GB2255811A - Bendable strut - Google Patents

Abstract

A hinge joint is capable of bending along its length about a series of points lying within the member so as to give a curve or approximate curve equivalent to a bend about a centre of curvature lying outside the member. A typical joint is showing a series of four vertebrae threaded by a common spine member (16) made of a resilient deformable material. The spine is also threaded by a pair of parallel leaf springs (40, 42) which are gripped in end fittings (50, 80). When the joint is curved, the vertebrae pivot on one another via the portions (24) and the flexing of the leaf springs causes them to rub frictionally on the radially outer faces of the slots in the vertebrae through which the springs extend, and this friction maintains the joint in a curved position but allows it to be reset as required. An elongated slot (70) in one or both ends of each spring at its anchorage point in the end fittings allows for the curvature but limits the extent possible.

Description

HIf!G J~IfT The invention relates to a structural member which is capable of bending along its length about a series of points lying within the ember, so es to give a curve, or approximate curve, equivalent to a bend about a centre of curvature lying outside the member. ror convenience the term hinge joint! will be used for this special meaning in this specification. The object is to provide improvements most particularly in two areas, namely in providing a joint which may be moved to a desired curve and stay there until resets and possibly one which is capable of adjustment to have such capability with varying loads, and in enabling manufacture at economically viable cost.

;according to the in'jettion a hinge joint comprises plurality of separate substantially identical components or vertebrae, threaded by a flexible spine which engages end Ll,- the assembled vertebrae and which holds the assembly together whilst allowing flexing.

The spine may be located between a pair of spaced parallel flexible leaf springs each of which also threads the vertebrae: the latter then require three spaces apertures, two for the springs and one for the spine, but the apertures could be different portions of a single common aperture. Further apertures or portions may be provided to accommodate for example conductors: preferably the spinal aperture is enlarged, for example is of cruciform shape in each vertebrae with limbs of the aperture for conductors and others for the spine.

Preferably a pair of vertebrae-like components are used, one at each end of the assembled vertebrae, and also held in assembled condition by the spine, and these vertebraewlike members may have integral connection or coupling means, brackets or the like extending in opposite directions away from the vertebrae for use in holding the joint to adjacent components in a structure.

The blade springs could be a frictional fit in the vertebrae but it is preferred to make them an easy sliding fit therein and provide means for anchoring ends of the springs relative to end ones of the vertebrae (or the vertebrae-like parts) or to end fittings for the complete joint. The anchoring may permit limited sliding movement of the springs and this places limits on the total angle of the hinge effect.

In the accompanying drawings Figure 1 is a plan view of a vertebra rigure 2 is an elevation rigure 3 a plan and Figure 4 a section on the line A-A of Figure , all relating to a first embodiment of the invention rigure 5 is a plan and Figure flj an elevation of th second embodiment.

Turning first to Figure 1 5 the vertebra is conveniently a plastics moulding 1). The central slot has two end portions 12 of a width U and total length Li corresponding to the spine 1 described below and a pair of symmet,ically located slots 14 each having narrow end portions 18 of a width W2 and a length L2. Slots 14 have wider portions between the narrow ends 18 for convenience in manufacture3 whereas the central slot is of cruciform shape with two limbs 20 forming substantial cavities for conductors or the like as later mentioned.

The peripheral shape of the vertebra is free for the designer and in this case is hexagonal.

A thickened portion 24 is provided on each face of the vertebra which substantially surrounds the narrower portions 12 of the spinal slot and these thickened portions are convex in a direction transverse to the slot lengthS or of a shallow inverted V-shape as best seen in Figure 2 so as to provide a contact line in the plane medium to the thickness of the spine in the assembled condition.

Turning now to Figure 2, the joint comprises an assembly of in this case four vertebrae located on a spine 16. The latter is of generally rectangular cross section to fill the spinal slots 12, 12 but not the cavity limbs 20. As best seen in Figure 3 the spine is not a simple rectangle at its end portions, end has a wider portion or head 30 at one end to form an end abutment for the vertebrae and at the other end 32 the tail of the spine has laterally projecting lugs 34 adjacent the slots 36. The spine is made of a resilient deformable material for example a suitable synthetic resin.The slots permit the lateral edges of the spine to be squeezed together to allow the lugs to pass through the slots 12 with subsequent resilient recovery so that the lugs hold the vertebrae assembled in face to face contact including the vertebra-like members if included.

Linen the joint comes into use, flexing is possible about a series of points or lines where the individual vertebrae contact one another, giving the same effect as bending about a point or points on one or other or both sides o, the length as seen in Figure 2.

it will be appreciated that the length of the spine is related to the thickness of the desired number of vertebrae plus the two end components, that is, is tailor-made for the design. However the spine is essentially a simple component which could possibly be forrou from a length of strip-like material having its ends deformed to provide the head and tail formations, without requiring elaborate tools which are different for one length of spine from another. However, individual spines can be moulded if desired.The vertebrae are much more complex mouldings and hence need more expensive tools, but because the design is standardized one and the same tool can be used however many vertebrae are needed in a design, and moreover the skilled plastics moulding tool designer will recognize the possibility of using a die-pair for the complete vertebra, and using one of the pair with a different die-half for making the vertebraelike part for the end formations.

The two sets of slots 14 are threaded by leaf springs 40, 42 which may be easy sliding fits in the narrow slot parts 18. However, because flexing involves curvature, the leaf springs will tend to thrust against the radially outer faces of the slots when bent, and b in contact because of the springiness.

The springs have anchored or sliding end portions and the choice controls the ability of the complete joint to bend, the direction of bending, and the limits of the same.

In the Figure 2 construction an end fitting 50 is used at one end of the spine and comprises a first vertebra-like portion 52 integral with a bracket 54 in a boss So. Bracket 54 anchors the adjacent ends of the two springs by means of screws 58. The word anchor is used herein to mean fixing in a manner which prevents relative movement in the vicinity of the anchor. The bracket and boss are received in a tube 60 of complementary section shaped t the periphery of the vertebrae, for styling reasons, ends boss 56 is to ix the two together by screws 62. Any other mounting or connection could be used.

At the other end of the spine both blade springs are provided with the elongated slots 70 so as to provide a sliding connection. Each spring is frictionally clamped between a pair of parts. Spring 4G lies between a part Sd forme with a vertebrd-litce part 82 and a central member 84. The latter has a boss 86 to locate the member 84 in the bracket 80. Spring 42 is clamped between inner and outer components 88s 90 which also have complementary formations 92 to locate them relative to one another. A compression spring 94 urges part 88 away from part 84 and a grub screw 100 is for fixing the axial separation.

oth parts 80 and 90 have external aligned bosses 104 for engagement in diametrically aligned holes in mountings 216. The assembled joint is connected to that tube by squeezing parts 80, 90 together, pushing them into the tube until aligned, when the spring forces the bosses into the holes. Tightening the screw increases the frictional loading on the springs and additionally prevents disconnection.

Any other end fitting can be used.

The joint illustrated in Figures 2 and 3 may be capajl of flexing approxiately 5G deres in either direction from the shown position. In such flexing the blade springs move relative to the end parts 80-104, and one spring moves in one direction and the other sprint in the opposite direction. The resistance to movement is due to the stiffness of the springs 4GS 42 a and to the frictional effect. The frictional effect is desirably sufficient to retain the spine in the curvature selected and adjusted, against whatever load is applied. within limits this can be varied by the use of the screw, and to different limits by selection of values of the spring C.

e.g. in certain cases the screw may be unnecessary. Ine surface finish of the spring, the nature of the plastics material and the clearances employer will all be relevant to the frictional effect.

In some applications it is possible that freedom to return will be advantageous e.g. if used as a Joint For a mechanism which is power-driven to and fro, and is not intended to be adjusted to a semi-permanent position.

Spring 94 may be minimal or alternative mounting means used to enable it to be eliminated, and in this eventuality ample clearances may be provided for the blade spring in the vertebrae, with a hign quality surface finish to minimize friction.

The enlargements 20 may carry electrical conductors, fibre optic conductors, ducts for fluid, or other alternative elongated articles inside the totality of the joint for connection at opposite ends thereof and the various end fittings desirably allow space for such to extend therethrough.

Turning now to Figures 5 and 6 the joint shown therein is generally similar to that in Figures 2 to 4 and uses the same vertebras in Figure 1. The essential differences include the use of more vertebrae, in this illustrative example to allow flexing of the order of 130 degrees, and the use of similar end fittings at both ends: these end fittings are similar to that shown at the right hand end of Figures 3 and 4 and allow movement of blade springs at each end fitting. The purpose herein is to distribute the required movement of the blade spring so as to avoid the use of a single particularly long slot in the blade springs. However, in this case and again for illustrative purposes only, flexing is to be in a single direction so that springs 40 42 are slotted but effectively in opposite directions. Thus, slot portions 120, 122, in the ends of spring 42 allow that spring to be on the inside of the curve represented by the spine 16 and slot portions 124, 126 in spring 40 allow that spring to be on the outside of that curve, but not (in either case) vice versa.

Figures 5 and 6 otherwise use like reference numbers to those used in Figures 3 and 4 for like parts.

Claims (10)

1. A hinge joint comprising a plurality of separate substantially identical components or vertebrae, threaded by a flexible spine which engages ends of the assembled vertebrae and which holds the assembly together whilst allowing flexing.

2. A joint as claimed in Claim 1 wherein the spine is located between a pair of spaced parallel flexible leaf springs, each of which also threads the vertebrae.

3. A joint as claimed in Claim 2 wherein each vertebrae has three spaced apertures, two for the springs and one for the spine.

4. A hinge joint as claimed in Claim 1 or Claim 2 wherein each vertebrae has a single aperture with lateral extensions for the spine or/and springs.

5. A joint as claimed in any of Claims 1 to 4 provided with a pair of vertebrae-like components, one at each end of the assembled vertebrae, and held in assembled condition by the spine.

6. A hinge joint as claimed in Claims 3 - 5 wherein the blade springs are a frictional fit in the vertebrae.

7. A hinge joint as claimed in Claims 3 - 5 wherein the blade springs are an easy sliding fit in the vertebrae and means are provided for anchoring ends of the springs relative to end ones of the vertebrae or the vertebraelike parts or to end fittings for the complete joint.

8. A hinge joint as claimed in any preceding claim herein each vertebra is a plastics moulding of platelike form having a thickened portion on each face and substantially surrounding parts of a slot through the vertebra.

9. A hinge joint as claimed in Claim 8 wherein the thickened portions are convex or are of shallow inverted Vee shape so as to provide a contact line with an adjacent vertebra in a plane median to the thickness of the spine in the assembled condition.

10. A hinge joint as claimed in Claim 7 wherein the anchoring means includes a slot in at least one end of at least one blade spring, to limit flexure of the joint.