Patent Application
20080119294
An Oldham coupling is used for connecting two shafts that are parallel, but may not be in perfect alignment. The Oldham coupling is particularly suited to joining shafts where one is a driving member and the other a driven member.
There are two general types of Oldham couplings, both sharing several basic components. Oldham couplings generally comprise two hubs fitted onto the ends of two shafts and joined together by at least one intermediate member. Each hub typically has a slot or groove.
The first type of Oldham coupling has an intermediate member comprising a floating member shaped as a disk. The disk has a projection or slot on each side, positioned perpendicular to each other. Each hub has a matching slot or projection to the disk. When assembled, two degrees of freedom are allowed, accommodating radial misalignment (where the driving and driven shafts are parallel but displaced with respect to their axial centers). Typically, radial misalignment up to 5% of the shaft diameter can be accommodated. Only one degree of angular misalignment is generally handled (where the axial centers of the driving and driven shafts intersect).
The second type of Oldham coupling has an intermediate member comprising a floating member shaped as a square block. The square block is adapted to fit between matching perpendicular slots of the two hubs, similarly providing two degrees of freedom to accommodate radial misalignment when the hubs and disk are assembled. This type of Oldham coupling typically compensates for radial misalignments as high as 10% of the shaft diameter. Three degrees of angular misalignment are also handled.
A disadvantage of known Oldham coupling designs is that such designs do not accommodate large angular misalignment and can be difficult to install in many cases. There is a need for an improved Oldham coupling which overcomes or substantially reduces the problems of the prior art.
The present invention provides an Oldham coupling assembly for connecting two shafts, where the coupling, as assembled, is one unitary piece. The assembly according to one embodiment includes a first hub having a first projection; a second hub having a second projection; an intermediate disk having a first and second slot, the slots on opposite sides of the disk and perpendicular to each other, the first projection received into the first slot and the second projection received into the second slot; and an elastomeric material formed around the circumference of the disk to retain the assembly together. In another embodiment, the hubs have slots and the disk has projections.
Another aspect is a method for making the assembly, including: joining first and second hubs to opposite sides of an intermediate disk; and forming an elastomeric material around the circumference of the disk to retain the assembly together.
Use of the unitary piece design of the present invention in actuator applications allows a coupling to be mounted without the motor. In addition, dampening aspects of embodiments help to reduce vibration transmission from the motor.
The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention.
In the preferred embodiment, surface 13 of disk 10 is characterized by splines 15. In other embodiments, surface 13 can be smooth, have cavities, or have slots, or disk 10 can have a larger or smaller diameter than hubs 5a and 5b. In yet other embodiments, the hubs 5a, 5b have slots rather than projections, and the disk 10 has projections rather than slots, with the slots and projections engaging in a similar manner as described above.
More specifically, referring to
In the preferred embodiment, splines 15 fully encompass surface 13 of disk 10, splines 15 having an essentially cylindrical shape. The height of the splines 15 may vary and help to guide material flow during injection molding.
Hubs 5a and 5b and disk 10 optionally can be of the same or different material. Examples of possible materials includes: aluminum, aluminum alloy, anodized aluminum, stainless steel, bronze, brass, sintered iron, or plastic. Preferably, hubs 5a and 5b are aluminum or steel and disk 10 is aluminum or thermoplastic.
Referring to
The elastomeric material 17 is formed around coupling 1 preferably by injection molding. Optionally, coupling 1 can be made by compression or transfer molding. When coupling 1 is fully assembled as described in the preferred embodiment, elastomeric material 17 dampens vibrations by placing naturally dampening material at interfaces of the components.
In the preferred embodiment, elastomeric material 17 can compress by about 0.010 inches, accommodating about 10 degrees of angular misalignment with displacement. Elastomeric material 17 can also stretch by 0.030 inches to accommodate 0.075 inches of radial misalignment.
While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.
