US 3580030 A
Description (OCR text may contain errors)
United States Patent I 13,580,030
 Inventors DennisP. Bean;  ReferencesCited John C- Perl L nge C lif- UNITED STATES PATENTS 3; Q $3 21 1968 2,442,908 6/1948 Sirp 72/401 gf Mia-25,1971 3,131,745 5/1964 Hotze 72/294 73 A Z 3,134,421 5/1964 Simmons... 72/294x 1 Q W 3,431,723 3/1969 Wattler 59/27x  COIL FORMER Primary Examiner-Milton S. Mehr AttomeyGolove & Kleinberg ABSTRACT: A method of making single-tum, planar, circular coils is disclosed in which a substantially linear rodlike element is cut and bent into a circle of predetermined radius through successive bending and cutting steps. The circular ring is formed, from an element which has been precut in the shape of an elongated C which has, at each of its ends, a 90 bend to a radius of curvature substantially equal to the predetermined radius.
MM Ma 25, 1971 Fig. 2.
Patented May 25, 1971 2 Sho ets-Sheet 2 Dennis P. Been, John C. Parks INVENTORS.
GOLOVE 8\ KLEINBERG,
COIL FORMER The present invention relates to a method and apparatus for making planar, circular rings from a linear, rod or wirelike element and, more particularly, for making precision, circular coils of the type that are useful in circular potentiometers.
Closed, circular rings can be made from continuous wire or rod stock, and, in the past have been made by first producing a cylindrical helix of the desired radius of curvature. By making a single cut in the axial direction of the helix, a plurality of single-tum, open coils, results. These individual coils are not planar, but can be made planar by bending the coil so that the cut edges abut one another. For most applications in which a single-tum ring is desired, this method is preferred in that the ring is initially open. Other articles can be placed on the ring, closing the loop.
Problems have been encountered, however, where the material from which the ring is to be made does not readily withstand the bending forces necessaryrto make a flat, planar ring or, if the bending operation does not result in a perfectly flat ring. Typically, single-tum, high precision circular potentiometers are made in this fashion. Errors are introduced if the finished, single-tum coil is not flat within'very close tolerances since a sliding contact that is arranged to move in a plane to cooperate with a side" of the coil, will not provide a resistance that is completely linear with respect to the rotation of the contact. Depending upon the accuracy required, deviations from the plane, introduce certain nonlinearities if the contact must rise and "fall into and out of the plane of the coil.
Generally, the. fragility of the resistance wire which is wound on a mandrel to produce a linear potentiometer winding makes it extremely difficult to apply substantial compressive forces to the winding for the purposes of bending. Further, the surface of the wound mandrel is extremely susceptible to damage from abrasion.
It is therefore deemed desirable to provide a method and an apparatus for producing flat, circular coils from substantially linear, continuous stock of rod or wire, which method and apparatus does not subject the rod or wire or the surface thereof to high compressive or abrasive forces.
According to the present invention, a circular ring of predetermined radius is formed from a substantially linear, continuous wire or rod, by providing a circular form for bending that is substantially of the radius of the curvature of the finished ring. A virtually continuous process is employed comprising the successive steps of bending the rod or wire using the free end of the rod as a lever arm in a 180 bend about one of the circular forms. A cut is made preferably at the apex of the curve, resulting in opposed piecesLeach having a substantially 90 bend to a radius of curvature equal to the predetermined radius.
Assuming that the process starts with a previously unbent, linear rod, the first cut results in a free, scrap piece which may be discarded. The rod is then advanced by an amount substantially equal to the circumference of a finished ring and the bending step is repeated, followed by the cutting step.
At this point a workpiece is provided in the shape of an elongated C whose ends have 90 curves of the predetermined radius. The workpiece can be transferred to another'circular form and may be held at the center of the straight section, against the form. In a succession of bending steps, the workpiece is conformed to the circular shape, thereby producing a coil which is flat and planar, since all bending has been done in the same plane.
In alternative embodiments, one end of the workpiece may be held against the circular form, and in a plurality of successive bending steps, the remainder of the workpiece is curled around the form to produce the desired circular shape. In either case, only the relatively straight portion has bending forces applied to it, since the ends have been bent prior to a cutting step.
It is clear that the principal difficulty encountered in the bending of straight stock into a circular shape is that the bending force must be disproportionately increased as the lever arm gets shorter and shorter. Therefore, when starting with straight workpieces, in order to bend at the very ends, extremely high compressional forces must be applied which would tend to deform the rod or wire rather than bend it about the circular form. Accordingly, such a straightforwar approach could not be used with an easily deformed workpiece.
Depending upon the material to be utilized, certain allowances' must be made for the natural resiliency of the workpiece and the spring-back" encountered when thebending steps are undertaken. Accordi gly, the size of the bending forms, relative to the predetermined size may change in particular applications but, in general, the predetermined radius would be used for'the bending form. Similarly, the length of straight stock that is metered into the first bending station depends, to a limited extent, upon the width of the cutting device and whether or not the circle must be closed.
The novel features which are believed to be characteristic of the invention, both as to organization and method of operation, together with further objects and advantages thereof will be better understood from the following description considered in connection with the accompanying drawings in which several preferred embodiments of the invention are illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.
FIG. 1 includes FIGS. la, lb, 10, and 1d, of which FIG. la is a side view of a prior art, cylindrical helix,-
FIG. lb is a side view of the cylindrical helix of FIG. la, with a single cut through one wallof the helix in the axial direction,
FIG. 1c is a top viewof a single turn of the cut helix of FIG. lb, and
FIG. 1d is a top view of the single turn of FIG. 10, flattened into a planar, circular ring;
FIG. 2 includes FIGS. 2a and 2f, inclusive, which illustrates the several steps of the method of the present invention in which FIG. 2a-shows a linear rod element and a circular bending form,
FIG. 2b is a too view of the rod after a bending step around the form,
FIG. 20 is a top view of the rod and form during the cutting step,
FIG. 2d is a too view of the rod, after the cutting step and prior to the next bending steps,
FIG. 2e is a top view after the second bending step, and
FIG. 2f shows thesecond cutting step which produces a workpiece;
FIG. 3 includes FIGS. 3a and 3b of which FIG. 3a is a too view of the workpiece held in place against a second bending form with a plurality of bending arms shown in an extended or open position, and
FIG. 3b shows the workpiece bent into the circular shape by the plurality of bending arms, all in the closed position;
FIG. 4 includes FIGS. 4a and 4b, of which FIG. 4a shows the workpiece held against a bending form in an alternative embodiment, and
' FIG. 4b shows the coil with a plurality of bending elements in the closed configuration to form a circular coil; and
FIG. 5 is an idealized view of apparatus suitable to practice the method of FIG. 2.
Turning first to FIG. 1,.there is shown in FIG. la, a conventional, prior art cylindrical helix 10 which is readily produced by conventional machinery now in use. As indicated in FIG. lb, the prior art then provides-a single, axial cut 12 through one wall of the cylinder to provide, as shown in FIG. 1c a plurality of single turn'coils 14, the ends 16 of which are displaced in the axial direction.
As seen in FIG. 1d, a ring 18 is produced by simultaneously applying bending forces in the axial direction to the opposite ends 16 of the coil 14, until, as a result, the edges abut and a substantially planar, circular ring is produced.
Turning next to FIG. 2, including FIGS. 2a through 2f, the various steps according to the present invention for forming a circular coil are shown. In a first step, a substantially linear rod or wire element 20 is applied to a circular form 22. When a substantial lever arm has been provided, a 180 bend in the rod 20 is made as seen in FIG. 2b. A cut is made in the rod 20 by a cutting element 24 which is positioned to cut the rod at the apex of the curve, thereby producing a free element 26 with a 90 bend to the left and the original rod 20 with a 90 bend to the right, as viewed in FIG. 2c. At this step, the free piece 26 may be discarded, in that it is notin proper form for use as a workpiece in the forming of a coil according to the present invention.
In FIG. 2d, the rod is then advanced from the position shown in FIG. 2c, by an amount equal to the circumference of the ring of the desired diameter. As shown in FIG. 2e, the rod 20 is again bent l80 around form 22. In FIG. 2f, the cutting element 24 is again utilized to cut the rod 20 at the apex of the curve, now producing workpiece 28 of elongated, C-shaped having 90 bends (to the left as viewed in the FIG.) at both of its free ends.
Turning next to FIG. 3, the workpiece 28 is then removed to a second bending form 30 and, shown in FIG. 3a can be held by one of a plurality of forming members 32. The members 32 are radially arranged about the circular form 30 and are sequentially brought into engagement with the workpiece 28.
The individual bending members 32 may be operated in such a fashion that as each member 32 engages the workpiece 28 and deforms it slightly, a next adjacent bending member 32 is brought into operation. The members 32 act both sequentially and cooperatively to conform the workpiece 28 to the shape of the circular form 30, as shown in FIG. 3b, thereby producing a flat, planar, circular ring 34.
By adjusting the length of the rod 20 between the bending operations, the finished ring 34 can have a variable amount of gap between the ends.
While the process, as shown and described, contemplates the use of more than one circular form about which the rod is to be bent, it is clear that a single form may be utilized. However, it has been more convenient to utilize two separate forming elements 22, 30, so that the production of workpieces 28 can be substantially continuous, and the forming of coils can proceed substantially simultaneously therewith.
An alternative method of forming a ring from a workpiece 28 is shown in FIGS. 4a and 4b. In this embodiment, the workpiece 28 is held near its ends and a plurality of forming arms 32 sequentially apply bending forces to wrap the workpiece 28 around the periphery of the form 30.
The above-described steps of the process of forming a flat, planar circular coil, can be performed by a machine specifically designed for the task, or the individual steps could be performed by hand. So long as the bar or rod can be firmly held adjacent a bending form, the form acts as a fulcrum about which the free end acts as a lever. If the lever is sufficiently long, forces of a fairly low magnitude are sufficient to bend the rod about the fulcrum without giving rise to deforming or abrading forces in the area of the bent portion. The cutting operation is accomplished, preferably using a thin, high-speed saw.
FIG. 5 is an idealized representation of apparatus suitable for practicing the process of the present invention. As illustrated in FIG. 5, the apparatus includes a first work station 110 and a second work station I50. At the first work station 110, there is a metering roller 112 which advances the wire or rod 20 by a predetermined amount during each actuation of the mechanism.
A bending mechanism 114 is positioned to continuously apply a bending force to that portion of the rod 20 extending beyond a circular form 116 which, during actuation, tends to bend the rod through 180 and substantially parallel to that portion of rod between the metering roller 112 and the turning form 116. A moveable saw member 118 is actuable to sever the rod or wire 20 at the apex of the 180 curve and moves in a line substantially parallel with the rod 20.
any given workpiece will have a short arc at one end but a A longer are at the opposite end so that the formed coil will have been bent only in portions of the workpiece remote from the ends. Moreover, the ends, when juxtaposed, will form a smooth circular arc. Accordingly, even though the preferred embodiment is shown with a cut at the apex of the 180 curve, it is clear that sufiicient latitude exists so that the cut can be made virtually anywhere within the curve. Obviously, if the cut is made too close tp the unbent portion, substantial difficulty will be encountered in attempting to bend the straight portion of the workpiece into the desired curve.
A transfer mechanism 120 is used to hold the workpiece 28 during the cutting operation and then physically transfers the workpiece 28 to the second, forming station 150. The transfer mechanism 120 can serve as a holding member and the second circular form 122 can be on a moveable arm which is brought into engagement with the workpiece 28. A plurality of bending arms 124 is sequentially operated to form the finished coil.
At the completion of the forming step, the form 122 is retracted and the finished coil can be removed therefrom. As shown, the forming of the workpiece 28 and the transformation of the workpiece 28 into a finished coil can proceed substantially simultaneously, once a first workpiece has been provided.
Accordingly, the transfer station during each cycle brings a new workpiece 28 from the first work station 110 to a second work station 150. The raw rod or wire stock is fedin by the metering rollers 112 to the forming and cutting elements, and separate mechanisms are provided for removing the finished coils from the second work station 150.
Thus, there has been shown a novel method for producing circular planar coils from a substantially linear, continuous rodlike element. Further, apparatus has been disclosed for practicing the process. It will be clear to those skilled in the art that the process is not limited to the forming of single-tum potentiometer coils, but can be utilized with other starting materials to produce circular shapes. Further, the method is applicable to the forming of other, closed shapes from rod or barlike starting material and where the free ends must conform to a predetermined curve.
Accordingly, the scope of the invention should be limited only by the scope and breadth of the claims appended below.
1. Apparatus for producing planar, circular rings from a substantially continuous supply of a linear, rodlike material, comprising in combination:
I first means for feeding the linear material;
2. second means positioned to receive linear material from said first means, for bending said linear material through around a form of predetermined radius R;
3. third means adjacent said second means and the form for cutting the bent linear material to produce sections, each having a free end with a portion bent to a radius of curvature R;
4. coil forming means adjacent said third means and adapted to receive cut sections having bent portions at the ends therefrom, for bending the sections into a circle of radius R.
2. Apparatus according to claim 1, and further including transfer means for transporting cut sections from said third means to said coil forming means and for holding and positioning the cut sections in said forming means.
3. Apparatus according to claim 1, wherein said coil forming means include:
fourth means for holding a cut section, a form of Radius R, and a plurality of forming members sequentially operable to conform the section with said form to produce a planar coil of radius R.
4. Apparatus according to claim 3, wherein said fourth means is adapted to hold a section intermediate the ends thereof and said fonning members are positioned on both sides of said fourth means.
5. Apparatus according to claim 3, wherein said fourth means is adapted to hold a section at one end thereof and said forming members sequentially apply a bending force to conform the section around the periphery of said form.
6. The process of making planar circular coils of predetermined radius from substantially linear, continuous stock com prising the steps of:
l. bending the stock about a form of the predetermined radius R to fonn a U;
2. cutting the stock in the bend;
3. metering an additional length of stock substantially equal to the circumference of the desired circular coil; 4. repeating step I on the additional length of stock; 5. repeating step 2 to produce a free, generally C-shaped section having a bent portion at each end; and
6. Bending the C-shaped element about-a circular form of predetermined radius by applying bending forces progressively about the periphery of the form.
7. The process of claim 6, wherein the several bending steps are done on the same form of predetermined radius.
8. The process of claim 6, wherein a first form is used in steps l and 4 and a second form is used in step 6.
9. The process of claim 6, wherein step 6'includes the holding of the element at a point intermediate the ends and sequentially applying bending forces at both sides of the point to conform the element to the form.
10. The process of claim 6, above, wherein step 6 includes the holding of the element at one end thereof and applying bending forces around the periphery of form to conform the element thereto.
11. Apparatus according to claim I wherein said third means produce sections each having a free end with a bend to a radius of curvature R.
12. The process of claim 6 above, wherein step 2 includes cutting the stock at the apex of the bend wherein said C- shaped sections produced have 90 bends at each end.