US 3793779 A
An apparatus and process are described for finishing a surface on a workpiece. At least one workpiece is rotatably supported by a chuck assembly provided on a turntable. The turntable can be indexed to advance the workpieces through one or more treatment zones. The workpieces on each chuck assembly are preferably engaged by a corresponding lapping disc that is releasably and floatingly supported by the main turntable. A pushrod assembly is provided for reciprocally moving each lapping disc in a direction radially of the rotatable turntable. This reciprocal movement combines with rotational movement of the lapping disc as derived from the floating mounting and frictional contact with the rotating workpiece, enabling wear of the surfaces in contact to be very uniformly distributed. Extreme smoothness and flatness of the workpiece surface being treated can be obtained. Each zone is provided with a recirculating conveyor for the lapping discs and a transfer mechanism that moves such discs at a predetermined time from one of the chuck assemblies to the recirculating conveyor, and vice versa. The treatment zones are independent of one another. By initial treatment in the first lapping zone followed by final finishing in the second zone, surface flatness can be obtained to within one-half of a lightwave band width of monochromatic light, for example, obtained from a sodium source.
Claims available in
Description (OCR text may contain errors)
United States Patent [1 1 Perrella [4 1 Fears, 1974 1 APPARATUS FOR TREATING A SURFACE Quebec, Canada  Assignee: DBM Industries Limited, Montreal,
Quebec, Canada 22 Filedz June2l, 1971  App1.No.': 155,151
 Foreign ApplicationPriority Data Jan. 29, 1971 Canada 103,996
 U.S. Cl 51/5, 51/54, 51/120,
51/134  Int. Cl 1324!) 7/04  Field of Search.. 51/133, 134,120, 3, 53, 56.5,
 References Cited UNITED STATES PATENTS 1,422,505 7/1922 Weaver 51/133 2,377,992 6/1945 Carlson 2,070,283 2/1937 Lewis 2,208,499 7/1940 Fiedler.... 1,905,651 4/1933 Raule 1,881,244 10/1932 Rattle 51/53 FOREIGN PATENTS OR APPLICATIONS 12,890 5/1914 Great Britain; 51/134 660,248 10/1951 Great Britain 51/56 e 'lfl 9' 9-.Y8l1it9bsed... a. Attorney, Agent, or Firm-Cushman, Darby & Cushman [5 7 ABSTRACT An apparatus and process are described for finishing a surface on a workpiece. At least one workpiece is rotatably supported by a chuck assembly provided on a turntable. The turntable can be indexed to advance the workpieces through one or more treatment zones. The workpieces on each chuck assembly are preferably engaged by a corresponding lapping disc that is releasably and floatingly supported by the main turntable. A pushrod assembly is provided for reciprocally moving each lapping disc in a direction radially of the rotatable turntable. This reciprocal movement combines with rotational movement of the lapping disc as derived from the floating mounting and frictional contact with the rotating workpiece, enabling wear of the surfaces in contact to be very uniformly distributed. Extreme smoothness and flatness of the workpiece surface being treated can be obtained. Each zone is provided with a recirculating conveyor for the lapping discs and a transfer mechanism that moves such discs at a predetermined time from one of the chuck assemblies to the recirculating conveyor, and vice versa. The treatment zones are independent of one another. By initial treatment in the first lapping zone followed by final finishing in the second zone, surface flatness can be obtained to within one-half of a lightwave band width of monochromatic light, for example, obtained from a sodium source.
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sum 17 1 APPARATUS FOR TREATING A SURFACE having at least one lapping zone a workpiece being rotatably supported is advanced through such zones automatically by timed indexing motion of that machine.
BACKGROUND OF THE INVENTION It is-well known in the machine-tool art that the purpose of a lapping machine and lapping operation is not to remove metal, but rather to finish the same'to some size or surface finish. The lapping operation normally involves the use of loose-grain abrasive flours mixed with oil or other such lubricant. Such a mixture is applied to the workpiece whose surface is to be treated, by means of a lap which might be a disc, or the like. The lap is often made of ametal softer than the workpiece to be lapped, and can be made of soft cast iron, brass, copper, lead or soft steel. It will be recognized that the harder the lap, the slower the cut, the duller the finish, and the faster the wearon the lap. The faces of laps, say on a lapping disc, are usually serrated to enable the working surface to remain clean and free of accumulations of abrasives or dirt.
US. Pat. No. 2,469,563 which issued May 10, 1949 to R. K. Kinard describes one type of lapping machine. That machine includes an element which is formed with a plurality of lapping surfaces surrounded by a retainin g element and co-operating with a relatively movable lapping plate to lap objects positioned on the lapping surface. The lapping plate is supported loosely upon the objects to be lapped, the workpieces, and is oscillated relative to the lapping members. In that particular patent, the lapping machine is' especially adapted to enable two parallel surfaces on opposite sides of a workpiece to be lapped.
Problems that have existed in this art arise, for example, when a person attempts to lap many small workpiece surfaces simultaneously and to a high degree of accuracy. To our knowledge, conventional lapping machines using discs have not been able to acieveaccuracy on a production basis better than one lightwave band width in flatness. This difficulty has persisted in some instances because of the problems associated with uneven or irregular wear of the surfaces in contact, and in others due to an accumulation of grit and the like upon the working surface of the lapping disc. It will be seen, for example, that in the above Kinard patent, a retaining element is provided for maintaining the workpieces to be lapped in place. An upper lapping plate is rotatably mounted and is moved recipr'ocally by an eccentrically mounted pin. Means are also provided to rotate the upper lapping plate periodically so as to reduce the possibility of continuous wear on limited parts of the gritted face of the lapping plate.
It will be recognized, however, that because of the significantly large size of the upper lapping plate, as well as of the lower workpiece retaining element, considerable difficulty could be experienced in maintaining the working surfaces in proper alignment, i.e. as close to being absolutely parallel to one another as possible. Uneven wear on the mounting surfaces and bearings, thermal distortion, and the like can nevertheless disable extreme flatness from being obtained of the workpiece surfaces being treated. Furthermore, it will be recognized that despite the kind of lapping compound used in the machine shown in this Kinard patent, whether it be coarse or fine in texture, a major cleanup of the working surfaces on the upper lapping plate and on the retaining element would be required to effect more than one stage of treatment to the workpiece surfaces on this one machine. In other words, the Kinard patent is wholly unsuited for the concept of more than one lapping zone in the same machine.
SUMMARY OF THE INVENTION In decided contrast to the problems encountered in prior art lapping machines such as that noted above, the present invention provides very significant improvements both in the quality and accuracy of fmishing a workpiece surface especially by lapping. A lapping machine is described herein which can lap a workpiece surface to within one-half a lightwave band width of flatness (measured using monochromatic light). In one aspect of the invention, there is afforded a technique by which a multiplicity of workpiece surfaces which are each quite small insize can be finished to extreme smoothness and a higher degree of flatness than had previously been possible. In that embodiment, individual workpieces of which a small surface is to be treated and finished are supported in a workpiece holder, such surfaces being positioned to lie in a common plane. A lap in the form of a disc is floatingly supported in contact with the surfaces to be treated. This disc is subjected to both positive reciprocal and induced rotational movement so as to undergo compound motion relative to the workpieces. The lapping disc is preferably made of a very hard steel that is extremely flat on its working surface. When subjected to the compound motion just mentioned, the lapping disc and workpiece surface in contact therewith wear uniformly, resultingin a surface finished to a higher order of flatness than had previously been possible.
A preferred embodiment of this invention provides two stages of lapping in two independent lapping or treatment zones, so as to enable a smooth finish to be obtained as well as one which is very flat. The lapping discs are floatingly supported in contact with the workpiece surfaces during passage of the workpieces through the particular treatment zone. The discs are then removed from contact with the workpieces and recirculated back to a starting position or point at which they are brought back into contact with new workpieces being advanced into that treatment zone. Different textures of lapping compound can therefore be used simultaneously in the separate and independent treatment zones on the one lapping machine. The first stage of treatment in finishing the workpiece surface can, for instance, be a lapping operation. This can subsequently be followed in the next treatment zone by, say, a burnishing procedure. An idle position is preferably provided intermediate the two treatment zones so as to enable inspection and/or cleaning of the workpiece surfaces prior to further treatment in the next treatment zone.
According to one aspect of the present invention, therefore, there is provided apparatus for treating a surface on a workpiece that can be placed from a load station onto a rotatable turntable and removed therefrom to an unload station, comprising: support means rotatably mounted on the turntable for carrying at least one workpiece; drive means for selectively rotating said support means; disc means for engaging the workpiece and effecting said surface treatment thereof, the disc means being floatingly supported on a support assembly provided on the turntable; actuating means operatively connected to the support assembly for reciprocally moving-said disc means to cause compound relative motion between the disc means and said workpiece, this compound relative motion causing wear of the workpiece and disc means to be uniformly distributed so that maximum flatness is obtained of the surface being treated; and, driving means operative for periodically indexing said turntable and advancing the workpiece through at least one treatment zone provided intermediate the load and unload stations. Contrary to earlier machines, loading and unloading herein is performed without stopping our machine. A transfer assembly is preferably provided in operative relation to each treatment zone for transferring the disc means to and from the support assembly on the turntable which carries the disc means in operative relation to the workpieces. It is also preferable that a recirculating conveyor be provided in operative relation to these transfer assemblies for receiving and carrying the disc means from one position at which they have been transferred from the turntable support assembly to another position from which said disc means is transferred to the turntable support assembly, movement of the recirculating conveyor being in synchronism to the indexing motion of the turntable.
It is therefore an object of this invention to provide an improved apparatus by the operation of which a surface on a workpiece can be finished to a degree of smoothness and extreme flatness of an order not possible with similar devices of the prior art.
It is an object of a preferred embodiment herein to provide more than one finishing operation in a single apparatus by providing two treatment zones in which finishing steps or procedures are effected separately of one another.
BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and features of this invention will become apparent from the detailed description below, as read with reference to the accompanying drawings which illustrate only one preferred form of the present apparatus, and in which:
FIG. 1 is a plan view showing schematically a preferred form of apparatus according to this invention;
FIG. 2 is an elevation view taken in cross section along line 2-2 of FIG. 1 and showing the main tumtable of that apparatus;
FIG. 2A is a side elevation view taken in central section to show detail of a disc-supporting and reciprocating assembly such as that illustrated at approximately the eight oclock position in FIG. 1;
FIG. 3 is an electrical control circuit illustrating one circuit which can be used to effect automatic control and operation of a preferred embodiment of the present invention;
FIG. 4 is a graphical representation showing the timing of various steps involved in the operation of the apparatus of FIG. 1;
FIG. 5 is-an elevation view taken partly in section to show detail of a chuck assembly that is rotatably mounted on the main turntable of the apparatus in FIG. 1, on which one or more workpieces are supported;
FIG. 6 is a top plan view taken partly in section showing details of one mechanism for automatically activating and deactivating the chuck assembly of FIG. 5;
FIG. 7 is an elevation view taken in cross-section along 7-7 of FIG. 6;
FIG. 8 is an elevation view taken in cross-section along line 8-8 of FIG. 9 to show details of a slipping clutch arrangement for driving the chuck assembly shown in FIG. 5, at the load and unload stations of the system illustrated in FIG. ll;
FIG. 9 is a top plan view partly in section and taken along line 9-9 of FIG. 2, to show the arrangement by which the chuck assemblies are rotated in the treatment zones of the system illustrated in FIG. 1;
FIG. 10 is a top plan view partly in section and taken along line 10-10 of FIG. 2 to show the drive means for periodically indexing the main. turntable shown in FIGS. 1 and 2;
FIG. 11 is a plan view showing schematically the operative relationship of a disc-recirculating conveyor and transfer assemblies associated therewith, in operative relation to each of the treatment zones of the system illustrated in FIG. 1;
FIG. 12 is an end elevation view partly in section and showing a stand for supporting the recirculating conveyor illustrated in FIGS. 1 and 11;
FIG. 13 is also an end elevation view taken partly in section to show details of the disc-recirculating conveyor and one associated transfer assembly shown at the unload station of FIG. 11;
FIG. 14 is a side elevation view taken partly in section to show an arrangement for providing swivelling motion of the transfer assembly illustrated in FIG. 11, it being noted that FIGS. 12 I3 and 14 are taken along section lines 12-12; 13-13; and 14-14 of FIG. 11;
FIG. 15 is a top plan view taken partly in section to show detail of a swivel arm forming part of the transfer assembly of FIG. 14;
FIG. 16 is an elevation view showing detail of a gripping mechanism supported by the swivel arm of FIG. 15;
FIG. 17 is an end elevation view taken partly in section and showing additional detail of the gripping mechanism of FIG. 16; and
FIG. 18 is a side elevation view taken in section along line 18-18 of FIG. 11 and showing an idler sprocket wheel in the disc-recirculating conveyor drive system.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning now to a detailed description of the preferred embodiments of this invention, reference should be made initially to FIGS. 1 and 2 of the accompanying illustrative drawings. In those drawings a preferred form of the present invention is embodied in a lapping machine shown overall at 10. In brief, this lapping machine 10 comprises a circular turntable 50 that is rotatably-supported on a pedestal-like base assembly 104. A multiplicity of chuck assemblies shown overall at and in greater detail in FIG. 5, are rotatably supported