Multi-piece flexural pivot

Abstract: A flexural pivot is configured as a multi-piece device which is specifically configured to tolerate vibration and shock loading. The flex pivot described uses pre-formed unitary (one-piece) support structures (12, 14) which have integral undercut areas, diametrically opposed slots for flexural member (16, 18) placement and key ways and the like, and near net shape geometry. The flexural members (16, 18) are pre-brazed to facilitate the assembly process. The design of the pre-formed support structures eliminates brazed joints which are common locations of fracture due to vibration and shock loading, resulting in a significantly strengthened pivot. The overall configuration and method described provides an economical flex pivot, whereby the flex pivots are accessible for applications which have not heretofore been feasible.

Description: This invention relates generally to flexural pivots and particularly to a multi-piece flexural pivot which is more tolerant to vibration and shock loading than prior art flexural pivots. Prior art flexural pivots are fabricated by brazing four quadrants, inner and outer flexural members, and a sleeve into a flexural (flex) pivot assembly. The described arrangement has a plurality of brazed joints which are prone to fracture when the pivot is subjected to vibration and shock loading. Failures in which individual quadrants of the four quadrants separate from the flexural members and outer sleeve, or in which the pivot core separates from the outer sleeve, by fracturing at the brazed joints are common. Another problem encountered with brazed flex pivots using an outer sleeve is a condition called "bridging." Bridging occurs when the braze material used to join the pivot and core to the outer sleeve flows into an undercut area of the pivot and hence prevents flexing. Flex pivots of the type suffering from these disadvantages are described, for example, in U.S. Patents 3,073,584; 3,142,873; 3,142,888; 3,181,851; 3,181,918; 3,319,951; and 3,811,665. US-A-3277555, for example, discloses a method of forming a flexural pivot comprising fitting a pair of arcuate elements on the center parts of the inner surface of respective arcuate clip members and bonding the elements to the respective arcuate clip members to form two arcuate units, each having a base section and an axially-projecting arcuate section, arranging the arcuate units in opposed relation to each other on a common circle projection with the base sections diagonal of each other so that the projecting sections are diametrical of said base sections and so that the ends of the projections are flush with the ends of the opposite base sections, placing a pair of leaf springs in crossed relation between the arcuate units, with the spring ends abutting the edges of the arcuate element and the inner surface of the arcuate clip member, inserting four arcuate wedges into the gaps between the spring ends and the lips of the arcuate clip members for contact therewith and to be flush with the ends of the respective arcuate units, and bonding the leaf springs and wedges to the arcuate units to provide a dual-reed flexural pivot having crossed springs whereby one of the arcuate units can be rotated relative to the other with flexing of the springs. Further, the manufacturing processes for these prior art flex pivots are lengthy and include a variety of expensive, labor intensive operations. The resulting flex pivot has a high cost and a long manufacturing lead time. This prevents the flex pivot from being used in many applications where it would otherwise be advantageous. This invention contemplates a multi-piece flex pivot, i.e. a flex pivot including a number of support structures and flexural members, which is specifically configured to be more tolerant of vibration and shock loading than have the prior art flex pivots. The flex pivot described herein uses unitary pre-formed support structures which have integral, matching undercut areas, diametrically opposed slots for supporting flexural members and near net shape geometry, i.e. geometry requiring few, if any, finishing operations to meet specified sizes and tolerances. A configuration of the type described eliminates the need for the prior art four quadrant and sleeve arrangement, and eliminates a significant number of the aforenoted labor intensive operations including assembly and undercutting of the pivot core assembly or sleeve. By eliminating the quadrants and sleeve, the presently disclosed flex pivot eliminates the quadrant/sleeve brazed joints, which are particularly susceptible to fractures, as aforenoted. One embodiment of this invention provides a method for fabricating a multi-piece flexural pivot comprising: forming first and second support structures as unitary structures so that each of said unitary structures has an outer portion with a diametrical opening extending therethrough and a reduced diameter arcuate portion extending therefrom and a pair of diametrically opposed slots extending in the opening and in the arcuate portion; applying a braze material to a strip of flexural material; forming first and second flexural members from the flexural material having the braze material applied thereto so that said first flexural member has a solid center and said second flexural member has an open center; inserting the solid center of the first flexural member in the open center of the second flexural member for providing a flexural assembly; disposing the first and second unitary support structures so that the reduced diameter arcuate portion of the first structure extends in the diametrical opening of the second structure and the reduced diameter arcuate portion of the second structure extends in the diametrical opening of the first structure; disposing the flexural assembly so that the first and second flexural members engage the diametrically opposed slots in the openings and in the arcuate portions of the first and second structures to provide a pivot assembly; and exposing the pivot assembly to a thermal environment for brazing the flexural assembly in the diametrically opposed slots to provide a flexural pivot permitting relative pivotal displacement between the first and second support structures. An alternative embodiment of the present invention provides a method for fabricating a multi-piece flexural pivot comprising: forming first and second support structures as unitary structures so that each of said first and second unitary structures has an outer portion with a diametrical opening extending therethrough and a reduced diameter arcuate portion extending therefrom, and a pair of diametrically opposed slots extending in the opening and in the arcuate portion; forming a third structural support as a unitary structure having an outer portion with a diametrical opening extending therethrough and oppositely disposed reduced diameter arcuate portions extending therefrom, and having diametrically opposed slots extending in the arcuate portions; applying a braze material to a flexural material; forming first and second flexural members from the flexural material having the braze material applied thereto so that said first flexural member has a solid center and said second flexural member has an open center; inserting the solid center of the first flexural member in the open center of the second flexural member for providing a flexural assembly; disposing the first, second and third unitary support structures so that the reduced diameter arcuate portions of the first and second unitary support structures extend in the diametrical opening of the third unitary support structure, and the oppositely disposed reduced diameter arcuate portions extending from said third unitary support structure extend in the diametrical openings of the first and second unitary support structures; disposing the flexural assembly so that the first and second flexural members engage the diametrically opposed slots in the first, second and third unitary support structures to provide a pivot assembly; and exposing the pivot assembly to a thermal environment for brazing the flexural assembly in the diametrically opposed slots to provide a flexural pivot permitting relative pivotal displacement between the first, second and third unitary support structures. Figure 1 is an exploded view of a flexural pivot constructed according to the present invention and showing a pair of relatively movable support structures. Figure 2 is a side view of one of the relatively movable support structures shown in Figure 1. Figure 3 is an outer end view of the support structure shown in Figure 2. Figure 4 is a sectional view taken along the line IV-IV in Figure 3. Figure 5 is an inner end view of the support structure shown in Figure 2. Figure 6 is a side view of the assembled flexural pivot herein disclosed. Figure 7 is an exploded view of a four piece flexural pivot having integrally formed platform and lever support structures. Figure 8 is an exploded view of a four piece flexural pivot having integrally formed flanged ends. Figure 9 is an exploded view of a four piece flexural pivot having integrally formed square ends. Figure 10 is an exploded view of a four piece flexural pivot having key ways formed in the two support structures. Figure 11 is an exploded view of a double ended flexural pivot formed from five parts. Referring now to the drawings, and to Figures 1 through 6 in particular, there is shown a cantilevered flexural pivot 10 constructed according to the teachings of the present invention. Flexural pivot 10 is formed from two support structures 12 and 14 which are resiliently supported with respect to each other by a flat outer spring 16 and a flat inner spring 18. Support structures 12 and 14 are unitary structures having semi-circular inner portions extending therefrom and can be assembled to form flexural pivot 10 which has only four pieces. Support structures 12 and 14 have diametrically opposed internal slots 20 and 22 (Figure 3) which engage portions of flat springs 16 and 18. Support structure 12 includes a cylindrical outer surrounding portion 24 and an arcuate reduced diameter or undercut portion 26 which, when flex pivot 10 is assembled, extends within mating support structure 14. Support structure 14 likewise has a cylindrical outer portion and a reduced diameter or undercut portion for the same assembled arrangement, as will be discerned from the drawing. Flat springs 16 and 18 are assembled so that a solid center of spring 18 is disposed within an open center of spring 16 as particularly shown in Figures 7 - 11. Generally, springs 16 and 18 are aligned perpendicular. While only one type of flexural spring arrangement is shown, it should be noted that many alternate spring arrangements can be used. The angular separation between members 12 and 14 determines the maximum angular displacement through which pivot 10 can be flexed. Referring now to Figure 7, a flex pivot 30 is shown as having a unitary support structure 34 formed with a platform bottom and a mating unitary support structure 32 formed with an exposed lever. Referring now to Figures 8, 9 and 10, other flex pivots having other unitary support structures are shown. In Figure 8 a flanged end plate 6 is shown on support structures 40, 42 of a flex pivot 40. In Figure 9 square ends are provided on support structures 52, 54 of a flex pivot 50. In Figure 10 external key way slots are formed in support structures 62, 64 of a flex pivot 60. Thus, the unique and relatively complex shaped support structures of the several flex pivots herein shown allows for predetermined positioning and facilitates use of the pivots in a variety of applications, as has not otherwise been the case. Referring now to Figure 11 there is shown a five piece configuration for a flex pivot 70 having unitary support structures 72, 74. Support structures 72, 74 have reduced diameter or undercut portions which project within center structure 76. Springs 16, 18 resiliently support structures 72, 74 with respect to center structure 76. Support structures 72, 74 can be formed with complex shapes as described above with respect to the cantilevered flex pivots shown in Figures 7 - 10. Support structures 12, 14 shown in Figure 1; 32, 34 shown in Figure 7; 42, 44 shown in Figure 8; 52, 54 shown in Figure 9; 62, 64 shown in Figure 10; and 72, 74, 76 shown in Figure 11 are unitary structures, as aforenoted. That is to say, these structures are formed as single pieces as by die casting, metal injection molding, powder metallurgy techniques, or by plastic molding techniques, as the case may be, depending upon size, tolerance and material requirements. In the preferred embodiment of the invention the support structures are of a suitable corrosion resistant steel and are fabricated by metal injection molding. These methods of fabricating the support structures provide sufficient quality and dimensional control so that generally few, if any finishing operations are required prior to assembly of springs 16 and 18. In other words, the methods for forming the support structures as described provide said structures with near net shape geometry as will be recognized as desirable. The flexibility thereby achieved allows for infinite flex pivot mounting and a variety of modification possibilities including reduced or expanded internal diameters, slotting, threading, cut-out external diameters, shorter or longer lengths, key ways, flanges, etc. Both cantilevered and double ended flex pivots as herein shown and described can be fabricated using these techniques for forming the respective support structures. Thus, pre-formed support structures are achieved which eliminate the need for core quadrants, outer sleeves and most of the labor intensive operations, including assembly and undercutting of a core assembly or sleeve that have heretofore been necessary. As a result, extensive cost savings are realized and the application of flex pivots to heretofore unavailable fields is now feasible. Further, by eliminating the quadrants and the sleeves as aforenoted, the pre-formed support structures eliminate the quadrant/sleeve brazed joints so as to render the assembled flex pivot more tolerant to vibration and shock loading, as has not heretofore been the case. Springs 16 and 18 are constructed from a suitable material such as, for example, a corrosion resistant steel. This material may be pre-rolled to finished thickness dimensions and may be in the form of strips, rolls or plates. In the preferred embodiment of the invention strip stock is used. A suitable braze material is first applied to the strip stock. This may be accomplished via electroplating or via a pre-mixed alloy laminated as foil onto the strip stock. In either case, and in the preferred embodiment of the invention, the braze material consists of a larger percentage of silver, a smaller percentage of copper and very small amounts of nickel. Other braze materials may be used as particular applications indicate, the same being within the spirit and scope of the invention. In the preferred embodiment of the invention, forming of springs 16 and 18 from the braze prepared stock is accomplished by stamping. However, other methods, such as fine blanking, can be used. Stamping and fine blanking methods provide sufficient quality and dimensional control so that no additional operations are required prior to insertion of the springs into the diametrically opposed slots in the respective support structures. Assembly of the springs into the support structures requires that the diametrically opposed slots of the support structures be slightly wider than the thickness of the spring material. This is necessary to accommodate the increased thickness of the springs due to the plated or laminated braze material as will be readily understood. The assembled flex pivots, i.e. flex pivots with springs 16 and 18 inserted into the diametrically opposed slots of the respective support structures, includes fixturing the assembly and then subjecting the fixtured assembly to thermal conditions for performing braze and heat treating functions and/or a combination thereof. The thermal conditions are achieved via an oven brazing technique with temperature for brazing and heat treating cycles being in the range of 982-1016°C (1800 - 1860 degrees F) for fifteen to fifty minutes, depending on the type of braze material used and the heat treatment required. Subsequent finishing operations of the flex pivot assembly may be required to insure specified dimensions or to accommodate design modifications. If this is the case, the assembled flex pivots can be filled with a suitable compound, such as a wax, to prevent the pivots from flexing during the finishing operations. It will be understood that the disclosed method may be changed to allow for various metallic, non-metallic and metallic/non-metallic flex pivot configurations. For example, the brazing process heretofore described is used for a metallic flex pivot but may be replaced with an adhesive or fusing process when plastic components are involved. A flex pivot configured and fabricated in accordance with the invention as described can be used in any application requiring limited pivotal (oscillating) motion. Due to its configuration, the flex pivot so provided is much more tolerant to vibration and shock loading than would otherwise be the case. It will also be recognized that the flex pivot has a higher load rating when the springs are loaded in the tensile direction then flex pivots with the referenced quadrant/sleeve type construction.

Claims: A method for fabricating a multi-piece flexural pivot (10;30;40;60) comprising: forming first (12;32;42;52;62) and second support structures (14;34;44;54;64) as unitary structures so that each of said unitary structures has an outer portion (24) with a diametrical opening extending therethrough and a reduced diameter arcuate portion (26) extending therefrom and a pair of diametrically opposed slots (20;22) extending in the opening and in the arcuate portion; applying a braze material to a strip of flexural material; forming first (18) and second flexural members (16) from the flexural material having the braze material applied thereto so that said first flexural member (18) has a solid center and said second flexural member (16) has an open center; inserting the solid center of the first flexural member (18) in the open center of the second flexural member (16) for providing a flexural assembly; disposing the first and second unitary support structures (12, 14) so that the reduced diameter arcuate portion of the first structure extends in the diametrical opening of the second structure and the reduced diameter arcuate portion of the second structure extends in the diametrical opening of the first structure; disposing the flexural assembly so that the first and second flexural members (16,18) engage the diametrically opposed slots (20,22) in the openings and in the arcuate portions of the first and second structures to provide a pivot assembly; and exposing the pivot assembly to a thermal environment for brazing the flexural assembly in the diametrically opposed slots to provide a flexural pivot permitting relative pivotal displacement between the first and second support structures. A method for fabricating a multi-piece flexural pivot (70) comprising: forming first (72) and second support structures (74) as unitary structures so that each of said first and second unitary structures has an outer portion with a diametrical opening extending therethrough and a reduced diameter arcuate portion extending therefrom, and a pair of diametrically opposed slots extending in the opening and in the arcuate portion; forming a third structural support (76) as a unitary structure having an outer portion with a diametrical opening extending therethrough and oppositely disposed reduced diameter arcuate portions extending therefrom, and having diametrically opposed slots extending in the arcuate portions; applying a braze material to a flexural material; forming first (18) and second flexural members (16) from the flexural material having the braze material applied thereto so that said first flexural member (18) has a solid center and said second flexural member (16) has an open center; inserting the solid center of the first flexural member (18) in the open center of the second flexural member (16) for providing a flexural assembly; disposing the first (72), second (74) and third unitary support structures (76) so that the reduced diameter arcuate portions of the first and second unitary support structures extend in the diametrical opening of the third unitary support structure (76), and the oppositely disposed reduced diameter arcuate portions extending from said third unitary support structure extend in the diametrical openings of the first and second unitary support structures; disposing the flexural assembly so that the first (18) and second flexural members (16) engage the diametrically opposed slots in the first, second and third unitary support structures to provide a pivot assembly; and exposing the pivot assembly to a thermal environment for brazing the flexural assembly in the diametrically opposed slots to provide a flexural pivot permitting relative pivotal displacement between the first, second and third unitary support structures. A method according to Claim 1 or 2, characterised in that forming first and second support structures as unitary structures includes forming the first and second support structures so that said structures have near net shape geometry. A method according to Claim 3, characterised in that the first and support structures are formed by metal injection molding. A method according to any one of Claims 1 to 4, characterised in that the braze material is applied to the flexural material by electroplating. A method according to any one of Claims 1 to 5, characterised in that the first and second flexural members are formed by stamping from a strip of flexural material having the braze material applied thereto. A method according to any one of Claims 1 to 6, characterised in that the diametrically opposed slots (20,22) are formed to be slightly wider than the thickness of the first and second flexural members (16,18) for accommodating the increased thickness of said flexural members due to the application of the braze material. A method according to any one of Claims 1 to 7, characterised in that exposing the pivot assembly to a thermal environment for brazing the flexural assembly in the diametrically opposed slots includes: fixturing the pivot assembly; and oven brazing the fixtured pivot assembly. A method according to Claim 6, characterised in that the oven brazing duration and temperature range are selected for heat treating the pivot assembly. A method according to any one of Claims 1 to 6, characterised by: filling the flexural pivot with a suitable material to prevent flexing; and performing finishing operations on the filled flexural pivot to insure specified net geometry.

Inventors: BACKUS ROBERT O, SALERNO DANIEL J, BACKUS, ROBERT O., SALERNO, DANIEL J.
Applicants: LUCAS WESTERN INC, LUCAS WESTERN, INC.
Application year: 1990
Main classification: F16C11
IPC codes: F16D3, B23K1