Note: Descriptions are shown in the official language in which they were submitted.
ELECTROHYDRAULIC PROPORTIONAL VALVE
Technical Field
This invention relates to electrohydraulic
proportional valves suitable for use in selective control
valve applications. In particular, it relates to a four-
way, electrohydraulic flow control valve with continuously
variable output flow which is proportional to the electrical
input signal.
Background of the Prior Art
Dynex/Rivett has developed several electro-
hydraulic control devices over the past several years
which employ the same basic design principles as those
described herein. These products have been refined through
years of ficld evaluation and laboratory testing into reliable,
easily maintained, durable products. ~lowever, this same
process oE continuous field cvaluation and laboratory testing
has shown the existence of room Eor considerable improve-
ment, particularly in the area of integratiny additional
fluid control functions into a single, compact assembly.
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In particular, in many applications it is necessary for
the main spool to have a "float" position whereby the
two working parts of a four-way valve are both simul-
taneously connected to the return line. In these same
applications, it is often necessary to totally block the
flow from the ~ork ports back to the return line whenever
the main spool is in the neutral position. The blocking
of flow from the work ports back to the return line is
usually accomplished by means of load-holding check valves
which prevent a machine member from slowly drifting due to
fluid leakage through the annular clearances between the
main spool and the valve body.
The "float" position is preferably located at
one extreme end of the main spool stroke, and thus it is
essential that the main spool consistently achieve full
stroke even under adverse conditions such as battery run-
down and electrical line voltage drops. Two-stage electro-
hydraulic proportional valves which employ a means of feed-
back between the main spool position and the pilot stage
generally have great difficulty in achieving a consistent
"float" position. This difficulty arises from the fact that
the feedback rate between the main spool and the pilot stage
is typically constant throu~hout the total range of main
spool movement. Thus a full ratcd clectric~l si~nal must be
applied to move thc main spool to the "~loat" position, and
relatively small input volta~e drops may prevent the main
spool from achievillg a full ;'float' condition.
In applicatiolls re~uirin~ both a "float" position
and load-holdin~ check, some mcans must be provided to open
the load-holding chec]c valves whenever the main spool is
moved to the "float" position so that fluid can freely pass
from either or both work ports to the return line. In the
past this has been accomplished by using an additional pilot
valve, either electrically or manually operated. Typically
this ad~itional pilot valve and associated load-holding check
.
valves wexe separate components in the hydraulic circuit,
thus resulting in additional hydraulic and electrical
circuitry.
Additionally, it has been found highly des-
irable to minimize the effect of contaminants in thehydraulic fluid on the operatio~ of the valve.
Objects of the Invention
It is, therefore, a general object of the
invention to provide an electrohydraulic proportional valve
which is improved in the area of integrated fluid control
functions.
It is a particular object of the invention to
provide such a valve having a "float" position and integral
load holding check valves.
It is a further object of the invention to provide
a means of opening the load-holding check
valves automatically whenever the main spool of the proportional
valve is moved to the float position.
It is a still furthcr objcct of the invention to
provide such a valve in which battery rundown or line losses
do not limit the ability of thc pilot actuator to move the
main spool to the full "float" position providecd that at least
a predetermined minimum voltage can be applied to the
electro-magnetic force motor.
Another objcct of the invention is to provide such
a valve in which the effect of contaminants in the hydraulic
fluid on the operation o the valve is minimized.
Other objects and advantages of the present invention
will become apparent from the appended detailed description
of a preferred embodiment taken in conjunction with the
accompanying drawings.
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Brief Summary of the Invention
The subject electrohydraulic proportional valve com-
- prises an electromagnetic force motor, a pilot actuator assembly,
and a main spool and body assembly.
The pilot actùator assembly comprises a pilot spool
slidably received in a pilot sleeve and a feedback spool which has
a camming surface against which the pilot sleeve rides. The cam-
ming surface comprises a first portion in which the position of
the pilot sleeve is a function of the axial position of the camming
surface and a second portion immediately adjacent the first por-
tion in which the position of the pilot sleeve is constant regard-
less of the axial position of the camming surface.
The main spool and body assembly comprises a main spool
connected to the pilot actuator assembly, first and second load
holding check plungers slidably disposed in a bore, first means
for communicating pilot supply pressure to a reduced diameter area
on the main spool when it is the float position, and second means
for communicating pilot supply pressure from the reduced diameter
area on the main spool to the bore between the first and second
load holding check plungers when the main spool is in its float
position.
In accordance with the present invention, there is pro-
vided an electrohydraulic proportional valve comprising: (a) a
pilot actuator assembly comprising a pilot spool slidably received
in a pilot sleeve and a feedback spool having a camming surface
against which said pilot sleeve rides, said camming surface com-
prising a first portion in which the position of said pilot sleeve
is a function of the axial position of said camming surface and a
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second portion immediately adjacent said first portion in which
the position of said pilot sleeve is constant regardless of the
axial position of said camming surface; (b) an electromagnetic
force motor assembly having an output member which is operatively
connected to said pilot actuator assembly such that motion of said
output member results in corresponding motion of said pilot spool;
: and (c) a main spool and body assembly comprising: (i) a main
spool which is operatively connected to said pilot actuator assembly
` such that motion of said feedback spool results in corresponding
: 10 motion of said main spool; (ii) first and second load holding check
valves slidably disposed in a bore; and (iii) first means of fluid
communication for communicating control pressure to said bore
between said first and second load holding check valves when said
pilot sleeve i.s in contact with said second portion of said cam-
ming surface.
In accordance with the present invention, there is also
provided in an electrohydraulic proportional valve comprising:
(a) a pilot actuator assembly; (b) an electromagnetic force motor
assembly having an output member which is operatively connected to
.. 20 said pilot actuator assembly such that motion of said output member
results in corresponding motion of said pilot assembly; and (c) a
main spool and body assembly comprising a main spool which is
operatively connected to said pilot actuator assembly such that
motion of said pilot actuator assembly rcsults in corresponding
motion of said main spool; the improvements wherein: (d) said
pilot actuator assembly comprises a pilot spool slidably received
in a pilot sleeve and a feedback spool having a camming surface
against which said pilot sleeve rides, said camming surface
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comprising a first portion in which the position of said pilot
sleeve is a function of the axial position of said camming surface
and a second portion immediately adjacent said fi~st portion in
which the position of said pilot sleeve is constant regardless of
the axial position of said camming surface; (e) said main spool
and body assembly further comprises first and second load holding
check valves slidably disposed in a bore; and (f) said main spool
and body assembly comprises first means of fluid communication for
communicating control pressure to said bore between said first and
second load holding check valves when said pilot sleeve is in con-
tact with said second portion of said camming surface.
.In accordance with the present invention, there is also
provided an electrohydraulic proportional valve comprising: (a) a
pilot actuator assembly comprising a pilot spool slidably received
in a pilot sleeve and a feedback spool having a camming surface
against which said pilot sleeve rides, said camming surface com-
prising a first portion in which the position of said pilot sleeve
.is a function of the axial position of said camming surface and a
second portion immediately ad~acent said first portion in which
the position of said pilot sleeve is constant regardless of the
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axial position of said camming surface; (b) an elec-tromagnetic
force motor assen~ly having an output member which is operatively
connected to said pilot actuator assembly such that motion of
said output member results in corresponding motion of said pilot
spool; and (c) a main spool and body assembly comprising: (i) a
main spool which is operatively connected to said pilot actuator
assembly such that motion of said main spool results in corres-
ponding motion of said feedback spool; (ii) first and second load
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holding check valves slidably disposed in a bore; (iii) first and
second load holding check plungers slidably disposed in said bore
between said first and second load holding check valves, said
first load holding check plunger being operatively associated with
said first load holding check valve and said second load holding
check plunger being operatively associated with said second load
holding check valve; and (iv) first means of fluid communication
for communicating control pressure to said bore between said first
and second load holding check plungers when said pilot sleeve is
in contact with said second portion of said camming surface.
In accordance with the present invention, there is also
provided in an electrohydraulic proportional valve comprising:
(a) a pilot actuator assembly comprising a pilot spool slidably
received in a pilot sleeve and a feedback spool having a camming
surface against which said pilot sleeve rides; (b) an electromag-
netic force motor assembly having an output member which is opera-
tively connected to said pilot actuator assembly such that motion
of said output member results in corresponding motion of said pilot
actuator assembly; and (c) a main spool and body assembly compris-
ing a main spool which is opcratively connected to said pilotactuator assembly such that motion of said main spool results in
corresponding motion of said pilot actuator assembly, the improve-
ments wherein: (d) said camming surface comprises a first portion
in which the position of said pilot sleeve is a function of the
axial position of said camming surface and a second portion imme-
diately adjacent said first portion in which the position of said
pilot sleeve is constant regardless of the axial position of
said camming surface; and (e) said main
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spool and body assembly further comprises: (i) first and secondload holding check valves slidably disposed in a bore; tii) first
and second load holding check plungers slidably disposed in said
bore between said first and second load holding check valves, said
first load holding check plunger being operatively associated with
said first load holding check valve and said second load holding
check plunger being operatively associated with said second load
holding check valve; and (iii) first means of fluid communication
for communicating control pressure to said bore between said first
and second load holding check plungers when said pilot sleeve is
in contact with said second portion of said camming surface.
Brief Description of the Drawings
Figure 1 is a partly cross-sectional view of an electro-
hydraulic proportional valve according to the present invention.
Figure 2 is a partly cross-sectional view on an enlarged
scale of the electromagnetic force motor and the pilot actuator
assembly of the valve shown in Figure 1.
Figures 3A through 3D are schematic views used to
illustrate the act.ion of the feedback spool.
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Figures 4A through 4C are, respectively, an enlarged eross-sectional
view of the pilot spool and the pilot sleeve, a schematic drawing illustrating
the elements of the pilo~ actuator assembly, and a graph used to illustrate the
effect of contaminants in the hydraulic fluid on the operation of the valve.
- Figures 5A and 5B are, respectively, a free-body diagram of the main
spool and a graph used to illustrate the effeet of eontaminants in the hydraulie
fluid on the operation of the valve.
Figures 6A through 6C are eross-sectional views of the main spool and
body assembly showing it in different positions than it is in Figure 1.
Detailed Description of a Preferred
Embodiment of the Invention
The electrohydraulie proportional valve shown in ~igures 1 and 2 com-
prises an electromagnetie force motor 10, a pilot actuator assembly 12, and a
main spool and body assembly 14. Each of these assemblies is designed as a com-
plete and separate unit for field servicing. The force motor 10 is threaded in-
to the pilot aetuator assembly 12 at 16, and the pilot actuator assembly 12 can
be detached from the main spool and body assembly l~ by removing two mounting
screws (not shown).
The eloctromagnotic force motor 1() is a bidireetional device which pro-
duces a linear output displaeement which is l~roportional to the magnitude and po-
larity ot the eleetrie signal. I'hc m~gnetie eireuit of the foree motor eontains
permanellt m~lgnots whicll crente a polari~ing magnetie flux in the working air
gaps. Tlle eoil tlux intoraets w1th the permanent ma~net flux to move the arma-
ture in one direetion or the otller depelldlng upon the polarity of the eleetrie
signal. Tlle armature of the force motor is spring-eentered so that it always re-
turns to a neutral position UpOIl the loss of the electrical signal. The arma-
ture is fully suspended from the rest
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of the force motor assembly. Thus there are no rubbing
contacts between the armature and the rest of the force
motor assembly, and hysteresis is recluced due to the
elimination of frictional forces acting on the armature.
Additionally, the force motor cavity is flooded with oil
in order to eliminate the use of small dynamic seals which
would be subjected to a large number of cycles and which
would place undesired frictional forces on the armature
assembly.
Since the force motor 10 is mounted on the pilot
actuator assembly 12 by means of threads 16, the force motor
10 can be nulled to the pilot actuator assembly 12 by merely
screwing the force motor 10 in or out of the pilot actuator
body 18 until the desired null position is achieved. Once
nulled, the force motor 10 is locked in position by means
of a set screw 20.
The pilot actuator assembly 12 comprises a
pilot spool 22 slidably received in a pilot sleeve 24 and
a feedback spool 26 having a cammin~ surface 28 against
which the pilot sleeve 24 rides. To minimize frictional
forces between the pilot sleeve 2~. and the camming surface
22, the wor]cing surface of the pilot sleeve 24 is a ball
bearing 30 captured in a plug 32 which is force fit in
internal bore 3~ which also receives the pilot spool 22.
The camming surface 28 comprises a first portion
36 in which the position of the pilot sleeve 24 is a function
of the axial pOSitiOIl of the cammin~ surface 28 and a
second portion 38 immediately acljacent thc portion 36 in
which the position of the pilot sleeve 2~ is constant regard-
less of the axial position of the camming surface 2S. In
particular, in the illustrated embodiment the portion 36
is linear, and that portion of the feedbac~ spool 26 is
in the shape of a truncated cone. Tlowever, other shapes
of the portion 36 of the camming surface 2a and of the feed-
; 35 back spool 26 are ohviously possible and are within the
contemplation of this invention.
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The pilot spool 22 is in direct contact with
the output member 40 of the force motor 10. A spring
42 is disposed between the force motor 10 and the pilot
sleeve 24 to bias the pilot sleeve 24 towards the feed-
back spool 26, and a spring 43 is disposed between theplug 32 and the pilot spool 22 to bias the pilot spool 22
towards the output member 40. Thus motion of the output
member 40 results in corresponding motion of the pilot spool
22, and the pilot sleeve 24 remains in contact with the
feedback spool 26 regardless of its axial position.
The pilot spool 22 comprises a central piston 45
snugly received in the bore 34 in the pilot sleeve 24, first
and second reduced diameter areas 44 and 46 on either side
of the central piston 45, and first and second distal pistons
48 and 50 snugly received in the bore 34 on either side
of the reduced diameter areas 44 and 46. As shown in
Figure 4A, the pilot spool 22 has an internal bore 52
which openS into the bore 34 at 54 and~ ~ ceA3
leading through the reduced diameter areas 44 and 46
to the bore 52. The bore 52 is also open at the other
end, but since that end of the pilot spool 22 is in
contact with the output member ~0 of the force motor 10,
a passageway 56 is provided to ensure fluid communication
between the bore 52 and a chamher 58. ~Iydraulic fluid
from the chambcr 58 in turn floods the force motor cavity,
as previously stated.
~ p~ssa~cw~y 60 in the pilot slceve 24 provides
fluid communication between the bore 34 past the distal
piston 50 and a chambcr 62 de~ined by a reduced diameter
portion of the pilot sleev~ 24 and a bore 64 in the pilot
actuator body 18 which slidably receives the pilot sleeve
24. The ch~mber 62 communicates in turn with a chamber
66 defined by the camming surface 28 and a bore 68 in the
pilot actuator body 18. ~ passageway 70 is provided
leading from the chamber 66 to tank. Thus the force motor
cavity, the chamber 58, the bore 52, the bore 34 past the
distal piston 50, the chamber 62, and the chamber 66 are
all maintained at tank pressure.
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In addition to the camming surface 28, the
feedbac]c spool 26 comprises first and second pilot pistons
72 and 74, one located on either side of the camming surface
28. The bore 68 and the pilot pistons 72 and 74 define
first and second control chambers 76 and 78 located on the
opposite sides of the pilot pistons 72 and 74 rom the
camming surface 28. The control chamber 76 is closed by
a plug 80 which slidably receives an extension 82 of the
feedback spool 26, and the control chamber 78 is closed by a
plug 84 which slidably receives an extension 86 of the main
spool 88.
Pilot supply pressure is communicated to the pilot
actuator assembly 12 through a bore 90 in the main spool and
body assembly 14 (shown in section in Figures 1 and 2), a
15 passageway 128 in the main spool and body assembly 14, and a
passageway 126 in the pilot actuator assembly 12. The passage-
way 126 opens into a chamber 92 containing a replaceable
pilot filter 94. Access to the chamber 92 to replace the pilot
filter 94 is provided by a threaded plug 95. A passageway 96
communicates pilot supply pressure from the chamber 92 to the
bore 64 adjacent a reduced diameter area 98 in the pilot sleeve
24. A passageway 100 through the reduced diameter area 98 in
the pilot sleeve 24 in turn communicates the pilot supply
pressure to the reduced diameter area 44 and/or the reduced
dic~meter area 46, dependin~ on the position of the pilot spool
22 in the pilot sleeve 24. From the reduced diameter areas
44 and 46 a portion o~ the pilot supply is communicated to
tank through the~r~rc~c~ A3, as previously explained.
The pilot supply is also communicatcd through~ ~ 102
30 and 104 in the pilot sleeve 24 to reduced diamet~r areas 106
and 108 in the pilot sleeve 2~. From the reduced diameter
areas 106 and 108 thc pilot supply pressure is in turn
communicated to the control chambers 76 and 78 via passageways
110 and 112, respectively.
Turning to Figure 4A, it will be seen that the
passageway 100 through the pilot sleeve 24 is just larger in
cross-section than the central piston 45. Accordingly, for
reasons explained hereinafter, reduced pilot supply pressure
is communicated to both reduced diameter area 44 and reduced
; 40 diameter area 46 when the central piston 42 ls in its null
position.
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As will be apparent from the foregoing, when
the pilot spool 22 is moved relative to the pilot sleeve
24 by the force motor 10, it meters the flow of pilot
supply pressure to one end or the other of the feedback
spool 26, causing it to move axially in the bore 68.
As the feedback spool 26 moves back and forth in the bore
68, the pilot sleeve 24 is forced up and down in the bore
64, providing a positive position feedback between the
feedback spool 26 and the pilot sleeve 24. ~
~ 10 ~ For example, if the pilot spool ~ is moved
: downward by the force motor 10, pilot flow is directed
to control chamber 76, ~orcing the feedback spool 26 to
the right. As the feedback spool 26 moves to the right,
the pilot sleeve 24 rides down the camming surface 28
until it again shuts off the flow to control chamber 76.
Similarly, if the pilot spool 22 is moved upwardly by the
: force motor 10, pilot flow is directed to the control
chamber 78, forcing the feedback spool 26 to the left.
As the feedback spool 26 moves to the left, the pilot sleeve
rides up the ca~ning surface 2~ until it again shuts off
the flow to control cha~ber 7~. Therefore, for every
position of the pilot spool 2~ there is a corresponding
steady-state position of the cedback spool 26.
: This uniquc method of mechanical fccdbac]c perrnits
the use of a variable feedback gain throughout the stroke
of the main spool ~ s shown in Figure 3, the feedback
gain is reduced to æcro for sclected voltagcs -- for
instance, -6 VDC to -12 VDC ~iynals. This results in the
same hard-over "float" position for all voltages in the
selected range. Thus normal voltage drops in the electrical
system due to battery rundown or line losses do not limlt
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the ability of the pi.lot actuator assembly 12 to move the main spool to the full
~'float" position provided that at least a pre-selected minimum voltage (such as
` -6 V~C) can be applied to the force motor coil.
As shown in Figures 4A through 4C the pilot valve is designed such
.~ that both the pressure PCl in control chamber 76 and the pressure PC2 in control
.. chamber 78 are reduced to very low levels when the electrical signal is removed.
This is accomplished by making the fixed orifices A3 relatively large (e.g.
0.025 to 0.030 inches in diameter~ compared to the variable orifices Al and A2
defined by the di.fference in dimensions between the central piston 45 and the
passageway 100. Thus if contamination in the fluid begins to silt up variable
orifices Al and A2 as shown in Figure 4C the effect is to further reduce the
pressure in control chambers 76 and 78.
I`he significance of low null pressures in control chambers 76 and 78
is better shown in Figure 5A which contains a free-body diagram of the main
spool 88 with the pilot pi.ston forces (Fp) acting on one end of the spool and
the spring-centering forces (Fs) acting on tlle opposite end. As shown in Figure
5B the preload force in the spring-centering mechanism attached to the mai.n
;. spool 88 is always groater thall the maximum p;ilot r)iston force wll:ich can be gen-
; erated :if one upstroam orifice (Al or A2) .is siltecl fully closed while the other
uI)stream or:i:fice remaills fully OpCIl (the worst case possible). Thus the main
.~ spool will :rc.~maill :in the "holcl" pOS:;t;.OII over long periocls of ti.me without the
.. ulldesirecl drifti.ng oftell iassoc~ tecl w:ith electrohycl-r;llJIic prol)ortional control
.~ valves.
Returllillg to ligures 1 alld 2 it will be seen that the extensi.on 86 of
~ the main spool 88 is attached to the pilot piston 74 by means of a pin/hook ar-
; rangement which
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permits easy removal of the entire pilot actuator assembly 12 to
facilitate field servicing. As will be apparent, the connection
of the main spool 88 to the pilot piston 74 translates motion of
the feedback spool 26 into corresponding motion of the main spool
88.
The main spool and body assembly 14 comprises a main
valve body 114 containing a bore 116 in which the main spool 88 is
slidably received and a bore 118 in which first and second load
holding check valves 120 and 122 and first and second load holding
check plungers 121 and 123 are slidably received. The main spool
88 has a reduced diameter area 124, and pilot supply pressure is
communicated to the reduced diameter area 124 from the bore 90
through a passageway 127 when the pilot sleeve 24 is in contact
with the portion 38 of the camming surface 28. A passageway 130 in
the main valve body 114 provides fluid communication from the re-
duced diameter area 124 to the bore 118 between the load holding
check plungers 121 and 123 when the pilot sleeve 24 is in contact
~; with the p~rtion 38 of the camming surface 28. A passageway 132 in
the main valve body 114 connects the passaqeway 130 to the bore 116
adjacent a passageway 134 leading to tank.
The load holding check valves operate in a conventional
fashion during the "hold", "raise", and "lower" modes of operation.
As shown in Figures 1, 6A, and 6B, the passageway 132 provides com-
; munication between tank and the bore 118 between the load holding
check plungers 121 and 123 during those modes. When the main spool
- is moved to the "float" position, however (i.e., when the pilot
sleeve 24 is in contact with the portion 38 of the camming surface
~` 28 as illustrated in Figure 6C), pilot pressure is communicated
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through the passayeway 127, the reduced diameter area 124, and
the passageway 130 to the bore 118 between the load-holding check
plungers 121 and 123, the passageway 132 is closed by a land 136
on the main spool 88, and the plungers 121 and 123 thereupon
separate to open both load-holding check valves 120 and 122.
(Of course, the area ratio between the check valves 120 and 122
and the plungers 121 and 123 must be sized to permit pilot pressure
to unseat the poppets at the highest design pressure.)
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As previously mentioned, spring centering forces (Fs) act on the main
spool 28. They are generated by a spring 138, preferably located in the main
spool and body assembly 14 and bearing on the main spool 88. The spring 138
biases the foedback spool 26 towards a centra] position wherein the pilot sleeve
24 is in contact with the portion 36 of the camming surface 28. As shown, the
spring 138 is conveniently housed in a separate spring housing 140 in which one
end bears against a cap 142 seated against the main valve body 114 and the other
end bears against a cap 144 carried by a head 146 on the main spool 88. How-
ever, many other arrangements for this spring are obviously possible.
Load sensing check valves 148 and 150 are located in the cylinder port
passage of each valve segment. They are ported such that only the highest cyl-
inder port pressure is fed back to a compensating spool in the inlet manifold or
to a pressure compensating pump.
Caveat
Wh;le the present invention has been illustrated by a detailed descrip-
tion of a preferred embodiment thereof, it will be obvious to those skilled in
the art that various changes in form and detail can bc made therein without de-
parting from the truc scopc of tho invontion. l:or that rcason, the invention
must be measurcd by the cl.lims aplcndod hcrcto and not by thc foregoing proFerred
embodiment.
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