Method for spring assembly

Abstract

The inventive method and apparatus produces a circular coiled wire spring by joining together and interlacing the successive spring convolutions at the ends of a straight coiled spring. The diameter of the spring wire is slightly greater than the lateral displacement between adjacent convolutions, so that the spring is both tensioned and compressed at the end tips. Thus, there is a very tightly gripped interlock, free of any sharp points or ends. A short rod is inserted within the coiled spring to guide and direct each spring as it winds into and intertwines with the opposite spring end.

Description

This invention relates to circular, coiled springs having radial uniformity and to methods and apparatus for making such springs.

Circular coiled springs of the described type have many purposes. However, so that the invention may be better understood, it may be well to here explain a specific device and purpose. Nevertheless, such specificity is not be construed as limiting upon the invention.

In greater detail, rubber diaphragms are often used in conjunction with various parts of the human body in order to seal off an opening, wound or the like. These diaphragms are usually domes of any suitable depth which terminate at their periphery in a circular, coiled spring, embedded in a ridge annularly formed as an integral portion of the dome. The circular, coiled spring stretches around and seals the dome over a body part. Therefore, the spring must not have any sharp ends, non-uniform rigidity, unanticipated distortions, or the like. Any such imperfections may cause failure, pain, or perhaps even a sickness. When the diaphragm is used as a birth control device, any such imperfections might destroy the peripheral seal and therefore, the utility of the diaphragm.

For convenience of expression, the sought-after spring characteristics are herein described as "radial uniformity." A radially uniform, circular, coiled spring is flat in its annular plane. When placed on a plane surface, it is in almost perfect contact with the plane throughout the entire 360.degree. of the circle. If almost any opposite sides of the circular spring are squeezed, the circular becomes oval without any loss of contact with the plane. Moreover, the diameter of the circular spring must be exactly controlled to avoid loss of seal at one extreme (i.e., too large a diameter) or interference with blood circulation at the other extreme (i.e., too small a diameter). Still other characteristics of radial uniformity will become more apparent, as this description proceeds.

Accordingly, an object of this invention is to provide a superior circular, coiled spring having an extremely high degree of radial uniformity. Here an object is to provide a circular spring which is free of all sharp ends or other irregularities which might cause failure, pain, or discomfort.

Another object of the invention is to provide circular, coiled springs which are and remain planar regardless of whether the spring is relaxed, contracted, or extended.

Still another object of the invention is to provide tools for making radially uniform circular, coiled springs. Here, an object is to provide low cost tools which do not require substantial capital outlay.

In keeping with an aspect of the invention, these and other objects are accomplished by a method and apparatus which produces a circular, coiled wire spring by joining together the ends of an elongated coiled spring. The spring ends are twisted together to interlace and entwine successive spring convolutions. The diameter of the spring wire is slightly greater than the lateral distance between adjacent convolutions of the relaxed spring. Hence, the spring end tips are both tensioned and compressed as they are intertwined, to form a very tightly gripped interlock. A short rod is inserted within the end of the coiled spring to guide and direct each spring end as it winds into the opposite spring end.

The nature of the invention apparatus, process, and method will be understood best from a study of the attached drawings wherein:

FIG. 1 is a perspective view of the tools used to manufacture a circular, coiled spring having radial uniformity;

FIGS. 2 and 3 are elevation views, respectively, showing the open and closed jaws of a vise in the tool of FIG. 1;

FIG. 4 is an exploded perspective view of the opposite end tips of an elongated coiled spring and a connector rod, just prior to a joining step;

FIG. 5 is a top plan view of the vise of FIG. 1, holding one end tip and connector rod and of the wrench of FIG. 1 holding the other end tip of the spring of FIG. 4, again just prior to a joining step;

FIGS. 6 and 7 are stop-motion views which show two steps in the manufacturing process;

FIG. 8 schematically shows the ends of the spring which are intertwined by the manufacturing process of FIGS. 6 and 7;

FIG. 9 schematically represents a circular, coiled spring with radial uniformity;

FIG. 10 schematically represents the circular spring of FIG. 9 compressed into an oval;

FIG. 11 is an end view of the compressed spring, taken along line 11--11 of FIG. 10, showing how the planar integrity is preserved in a non-defective spring; and

FIG. 12 is an end view similar to FIG. 11 showing the loss of planar integrity in a defective spring.

The inventive tool FIG. 1 includes three parts, a vise 20, a wrench 21, and a gauge block 22. By way of example, these tools are here shown as hand tools; however, they may easily be made into a unified machine, which may or may not be completely automatic.

The vise 20 comprises any suitable stationary support 25 which may be secured in place by any suitable means (not shown). Pivotally mounted at 26, 27 on the support 24 are a pair of jaws 28, 29, each having an end channel 30, 31 with semi-circular cross-section. The jaw 28 is fixed in a preselected vertical position by means of a set screw 32. The jaw 29 is normally urged to an open position away from jaw 28 by means of a bias spring 34. When the jaws 28, 29 are closed, a spring 33 (FIG. 5) is gripped within the mating channels 30, 31.

Adjacent the outer or unobstructed end of channel 31 is a rod clamp 35, having an edge 36 which projects into the channel 31. The thickness of edge 36 is such that it fits between adjacent spring convolutions 37, 38 (FIG. 5) without in any way stretching the spring. The edge 36 projects far enough into the channel 31 to grip a connector rod 40, which fits loosely in the center of the coiled spring 33.

A jaw actuator comprises a cam 42 integrally joined to one end of a control rod 43 which is rotatably mounted in a bearing in support 25. A lever arm 44 is integrally joined to the other end of the control rod 43. Handle 45 raises and lowers lever arm 44, which swings in directions A, B, respectively. When handle 45 is all the way down (in direction B), cam 42 is in a position (FIG. 2) where spring 34 forces apart jaws 28, 29. In this open position, the spring 33 may easily be placed between the jaws and within channels 30, 31. When handle 45 is raised in direction A, cam 42 rotates in direction A (FIG. 3) to force together the jaws 28, 29 which grip spring 33 and rod 40, via rod clamp 35.

Wrench 21 comprises a pair of elongated jaws 50, 51 hinged together at one end by means of a hinge pin 52. Semi-circular channels 53, 54 grip the spring 33 when the jaws 50, 51 are closed. Pivoted at 57, a screw 56 may swing between the ends of a fork 57, where a nut 58 may be tightened to lock together the two wrench jaws with the end tip of spring 33 held in channels 53, 54, between the jaws 50, 51.

FIG. 4 shows how the spring 33 is prepared for manufacture. First a coiled spring is wound and then cut to a precise length which is equal to the desired circumference of a diaphragm plus an overlap OL for interconnecting the ends. The outside diameter OD of spring 33 is fixed by (a) the diameter (not shown) of a peripheral rib annularly formed on a diaphragm, which is a well-known dimension and, (b) the desired strength and spring characteristics of the circular spring, which are also well-known. The inside diameter ID is established by the outside diameter and the diameter of the spring wire which is used.

When the spring 33 is cut to length, an overlap distance OL (FIG. 8) is included, in addition to the desired circumference of the circular spring. Preferably, the overlap is the amount which the spring end tips mesh together when they are intertwined or would together by, say, two or three complete 360.degree. turns (two turns are preferred). However, the overlap may be any suitable distance. When the convolutions are cut, the spring ends 60, 61 are aligned (FIG. 4) in such a manner that they come together as meshing threads when the two tip ends 63, 64 are brought together in a face-to-face relationship. The cutting of a coiled spring also forms the wire end cross-section into tapered sections (as seen in FIG. 4), which taper guides and directs the ends into a threading fit.

Just before the spring is placed in the vise 20, connector rod 40 is fitted inside the spring tip end 63. The outside rod diameter is such that the rod slips into the spring, but does not easily fall out. The length of the rod is such that it fills the overlap area OL without appreciably changing the spring characteristics of the circular spring.

After connector rod 40 is slipped into the tip end 63 of spring 33, it is clamped in vise 20 (FIG. 5). Edge 36 of rod clamp 35 fits between and without stretching adjacent convolutions of spring 33 and grips connector rod 40, to prevent it from moving with respect to spring tip end 63 during fabrication. The spring itself is gripped in channels 30, 31 of jaws 28, 29. Then, the other tip end 64 of spring 33 is fitted into channels 53, 54 of wrench 21. Screw 56 is swung on pivot 57 and into fork 57. Nut 58 is tightened to hold together jaws 50, 51.

The spring 33 is now suspended from vise 20, as shown in FIG. 6. Thereafter, the end 64 is rotated in direction C by a number of preliminary turns which exactly equals the number of turns by which the spring ends will be twisted together. The direction C is opposite to the direction E, in which the tip ends are turned in order to intermesh them.

Next, the spring 33 which has been preliminarily turned (FIG. 6) is formed into a loop (FIG. 7) around post 70 with the two spring end tips 63, 64 in an opposed face-to-face relationship, as shown in FIG. 4. A groove 71 on post 70 helps maintain the loop position during fabrication. Then, the end tip 64 is slipped over the end of connector rod 40, and wrench 21 is turned in direction E. Since the cut wire ends 60, 61 have a single, fixed position, there is a precisely fixed point at which the two tip ends begin to intertwine. Thus, an exact number of turns in direction E will exactly compensate for the exact number of preliminary turns illustrated in FIG. 6. As a result, all rotational stress is removed from the spring 33 when the preliminary twisting stress imparted during the step of FIG. 6 is removed by twisting in the opposite direction during the step of FIG. 7. No residual stress should remain after the tip ends are properly intertwined. This no-stress condition may be verified by observing the tip ends 60, 61 lying on a line 62, which is the same line that they lie on in the relaxed condition of FIG. 4.

At this time, the two tip ends are intertwined, as shown in FIG. 8 with the connector rod 40 keeping the intertwined convolutions in perfect alignment. Since the diameter of the spring wire is much greater (Y) than the space (X) between the convolutions, the wire in both tip ends is both tensioned and compressed. Hence, there is a very tight grip. Accordingly, there are no loose ends or projecting points to break through the diaphragm, to scratch, or to cause discomfort.

The vise 20 is opened, the wrench 21 is removed, and the completed circular, coiled spring 75 is fitted into an annular groove 77, cut into a gauge block 22 (FIG. 1). Thus, the gauge block automatically checks for radial, circular and circumferential accuracy. If the diameter of the circular spring is too large or too small, the spring does not drop freely into the annular groove 77. Also, the bottom of the groove 77 lies in a single plane which is exactly parallel to the plane of the top of the gauge block 22. Therefore, if the spring 75 is not planar, such defect is immediately visible.

The circular spring 75 is supposed to exert a uniform tension, or compression force in all radial directions lying within the plane of the circle, as illustrated in FIG. 9. One way to test for this planar uniformity is to slightly squeeze the opposite sides of the circular ring 75, as illustrated in FIG. 10. When the squeezed ring is viewed from the end (as at line 11--11, looking in the direction of the arrows), it is seen as having retained its planar geometry. Therefore the end of the oval ring projects a straight line.

If the spring pre-rotation (FIG. 6) is not exactly compensated by the counter-rotation during the intertwining step, (FIG. 7), some degree of rotational stress remains in the spring 33 after it is formed into circle 75. Therefore, when the ring 75 is squeezed into an oval (FIG. 10), the residual stress, remaining after the intertwining, is relieved by non-planar motion. When viewed along line 11--11, the projection of the squeezed ring is now in the form of the FIG. "8". Mechanically, the problem of residual spring tension can be overcome by properly indexing both the pre-stressing rotation of FIG. 6 and the de-stressing rotation of FIG. 7. Thus, great production accuracy can virtually insure a removal of all residual stress, by completing the assembly step of FIG. 7 under a microscope, wherein the relative positions of spring ends 60, 61 may be viewed as they come into final alignment against the background of a hairline.

While the circular, coiled spring has been described as a peripheral terminal for a diaphragm--and particularly, for a birth control device--those who are familiar with the pertinent spring art will readily perceive many other uses for the radially uniform spring. Also, various tools and techniques have been described herein. These tools may be altered or modified according to particular needs, as to provide automatic tooling. Therefore, the appended claims are to be construed to cover all equivalent structures falling within the true scope and spirit of the invention.

Claims

I claim:

1. A method of producing planar circular, coiled springs having radial uniformity, said method comprising the steps of:

a. coiling wire into elongated helical spring;

b. cutting said spring to a precise length which is equal to the circumference of said circular spring plus an overlap length;

c. inserting a connecting rod into one end of said circular spring helix, the diameter of said rod fitting into the helix with a snugness such that it does not easily fall out, and the length of said rod being approximately equal to the overlap length;

d. preliminarily turning said spring a predetermined rotary distance in a first direction to pre-stress said spring, and

e. bringing together and intertwining the tip ends of said elongated spring by turning said spring said predetermined rotary distance in a direction opposite to said first direction, whereby no residual pre-stress remains in said spring.

2. The method of claim 1 wherein the successive convolutions of said spring are separated by a distance which is less than the diameter of said wire whereby said intertwined tip ends are simultaneously in tension and compression.

3. The method of claim 1 wherein the tips of the wire ends of said helical spring have a predetermined spacial relationship with respect to each other and to the 360.degree. of the convolutions of said helix, whereby the relative positions of said ends in said intertwined condition may be observed to determine when no residual pre-stress remains.

4. The method of claim 1 and the added step of fitting said circular spring into a gauge block to verify the diameter, circumference, and planar trueness of said circle, said gauge block having a circular groove with the root of the groove lying in a plane which is parallel to the plane of the surface of said block.

5. The method of claim 4 and the further steps of squeezing said circular spring into substantially an oval and of detecting any loss of planar alignment while said spring is in an oval shape.

6. The method of claim 5 and the further steps of observing the end of said oval for planar alignment.

7. The method of claim 1 wherein each of the successive coils of said spring are separated by a distance which is less than the diameter of said wire whereby the wire spring within the area of said intertwined tip ends are simultaneously in tension and compression, the wire tips of the intertwined ends of said helical spring wire having a predetermined relationship with respect to each other and to the 360.degree. of the convolutions of said helix, whereby the relative positions of said tips may be observed in said intertwined condition to determine when no residual pre-stress remains.

8. The method of claim 7 and the added steps of:

a. fitting said circular spring into a gauge block to verify the diameter, circumference, and planar trueness of said circle, said gauge block having a circular groove with the root of the groove lying in a plane which is parallel to the plane of the surface of said block;

b. squeezing said circular spring into substantially an oval; and

c. detecting any loss of planar alignment while said spring is oval.