GB2158646A - Rotary switch - Google Patents

Abstract

A small rotary switch comprises a housing 10, 11 and operating shaft 12 rotatably mounted within the housing, a plurality of cams 14 which are angularly movable with said shaft 12 and a plurality of movable contacts, such as contacts 16a and 18 which are engageable by said cams 14 on rotation of the shaft 12. The switch is provided with a plurality of fixed contacts which are provided on a flexible printed circuit board 20 which extends at least part way around the interior periphery of the housing 10, 11. There are also provided a plurality of terminal pins 21 which are each formed intermediate their ends with a shoulder 22 which abuts the exterior of the housing, the inner end of each pin extending through an aperture formed in the printed circuit board 20 and an aperture formed in the wall of the housing so as to be electrically connected at said inner end 23 to the printed circuit board. <IMAGE>

Description

SPECIFICATION Rotary switch This invention relates to a rotary switch and has as one of its objects the provision of such a switch which is especially capable of being manufactured in a relatively small size. For example, it may be required, for the purpose of controlling the actuation of electrically operated hand-held apparatus, to provide a reliable rotary switch which has a maximum cross-section having dimensions of the order of 10 mms. x 10 mms.It is therefore a design requirement of the present invention that it provides a reliable rotary switch which, inter alia, is capable of being manufactured to such a small size, In accordance with the invention there is provided a rotary switch which comprises a housing, an operating shaft mounted for rotary movement in the housing, a plurality of cams mounted on the shaft so as to be angularly movable therewith, and a plurality of movable contacts mounted in the housing and engageable by said cams on rotation of said operating shaft, characterised in that there is provided a plurality of fixed contacts which are formed on a flexible printed circuit board which is disposed within the housing so as to extend at least part way around the interior periphery thereof, and in that there is also provided a plurality of terminal pins which are each electrically connected at one end, namely the inner end, to said printed circuit board and which each extend through an aperture formed in the flexible printed circuit board and an aperture formed in the wall of the housing so as to be adapted at the other, outer, end to be electrically connected to an external circuit, each of said terminal pins being formed intermediate its ends with a shoulder which abuts the exterior of the housing.

Conveniently, said one end of each of said terminal pins is electrically connected to the printed circuit board by means of a welding operation, said one end of the terminal pin being initially of a constant cross-sectional configuration so that the pins can be assembled on the switch from the exterior thereof by effecting relative vertical movement between the switch housing and said pins to cause the inner end of each pin to enter into the associated apertures formed in the wall of the housing and the printed circuit board until a position is reached in which all of the pin shoulders engage the exterior of the switch housing and in which the inner ends of the pins project into the interior of the housing through said apertures, the innermost portions of said inner ends then protruding inwardly of the printed circuit board so that they can be engaged by a welding electrode introduced into the housing and thereby welded to appropriate conductors of said printed circuit board.

The invention will now be more particularly described with reference to the accompanying drawing which is a sectionai elevation of one example of a rotary switch constructed in accordance with the invention.

The accompanying drawing illustrates the new arrangement so far as said terminal pins are described. Referring to the drawing, the embodiment illustrated therein includes a switch housing which is conveniently formed of two channel-shaped polycarbonate mouldings 10 and 11 which are connected together after assembly of the inner parts of said switch. The drawing also shows a rotatable operating shaft 12 on which is mounted a plurality of cams of which one, namely cam 13 is seen in the drawing, said cam having a projecting lobe 14 and a peripheral recess 15.

There is also provided a plurality of movable contacts which are formed in two contact plates 16 and 17 located within the housing, said contact plate 17 having a movable contact 18 which has a generally V-shaped portion 19 which, in one relative position of the cam 13 and movable contact 18 is adapted to be located within said recess 15. An appropriate angular movement of the cam 13 via the shaft 12 on which it is mounted (a counter-clockwise movement in the drawing) will displace the recess 15 from the portion 19 causing said portion 19 to ride on the unrecessed part of the periphery of the cam 13.Movement of the V-shaped portion 19 out of recess 15 and onto the unrecessed part of the cam has the effect of moving said movable contact 18 outwardly for engagement with a co-acting fixed contact in the form of a conductive strip formed on the interior of a flexible printed circuit board 20 which is disposed within the housing so as to extend part way around the internal periphery thereof, said printed circuit board 20 being, as shown in the drawing, of generally channel-shaped configuration.

Said flexible printed circuit conveniently comprises a polyamidefilm, 50 > m thick, and a copper conductor track, 35ism thick, coated with gold which is 5wm thick. Further counter clockwise rotation of the cam 13 brings the lobe 14 into contact with the movable contact 1 boa which is disposed opposite the contact 18, and displaces the contact 1 boa outwardly so that it also engages a fixed contact of the printed circuit board 20.

In order that some of the conductive strips of the printed circuit board 20 can be connected to an external electrical circuit or circuits a plurality of terminal pins 21 are provided, said pins being made of tin plated copper. Each of said pins is formed intermediate its ends with a shoulder 22 and initially both ends of each pin 21 namely the outer end 21a and a relatively short inner end 21b are each formed two a plain cylindrical configuration. The wall of the housing part 10 is formed with a plurality of apertures through which said pins 21 can pass and the base portion of the printed circuit board 20 is also formed with a plurality of corresponding apertures through which said inner ends 21b of the pins can project.

Initially said pins 21 may be placed in a holder or jig in which the pins extend in generally vertical directions said flanges 22 abutting against the upper surface of the holder or jig whilst the ends 21a project downwardly through suitable apertures formed in the holder or jig. With the printed circuit board 20 in position in the housing part 10, relative vertical movement between said housing part 10 and the aforesaid holder or jig can be effected in order that the inner ends 21b of the terminal pins 21 will be caused to extend through the apertures formed in the wall of the housing and through the corresponding apertures formed in the printed circuit board.In this position the innermost portion of each of said inner ends 21b will protrude slightly above said printed circuit board and a welding electrode can then be introduced into the interior of the housing part 10 in order to weld said protruding end portions to the appropriate conductive strips of the printed circuit board, heads, indicated by reference numerals 23, being formed on the terminal pins in this operation. Whilst carrying out this welding operation of course the terminal pins will be held securely in position by a relative inward pressure applied between the housing part 10 and the aforesaid holder or jig, the flanges 22 of the terminal pins 21 being thus firmly located between the upper surface of the holder or jig and the lower surface of the exterior of the housing part 10.The holder or jig may constitute the second electrode of a resistance welding apparatus although a separate electrode can be provided if desired. After the welding has been effected the terminal pins 21 will be securely held in position by virtue of the engagement between the heads 23 and the interior of the printed circuit board on the one hand and between the flanges 22 and the exterior of the housing part 10 on the other hand. A very secure electrical connection can thus be made between said terminal pins 21 and the printed circuit board 20, whilst at the same time the terminal pins can be readily assembled to the switch from the exterior of the housing part 10 by utilizing a holder or jig as above explained. Furthermore when it is required to make electrical connections to the projecting outer ends of said terminal pins 21, the above-mentioned firm location of each terminal pin by the head 23 and the flange 22 will ensure that no disturbance of the electrical connection between the pin and the printed circuit board will take place whilst the outer end of each pin is being handled or otherwise engaged to make the aforesaid external connection.

Any suitable known apparatus can be used for welding the terminal pins to the flexible printed circuit board. It may for example be one which uses a 50 watt-second welding power supply, welding being carried out on a "long pulse" setting having a peak of 2250A at 3.5m.secs on an energy setting of 18 watt seconds. A pressure of 101b.ft may be applied during welding, using a concave electrode to control weld spatter.

Claims (4)

1. A rotary switch comprising a housing, an operating shaft mounted for rotary movement in the housing, a plurality of cams mounted on the shaft so as to be angularly movable therewith, and a plurality of movable contacts mounted in the housing and engageable by said cams on rotation of said operating shaft, characterised in that there is provided a plurality of fixed contacts which are formed on a flexible printed circuit board which is disposed within the housing so as to extend at least part way around the interior periphery thereof, and in that there is also provided a plurality of terminal pins which are each electrically connected at one end, namely the inner end, to said printed circuit board and which each extend through an aperture formed in the flexible printed circuit board and an aperture formed in the wall of the housing so as to be adapted at the other, outer, end to be electrically connected to an external circuit, each of said terminal pins being formed intermediate its ends with a shoulder which abuts the exterior of the housing.

2. A rotary switch as claimed in Claim 1 whereinsaid inner end of each of said terminal pins is electrically connected to the printed circuit board by means of a welding operation.

3. A rotary switch as claimed in Claim 2 wherein said inner end of each terminal pin is initially of a constant cross-sectional configuration so that the pins can be assembled to the switch from the exterior thereof by effecting relative vertical movement between the switch housing and said pins to causethe inner end of each pin to enter into the associated apertures formed in the wall of the housing and the printed circuit board until a position is reached in which all ofthe pin shoulders engage the exterior of the switch housing and in which the inner ends of the pins project into the interior of the housing through said apertures, the innermost portions of said inner ends then protruding inwardly of the printed circuit board so that they can be engaged by a welding electrode introduced into the housing and thereby welded to appropriate conductors of said printed circuit board.

4. A rotary switch substantially as hereinbefore described with reference to and as shown in the accompanying drawing.