GB2076502A

GB2076502A - A Load Supporting Spring System

Info

Publication number: GB2076502A
Application number: GB8112148A
Authority: GB
Original assignee: Popper Engineering Ltd
Current assignee: Popper Engineering Ltd
Priority date: 1980-04-18
Filing date: 1981-04-16
Publication date: 1981-12-02
Also published as: AU6964681A; DE3115564A1; ZA812325B; IL59861A0; FR2480884A1; JPS56164243A

Abstract

A load supporting spring system comprising a base (10), one or more buckling spring members (14) defining a buckling axis and having first and second ends (16 and 18) and being supported (20) at a first end thereof on the base, a load support (28) associated with the second end of the one or more spring members, and apparatus (22, 24, 26) for guiding the motion of the load support generally along a pathway (P) which is angled with respect to the buckling axis. <IMAGE>

Description

SPECIFICATION A Load Supporting Spring System The present invention relates to springs and spring systems generally and more particularly to spring systems employing a bendable leaf element.

A great variety of springs and spring systems are presently known for a variety of applications.

In many applications it is necessary to have particular force characteristics as a function of displacement. It is also desirable in many applications to reduce the lateral load displacement and to reduce insofar as possible the weight and thus the cost of the springs employed.

It is appreciated that a buckling spring provides desirable spring characteristics, i.e. a small force increase with displacement, while being of relatively light weight and cost. The buckling spring suffers from the disadvantage that the permissible displacement range is relatively small and that the buckling force is relatively high.

In order to overcome these difficulties, the applicant has developed a spring system in which a load is coupled to a buckling leaf element via a lever, which system is disclosed in Israel Patent Applications 54767 and 56372. In this system, the lever, which is pivotably mounted, reduces the buckling force while increasing the effective displacement range. Although this system is emminently suitable for a large number of applications, its applications are limited by its relatively large bulk, the inability of the lever pivots to bear heavy loads and the lateral motion of the load.

The present invention seeks to provide a new class of spring systems employing bendable elements wherein a mechanical advantage and thus selectable spring force characteristics of a large displacement range producing relatively little buckling at relatively low forces are realized but without the use of a levered construction as described in the aforesaid Israel Patent Applications.

There is thus provided in accordance with an embodiment of the present invention a load supporting spring system comprising a base, at least one buckling spring member defining a buckling axis and having first and second ends and being supported at a first end thereof on the base, a load support associated with the second end of the at least one spring member, and apparatus for guiding the motion of the load support generally along a pathway which is angled with respect to the buckling axis.

The guiding apparatus may comprise an arm which may be rigid or buckling or alternatively a fixed supporting surface against which the load support travels along a pathway parallel thereto.

Linear spring apparatus may be associated with the load support for prestressing thereof and to provide a selectable spring rate.

Selectable prestressing apparatus may be provided for enabling selection of the spring supporting force of the system.

The invention will be more fully understood and appreciated from the following detailed description taken in conjunction with the drawings in which: Figs.1,2,3 and 4 illustrate spring systems and operative in accordance with an embodiment of the present invention; Fig. 5 illustrates a spring system constructed and operative in accordance with an embodiment of the present invention and providing zero lateral movement of the load under displacement; Figs. 6 and 7 show spring systems of the type illustrated in Figs. 1-5 and also comprising a linear spring; Figs. 8, 9 and 10 each illustrate a spring system constructed and operative in accordance with an embodiment of the present invention and including a selectable prestressing feature;; Fig. 11 illustrates a spring system similar to that shown in Fig. 8; Fig. 12 illustrates an alternative embodiment of spring system; and Fig.13 illustrates a preferred embodiment of spring system.

Referring now to Figs. 1-4 and in particular to Fig.1, there is seen a spring system comprising a base 10, which may be supported from above as by a cable or threaded bar. A conventional buckling spring 14, and having first and second ends 16 and 18 is supported as its first end 16 onto the base 10 by means of a cup-type seat 20 which is formed with the base. Seat 20 is designed to support the leaf spring while permitting relatively low friction pivotal displacement thereof relative to the base.

A rod 22 having first and second ends 24 and 26 is pivotably mounted at its first end, as by a ring and pin or bearing arrangement onto base 10. The respective second ends of the leaf spring 14 and the rod 22 are coupled to a load support 28 which typically comprises a hook 30 for supporting a hanging load.

The coupling between the second ends of the spring 14 and the rod 22 and the load support 28 may be any suitable type of coupling which preferably allows relative pivotal movement of the elements with limited friction and hysteresis. The spring 14, rod 22 and load support 28 need not necessarily be attached together, but may instead be seated in a coupled arrangement.

In the embodiment of Fig. 1, spring 14 is bowed downwardly. Fig. 2 illustrates a spring system substantially similar to that of Fig. 1 except for the following differences: Whereas in Fig. 1, the spring 14 is bowed downwardly, in the embodiment of Fig. 2 the corresponding spring 34 is bowed upwardly. Secondly, the ratio between the lengths of the rod 22 and the spring 14 is greater than the corresponding ratio of the rod 36 and spring 34 in the embodiment of Fig. 2.

Both the embodiments of Fig. 1 and Fig. 2 define negative rate spring systems.

Referring now to Fig. 3 there is seen an alternative embodiment of spring system in which there is provided a base 40, a leaf spring 42 having first and second ends 44 and 46 respectively, and a rod 48 having first and second ends 50 and 52 respectively. The first end of spring 42 is seated in a seat 54, similar to seat 20 (Fig. 1) and the first end of rod 48 is pivotably mounted onto the base at a location above and to the side of seat 54.

The second end of rod 48 is formed with a second spring seat 56 which supports the second end of spring 42. A load support 58 is also pivotably joined to the second end of rod 48. This embodiment has a positive rate due to its geometry, wherein an increase in the load and a downward displacement of the load support 58 causes increased buckling of the leaf spring, which has a positive rate.

Referring now to Fig. 4 there is seen a spring system which is generally similar to that illustrated in Fig. 3. A leaf spring 60 having first and second ends 62 and 64 is seated at its first end 62 in a seat 66 formed on a base 68. A rod 70 having first and second ends 72 and 74 is pivotably mounted at its first end at a location slightly above and to the side of seat 66 in the direction of a load support 76 which is pivotably mounted onto the second end 74 of the rod. A second seat 78 is formed on the second rod adjacent the second end for receiving the second end of spring 60 which is bowed downwardly.

It is appreciated that by suitable selection of the dimensions, characteristics and mounting locations of the elements of the spring system, a system having a selected positive, negative or zero rate can be realized for small displacements.

It is noted that all of the devices described hereinabove have a force/displacement function given as follows: P=P0(1-qx) (1) where P is the force under displacement PO is the force under no load conditions x is the displacement q is a function of x In practice, for small displacements, q can be considered to be constant. In the embodiment of Fig. 4, q is approximately zero.

Reference is now made to Fig. 5 which illustrates an embodiment of the invention in which the lateral motion of the load is substantially zero under deflection. The embodiment of Fig. 5 comprises a generally symmetrical construction of a pair of leaf springs 80 and 82 having their respective first ends 84 and 86 supported in respective seats 88 and 90 formed on a base 92. The respective second ends 94 and 96 of the leaf springs support a load support 98 which is formed with a hook 100. Due to the symmetry of the construction and disposition of the leaf springs 80 and 82 and their identical length and characteristics, the load support undergoes only substantially vertical motion in response to the application of a vertical force.

It is appreciated that the various embodiments illustrated in Figs. 1-5 and described hereinabove may also be useful for receiving compressive forces. For example load support 98 of Fig. 5 may be provided with a vertical extension 99 extending through the top of base 92 for receiving a compressive force. Similar extensions may be provided in the embodiments of Figs. 1- 4.

The spring constructions described hereinabove with reference to Figs. 1-5 may be characterized in that the applied load is provided along an axis which is oriented at a selected angle with respect to the normal to the buckling element. As that angle decreases, the load component becomes reduced relative to the buckling force of the buckling element. Thus by judicious choice of the angle at rest, the changes in the angle under displacement compensate for the positive rate of the buckling element in a desired way to provide as desired, a constant force spring or alternatively a spring with a desired positive or negative rate.

Reference is now made to Fig. 6 which illustrates a symmetric spring system of the type illustrated in Fig. 5 with the addition of a coil spring 102 disposed between the load support 98 and a spring seat 104 mounted on base 92. Coil spring 102 is a linear spring of constant k and enables ready selection of the spring rate of the system to be realized, whether positive, negative or zero. The spring system of Fig. 6 may also be configured for receiving a compressive force in a manner similar to that shown in Fig. 5.

The force/displacement function for the embodiment of Fig. 6 is given by the following expression: P=P0(1-qx)+kx (2) A zero spring rate is realized when POq=k (3) It is appreciated that in the embodiment of Fig.

6 when no pretension is applied to the system, the entire energy stored in the spring is employed in carrying the load.

Reference is now made to Fig. 7 which illustrates another version of the linear springbendable element combination of Fig. 6. Here instead of a coil spring as in the embodiment of Fig. 6 there is provided a leaf spring 110 which is firmly mounted at its first end 112 onto a base 114 and also serves as the analog of the rod 22 in the embodiment of Fig. 1. A load support 11 6 is pivotably mounted onto the second end 113 of spring 110 which also defines a seat 11 8 for the second end 120 of a leaf spring 122 which is analogous to leaf spring 14 of the embodiment of Fig. 1. It may be appreciated that the embodiment of Fig. 7 is similar to that of Fig. 1 with the addition of a linear spring, thus enabling selection of the spring rate by means of selection of the rate of the spring 122.

Reference is now made to Fig. 8 which is analogous to Fig. 6 with the addition of means for prestressing of the linear spring. In such a case the force/dispiacement expression of equations (1) and (2) becomes P=P0(1 -qx)+kx+f (4) where F is the prestressing force By transposing equation (3) into equation (4), one obtains the expression: P=Po+F (5) which indicates that a constant force system is realized with the possibility of varying the force capacity of the system by varying the pretension F of the linear spring but without changing the spring rate.

In the embodiment of Fig. 8 there is provided a base 130 and a load supporting member 132 supported thereon by means of a pair of linear leaf springs 134 and 136 spaced from each other. A non-linear leaf spring 138, analogous to leaf spring 14 of the embodiment of Fig. 1 is disposed therebetween, interconnecting the load supporting member 132 and the base 130. A linear coil spring 140 is seated in a recess 142 in the base of the load supporting member 132 and is selectably prestressed by means of a threaded bolt 144 which engages a threaded socket disposed in base 130 facing the load supporting member 132.

In accordance with a preferred embodiment of the invention, the system of Fig. 8 is constructed such that q=ka+kc (6) where ka is the spring rate of the linear leaf springs 134, 136 and ke is the spring rate of the coil spring.

If the coil spring 140 is prestressed by a displacement z, the displacement is given by F=kez (7) Reference is now made to Fig. 9 which illustrates an alternative embodiment of a spring system having selectable pretension. Here there is defined a supporting surface 150 which defines the travel path of a load support 152, which moves slidably parallel thereto supported on a plurality of rollers 154, which permit relatively low friction motion thereagainst. A buckling member 156 has one end supported on a base 158, which in the illustrated example also defines the supporting surface, and a second end engaging and supporting the load support 152 against surface 150.

The load support 152 is also supported by a linear helical spring 160 which is in turn mounted on a threaded support 162 which is selectably displaceable in a threaded socket in base 158 for providing a selectable pretensioning feature as described hereinabove, with the attendant desired selectability of the force capacity of the system without requiring a change in the spring rate thereof.

Another embodiment of spring system similar to that shown in Fig. 9 is illustrated in Fig. 10. The system is substantially identical to that shown in Fig. 9 except that wheels 164 replace rollers 154.

Also in the illustrated embodiment a pair of upward bowing leaf springs 166 replace the single downward bowing leaf spring 156 of Fig. 9.

It is appreciated that in all of the illustrated embodiments, any suitable combination of one or more leaf springs or other suitable buckling elements may be employed and may be arranged to bow in any desired direction.

According to a further alternative embodiment of the present invention the embodiments illustrated in Figs. 9 and 10 may be constructed without the linear springs shown.

Reference is now made to Fig. 11 which shows a system similar in construction to that illustrated in Fig. 8 hereinabove but which instead of linear leaf springs 134 and 136 employs a pair of rigid arms 170. A linear spring and selectable pretensioning means are not illustrated but may be provided.

Referring now to Fig. 12 there is seen a system having the advantage of relatively small width as compared with other embodiments described hereinabove. In this embodiment, the load may be applied to an upper member 180 as a tensile load by means of a hook 182 or to the upper member 180 as a compressive load. The upper and lower members are interconnected by crossed buckling elements 186. Any suitable combination of buckling elements 186 may be employed provided that the sum of buckling elements arranged along each direction is equal and symmetrically arranged with respect to the horizontal force component. A linear spring 188 interconnects the upper member 180 and the lower member 184 to provide a selected amount of prestressing.

In accordance with an embodiment of the invention, linear spring 188 may be mounted on a selectably positionable base in order to provide selectable prestressing of the spring.

Reference is now made to Fig.13 which illustrates a preferred embodiment of spring system constructed and operative in accordance with the present invention, in accordance with a precise example. Here the system is required to support a force of 500 Kg. over a displacement of up to 80 mm.

Using computer techniques of a conventional nature, the following requirements and characteristics are set forth: Length of buckling leaves: 721 mm Width of buckling leaves: 100 mm Thickness of each buckling leaf: 2.5 mm Number of buckling leaves: 9 each side The buckling leaves are bent at rest and oriented such that each defines a vertical span A of 405 mm and a horizontal span B of 596 mm.

The maximal bending stress in the buckling leaves is 59 kg/mm2 The maximal force of the linear spring 192 for a zero rate device is 20 kg The rate of the linear spring 192 is 25 kgfmm The ratio of the energy stored in the linear spring to the total energy of the system is 2% Maximum theoretical deviation from the constant 500 kg force (with the linear spring incorporated) is 0.8% It is noted that spring systems having the general configurations of the systems illustrated in Figs. 8, 9, 10 and 12 may be constructed also without the addition of the linear springs and will then have the operational characteristics of the springs illustrated in Figs.1~4. It is also noted that the use of rollers and wheels for providing slidable motion of the load supporting members along a plane in Figs. 9 and 10 is equivalent to the use of other mechanisms for achieving the same result such as a roller in addition to a slidable cam and slot combination.

In the embodiments of the invention illustrated so far, the motion of the load receiving member has been constrained to lie along an axis which is generally parallel to the axis of the applied force.

Reference is now made to Figs. 14 and 15 which show spring systems wherein the motion of the load receiving member is constrained to lie along an axis which is angled with respect to the axis of the applied force, such that the load receiving member undergoes a small lateral displacement under deflection. The choice of the angle between the axis of the applied force and the axis of travel of the load receiving member provides another vehicle for determination of the load capacity of the system.

It is appreciated that the load receiving member may be constrained to move along a path that need not necessarily be straight.

Alternatively the path may be constrained to be curved or to have bends or turns or to define a complex shape.

The embodiment of Fig. 14 shows a spring system wherein the travel axis of the load receiving member is inclined towards the axis of the buckling element. The embodiment of Fig. 15 shows a system wherein the travel axis of the load receiving member is inclined away from the axis of the buckling element and may be perpendicular thereto. The embodiment of Fig. 15 also shows the provision of a linear spring 200 in operative association with the load receiving member 202 for providing a constant force spring system or alternatively a spring system with a desired positive or negative rate.

Reference is now made to Fig. 16 which illustrates a spring system similar in construction to that illustrated in Fig. 1 5 but wherein the axis of travel of the load receiving member 204 is selectable. In this case the travel axis is defined by a support member 206 which is pivotably mounted onto a base 208 by means of an adjustable and fixable pivot mounting arrangement which may be entirely conventional.

Reference is now made to Fig. 17 which illustrates a spring system constructed and operative in accordance with a preferred embodiment of the invention and which comprises a base 210 and a load receiving element 212 which is supported on the base by means of one or more linear springs 214 and by a buckling element in the form of one or more leaf springs 216. The load receiving element 212 is constrained to move under deflection along an axis which is selected to be parallel to the axis of force application to the system. It is a particular feature of this embodiment that the end of the leaf spring 21 6 opposite to that seated on the load receiving element is seated on a moveable carriage 218 mounted onto base 210 by a threaded mounting 219 whose position may be changed selectably to vary the load capacity of the spring system in a rather convenient manner.

Carriage 218 may be selectably positioned along an axis 220 which in this case is generally perpendicular to the axis of the buckling element 216 but need not necessarily be so.

According to an alternative embodiment of the embodiment of Fig. 17, carriage 218 may be pivotably mounted onto leaf spring 216. Further in accordance with an embodiment of the invention, carriage 218 may be arranged for selectable positioning along a vertical axis, parallel to the axis of force application to the system.

It is noted that wherever rollers have been shown in the drawings, these may be replaced by balls which travel along suitably formed races.

It will be appreciated by persons skilled in the art that the invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the invention is defined only by the claims which follow:

Claims

1. A load supporting spring system comprising; a base; at least one buckling spring member defining a buckling axis and having first and second ends and being supported at a first end thereof on said base; a load support associated with said second end of said at least one spring member; and means for guiding the motion of said load support generally along a pathway which is angled with respect to said buckling axis.

2. A load supporting spring system according to claim 1 and wherein said pathway defines an angle with respect to said buckling axis which changes during deflection.

3. A load supporting spring system according to either of the preceding claims and wherein said means for guiding comprises at least one arm, having first and second ends and supported at a first end thereof on said base and wherein said load support is joined to said second end of said at least one arm.

4. A load supporting spring system according to claim 3 and wherein said at least one arm comprises a rigid arm which is pivotably mounted onto said base at said first end thereof.

5. A load supporting spring system according to claim 3 and wherein said load support is joined also to said second end of said at least one spring member.

6. A load supporting spring system according to any of claims 3-5 and wherein said at least one arm comprises a buckling spring member.

7. A load supporting spring system according to any of the preceding claims and also comprising linear spring means associated with said load support and said base.

8. A load supporting spring system according to any of the preceding claims and also comprising means for selectably prestressing a linear spring associated with said base and said load support.

9. A load supporting spring system according to claim 8 and wherein said means for selectably prestressing comprises tensioning means.

10. A load supporting spring system according to claim 8 and wherein said means for selectably prestressing comprises compressing means.

11. A load supporting spring system according to any of the preceding claims and wherein said means for guiding comprises a fixed supporting surface and slidable bearing means associated with said load support for permitting motion thereof parallel to said fixed supporting surface.

12. A load supporting spring system according to any of claims 3-6 and wherein said at least one arm comprises a linear leaf spring.

13. A load supporting spring system according to any of the preceding claims and wherein the spring rate thereof is positive.

14. A load supporting spring system according to any of the preceding claims and wherein the spring rate thereof is negative.

15. A load supporting spring system according to any of the preceding claims and wherein the spring rate thereof is zero.

16. A load supporting spring system according to claim 8 and wherein the spring supporting force thereof is selectable in accordance with the amount of prestressing of the linear spring.

17. A load supporting spring system according to claim 1 or claim 7 and wherein said pathway is angled with respect to the angle of application of a load.

18. A load supporting spring system according to any of the preceding claims and wherein the orientation of said pathway is selectably determinable for governing the load capacity of the spring system.

19. A load supporting spring system according to any of the preceding claims and comprising means for selectably determining the position of said second end of said at least one spring member on said base of governing the load capacity of the spring system.

20. A load supporting spring system substantially as described with reference to or as shown by Fig. 1 or Fig. 2 or Fig. 3 or Fig. 4 or Fig.

5 or Fig. 6 or Fig. 7 or Fig. 8 or Fig. 9 or Fig. or Fig. 11 orFig. 12orFig. l3orFig. l4orFig. 15or Fig. 16 or Fig. 17 of the drawings.