Joints and connections – Articulated members – Pivoted
Reexamination Certificate
2000-03-14
2001-11-20
Browne, Lynne H. (Department: 3629)
Joints and connections
Articulated members
Pivoted
C464S051000, C464S078000, C464S086000, C464S097000, C464S112000
Reexamination Certificate
active
06318923
ABSTRACT:
TECHNICAL FIELD
This invention relates to devices for providing low friction, rotational couplings, in particular, a stable bi-axial pivot flexure coupling to provide rotationally compliant ends for kinematic linkages.
BACKGROUND
A simple spherical ball and socket connection provides a coupling that is rotationally compliant and axially stiff . A coupling of this type is used as an end fitting for linkages or rods or struts where axial forces must be rigidly transferred, and rotations are relatively unconstrained. The ball and socket end connection is however characterized by large friction losses, making it undesirable for low power, precision coupling and in particular closed loop feedback controls, which can become unstable when too much stick-slip motion is present. Pivot flexures, like the coupling
4
shown in
FIG. 4
, are generally more useful in those applications. This device operates in a completely linear fashion by means of elastically deflecting flexure blades
4
a
that produce the desired linkage
4
c
end rotation with a fixed end or other linkage
4
d.
Rotational compliance about the two axes orthogonal to the link axis (direction
4
b
in
FIG. 4
) is desired thus the term biaxial is often used to describe these flexures. Some rotational compliance about the link axis is also achieved with this type of flexure although it is not critical in most applications
Even though blade type pivot flexures have been used successfully, they possess certain performance limitations, in particular weak axial load carrying capacities. To achieve low rotational stiffness, the interleaved blades
4
a
must be slender which makes them susceptible to buckling under compressive or axial loads, in the direction
4
b.
To increase their load bearing capacity, the blades
4
a
conceivably can be made thicker, which makes them less flexible and increases rotational stiffness reducing the coupling's effectiveness. The goal is minimal rotational stiffness, which requires the thinnest possible blades but maximum axial strength.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a biaxial rotational coupling with minimal rotational friction and losses of the blade type and also capable of bearing higher axial compressive loads.
According to the present invention, a stable pivot flexure coupling uses thin flexures (blades) to connect the rotating end members and the pivot joint is located near the midpoint of each flexure.
According to the invention, a flexure coupling comprises a first end member normal to a load axis (i.e.,
4
b
in FIG.
4
); a second end member normal to said load axis at a first distance from the second end member; an aperture in said first end member on said axis; an aperture in said second end member on said axis; first and second flexures connecting said end members, said first and second flexures being parallel to said load axis and diametrically opposed; third and fourth flexures connecting said end members, said third and fourth flexures being parallel to said load axis and diametrically opposed; a first cross member normal to said load axis and connected near the midpoints of the first and second flexures; a first rod along said axis and extending through the aperture in said first end member and attached to said first cross member; a second cross member normal to said axis and connected near the midpoints of the third and fourth flexures; a second rod along said axis and extending through the aperture in said second end member and attached to said second cross member, both said first and second rods are used to attach the coupling to a linkage and/or desired fixed mounting point where the device may operate to transfer axial loads rigidly between said hardware while allowing relative unconstrained or compliant rotations.
According to one aspect of the invention four axial connecting rigid spacers, diametrically arranged, secure the first and second end members with the flexures located between the end members and the spacers to form a cage for the flexures.
According to one aspect of the invention, each flexure is formed with base at each end which is secured to the end members with the rigid spacers.
A benefit of the invention is that each blade flexure reacts axial loads in both compression and tension. As a result, flexure failure, i.e., failure of a blade, can only occur when the elastic limit of the flexure material is reached.
With the benefit of the previous discussion of the invention, one of ordinary skill in the art may be able to modify the invention in whole or in part without departing from the true scope and spirit of the invention.
REFERENCES:
patent: 3272492 (1966-09-01), Jones
patent: 3712081 (1973-01-01), Philipp et al.
patent: 4405184 (1983-09-01), Bahiman
patent: 4802784 (1989-02-01), Brooks
Browne Lynne H.
Dunwoody Aaron
Greenstien Robert E.
Honeywell International , Inc.
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