GB2084404A - Rotary switch - Google Patents

Abstract

A rotary switch for mounting on a printed circuit board, has an axle (1) on which first and second discs (19, 20) are mounted so as to be rotatable with the axle. These discs are used to set up connections, dependent on the angular setting of the axle (1), between brushes (16, 16') each of which is integral with an external tag portions (4, 4'). One disc (19) has slots (28) while the other disc (20) has a conductive pattern (46), which is engageable by the brushes (16, 16') through the slots (28) when the axle (1) is rotated. <IMAGE>

Description

SPECIFICATION Rotary switch This invention relates to a rotary switch, and especially to a printed circuit board rotary switch capable of breaking or establishing the continuity of circuits in which flow electrical signals whose power may reach several watts.

In low current applications, e.g. in electronics, rotary switches are used to establish or break the continuity between their connecting tags dependent on the angular position given to a rotary knob by an operator. These switches are small since they are usually mounted on printed circuit boards and must provide different electrical combinations between their connecting tags to meet the various cases of use. In certain rotary switches of this type, the continuities between the tags are established via brushes integral with these tags which wipe the conducting areas of a disc including a printed circuit. The possible electrical combinations with such a switch thus result from a sort of coding corresponding to the combinations of the printed circuit conducting and insulating areas.In other models of switches, the metallic printed circuit is replaced by conductive patterns obtained by depositing of an ink loaded with appropriate metallic particles.

These rotary switches are appropriate as long as their brushes establish or break circuits in which flow low-powered signals, e.g. of about 100 mW and generally less than 1/2 W. However, as soon as signals of several watts are concerned -- e.g. 100 mA signals at a 60 V voltage -- such switches are not appropriate.

Indeed, among other disadvantages, an electric arc occurs when a brush breaks a signal of this power as it passes from a conductive area to a neighbouring insulating area: thus metal is progressively driven onto this insulating area, causing breakdown of the insulating material.

An object of this invention is to avoid these drawbacks by simple and economical means which make it possible to obtain a "super-flat" small rotary switch for printed circuits capable of switching relatively high-powered signals.

According to the invention there is provided a rotary switch wherein the tags for the external connection are integral with internal brushes so arranged as to be respectively in contact with the insulating or conducting parts of an element secured on the rotary switch control axle according to the angular position of said element, wherein the control axle of the switch carries two electrical coding elements, which are rotatable with-that axle, wherein the first of said coding elements is constituted by a disc of an insulating material provided with openings whose length and location correspond to the coded combinations appropriate to each angular position of the control axle, and wherein the second of said coding elements is constituted by another disc bearing electrical conducting material areas according to a pattern related to the openings of the first disc.

In other respects, the position of the brushes and of the connecting tags with which they are integral, their respecting spacing and their securing together are determined by nipples which are part of one of the two half-shells constituting the switch case, and which enter corresponding openings of the other half-shell when juxtaposing both half-shells during the case assembly.

An embodiment of the invention will now be described with reference to the accompanying drawings in which: Fig. 1 is a perspective view of a rotary switch embodying the invention; Fig. 2 is an exploded perspective view of the components of the switch of Fig. 1; Fig. 3 is a perspective view of certain components of Fig. 2, but at an angle making it possible to show details not visible in Fig. 2; Fig. 4 is a plan view on an enlarged scale of the disc having the openings used to establish the electrical coding combinations between the rotary switch brushes of a switch as shown in Figs. 1, 2 and 3.

Fig. 5 is a large scale cross-section, showing the bevelled profile of the edges of the coding openings of the disc of Fig. 4; Fig. 6 is a large scale plan view of the disc having an example of electrically conducting patterns, associated with the disc of Fig. 4.

The rotary switch, shown in Fig. 1 has a control axle 1, a case made of two half-shells 2 and 3 entrapping the connecting tags 4, whose spacing is such, as to allow their positioning on a printed circuit board. A similar connecting tag configuration, not visible in Fig. 1, but identical to that of the tags 4, is arranged on the side 5 of the switch.

Although not shown in Fig. 1, the control axle 1 can receive the usual control knob. Similarly, the switch may have a threaded sleeve mounted on the axle 1 and allowing, in a well-known way, the switch to be fixed on a panel through a nut, the panel being sandwiched between the nut and the switch.

Now we refer to Fig. 2, which shows the switches component and in which are found the elements of Fig. 1 such as, the control axle 1, half shells 2 and 3, and tags 4 and 4'. We also refer to Fig. 3, which shows parts of the axle 1 and of the half-shell 2 which are not visible in Fig. 2.

The half-shell houses the control axle 1 and elements associated with it such as a spring 6 and ball 7, and a cylindrical stop 8. The latter is forcefitted in one of the opening 9 which are regularly spaced around the central opening 10 for the axle.

Thus, dependent on the opening in which the stop 8 is fitted the angular displacement available for the axle 1 is greater or less. The ball 7 co-operates with the spring 6 to constitute a snap fastening, so that the operator who controls the axle 1 physically feels an opposing force at a certain point for passing from an angular position of the switch to another, which corresponds to the angular spacing of the openings 9. To this end, the spring 6 and the ball 7 are lodged in the opening 12 (Fig. 3): thus when the axle 1 is positioned in the half-shell 2, the spring 6 pushes the ball 7 against the semi-cylindrical protrusions 1 3 or against the hollows between them.The half-shell 2 also includes four centering posts 14 which are used for the case assembly and six nipples 1 5-1 5' used for the positioning and the holding of the connecting tags 4-4' which, are each as can be seen in the Fig. 2, part of one single piece one end of which is a connecting tag, the other end being a brush 1 6-1 6'. Each brushconnecting tag 1 6-4 or 1 6'-4' has two semi- circular cuts 1 7-18 and 1 7'-1 8' for the passage of the nipples 1 5-1 5' of the half-shell 2.

The control axle 1 is associated with the two discs 1 9 and 20 so that its rotation simultaneously causes that of both discs, To this end, the axle 1 terminates, in the part which is normally inside the case, by a pivot 21 visible in Fig. 3 and by two flat parts one of which referenced 22 is only visible in this Figure, the other flat part being symmetrically placed in the hidden part. These flat parts 22 and the semi-circular segments joining them are provided for slightly force-fitting within the corresponding openings 23 and 24 of the discs 19 and 20. The disc 19 includes a collar 25 around the opening 23 which gives it mechanical rigidity.

When the discs 1 9 and 20 are on the control axle 1, this collar 25 abuts the face 26 (Fig. 3). The thickness of the collar and the position of the face 26 with respect to the face 27 (Fig. 3) ensure that the disc does not contact this face 27 but that there exists between them a clearance. It is in this space between the disc 1 9 and the face 27 that the brushes 1 6-1 6' are housed.Their camber causes them to exert a pressure against the surface of the disc 1 9 which is made of insulating material, e.g. nylon loaded with Teflon (Registered Trade Mark). As the disc 19 has openings 28, the brushes 1 6-1 6' may individually be located in front of the disc insulating material, or on the contrary, in front of an opening 28, dependent on the angular position of the disc 1 9 and on the location of the openings 28.

To facilitate the understanding, we refer to Fig. 4 which is a large scale view of the disc 19 in Fig. 2. There can be found the opening 23 and its collar 25; it will be noted that the semi-circular segments 29 and 30 are not identical. This gives a polarizing effect, since as the male part of the axle 1 has a similar profile, there is only one possible positioning of the disc on the control axle 1. The openings 28 are located according to seven concentric circles 31 to 37, which corresponds to the number of brushes 1 6-1 6' (Fig. 2). The width of these openings is such that the brushes may enter them with no difficulty. By examining the openings 28, it can be seen that their lengths are variable as well as their locations on the disc.

Moreover by examining the external circle 37, it will be seen that the openings have the shape of half-circles separated by a sort of insulating material tooth 38-38'. Thus, each disc comprises a proper combined arrangement of the location and the length of the openings; there is thus obtained a particular code for each type of disc. That is why the insulating disc 1 9 is called "coding disc". Moreover, from Fig. 5 which is a cross-section of one end of an opening such as the end 39 of Fig. 4 - it can be seen that it has a bevel 40 connected to the faces 41 and 42 by bends 43 and 44.Thus, during the rotation of the coding disc, when the corresponding brush leaves the opening, it passes from the approximative level of the opening bottom 45 to the level of the face 42 by the transition due to the bevel and the two bends. The same process happens in reverse when the brush wipes the face 42 and enters the opening down to its bottom 45. Hence the mechanical performance of the brush is improved, as is the quality of the contact between the brushes and the disc 20 (Fig. 2).

Since the coding disc 1 9 is associated with the disc 20, when a brush goes through an opening 28 (Fig. 2) of the coding disc, it wipes the surface of the disc 20. Now, this disc bears conducting patterns 46, printed on an appropriate insulating substrate so that these patterns supply the appropriate electrical connections between the brushes 1 6-1 6' which have reached it through the openings 28 of the coding disc 19. These configurations of the conducting disc 20 are variable; besides the patterns 46 iliustrated in Fig. 2, another example of patterns forming conducting tracks roughly distributed in two sectors is shown in Fig. 6 (large scale). For another application, the disc 20 could have a completely conducting face.It will be noted that this disc 20 has an opening 47 identical to the opening 23 of the disc of Fig. 4, so it has the same polarizing arrangements to facilitate its positioning on the control axle 1.

Now returning to Fig. 2 and more specially to the half-shell 3, this includes two recesses 48 and 49, the first one for receiving and holding in position the pivot 21, Fig. 3, of the control axle 1, and the second one for providing a better seating of the disc 20 against the surfaces 50 and 51.

Four blind holes 52 are provided for receiving the centering posts 14, whereas the groups of six blind holes 53 receive the nipples 1 5-1 5' (Fig. 3). Two sides of the half-shell 3 include the grooves 54 separated by the ribs 55. The grooves 54 receive the parts 56 of the connecting tags 4-4', the ribs 55 contributing to the holding and insulation of the tags by being inserted between their parts 56.

The centering posts 14 each have a diameter slightly greater than that of the corresponding blind holes 52. This arrangement avoids the need for a complementary piece to ensure correct switch assembly. Thus, when the discs 1 9 and 20 are on the control axle 1 , the latter having its pivot 21 in the recess 48 and its opposite extremity going through the opening 10 of the half-shell 2, and the brushes 1 6-1 6' are between the coding disc 19 and the face 27 (Fig. 3) and when the tags 4-4' are lodged in their respective housings 54, it is only necessary to render each half-shell 2 and 3 tightly integral with the other. This is obtained by submitting them to such a pressure that the centering posts 14 are force-fitted within the blind holes 52 until the two half-shells 2 and 3 are tightly juxtaposed.

It is obvious that the preceding description has only been given as an unrestrictive example and that numerous alternatives may be considered without departing from the scope of the invention.

Claims (6)

1. A rotary switch wherein the tags for the external connection are integral with internal brushes so arranged as to be respectively in contact with the insulating or conducting parts of an element secured on the rotary switch control axle according to the angular position of said element, wherein the control axle of the switch carries two electrical coding elements, which are rotatable with that axle, wherein the first of said coding elements is constituted by a disc of an insulating material provided with openings whose length and location correspond to the coded combinations appropriate to each angular position of the control axle, and wherein the second of said coding elements is constituted by another disc bearing electrical conducting material areas according to a pattern related to the openings of the first disc.

2. A switch, according to Claim 1, and wherein the internal brushes are arranged to wipe exclusively the first insulating disc and to contact the conducting material areas of the second disc solely through the openings of said first disc.

3. A switch, according to Claim 1 or 2, and wherein bevelled parts are provided at the ends of the openings in the first disc to facilitate the brushes entering or leaving said openings.

4. A switch, according to Claim 2, and wherein the brushes each have cuts for co-operating with centering elements integral with at least one part of the switch casing.

5. A switch, according to Claim 1, 2, 3 or 4, and wherein each of said discs has a central opening for an interference fit on the control axle and located inside the switch, said opening being at least partially asymmetric to constitute a polarizing effect which is advantageously used when positioning the discs on the control axle.

6. A rotary switch substantially as described with reference to the accompanying drawings.