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Патент USA US2404282

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July 16, 1946.‘
H, F. FRUTH _
' 2,404,282
APPARATUS FOR MAKING PIEZOELECTRIG CRYSTALS
Filed April 24, 1944
INVENTOR,
F 222272,
yk/W
' @2
Patented July 16, 1946
2,404,282
UNITED‘ STATES PATENT ‘OFFICE ‘
2,404,282
APPARATUS FOR MAKING PIEZOELECTRIC
CRYSTALS
Hal F. Fruth, Chicago, Ill., assignor to Galvin
Manufacturing Corporation, Chicago, 111., a
corporation of Illinois
.
Application April 24, 1944, Serial No. 532,430
3 Claims.
(Cl. 51-124)’ .
1
2
each slab into rectangular blanks of the'approx
The present invention relates to improved ap
paratus for manufacturing piezoelectric crystals,
imate desired dimensions, all three dimensions of
each blank being considerably greater than the
desired dimensions in order to permit the grind
impart predetermined frequency characteristics 5 ing operations to be carried out. The rough cut
and more particularly, to improved apparatus
for grinding the faces of piezoelectric crystals to
thereto.
crystal blanks are next placed in the‘lap grinding
a
In the manufacture of piezoelectric crystals,
such, for example, as quartz crystals adapted for
apparatus shown in Figs. 1, 2 and 3 of the draw
ing, and subjected to a lap grinding operation
use in communication circuits, and more partic
ularly, for use in crystal microphones, radio
for a de?nite interval of time sufficient to insure
that one face of each crystal will be ground ex
actly fiat. After one face of each crystal has
been thus ground to impart a ?at contour there
transmitting and receiving systems, and the like,
the crystal blanks are ?rst cut from the crystal
stock and are then ground to the dimensions re
to, belt grinding apparatus‘ is used to pressure
grind the opposite face of each crystal for the
quired to provide the desired frequency and ac
tivity characteristics.
More particularly, the
purpose of reducing the thickness of the crystal.
Following this operation, which is utilized to re
duce the thickness of each crystal more nearly.
usual crystal blank is cut in the form of a wafer
like rectangular piece, having dimensions slight
, to approach the desired thickness with consid-l
ly larger than the desired dimensions, is then re
duced in size to approach the desired rectangular
erablegrindin-g rapidity, the crystal blanks are
dimensions by the use of lap-and edge grinding 20 returned to the lap grinding apparatus and both
apparatus, and ?nally is reduced to the exact de
face surfaces of each crystal are ground in this
sired dimensions by ?nish grinding operations.
apparatus in order to remove deep scratches and
It is an object of the present invention to pro
pits from the crystal faces and to further reduce
vide improved grinding apparatus for rapidly
the thickness of each crystal more nearly to ap
grinding the faces of a crystal to render the faces 25 preach the desired thickness. In this regard, it
substantially flat and substantially parallel,
will be understood that the thickness of “each
without the production of deep scratches or
crystal determines its resonant frequency, the
whole object of the face grinding step being that
of reducing the thickness'of the crystal to the
other surface irregularities therein.
‘
It is another object of the invention to provide
' improved lap grinding apparatus which may be 30 exact desired thickness in order to impart a pre
determined resonant frequency to the crystal,
while at the same time obtaining a highly pol
ishedand scratch-free surface. In other words,
easily loaded with a plurality of crystal blanks
and in which the contact pressures used in grind
ing the different crystals may be determined on
the thickness of each crystal may be measured in
‘
,
The invention, both as to its organization and 35 terms of the resonant frequencyof the crystal, ‘
an individual crystal basis.
method of operation, together with further ob
jects and advantages thereof will best be under
stood by reference to the following speci?cation
taken in connection with the accompanying
drawing, in which:
During the third described step of lap grinding
the crystal faces, the crystals are ground until
the resonant frequency of each‘crystal is from
ten to sixty kilocycles lower than the particular
40 desired resonant frequency, in preparation for
Fig. lis atop perspective view illustrating im
proved lap grinding apparatus characterized by
?nish grinding to the exact desired frequency.
Referring now more particularly to the struc
tural arrangement of the lap grinding apparatus
illustrated in Figs. 1, 2 and 3 of the drawing, this
45 apparatus comprises a circular plate 10 whichis
proved methods;
.
Fig. 2 is a side View of the apparatus shown
rigidly mounted at the upper end of a shaft 12
for rotation about its center, and is provided with
in Fig. 1'; and
certain features of the present invention and
utilized in part in the practice of the present im
Fig. 3 is a fragmentary sectional view illus- ‘
a ?at upper abrading surface lllbr The shaft I2
trating the arrangement of the weights which
is iournaled for rotation in bearing members _ [3
are individually utilized to maintain the crystals 50 which are mounted upon opposite sides of a sup
in engagement with the abrasive surface of the ' porting platform I I. This platform is held in ele-'
vated position above a base, not shown, by means
apparatus shown in Figs. 1 and 2.
"
.
In using the present improved apparatus, th
, of side members, one of which is indicated at I la,
crystal wafers or blanks are obtained by sawing
andtheshaft I2 is adapted to be rotated by means
thin slabsfrom the crystal stock-and by dicing
of an. electric. mom, 'Pari'ied, by . the. base. The
2,404,282
3
4
sociated crystal 9 may be produced by the liquid
3| with which the cup is partially ?lled. Any
liquid, such, for example, as mercury, having great
weight per unit volume, may be utilized in ?llingr
the cups 3|] to the level required to establish the
desired contact pressure. After the pockets of
the holders I8 and I9 have been loaded in the
platform II also supports stationary members I4
and I5 having circular edges Ma and I5a which
embrace but do not touch opposite peripheral arcs
of the plate I0. These stationary members are
held in elevated positions above the platform II,
such that the top‘ surfaces thereof are exactly»
flush with the top abrading surface of the plate
In, by means ‘of supporting posts-I6, which-are
anchored to the top of the platform 'II ‘in any
manner just explained‘, the 'abrading surface Illb
of the plate I!) may be sprinkled ‘with diamond
dust or another loose abrasive of suitable ?neness,
suitable manner.
“following which operation of the driving motor
‘or motorsto-rotate the two shafts l2 and 21 may
‘be initiated.
tals in engagement with the ‘top abrasive surface , x In :response to rotation of the shaft 21 the
“lb of the plate I0. More - - speci?cally, these . .15 arm l:'l;isupivoted:back and forth about the pivot
‘ipinlzl'through failimited angle by means of the
holders are rotatably supported at the ends Fla
pimand slotconnection between this arm and the
and Nb of a bifurcated arm I11, 'pivotpinsilland
plate 26. As a result, the crystal holders I8 and
2| being utilized to rotatably mount the ,plates 18
Circular crystal holding plates I8 and ‘[9, each ‘I
' provided with a plurality *of r-crystal receiving
' pockets 22 and 23, are utilized to support the crys
I‘9‘ are ‘moved back and forth across the center
and I9 at the ends of the two arm bifurcations."
The arm I‘! is pivotally mounted at the upper 20 of the plate I9, so that peripheral portions there
of alternately overlap the 5two stationary mem
bers I4 and l'lii. Incident to this movementof
the crystal holders, each crystal is moved across
mounting screws 25; For the purpose of ‘pivoting
the abrading surface I91; from one‘ sided the
the'arm 1:‘! back and'forth through a predeter
mined angle, thereby to sweep the crystal holders 2,5 center of rotation of the plate H! to "the'other,
end‘o'f a post zlllextending ‘upright from ‘the plat-‘
form "I I and rigidly ‘anchoredthereto'byimeans of
with the result that the lower surfaces of 'the
I8‘ and vI9 back and forth through ‘a limited are
crystals are rapidly abraded. During movement
which overlies the abrasive upper surface ‘Iii‘b ‘of
of the arm I‘! fromon‘e limit'of its range of move;
the ‘plate l9, this arm is connected to a rotatable.
ment to the other, each oft-he "two crystal hold-w
crankplate 26 through a pin- and'slot connection
which comprises-spin 2 9 extending upwardly from 30 ers 5I8 and I9 is rotated ‘relative‘to the plate ‘IE3
in order ito' change the vposition of each crystal
the plate ‘26 within :a slot 2% formed longitudi
relative to the abrasivesurface ‘I06 of the plate
nally of the'arm. ‘The plate 26 isset screw mount
It]. Thus assuming‘ that- the-plate ‘I'll lis‘rotating
ed uponlthe upper end of a second rotatable shaft
in a counterclockwise direction, as viewed _~ in
2 ‘I which‘is'journaled intermediate'theends there~
Fig. l' of the drawing, and that; [the crystal
of‘withinbearing members '28‘ disposed upon op
holder ‘I9, for example, occupies the ‘position
posite sides of the platform II, and is driven at
shown in ‘full lines in "this ?gure of ‘the drawing,
a-slow-spejedeither'through a, speed reducing gear
the frictional engagement between the abrading
box' ‘actuated by ‘the driving motor- for ‘the shaft
surface lllb of ‘the plate- It» and the-‘engaging
I2 or-by ‘a second‘slow speedrelectric motor di
facesiof ‘the crystals within the pockets ‘2'3 of the
rectly "connected to the shaft 721'! and carried by
holder causes the holder to berotated' in a coun
the‘base located at ithe bottom ends of the side
members‘ Ila.
‘
‘I ‘
tereclockwise ‘direction, suc'h'that- ‘the positions
1
“ r'ie'?y to consider the operation of‘ the de
scribed lapping apparatus, it may be pointed out
of ‘the crystals relative’ to-‘the abrading surface
that before rotation of the shaft l'l‘to-drive’the
moved from this position to a‘ position wherein
the "center. of» the holder substantiallyoverlies
are continuously -'ch'anged.- Y As the holder I9 ‘is
abradin'g plate‘lo'and rotation ‘of thesh'af't 21 to
the center of thee-plate ‘HI,- the ‘retatienal'forces
pivot vthe arm 'I‘I back and forth are initiated,ja
crystal 9' is placed in ‘each or a portion 'of' the
acting upon this holder are i’more‘ effectively
utilized to cut down the degree of slipibetween,
the platelil'and the holder, with the result that
the speed of rotation‘ of the holder is'increased.
pockets "22 and 23 respectively pro‘videdin the two
holders I8 and ‘i9. Depending ‘upon the position
of'the' arm Il, each crystal is ‘disposed facedo'wn
During ) continued movement of ‘the holder 1'I‘9i'to~
wards the‘ stationary‘ ‘member I and- away frém
wardly'against the upper-surface of-one *of the
twostationary members 1'4 and ‘I5 or theu-pper
the center of the plate-I0 the’fo‘r'ces "tending to
rotate this holder are tlesseffectively utilized ‘with
the r'esu-lt‘thatithe speed of retati'clntif the holder
relative‘to the plate'i'Iill ‘is decreased. Thistle
abrading’surface Il'li'b'of ‘the plate "I0. In this‘ re
gard it'is noted that the ,abradingjsurface I706 ‘of
the‘p'late I'll is ground perfectlyilat,that-the‘upp'er
surfaces of ‘the ,twoimembers' 14 and l'571'are like
wise perfectly flat and ‘are exactly ?ush withv the
surface I'llb of the plate lid. 'Weight's in the form
of liquid ?lled rubber cups ‘316 are ‘utilized ‘to es
tablish the desired contact 'pressure‘be'tweeh‘the \
‘bottom-surface of each crystal 9 and the upper
surface of the m‘emberj?l, I4‘or f5 againstiwhich
the‘, particular crystalbears; More speci?cally,
each partially ?lled liquid‘ receiving‘- cup indeter
min'es the'contajct pressure’betweenthe lower ‘face
' of the crystal which-it‘ Weightsjand the ‘upper
abrasive surface Illbfovf'tlie plat'ef'l‘?. E'achicupqiiil
loosely
and‘ is flirts
provided-with
within 'itsla‘ssoci‘ated
relatively pocket
‘heavy;‘22*or‘
sidewall
portion 36a to'prevent expansion of thesidewall
into binding, engagement with the 'WaHSfOf' ‘the
pocket. ‘Ea'ohfcu'p ishalso 'providedwith a :thin,
. ii'eiiible‘bottorhwall 39bin‘orderthat‘adistributed
pressure "over the» entire 'upper surface ‘of the ‘as;
' crease-in the ‘speedof rotationbf’theholderdg
as the 'helder is moved tower
to
the edge of the
plate 1c is accompanied by
increase in"‘the
linearspee’d at which the abrasive' surfaceil'l'?b
underlying» thev ‘crystal faces is--'~meved relative/‘to
these faces‘; Thus it'willibefappairerit'ethat the
rate ‘of abrasion ‘is "increased as the ‘liolderil‘9 ' is
' moved towards the edge of'the p‘late *‘I‘ll; t?lfir'ing
continued ‘movement/of the holder ['9 'in-the in
dicated direction, a point is reached fat‘ whichv
the edge ‘portion of- -'the holder engages", the "edge
of» the’ stationary member 115:; 1When ‘this occurs
andedu'e ‘to the if'ricti'onal’i‘di'a'g between the en
gaging,surfacesvcf‘ithe ‘parts’ it and 19, the'di-i
rection of rota'?ihni'lof ‘the! holder I59 ‘about its
pivot vpoi'nl'l2'l~ is reversed
the'de'gre
fiov'er
lap‘bétween the-two par wand "I 9 is increased,
the resultant ‘of I‘the rotational forces-acting 5’up0n
2,404,282
5
the holder I9 is shifted in a direction to increase
the speed of rotation of the holder l9 about
its pivot point 2| vin the reversed direction.
Thus it will be apparent that the speed of
rotation of the holder I9 is substantially
constantly changed during movement of this
holder from its illustrated full line position
to its illustrated dotted line position. During
movement of the arm I‘! in the reverse direction,
the action is the reverse of that just described. 10V
As each crystal 9 within a pocket 23 of the holder
I9 is moved to a position where the lower face
thereof partially overlies and engages the abrad
ing surface lllb and partially overlies and en
gages the upper surface of the stationary mem 15
I claim:
6,
1. Apparatus for face grinding piezoelectric
crystals, comprising a circular abrading plate
rotatable about its center and having a ?at upper ’ I I
abrading surface, a stationary member having 7
a top surface flush with the upper surface of ,
said plate and having an edge closely adjacent
at least a portion of the periphery of said plate,
an arm pivotally movable about a point removed
from the axis of rotation of said surface, a
crystal holder pivotally connected to said arm -
for free rotation relative‘to- said abrading plate,
and means for pivoting said arm back and forth '
through a limited angle which is so related to
said abrading plate and stationary member'that
ber I5, the frictional forces acting thereon tend
said holder partially overlies said member each
to rotate the crystal within the pocket 23 in
time said arm is moved to one limit of said
which it is disposed. Rotation of the crystal
within its pocket is permitted due to the loose
2. Apparatus for face grinding piezoelectric
inter?tting relationship between the side walls 20 crystals, comprising a circular abrading plate '
angle.
30a of the rubber cup 3!) and the walls of the
pocket. Thus each crystal is not only rotated
about the axis 2| of the holder l9, but is also
7
'
rotatable about its center and having a. flat upper
abrading surface, stationary members having top
surfaces ?ush with the ‘upper ‘surface of said
plate andhaving edges closely adjacent portions
rotated about its own center during each move
ment of the arm I‘! from one limit of its range 25 of the periphery of said plate upon opposite sides
of pivotal movement to the other.
of said plate, a bifurcated arm pivotally movable
From the foregoing explanation it will be un
about a point removed from the center of said
derstood that due to the rotation of each crystal
abrading plate,.crystal holders respectively con
9 in a plane parallel to the surfaces of the parts
nected to the bifurcations of said arm for free
l4, l5 and ill, the edge sector of the crystal ini 80 rotation relative to said abrading plate and said
tially engaged by the rotating abrasive surface
arm, each of said holders including pockets for
lub of the plate Ill is continuously changed in a
maintaining crystals face downward against said ,
more or less random manner with the result that
abrading surface, and means for pivoting said'
the direction of cut across thecrystal face is
arm back and forth through a limited angle
continuously shifted at random. The same ac 85 which is so related to said abrading plate'that‘
tion of rotating each crystal'disposed within a
pocket 22 of the holder I8 about two‘ different
said holders are alternately moved to overlie
centers of rotation during back and forth move
ment of this holder between the limits of its
moved from either limit of said angle to the
different ones of said members as said arm is
other.
'
'
~
.
3. Grinding apparatus comprising ‘a circular
back and forth pivotal movement of the arm
abrading plate rotatable about its center and
I]. The purpose of thus continuously changing
having a ?at upper abrading surface, a stationary
the edge sector of each crystal which is initially
member having a, top surface flush with the upper
engaged by the abrasive surface is that of pre
surface of said plate and having an edge closely
venting scratches from being formed in the crys 45 adjacent at least a portion of the periphery of
said plate, a rotatable work holder for holding a
tal face being abraded, due to recurrent move
work piece in a position offset with respect to
ment of the same abrasive particles along the
same lines of abrasion across the crystal face.
the axis of rotation of said work holder and in
Thus it is possible with the described apparatus to
contact with said abrading surface, means sup
obtain relatively rapid grinding of the crystal 60 porting said holder for free rotation about its
range of movement, is also obtained during the 40
faces to a substantially ?at contour Without pro
ducing scratches or other surface marks in the
axis of rotation, and means for so moving said
supporting means that said work holder is moved
abraded crystal faces. Moreover, by the system
of individual Weights comprising the cups 30 filled
transversely back and forth across said abrading '
surface and overlies the upper surface of, said
to the same or different liquid levels, either uni 55 plate, whereby engagement of the work piece with
said abrading surface and the upper surface of
form or non-uniform grinding of the different
said plate rotates said work holder relative to
crystals may be obtained, as desired.
said supporting means and thus changes the line
While one embodiment of the invention has
of cut across said work piece.
been described, it will be understood that various
modi?cations may be made therein which are 60
HAL F. FRUTTH.
within the true spirit and scope of the invention
as de?ned in the appended claims.
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