflect and focus solar energy onto a solar cell. A back
panel and housing enclose the assembly and provide structural
integrity. The surface area of the solar cell in such a system is
much smaller than what is required for non-concentrating systems,
for example less than 1% of the entry window surface area. Such a
system has a high efficiency in converting solar energy to
electricity due to the focused intensity of sunlight, and also
reduces cost due to the decreased amount of costly photovoltaic
cells required. Because the receiving area of the solar cell is so
small relative to that of the power unit, the ability of the
mirrors to accurately focus the sun's rays onto the solar cell is
important to achieving the desired efficiency of such a solar
concentrating system.
[0003] In this type of solar concentrator panel, one of the key
factors in mirror alignment is the process by which a mirror is
adhered to the front or back panel. Uncontrolled adhesive
application may result in variations in adhesive thickness across
the bonding area of the mirror, which in turn may affect the
alignment of the mirror as well as the bond strength which is
important for withstanding high temperature conditions in the solar
power assembly. In another instance, the proper amount of adhesive
may be applied, but pressing the mirror and panel together in an
uncontrolled manner may cause the adhesive to be exuded beyond the
desired bond area and into the clear aperture of the system.
Difficulty in attaining consistent adhesive application can
decrease manufacturability and thus the commercial feasibility of
such a design.
[0004] One solution to this problem of mirror alignment and
attachment is using spacers to set the distance between the mirror
and panel to which it is to be bonded. U.S. Pat. No. 5,433,911
entitled "Precisely Aligning and Bonding a Glass Cover Plate Over
an Image Sensor" discloses an electronics package which includes a
spacer plate, a glass cover plate, an image sensor, and a carrier.
In order to achieve the tight tolerances for spacing and
parallelism which are required to align the various planar
components in this assembly, precision ground and lapped spacers
are used. While the spacers result in the desired alignment and
spacing between the plates and image sensor, the precision to which
they must be made and the accuracy with which they are mounted
increase the labor and cost of the assembly. The fact that the
spacers are separate components also adds complexity to the
manufacturing process.
[0005] Spacer particles are another approach to setting uniform
distances between surfaces. U.S. Pat. No. 7,102,602 entitled
"Doubly Curved Optical Device for Eyewear and Method for Making the
Same" discloses a pair of substrates sealed together by a fluid
material with spacers disbursed therein. The substrates thus have a
uniform controlled distance there between due to the presence of
the spacers. The spacers may be placed between the substrates prior
to application of the fluid, or they may be mixed into the fluid
material first and then applied to the unopposed substrates. While
spacer particles are useful in setting the gap of a critical
dimension, an assembly with more than one critical dimension would
require specifically-sized spacer particles for each application.
Such a situation raises the likelihood for potential manufacturing
errors should one spacer size be mistakenly used in place of
another size. Furthermore, each batch of adhesive would require
verification of the proper ball diameter, and the step of mixing
spacers into the fluid or adhesive adds labor to the manufacturing
process.
[0006] Thus it is desirable to facilitate reliable alignment and
attachment of the mirrors in a solar energy system in a manner
which enhances manufacturability and therefore reduces overall cost
and improves mechanical robustness.
SUMMARY OF THE INVENTION
[0007] The present invention is a solar energy system, including a
front panel and at least one mirror. In the preferred embodiment,
three or more nubs are an integral part of the mounting surface of
the mirror. When the system is assembled, these nubs are configured
between the panel and the mirror and provide a substantially
uniform gap for an adhesive. The mirror is secured to the panel by
the adhesive. Thus, the nubs assist with desired attachment and
alignment of the mirror to the panel in the solar energy
system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 provides a perspective illustration of an exemplary
embodiment of the solar power unit;
[0009] FIG. 2 shows a cross-sectional view of the assembly of FIG.
1, with additional housing components;
[0010] FIG. 3 illustrates a side view of a secondary mirror with
nubs mounted onto a front panel;
[0011] FIG. 4 provides a plan view of one embodiment of nubs on a
secondary mirror;
[0012] FIG. 5A gives a perspective view of an alternative
embodiment of a secondary mirror;
[0013] FIG. 5B is a cross-sectional view of the embodiment of FIG.
5A;
[0014] FIG. 6 shows a perspective view of an exemplary primary
mirror with nubs on its perimeter;
[0015] FIG. 7 shows an exploded perspective view of an embodiment
of the assembly process for aligning and attaching a secondary
mirror onto a front panel; and
[0016] FIG. 8 is a simplified flowchart illustrating basic steps in
the fabrication process.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0017] Reference now will be made in detail to embodiments of the
disclosed invention, one or more examples of which are illustrated
in the accompanying drawings. Each example is provided by way of
explanation of the present technology, not limitation of the
present technology. In fact, it will be apparent to those skilled
in the art that modifications and variations can be made in the
present technology without departing from the spirit and scope
thereof. For instance, features illustrated or described as part of
one embodiment may be used on another embodiment to yield a still
further embodiment. Thus, it is intended that the present subject
matter covers such modifications and variations as come within the
scope of the appended claims and their equivalents.
[0018] The alignment and attachment means described in this
disclosure are based on a solar power unit design incorporating
optically aligned primary and secondary mirrors. The solar power
unit design is described in detail in related, co-pending patent
applications as follows: (1) "Concentrator Solar Photovoltaic Array
with Compact Tailored Imaging Power Units;" Ser. No. 11/138,666;
filed May 26, 2005; and (2) "Optical System Using Tailored Imaging
Designs;" Ser. No. 11/351,314; filed Feb. 9, 2006, which claims
priority from U.S. provisional patent application 60/651,856 filed
Feb. 10, 2005; all of which are hereby incorporated by reference as
set forth in full in this application for all purposes.
[0019] Note that variations on the design described in the priority
applications may be achieved by modifing specific steps and/or
items described herein while still remaining within the scope of
the invention as claimed.
[0020] With reference to FIG. 1, a simplified perspective view of
an exemplary solar power unit 100 is shown. The main optical
elements of the power unit 100 are a protective front panel 110, a
primary mirror 120, a secondary mirror 130, and a receiver assembly
140. Note that for commercial application, the single power unit
100 would typically be replicated to form an array of adjoining
power units as part of a complete solar panel. Protective front
panel 110 is a substantially planar surface, such as a window or
other transparent covering, which provides structural integrity for
a power unit and protection for other components thereof In a
preferred embodiment, front panel 110 is composed of glass;
however, any type of transparent or transmissive planar sheet, such
as polycarbonate, may be suitable for use in the solar power unit.
Sunlight enters the solar unit 100 through front panel 110 and
reflects off of primary mirror 120 to secondary mirror 130, where
it is further reflected and focused onto receiver assembly 140. In
the preferred embodiment, receiver assembly 140 houses an optical
rod and a photovoltaic cell where the intensified sunlight is
converted into electrical energy.
[0021] In reference still to FIG. 1, primary mirror 120 and
secondary mirror 130 are substantially co-planar, at least a
portion of both mirrors being in contact with front panel 110. In
the depicted configuration, primary mirror 120 is generally
circular such that the entire perimeter 160 of primary mirror 120
is contact with front panel 110. Primary mirror 120 is preferably a
second surface mirror using, for example, silver, and slump-formed
from soda-lime glass. In one exemplary embodiment, primary mirror
120 may have a diameter of approximately 280 mm and a depth of
approximately 70 mm. Secondary mirror 130 is also generally
circular, and is typically a first surface mirror using silver and
a passivation layer formed on a substrate of soda-lime glass. In a
preferred embodiment, secondary mirror 130 may have a diameter of
approximately 50 mm. Nubs 150, to be described in further detail in
reference to later figures, are present on the surface of secondary
mirror 130 which is facing panel 110.
[0022] Turning now to FIG. 2, a cross-sectional view of a solar
power unit 200 is shown. The same elements given in FIG. 1 of a
front panel 210, primary mirror 220, secondary mirror 230 with nubs
250, and receiver assembly 240 are shown. In the view provided in
FIG. 2, however, the additional components of a housing 260 and
back panel 270 are illustrated in basic form. Housing 260 may be
built from more than one piece of material, such as but not limited
to stamped metal or polyethylene terephthalate (PET) and is
designed to accommodate the total number of power units provided in
a given solar energy system. The housing contains a lip 262 that
allows the front panel 210 to be mounted, preferably with a rubber
gasket (not shown) to seal the edges of panel 210. Back panel 270,
which may also be referred to as a base plate, serves as a heat
dissipation element for the solar unit and may be formed of
phosphor-bronze or an aluminum alloy. Housing 260 and back panel
270 may be secured to the solar energy system by bolts, screws, or
similar means (not shown) well-known in the art.
[0023] FIG. 3 provides a closer view of secondary mirror 330 and
front panel 310. Nubs 350 are shown as projections from mounting
surface 340 of secondary mirror 330. Nubs 350 can be separate
pieces from the secondary mirror 330, or are preferably integrally
fabricated as part of secondary mirror 330. By having nubs 350
integral to secondary mirror 330, any manufacturing tolerances
resulting from either fabricating separate nub components or
adhering nubs 350 to surface 340 are eliminated. Integral nubs
fabrication could entail the nubs 350 being molded into the shape
of the mirror 330 during the mirror pressing process.
Alternatively, nubs 350 could be separate components that are
insert-molded into the mirror during the pressing process. The
height of nubs 350 are substantially equal, which advantageously
sets a substantially uniform gap between mounting surface 340 of
secondary mirror 330, and bottom surface 360 of front panel 310.
This uniform gap thereby substantially aligns secondary mirror 330
in parallel to front panel 310. In a typical embodiment, the
distance between mounting surface 340 of secondary mirror 330 and
back surface 360 of the front panel 310 is 50 microns to 2.0 mm.
Secondary mirror is secured to front panel 310 by adhesive 320,
which fills the space between surfaces 340 and 360. In a preferred
embodiment, silicone adhesive is used; however, any adhesive
(epoxies, RTV, acrylics, etc.) which is appropriate for the
substrates and operating conditions of this assembly may be
utilized.
[0024] FIG. 4 next illustrates a plan view of the mounting surface
of secondary mirror 410. In this embodiment, three nubs 420 are
shown to be equally distributed near the circumference 430 of the
mirror 410. The presence of three nubs 420 establishes the planar
stability of secondary mirror 410. Alternatively, more than three
nubs may be used for aiding the visual inspection that nubs 420 are
contacting the front panel (surface 360 of FIG. 3), or for
mechanical redundancy should any of the nubs 410 be damaged during
the manufacturing process. While the placement of nubs 410 near
circumference 430 as shown is desirable for increasing planar
stability, the nubs may be placed in other configurations away from
the circumference. For example, a nub positioned in the center of
the secondary mirror 410 could be used to help center the secondary
mirror onto the front panel. In another instance, the placement of
nubs can assist in outlining the zones in which adhesive is to be
dispensed.
[0025] Still referring to FIG. 4, nubs 420 are shown to be
circular. However, other shapes may be used, such as rectilinear
footprints, or even a hemispherical nub wherein the contact surface
with the front panel would be a point. The specific cross-sectional
area of nubs 420 chosen would be determined by the level of visual
inspection desired as well as by the manufacturing limitations of
the process by which the secondary mirror is fabricated. Also to be
taken into account is that the shape and size of the nubs should
not be conducive to damaging the panel, which may be glass, against
which they are being placed. Furthermore, the impact of the total
surface area occupied by the nubs would need to be considered so as
not to impact the bond strength of this joint.
[0026] FIG. 5A depicts an alternative embodiment of the secondary
mirror 510. While previous embodiments have shown secondary mirror
510 to be a solid entity, FIG. 5 shows secondary mirror 510 in the
case where it is hollow. Moreover, an alternative nubs embodiment
consisting of four nubs being present and equally distributed
around the mounting surface 530 of secondary mirror 510 is given.
In this exemplary embodiment depicted in cross-section in FIG. 5B,
nubs 520 are integral to secondary mirror 510. That is, nubs 520
are formed during the fabrication of secondary mirror 510. The nubs
520 are shown to be cylindrical in nature, but as previously
described, they may take the form of rectilinear or other shapes as
desired to facilitate fabrication of the secondary mirror, or to
aid in the process of assembling the solar power unit. Edges 540 of
nubs 520, in this embodiment as well as others described in this
disclosure, are preferably filleted to prevent damage to the front
panel when the mirror 510 is placed in contact with the front
panel.
[0027] FIG. 6 illustrates a further embodiment of primary mirror
610. In this embodiment, primary mirror 610 is shaped such that
there are truncated sections 620 of the curved primary mirror 610.
The truncated sections advantageously allow adjacent power units to
fit tightly together in a solar array, thus maximizing the number
of power units which can be packed into a solar energy system. For
example, in the depicted configuration where there are four
truncated sections, adjacent power units would fit together to form
an orthogonal grid. The peaks of the truncated sections terminate
in flat mounting tabs 630, upon which nubs 640 are placed or
formed. In the truncated design, only the mounting tabs 630 with
the nubs 640, rather than the entire perimeter of primary mirror
610, are in contact with the front panel. The heights of nubs 640
are substantially equal, thus setting a substantially uniform gap
for adhesive to be applied, and thus substantially aligning the
primary mirror to the front panel.
[0028] Returning to the secondary mirror, FIG. 7 gives an exploded
view of a template tool being used in the manufacturing process to
secure secondary mirror 710 to front panel 720. Template tool 730
includes a precision cutout 740 for centering secondary mirror 710
over the transparent front panel 720. It should be appreciated that
for manufacturing an array of solar power units, the template tool
730 would incorporate multiple cutouts 740 for the multiple mirrors
in the array. Template tool 730 could also be a part of a larger
tool which includes additional functionality. While cutout 740
provides for proper planar positioning along the face of front
panel 720, nubs 750 ensure that the mounting surface 760 of
secondary mirror 710 is aligned substantially parallel to front
panel 720. That is, nubs provide alignment in the axis
perpendicular to the front panel. Placement of the mirror 710 onto
the front panel 720 could be achieved by automated machinery, in
which case the fixed spacing provided by the nubs would have
further importance in manufacturing reliability.
[0029] FIG. 8 is a simplified flowchart illustrating the basic
steps in securing a mirror to the front panel. In FIG. 8, flowchart
800 is entered at step 810. Step 820 is first performed to position
the template tool over the front panel. This can be accomplished by
registering the template tool with the front panel using visual,
mechanical, or other means well-known in the art (pin registration,
magnetic or other sensing, etc.). Next, if the nubs are not
integral to the mirror, step 830 is performed to fix the nubs onto
the mirror. In step 840, adhesive is dispensed onto either the
front panel or mirror. Typically, the adhesive is dispensed in a
discrete location or locations such as lines or dots. In step 850,
the mirror is placed on the front panel through the aforementioned
cutout on the template tool. Step 860 is then performed to
distribute the adhesive over the mounting surface of the secondary
mirror. For example, in the case of a solid secondary mirror (FIG.
4), the adhesive could be first applied in two lines forming an "X"
in step 840. Then, rotating the mirror in step 860 would distribute
the adhesive across the circular mounting surface. In the case of a
hollow secondary mirror (FIG. 5A), the adhesive could be dispensed
in dots between the nubs. Rotation of the mirror in step 860 would
then distribute the adhesive around the perimeter of the mirror's
mounting surface. In an alternative embodiment, after the adhesive
is applied, compression may be used to distribute the adhesive
between the mounting surface of the mirror and the front panel.
This pressure could be applied through the mirror, through the
front panel or from both sides.
[0030] Still referring to FIG. 8, step 870 provides verification of
proper adhesion. In the preferred embodiment, after the adhesive
has been distributed the operator would verify in step 870 whether
the nubs are in full contact with the front panel. Verification
methods could include a qualitative visual check, or quantitative
means such as measurement of the mirror height before and after
bonding. Failure for all nubs to be in contact would imply that a
uniform adhesive gap has not been achieved, and that the mirror is
misaligned. In this case, step 880 calls for adjusting mirror
placement. Adjustment could involve such measures as applying more
pressure to the mirror or removing excess adhesive which may have
seeped under the nubs. Once it is verified that nubs are properly
in contact with the front panel, the subassembly is complete.
[0031] Although embodiments of the invention have been discussed
primarily with respect to specific embodiments thereof, other
variations are possible. Lenses or other optical devices might be
used in place of, or in addition to, the primary and secondary
mirrors or other components presented herein. For example, a
Fresnel type of lens could be used to focus light on the primary
optical element, or to focus light at an intermediary phase after
processing by a primary optical element. Beyond solar energy
systems, nubs may be used to align a lens in an optical assembly,
or to provide spacing with respect to mating components.
[0032] It may be possible to use non-planar materials and surfaces
with the techniques disclosed herein. Other embodiments can use
optical or other components for focusing any type of
electromagnetic energy such as infrared, ultraviolet,
radio-frequency, etc. There may be other applications for the
fabrication method and apparatus disclosed herein, such as in the
fields of light emission or sourcing technology (e.g., fluorescent
lighting using a trough design, incandescent, halogen, spotlight,
etc.) where the light source is put in the position of the
photovoltaic cell. In general, any type of suitable cell, such as a
photovoltaic cell, concentrator cell or solar cell can be used. In
other applications it may be possible to use other energy such as
any source of photons, electrons or other dispersed energy that can
be concentrated.
[0033] Steps may be performed by hardware or software, as desired.
Note that steps can be added to, taken from or modified from the
steps in this specification without deviating from the scope of the
invention. In general, any flowcharts presented are only intended
to indicate one possible sequence of basic operations to achieve a
function, and many variations are possible.
[0034] While the specification has been described in detail with
respect to specific embodiments of the invention, it will be
appreciated that those skilled in the art, upon attaining an
understanding of the foregoing, may readily conceive of alterations
to, variations of, and equivalents to these embodiments. These and
other modifications and variations to the present invention may be
practiced by those of ordinary skill in the art, without departing
from the spirit and scope of the present invention, which is more
particularly set forth in the appended claims. Furthermore, those
of ordinary skill in the art will appreciate that the foregoing
description is by way of example only, and is not intended to limit
the invention.
* * * * *