U.S. patent application number 13/615540 was filed with the patent office on 2013-01-10 for automated electropolishing process.
This patent application is currently assigned to ABBOTT CARDIOVASCULAR SYSTEMS, INC. Invention is credited to Anthony S. Andreacchi, Dan Joel Dirilo, Andreina P. Gomez, Han Juanta, Jessie Madriaga.
Application Number | 20130008780 13/615540 |
Document ID | / |
Family ID | 40801807 |
Filed Date | 2013-01-10 |
United States Patent
Application |
20130008780 |
Kind Code |
A1 |
Andreacchi; Anthony S. ; et
al. |
January 10, 2013 |
AUTOMATED ELECTROPOLISHING PROCESS
Abstract
An electropolishing system including an anode, a cathode, a
rolling block and a motion controller. The anode is configured to
removably retain a metal device to be electropolished, and may be
formed as a bar made from a solid cylindrical piece of metal or
other configurations, such as wires with hooks. The anode transfers
the electricity to the metal device while grooming the surface of
the metal device as it contacts the rolling block. The cathode may
be configured as a mesh and completes the electrical circuit. The
rolling block is formed from a relatively smooth, solid material
and positioned so as to allow the metal device to roll against the
surface of the block. The motion controller is configured to
provide vertical and horizontal movement of the anode and metal
device, using force transducers to control the compression of the
metal device against the rolling block.
Inventors: |
Andreacchi; Anthony S.; (San
Jose, CA) ; Gomez; Andreina P.; (Santa Clara, CA)
; Juanta; Han; (Milpitas, CA) ; Madriaga;
Jessie; (San Jose, CA) ; Dirilo; Dan Joel;
(Union City, CA) |
Assignee: |
ABBOTT CARDIOVASCULAR SYSTEMS,
INC,
Santa Clara
CA
|
Family ID: |
40801807 |
Appl. No.: |
13/615540 |
Filed: |
September 13, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12100991 |
Apr 10, 2008 |
|
|
|
13615540 |
|
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Current U.S.
Class: |
204/199 ;
204/198; 204/279; 204/297.16 |
Current CPC
Class: |
C25F 7/00 20130101; A61F
2/91 20130101; A61F 2240/001 20130101; C25F 3/24 20130101 |
Class at
Publication: |
204/199 ;
204/198; 204/279; 204/297.16 |
International
Class: |
C25F 7/00 20060101
C25F007/00; C25F 3/16 20060101 C25F003/16; B23H 3/04 20060101
B23H003/04 |
Claims
1. A system for electropolishing a metal device, comprising: a
reservoir for retaining an electrolyte solution; a cathode
subassembly disposed in the reservoir; a roller plate disposed in
the reservoir; an anode disposed between the cathode subassembly
and the roller plate, the anode being configured to removably
retain at least one metal device and being operably connected to a
positioning subassembly.
2. The system of claim 1, wherein the positioning subassembly
includes at least one force transducer and a vertical controller
for position the anode proximate the roller plate.
3. The system of claim 2, wherein the positioning subassembly
includes a longitudinal controller for positioning the anode along
the length of the roller plate.
4. The system of claim 1, further including a stent removably
secured to the anode.
5. The system of claim 1, wherein the anode is configured to
removably retain at least two stents.
6. The system of claim 1, further including a second cathode formed
from a mesh, the second cathode being disposed with a lumen of the
metal device and being connected to a source of electricity.
7. The system of claim 1, further including a second cathode formed
from a rod, the second cathode being disposed with a lumen of the
metal device and being connected to a source of electricity.
8. A system for electropolishing a medical device, comprising: a
reservoir for retaining an electrolyte solution; a cathode
subassembly disposed in the reservoir; a roller plate disposed in
the reservoir and configured as an anode; and a non-conducting rod
disposed between the cathode subassembly and the roller plate, the
non-conducting rod being configured to removably retain at least
one metal device and being operably connected to a positioning
subassembly.
9. The system of claim 8, wherein the positioning subassembly
includes at last one force transducer, a vertical controller for
contacting the metal device with the roller plate and a
longitudinal controller for positioning the anode along the length
of the roller plate.
10. The system of claim 9, further including a stent removably
secured to the non-conducting rod.
11. An apparatus for use in electropolishing a device, comprising:
a first wire having a proximal end connected to an electrical
source and a distal end configured to contact a medical device; and
a second wire having a proximal end connected to an electrical
source and a distal end configured to contact the medical
device.
12. The apparatus of claim 11, wherein the distal end of the first
wire is configured with a hook for removably retaining the medical
device and the distal end of the second wire is configured with a
hook for removably retaining the medical device.
13. The apparatus of claim 12, wherein the first wire and the
second wire are configured to contact and removably retain a
stent.
14. An apparatus for use in electropolishing a device, comprising:
an electrically conducting mandrel having a proximal end connected
to an electrical source and a distal end configured to contact a
medical device on at least two contact points on the medical
device; and a non-conducting mandrel for removably retaining the
medical device.
15. The apparatus of claim 14, wherein the distal end of the
electrically conducting mandrel is configured with a hook for
contacting the medical device.
16. The apparatus of claim 15, wherein the electrically conducting
mandrel is configured to contact and removably retain a stent.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional application of U.S. patent application
Ser. No. 12/100,991 entitled "Automated Electropolishing Process",
filed Apr. 10, 2008 which is incorporated herein by reference in
its entirety.
BACKGROUND
Background and Relevant Art
[0002] The present invention relates to devices, systems and
methods for electropolishing metallic material, and more
particularly to an anode/cathode system having a rolling block and
unique mandrel configurations.
[0003] Medical devices, such as intravascular stents, may be
constructed of a metal or polymer and generally cylindrical in
shape and hollow, are implanted within the vessel to maintain lumen
size. The stent acts as a scaffold to support the lumen in an open
position. Configurations of stents include a cylindrical sleeve
defined by a mesh, interconnected stents, or like segments.
Exemplary stents are disclosed in U.S. Pat. Nos. 4,739,762;
5,133,732; 5,292,33; 5,421,955 and 6,090,127, the contents of which
are hereby incorporated herein in their entirety by reference
thereto.
[0004] One method of making a stent is by using a machine
controlled laser to cut a thin walled tubular member, such as
stainless steel tubing, to remove portions of the tubing in the
desired pattern for the stent, leaving relatively untouched the
portions of the metallic tubing that are to form rings or other
patterns in the tubing. The stent may be manufactured by direct
laser cutting from a single metal tube using a finely focused laser
beam passing through a coaxial gas jet structure to impinge on the
working surface of the tube as the linear and rotary velocity of
the tube is precisely controlled. An exemplary system and process
for laser cutting may be found in U.S. Pat. No. 5,759,192, the
content of which is hereby incorporated herein in its entirety by
reference thereto. Further, other processes of forming stent rings
are possible and are known in the art, such as, but not limited to,
chemical etching, electronic discharge machining and stamping. An
exemplary system and process for chemical etching may be found in
U.S. Pat. No. 5,735,893, the content of which is hereby
incorporated herein in its entirety by reference thereto.
[0005] There is a need for, and what was heretofore unavailable, an
automated system and method for electropolishing medical devices,
such as laser cut stents. The present invention solves these and
other needs.
BRIEF SUMMARY
[0006] The apparatus and method of the present invention are
directed to automated electropolishing of metallic material, such
as, but not limited to, metal plates, biocompatible medical devices
and implants (for example, stents) and dental devices (for example,
bridges). The system of the present invention is configured to
automate the electropolishing process so as to reduce/eliminate
errors or defects due to operator handling while increasing
throughput, including eliminating or reducing the need for off-line
device grooming and rotation. The mandrels of the present invention
are configured to be used in any electropolishing process designed
for devices made from stainless steel, cobalt-chromium, nitinol,
and/or any other metal or alloy suitable for electropolishing.
[0007] The system of the present invention for electropolishing a
metal device includes a reservoir for containing an electrolyte
solution with a cathode subassembly and a roller plate disposed in
the reservoir. The system further includes an anode disposed
between the cathode subassembly and the roller plate. The anode
being configured to removably retain at least one metal device
(such as an implantable medical device) and being operably
connected to a positioning subassembly, such as a vertical and
longitudinal motion controller. The positioning subassembly
includes at least one force transducer, a vertical controller for
positioning the anode proximate to the roller plate and a
longitudinal controller for moving the anode along the length of
the roller plate. The anode may be configured to removably retain
one or more stents. The anode may be formed as a mandrel having one
or more hooks for single or dual-point contact with the stent, or
formed using other mandrel configurations (such as but not limited
to a cylindrical rod, coiled mandrel, or a spiral mandrel), all of
which may have differing degrees of effectiveness. A second cathode
formed from a mesh or rod may be disposed within the lumen of the
stent. Alternatively, a non-conducting rod may be used to removably
secure the device to be electropolished and the roller plate may be
connected to an anodic electrical source.
[0008] The method for electropolishing a metal device (such as an
implantable medical in accordance with the present invention
includes providing a reservoir containing an electrolyte solution,
a roller plate and a cathode. The process includes connecting the
cathode to a source of electricity and providing an anode disposed
between the cathode and the roller plate. The anode is connected to
a source of electricity and is operably connected to a positioning
subassembly. At least one medical device, such as a stent, may be
removably secured to the anode. The positioning subassembly is
activated so as to engage the medical device with the roller plate
and to move the medical device along a longitudinal axis of the
roller plate while electric current flows between the anode and the
cathode subassembly. After the electropolishing process is
completed, the positioning subassembly is further activated so as
to disengage the medical device from the roller plate and allow the
user to remove the medical device from the anode.
[0009] Some of the advantages of the system and method of the
present invention over current manufacturing processes may include:
(i) the stent is not handled by an operator during the polishing
process, thereby eliminating and/or reducing handling defects; (ii)
the process is automated, thereby eliminating and/or reducing
operator variability while increasing uniformity and consistency;
(iii) better control over operating parameters since the applied
current can be continuous or pulsed, the devices may not need be
removed between polishing cycles; (iv) the stent is in continuous
motion, thereby eliminating and/or reducing the need to flip and
rotate the stent between cycles, which reduces handling, polishes
the stent more uniformly; (v) the stent is continuously groomed,
reducing the probability of melted or burned strut defects.
[0010] The aforementioned and other features and advantages of the
invention will become further apparent from the following detailed
description of the presently preferred embodiments, read in
conjunction with the accompanying drawings. The detailed
description and drawings are merely illustrative of the invention
rather than limiting, the scope of the invention being defined by
the appended claims and equivalents thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic representation depicting the automated
electropolishing system of the present invention in the `loading`
position.
[0012] FIG. 2 is a schematic representation depicting the automated
electropolishing system of the present invention in the `run`
mode.
[0013] FIG. 3 is a schematic representation depicting the automated
electropolishing system of the present invention at the end of a
polishing run.
[0014] FIG. 4 is a schematic representation depicting the automated
electropolishing system of the present invention processing
multiple stents.
[0015] FIG. 5 is a schematic representation depicting an
alternative embodiment of the automated electropolishing system of
the present invention configured to selectively control and polish
the lumen of a metal device.
[0016] FIG. 6A is a photograph depicting a mandrel of the present
invention with a dual hook design being attached to an unpolished
stent.
[0017] FIG. 6B is a photograph depicting the stent in FIG. 6A after
electropolishing with the dual-hook mandrel.
[0018] FIG. 7 is a photograph depicting a single-arm, dual
point-of-contact electropolishing mandrel in accordance with the
present invention.
[0019] FIG. 8 is a photograph depicting an alternative embodiment
of an electropolishing mandrel of the present invention.
[0020] FIG. 9 is a SEM side view image of a stent with variable
thickness tubing on the lumen side of the stent that was
electropolished using a mandrel of the present invention.
[0021] FIG. 10 is a SEM end view image of the sidewalls of a stent
with variable thickness tubing on the lumen side of the stent that
was electropolished using a mandrel of the present invention.
[0022] FIG. 11 is a SEM perspective image of a stent
electropolished using a mandrel of the present invention.
DETAILED DESCRIPTION
[0023] The apparatus, system and method of the present invention
are configured to automatically groom and polish metallic material
in a single electropolishing process. The devices and processes are
designed to automate the electropolishing process so as to reduce
and/or eliminate errors or defects due to operator handling while
increasing throughput, including eliminating or reducing the need
for off-line device grooming and rotation. The mandrels of the
present invention are configured to be used in a system and process
configured for polishing devices made from stainless steel,
cobalt-chromium, nitinol and other alloys or metals that are
suitable for electropolishing.
[0024] In one embodiment, the system of the present invention is
designed to electropolish medical devices, such as, but not limited
to, stents, dental appliances and other biocompatible metal
implants. The system, although not optimal, could use a spiral
mandrel typical in prior art electropolishing systems to hold the
medical device during the polishing process or to provide the
electrical contact between the medical device and the power supply
(anodic connection). However, this would require thicker and
stiffer spiral mandrels than are currently being used. Instead of
the spiral mandrel, a straight rod is placed within the medical
device and is used to groom the medical device and provide the
electrical connection from the anode (+) power supply (attracts
negative ions; repels positively charged ions) through the medical
device. In other embodiments, the mandrels are formed with bends,
hooks or other configurations to removably engage the medical
device. Although the description and figures herein may be
specifically directed towards stents, the scope of the present
invention is not intended to be limited for use with such medical
devices and is applicable to electropolishing any metal
structure.
[0025] The general components of the stent electropolishing system
of the present invention are an anode, a cathode subassembly, a
rolling block and a positions subassembly, such as a vertical and
longitudinal motion controller. The anode is configured to
removably retain the stent (device to be electropolished), and may
be formed as a bar made from a solid cylindrical piece of metal.
The anode also conducts electricity and transfers the electricity
to the stent, while at the same time grooms the surface of the
stent as it contacts the rolling block. The cathode subassembly may
be configured as a mesh and completes the electrical circuit by
providing the electrical connection from the cathode (-) power
supply (attracts positively charged ions; repels negatively charged
ions). The rolling block (grooming bar) is configured and
positioned so as to allow the stent to roll against the surface of
the block and may be formed from a relatively smooth, solid piece
of polytetrafluoroethylene (PTFE, TEFLON), polyvinylidene fluoride
(PVDF, KYNAR) or other material that is resistant to corrosion from
the electropolishing solution. The motion controller is configured
to provide vertical and horizontal movement of the anode and device
to be polished. One or more force meters or transducers may be used
to control the tension or compression of the stent against the
rolling block. The anode, cathode subassembly and motion controller
may be connected to a programmable logic computer (PLC) or computer
configured to control the process parameters.
[0026] A stent suitable for use with the electropolishing mandrels,
systems and methods of the present invention may be configured with
a plurality of cylindrical elements connected by connecting
members, wherein the cylindrical elements have an undulating or
serpentine pattern. The stent, however, can have virtually any
pattern suitable for electropolishing. The stent may be made to be
either balloon expandable or self-expanding. The stent can be
formed from any of a number of materials including, but not limited
to, stainless steel alloys, nickel-titanium alloys (the NiTi can be
either shape memory or pseudoelastic), tantalum, tungsten, and
other biocompatible metal or alloy materials. Such materials of
manufacture are known in the art.
[0027] The stent may be manufactured by direct laser cutting from a
single metal tube using a finely focused laser beam. Other
processes of forming stent rings are possible and are known in the
art, such as, but not limited to, chemical etching, electronic
discharge machining and stamping. After laser cutting, the stent
rings may be electrochemically polished in an acidic aqueous
solution such as a solution of ELECTRO-GLO #300 (ELECTRO GLO Co.,
Inc. in Chicago, Ill.), which is a mixture of sulfuric acid,
carboxylic acids, phosphates, corrosion inhibitors and a
biodegradable surface active agent. Additional suitable
electropolishing solutions include various acids, such as, but not
limited to, HF, HC1, HNO3, H2504 and Phosphoric Acid (H3PO4).
[0028] Turning now to the drawings, in which like reference
numerals represent like or corresponding aspects of the drawings,
the automated electropolishing system 100 of the present invention
includes a stent 110 or other metal device to be electropolished
loaded onto an anode rod (bar) 120 that is contained along with a
cathode subassembly 130 and a rolling block (grooming pad) 140
within a housing 150. The housing is configured for retaining an
electropolishing solution, and may include inlet and outlet
fittings (not shown) for filling and emptying the solution. As
shown in FIG. 1, the `Loading` position of the electropolishing
system is configured such that the anode rod is positioned adjacent
to (below) the cathode subassembly mesh and adjacent to (above) the
rolling block, so as to allow the user to place the stent (or stent
assembly, which consists of the stent 110 and the anode rod 120) on
the anode. The anode rod 120 is electrically and mechanically
connected to one or more force transducers (FT) 122, 124 that
control the amount of pressure that is applied to the stent 110
against the rolling block 140. A motion controller (positioning
subassembly) 125 is mechanically and electrically attached to the
force transducers and the anode rod. The motion controller provides
longitudinal movement 170 of the stent along the rolling block. The
motion controller also provides vertical movement 190 of the anode
rod to lower the stent against the rolling block and to lift the
anode rod away from the rolling block. The force transducers are
also connected to an anode power supply (not shown), which applies
the electric current through the stent (but not necessarily through
the force transducers). The cathode subassembly 130 is suspended
above the rolling block and includes connectors 132, 134 to the
electrical power supply, which completes the electrical circuit.
The electropolishing solution is filled to a level in the housing
150 to cover the rolling block, the cathode mesh, the anode and the
stent (in the `Run` mode).
[0029] After loading the stent on the anode, the automated
electropolishing process is continued in the `Run` mode (FIG. 2).
The vertical control of the motion controller 125 lowers the stent
110 onto the rolling block 140 via electrical and mechanical
connectors 126, 128. The linear control of the motion controller
starts moving (rolling) the stent along the rolling block. The
force transducers 122, 124 control the pressure being applied to
the stent via electrical and mechanical connectors 127, 129 to the
anode rod 120. The anode rod provides the electrical connection
between the stent and the anode power supply. The applied force
(controlled by the force transducers) continually grooms the stent,
and the linear motion rolls the stent so as to continually change
the contact point between the stent and the anodic connection.
[0030] A computer subsystem (not shown), such as a PLC, controls
the voltage, current, applied force, linear speed and cycle time
for the polishing process. At the end of a polishing run (FIG. 3),
the electric current is turned off, and the motion controller 125
moves the stent 110 away from the rolling block 140 and the cathode
mesh 130, and lifts the stent out of the polishing solution. The
motion controller then `homes` the device to the `Start/Load`
position (see FIG. 1), a new stent is loaded and the process begins
again (see FIG. 2). Since the entire process (excluding loading and
removing the stent) is computer controlled, much of the process
variation and damage due to operators is eliminated. In addition,
the system and method of the present invention should result in a
more uniformly polished stent with a lower defect rate and a faster
polishing time (overall lower processing time).
[0031] As shown in FIG. 4, an alternative embodiment of the
electropolishing system 200 of the present invention allows for
simultaneously processing multiple metal devices (such as two or
more stents 112, 114) by configuring the anode rod 120 to removably
retain multiple devices. The size and configuration of the rolling
block 140 may also be adapted to allow for more than one stent to
be polished at one time. The stents are lowered into the polishing
solution then compressed against and moved along the rolling block
by the motion controller 125 and force transducers 122, 124 while
current is applied to the anode rod and cathode mesh 130. This
allows continual contact and grooming of the stents, and provides
for stent polishing. The computer subsystem controls the current,
cycle time, linear speed, tension, and residence time in the bath,
which all control surface finish. At the completion of the
polishing process, the stents are raised from the bath (FIG. 3) and
the system is repositioned to begin polishing the next set of
stents.
[0032] As shown in FIG. 5, a further alternative embodiment of the
automated electropolishing system 300 of the present invention is
configured to selectively control and polish the lumen of the
device(s) to be electropolished, such as a stent 310. A retaining
rod 320, which was previously the anode, is formed from a
non-conducting material and is configured to removably secure the
stent(s). The non-conducting rolling block has been replaced with a
conducting metal plate 340, which acts as the anode and includes
electrical connections 342, 344. In addition, a second cathode 135
can be attached to or positioned adjacent the non-conducting rod
and electrically connected to the motion controller 125. The second
cathode may be formed from a fine wire, rod or mesh. The retaining
rod applies the pressure of the stent against the rolling block
(see FIG. 2), except that the rolling block is now the conducting
anode. In this configuration, the polishing of the lumen of the
stent can be selectively controlled (as well as the external
surface of the stent), which can lead to a smoother inner surface.
This allows the lumen of the stent to be polished selectively,
since the second cathode is in close proximity to the lumen of the
device. In this configuration, the lumen surface may be polished to
a finish substantially equal to the exterior surface.
[0033] Stent electropolishing is a critical stent in the stent
manufacturing process, and is used to convert a laser-cut (or
welded) stent into a smoothly polished, highly glossed stent. The
electropolishing process can be highly variable; therefore,
reducing the variability of the electropolishing process will
reduce the variability of the polished stent, which results in a
much more uniform finished device. The result is a more consistent
product available to the marketplace. One aspect for reducing the
electropolishing variability is to redesign the `spiral mandrel`
common in prior art systems. The spiral mandrel is typically a
disposable stainless steel spiral wire that is used to hold the
unpolished stent and provide for electrical connection during the
electropolishing process. The spiral mandrel does an adequate job
but has a few shortcomings [0034] First, the stent is typically
over polished (that is defined as more material removed relative to
the rest of the stent) at the points of contact between the spiral
mandrel and the stent. This results in about one-third of each
stent ring (the number of contact points) being `thinner` than the
remainder of the stent. [0035] Second, the spiral mandrel does not
adequately polish a stent with variable thickness in the lumen.
[0036] Third, the spiral mandrel has to be `screwed` into the lumen
of the stent, which results in handling damage and/or twisting of
the stent (accounts for the majority of the defects prior to
electropolishing and also during the polishing process for
cobalt-chromium stents).
[0037] Referring now to FIGS. 6-11, the automated electropolishing
system of the present invention includes novel mandrel designs that
are configured to electropolish metal devices, such as stents. The
mandrels may be formed from stainless steel, platinum,
platinum-iridium, nitinol, or any other suitable electo-conducting
material. FIG. 6A depicts a reusable dual-hook mandrel attached to
an unpolished stent 610. The mandrel includes a first segment 620
having proximal portion connected to an electrical source to form
the anode. The distal portion of the mandrel is formed with a first
hook or bend 622 that provides a first contact point 624 on the
stent. The mandrel includes a second segment 640 having proximal
portion connected to the electrical source and a distal portion
having a second hook or bend 642 that provides a second contact
point 644 on the stent. FIG. 6B shows the stent after
electropolishing with the dual-hook mandrel of the present
invention.
[0038] As shown in FIG. 7, an alternative embodiment of a reusable
electropolishing mandrel 720 in accordance with the present
invention may be configured with a single distal arm 722 having
proximal portion 724 connected to an electrical source to form the
anode. The distal portion of the mandrel provides a dual
point-of-contact 726, 728 on the stent 710. The stent sidewalls are
also polished with this dual point-of-contact design. The stent may
be secured in the housing and solution with a non-conducting rod
740.
[0039] Referring to FIG. 8, a further alternative embodiment of a
reusable electropolishing mandrel 820 in accordance with the
present invention may be configured with a single distal arm 822
having proximal portion 824 connected to an electrical source 825
to form the anode. The distal portion of the mandrel provides a
single point-of-contact 826 on the stent 810. The stent may be
secured in the housing and solution with a non-conducting rod 840
connected to a fixture 850.
[0040] FIG. 9 is a scanning electron microscope (SEM) image of an
eight millimeter (mm) stainless steel stent 900 with variable
thickness tubing on the lumen side of the stent. The outside
surfaces 920 and inner walls 940 of the stent were adequately
electropolished with the mandrel design shown in FIGS. 6A and 6B.
As shown in FIG. 10, the lumen walls 1120 and undulations 1110 were
adequately polished on the stent 1100. FIG. 11 is an SEM image of a
cobalt-chromium stent 1100 electropolished with the mandrel design
shown in FIGS. 7 and 8. The outside surfaces 1110, side walls 1120
and lumen walls 1130 of the stent were adequately
electropolished.
[0041] Some of the advantages of the new mandrel designs in
accordance with the present invention are: [0042] The mandrels are
reusable, thus reducing overall manufacturing costs. [0043] The
mandrels work (the stents are electropolished). [0044] The number
of contact points are minimal (usually only two points of contact),
which results in less random thinning of struts due to minimizing
the number of contact points.
[0045] There are less handling defects because of the ease of use
and simplicity of the design. While particular forms of the present
invention have been illustrated and described, it will also be
apparent to those skilled in the art that various modifications can
be made without departing from the spirit and scope of the
invention. Accordingly, it is not intended that the invention be
limited, except as by the appended claims.
* * * * *