Note: Descriptions are shown in the official language in which they were submitted.
~25S7;~'~
804P107CD
11/11/86
SE~OClC--~;AFI~ F~JS131IOLD~R ASS1~13L~
DFSCRI PTI ON
T~CHl~I CAL F I ~.LD
The technical field of the invention
is the automatic circuit-breaking art, and in
particular electrical fuses.
BACRGROUN~ OF TH~ I~VFNTION
.
One commonly used form of electrical
fuseholder assembly includes a socket-forming
body designed to be mounted on a panel so as to
accept insertion of fuses from the front of the
panel. The fuse i.s carried and held in place
by a knob of one form or another which fits
into an opening on the front of the body.
2 ~25~
~requently such knobs have a bayonet-type
retention lock, i.e., a retention lock
configured with locking members so that the
knob is first axially inserted to a certain
depth into the body opening against the force
of a fuse-retaining spring and then rotated to
a position so that upon removal of the
insertion pressure the retaining spring forces
the locking members into locking engagement~
Removal of the knob is achieved by first
pressing axially inward on it to separate the
locking members, then rotating the knob in a
direction opposite to the locking dire~tion,
and then releasing the pressure thereon,
whereupon the retaining spring force ejects the
knob from the body.
Such fuseholder assemblies permit
rapid insertion of the fuse-carrying knob as
compared with alternative types wherein screw
threads are provided on the knob and body. ~he
former type of fuseholder assembly is shown in
the patent literature, as for example, in U.S.
Patent No. 4,448,476 issued May 15, 1984 to
Perlman et al. Such assemblies typically
include a conducting sleeve coaxially mounted
in the fuseholder knob and carrying an axial
spring mounted therewithin, the socket-forminy
body having an electrical side terminal contact
which is configured to lockingly engage with
the sleeve so as to provide not only the
mechanical locking action, but also electrical
contact from the side terminal to the outer end
o an inserted fuse.
3 ~ 2 ~
Such fuseholder assemblies typically
exhibit a variety of drawbacks. ~irst, the use
of the two metallic structures to form the
locking means and the electrical contact as
well can give rise to undesirably high contact
resistance between the locking members. This
ariseS from the fact that, particularly in the
case of high amperage fuses, fuseholders may
run rather hot. Since there are normally many
plastic insulating portions in the fuseholder
assembly, the result is that the engaging
surfaces of the locking members may become
contaminated by organic compounds volatilized
from the plastic. ~dditionally, such loc~ing
means are fragile, and if the knob is not fully
inserted prior to rotation, portions of the
lock member elements may be improperly engaged
after rotation of the knob and become deformed
so as to become inoperative.
An additional problem arises in such
fuseholder assemblies in that they tend to be
unstable in the event of incomplete final
rotation of the knob during insertion, i.eO, if
the knob is not sufficiently rotated that the
fuse-retaining spring is able to move the knob
slightly outward to the locking position, then
subsequent vibration may allow the fuse knob to
rotate to a point where the knob is undesirably
ejected~
In addition to the instability
associated with the use of conventional bayonet
lock means to retain the fuse knob in the
fuseholder body, a further problem is commonly
experienced when the fuseholder knob has a
~ 5q~ ~
screwdriver slot head which, when the knob is
in place and finally positioned within the
fuseholder body, does not project beyond the
outer surface of the fuseholder body (or would
not do so in the absence of spring pressure).
The knob can be removed by inserting a
screwdriver into the slot in the knob head and
rotating it into its unlocked position where
spring pressure forces the knob outward where
it can be grasped and removed from the
fuseholder body. However, it is not an
uncommon experience for an operator to extract
a suspect fuse, find that it is blown, and
place the knob back in the holder temporarily
while he goes off to find a replacement fuse.
~t this point the customary knob spring
pressure bearing on the fuse, which normally
will eject the knob in the released orientation
thereof as described above, is missing. Thus,
upon attempting to remove the knob with the
spring in this relaxed condition by rotating
the knob with a screwdriver, the user finds
that the knob remains depressed within the
fuseholder body where he cannot grasp it. A
sharply pointed knife or the like is then
needed to pry or pull the knob out of the
fuseholder body.
~ similar situa~ion is also
encountered in those cases where the pressure
spring is carried within a conducting sleeve
mounted as an extension of the knob assembly,
and wherein the fuse end cap accommodated
therein has become so corroded so as to freeze
to the sleeve. Under such conditions the
~s~
spring force cannot act against the fuse to assist in the
extraction of the knob.
Finally, it is well known that there exis-t a great
variety of fuses manufactured in cartridges of identica:L diameter,
but of different length. If a fuse of accidentally oversize
length is inserted into a conventional axial fuseholder r then
upon forcing the fuse knob inward to retain the fuse, the axial
spring may easily be stressed to the point of permanent
deformation. This results in reduced axial seating pressure
when a fuse of proper length is installed thereafter. This can
cause a fuseholder to run hot at the terminals because of
inadequate seating pressure to maintain the contact.
SUMMARY OF THE INVENTION
A fuseholder configured for axial insertion of
cartridge-type fuses comprises a socket-forming body having a
fuse-accepting passageway or socket and a fuse-retaining knob.
T~e body passageway and the knob preferably have complementary
portions configured for guiding engagement when the knob is
forced axially inward, usually against the force of an ejecting
spring. In accordance with one aspect of the invention,
circumferential motion guiding means are provided in the passage-
way, preferably on the insulating walls thereof, and the knob
is provided with corresponding outwardly extending projections,
formed preferably on an insulating knob extension which enters
the passageway. Coaxially mounted in the knob extension is a
conducting sleeve for receiving and making contact with the outer
end of the fuse. In the preferred form of the invention, engaging
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~2 ~
surfaces on portions of the passageway guide grooves are
configured so that initial insertion of the knob is constrained
substantially to non-rotating axial movement until the knob is
in a nearly seated position. Helical camming surfaces, prefer-
ably part of said gulde grooves, are arranged so that as the
seated knob is pushed fully inward against a spring force, the
knob is cammingly rotated by said camming surface into a
position where either by a further manual rotation, or by
release of axial pressure on the knob without a forced rotation,
the knob is in a position where the spring which creates said
spring force urges the knob outwardly into an interlocked
position with an inwardly facing locking shoulder on the fuse-
holder body. If the knob has been inserted without a fuse in
the knob, the spring force referred to is not present, as
previously explained. However, in accordance with the present
invention, if such a knob is rotated by a screwdriver from its
locked to its unlocking direction, the knob projections will
engage said camming surfaces, which will then guidingly urge
the knob into a position where it extends beyond the plane of
~a the insertion aperture of the fuseholder body where it can be
readily grasped by the operator for convenient removal.
Another advantage of the preferred form of the
invention just described is that the
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7 ~2 ~ 5 ~ ~
interlocking surfaces of the knob and
fuseholder body described are insulated from
the current-carrying portions of the
fuseholder. In some prior art fuseholder
structures the axially facing interlocking
surfaces are current-carrying surfaces which
can cause general overheating of the assembly
to cause distillation of organic matter to
contaminate the conducting surfaces.
The applicant knows of no fuseholder
having the camming and insulating bayonet-type
features just described. The only prior art
known to the applicant which has a cam-like
guide is used for a completely different
purpose than the present invention, and is
co~structed so as not to be applicable to a
fuseholder. ~hus, U.S. Patent No. 3,477,062
issued to Wagstaffe shows a half-turn helical-
lock type lamp bulb holder configured to
lockingly to accept the base of a lamp bulb
having a pair of radially extending bosses on
the base thereof. The bulb holder, which is
obviously not event remotely useful with a
fuse, is always expected to be grooved and so
does not have the problem solved by the unique
fuseholder of the invention just described.
Moreover, the bulb holder receptacle relates to
the bulb holder in a substantially diferent
manner than the fuseholder body of the
invention. ~or example, the bulb holder
receptacle is a metal sleeve configured with a
pair of boss-receiving half-turn helical slots.
When the bosses are inserted in the grooves,
the lamp is immediately rotated, and when the
8 ~ 5 ~ 7~ ~
knob bosses reach the end of the grove, the
bosses are trapped by a groove enlargement.
~his sleeve serves as a spring to urge the
bosses, and hence the base of the lamp~ having
a pair of projecting contacts on the inner end
thereof, into contact with a pair of outwardly
facing terminals in the bulb holder. Clearly
the lamp holder of this patent would not be
consi~ered to be relevant prior art to a
fuseholder, and is substantially structurally
different from the fuseholder of the invention
described.
According to a further feature of the
invention, additional inwardly facing camming
surfaces are provided so that during knob
insertion and rotation to a locking condition,
upon release of the axial insertion pressure
the ejecting force of the fuse-retaining spring
causes the knob assembly to be further urged in
the locking direction ~y this means the
possibility of accidental later ejection of the
knob arising from incomplete locking rotation
by the operator is substantially eliminated.
~ ccording to a further feature of the
invention, in the event that the operator fails
to force the fuseholder knob sufficiently into
the assembly to rotate the locking portions
into confronting engagement, no capture
whatever occurs, and the knob will be
immediately ejected upon release of pressure
thereto, thus notifying the operator that he
has failed to seat the assembly properly. If,
on the other, sufficient rotation has occurred
that even a partial locking engagement occurs,
9 ~2 ~7~2~
on release of axial insertion pressure to the
fuseholder knob the knob assembly is
automatically urged towards full locking
engagement~
According to a further feature of the
invention, a safety feature is provided which
efectively prevents permanent damaging
compression of an axial pressure spring carried
in the fuseholder knob. As is well known in
the art, a conducting sleeve in the knob which
carries and makes contact to the outer end of
an inserted fuse frequently carries the axial
pressure spring integrally contained therein.
~t the end of the sleeve which resides
outermost in the knob, i.e., closest to the
outer face of the knob, there are provided
retention fingers~ A central inwardly
extending axially disposed tapered post is
provided on the inwardly facing surface of the
knob, and is configured to engagingly pass
between these fingers when the sleeve is
pressed against this inwardly facing surface of
the knob during assembly, to be captively
retained thereon. This same post is configured
to extend partially along the length of the
compression spring, and is deliberately made
sufficiently long that if an oversi2ed fuse i
inserted into the assembly, and the knob is
then pushed in for engagement, the post will
strikP the outer end cap of the fuse so as to
prevent engagement of the locking system, and
further to prevent permanent compressive
damaging deformation to the spring.
~2 5 ~7 ~ ~
Other features and aspects of the
invention will become apparent upon making
reference to the specification, claims, and
drawings to follow.
~SCRIPTION O~ T~ DRAWI~GS
Figure 1 is a partially cutaway cross-
section view of the fuseholder of the present
invention with a fuse inserted, the structure
consisting generally of a body having a panel
mounting flange, and an inserted knob assembly.
Figure 2 is a partial cross-section
end view of an inner portion of the body
indicated by cut lines in Fig~re 1, with
central body elements and peripheral portions
of the flange removed.
Fig~re 3 is an end view of one form
of contacting sleev~ for accepting the outer
end of a fuse.
Figure ~ is a plan view of the sleeve
shown in Figure 3.
~ ig~re S is a plan view of the knob
assembly shown in Figure 1.
Figure 6 is a circumferential fold-
out view of the body portion shown in Figure 2,
further showing in phantom outline a locking
boss shown in Fig~re 9 partially axially
inserted to engage a camming portion on the
wall of the fuseholder body, and further
showing the relative positions of the mounting
flange and knob in phantom outline.
.
Figure 7 shows a further phase of
insertion beyond that shown in Figure 6,
showing a camming rotation of the locking boss.
Fig~re 8 shows the final stage of
rotation indicated in Figure 7, the locking
boss having been rotated to full rotation.
Figure 3 shows the final phase of
locking engagement of the boss with the
fuseholder boss o ~igure~ 6, 7, and 8 with the
fuseholder body, axial pressure having been
removed from the structure.
Figure 10 is a cross-~ection view of
the knob shown in Figure 5 using the form of
sleeve shown in ~igure~ 3 and 4.
Figure ll shows the structure of
Figure 10 with a fuse compressingly inserted
against an arresting stop.
Figure 12 is a cross-section view of
the fuseholder body along the cut lines shown
in Figure 14, showing locking shoulders for
holding the knob in position.
Figure 13 is a cross-section view of
the knob taken along the cut lines shown in
Figure 5, and showing a pair of knob locking
projections.
Figure 14 is--a cross-section view
similar to ~ig~re 1, but with the fuse and knob
removed.
Figure lS is a cross-~ection view
similar to Figure 1~, but rotated approximately
90 degrees.
~SC~IPTION OF THF INV~NTION
12 ~2;$ ~ ~
Figure 1 shows a representative
fuseholder assembly 10 consisting of a body 12
captively retaining a ~nob 14. The body
includes a threaded insulating sleeve 13
integral with an apertured mounting collar 15
having an outer face 22. The customary
retention nut configured to engage the sleeve
13 for mounting purposes is not shown. The
knob 14 is held in place by locking means to be
discussed subsequently to retain an inserted
fuse lb. In this position the outer surface 18
of the knob 14 is generally coplanar with the
outer face 22 of the body 12. A screwdriver
slot 20 is centrally located in the knob outer
face 18. For purposes of all subsequent
discussion, the term "inward" or "inner" will
refer to directions deeper towards the interior
of the fuseholder 10, and the term "outer" will
refer to regions closer disposed to the outer
faces 18 and 22. Similar terminology will be
applied to the knob 14.
The knob 14 features an insulating
cylindrical inwardly extending shroud extension
24 within which is captively secured a
conductinq sleeve 26 having cylindrical
expanded skirt portions 28 at the inner end
thereof, and in the preferred form tsee ~igure~
3, 4, 10~ and 11) has radially extending
tension fingers 30-30 at the outer end thereof.
These fingers are configured for securely
gripping an axially inwardly extending post 32
during assembly to hold the sleeve 26 securely
emplaced within the shroud 24. ~ compression
spring 34 is secured at the outer trightmost)
13 ~ 7 ~ ~
end of the interior of the sleeve 26 by press-
in insertion, the inner end of the spring being
compressively engaged against the outer end cap
(terminal) 36 of the fuse 16. The spring 34
thus serves the purpose that when the fuse 16
is inserted the fuse 16 is pressed inward
against a end cap contact 38 a~ the inner end
of the fuse insertion passage 40, so as to
establish good contact with the inner end cap
4~ of the fuse.
~ urthermore, when the knob 14 is
rotated to a unlocked condition, as will
subsequently be discussed, the spring 34 serves
to ~ject the knob outward to a point where it
may readily be grasped and removed by the
operator, simultaneously removing the fuse 16.
It should be noted at this point that if no
fuse is present, no such ejecting force will be
applied to the knob 14, with the result that
removal of a knob of the type shown, having an
outer surface 18 depressed within or flush with
the body face 22, will be difficult to remove.
As will subsequently be shown, the instant
invention provides a positive knob extraction
feature irrespective of whether a fuse is
present or not.
~ xternal contact to the outer end cap
36 of the fuse 16 via the sleeve ~6 is secured
by means of ~ end cap contact 44 having as an
interior portion 46 configured in the form of a
ring coaxially disposed in the insertion
passage 40, and positioned so that the skirt
portions 28 of the sleeve 26 make wiping
contact thereto. ~o prevent the inner end cap
5~
42 of the fuse 16 from contacting this side
ring 46 during fuse insertion or withdrawal, an
insulating shroud 48 is provided integral with
the body a~sembly and coaxially disposed to
ex~end along a central portion of the insertion
passage 40 so as to confront the interior
surfaces of the terminal ring ~6. ~he outer
radius of the shroud 48 is chosen so as to
leave an annular passage 50 leading past the
inner surface of the ring to allow insertion of
the skirt portions 28 of the sleeve 26.
~ etails of the locking structure of
the present invention are best shown in Figures
2, 5-9; and 12-15. Figure~ 5 and 13 show the
knob 14, having a pair of ].ocking lugs (locking
projections) 52 diametrically disposed on and
extending outward from the outer cylindrical
surface of the knob shroud extension 24 and
having cylindrical outer faces 57. ~ach of the
lugs 52 is configured with axially extending
side facets 54 joined at their inner ends by an
inner facet 56 disposed generally perpendicular
thereto. The outer ends of the side facets 54-
54 are joined by a generally outwardly facing
facet 58 oriented as shown in Figure 5 to
present an inclined side profile.
Figure~ 14 and lS show cross-section
views of the fuseholdar body 12 as shown in
~igure 1, but with the fuse and knob removed.
The principal details of the locking structure
are shown in Figures 14 and lS, as well as in
the circumferential fold~out view of Figure 2
Lines 73-73 in Figuren 6-9, 14 represent
optional molding grooves which facilitate the
~ rdJ~
manufacturing process, but which bear no
relevance to the locking system. These
optional groove boundaries are shown in dotted
outline in Figures 6-9.
~ o maintain alignment of the knob 14
during insertion thereof, a pair of axial
grooves 62-62 (Fig~re 12) are formed along
interior walls of the fuse insertion passage 40
so as to form a pair of channels (referred to
in the claims as entry sections) extending
axially inward along the walls of the insertion
passage 40, and having opposing side walls
64,65. Insertion of the knob assembly 14 with
the locking lugs 52 generally centered between
the walls defining these grooves 62 (referred
to in the claims as entry section walls) will
allow for generally axially confined sliding
engagement of the knob assembly 14 into the
fuseholder body 12.
With particular reference to the fold-
out view of Fig~re 6, it will be seen that the
interior end of each axial groove 62 joins a
generally transversely disposed short radially
extending circumferential terminal groove 66
(referred ~o in the claims as terminal section)
further provided in the interior walls of th~
insertion passage 40, this circumferential
groove terminating in a circumferentially
facing end wall 68. The radially inwardly
extending groove 66 is generally defined by an
axially outwardly facing inner wall 70 joining
the axial groove side wall 64 by an inner
axially outwardly facing helical camming
surface 72 ~see Figure 2) making an angle with
~ 2 ~
respect to the wall 70, and by an axially
inwardly facing locking shoulder-forming
camming surface 74 (Figure 12~ which has a
helical curvature in the opposite direction
(because it i5 an oppositely facing surface) as
that of the helical camming surface 72
(referred to in the claims as first helical
camming surface).
When the knob 14 is initially
inserted, each locking lug 52 will be generally
axially guided until a corner of the interior
facet 56 of each lug strikes the inner camming
surface 72, at which time rotary displacement
automatically occurs, i.e., the lug 54 will
then proceed to cam downward as shown in
~igure~ 6 and 7 corresponding to a clockwise
rotation with respect to the orientation shown
in Figure 2. ~ach locking lug 52 is preferably
placed in an orientation so that upon full
axial insertion automatic rotation positions
its outer facet 58 to establish at least a
partially conronting overlap with respect to
the inclined camming surface 74 (referred to in
the claims as second helical camming surface)
of its associated radially extending groove 66.
In the event that ~he operator should fail to
induce full manual clockwise rotation of the
knob assembly 14 on insertion r release of
insertion pressure to the knob assembly will
cause it to be urged axially outwardly by the
spring 34 to place the outer facet of the lug
58 at least in partially overlapping
confronting ensagement with t'ne helical camming
surface 74 of the radially extending groove 66,
17 ~2~7~2~
as shown in phantom outline 52' in ~igure ~.
The spring 34 will thus have the effect of
continuing to supply a clockwise rotating force
with respect to the orientation of Pigure ~ to
the knob assembly to urge the locking lugs 52
towards their final seated position shown in
Figure 90
Two benefits are immediately evident
from such a configuration of the engaging
surfaces. Pirst~ ~he capture system is
inherently stable, i.e., provided the knob
assembly 14 has rotated far enough to establish
any kind of capture condition, the tendency of
the system, either alone or assisted by
vibration, is to move towards a more stable
locking configuration. Prior art systems known
to the applicant do not provide this; they
typically provide the functional equivalent of
a pair of inner and outer facets placed at
right angles to the side facets 54,54. The
result is that if the operator should fail to
rotate them to a fully seated condition, but
merely establishes initial partial confronting
contact of the type shown in phantom outline
52' in Figure 8, then subsequent vibration can
easily cause the knob to rotate back to an
ejecting position. A well-recognized mode of
failure is thus avoided. It is equally evident
that if no such overlap is initially achieved,
the knob 14 will immediately be ejected, thus
warning the operator to seat the knob 14 again.
This feature is advantageous as
applied either to flush- or depressed-type
fuseholders as shown in Figure 1, having a knob
.
~2~5~2
outer surface 18 generally depressed within or
coplanar with the body outer face 18, or in the
alternative as applied to fuseholders wherein
the knob 14 is provided with a large, readily-
gripped knob extension extending substantially
outward beyond the fuseholder body outer face.
Second, it is evident by inspection
of ~igures 6-9 that if the knob has been
inserted and moved to a locking orientation
with no fuse in the passageway 40, then a
screwdriver rotation of the knob 14 in the
unlocking direction will cause the locking lugs
52 to rotate so that they are automatically
cammed in an ejecting direction upon traversing
the inner camming surfaces 72. This causes the
outer face 18 of the knob 14 to be displaced
outward to extend in a raised condition with
respect to the fuseholder body face 22 where it
may be grasped and removed by the operator, as
is evident in ~igure 6. ~s mentioned in the
Background of the Invention and Summary of the
Invention, this i5 particularly useful when the
locking system shown herein is used in
canjunction with flush-type mounting system as
shown in Figure 1.
- Referrin~ next to Figures 3, 4, 10,
and 11, it will be noted that the conducting
fuse-retaining sleeve 26 is preferably
fabricated from a properly confiyured piece of
resilient sheet stock material. In particular,
it will be noted that the radially extending
fingers 30-30 are generally coplanarly disposed
to define between the terminal ends thereof an
aperture 78. The fingers 30 are dimensioned so
.
19 ~ 7.~ ~
that during fuse assembly sleeve 26 is forced
over a axially disposed tapered post 32 of the
knob 14. Full inser~ion of the sleeve 26 into
the shroud extension 24 causes these fingers 30-
30 to lockingly engage the tapered post 32 to
place portions of the fingers generally in
confronting contact with the interior wall of
the shroud 24 immediately adjacent ~he base of
the tapered post 32~ As previously mentioned,
the spring 34 is press-fitted so that the outer
end thereof is captively secured in position
against the inner surfaces of the sleeve 26
close to the fingers 30-30, leaving the inner
end thereof free for axial movement against the
end cap 36 of an inserted fuse 16.
The post 32 i5 deliberately
configured overlength so as to provide a useful
safety feature. ~s mentioned in the Background
of the Invention and Summary of the Invention,
if one inadvertently attempts to lock the knob
14 over the wrong kind of fuse, i.e~, a fuse
h.~ving proper diameter for acceptance into the
insertion passage 40, but being too long for
proper operation therein, upon axial insertion
of the knob 14, the post 32 will arrPstingly
strike the outer end cap 36 of the inserted
fuse 16 to prevent further insertion of the
knob as shown in ~igure 11. Thus, the spring
34 cannot be overcompressed by an oversized
fuse to the point where it suffers permanent
compressive deformation. Similarly, it is
equally evident that by proper configuration of
the various camming surfaces shown in Figure~ 6-
~2~
9 locking engagement with an overlength fuse inplace will be impossible.
~ his reduces the possibility of a
type of subsequent malfunction encountered in
prior art structures no~ having this protective
feature, where a proper length fuse is
subsequen~ly inserted and the knob locked
thereto. Such a permanently over-compressed
spring frequently cannot thereafter apply
adequate seating pressure to the fuse, as a
result of which inferior contact will
frequently be experienced, particularly with
respect to the fuse inner end cap 42 contacting
the inner terminal contact 38. Insufficient
pressure gives rise to inadequate contact,
which in turn gives rise to undesirably high
temperature operation of the fuse body in the
vicinity of this contact.
Thus, there has been provided a
fuseholder of the bayonet-type which provides
an instantaneous warning that proper locking
has not been achieved, which provides for
positive stable locking even in the case of
incomplete rotation of the knob, which provides
a positive camming extraction feature forcing
the knob outward even when no fuse is inserted,
and which further provides for prevention of a
dangerous permanently over-stressed spring
condition if an over-sized fuse is accidentally
inserted. All of the foregoing are
accomplished in a novel, but inexpensive way.
While the invention has been
described with reference to a preferred
embodiment, it will be understood by those
21 ~'2'~;'~
skilled in the art that various changes may be
made and equivalents may be substituted for
elements thereof without departing from the
broader aspects of the inventionO Also, it is
in~ended that broad claims not specifying
details of a particular embodiment disclosed
herein as the best mode contemplated for
carrying out the invention should not be
limited to such details. ~urthermore, while,
generally, specific claimed details of the
invention constitute important specific aspects
of the invention in appropriate instances even
the specific claims involved should be
construed in light of the doctrine of
equivalents.
