The invention relates to a universal bearing supporting rotational movement of one member relative to another while allowing off-axis movement of one rotary member relative to the other.

Rotationally-driven hand tool attachments, for example sanders and nut- or screw- drivers, are conventionally coupled rigidly to rotational driving means, for example through the chuck of an electric hand drill. The joint between the attachment and the driving means, for example the electric drill chuck, does not accommodate off axis movement of the attachment as it rotates; this places limitations on the angle at which the hand tool is operated, rendering it unsuitable for use in particularly inaccessible corners and, in the case of rotary sanders, requiring precise control of the position of the hand tool in order to avoid uneven surface treatment. Further, with such conventional rigid coupling means, varying axial thrust forces are transmitted directly to the prime mover, leading to excess wear and difficulties in control of the tool. Accordingly, there is a demand for a more flexible coupling between the driving and driven rotary members.

The invention provides a universal bearing

comprising a seating member which supports a rotary member for relative rotation, the rotary member comprising a first member having a cavity which receives a ball bearing such that a substantial portion of the surface of the ball bearing projects from the first member, the ball bearing being releasably and rigidly connected to the firstf. member by interlocking

I. means, and the seating member having a part-spherical bearing cavity receiving the said projecting portion of the ball bearing.

In order that the invention may be better understood, a preferred embodiment of the invention will now be described, by way of illustration only, with reference to the accompanying diagrammatic drawings in which:-

Figure 1 is a side view, partially in section, of a slip clutch incorporating a universal bearing embodying the invention;

Figures 2a to 2e are side views corresponding to Figure 1 illustrating different combinations of the components of the slip clutch in which:-

Figure 2a is a section through a first rotary member of the clutch;

Figure 2b is a side view of a pin for locking a ball bearing to the first rotary member;

Figure 2c is a side view of the ball bearing;

Figure 2d is a side view, partially in section, of the slip clutch of Figure 1 but omitting the first rotary member and the pin for the sake of clarity; and Figure 2e is a side view of the slip clutch of Figure 1, under a greater compressive axial load then is shown in Figure 1;

Figure 3a is a sectional view of the first rotary member pinned to the ball bearing;

Figure 3b is a diagram illustrating a multiple ball bearing arrangement between the main ball bearing and its seating;

Figure 3c is a further diagram illustrating part of the second rotary member of the slip clutch of Figure 1; Figure 3d is a transverse section taken on the line A-A of Figure 3c; and

Figure 4 is a top plan view of the slip clutch of Figure 1.

The slip clutch incorporating a universal bearing comprises a first rotary member 1 coupled to a second rotary member 20 by way of a spherical ball bearing 7. The first rotary member 1, shown most clearly in Figure 2a, consists of a disk with a flat upper surface and a lower surface having a part-spherical recess 6 which seats the ball bearing 7 and is complementary in shape

thereto. Two colinear radial bores 2 through the disk 1 communicate with the seat 6 and receive a connection pin 3 which is also threaded through a bore 72 through one side, the upper side, of the ball bearing 7. The connection pin 3 thus rigidly secures the ball bearing 7 to the first rotary member 1.

The surface of the ball bearing 7 remote from the pin 3 is seated in a cup-shaped, part-spherical seating -]» by way of a ball bearing arrangement consisting of a plurality of balls 9 whose diameter is substantially smaller than that of the ball bearing 7. The smaller balls 9 are free to roll between the spherical outer surface of the ball bearing 7 and the spherical inner surface of the seating . _ ~~ffl The second rotary member 20 comprises two telescopically-connected cylindrical members 12, 17, of which the overlapping ends are provided with respective stops, or piston type rings 14, 141 which act as stops. The outer cylindrical member 17 has thin walls and a closed base. The inner cylindrical member 12 has thicker walls than the outer cylinder and has eight cylindrical sockets bored parallel to its axis and disposed at equi-angular positions in the cylinder wall, as shown in Figures 3d and 4, for a purpose to be described below.

A coil compression spring 13 is accommodated

aαially of the inner and outer cylinders 12, 17» the lower end of which spring abuts the inner surface of the base of the outer cylinder 17» and the upper end of which is secured to the outer surface of the seating 7 ^a » for the ball bearings 9 _ι ^be compression spring 13 thus resiliently urges the seating 7 ^a axially away from the second rotary member 20 .

As shown nost clearly in Figure 2d and in Figure 3b, the ball bearing 7 is retained in its seating 7 ^a against axial displacement away from the seating a by means of a centrally-apertuxed disk plate 21 secured over the seating 7a constititing an end closure for the otherwise open inner cylinder 12. The diameter of the central aperture in the disk plate 21 is slightly smaller thai! the diameter of the ball bearing 7» and the larger part of the ball bearing 7 is disposed between the seating 7a and the disk plate 21, so that the ball bearing 7 s retained by the circular edge of the disk plate 21 bearing against the surface of the ball bearing 7« The disk plate 21 also serves to retaine the smaller ball bearings 9 i ^* Q the gap between the seating 7a and the ball bearing 7 _*

Rotational drive is transmitted between the first and second rotary member 1 , 20, by means of eight elongate bearings 11 which are received in the respective eight elongate sockets in the wall of the

inner cylinder 12. As shown in Figure 1 and Figure 2d, each elongate bearing 11 is constrained to slide axially in its corresponding socket, and is urged resiliently towards the first rotary member 1 by means of a respective coiled compression spring 18 mounted in the socket between the base of the socket and an end surface of the elongate bearing 11. The other end 10 of each elongate bearing 11 has a part- spherical bearing surface which bears against a corresponding concave part-spherical bearing surface 5 formed as a recess in a peripheral portion of the underside of the first rotary .member 1, as shown in Figure 2a. The part-spherical recesses 5 are equi-angularly disposed around the periphery of the first rotary member 1, at positions corresponding to the sockets in the wall of the inner cylindrical member

1

12. The elongate bearings 11 are free to pivot relative to the axis of the first rotary member 1, so as to accommodate off-axis movement of the first rotary member 1 relative to the second rotary member 20. The elongate members 11 transmit rotational drive through their bearing surfaces 10 tangentially to the corresponding side walls of the recesses 5 in the first rotary member 1, thus transmitting rotational drive between the first and second rotary members 1, 20.

It will be appreciated that the elongate bearings

not only provide the rotational drive but also function as stabilizing bearings, resiliently resisting off-axis tilting movement of one rotary member relative to the other. x e first rotary member 1 is removable or replaceable, by removing the connecting pin 3 and lifting the first rotary member 1 away from the remainder of the universal bearing joint. The elongate bearings 11 remain in their sockets in the second rotary member 20, and are preferably retained therein by suitable stops (not shown). It is thus possible to use the same rotational drive means, for example an electric power drill, coupled rigidly to the second rotary member 20, to drive several different rotary attachments, for example sanders or nuts- or screw¬ drivers, each attachment being coupled rigidly to a different first rotary member 1.

The universal bearing _β ϊ±Lxxήfis lubricated as follows. As shown in Figure 2c, the ball bearing 7 has a further lubrication channel 8 bored axially through part of the sphere and linking the centre of the main bore 72 for the connecting pin 3 with the outer surface of the sphere adjacent the centre of the seating 6. The ball bearing 7 is thus provided with a lubrication network having a "T" shape. The connecting pin 3, as shown in Figure 2b, is provided with an internal

lubrication channel 4 communicating one open end of the pin 3 with three or more lubrication ports 41 disposed along the length of the connecting pin 3.

As shown in Figure 2a, still further lubrication channels 51 are provided in the first rotary member 1 linking the main bore 2 for the connecting pin 3 with each of the part-spherical recesses 5 for the elongate bearings 11.

Thus lubrication of all the moving parts is provided from a single point, namely the open end of the connecting pin 3, from which lubricating fluid passes through the ports 41 and along the main bore 2, firstly through the further bore 8 to the seating 6, and secondly through the lubrication channels 51 to the part-spherical recesses 5.

As an alternative to the coiled compression spring 13, the second rotary member 20 may be sealed against the flow of fluid from its exterior, and the resultant fluid compression spring constituted by the fluid within the second rotary member 20 performs the same

-7A function of resiliently urging the seating away from the base of the outer cylindrical member 17. The fluid may be air or a suitable compressible liquid such as freon. Preferably, with such a fiuid spring, the seating is rigidly secured to the disk plate 21 or to some other portion of the inner cylindrical member 12.

The slip clutch functions as follows. Rotational drive applied to one of the rotary members, preferably to the second rotary member 20 , is transmitted to the other rotary member through the elongate bearings 11, while compressive thrust forces on the first and second rotary members 1, 20 are supported by the ball bearing 7 and the compression spring 13. Off-axis movement of the two rotary members 1, 20 is accommodated, at least up to an angle of 30 ^* or 40 ^* , by the sliding movement of the ball bearing 7 in its seating 6 and by the axial sliding movement of the elongate bearings 11 in their sockets. When one rotary member rotates off the axis of the other rotary member, it will be appreciated that -the elongate bearings 11 reciprocate in their sockets with a frequency equal to the frequency of rotation, and with an amplititude corresponding in size to the extent to which one rotary member lies off the axis of the other. The clutch action is as follows. Below a predetermined level of torque applied between the first and second rotary members 1, 20, the elongate bearings 11 lodge in the corresponding recesses 5 in the first rotary member 1, and the bearing is locked to transmit drive. Above that torque level, the elongate bearings 11 slide out of their recesses 5, against the resilient

bias of the springs 18 in the sockets, allowing relative rotation of the rotary members 1, 20 and thus slipping of the clutch. The said predetermined torque level depends on the spring constant of the springs

05 is.

In an alternative form of slip clutch, the eight recesses 5 are replaced by a single annular recess 5 of the same sectional shape as shown in Figure 2A. The clutch then slips unless the force on the elongate

10 bearings 10 is sufficient to provide a sufficient dynamic frictional force tangentially between the surfaces 11 of those bearing 10 and the recess 5. Thus the torque setting again depends on the strength of the springs 18.

1 Whilst the invention has been described with reference to particular characteristics of the described embodiment, many modifications and variations thereof are possible within the scope of the invention. ^" " ^" 0 in one such variation, the second rotary member 20 functions instead as a stationary platform, while the first rotary member 1 is free to tilt off axis and/or rotate about its axis. One application of such a universal bearing is in a rotatable display stand for n c

*- ^J postcards, for example, in which the first rotary member is connected to a vertical spindle on which

display racks are mounted, and the second rotary member 20 rests on the ground.

In another variation, the second rotary member 20 is again mounted stationarily, while rotational drive is imparted to the first rotary member by external drive means.

In both these variations, the elongate bearings 11 have an important stabilizing function, limiting and resiliently resisting the off-axis tilting movement of the first rotary member, whether or not it is rotating.