GB2486415A - Concentric shaft anti-rotation mechanism - Google Patents

Abstract

The mechanism uses three or more concentric shafts 6, 7, 11 and interconnecting rotating elements 13 in continuous tracks 12. The mechanism allows the driven rotation of intermediate shaft 6 whilst rotational retention of outer shaft 7 retains inner shaft 11. An example of its application is an adapter which can be fitted to a conventional socket driving device to simultaneously hold a bolt whilst driving a nut. The adapter may be attached to a driving device using a drive socket. The bolt may be held using drive socket (9, Figure 5) and the nut may be tightened or loosened using socket 8.

Description

Concentric Shaft Anti-Rotation Mechanism This invention relates to a mechanism which controls the relative rotation of a series of concentric shafts.

As an example of its use, in an ideal nut-and-bolt connection the user would have good access to both the nut and the head of the bolt. There are certain applications of nut-and-bolt connections where access to the bolt head is restricted or the head has no facets, slots or other alTangement to prevent its rotation. In this case the connection can be tightened by holding the bolt shank on the same side as the nut to prevent its rotation and then rotating the nut. Such anangements are sometimes described as hold and turn' or hold and drive' bolts. Typically the tightening device incorporates a socket which rotates the nut plus a device to hold the bolt which is concentric with, and passes through, the socket. This is a specialist piece of equipment designed for this one application.

The present invention is a mechanism which when implemented can perform the hold and turn' operation. It uses concentric shafts and interconnecting rotating elements to control the relative angular movement of the shafts.

This invention relates to the mechanism itself, however for explanation an application will be used to elaborate and clarify. The application is an adaptor, which can be fitted to a conventional socket driving device (now referred to as the driver'), which performs the hold and turn' operation. It has three concentric shafts -an inner shaft, a middle drive section and a outer band. The drive section takes the input from the driver and transfers it to the nut. The inner shaft and outer band work in unison to prevent rotation of the bolt. The mechanism links rotation of the inner shaft to the outer band while allowing the drive section to freely rotate between them. Coupling of the inner to the outer is achieved by a number of rolling elements which contact them both. These elements run in tracks in the external face of the inner shaft and the internal face of the outer band. The rolling elements are further constrained to run in slots cut in the drive section. The drive section turns between the inner shaft and outer band, causing the rolling elements to move in their tracks in a manner which keeps the inner shaft and outer band always aligned. Thus by preventing rotation of the outer band, rotation of the inner shaft is also prevented. The outer band rotation can be prevented by holding it by hand, by attaching it to the drive device or any other stationary object.

The invention can be applied to any system demanding the restraint of a central shaft within a fully surrounding rotating body.

The invention allows any bolt tightening device to be speedily converted for use with turn and hold' bolts simply by inserting the driver fitting into a corresponding fitting, on or in the invention. Typically the drive would be a square peg with a corresponding female square socket set into the invention. The device can be used both to tighten and to loosen a bolt. In the description presented here, purely to simplify the explanation, reference will be made to bolt tightening but this should be taken to also fully encompass the action of undoing the bolted connection. Similarly the central shaft is described as being stationary but the invention can be employed in any situation where this shaft's rotation needs to be controlled.

An example of the invention will now be described by referring to the accompanying drawings and a key of all referenced items is below. Item numbers are consistent between drawings.

Key -Item list for figures 1. Hold and turn bolt 2. Screw thread on hold and turn bolt 3. Hexagonal head on hold and turn bolt 4. Nut 5. Female drive socket in drive section 6. Drive section 7. Outer band 8. Socket which turns the nut 9. Socket which stops rotation of bolt 10. Connecting shaft 11. Inner shaft 12. Tracks in inner shaft and outer band 13. Rotating elements 14. Slot for rotating element in drive section 15. Spring 16. Slot in inner shaft to accept the connecting shaft List of figures: Figure 1 shows a typical hold and turn' bolt.

Figure 2 shows the outward appearance of an application of this invention.

Figure 3 shows the shape of the track 12 on the inner shaft 11.

Figure 4 shows the shape of the track 12 in the outer band 7.

Figure 5 shows a cross sectioned view of a possible application of the invention.

Figure 6 shows an exploded view of an application of the invention.

Figure 1 shows a typical hold and turn' bolt. In this application example rotation of the bolt 1 is effected by a section at the end of the screw thread 2 which has a hexagonal cross-section 3 which can be set into a suitably sized and shaped socket to be prevented from rotating while the nut 4 is rotated to tighten or loosen.

Figure 2 shows the outward appearance of an application of this invention. A square female socket 5 is shown into which the square section shaft of the driver is inserted.

The points indicated by 5 and 6 are part of the same body known as the driven section. The outer band 7 is prevented from rotating, in this instance, by the user holding the band while mechanism is being operated. The socket which turns the nut is indicated as item 8. The socket which holds the bolt stationary is item 9, which is attached to the central shaft 10.

Figure 3 shows the shape of the track 12 on the inner shaft 11. It is continuous around the circumference so that a rolling element following it will move axially backwards and forwards. A slot 16 which accepts the connecting shaft is also shown. This slot shape depends on the connecting shaft 10. If the coupling shaft had a circular section it would incorporate a key or alternative method to prevent rotation.

Figure 4 shows the shape of the track 12 in the outer band 7. This track shape exactly follows that of the inner shaft so that the rolling elements sitting at different positions in the tracks effectively lock the inner shaft to the outer band. The rolling elements are kept in position around the track by the cage in the drive section. Rotating the cage will cause the elements to move in the track but the outer band and inner shaft will be prevented from independently moving.

Figure 5 shows a cross sectioned view of a possible application for the invention.

Parts of the driven section are labelled 6. The outer band 7 and the inner shaft 11 are shown to have tracks in their surfaces 12. These tracks are looped and are of matched shape, being inclined to the shaft axis. Rotating elements 13, are shown as balls, but could be cylinders or other rolling shapes. They run in these tracks. Each rolling element sits in its own slot 14 in the driven section 6. The number of slots and rolling elements can vary but has to be at least two. If three or more slots are employed, they can be disposed uniformly around the circumference of the driven section 6, forming a cage. When this cage is rotated, the rolling elements follow the tracks and in so doing are constrained to move along the slots. The slots in the drive section must be of a length which will freely allow this axial movement. A connecting shaft 10 is used to transfer the constraint of the inner shaft 11 through the driven section 6 and the drive socket 8 to the smaller non-rotating socket 9 which will hold the bolt stationary during operation. In this figure, a spring 15 is used to allow connecting shaft 10 to retract in to inner shaft 11. This feature is not an essential part of the invention but is included here for context. Connecting shaft 10 must not be allowed to turn in inner shaft 11; this can be achieved with a square section shaft as shown here, or via a keyway in a cylindrical shaft.

Figure 6 shows an exploded view of an application if the invention and helps show the necessary geometry of the parts.

Claims (2)

1. Claims 1. A mechanism using at least three concentric shafts and interconnecting rotating elements in continuous tracks which allows the driven rotation of an intermediate shaft whilst rotational retention of the outer shaft retains the inner shaft.
2. 2. An adaptor according to claim 1, which can be fitted to a conventional socket driving device which simultaneously holds the bolt, whilst driving the nut.