GB2249606A

GB2249606A - Ballscrew assembly

Info

Publication number: GB2249606A
Application number: GB9024109A
Authority: GB
Inventors: Roy Sharpe
Original assignee: IBL
Current assignee: IBL
Priority date: 1990-11-06
Filing date: 1990-11-06
Publication date: 1992-05-13
Also published as: GB9024109D0

Abstract

A ballscrew assembly comprising two ballnuts (12, 14) preloaded together on a screw shaft (10) by a spring (16, 32), wherein the spring (16, 32) is located internally of the ballnuts within a space (18) provided between their two opposing ends. The spring has outturned ends (24, 26) each located in one of a series of blind holes the provision of which allows the amount of preload to be adjusted. The spring may be of coiled form, C-shaped, or be of helical form and extend transversely of the ballnuts (see Fig 4). <IMAGE>

Description

Ballscrew Assembly This invention relates to ballscrew assemblies.

In JP-A-60 22 02 56 and JP-A-62 15 98 52 there are described ballscrew assemblies comprising a screw shaft on which two ballnuts are screwed so as to abut one another.

On the outer end face of one of the ballnuts there is an elastic member which urges that ballnut resiliently towards the other ballnut. In this way any backlash is taken up by the elastic member.

A disadvantage however of these two assemblies is that the elastic member in each case is exposed to the ingress of dirt during use, with the result that the elastic member can become ineffective.

SE-A-86 02 777 describes a somewhat different ballscrew assembly wherein a spring is located circumferentially of one of the ballnuts. This spring is therefore exposed to dirt and possible damage to an even greater extent than the elastic member in the two Japanese publications referred to above.

Finally, FR-B-80 090 (first addition of FR-B-12 44 838) describes a ballscrew assembly in which a spring is located in one of the two ballnuts so as to be substantially tangential thereto. The bore containing the spring is open at both ends, thereby allowing the ingress of dirt into the bore, whereby the spring can become ineffective as in the two Japanese publications.

The aim of the present invention is to provide a ballscrew assembly wherein a spring is located in a more advantageous position so that dirt cannot reach it.

To this end, the invention is directed to a ballscrew assembly comprising two ballnuts preloaded together on a screw shaft by a spring, characterised in that the spring is located internally of the ballnuts within a space provided between their two opposing ends.

Such a construction ensures that the spring is located in a space which is closed to the outside. Dirt cannot therefore reach the spring, nor can it be damaged.

The subsidiary claims indicate further preferred features of the invention.

An example of a ballscrew assembly in accordance with the invention is shown in the accompanying drawing in which: Figure 1 is a part-sectional side view of one form of ballscrew assembly; Figure 2 is a section taken on the line II-II in Figure 1; Figure 3 is a section taken on the line III-III in Figure 1; and Figure 4 is a view similar to Figure 1 of a second form of ball screw assembly.

The ballscrew assembly shown in Figure 1 comprises a screw shaft 10 on which two ballnuts 12 and 14 are preloaded together by a torsion spring 16. This spring is located internally of the ballnuts within a space 18 provided between the two opposing ends of the ballnuts, the space 18 being formed by two matching circular recesses 20, 22 of identical size and shape, one formed in the end of one ballnut and the other formed in the opposing end of the other ballnut. The spring 16 is accordingly completely enclosed so that dirt from the outside cannot reach it. Also, being surrounded by the ballnuts, it cannot be damaged in use.

The spring 16 has out-turned ends 24 and 26 which are located in blind holes formed in the bottom portions of the recesses 20 and 22. In order to permit the amount of preload provided by the spring 16 to be adjusted to a customer's requirement, a series of blind holes for reception of the spring ends 24 and 26 are provided in each ballnut. Thus, the ballnut 12 has four blind holes 28 extending over an arc , while the ballnut 14 has a corresponding series of four holes 30 extending over the same arc. It will be appreciated that, once the preload of the spring has been set by locating its ends 24 and 26 in an appropriate pair of holes 28,30, the preload of the spring will not subsequently be changed for that particular assembly.

It will be understood that a torque can be applied to separate the two ballnuts but that, when this torque is removed, the ballnuts will be rotated back to a predetermined preloaded condition by the torsion spring 16.

The spring 16 can be of coiled form with just one or two complete turns, as shown in Figure 1. It could however have more than two turns, and it could even be a C-shaped spring similar to a circlip. Yet another possibility is for the spring to be of helical form and to extend transversely of the ballnuts as shown in Figure 4 where a helical tension spring 32 has its ends held by pegs or pins 34, 36 located in holes corresponding to the holes 28 and 30 shown in Figures 2 and 3.

The ballscrew assemblies shown in the drawing are compact, will always be backlash-free in an axial direction, will never need to have the preload adjusted once it has been set during the assembly stage, and will permit a screw shaft 10 and/or the ballnuts 12, 14 to be changed without changing the balls or calling for additional machining operations.

Claims

1. A ballscrew assembly comprising two ballnuts (12, 14) preloaded together on a screw shaft (10) by a spring (16, 32), characterised in that the spring (16, 32) is located internally of the ballnuts within a space (18) provided between their two opposing ends.

2. A ballscrew assembly according to claim 1, characterised in that the Space (18) for the spring (16, 32) is formed by two matching recesses (20, 22) of identical size and shape, one recess being formed in the end of one ballnut and the other recess being formed in the opposing end of the other ballnut.

3. A ballscrew assembly according to claim 2, characterised in that the spring (16) has out-turned ends (24, 26) which locate in blind holes (28, 30) in the bottoms of the recess (20, 22).

4. A ballscrew assembly according to claim 2 or clair..

3, characterised in that a series of blind holes (28, 30) are provided to receive the ends (24, 26) of the spring (16) so that the preload applied to the ballnuts by the spring is adjustable at the assembly stage.

5. A ballscrew assembly according to any one of claims 1 to 4, characterised in that the spring is of coiled for with one or more complete turns, or is a C-shaped spring, or is a helically-coiled spring extending transversely of the ballnuts.