Joints and connections – Articulated members – Pivoted
Reexamination Certificate
1997-10-14
2001-09-04
Browne, Lynne H. (Department: 3629)
Joints and connections
Articulated members
Pivoted
C403S220000, C439S067000, C439S492000
Reexamination Certificate
active
06283666
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a unitary module for a planar flexible pivot as well as to a planar flexible pivot formed by a stack of unitary modules. It relates especially to a method for the manufacture of said unitary module and to assemblies and applications of said planar flexible pivots.
The invention can be applied to special advantage in the field of elastic joints, especially cross-band pivots.
2. Description of the Prior Art
The technology of elastic joints conventionally teaches that, for systems of guidance with low amplitude of displacement, it is advantageous to use a thin and elongated spring band (hereinafter called a band) that is embedded at one end and subjected to forces at the other end, with the property of easily lending itself to a flexing motion in the direction perpendicular to the band while at the same time remaining rigid in the parallel directions.
When the strains are calculated so that they remain well within the elastic limits and the buckling loads, a perfectly precise and reproducible device is obtained, free from play, friction or wear and tear, and with no phenomena of jamming. The reproducibility is limited only by the residual hysteresis applied to the non-compensated effects due to the variation of the loads and the finite rigidity of the bands. It must also be added that no lubrication is necessary.
Within the limits of static deflection mentioned, elastic joints thus have major advantages over conventional kinematic joints such as blocks, slides, bearings, etc. The permitted load limits are all the higher as the deflection required is low and as the thickness of the elastic joints may be great.
The principle of a one-band flexible pivot is shown in
FIG. 1
which gives a side view of a flexible band
10
with a length L, one end
10
a
of which is embedded. When a torque T is applied to the free end
10
b
of the band
10
, this band gets curved and said free end
10
b
shifts in pivoting roughly about the axis passing through the center
11
of the band
10
at rest, thus defining a flexible-band pivot.
However, a one-band pivot is not stable under the action of a load perpendicular to the plane of the band. To overcome with this drawback, the cross-band pivot has been designed. An example of such a pivot is shown in the view in perspective of FIG.
2
. In this example, the two bands
10
,
20
are crossed at right angles, their ends being fixed by screws to supports
1
,
2
.
In order to make the flexible cross-band pivot less sensitive to the effect of off-plane loads, it is possible to use two pairs of crossed bands located symmetrically at a certain axial distance from each other. Thus, a great traversal rigidity and high resistance to unwanted action is obtained. Furthermore, the instantaneous center of rotation is practically fixed up to pivoting angles of 10°.
It has also been sought to compensate for the elastic reaction of rotation of the flexible-band pivots-by subjecting the bands to a traction force, the elastic energy being exchanged between the bands and draw springs. Among the pivots of this type, there is a known device with three bands positioned at 120° which furthermore has the advantage of enabling, in principle, a rotation about an invariable axis as a function of the pivoting deflection.
However, the known cross-band flexible pivots have a certain number of drawbacks.
Indeed, all the pivots mentioned here above are based on the concept of distinct separate bands that have to be screwed in, bonded or soldered to supports. In every case, the band/support joining area is subjected to a set of stresses due to the combined effects of the rotational deflection of the bands, the external load, especially the axial load, and internal hyperstatic stresses (membrane effects) acting on the pivot. This state of mechanical stress is a major factor in the loosening or disconnecting of assemblies and may lead to the breakage of the soldered parts through cyclical fatigue.
Furthermore, the position of the pivoting axis varies with the rotation, which corresponds to the lack of balance of the pivot. In addition to the systematic variation provided for by theory, it is also possible to observe variations that are reversible in varying degrees and random due to the effects of membrane hyperstaticity. This last-mentioned form of behaviour also depends on clamping strains when the pivot-fastening supports are cylindrical.
Finally, it is difficult to achieve the automation of the assembly process as also the miniaturization of the separate-band pivots. This makes the cost of the small-sized pivots comparatively high.
SUMMARY OF THE INVENTION
Thus, an aim of the present invention is to propose a flexible-band pivot that would make it possible to simplify and automate the assembling operations, attenuate the effects of stresses in the supports and enable the miniaturization of the parts.
To this end, the invention provides for the making of a planar type band pivot out of unitary modules that can be stacked. This is why the present invention proposes a unitary module for a planar flexible pivot wherein said module forms a monolithic unit comprising two coplanar rigid linking elements positioned substantially so as to be facing each other and connected diagonally by an essentially rectilinear flexible band.
According to the invention, there is provided a planar flexible pivot consisting of an axial stack of unitary modules wherein said unitary modules are assembled by their respective linking elements. Each assembly of linking elements forms an interfacing of the pivot with an external component. Preferably, the assembly of linking elements is further stacked on a planar area of the external element.
According to an embodiment of the planar flexible pivot of the invention, the unitary modules are assembled so that the flexible band of a unitary module is crossed with the flexible band of a neighboring unitary module. In particular, said flexible bands are crossed at right angles.
In order to prevent the concentration of high stresses and their transmission to the linking elements, it is planned according to the invention that, for each module, said flexible band will have at each end a transition area with a gradually variable section forming a junction between the band and each linking element.
For the efficient functioning of the planar flexible pivot that is the object of the invention, the cross bands of two neighboring modules will preferably not touch each other after stacking. To this end, it is provided in the invention that said flexible band will have a thickness-reducing area between the two linking elements. An alternative approach would use thickness shims.
As already mentioned here above, the pivoting axis of the structures that are hinged on cross bands shifts during rotation. This leads to effects of unbalance. The planar flexible pivots according to the invention provide possibilities of making assemblies with means of compensating for the effects of unbalance.
Two different assemblies which shall be described in detail further below are proposed by the invention e to obtain this effect of compensation.
According to the invention, a first assembly, known as a series compensation assembly, has an internal interface connected at each end to an external interface by means of a set of planar flexible pivots with two cross-band unitary modules arranged in series.
A second assembly, known as a parallel compensation assembly, comprises, on the one hand, a first planar structure of at least one planar flexible pivot with two cross-band unitary modules, of which first linking elements form a first rigid interface and of which second linking elements form an intermediate recoil interface that is connected to a second rigid interface by an elastic parallelogram orthogonal to the pivot and, on the other hand, a second planar structure, identical to the first planar structure, said first and second planar structures being superimposed in parallel in a back-to-front position an
Browne Lynne H.
Connolly Bove & Lodge & Hutz LLP
Cottingham John R.
Csem Centre Suissee d'Electronique et de Microtechnique SA
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