GB2088142A - Small diameter slip ring assemblies - Google Patents

Abstract

A flexible printed circuit board 13 is wrapped around a rotatable shaft 12 such that conductive contact regions 15 and 16 thereon face outwardly; each contact region has an integral lead portion 17, 18 for external electrical connections; and a pair of slip rings 10 and 11 are mounted around the circuit board 13 with their inner peripheries in electrical contact with the regions 15 and 16 respectively. The lead portion 17 connected to the slip ring 10 extends beneath the other slip ring 11 but is insulated therefrom by an insulating layer 21 on the circuit board 13. In an alternative embodiment (Fig. 5, not shown) the circuit board and slip rings are mounted on an insulating sleeve (22) provided on the shaft 12. During manufacture electrical contact between the slip rings 10, 11 and the contact regions 15, 16 is ensured by shrinking the slip rings and/or by expanding the shaft or sleeve. <IMAGE>

Description

SPECIFICATION Small diameter slip ring assemblies This invention relates to small diameter slip ring assemblies.

As is well known, it is desirable to make the diameter of a slip ring assembly as small as possible in order to reduce its peripheral velocity.

It is an object of the present invention to provide such a slip ring assembly which is simpie to produce and which has a minimum of component parts.

According to one aspect of the present invention, there is provided a slip ring assembly comprising at least one slip ring carried by a rotatable shaft or a sleeve for mounting on such a shaft with a flexible printed circuit board interposed therebetween, the flexible printed circuit board including, for the or each slip ring, a contact portion which is conformed in shape to the internal periphery of the slip ring and which has a conductive contact region in electrical contact therewith and an integral lead portion having a conductive layer which is electrically connected to said contact region whereby external electrical connections can be made to said slip ring.

Preferably, the slip ring assembly includes two slip rings and the contact portions and lead portions therefor are provided on a common flexible printed circuit board. Desirably, the lead portions extend from a common axial end of the slip ring assembly, and the conductive layer of the lead portion for one of the slip rings passes beneath the other slip ring and is insulated therefrom by an electrically insulating layer provided over said lead portion. Conveniently, the lead portions are disposed generally diametrically opposite one another with respect to said shaft or sleeve. The slip rings can be formed so that they are initially axially interconnected by an integral connecting piece which is machined away after mounting of the slip rings on the shaft or sleeve.

Advantageously, the or each contact region extends around a substantial part of the outer periphery of the shaft or sleeve.

According to a second aspect of the present invention there is provided a method of manufacturing a slip ring assembly, comprising providing at least one slip ring and a flexible printed circuit board which includes, for the or each said slip ring, a contact portion having a conductive contact region and an integral lead portion having a conductive layer electrically connected to the contact region; wrapping the flexible printed circuit board around a rotatable shaft or a sleeve for mounting on such a shaft so that the or each contact region faces outwardly thereof: mounting the or each slip ring on the shaft or sleeve and over the flexible printed circuit board such that its inner periphery is in axial registration with the contact region or a respective one of the contact regions; and securing the or each slip ring to the shaft or sleeve by shrinking the slip ring and/or expanding the shaft or sleeve, thereby bringing the inner periphery of the slip ring into electrical contact with the respective contact region of the flexible printed circuit board.

The present invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an axial section through a slip ring assembly according to the present invention Figure 2 is a view on an enlarged scale of part of the slip ring assembly shown in Figure 1; Figure 3 is a plan view of a flexible printed circuit board which forms part of the slip ring assembly; Figure 4 is an exploded perspective view of the slip ring assembly; and Figures 5 to 7 are similar views to Figure 1 but show various modifications which can be made to the slip ring assembly.

Referring first to Figure 1 , the slip ring assembly shown therein comprises a pair of electrically conductive slip rings 10 and 11 mounted in axially spaced relation on a rotatable shaft 12, a flexible printed circuit board 1 3 being interposed between the slip rings and the shaft.Figure 3 shows the flexible printed circuit board 1 3 before mounting on the shaft 12, and it can be seen that the circuit board 1 3 is composed of a rectangular contact portion 14 having two rectangular conductive contact regions 1 5 and 1 6 thereon, and a pair of integral lead portions 1 7 and 1 8 having conductive layers 1 9 and 20 which are electrically connected to the contact regions 1 5 and 1 6 respectively.The contact portion 14 is wrapped around the shaft 12 so that the contact regions 1 5 and 1 6 face outwardly thereof, and these regions engage and are in electrical contact with the slip rings 10 and 1 respectively. The lead portions 1 7 and 18 extend from the same axial end of the contact portion 14 and are arranged so that they are disposed diametrically opposite one another with respect to the shaft. The lead portion 1 7 thus passes beneath the slip ring 11, but as shown in Figure 2 is insulated therefrom by an electrically insulating layer 21 on the flexible printed circuit board 13.The extent of the layer 21 is indicated by stippling in Figure 3, from which it can be seen that only the contact regions 15, 1 6 and ends of the conductive layers 1 9, 20 remote therefrom are exposed. The exposed ends of the conductive layers 19, 20 are connected in use to external electrical connections for the slip rings 10, 11 respectively. It will be manifest that the substrate of the flexible printed circuit board 13, being made of electrically insulating material, insulates the slip rings 10, 11 from the shaft 12, and that the layer 21 insulates the slip rings from each other.

As illustrated in Figure 5, instead of being interposed between the slip rings and the shaft, the flexible printed circuit board 1 3 can be interposed between the slip rings and an insulating sleeve 22 adapted to be mounted on a reduced diameter portion 23 of the shaft 12. This form of construction enables the slip ring assembly to be fabricated as a separate unit for subsequent mounting on the shaft.

The slip ring assembly is constructed by firstly wrapping the flexible printed circuit board 1 3 around the shaft 1 2 or the sleeve 22 as the case may be, and then mounting the slip rings 10, 11 on the shaft and around the circuit board 13 so that thay are in registration with the contact regions 1 5 and 1 6 respectively. The various components are then secured together by shrinking the slip rings, for example hydraulically, mechanically or by rolling; preferably, however, this is performed by an electromagnetic forming operation, for instance using a MAGNEFORM machine. Alternatively, the components may be secured together by expanding the shaft 1 2 or the sleeve 22.In the case where the components are mounted directly on the shaft, the shaft can be provided with a hollow end and can be expanded by driving a slug into the hollow end. Where the components are mounted on the sleeve 22, the operation of inserting the reduced diameter portion 23 into the sleeve can be utilised to expand the latter. Finally, the outer peripheries of the slip rings are machined so that they are accurately concentric with the shaft, and the exposed ends of the conductive layers 19, 20 on the lead portions 1 7, 1 8 are connected for example to armature windings in the usual manner.

Referring now to Figure 6, the slip rings 10 and 11 can be manufactured initially so that they are axially joined by means of an integral connecting piece 24. As illustrated, this can be done by forming an annular groove 25 in the internal periphery of a copper tube, the dimensions of the tube on either side of the groove 25 corresponding to the dimensions of the slip rings. After securement of the slip rings to the shaft, the connecting piece 24 (which extends radially outwardly beyond the external peripheries of the slip rings) can be machined away to separate the slip rings. This is preferably accomplished during machining of the slip rings for concentricity with the shaft 12.

As indicated in Figure 7, an insulating washer 26 can be axially interposed between the slip rings 10 and 11.

The slip ring assemblies described above have the following advantages.

(1) Because the flexible printed circuit board provides a comparatively thin layer of insulation between the slip rings and the shaft, the slip rings themselves can be made comparatively small in diameter, the only limitation being the flexibility of the circuit board.

(2) Since the slip rings can be made small in diameter, their peripheral velocity is reduced.

Consequently, smaller brushes and brush boxes can be used, and there is less brush wear.

(3) The slip rings being of reduced diameter require less material for their production.

(4) The diameter of the slip ring assembly can be reduced sufficiently to enable a bearing to be assembled thereover.

(5) Only a few component parts (i.e. the two slip rings, the printed circuit board and the insulating sleeve where used) are required.

(6) The flexible printed circuit board provides a layer of insulating material between the slip rings and the shaft which is relatively thin as compared with prior art constructions, and therefore conduction to the shaft of heat generated in operation is improved, resulting in a reduced and stable running temperature and less brush wear.

(7) There is no need to injection mould a carrier for the slip rings using inserts, which is often the conventional practice with larger diameter slip ring assemblies, for example as disclosed in British Patent No. 1419277.

(8) Manufacture of the slip rings is facilitated since they are of similar size and shape; this is to be contrasted with the arrangement disclosed in British Patent No. 1,547,618.

(9) Because a flexible printed circuit board is used to make the electrical connections to the slip rings, there is little risk of the insulating layer between the slip rings and the shaft being damaged when the electrical contact between the circuit board and the slip rings is established, which is to be contrasted with prior art constructions in which electrical leads are connected directly to the slip rings, for example, by soidering or ultrasonic welding.

(10) The slip ring assembly has a compartively short axial dimension.

( 1 1 ) The assembly can readily be adapted to the provision of more than two slip rings.

Claims (11)

1. A slip ring assembly comprising at least one slip ring carried by a rotatable shaft or a sleeve for mounting on such a shaft with a flexible printed circuit board interposed therebetween, the flexible printed circuit board including, for the or each slip ring, a contact portion which is confirmed in shape to the internal periphery of the slip ring and which has a conductive contact region in electrical contact therewith and an integral lead portion having a conductive layer which is electrically connected to said contact region whereby external electrical connections can be made to said slip ring.

2. A slip ring assembly as claimed in Claim 1, wherein a plurality of such slip rings are provided and the contact portions and lead portions therefor are provided on a common flexible printed circuit board.

3. A slip ring assembly as claimed in Claim 2, wherein the lead portions extend from a common axial end of the slip ring assembly, and the conductive layer of the lead portion for at least one of the slip rings passes beneath another slip ring and is insulated therefrom by an electrically insulating layer provided over said lead portion.

4. A slip ring assembly as claimed in Claim 3, wherein said electrically insulating layer covers the whole of the common flexible printed circuit board except for the contact portions and parts of the lead portions remote therefrom.

5. A slip ring assembly as claimed in Claim 1, 3 or 4, wherein two such slip rings are provided and the lead portions are disposed generally diametrically opposite one another with respect to said shaft or sleeve.

6. A slip ring assembly as claimed in any one of Claims 2 to 5, wherein the slip rings are formed so that they are initially axially interconnected by an integral connecting piece which is machined away after mounting of the slip rings on the sleeve or shaft.

7. A slip ring assembly as claimed in any preceding Claim, wherein the or each contact region extends around a substantial part of the outer periphery of the shaft or sleeve.

8. A method of manufacturing a slip ring assembly, comprising providing at least one slip ring and a flexible printed circuit board which includes, for the or each slip ring, a contact portion having a conductive layer electrically connected to the contact region; wrapping the flexible printed circuit board around a rotatable shaft or a sleeve for mounting on such a shaft so that the or each contact region faces outwardly thereof; mounting the or each slip ring on the shaft or sleeve and over the flexible printed circuit board such that its inner periphery is in axial registration with the contact region or a respective one of the contact regions; and securing the or each slip ring to the shaft or sleeve by shrinking the slip ring and/or expanding the shaft or sleeve, thereby bringing the inner periphery of the slip ring into electrical contact with the respective contact region of the flexible printed circuit board.

9. A method as claimed in Claim 8, wherein two such slip rings are provided and are initially interconnected by an integral connecting piece, and after the slip rings have been mounted on the shaft or sleeve the connecting piece is machined away.

10. A slip ring assembly substantially as hereinbefore described with reference to the accompanying drawings.

11. A method of manufacturing a slip ring assembly, substantially as hereinbefore described with reference to the accompanying drawings.