Патент USA US2404282код для вставки
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.