US3867797A

US3867797A - Lapping fixture

Info

Publication number: US3867797A
Application number: US421327A
Authority: US
Inventors: Markus B Meier
Original assignee: Burroughs Corp
Current assignee: Unisys Corp
Priority date: 1973-12-03
Filing date: 1973-12-03
Publication date: 1975-02-25
Anticipated expiration: 1992-02-25
Also published as: GB1435049A

Abstract

A lapping fixture adapted for use with flat lapping-plates for grinding and polishing a workpiece to have a plural-faceted or cylindrical face. Workpiece-holding-stations, each capable of holding a plurality of workpieces in precise alignment for batch production, are rotatably mounted to a fixture body. The body is maintained at a substantially constant orientation during lapping by flat-bottomed spacing members, or feet, adapted to be urged against the lapping-plate. The workpiece-holding-stations are mounted on the arms of a pantograph-like linkage adapted to rotate the stations about axes of rotation, spaced apart from the lapping-plate, to a selected orientation.

Description

O Unlted States Patent 1 91 1111 3,867,797

Meier Feb. 25, 1975 LAPPING FIXTURE Primary Examiner-Al Lawrence Smith Assistant Examiner-Nicholas P. Godici t k B. M N b P k, [75] Inven or g fi us eler ew my at Attorney, Agent, or Fzrm-G1lbert H. Friedman;

Nathan Cass; Edward G. Fiorito [73] Assignee: Burroughs Corporation, Detroit,

Mm 57 ABSTRACT [22] Filed: 1973 A lapping fixture adapted for use with flat lapping- 21 AppL 421,327 plates for grinding and polishing a workpiece to have a plural-faceted -or cylindrical face. workpieceholding stations, each capable of holding a plurality of [52] US. Cl. 51/216 A, 51/131, 51/237 R workpieces in precise alignment for batch production [51] Ill. Cl B241) 37/04 are rotatably mounted to a fixture y The y is [58] new of Search 9 216 237 R1 maintained at a substantially constant orientation dur- 51/237 277 ing lapping by flat-bottomed spacing members, or feet, adapted to be urged against the lapping-plate, The [56] References cued workpiece-holding-stations are mounted on the arms UNITED STATES PATENTS of a pantograph-like linkage adapted to rotate the sta- 2,722,0s9 11/1955 Boeticher 51/131 t o out axes o rotation, pace p r from the 2,842,906 7/1958 Carter 5l/l3l X lapping-plate, to a selected orientation. 2,97l,298 2/1961 Garthwaite 51/131 23 Claims, 9 Drawing Figures PATENIEB FEBZSISYS 7' 797,

SHEET U 0F 5 PATENIED FEBZS I975 SHEET 5 BF 5 LAPPING FIXTURE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to improvements in 5 fixtures for holding an article or workpiece for grinding and polishing by lapping. More particularly, the invention pertains to fixtures useful in precision lapping procedures wherein substantially identical plural-faceted or cylindrical surfaces are simultaneously formed on a plurality of similar workpieces.

2. Description of the Prior Art This discussion of the prior art and the discussion of the invention which follows uses the example of the manufacture of articles such as flying heads to explain the utility and structure of certain lapping fixtures.

However, the subject invention is not limited to use in on moving magnetic data storage media such as rotating disks. The motion of the medium, produces a laminar flow of the surrounding fluid, usually air. As the air is compressed to pass through the narrow space separating the medium and the adjacent head, an air bearing for the head is formed. Lapping is a convenient and efficient method for forming and polishing the airbearing-face of a flying head to produce suitably stable and uniform aerodynamic and electromagnetic characteristics. The air-bearing-face may be lapped to be substantially flat. However, superior aerodynamic and mechanical characteristics for a head and its supporting structure are realized by using either a cylindrical airbearing-face or one having two or more angled flat portions or facets. In one commonly used design, the airbearing-face is created by first lapping an entire face of the head to be substantially flat and then lapping a second facet on a portion of the same face at an angle of about twelve minutes of arc with respect to the originally lapped portion. The line defined by the intersection of the two facets is intended to-lie in the plane of motion of the air at right angles to the direction of that motion when the head is mounted for use adjacent the rotating disk.

Flying heads often comprise a substantially rectangular block, or prism, or a ceramic material such as glass which supports the electrical and magnetic elements of one or more transducers. It is primarily the ceramic material which is formed and polished by the lapping process. It is irrelevant to this discussion whether the processing occurs before or after the electrical or magnetic elements are combined with the supporting material.

Prior-art fixtures for lapping the commonly used twofacet air-bearing-face described above comprise a fixture body having a substantially planar lower end surface for being positioned adjacent but spaced a predetermined distance apart from a substantially flat rotating lapping-plate. A workpiece-holding-station is pro vided on the lower end surface for firmly holding one or more heads at a predetermined fixed orientation with respect to the fixture body. This orientation remains fixed unless and until a head is remounted on the .cide.

fixture. body at a different attitude. Thus, any orienta tion established for the fixture body with respect to a lapping-plate also determines the orientation of the head with respect to the lapping-plate. The desired fixture orientation for lapping is determined by three spacing numbers, or feet, mounted to the fixture body by independently adjustable threaded bolts. The feet extend from the fixture body at right angles to the planar lower end surface, preferably at equal distances from each other and symmetrically disposed with respect to the center of the surface. A conical or pointed tip is provided at the end of each foot. The tips are of a hard material, such as diamond, adapted for urging against the lapping-plate.

The lapping-plate commonly has a diameter which is in excess of twice the diameter of the lapping fixture so as to provide a lapping surface of an area sufficient to simultaneously engage all three feet and all workpieces affixed to the workpieceholding-station. The extremities of the diamond-tipped feet define a lapping plane. Any portion of the mounted heads extending beyond this plane is removed by the rotating lapping-plate as the fixture is urged against it. When all such extending head material has been removed, the three feet simultaneously contact the lapping-plate whereupon the lapping plane and the surface of the lapping-plate coin- When the tips of allthree feet are adjusted to extend the same distance from the lower end surface, the fixture is said to be leveled. A leveled fixture provides a uniform spacing between the lapping plane and the lower end surface and the workpiece-holding-station thereon. However, to produce the two-facet air- 5 bearing-face described above, the workpiece-holdingstation is restricted to be disposed under a line defined by the extremities of the tips on two of the three feet. For this prior-art fixture, the workpiece-holding-station must be adapted to orient and position a head so that the aforementioned line crosses the air-bearing-face in coincidence with the intended line of intersection of the two facets. After the first lapping operation with the fixture leveled, the third foot is either advanced or retracted by a predetermined amount to cause tilting of the entire fixture to a predetermined angle whereupon the fixture is again urged against the lapping-plate. Subsequent lapping then produces the second facet at that angle.

This prior-art lapping fixture has a disadvantage in that the number of workpieces which may be mounted thereon to be lapped simultaneously to produce a twofacet air-bearing-face on each of the workpieces is limited. This is because of the requirement to mount the workpieces only along the line defined by two of the three feet. In one prior-art fixture having a convenient size, only two workpieces can be mounted and lapped simultaneously in the space available. Also, the priorart fixture is limited to forming faces having a maximum of only two facets for a single mounting of the workpieces. Another problem confronting the developers of improved lapping processes has been the need for a lapping fixture which would be suitable for use with grooved lapping-plates. Free rotation of the priorart fixture upon such plates is impeded because of the tendency of the pointed-tip-feet to engage the grooves. These and other difficulties are overcome by the present invention.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved lapping fixture useful for forming and polishing a face of a workpiece to be cylindrical or to have two or more faceted portions.

Another object of the present invention is to provide a lapping fixture useful for forming and polishing a face of a workpiece to be cylindrical or to have a plurality of faceted portions whereby lapping may be conveniently accomplished on a grooved lapping-plate.

Still another object is to provide a single lapping fixture for simultaneously forming and polishing precisely similar cylindrical or faceted portions on the faces of relatively large number of workpieces.

According to the present invention, the foregoing and other objects are attained by a lapping fixture having at least one workpiece-holding-station mounted on a rotatable arm comprising part of a linkage adapted to vary and control the orientation of the workpieceholding-station with respect to the body of the fixture. Since the workpiece-holding-station is controllably rotatable to a selected orientation, the orientation of the fixture body is held substantially constant while a cylindrical or faceted face of aworkpiece is formed and polished. The lapping fixture of the invention is equipped with at least one flat-bottomed spacing-member or foot having sufficient area at its extremity, or contact surface, to span any grooves in a lapping-plate against which the foot is urged during lapping. The contact surface of a foot defines a lapping plane. A plurality of feet is preferably used and, where this is the case, their contact surfaces are disposed in the same lapping plane, i.e., the fixture is always used in a leveled condition. The orientation of a workpiece-holding-station is varied and controlled by rotating the station about a pivot having an axis of rotation spaced apart from and parallel to the lapping plane. The use of an alwaysleveled fixture permits relatively efficient use thereof since a greater number of workpiece-holding-stations may be mounted thereon than on a prior-art fixture of comparable dimensions. In addition, each such workpiece-holding-station may be located in a plane on the fixture body which permits the station to be adapted to hold a greater number of workpieces than was previously practical.

The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1, 2 and 3 are perspective views of articles representative of flying heads.

FIGS. 4 and 5 are elevation and bottom view sketches, respectively, of a prior-art lapping fixture.

FIGS. 6 and 7 are elevation and bottom view sketches, respectively, of a lapping fixture in accordance with the subject invention.

FIG. 8 is a perspective view of a preferred embodiment of this invention, broken away to reveal details of the linkage and other features in the interior of a fixture body.

FIG. 9 is a perspective view of a workpiece-holdingstation, or head-mounting-plate, having a plurality of workpiece-holders thereon.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. 1, 2 and 3 show flying heads 10, 22 and 36, respectively, each of which has a representative airbearing-face formed on a substantially rectangular prism by lapping.

In FIG. 1, the polished air-bearing-face of the head 10 comprises a first facet 12, substantially parallel to the opposing face (not shown), and a second facet 16.

The second facet 16 is at an angle W with respect to the first facet 12. The line of intersection 18 of facets 12 and 16 is parallel to both the leading edge 14 and the trailing edge 20 of the air-bearing-face. The general direction of the air flow, as indicated by the arrow, is perpendicular to

edges

14 and 20 and to line 18.

In FIG. 2, the polished air-bearing-face of the head 22 comprises the three

facets

24, 28 and 30. Facet 24 is an interior facet substantially parallel to the opposing face (not shown) of the head 22.

Exterior facets

28 and 30 are at angles X and Y, respectively, with respect to the interior facet '24. The line of intersection 32 of

facets

24 and 28 and the line of intersection 34 of

facets

24 and 30 are parallel to each other and both

lines

32 and 34 are parallel to both the leading edge 26 and the trailing edge 27. The general direction of the air flow, as indicated by the arrow, is perpendicular to the

lines

32 and 34 and to the

edges

26 and 27.

In FIG. 3, the polished air-bearing-face of the head 36 is a continuously curved cylindrical surface 38 extending from the leading edge 40 to the trailing edge 42. Edges 40 and 42 are parallel to each other and are perpendicular to the general direction of the air flow indicated by the arrow. Cylindrical surface 38 may be viewed as comprising an infinite number of angled facets, all extending the same distance in the direction parallel to both leading edge 40 and trailing edge 42 but each having infinitesimal width in a direction perpendicular to those edges.

FIGS. 4 and 5 show the essential features of the priorart lapping fixture 44 discussed above. Common reference numerals are used in FIGS. 4 and 5 for the same features. The fixture 44 comprises a rigid cylindrical fixture body 46 having substantially planar opposing end surfaces 48 and 50 which are machined to be parallel to each other to a high degree of precision. This parallelism facilitates certainty in making measurements associated with adjusting the fixture for appropriate spacing and orientation with respect to a lapping surface. Three equidistant spacing-members, or feet, 52, 54 and 56, symmetrically disposed about the major axis of the cylindrical fixture body 46, extend from the lower end surface 50 at right angles thereto. Pointed or

conical tips

58, and 62 are attached to the end of each of the

feet

52, 54 and 56, respectively. As mentioned above, the tips are preferably of diamond to insure adequately long service. The radius of curvature of each end of the

tips

52, 54 and'56 at their apexes is preferably about five-thousandths of an inch. Each of the three

feet

52, 54 and 56 may be attached to or be an extension of three similar bolts 64 (FIG. 4 only) which extend through and are threadably engaged with the fixture body 46. When a bolt 64 is advanced or retracted by turning a knurled knob 66 at the top thereof, the spacing between the extremity of the

corresponding foot tip

58, 60 and 62 and the lower end surface 50 is varied. When the extremities of all three

tips

58, 60 and 62 are adjusted to extend equal distances from the lower end surface 50, the fixture is leveled. Broken line 68 in FIG. 4 may be taken to represent the lapping plane of the fixture 44 in coincidence with the Surface of a lapping plate (not shown) when the fixture 44 is leveled. Broken line 70 may be taken to represent the lapping plane defined when tip 62 has been retracted a predetermined distanceto adjust the fixture 44 for operation at an angle of tilt W. The retracted position of the foot 56 is indicated by the dashed-line representation of its tip, as indicated by the reference numeral 62. A plurality of workpieces 72, here two, are firmly attached to the workpiece-holding-station (not shown) on the lower end surface 50. workpiece-holders (not shown) on the workpiece-holding-station (not shown) provide for precise alignment of the workpieces 72 along the broken line 74 (FIG. 5 only) joining the extremities of

tips

58 and 60. Broken line 74 passes across the workpieces 72 along the line 18 in FIG. 1 where it is intended to have facets 12 and 16 (FIG. 1) intersect.

Broken line 74 is, in essence, the axis of rotation for tilting the fixture 44. It is because this axis of rotation lies in the lapping plane that this fixture 44 of the priorart is best suited for producing polished faces having no more than two facets. The air-bearing-face of the head in FIG. 1 may be formed by performing a first lapping operation with the fixture 44 leveled. This first operation reduces the thickness of the workpiece to the precisely determined spacing between the extremities of the

tips

58, 60 and 62 and a plane associated with the workpiece-holding-station parallel to the lower end surface and polishes the face of the workpiece 'including that portion which will remain as facet 12 (FIG. 1) when processing is completed. After the fixture 44 is tilted, as discussed above, the fixture 44 is again urged against the lapping plate to form the facet 16 (FIG. 1).

After mounting the workpieces 72 thereon, the fixture 44 is leveled on a microflat, a block of granite having a surface polished to be flat to a high degree of precision. Using height gages for measurement, each one of the

feet

52, 54 and 56 is adjusted using an appropriate one of the bolts 64 to provide a predetermined spacing between the lapping plane and all points on the workpiece-holding-station to which the workpieces are attached. Sincethe pitch of the threads of bolts 64 is known, subsequent tilting of the fixture 44 may be accomplished by rotating the threaded bolt 64 to which foot 56 is attached a predetermined number of turns.

FIGS. 6 and 7 show essential features of a lapping fixture 76 in accordance with the subject invention. Common reference numerals are used in FIGS. 6 and 7 for the same features. The fixture 76 comprises a rigid cylindrical fixture body 78 having substantially planar opposing end surfaces 80 and 82 which are machined to be parallel to each other to a high degree of precision. This parallelism facilitates certainty in making measurements associated with adjusting the fixture for appropriate spacing and orientation with respect to a lapping surface. Three identical spacing members, or feet, 84, equidistant from each other and symmetrically disposed about the major axis of the cylindrical fixture body 78, extend from the lower end surface 82 at right angles thereto.

Pads 86, having a fiat contact surface at the extremities thereof, are attached to the end of each of the feet 84. The pads 86 are preferably made of fused alumina.

-'diamond tips 58, and 62 (FIGS. 4 and 5) of the pri or-art fixture 44.

Each of the three feet 84 may be attached to or be an extension of bolts (not shown) similar to the three bolts 64 shown in FIG. 4. These bolts are similarly adapted for l leveling the fixture 76 and (2) adjusting the spacing between a lapping plane defined by the contact surfaces of the pads 86 and head-attachmentsurfaces (not shown) on workpie'ce-holding-stations 88. The fixture 76 is intended to be used for lapping only in a leveled condition. As in FIG. 4, broken line 68 in FIG. 6 may be taken to represent the lapping plane of the fixture 76 in coincidence with the surface of a lapping-plate (not shown).

Two workpiece-ho]ding-stations 88 are provided on the fixture 76, each having a plurality of workpieces 72, here four, firmly attached to workpiece-holders (not shown) thereon. The workpiece-holding-stations 88 are rotatably mounted on the fixture body 78 by pivots 92 (indicated in FIG. 6 only). The pivots 92 adapt the workpiece-holding-stations 88 for controlled simultaneous and equal rotation with respect to the fixture body 78. The axes of rotation defined by the pivots 92 are parallel to each other and parallel to and equidistant from the lower end surface 82 of the fixture body 78. Furthermore, these axes of rotation are spaced a predetermined distance apart from the lapping plane 68 of the fixture 76. Details of the preferred means for controlling the orientation of the workpiece-holdingstations 88 are more fully discussed hereinafter in connection with FIG. 8. Details of a workpiece-holding station 88 having a plurality of individual workpieceholders thereon are more fully discussed hereinafter in connection with FIG. 9.

To produce a two-facet air-bearing-face such as the one shown on the head 10 in FIG. 1, the fixture is first urged against a rotating lapping plate with the workpiece-holding-stations 88 held at a first fixed orientation. After a first lapping operation is completed, the workpiece-holding-stations 88 are rotated through an angle W to a second orientation which is held fixed during a second lapping operation. The line of intersection of the two facets to be formed by following the above procedure will not, in general, lie directly beneath the axis of rotation defined by a pivot 92 during lapping. This is so since the axis of rotation is spaced apart from the lapping plane 68. However, the dimensions of a desired finished head are presumably known in advance. The dimensions of all parts of a fixture 76 which control or affect the result of lapping procedures can be predetermined prior to fabricating the fixture 76 or adjusted prior to starting a lapping operation. Therefore, given the desired dimensions and configuration for a finished workpiece, a suitable lapping fixture may be readily manufactured for producing it.

In this invention, the spacing of an axis of rotation for orienting a workpiece apart from the lapping plane is the feature which permits the fixture to be used for forming cylindrical air-bearing-faces such as the face 38 on head 36 in FIG. 3. A cylindrical face may be formed by continuously varying the orientation of a workpiece between predetermined limits during lapping. The radius of curvature of the cylindrical surface will be equal to the distance between the axis of rotation defined by a pivot 92 and the lapping plane 68. It follows that air-bearing-faces having more than two facets, such as that on the three-faceted head 22 of FIG. 2, may be readily formed by a succession of lapping operations at as many different fixed workpiece orientations as required.

The sketches of the prior-art lapping fixture 44 in FIGS. 4 and 5 and the new lapping fixture 76 in FIGS. 6 and 7 were drawn to represent fixtures and workpieces having the same dimensions. For these dimensions, which were chosen by way of example, it is evident that four times as many workpieces 72 may be mounted on the new lapping fixture 76 (FIGS. 6 and 7) as on the prior-art lapping fixture 44 (FIGS. 4 and 5). This increase results from the independent rotatability of the workpieceholding-stations 88 relative to the fixture body 78 (FIGS. 6 and 7). The added degree of freedom permits design flexibility in the placement of workpiece holding means to maximize efficient utilization thereof. I

FIG. 8 shows details of a preferred embodiment of a lapping fixture 94 in accordance with the subject invention. Where the features of the lapping fixture 94, as shown in FIG. 8, correspond substantially to the features of the lapping fixture 76 shown in FIGS. 6 and 7 and discussed above in connection with the latter drawings, common reference numerals are used. Similarly, common reference numerals are used in FIGS. 4, 5 and 8 to denote features of the lapping fixture 94 (FIG. 8) which correspond substantially to the features of the prior-art lapping fixture 44 (FIGS. 4 and 5).

The lapping fixture 94 comprises a rigid, substantially cylindrical fixture body 78 having substantially planar and parallel opposing end surfaces 80 and 82.

In this preferred embodiment, each spacing-member, or foot, 84 comprises a substantially cylindrical guidebushing 126 having an annular flange 128 at the upper end thereof and an alumina pad 86 affixed to the lower end thereof. The fixture body 78 is adapted to receive the guide-bushing 126 in a bored hole 130 closely fitted to the bushing 126 and extending to the lower end surface 82 at right angles thereto. A set-screw 134, adjustable from outside the fixture body 78 and threadably engaged therewith, is disposed to extend into a longitudinally extending keyway 132 on the bushing 126 to prevent rotary motion thereof and, once the spacing member 84 is adjusted as discussed below, to lock the bushing 126 into position. The guide-bushing 126 is inserted into the hole 130 through a well 136 in the fixture body 78 disposed above the hole 130. The well 136 has a diameter large enough to accommodate the annular flange 128.

Each spacing member 84 further comprises an adjusting-screw 142 adapted to urge the guide-bushing 126 against the spring 138. Adjacent its lower end, the adjusting-screw 142 is threadably engaged by a first set of threads 144 with the interior of the guide-bushing 126. Adjacent its upper end, the adjusting-screw 142 is threadably engaged by a second set of threads 146 with a bore 148 in a cover 150 fastened to the fixture body 78 over the well 136. The second set of threads 146 is right-handed and has a pitch of 44 (44 threads per inch). The first set of threads 144 is right-handed and has a pitch of 46 (46 threads per inch). There is thus provided a differential adjusting-screw 142 which provides for ease and sensitivity in precisely adjusting the spacing-member 84 since one full revolution of the knurled knob 66 at the top of the adjusting-screw 142 will advance or retract the guide-bushing 126 by only one one-thousandth of an inch relative to the fixture body 78. A coiled compression spring 138 is disposed to extend between and contact both the floor 140 of the well 136 and the under-surface of the flange 128 to bias out any play existing due to tolerance in the threads I44 and 146.

Leveling of the lapping fixture 94, as discussed above, is facilitated by the provision of a plurality of posts, or stand-offs, 124 mounted on the upper end surface of the fixture body 78. Three stand-offs 124 are provided on the preferred embodiment, only one of which is visible in FIG. 8. The stand-offs 124 are mounted to be equidistant from each other and symmetrically disposed about the rnajor axis of the cylindrical fixture body 78 at locations intermediate the locations of the adjusting-screws 142. Each stand-off 124 is mounted to be parallel to all three of the spacing members 84 and to extend beyond all of the knurled knobs 66 on the adjusting-screws 142. The end surfaces 152 of all of the stand-offs 124 are machined to be precisely parallel to and equidistant from the lower end surface 82 of the fixture body 78. It follows then that the end surfaces 152 of the stand-offs 124 establish a plane which may be used, instead of the upper end surface 82, as a reference to establish a parallel leveled-fixture lapping plane. To do so, the lapping fixture 94 may be placed on a microflat with the end surfaces 152 in contact therewith. A precision height gage may then be conveniently used to verify the adjustment of each foot 84 so that the extremity or contact surface of each pad 86 extends the same predetermined distance from the microflat.

The lapping fixture 94 of FIG. 8 is equipped with a plurality, here two, of linkage arms 98. Each arm 98 is rotatably attached to and supported on the fixture body 78 by a flexural joint, or pivot, comprising a rectangular strip of resilient material, a leaf spring 102. Each leaf spring 102 is firmly fastened to a portion of an arm 98 along one edge of the spring 102 by one or more bolts 104. Each leaf spring 102 is also firmly fastened to an interior portion of the fixture body 78 along the opposing edge of the spring 102 by one or more bolts 106. One workpiece-holding-station 88 is rigidly attached to each arm 98 and disposed thereon between the flexural joint defined by the leaf spring 102 and the lapping plane defined by the pads 86. Each leaf spring 102 defines an axis of rotation, relative to the fixture body 78, for its associated arm 98. The leaf springs 102 are sufficiently stiff to maintain substantially fixed any orientation established for an arm 98 during lapping when workpieces (not shown) on the workpieceholding-station 88 are being urged against a lapping 1 surface.

Pivot pins supported in bushings could be used for mounting the arms 98 to the fixture body 78. However, since the pivots in question are located relatively close to the lapping plane, they will be subject to having abrasive lapping compound splashed upon them. The eventual result could be undesirable erosion of the pivot pins and their support bushings. The flexural 9 joints using leaf springs 102 avoid-this problem and are preferred for this reason.

Eachof theplurality of linkage arms 98 is pivotally attached to a link-bar 96 by a pivot pin 100 at a point on the arm 98 spaced a predetermined distance apart from the axis of rotation defined by the corresponding created, in effect, a linkage resembling a pantograph wherein a given translational displacement of the linkbar 96 produces a corresponding rotational displacement of each arm 98 relativeto the fixture body 78.

Each arm 98 is constrained .to be rotated through equal angles, relative to the fixture body 78, by its pivotal attachment 100 to the link-bar 96. The orientation relative to the fixture body 78 of each of the plurality of workpiece-holding-stations 88 secured to the arms 98 is also constrained to be identical.

The link-.bar 96 is supported entirely by the'plurality of arms 98 acting through the several pivot pins 100, each of which extends through both an arm 98 and the link-bar 96. The link-bar 96 is equipped with two rods, one extending from each of its two ends. A first rod, actuation rod 114, extends through a hole 116 in the fixture body 78 to a cam 108. A second rod, guide rod 118 at the opposing end of the link-bar 96, maintains the alignment of a coil spring 120 compressed between a retaining well 122 in an interior surface of the fixture body 78 and the aforementioned opposing end of the link-bar 96. The axial force of the compressed coil spring 120 acting on the link-bar 96 urges the free end of the actuation rod 114 against, and into slideable engagement with, the peripheral surface 109 of the cam 108.

The cam 108 is precisely machined so that its peripheral surface 109 lies at a plurality of different predetermined distances, or radii, from its axis of rotation. To

define that axis of rotation and hold it fixedrelativ'e to the fixture body 78, the cam 108 is securely mounted on a cam shaft 112 which is, in turn, rotatably mounted and supported in bushings (not shown) provided in the fixture body 78. As the cam 108 is rotated, the actuation rod'114is displaced longitudinally in conformity with the variation in the distance of the peripheral surface 109 from the axis of rotation of the cam 108. The resulting longitudinal displacement of the link-bar 96, as indicated by the straight double-ended arrow thereon, causes a corresponding rotation of the arms 98 and workpiece-holding-stations 88 affixed thereto. The rotation of the arms 98 produces, in turn, an additional transverse displacement of the link-bar 96 perpendicular to the pivots 100. To accommodate this two-dimensional translation of the link-bar 96, the hole 116 is made large enough so that no contact occurs between the actuation rod 1 14 and the material of the fixture body 78 as the cam 108 is rotated.

In one preferred embodiment of this invention, the peripheral surface 109 of the cam 108 is machined to have a first region, extending about ninety degrees, having a first predetermined radius and a second region diametrically opposite the first region, also extending about 90, having a second larger predetermined radius. The intermediate quadrants along the peripheral surface 109 are transition regions not used during lapping. The rotation of the cam 108 is controlled manually by an operator using a lever 110 mounted securely -tothe cam shaft 112. With the lever 110 rotated to rest securely against the edge of the upper end surface of the fixture body 78, as shown by the solid-line representation of the lever in FIG. 8, the actuation rod 114 contacts the peripheral surface 109 in the first region. Thus, a first orientation for the workpieceholding-stations'88 is established. With the lever 110 rotated approximately one-half revolutionto rest securely against the fixture body' in the position indicated by its dashed-line representation 110', the actuation rod 114 contacts-the peripheral surface 109 in the second region. Thus, a second orientation for the workholding-stations 88 is established. The two-contactregion cam described above controlled by a manually operated lever having two stable positions. is suitable for a lapping fixture intended to be used in forming heads such as the head 10 of FIG. 1. Three-region cams for producing heads similar to the head 22 of FIG. 2 are readily fabricated. Controlfor such a cam may be effected by a manually operated lever provided with a third detent position. Cylindrical air-bearing surfaces such as the surface 38 on the head 36 in FIG. 3 may readily be produced using a cam having a radius varying approximately linearly. In this case, the cam would preferably be controlled for continuous angular reciprocation during lapping by an'automatic' mechanism mounted on the lapping fixture body for that purpose. FIG. -9 shows details of the exposed head-mountingsurface 158 of a workpiece holding-station or headmounting-plate 88. The reference numerals used in FIG. 9 are common tovthose used in FIGS. 4-8, inclusive, for the sameelements. Precise alignment of the head-mounting-plate 88 with respectto the linkage arm 98 is assured by a plurality of registration pins 156, here two, extending from the arm 98 through mating holes in the head-mounting-plate 88 closely fitted to the pins 156. The head-mounting-plate 88 is secured to the linkage arm 98 by a plurality of bolts 154, here two, the tops of which are shown in FIG. 9 advanced into counter-sunk recesses in n the head-mounting-surface 158.

Each head-mounting-plate 88 has a plurality of workpiece-holders 160, here three, provided thereon for holding the workpieces 72 to be lapped in precise alignment with each other and with the other elements of the lapping fixture 94 (FIG. 8). Two of the workpieceholders 160 in FIG. 9 have workpieces 72 mounted thereon while the third is empty and exposed to show its details. Each workpiece-holder 160 comprises a segmented planar head-attachment-surface or platform for a workpiece 72. The platform is defined by a plurality of spaced-apart rectangular posts 162, here three, extending from the head-mounting-surface 158. The platforms for all workpiece-holders 160 on a headmounting-plate 88 are coplanar. Furthermore, all such platforms on the lapping fixture 94 are parallel to and equidistant from their respective axes of rotation defined by their associated leaf spring pivots 102 (FIG. 8). The posts 162 are disposed so that the top of each will contact a portion of that face of a workpiece 72 which opposes the face to be lapped near the perimeter thereof. The elevation of the tops of the posts 162 with respect to theadjacent portion of the head-mountingsurface 158 is relatively small, preferably about twenty thousandths of an inch.

Each workpiece-holder 160 further comprises at least three spaced-apart dowel pins 164, extending from the head-mounting-surface 158 at right angles thereto, for locating a workpiece on the platform defined by the posts 162. Two of the three dowel pins 164 are aligned to define and provide a plane of contact for a first side of a workpiece 72 while the third dowel pin 160 is disposed to provide a contacting stop for a second side of the workpiece 72 adjacent the aforementioned first side. The plane of contact defined by the former two of the three dowel pins 164, as shown in FIG. 9, is parallel to the axis of rotation for the headmounting-plate 88 defined by the leaf-spring pivot 102 (FIG. 8) for the arm 98. Furthermore, the planes of contact defined by the corresponding two dowel pins 164 in each of the several workpiece-holders 160 on a head-mounting-plate 88 are coincident. The elevation of the dowel pins 164 with respect to the adjacent portions of the head-mounting-surface 158 is sufficient to engage the workpieces 72 but not so great that the dowel pins 164 will engage a lapping surface in normal use.

The workpieces 72 may be secured to the several workpiece-holders 160 by first clamping each of them into position against the posts 162 and the dowel pins 164 as indicated above. The assembly is then warmed to a temperature sufficiently high to melt a suitable wax. A stick of that wax is then moved about the periphery of each workpiece 72 in contact therewith and in contact with the adjacent portion of the headmounting-surface 158 in a manner which causes a small amount of melted wax to flow beneath the clamped workpiece 72 into the space under the platform defined by the posts 162. When the wax is allowed to cool, it

securely fastens the workpieces 72 to the workpieceholders 160.

While the invention has been shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in detail may be made therein without departing from the spirit and scope of the invention as set out in the following claims.

I claim:

1. In a lapping fixture for holding a workpiece to be lapped, the lapping fixture being adapted for urging a workpiece against a substantially flat lapping surface for grinding away portions of the workpiece extending beyond a lapping plane associated with the lapping fixture and polishing portions of the workpiece lying substantially in the lapping plane, the combination which comprises:

a. spacing means having a substantially flat contact surface adapted to be urged against the lapping surface, the contact surface defining the lapping plane;

b. a fixture body mounted to said spacing means at a fixed angular orientation with respect to the lapping plane;

c. means for holding a plurality of workpieces along aline of disposition substantially parallel to an axis of rotation for said holding means; and

d. means for rotatably mounting said holding means to said fixture body.

2. A lapping fixture as recited in claim 1 wherein said rotatable mounting means comprises:

a. a first linkage member having said holding means mounted thereto adjacent to and spaced apart from the lapping plane; and

b. first pivot means for mounting said first linkage member to said fixture body, said first pivot means defining the axis of rotation parallel to the line of disposition for the workpieces, the axis having a fixed orientation with respect to said fixture body.

3. A lapping fixture as recited in claim 2 wherein said first pivot means defines the axis of rotation to be substantially parallel to' and spaced a selected distance apart from the lapping plane.

4. A lapping fixture as recited in claim 2 having means for controllably rotating said rotatable mounting means which comprises:

a. a second linkage member adapted for translation with respect to said fixture body;

b. second pivot means for mounting said second linkage member to said first linkage member to cause rotation of said first linkage member about the axis of rotation defined by said first pivot means when said second linkage member is translated;

c. a cam rotatably mounted to said fixture body; and

(1. means for engaging said second linkage member with said cam to cause translation of said second linkage member in response to rotation of said cam.

5. A lapping fixture as recited in claim 1 which comprises means for controllably rotating said rotatable mounting means.

6. A lapping fixture as recited in claim 4 which comprises means for rotating said cam:

7. In a lapping fixture for holding a workpiece to be lapped, the lapping fixture being adapted for urging a workpiece against a substantially flat lapping surface for grinding away portions of the workpiece extending beyond a lapping plane associated with the lapping fixture and polishing portions of the workpiece lying substantially in the lapping plane, the combination which comprises:

a. spacing means having a substantially flat contact surface adapted to be urged against the lapping surface, said contact surface defining the lapping plane;

b. a fixture body mounted to said spacing means;

c. holding means for a plurality of workpieces, said holding means comprising a plurality of distinct workpiece-holding-stations each being rotatable about a distinct axis of rotation, the axis of rotation for each workpiece-holding-station being coplanar with all other axes of rotation for workpieceholding-stations; and

d. means for rotatably mounting said holding means to said fixture body.

8. A lapping fixture as recited in claim 7 wherein said rotatable mounting means comprises:

a. a plurality of first linkage members each having one of the distinct workpiece-holding-stations mounted thereto adjacent to and spaced apart from the lapping plane; and

b. first pivot means for independently mounting each of said plurality of first linkage members to said fixture body, said first pivot means defining the several distinct axes of rotation for the plurality of workpiece-holding-stations.

9. A lapping fixture as recited in claim 8 wherein said first pivot means defines the several distinct axes of rol3 tation for the plurality of workpiece-holding-stations to lie spaced apart from each other in a plane substantially parallel to and spaced a selected distance apart from the lapping plane.

10. A lapping fixture as recited in claim 8 having means for controllably rotating said rotatable mounting means which comprises:

b. second pivot means for mounting said second linkage member to said first linkage members to cause simultaneous and substantially equal rotation of said first linkage members about the axes of rotation defined by said first pivot means when said second linkage member is translated;

c. a cam rotatably mounted to said fixture body; and

d. means for engaging said second linkage member with said cam to cause translation of said second linkage member in response to rotation of said cam.

11. A lapping fixture as recited in claim 7 wherein each distinct workpiece-holding-station comprises means for mounting a plurality of workpieces thereon along a line of disposition substantially parallel to its axis of rotation.

12. A lapping fixture as recited in claim 7 which comprises means for controllably rotating said rotatable mounting means.

13. A lapping fixture as recited in claim 10 which comprises means for rotating said cam.

14. In a lapping fixture for holding a workpiece to be lapped, the lapping fixture being adapted for urging a workpiece against a substantially fiat lapping surface for grinding away portions of the workpiece extending beyond a lapping plane associated with the lapping fixture and polishing portions of the workpiece lying substantially in the lapping plane, the combination which comprises:

b. a fixture body mounted to said spacing means;

c. holding means adapted to have at least one workpiece mounted thereon;

(1. means for rotatably mounting said holding means to said fixture body which includes 1. a first linkage member having said holding means mounted thereto adjacent to and spaced apart from the lapping plane and 2. first pivot means for mounting said first linkage member to said fixture body, said first pivot means defining an axis of rotation for said first linkage member, the axis having a fixed orientation with respect to said fixture body; and

e. means for controllably rotating said rotatable mounting means which includes 1. a second linkage member adapted for translation with respect to said fixture body,

2. second pivot means for mounting said second linkage member to said first linkage member to cause rotation of said first linkage member about the axis of rotationdefined by said first pivot means when said second linkage member is translated,

3. a cam rotatably mounted to said fixture body,

and

4. means for engaging said second linkage member with said cam to cause translation of said second linkage member in response to rotation of said cam.

15. A lapping fixture as recited in claim 14 which comprises means for rotating said cam.

16. A lapping fixture as recited in claim 14 wherein the axis of rotation defined by said first pivot means is substantially parallel to and spaced a selected distance apart from the lapping plane.

17. A lapping fixture as recited in claim 14 wherein said holding means comprises means for mounting a plurality of workpieces thereon disposed along a line substantially parallel to the axis of rotation defined by said first pivot means:

18. A lapping fixture as recited in claim 14 wherein said holding means maintains the same distance between the lapping plane and corresponding points on each of any workpieces mounted on said holding means for any angular orientation of said holding means.

19. In a lapping fixture for holding a workpiece to be lapped, the lapping fixture being adapted for urging a workpiece against a substantially fiat lapping surface for grinding away portions of the workpiece extending beyond a lapping plane associated with the lapping fixture and polishing portions of the workpiece lying substantially in the lapping plane, the combination which 1 comprises:

b. a fixture body mounted to said spacing means;

0. holding means comprising a plurality of distinct workpiece-holding-stations each of which is adapted to have at least one workpiece mounted thereon;

d. means for rotatably mounting said holding means to said fixture body which includes 1. a plurality of first linkage members each having one of the distinct workpiece-holding-stations mounted thereto adjacent to and spaced apart from the lapping plane and 2. first pivot means for independently mounting each of said plurality of first linkage members to said fixture body, said first pivot means defining axes of rotation for said first linkage members, all of the axes having the same fixed orientation with respect to said fixture body; and

e. means for controllably rotating said rotatable mounting means which includes 1 a second linkage member adapted for translation with respect to said fixture body,

2. second pivot means for mounting said-second linkage member to said first linkage members to cause simultaneous and substantially equal rotation of said first linkage members about the axes of rotation defined by said first pivot means when said second linkage member is translated,

3. a cam rotatably mounted to said fixture body,

and

20. A lapping fixture as recited in claim 19 which comprises means for rotating said cam.

disposed along a line substantially parallel to the axes of rotation defined by said first pivot means.

23. A lapping fixture as recited in claim 19 wherein said holding means maintains the same distance between the lapping plane and corresponding points on each of any workpieces mounted on said holding means for any angular orientation of said holding means.

Claims

1. In a lapping fixture for holding a workpiece to be lapped, the lapping fixture being adapted for urging a workpiece against a substantially flat lapping surface for grinding away portions of the workpiece extending beyond a lapping plane associated with the lapping fixture and polishing portions of the workpiece lying substantially in the lapping plane, the combination which comprises: a. spacing means having a substantially flat contact surface adapted to be urged against the lapping surface, the contact surface defining the lapping plane; b. a fixture body mounted to said spacing means at a fixed angular orientation with respect to the lapping plane; c. means for holding a plurality of workpieces along a line of disposition substantially parallel to an axis of rotation for said holding means; and d. means for rotatably mounting said holding means to said fixture body.

2. A lapping fixture as recited in claim 1 wherein said rotatable mounting means comprises: a. a first linkage member having said holding means mounted thereto adjacent to and spaced apart from the lapping plane; and b. first pivot means for mounting said first linkage member to said fixture body, said first pivot means defining the axis of rotation parallel to the line of disposition for the workpieces, the axis having a fixed orientation with respect to said fixture body.

2. second pivot means for mounting said second linkage member to said first linkage members to cause simultaneous and substantially equal rotation of said first linkage members about the axes of rotation defined by said first pivot means when said second linkage member is translatEd,

2. first pivot means for independently mounting each of said plurality of first linkage members to said fixture body, said first pivot means defining axes of rotation for said first linkage members, all of the axes having the same fixed orientation with respect to said fixture body; and e. means for controllably rotating said rotatable mounting means which includes

2. second pivot means for mounting said second linkage member to said first linkage member to cause rotation of said first linkage member about the axis of rotation defined by said first pivot means when said second linkage member is translated,

2. first pivot means for mounting said first linkage member to said fixture body, said first pivot means defining an axis of rotation for said first linkage member, the axis having a fixed orientation with respect to said fixture body; and e. means for controllably rotating said rotatable mounting means which includes

3. a cam rotatably mounted to said fixture body, and

3. A lapping fixture as recited in claim 2 wherein said first pivot means defines the axis of rotation to be substantially parallel to and spaced a selected distance apart from the lapping plane.

4. A lapping fixture as recited in claim 2 having means for controllably rotating said rotatable mounting means which comprises: a. a second linkage member adapted for translation with respect to said fixture body; b. second pivot means for mounting said second linkage member to said first linkage member to cause rotation of said first linkage member about the axis of rotation defined by said first pivot means when said second linkage member is translated; c. a cam rotatably mounted to said fixture body; and d. means for engaging said second linkage member with said cam to cause translation of said second linkage member in response to rotation of said cam.

6. A lapping fixture as recited in claim 4 which comprises means for rotating said cam.

7. In a lapping fixture for holding a workpiece to be lapped, the lapping fixture being adapted for urging a workpiece against a substantially flat lapping surface for grinding away portions of the workpiece extending beyond a lapping plane associated with the lapping fixture and polishing portions of the workpiece lying substantially in the lapping plane, the combination which comprises: a. spacing means having a substantially flat contact surface adapted to be urged against the lapping surface, said contact surface defining the lapping plane; b. a fixture body mounted to said spacing means; c. holding means for a plurality of workpieces, said holding means comprising a plurality of distinct workpiece-holding-stations each being rotatable about a distinct axis of rotation, the axis of rotation for each workpiece-holding-station being coplanar with all other axes of rotation for workpiece-holding-stations; and d. means for rotatably mounting said holding means to said fixture body.

8. A lapping fixture as recited in claim 7 wherein said rotatable mounting means comprises: a. a plurality of first linkage members each having one of the distinct workpiece-holding-stations mounted thereto adjacent to and spaced apart from the lapping plane; and b. first pivot means for independently mounting each of said plurality of first linkage members to said fixture body, said first pivot means defining the several distinct axes of rotation for the plurality of workpiece-holding-stations.

9. A lapping fixture as recited in claim 8 wherein said first pivot means defines the several distinct axes of rotation for the plurality of workpiece-holding-stations to lie spaced apart from each other in a plane substantially parallel to and spaced a selected distance apart from the lapping plane.

10. A lapping fixture as recited in claim 8 having means for controllably rotating said rotatable mounting means which comprises: a. a second linkage member adapted for translation with respect to said fixture body; b. second pivot means for mounting said second linkage member to said first linkage members to cause simultaneous and substantially equal rotation of said first linkage members about the axes of rotation defined by said first pivot means when said second linkage member is translated; c. a cam rotatably mounted to said fixture body; and d. means for engaging said second linkage member with said cam to cause translation of said second linkage member in response to rotation of said cam.

14. In a lapping fixture for holding a workpiece to be lapped, the lapping fixture being adapted for urging a workpiece against a substantially flat lapping surface for grinding away portions of the workpiece extending beyond a lapping plane associated with the lapping fixture and polishing portions of the workpiece lying substantially in the lapping plane, the combination which comprises: a. spaCing means having a substantially flat contact surface adapted to be urged against the lapping surface, the contact surface defining the lapping plane; b. a fixture body mounted to said spacing means; c. holding means adapted to have at least one workpiece mounted thereon; d. means for rotatably mounting said holding means to said fixture body which includes

17. A lapping fixture as recited in claim 14 wherein said holding means comprises means for mounting a plurality of workpieces thereon disposed along a line substantially parallel to the axis of rotation defined by said first pivot means.

19. In a lapping fixture for holding a workpiece to be lapped, the lapping fixture being adapted for urging a workpiece against a substantially flat lapping surface for grinding away portions of the workpiece extending beyond a lapping plane associated with the lapping fixture and polishing portions of the workpiece lying substantially in the lapping plane, the combination which comprises: a. spacing means having a substantially flat contact surface adapted to be urged against the lapping surface, said contact surface defining the lapping plane; b. a fixture body mounted to said spacing means; c. holding means comprising a plurality of distinct workpiece-holding-stations each of which is adapted to have at least one workpiece mounted thereon; d. means for rotatably mounting said holding means to said fixture body which includes

21. A lapping fixture as recited in claim 19 wherein the axes of rotation defined by said first pivot means lie substantially parallel to and spaced apart from each other in a plane substantially parallel to and spaced a selected distance apart from the lapping plane.

22. A lapping fixture as recited in claim 19 wherein each distinct workpiece-holding-station comprises means for mounting a plurality of workpieces thereon disposed along a line substantially parallel to the axes of rotation defined by said first pivot means.