US3395494A - Lapping machine - Google Patents

Description

Aug. 6, 1968 T. SOGN 3,395,494

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United States Patent 3,395,494 LAPPING MACHINE Leland T. Sogn, Kettering, Ohio (8700 Metcalf Ave., Apt. 101E, Overland Park, Kans. 66202) Filed May 25, 1965, Ser. No. 458,646 22 Claims. (Cl. 51-161) ABSTRACT OF THE DISCLOSURE A lapping machine has drive means to orbit carriers for elements to be lapped between upper and lower lapping plates, the drive means contacting the carriers through free spinning parts so that the drive means does not restrict the natural tendency of the carriers to undergo a spin rotation about their own geometric axes in progressing through their orbital path. Lapping pressure is supplied by the weight of the upper lapping plate which rests upon the elements to be lapped and lapping thickness is controlled by limit devices which intercept downward movement of the upper lapping plate as the lapping progresses, whereby the support for the upper lapping plate is transferred from the elements being lapped to the limit devices. Plural limit devices which provide a stable three point support for the upper lapping plate at termination of the lapping operation are adjustable in unison by a single operating device to predetermine the thickness desired for the finally lapped elements. To assure uniform lapping of all elements, control circuit means responsive to contact between said limit devices and cooperating stop elements carried by said upper lapping plate terminate the lapping operation a predetermined time after first contact between any limit device and its cooperating stop member.

This invention relates to a lapping machine and, more particularly, to an instrument for lapping elements, such as piezoelectric crystals, semi-conductors or the like, to precise thicknesses, however, the invention is not necessarily so limited.

While, as above indicated, the present invention can be applied to the lapping of diverse types of elements, the invention herein is particularly described with reference to the lapping of piezoelectric crystals and especially quartz crystals, there being no intention to thereby limit the invention to such application. In the production of quartz crystals for use as frequency control elements, electrical filters and the like, the crystal to be produced is first cut in a comparatively crude fashion to roughly the shape and size required for the particular operating frequency or frequencies sought. In this rough cut the crystal is deliberately cut to an oversize.

In ordinary production, a large quantity of crystals intended to operate at or near the same frequency are produced in a single batch. In a second operating step the precut batch of crystals is simultaneously lapped to the thickness required for the operating frequency or frequencies sought.

"An object of the present invention is to provide an improved lapping device for simultaneously lapping large quantities of crystals.

Another object of the present invention is to provide an improved lapping movement.

A further object of the present invention is to provide improved means to terminate a lapping operation at a predetermined thickness for the elements being lapped.

Still a further object of the present invention is to provide an improved means to lap elements such as piezoelectric crystals.

Other objects and advantages reside in the construction of parts, the combination thereof, the method of manu- 3,395,494 Patented Aug. 6, 1968 'facture and the mode of operation, as will become more apparent from the following description.

In the drawings:

FIGURE 1 is a fragmentary perspective view, with poriions broken away, illustrating the basic operating elements of a lapping machine embodying the present invention.

FIGURE 2 is a fragmentary sectional view, with parts broken away, taken substantially along the line 2-2 of FIGURE 1 and primarily illustrating the means for driv ing the basic operating elements illustrated in FIGURE 1.

FIGURE 3 is a plan view illustrating a carrier suitable for use in the lapping machine of FIGURES 1 and 2.

FIGURE 4 is a plan view schematically illustrating a first modification.

FIGURE 5 is a plan view schematically illustrating a second modification.

FIGURE 6 is a perspective view with portions broken away illustrating a third modification.

Referring to the drawings in detail, the lapping machine illustrated in FIGURES 1 and 2 utilizes generally toroidal lapping plates 10 and 12 to accomplish the lapping function. The lapping plates 10 and 12 have confronting planar but slightly roughened surfaces, which may be steel, as an example. The lapping action may be enhanced by introducing a suitable abrasive powder through the perforations 11 in the plate 12, powder being added from time to time as the operator may deem necessary or desirable.

The lower plate 10' is fixedly supported upon a main frame by means to be described subsequently. The upper plate 12 is supported above the plate 10 by the elements to be lapped. Thus, in FIGURE 1 there are illustrated elements 16, representing the elements to be lapped, deposited in perforations 17 which pass through comparatively thin carriers 14. The lapping plates 10 and 12 thus directly engage the upper and lower surfaces of the elements 16 which are to be lapped. For convenience, the elements 16 are sometimes hereinafter referred to as crystals.

The carriers 14, as shown in FIGURE 3, are circular perforated discs, the diameter of each disc exceeding the radial separation between the inner and outer peripheries of the lapping plates 10 and 12.. Thus, the carriers 14 have portions projecting outside both the inner and outer peripheries of the lapping plates.

In the preferred practice of the present invention three or more carriers 14 are distributed at equal intervals in the annular lapping region established by the plates 10 and 12. Illustrated are three carriers spaced at intervals. 'Ihe lapping motion of the present invention is achieved by advancing the three carriers 14 one behind the other and in unison along a circular or orbital trajectory about the geometric center of the lapping plates 10 and 12. This orbital movement is imparted to the carriers 14 by means of driving posts 1.8a and 18b which are moved orbitally and in unison about the geometric axis of the plates 10 and 12. There is one post 1 8a engaging each carrier 14 near the innermost projection thereof. Similarly, there is one driving post 1811 engaging each carrier 14 near the outermost projection thereof. The specific construction of the driving posts 18a and 18b and the means for moving such posts in unison will be described subsequently.

Due to the lapping friction between the elements 16 and the confronting lapping surfaces of the lapping plates 10 and 12, the orbital movement impressed upon the carriers 14 by the driving posts 18a and 18b will be transmitted to the upper lapping plate 12. So that both the upper and lower surfaces of the elements 16 will be lapped in a uniform fashion, it is necessary to restrain the upper lapping plate 12 against rotation.

For proper operation of the present machine it is also important that this rotational restraint on the plate 12 be accomplished with a minimum restraint on free axial movement of the plate 12. Thus, it is the weight of the plate 12 and anything placed thereon which determines the lapping pressure and any resistance to axial movement of the plate 12 changes the lapping pressure.

The lapping plate 12 is restrained against rotation by means of three radially disposed arms 20, these arms being spaced at approximately 120 intervals and overlying the plate 12. Each arm is mounted pivotally on a shaft 22 supported by a clevis 24. The three clevises 24 are fixedly supported by a vertically disposed cylindrical wall 26 integral with the frame 100.

The innermost end of each arm tapers to a downwardly directed finger 28, the three fingers 28 being adapted to centrally contact a supporting table 30 located at substantially the geometric axis defined by the plates 10 and 12. The table 30 rests upon an axially extending shaft 32.

Each of the arms 20 further includes a V-shaped notch 42 located on one side thereof in overlying relation to the plate 12. For reasons to be described later, each notch 42 is preferably lined with an electrically insulating liner 44, which preferably has a low coefficient of friction when in contact with steel. As viewed in FIGURE 1 each notch 42 is located on the counter-clockwise side of each arm 20.

The lapping plate 12 carries on its upper surface three brackets 34 spaced at 120 intervals about the geometric axis defined by this plate. Each of the brackets 34 includes an upstanding abutment 36 having a rounded wall portion 37 facing circumferentially and in the counterclockwise direction as viewed in FIGURE 1. The brackets 34 are attached to the plate 12 at such radial position that the rounded wall portion 37 thereof are approximately centered on an imaginary circular line bisecting the notches 42. Thus, upon orbital travel of the carriers 14 between the lapping plates 10 and 12, the curved wall portions 37 on the brackets 34 are moved orbitally into the notches 42 on the arms 20 so as to each make contact with the insulating liners 44 placed in the notches 42.

The brackets 34 which limit rotation of the upper plate 12 perform a second important function. Extending horizontally and in the counter-clockwise direction, as viewed in FIGURE 1, from the top of each abutment 36 is a bifurcated plate 38 integral with the abutment. The furcations in each plate 38 have confronting margins which define an approximately circular recess 39 to slidably receive a vertically disposed stop pin 40. The pins 40, which are adjustable in the direction of their own axes, are located at a position of fixed adjustment by a screw 41 passing through one furcation to threadedly engage the adjacent furcation and thereby compress the pin 40 between such furcations.

The adjustable pins 40 are used in combination with the following adjustment assembly to control the uniformity as well as the final thickness to which the crystals 16 are lapped.

Fixedly attached to the main frame 100 is a bracket which slidably receives the lower end of the shaft 32, this lower end being threaded as indicated at 48. The shaft 32 is keyed against rotation relative to the bracket 50 by means of a key 54 carried by the bracket 50 and projecting into an auxiliary disposed keyway 52 in the shaft 32. The key 54 slides freely in the keyway 52 so as not to restrict axial movement of the shaft 32 relative to the bracket 50.

The axial elevation of the shaft 32 is controlled by means of a worm gear 58 seated within a window 57 in the bracket 50 and bearing against the bottom of such window. The worm gear 58 threadedly engages the threaded end 48. of the shaft 32.

The worm gear 58 is driven by a worm seated within a clevis 56 integral with the bracket 50 and fixed to 4 a shaft 60. The shaft 60 is rotated by a crank 62. A metering drum 64 mounted on the shaft 60 in driving connection with the crank '62 is provided with indicia which can be used in cooperation with a stationary pointer 66 to measure the angular turn of the worm 55 and thereby the change in elevation of the shaft 32.

A parallel alignment between the lapping plates 10 and 12 is established in the following manner. With the carriers 14 and the crystals to be lapped removed from between the lapping plates and with each of the pins 40 released for sliding movement by adjustment of the screws 41, the upper lapping plate 12 is lowered into contact with the lapping surface of the plate 10. As the plate 12 is lowered onto the plate 10, the abutments 36 carried by the plate 12 are also seated into the notches 42 carried by the arms 20. Thereafter the shaft 32 is positioned by rotation of the crank 62 so as to lift the arms 20 away from contact with the plate 12 but not so high that any of the arms contact the bifurcated plates 38 overlying such arms.

After checking to ensure that each of the pins 40 firmly contacts the upper surface of the underlying arm 20, the screws 41 are carefully turned to firmly clamp the pins 40 in the bifurcated plates 38. Then, by rotation of the crank 62, the shaft 32 carrying the table 30 is elevated to lift the plate 12 off the plate 10 by raising the arms 20. The lower ends of the pins 40 are rounded so that in such raising of the plate 12 parallelism between the plates 10 and 12 will be maintained. Assuming care has been taken to ensure that the pins 40 are at equal radial positions, the elevating of the plate 12 can be accomplished with great precision.

In raising the plate 12 by rotating the crank 62, the plate 12 is elevated, as accurately as possible, distance which will result in the final crystal dimension desired. Having thereby located the proper elevation for the table 30, the plate 12 is carefully lifted and rotated in the clockwise direction as viewed in FIGURE 1 so as to disengage the pins 40 from the arms 20, then returned to contact with the plate 10. The arms 20 are then pivoted away from the lapping plates and the lapping plate 12 temporarily removed. The carriers 14 are then positioned on the lapping plate 10, the crystals to be ground inserted in the perforations in the carrier plates, the plate 12 returned to position above the plate 10 and the arms 20 returned to the position in which the fingers 28 engage the table 30.

The crystals 16 now support the plate 12 at an elevation which places the pins 40 above the arms 20. If the carriers 14 are now driven orbitally by their respective driving posts 18a and 18b the crystals 16 will be lapped under the pressure established by the weight of the plate 12 and the brackets 34 carried thereby. Lapping in this fashion will continue until the pins 40 engage the arms 20 which serve as limit members to limit downward movement of the plate 12. As the pins 40 move into contact with the arms 20 the weight of the plate 12 will be gradually transferred to the arms 20, with the result that as the crystals 16 approach the thickness established by the setting of the crank 62 the lapping pressure diminishes and then disappears when the crystals have reached the thickness which results from presetting of the crank 62.

In any lapping operation it is important that the lapping action is distributed uniformly over the surfaces of the lapping plates. This helps to maintain the flatness of the lapping surfaces. In the present embodiment a uniform distribution of the lapping action is accomplished by permitting the carrier plates 14 to spin about their own axes as they orbit about the axis defined by the geometric center of the lapping plates. It is found that by distributing the crystals uniformly and in off center positions in the carrier plates 14, the crystals apply a torque to the carrier plate which tends to induce the carrier plate to spin about its own axis. It is considered that this transfer of torque to the carrier plates 14 results from the fact that the crystals, when under the radially outer areas of the lapping plates, are subjected to the same forces and move the same distances as the corresponding crystals which are under the radially innermost periphery of the lapping plates. Due to the larger orbit which must be executed by the radially outermost crystals, the radially outermost crystals lag behind the radially innermost crystals .although traveling at the same speed, with the result that the carrier plates 14 tend to spin in the clockwise direction as viewed in FIGURE 1. The drive mechanism by which the carriers 14 are caused to orbit between the lapping plates and 12 is specifically designed to utilize this tendency of the carrier plates 14 to spin about their own axes so as to distribute the lapping action uniformly between the plates 10 and 12.

Referring to FIGURE 2, the drive mechanism for the present lapping instrument is assembled on the main frame 100. The frame 100 includes an annular base 104 adapted to be mounted upon suitable supporting legs, not shown. The cylindrical wall 26 which supports the arms 20 projects upwardly from the periphery of the base 104.

The base 104 has an annular depending hub 102 which has a central aperture 106 which receives the base 108 of a tubular column 110, the base 108 being fastened to the hub 102 by bolts 107.

The column 110 receives and aligns the interior races of ball bearing assemblies 113 and 117. A spacer 118 surrounding the tubular column 110 supports the bearing assemblies 113 and 117 in their spaced relation,

The inner race of the bearing assembly 113 receives the Weight of an interior table 112 which supports the stationary lapping plate 10 through the medium of upright pedestals 116, there being a total of three pedestals 116 extending between the lapping plate 10 and the interior table 112.

The weight of the lapping plate 10 is transmitted through the pedestals 116 to the interior table 112 and the combined weight of this assembly transmitted through the inner race of the bearing assembly 113, the spacer 118, the inner race of the bearing assembly 117 and the base 108 of the column 110 to the frame 100. The table 112, and thereby the plate 10, is restrained against rotation on the column 110 by means of a key 114.

A first bearing assembly 120 seated in the base of the column 110, and a second bearing assembly 124 seated in a hub 123 projecting upwardly from the interior table 112 cooperate to rotatably support a tubular drive shaft 122 passing vertically through the column 110.

Seated on the upper end of the drive shaft 122 is a dust cover 126 which shields the bearing 124. Spaced above the dust cover 126 by means of a spacer 128 is a spider 130 carrying three ball bearing assemblies 134 spaced at 120 intervals. The spider 130 is keyed to the drive shaft by a key 131. A nut 132 engaging the drive shaft 122 locks the key 131 against removal.

Each of the bearing assemblies 134 supports a vertically disposed shaft 136 which is enlarged at the lower end thereof to carry a rubber tire 138. The three tires 138 engage in rolling contact with a conically tapered ring 139 encircling the hub 123. With rotation of the spider 130 so as to orbit the shafts 136 about the ring 139, rolling of the tires 138 on the outer periphery of the ring 139 causes the shafts 136 to spin about their own axes. The tires are axially slidable on the shaft enlargements which support the same so that wear can be compensated.

. Above the spider 130 each of the shafts 136 supports one of the driving posts 18a, which fits the shaft 136 as a bushing. Each post 18a carries a dust cover 142 protecting the underlying bearing 134.

. The drivingv posts 18a, while fitted accurately to the shafts 136 are fitted with sufficient clearance that the driving posts spin freely about the axes of the shafts 136. Thus, the shafts 136 which are caused to spin about their own axes by engagement of the tires 138 with the ring 139 are incapable of efficiently transmitting a torque to the driving posts 18a. As will be explained more fully in later remarks, the reason for this construction is to reduce, as much as possible, any frictional drag opposing natural spin movements of the carriers 14.

The spiler is caused to rotate by means of a gear 144 fixedly attached to the drive shaft 122 at the lower end thereof. The gear 144 is driven by a meshing gear 148 receiving torque from a suitable prime mover such as an electric motor through the shaft 150.

Power for rotating the driving posts 18b is derived from the same source through the gear 152 which meshes with the gear 144. Gear 152 in turn drives gear 156 through the shaft 154. The :gear 156 drives a ring gear 158 surrounding the bearing 117 and fixedly attached to a cylinder 160 concentric to the drive shaft 122. The cylinder 160 is supported for rotation *by the outer races of the bearing assemblies 113 and 117.

Fixedly attached to the cylinder 160 is an annular dust cover 164 which shields the bearing assembly 117 against dust and the like. The dust cover 164 in turn supports an interior frame 168 which is fixedly attached to the dust cover.

The interior frame 168, being fixedly attached to the dust cover 164- and the cylinder 160, rotates with the ring gear 158. The gear ratios between the ring gear 158 and the gear 144 are such that the interior frame 168 rotates in exact unison with the drive shaft 122.

The interior frame 168 carries three upright arms 170 spaced at 120 intervals around the axis of the drive shaft 122. The arms 170 support a ring 170a concentric to the lapping plates to which brackets 171, each carrying two vertically spaced bearing assemblies 174 and 178 are pivoted. These bearing assemblies journal shafts 180. The shafts 180 each carry a tire 182 having rolling contact with the outer periphery 184 of the table 112. The outer periphery 184 may have a downwardly divergent conical taper, as shown.

Each shaft 180, there being a total of three such shafts, passes upwardly from its supporting bearing assembly 174 to support one driving post 18b. The driving posts 18b, which fit the shafts 180 as bushings, include dust shields which, in cooperation with the brackets 171 shield the several bearing assemblies 174 and 178.

In the present construction the driving posts 18b are prevented from sliding axially upwardly on the shafts 180 by spring devices 192 attached to the upper ends of the brackets 171. The spring devices 192 are positioned so as not to bear against the posts 18b except when the posts have moved upwardly on the shafts 180. Further, the spring devices 192 are designed to have substantially point contact with the tops of the driving posts 1812 at the geometric centers thereof so as to offer minimum resistance to spinning of the driving posts 18b about the axes of the shafts 180. Similar devices, not shown, may be provided for the driving posts 18a.

The driving posts 18b, which drive the carriers 14 orbitally, react against the carriers so as to urge the upper ends of the shafts 180 radially outwardly. This causes the brackets 171 to pivot on the arms 170 so as to press the tires 182 against the surface 184, thereby assuring agood traction between the tires and their running surface.

As previously noted the drive shaft 122 and inner frame 168 are rotated at exactly the same speed. Thus, the driving posts 18a and 1812 are orbited at the same speed. These driving posts cooperate in pairs to drive the carriers 14 along an orbital path between the lapping plates 10 and 12.

Also, as previously noted, the carriers 14, when orbited between the lapping plates, have a natural tendency to spin about their own axes due to friction between the elements carried by the carriers and the lapping plates. The speed at which the carriers 14 tend to spin about their own axes can be determined empirically for any given operatin g condition.

In the preferred construction, the angular velocity imparted to the shafts 136 through the tires 138 and to the shafts 180 through the tires 182 is predetermined to equal approximately the angular velocity imparted to the driving posts 18a and 18b by the carriers 14, with the result that very little, if any, relative rotation occurs be tween the shafts 136 and 180 and their respective driving posts 18a and 1812. This condition promotes a substantially frictionless rolling movement between the carriers 14 and their driving posts, and also minimizes any drag on the natural spinning movements of the carriers.

From the foregoing remarks it will be apparent that the structure of FIGURE 2 provides a driving mechanism which affords a stationary support for the lower lapping plate 10, prevents rotational movement of the upper lapping plate 12 without restricting axial movement thereof, and advances the circular carriers 14 orbitally between the lapping plates and 12 without restricting rotation of the carriers 14 about their own axes. The tubular character of the drive shaft 122 permits installation of the shaft 32 for controlling the final thickness reached by the elements being lapped, such shaft being supported by the bracket 50 fixedly attached to the frame 100 by means of the bolts 157. The bolts 157 also support the bracket 155 which journals the shaft 154 carrying the gears 152 and 156 in the drive train for the driving .posts 1811.

In lapping operations such as those to be performed by the present apparatus, the lapping action of the plates 10 and 12 removes material from the elements being lapped in the form of a fine dust. It is for this reason that the apparatus of FIGURES l and 2 has been carefully designed so that each ball bearing included therein is shielded with a dust cover.

As previously indicated the carriers 14 have a diameter exceeding the radial width of the lapping plates 10 and 12. This allows a portion of each carrier to project both inwardly and outwardly from between the carrier plates 10 and 12 for driving engagement with the driving posts 18a and 18b. As shown in FIGURE 3, the perforations in the carriers 14 are distributed in a ring within the carrier. The outer diameter of such ring preferably exceeds the radial width of the lapping plates 1% and 12. Because of the spinning action of the carriers 14, the crystals carried by the carriers 14 are each caused to move from a position wherein the crystal projects partly outside the outer periphery of the lapping plates, across the width of the lapping plates, to a position partially inside the inner periphery of the lapping plates. This movement of the elements being lapped assures a substantially uniform wear on the lapping surfaces of the lapping plates.

An alternate means for producing substantially the same lapping motion achieved in the preferred embodiment as illustrated schematically in FIGURE 4. In this modification, the driving posts 181') and the mechanism for driving the same, is left undisturbed. The driving posts 18a on the other hand, are removed and replaced by an annular wall 200 which may be supported and driven by the spider 130. The diameter of the annular wall 2% corresponds substantially to the innermost diameter reached by the carrier plates 14 in the preferred embodiment.

As the driving posts 18b are orbited about the lapping plates in the same manner of the preferred embodiment, the driving posts 181) act against the peripheries of the carriers 14 so as to exert radial inward forces on the carriers, constantly urging the carriers 14 against the Wall 200. As these carriers are or-bited between the lapping plates this radial inward force exerted by the driving posts 18b offsets the tendency of the carriers 14 to work outwardly from between the carrier plates and 8 causes the carrier plates to follow an orbital path concentric to the wall 200, this being an orbital path identical to the path followed by the carriers 14 in the preferred embodiment.

Friction between the carriers 14 and the wall 200 is minimized by driving the wall 200 at substantially the same circumferential speed as the natural peripheral speed of the carriers 14 so that the carriers roll without slipping on the wall 260. Speed control for this purpose is established by selection of gears 144 and 152 having the proper gear ratio.

A similar result is achieved in the second modification of FIGURE 4. In this modification the carrier driving posts 1% have been eliminated and replaced by a cylindrical wall 202 encircling the lapping plates 10 and 12 at substantially the outermost diameter reached by the carriers 14.

In this modification, the driving posts 18a are driven in the same fashion illustrated in the preferred embodiment and, in this case, act against the peripheries of the carriers 14 to urge the carriers into rolling contact with the wall 202. The wall 202 may be supported and driven by the inner frace 16-8 at a circumferential speed approximately matching the peripheral speeds of the carriers 14 so as to establish pure rolling contact with the carriers.

An important feature of the present invention resides in the ability of the apparatus to lap to a predetermined crystal thickness without the manner in which the lapping operation is terminated being critical. It is known to lap piezoelectric crystals to a predetermined frequency by monitoring the frequency signals generated by the crystals themselves. In such procedure the lapping operation is continued until the noise generated by the crystals in the operating frequency range sought reaches a maximum, at which time the lapping apparatus is shut off. A difficulty with such procedure is that, while perfect parallelism between the lapping plates is sought, it is never obtainable in practice. Thus, when the lapping operation is abruptly terminated based on information received from noise monitoring, only a statistical portion of the crystals will be in the desired frequence range. Due to the unavoidable non-parallelism between the lapping plates certain of the crystals will be too thin and others too thick, thus necessitating a crystal by crystal sorting operation.

With the present equipment the effects of nonparallelism between the lapping plates are minimized to such extent that in most cases the need for sorting individual crystals is eliminated. Thus, in the present lapping operation the lapping continues until substantially the entire weight of the upper lapping plate has been transferred to the arms 20 which limit the downward travel of the lapping plate. As this condition is approached, the orbital movement of the carriers 14, coupled with the spin movement of these carriers about their own axes, causes all crystals to move into all available areas between the lapping plates. If the lapping plates are not perfectly parallel, such that in one area the gap between the lapping plates is less than in other areas, all crystals will eventually move through the smallest gap between the lapping plates with the result that all crystals will eventually reach the same thickness. Such a result is not possible when the lapping operation is discontinued before the pressure of the upper lapping plate has been removed from the crystals.

FIGURE 1 illustrates control circuitry suitable to automatic termination of the lapping operation performed by the present lapping apparatus. In this circuit a voltage from a suitable source 300 is applied to a conventional time delay device 302 through a conductive path including the upper plate 12, the limit pins 40 mounted thereon, the arms 20, the frame and the lower lapping plate 11). This conductive path is open circuited due to the presence of the crystals 16 between the lapping plates until such time as one or more of the pins 40 contacts one or more of the arms 20. Such contact can result in the present apparatus only when the crystals have been lapped to substantially the final thickness sought. When the time delay device is energized, a predetermined time delay is commenced and, at the end of the predetermined time delay, the voltage is applied to a relay 304 which deenergizes the prime mover driving the power input shaft 150, thus terminating the lapping operation.

The time delay built into the time delay device 302 is adjusted to provide a time period greater than that normally required to complete a lapping operation after first contact between any pin 40 and its underlying arm. This time period is readily established empirically by measuring the time interval from first contact between the pin 40 and its underlying arm 20 to total transfer of the weight of the lapping plate 12 to the arms 20. Using such mechanism the present apparatus is caused to stop operating automatically after all crystals being lapped reach the desired thickness.

In some applications, especially when very thin elements are to be lapped in metallic carriers, there is a danger of the carrier short circuiting the gap between the lapping plates and 12. Such short circuiting would energize the time delay mechanism and prematurely terminate the lapping operation. In applications where this might be a problem, it is desirable to insulate the arms from the frame 100, as by employing nonconducting clevises 24, and to connect the terminal for the time delay mechanism shown to be mounted on the lapping plate 10 directly to one or more arms 20, so as to remove the lower lapping plate 20 and frame from the time delay circuitry.

Another important feature of the present apparatus resides in a simplification of the travel limiting mechanism whereby only a single adjustment control, namely the crank 62, is required. It will be recognized, how ever, that the specific single control adjusting apparatus of FIGURE 1 is not applicable to all types of lapping machines, especially lapping machines which utilize an eccentric lapping motion.

A single control adjustment mechanism suitable for use on eccentric lapping machines and deemed within the purview of the present invention as illustrated in FIG- URE 6. The lapping machine of FIGURE 6 includes toroidal lapping plates 210 and 212 similarly shaped to those of the preferred embodiment. The plate 212 is mounted fixedly on suitable supporting apparatus, not shown. The plate 210 is mounted floatingly above the plate 212 and separated therefrom only by the work elements 218 which are to be lapped.

The elements 218 are disposed in perforations 216 arranged in an annular array in a carrier 214. A drive pin 220, which engages and moves the carrier 214, is driven orbitally about the geometric axis of the lapping plates 210 and 212 by driving means well known and understood in the art. The drive pin 220 thus imparts an eccentric or orbital movement to the carrier plate 214.

As illustrated, the degree of eccentricity in the movement of the carrier plate 214 is suificient to carry the work elements 218 partially beyond both the inner and outer peripheries of the lapping plates so as to produce uniform wear on the lapping plates.

The single control mechanism for adjustably limiting the axial travel of the plate 210 toward the plate 212 comprises three arms 222 which overlie the plate 210 and which extend radially at a 120 angular spacing. Each arm 222 is pivoted upon a shaft 228 located in a clevis 226. The downward pivotal movements of the arms 222 are limited by a stop member 230 integral with the clevis 226.

Each of the arms 222 is provided with a V-shaped notch 224 analogous in function to the notches 42 of the preferred embodiment. For a counter-clockwise orbital movement of the drive pin 220 the notches 224 are located in the clockwise margins of the arms 222. Brackets 234 serving as abutments to engage in the notches 224 and carrying vertically adjustable pins 236 analogous to the pins 40 of the preferred embodiment are mounted at a spacing on the upper lapping plate 210. As previously described with reference to the brackets 34 of the preceding embodiment, the brackets 234 restrain the upper lapping plate 210 against rotation relative to the lower lapping plate 212 and the supporting pins 236 provide the means for limiting the axial travel of the plate 210. To prevent radial slippage of the brackets 234 in the notches 224, sometimes a problem when using an eccentric carrier movement of the type illustrated, the notches 224 may have side walls less divergent than those shown and, in extreme cases, may be of rectangular shape so as to have parallel side walls.

The clevises 226 which pivotally support the three arms 222 are each mounted upon a vertically movable post 238. Each post 238 is supported by a fixedly mounted bracket 240 having spaced horizontal arms 242 and 244. The arms 242 and 244 are bored to s'lidably receive the post 238 and to guide the vertical movements of the post 238.

Rotation of the posts 238 about their own axes is prevented by keys 248 which enter axially extending keyways 250 in the posts 238. Thus, the brackets 240 support the posts 238 for unrestricted vertical movement over a limited range but prevent rotational movements thereof.

The vertical elevation of each post 238 is controlled by means of a Worm gear 252 threadedly engaging the lower end. thereof. Fixedly supported arms 246 support the worm gears 252 against axial travel.

The three worm gears 252 are arranged to be driven by individual worms. Two of the worms 254a and 2541) appear in the drawing, the third being obscured in the perspective view. The worms 254a and 25412 are mounted on a common shaft 256 which carries a crank 266 for manual rotation thereof. Thus, the worms 254a and 254b are part of an integral structure and necessarily move 1n unison.

The shaft 256 also carries a fixedly attached bevel gear 258 meshing with a complementary bevel gear 260. The bevel gear 260 is fixedly attached to a shaft 262 carrying the third worm. By means of the bevel gears 258 and 260 the shaft 262 is caused to rotate in unison with the shaft 256, with the result that each of the supporting posts 238 are moved in unison and through. the same vertical distances by the crank 266.

To effectively utilize a unison adjustment mechanism of the type described, it is essential that the pins 236 be adjusted to engage the arms 222 at the same lapping plate elevation whereby the lapping plate 210 is substantially parallel to the lapping plate 212 at termination of the lapping operation. This result is readily achieved. With the carrier plate 214 and elements 218 removed from between the lapping plates 210 and 212, the lapping plate 210 is permitted to bottom against the lapping plate 212 with the brackets 234 firmly abutting in the notches 224. With the supporting posts 238 in a low position the pins 236 are carefully lowered to contact with the arms 222 and firmly locked into position. The apparatus is now prepared for elevation of the lapping plate 210 to the desired limiting crystal thickness.

The lapping plate 210 is removed for insertion of the carrier plate 214 and the work elements 218 by a slight clockwise rotation as viewed in FIGURE 10 to disengage the brackets 234 from the arms 222 which may then be pivoted away from their position overlying the lapping plate 210 so as to free the lapping plate 210 for complete removal.

It will be appreciated by those skilled in the art that once the pins 236 have been adjusted to the proper elevation in the brackets 234, numerous lapping operations may be effected without further attention to this adjustment. The only opera-tor attention required is that of ad- 1 1 justing the crank handle 266 to establish the desired limiting thickness.

Although the preferred embodiments of the device have been described, it will be understood that within the purview of this invention various changes may be made in the form, details, proportion and arrangement of parts, the combination thereof and mode of operation, which generally stated consist in a device capable of carrying out the objects set forth, as disclosed and defined in the appended claims.

Having thus described my invention, I claim:

1. In a lapping machine, a pair of lapping plates disposed in confronting relation, a carrier for elements to be lapped disposed between said plates, said carrier having a circular periphery and supporting the elements to be lapped in eccentric relation to the axis thereof, and drive means to move said carrier relative to said plates along an orbital path between said lapping surfaces, said drive means including a free spinning part to contact said carrier, s-aid part having rolling engagement with the periphery of said carrier whereby said drive means does not control spin rotation of said carrier about its own axis.

2. In a lapping machine, a toroidal lapping plate having inner and outer peripheries concentric to a geometric axis therefor, -a second lapping plate confronting said first plate, a carrier for elements to be lapped disposed be tween said plates, said carrier being circular and having an unvarying periphery of diameter exceeding the radial separation between said inner and outer lapping plate peripheries and supporting the elements to be lapped in positions eccentric to the axis of said carrier, and means to move said carrier relative to said lapping plates along a circular path concentric to said geometric axis, said means including parts respectively inside and outside of said inner and outer lapping plate peripheries having rolling engagement with said periphery of said carrier.

3. In a lapping machine the assembly according to claim 2 wherein one of said parts is a cylindrical wall concentric to said geometric axis and against which said carrier has rolling contact.

4. In a lapping machine the assembly according to claim 3 wherein said wall circumscribes said outer periphery.

5. In a lapping machine the assembly according to claim 3 wherein said inner periphery circu-mscribes said wall.

6. In a lapping machine the assembly according to claim 3 including means supporting said wall for rotation about said geometric axis.

7. In a lapping machine the assembly according to claim 2 wherein said parts comprise free spinning driving elements, one disposed inside said inner perphery and the other disposed outside said outer periphery.

8. In a lapping machine the assembly according to claim 7 including driving shafts journalling said driving members each for rotation about an axis parallel to said geometrical axis, there being one driving shaft for said one driving member and another driving shaft for said other driving member.

9. In a lapping machine the assembly according to claim 8 wherein the means to move said carrier relative to said lapping plates includes means to rotate said driving shafts each about its own axis in a direction and at a speed substantially matching the direction and speed of rotation imparted to said driving members by rolling action of said carrier against said driving members.

10. In a lapping machine the assembly according to claim 9 wherein the means to rotate said driving shafts each about its own axis includes stationary circular walls each concentric to said geometric axis, a tire member carried by said one driving shaft engaging one of said walls with rolling contact, and a tire member carried by said other driving shaft engaging the other of said walls with rolling contact.

11. In a lapping apparatus a pair of lapping plates each having a planar lapping surface, said plates being disposed with their lapping surfaces in confronting relation and being adapted to receive an element to be lapped therebetween, carrier means for said element disposed between said lapping surfaces, said carrier means having an annular peripheral edge and having an eccentrically located aperture therethrough to receive said ele ment, one of said lapping plates having an annular margin and said carrier means having a portion of said peripheral edge projecting from between said lapping plates beyond said annular margin, a free spinning driving member adjacent said annular margin for engaging said peripheral edge of said carrier means, motive means to produce relative rotation between said driving member and said lapping plates whereby said carrier means is moved between said lapping plates by engagement of said driving member with said peripheral edge, and means contacting the peripheral edge of said carrier plate at a location spaced peripherally from said driving member and cooperating with said driving member to confine the movement of said carrier means to an annular orbit between said lapping plates.

12. In a lapping apparatus, the assembly according to claim 11 wherein said means contacting the peripheral edge of said carrier plate at a location spaced peripherally from said driving member is an annular wall against which the peripheral edge of said carrier member is pressed by said driving member upon relative rotation between said driving member and said lapping plates.

13. In a lapping apparatus, the assembly according to claim l2 wherein said annular wall is encircled by said annular margin.

14. In a lapping machine, a lower lapping plate and frame means supporting said lower plate against vertical movement, an upper lapping plate overlying said lower plate and having freedom for vertical movement relative thereto, said upper and lower plates being adapted to receive elements to be lapped therebetween under pressure supplied by the weight of said upper lapping plate, said upper lapping plate having plural stop members thereon, individual limit members each supported by said frame means for vertical movement relative thereto, there being one limit member disposed vertically below each said stop member for contact therewith, and means having a single operator element to simultaneously adjust the vertical positions of said limit members to a selected vertical elevation relative to said frame means.

15. In a lapping machine a lower lapping plate of annular configuration having an aperture therethrough, frame means supporting said lower plate, an upper lapping plate of annular configuration and also having an aperture therethrough, said upper plate overlying said lower plate and having freedom for vertical movement relative thereto, plural stop members, means carried by said upper lapping plate supporting said stop members vertically above said lapping plate, said stop members being spaced circumferentially about the central aperture in said upper lapping plate, a plurality of radially disposed arms overlying said upper lapping plate and each pivotally supported at its outermost end by said frame means, there being one arm underlying each said stop member and adapted to coact with such stop member to limit vertical downward movement of said upper lapping plate, arm support means supported by said frame means and movable vertically through said apertures to support the innermost ends of said arms, and position control means having a single operator element to vertically move and position said arm support means to thereby simultaneously and in unison position said arms each to a preselected vertical elevation.

16. In a lapping machine the assembly according to claim 15 wherein the means supporting said stop members above said upper lapping plate includes a plurality of abutment members, there being one abutment member supporting each stop member, each said abutment memher having a vertically extending surface confronting the arm underlying the stop member supported thereby, said assembly including means to orbit elements to be lapped between said lapping plates and circumferentially about the apertures therein, said vertically extending surfaces restraining rotation of said upper lapping plate by engagement with said radially extending arms.

17. In a lapping machine, a lower lapping plate and frame means supporting the same, an upper lapping plate overlying said lower plate and having freedom for vertical movement relative thereto, said lapping plates being adapted to receive elements to be lapped therebetween, and means to limit the vertical downward movement of said upper lapping plate toward said lower lapping plate comprising a plurality of arms overlying said upper lapping plate, a plurality of stop members overlying said arm, there being one stop member for each said arm, means attaching each said stop member to said upper plate, vertically movable means supporting each said arm at a stationary operating posit-ion on said frame means, there being one said movable means for each said arm, and position control means having a single operator element to simultaneously and in unison move and position said movable means so as to simultaneously and in unison move and position said arms at stationary operating positions.

18. In a lapping apparatus, a pair of lapping plates each having a planar lapping surface, said plates being disposed with their lapping surfaces in confronting rela tion and being adapted to receive an element to be lapped therebetween, carrier means for said element disposed between said lapping surfaces, said carrier means having a circular peripheral edge and having an eccentrically located aperture therethrough to receive said element, one of said lapping plates having an annular periphery and said carrier means having a portion of said circular edge projecting from between said lapping plate beyond said annular periphery, a free spinning driving member adjacent said annular periphery for engaging said projecting portion of said carrier means, motive means to produce relative rotation between said driving member and said lapping plates whereby said carrier means is moved between said lapping plates by engagement with said driving member, and means contacting the peripheral edge of said carrier plate at a location spaced peripherally from said driving member and cooperating with said driving member to confine the movement of said carrier means to a circular orbit disposed between said lapping plates and adjacent said annular periphery.

19. In the method of lapping wherein plural lapping elements are disposed in plural openings located eccentrically in a circular carrier member and contacted from opposite sides by confronting lapping plates at least one of which is toroidal, said carrier member having a diameter exceeding the separation between the inner a nd outer peripheries of said toroidal plate and being disposed between said peripheries so as to have a portion projecting outwardly of at least one of said peripheries, the steps of supporting a driving member for free spinning rotation about an axis parallel to the geometric axis of said toroidal plate, advancing said driving member peripherally adjacent said one periphery whereby said driving member rotatably contacts the periphery of said carrier member and acts thereupon to orbit said carrier member between said lapping plates and about the geometric axis of said toroidal plate, and continuously and rotatably contacting the periphery of said carrier member adjacent the other periphery of said lapping plate to from said upper lapping plate, an arm member supported by said frame means and disposed above said upper lapping plate adjacent said abutment member, said abutment member having a circumferentially extending projection supporting a stop member overlying said arm, said stop member being adapted to limit axial downward movement of said upper lapping plate by engagement with said arm upon a predetermined downward travel of said upper plate.

211. In a lapping machine, a lower lapping plate and frame means supporting said lower plate against vertical movement, an upper lapping plate overlying said lower plate and having freedom for vertical movement relative thereto, said upper and lower plates being adapted to receive elements to be lapped therebetween under pressure supplied by the weight of said upper lapping plate, motive means for moving said elements relatively between said lapping plates to lap said elements, said upper lapping plate having a stop member supported at a stationary operating position thereon, a limit member supported at a stationary operating position by said frame means and disposed vertically below said stop member for contact therewith, said elements to be lapped supporting said upper lapping plate at an elevation separating said stop and limit members except after lapping of said elements to a predetermined thickness whereupon said stop element contacts said limit member, said limit acting through said stop member to support said upper lapping plate against downward movement upon contact with said stop member, a timing device, means responsive to contact between said stop and limit members to initiate a timing cycle by said timing device, and means responsive to said timing device at the end of said timing cycle to de-energize said motive means.

22. In the method of lapping wherein plural lapping elements are disposed in plural openings located in a carrier member and contacted from opposite sides by confronting lapping plates, the steps of peripherally engaging said carrier member with a free spinning driving member and advancing said driving member orbitally to move said carrier member orbitally between said lapping plates, said driving member spinning freely to accommodate Whatever spin rotation the lapping action of said plates may induce in said carrier.

References Cited UNITED STATES PATENTS 626,895 6/ 1899 Fondu 51-133 1,257,046 2 /1918- Surerkrop 51-161 1,536,714 5/1925 Hoke 51161 1,577,097 3/1926 Barthel 51--118 2,033,922 3/1936 Cole 51-118 2,369,107 2/1945 Indge 51--161 2,401,953 6/ 1946 McCain 51-118 X 3,063,206 11/ 1962 Meyerhoif 51--161 3,089,292. 5/ 1963 Hunt 51--118 3,110,988 11/1963 Boettcher 51131 HAROLD D. WHITEHEAD, Primary Examiner.

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