US3537214A - Optical surfacing apparatus - Google Patents

Description

N 3, 1970 T, L, FORD 3,537,214

l OPTICAL SUREACING APPARATUS Filed Aug.- 21 1967 v 2 Sheets-Sheet 2 ams [79rd] BY (da, @aeg Q/gn; L

wal-"bm ATTORNEYS "United States Patent Office 3,537,214 Patented Nov. 3, 1970 3,537,214 OPTICAL SURFACING APPARATUS Thomas L. Ford, San Antonio, Tex., assignor to H. Dell Foster Co., San Antonio, Tex., a corporation of Texas Filed Aug. 21, 1967, Ser. No. 661,975 Int. Cl. B241 7/00 U.S. Cl. 51-113 1 Claim ABSTRACT F THE DISCLOSURE Apparatus for preparing optical surfaces by grinding and polishing comprising a work holder supporting one or more articles to be surfaced, a grinding and polishing tool for contacting the articles, and driving means irnparting to the tool and articles relative asynchronous motions, e.g., in rotation, oscillation, and translation, to effect a random nonrepetitive grinding action. Preferably the articles are loosely retained on the work holder and are capable of limited freedom of movement thereon independently of the driving means, further insuring random abrasive action.

This invention relates to the working of optical glass and similar materials and especially to machines for automatically or semi-automatically grinding and polishing optical surfaces.

The basic techniques required in grinding and finishing optical parts such as flats, prisms and lenses have evolved over a long period of time. Basically, such glass surfaces are ground roughly to the desired shape, by the use of fast cutting coarse grinding material, and then fine ground and polished to provide a surface of the required smoothness. -It is well known that the desired basic shaping must be achieved in the rough grinding since errors and flaws in shape seldom can be corrected economically, e.g., by special figuring, in the fine grinding and polishing steps.

In the prior art, therefore, the usual approach to optical working has been to do the rough grinding on one machine, transfer to another for fine grinding, and to still another for the final polishing. Although the same basic grinding motionsV may be used in all or most of the operations, there vremains the requirement for different setups to provide for special figuring to rectify errors made in rough grinding, and to facilitate use of different grinding and polishing materals, grinding pressures, etc. In general, the optical part being processed must progress through a half dozen or more operations from the rough blank to the finished iiat or other desired surface.

Typically, in ran optical surfacing arrangement, a tool is charged with a grinding or polishing material, placed in contact with the work to be surfaced, and moved under pressure in rotary and translatory motions which are selected to produce the desired shaping or polishing. As the grinding material, such as Carborundum or emery, becomes worn, it must be removed and replaced. From time to time the surfaces must be checked to insure that the desired shape, smoothness or other characteristic is being effected. A primary factor in all such `grinding is the relative overall motion between the tool and the work, and a major diiiculty is that of preventing zonal distortions 'which result from nonuniform grinding. It is to the solution of these problems that the present invention is directed.

Traditionally, and until quite recent times, high quality optical work has required hand processing to insure optimum characteristics such as shape, size, and minimum distortion. In hand grinding the optical worker applies certain chosen motions for awhile, using abrasives of the desired coarseness, and tests his Work from time to time to determine progress. As defects are discovered, corrective motions and figuring are applied. Finally, the finished part is tested very carefully to determine the resultant lflatness, curvature or other desired characteristic. Such a procedure obviously is time--consuming and has been replaced in industrial optical plants long ago by automatic or semi-automatic grinding and polishing machines.

While automatic machines effect a great speed-up in optical processing, there have been many difliculties with zonal distortions due to nonuniform grinding. -In machine grinding the motions tend to be more recurrent and, of course, more powerful than in hand grinding. Further, the grinding speeds are so greatly increased that zoning or similar distortion may progress rapidly and become uncorrectable by the usual procedures. Thus, in high quality surfacing it has been necessary to grind in stages, check the progress, and make corrections where practical `as the grinding proceeds. This step-by-step machine grinding and polishing also is relatively time-consuming and increases the cost of producing high quality optical parts.

In the prior art it has been understood that a combination of rotary and translatory motions is required to provide uniform grinding of optical surfaces. Accordingly, many arrangements have been devised to produce such motions. Perhaps the most widely used approach has been to utilize a planetary gearing arrangement in which the tool is moved in various spiral motions across the work. While processing speed is increased greatly, all such gear arrangements, utilizing definite fixed ratios between the various motions, have resulted in nonuniform grinding.

Another approach to increasing the production rate has been to grind many parts on the same machine simultaneously. For example, a large number of flats or prisms may be assembled and held in proximity in plaster of paris, or similar matrix material, on a work support, so as to permit multi-element grinding and polishing. A1- thou'gh such a procedure facilitates processing, it is apparent that the same limitations apply, with respect to nonuniform grinding, as for separate processing.

In accordance Iwith the present invention, improved surfacing is provided by machine arrangements in which the necessary rotary and translatory or other motions are combined in a purely random manner so as to result in a minimum of nonuniform grinding.

Accordingly, it is an object of this invention to provide improved apparatus for surfacing optical parts of high quality in Which the relationship between the various grinding and polishing motions is purely random. A further object is to provide an apparatus in which a large number of optical parts may be simultaneously surfaced by a random relationship of the grinding motions. Still another object is to provide for accurate grinding and polishing of optical parts on a single machine. Further objects will be apparent from the following description and the accompanying drawings, in which:

FIG. l is a transverse vertical section on the line 1-1 of FIG. 3, illustrating a preferred form of apparatus embodying the invention;

FIG. 2 is a plan view taken on the line 2 2 of FIG. l;

FIG. 3 is a side elevation of the same apparatus;

FIG. 3a is a partial plan view of FIG. 3;

FIG. 4 is a fragmentary view on a reduced scale of the primary driving means; and

FIG. 5 is a view in perspective of the inner mask o1' cage which hold the optical elements in relative, but not rigid, relationship.

Referring to FIG. l of the drawings, there is shown a work support 1 which may be mounted on a base housing 37 for rotation on a vertical axis. Work support 1 may be rotated by shaft 2 which is suitably journaled in housing 37 and driven by motor3 through a gear reduction box 4: The speed and torque applied to work support 1- may be varied by appropriate regulation of motor 3, or of the gearing, to meet the particular surfacing requirements.

Mounted above work support 1 for rotation on a vertical axis is a grinding and polishing tool 5, the tool being rotated by motor 6 through gear reduction box 7, shaft 9, pulleys 10 and 12 with belt 11, and upper driving shaft 13. Grinding tool is preferably fitted with a pressure control collar 14, threaded on shaft 13, and cooperating spring 15 by means of which adjustments of the grinding pressure may be made. Thus driving member 40 may be splined or keyed within shaft 13 to slide axially within and be rotated by shaft 13. Set screws 42, threaded in opposite sides of shaft 13, engage longitudinal slots in driving member 40 to retain the driving member within upper driving shaft 13 while permitting relative axial movement therebetween. When pressure control collar 14 is threaded downwardly on shaft 13, the compressive force of spring 15 is transmitted to grinding tool 5, re-4 sulting in increased grinding pressure on optical elements 31 as they rest on work support 1. The rotary speed and torque applied to grinding tool 5 may be adjusted, in similar manner to work support 1, by use of suitable electrical controls of motor 6 or by regulation of gear box 7.

Between driving member 40 and work support 1 there is interposed a self-adjusting driving joint 41, for the purpose of providing parallelism between the surfaces of the grinding tool 5 and work support 1 during the surfacing operation. This self-aligning action of driving joint 41, shown as a conventional flexible coupling, may be a double gimbal, a ball-joint or other universal joint drive, is `essential in the grinding o f optical elements 31 `as parallel flats. The various random grinding motions, hereinafter described, plus the self-adjusting feature of driving joint 41, provide the grinding and/or polishing action necessary to produce parallel flats' of exceedingly high quality.

Resting movably on work support 1 is outer mask or cage 16 which is fitted with reciprocating drive rod 19 and lateral drive rod 17. Reciprocating drive rod 19 is journaled on crank pin 25, which is rotated by reciprocating crank disk 26 which in turn is driven by motor 6 through gear reduction box 7, pulleys 28 and 29, associated belt 30 and shaft 27. Lateral drive rod 17 is shaped so as to tit loosely and slidably in crank pin 18, carried by lateral crank disk 20, which is rotated from motor 3 through gear box 4, pulleys 23 and 22, and belt 24. Thus outer mask 16 is driven in the horizontal plane by reciprocating motion of crank pin 25 and by essentially lateral motion of crank pin 18.

Motors 3 and 6 are lasynchronous, and the relative speeds at which work support 1 and grinding tool 5 are rotated will therefore vary with time, as will the rate of rotation of crank disks 20 and 26. The two motors and/ or their associated gear boxes are preferably so regulated as 'to` establish, apart from this variation, a differential rotation between work support 1 and grinding tool 5; usually the supportv and tool are driven in opposite directions and the rate of rotation of each is selected to provide optimum grinding conditions.

WhileV the relativespeeds of Ithe several elements is not critical, the tool is preferably rotated at about three times the speed of the work support, usually varying from about 5 r'.p.m. to vabout 30 r.p.m. Oscillatory and translatory movements in a speed ratio of 3:L and in the range of 5 to 10 strokes per minute are effective. All of these relative' speeds vary widely in practice, depending upon the stage of grinding the particular work requirements, and various other -factors and are within the skill of the artisanto select.

' One or more optical elements 31 are placed on work supporti. and are held loosely Ain position thereon by inner mask 34, shown separate-ly in FG.` The arrange-- "ment of outer maskV 16 `andinner mask34'with respect to 'surfacing on a single machine..

the optical elements 31 may` be understood more clearly from FIG. 2 in which there is shown also the driving arrangement for the outer mask. As will be noted, the optical elements 31 are` placed'loosely in, holes cut in the` inner mask 34,-which itself is heldloosely within the larger circular opening provided in the outerA mask 16'. Additionally, the periphery of inner mask 34 is discontinuous so that in certain positions the outer edges of the optical parts 31 may contact and be moved by outerfmask 1-6. It will be noted also, as shown in FIG. 1, that inner mask 34 and the optical elements 31`rest on the rotating work support 1 i Thus a rotary motion is applied to optical elements 31 by work support 1 'and a combined translatryfoscils lating motion is imparted to the inner mask 34 by the motion of outer mask 16. Itwill be seen that the --reciprocating drive rod 19 of thel outer mask is connected to crank 'pin 25 so as to drive outer mask 16 in es-., sentially longitudinal or 4reciprocating' motion whenl refciprocating drive box 26 is actuated. Likewise, the lateral drive rod 17 lits in slotted lateralmotion crankpin 18 so as to move outer maskV 16 in essentially lateral motion when lateral drive crank disk 20 is actuatedjIhus the overall motion of outer mask 16 is under the randomly associated control of motor 3 and 'motor 6 by way of the separate gearing and power transmission means. Since the two motors are asynchronous, a repetitions pattern of grinding is precluded. f Referring again to FIG. l, the upper surfaces of the optical elements 61 project slightly above the upper sides of inner mask 34 and outer mask 16; thus the grindingl pressure from grinding tool 5, along with the rotary` motion, is appliedv only to the upper surfaces of optical elements 31.

From the description of` thesev'eral motions, drives and loose couplings, it should be apparent that the novel surfacing arrangement is intended to produce the necessary grinding or polishing motions in an essentially random relationship so as to prevent nonuniformgrind-- ing of zones Likewise, reciprocating drive box` 26 and lateral drive box 20 are driven in oppositedirections and at different speeds, so that the translatory oscillating motion of outer mask 16 is random in nature. Still another random motion is introduced as optical. elements 31 move on the work supporti independently of masks 16 and 34. The resultant overallgrindingpath of optical elements 31 is thus derived from a considerable number of translatory and rotational motions and forms a randomly oriented rosette-shaped figure with reference to the centerof the driving force system which is completely nonrepetitive. As a result, surfacing is quite uniform, zoning distortions. are eliminated or minimized, and it is possible to accomplish all or most of the Certain precautions common to `the optical surfacing art should be observedforbest results. For example, the surfaces' of grinding tool Sand work support 1 should be arranged with grooves' or 'slots to facilitate access 0f the grinding fluid or compound to all parts of the working surfaces. The work. support thus Vserves both'asl a support and a surfacing orA grinding tool, opposite'surq faces of the work being' thus concurrently surfaced or ground. Similarly, provisionmay be`.made `for intro: ducing the grinding material automatically, 'at leastl 'for rough grinding, and for circulating the material.V All such procedures are well known and Widely used in optical workshops.v

`'Ihe driving system for grinding .tool'5 may been, closed in a protective column 32 and upper hous ing35l so as to prevent damage byv grinding or` polishing majterial. As shown in fFIG; 3, housing 35 is pivotedat- 33 on column 32 inV order that grinding tool. 5 may be swung` upwardly, for adjustment. .Cleanina raddngrgfindinemaf terial and similar operations. Belt retainers 62 and 63 mounted on housing 35 retain belt 11 in place when housing 35 is tilted. Counterweight 64 serves to balance out some of the weight of tool plate 5, shaft 13 and housing 35, so as to bring the grinding pressures within the desired range. Base housing 37 is suiciently heavy and rigid to prevent vibration and other movements which might result in nonuniform surfacing. When desired, housing 35 may be held in upward position by means of spring-loaded retaining pin 100 and associated indentation 101 in column 32.

In the interest of clarity the preferred embodiment of the invention has been illustrated and described in detail. It will, nevertheless, be understood that the invention is not limited except as hereinafter defined, and that Various changes and alterations within the scope of the appended claim are contemplated.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. Apparatus for preparing optical surfaces by abrasion comprising, in combination:

a work support having a surfacing face for articles to be surfaced,

a surfacing tool supported to engage the articles,

driving means imparting relative asynchronous rotation to said work and surfacing support and said surfacing tool, and

reciprocating means for displacing said articles on said work support in random, nonrepetitive fashion during the surfacing operation, said reciprocating means comprising,

an inner mask loosely embracing and separating the articles,

an outer mask loosely embracing said inner mask and said articles as they rest on said work support to allow limited but independent freedom of movement of the articles on the support during the surfacing operation, and

devices connected to said outer mask for imparting concurrently thereto movement to said mask and the embraced articles in a plurality of dilerent directions.

References Cited UNITED STATES PATENTS 657,724 -9/ 1900 IBeatty 51--114 1,485,321 2/ 1924 Wilkinson 51-113 1,577,137 3/1926 Maynard 51-133 2,740,237 4/ 1956 Day 51-133 3,224,148 12/ 1965 Mitchell 51-124 X FOREIGN PATENTS 318,986 2/ 1920 Germany.

HAROLD D. WHITEHEAD, Primary Examiner

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