Flexible coupling

Details Flexible coupling Flexible coupling

1999-04-22

2001-03-20

Browne, Lynne H. (Department: 3629)

Rotary shafts, gudgeons, housings, and flexible couplings for ro

Torque transmitted via flexible element

Element is tube with slot through wall to provide flexibility

C403S220000

Reexamination Certificate

active

06203437

ABSTRACT:

The present invention relates to a flexible coupling adapted to provide a connection between two shafts, each of the shafts being capable of rotational movement or at least limited rotational movement and the arrangement being such that the rotational axis of one shaft may at some time be out of alignment with the rotational axis of the other.
It may be important, particularly with control devices that the position of one shaft is accurately transmitted to another shaft and, when as aforementioned, the rotational axes of the shafts are out of alignment with each other. A flexible coupling between the two shafts that enables the angular position of one shaft to be accurately transmitted to the other, is of great importance.
Flexible couplings are known and may comprise a cylindrical piece of material, each end of the cylinder having connection means to enable a shaft to be connected thereto and an intermediate part of the cylinder being provided with a plurality of radial slits spaced longitudinally from each other, to enable some flexibility in the cylinder, i.e., bending about its longitudinal axis.
It is an object of the present invention to provide a new or improved flexible coupling.
According to one aspect of the present invention, we provide a flexible coupling for connecting a pair of elements capable of at least limited rotational movement, the flexible coupling comprising a body part having two ends, each end being connectable to a respective one of said pair of elements, said body part having at least four slits, each slit extending through the body in a radial direction to a depth beyond the centre-line of the body and each slit being spaced from the others, in a direction between the ends of the body and being angularly spaced around the circumference of the body, each slit terminating in a concave face.
Preferably, the four slits comprise a first slit, a second slit adjacent thereto, angularly spaced around the circumference by approximately 180°, a third slit adjacent to said second slit and angularly spaced around the circumference by 90° to the first and second slits, and a fourth slit adjacent said third slit, angularly spaced at 180° to said third slit.
Preferably, said flexible coupling comprises two sets of four slits and conveniently, each set of four slits is as above described.
A coupling having only one set of four slits is able to accommodate the situation wherein the rotational axes of the elements it connects intersect but are inclined to one another whilst a coupling having two sets of four slits is able additionally to accommodate the situation wherein the axes of the elements it connects do not intersect. In the latter case the coupling can be considered as analogous in its behaviour in some respects to a drive shaft assembly comprising two Hookes universal joints connected by an intermediate shaft element. Thus the two sets of slits may be separated by a length of the body part which is relatively greater than the length of the body part occupied by a single slit—the length of the separating body part approximating to the length of the intermediate shaft element in the analogy referred to, and a greater such length allowing a greater offset between the axes.
Preferably the arrangement of the slits in one set is the same as that in th set, considered in one direction lengthwise of the coupling (as distinct from the sets being mirror images of one another).
Preferably, each of said slits extends into the body by the same depth as the other slits.
By way of example, each slit may extend into the body to a maximum depth of between ⅝ to ⅞ the dimension of the body in a radial direction. Conveniently, the maximum depth of each slit is approximately ¾ of the dimension of the body in a radial direction.
Conveniently, the radius of the concave surface at which each slit terminates may be between 1.2 and 2 times the dimension of the body in a radial direction. Conveniently, the radius of the concave surface at which each slit terminates is approximately 1.5 times the dimension of the body in the radial direction. As described hereafter, such an arrangement of slits produces the effect that as a set of slits is viewed axially of the coupling, the areas of material remaining at the slits overlap one another. There would be four such overlap areas in a set of four slits, in a “square” array.
Preferably, the body is cylindrical, the ends of the cylinder comprising the two ends of the body.
Preferably, said connection means comprises a bore at each end of the body, into which said pair of elements may respectively be inserted. Securing means may be provided to secure the ends of said elements in the ends of the body.
A flexible coupling according to the present invention has been found to provide a coupling of high torsional stiffness, hence minimising any wind-up in the coupling that may be caused by resistance in the driven side of the coupling caused by friction and/or inertia that may otherwise happen during acceleration of the driving side of the coupling.
The coupling has a low radial rigidity, i.e. is sufficiently flexible to minimise the loads induced on bearings of both the driving and driven elements when there is mis-alignment between the respective rotational axes. Also this results in a long service life for the coupling.
The form of the coupling, in conjunction with the combination of the torsional stiffness and low radial rigidity, ensures that accurate transmission of velocity and hence an accurate reproduction of the position of the driven member to the driving member is provided.
The slits may be provided in the body by cutting with a rotating cutting tool and preferably, the radius of the rotating cutting tool is the same as the radius of the arcuate shape required at the base of each slit.
A cutting tool rotating about an axis parallel to the axis of the body part of the coupling may be moved radially of the body part to form each slit, and then withdrawn in the opposite direction. When the coupling comprises two sets of four slits which are in the same arrangement as each other, a spindle carrying two cutters may be used to form the corresponding slits of each set simultaneously.
However, it will be appreciate that other methods could be utilised to form the slits in the coupling.
The body part of the coupling may be of metal, e.g. an aluminium alloy, a stainless steel, or any other material suitable for the use to which the coupling is to be put. For example, the coupling could be of a plastics material. It may be possible for the coupling to be made by a casting or moulding process, with the slits being provided in the course of such process rather than as a subsequently performed cutting operation.


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