WO1991012621A1

WO1991012621A1 - Improvements in or relating to switch apparatus

Info

Publication number: WO1991012621A1
Application number: PCT/GB1990/000257
Authority: WO
Inventors: David Paul Erlam
Original assignee: Alphameric Keyboards Limited
Priority date: 1990-02-16
Filing date: 1990-02-16
Publication date: 1991-08-22

Abstract

Switch apparatus (1) comprises a housing (2), a switch means (16), an actuator (7) reciprocatably movable in the housing to actuate the switch means, spring means (15, 38) providing spring bias of the actuator into a rest position and cam means (25, 26, 33) operable between the spring means and the housing to control the spring bias as a function of actuator travel from the rest position, the cam means comprising a cam follower portion (25, 29) of the spring means co-operating with a cam surface (26, 34, 35) of the housing. The housing and plunger are selectively assemblable with either one of a first and second springs (15, 38) having different first and second cam follower portions (25, 29) respectively co-operable with different portions (26, 34, 35) of the cam surface, the selected first or second spring constituting the spring means to provide distinct first and second characteristics of spring bias as a function of actuator travel, whereby the required characteristic is selectable by selection of the first or second springs during assembly. A keyboard having tactile and non-tactile response keys can be assembled from keys having like housings and actuators.

Description

- 1 -

"IMPROVEMENTS IN OR RELATING TO SWITCH APPARATUS"

This invention relates to switch apparatus and in particular but not exclusively to keyboard switch apparatus having capacitive switch means and means for selectively providing a tactile response to a user depressing a switch actuator.

It is known to provide switch apparatus in which a switch means is actuated by manual depression of an actuator against bias provided by a spring means, the action of the switch means itself being such that it contributes no discernable tactile feedback to the user. In some applications the presence of tactile feedback is desirable so that the actuation mechanism is- supplemented by an additional means providing a tactile response to make the user aware that a switching operation has been initiated or completed.

In GB-1555764 for example the spring bias provided by a coil spring is varied during depression of a switch actuator bf cam action between free ends of the spring and ramp-like faces formed on part of a housing. The characteristic of spring bias as a function of actuator travel from the rest position is arranged to include a negative gradient portion resulting in a tactile sensation referred to as "fall through".

It is desirable to provide an array of such switch apparatus in a keyboard or the like where some of the keys may be required tσ have a tactile response whereas others may not. There is therefore a need to provide swif_c^*h apparatus in which tactile response may be selectively provided in an effective manner whilst maintaining the number of components in the switch apparatus to a minimum and enabling the provision of tactile response to be selected as may be required during assembly without undue complexity or cost.

According to the present invention there is disclosed switch apparatus comprising a housing, a switch means, an actuator reciprocatably movable in the housing to actuate the switch means, spring means providing spring bias of the actuator into a rest position and cam means operable between the spring means and the housing to control the spring bias as a function of actuator travel from the rest position, the cam means comprising a cam follower portion of the spring means co-operating with a cam surface of the housing, wherein the housing and plunger are selectively assemblable with either one of a first and second springs having different first and second cam follower portions respectively co-operable with different portions of the cam surface, the selected first or second spring constituting the spring means to provide distinct first and second characteristics of spring bias as a function of actuator travel, whereby the required characteristic is selectable by selection of the first or second springs during assembly.

An advantage of such an arrangement is that a housing and actuator of the same shape can be used in assembling switch apparatus having tactile response or not having tactile response as may be required simply by selection of either the first or second springs during assembly of the switch apparatus. This reduces the number of different components required when assembling an array of switch apparatus where some are required to have tactile response and others are not.

This is particularly advantageous in a keyboard for example where an array of such switch apparatus is required to be visually indistinguishable as far - 3 -

as the construction of the housing is concerned whilst certain switch keys may be required to have tactile response and other keys may not e.g. shift keys. Preferably the profile of the cam surface includes a smooth profiled portion and a projection co-operable with the cam follower portion of the spring means when constituted by the first spring to provide a non-linear variation in the spring bias of the actuator during a predetermined portion of the actuator travel so as to produce a tactile response to a user manually depressing the actuator.

Such a non-linear variation in spring bias may thereby be arranged to give "negative tactile response" to the user in that the non-linear variation of spring bias felt by the user when characterised by a graph of spring bias as a function of travel from the rest position includes a negative gradient portion of the graph. The resulting tactile event is preferably arranged to coincide with an electrical switching event so that the user is aware of when switching has occurred. Subsequent over-travel of the plunger may then continue until travel is arrested. Preferably the cam follower portion of the spring means when constituted by the second spring engages only the smooth profiled portion of the cam surface such that the spring bias is substantially linearly dependent on the actuator travel thereby providing a substantially linear response to a user manually depressing the plunger.

In this instance the spring bias felt by a user depressing the actuator increases substantially uniformly with travel of the actuator and the user is given no tactile indication of the electrical switching event. - 4 -

Conveniently the cam surface has a recess in the smooth profiled portion defining a recessed surface portion of the cam surface and the projection is formed on the recessed surface portion, the cam follower being biassed into sliding contact with the smooth profiled portion.

The first spring may comprise a leaf spring which includes a detent normally extending into the recess such that the detent engages the projection at the predetermined portion of actuator travel. The second spring may then comprise a leaf spring which does not include such a detent and therefore does not engage the projection.

Alternatively the cam follower portion of the spring means when constituted by the first spring extends into the recess continuously throughout travel of the actuator and follows a path defined by a portion of the cam surface within the recess. The cam follower portion of the spring means when constituted by the second spring may then be shaped such that it cannot extend into the recess and contacts only the smoothed profile portion of the cam surface as described above.

Advantageously the actuator is a plunger longitudinally slidable in the housing, the spring means comprising a leaf spring having one end portion fixed relative to the housing and a free end portion movable in response to plunger movement. The plunger may then be engaged by the leaf spring at a contact location intermediate the fixed and free end portions of the leaf spring.

Advantageously the switch means comprises a capacitive switch of which an electrically conductive portion of the spring means comprises a conductor movable into and out of proximity with at least one fixed conductor to make and unmake the capacitive - 5 -

switch respectively.

Conveniently the or at least one of the fixed conductors is formed on a circuit board on which the housing is mounted. Specific embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings of which:-

Figure 1 is a perspective part cut-away view of switch apparatus in accordance to the present invention;

Figure 2 is an exploded perspective view of a plunger and a first type of leaf spring of the switch apparatus of Figure 1;

Figure 3 is a sectioned elevation of the switch apparatus of Figure 1 showing the plunger in the rest position;

Figure 4 is a sectioned elevation of the switch apparatus of Figures 1 to 3 showing the plunger in a partially depressed position; Figure 5 is a sectional elevation of the switch apparatus of Figures I to 4 showing the plunger in the fully depressed position;

Figure 6 shows detail of the cam follower portion of the leaf spring of the switch apparatus of Figures 1 to 5;

Figure 7 shows detail of the cam follower portion of an alternative second type of leaf spring providing a linear response;

Figure 8 is a perspective view of part of the housing of the switch apparatus of Figures l to 5 showing a recessed cam surface;

Figure 9 is a perspective view of an alternative switch apparatus having a modified housing; Figure 10 is a perspective view of a housing of a further alternative switch apparatus; - 6 -

Figure 11 is a perspective view of an alternative leaf spring cooperating with a cam surface to provide a tactile response; and

Figure 12 is a perspective view showing part of the housing and the leaf spring of Figure 7.

Figure 1 shows a switch apparatus 1 comprising a housing 2 in the form of a square plate 3 having at each corner a supporting leg 4. An annular collar 5 is upstanding centrally from the plate and defines a generally cylindrical channel 6 in which a plunger 7 is vertically reciprocatable.

The plunger 7 and the collar 5 include interfitting key formations 8 which prevent rotation of the plunger when assembled. The plunger can be assembled in either of two orientations i.e. turned through 180° about its longitudinal axis.

The housing 2 is provided with clips 9 depending from the plate 3 between two opposite pairs of supporting legs 4 and is also provided with a post 10 depending between one other pair of the legs 4. As seen in Figure 3 the switch apparatus 1 normally rests with its supporting legs 4 on a printed circuit board 11 and is retained in position by means of a chassis (not shown) which engages the clips 9 with a snap-fit action. Flexure of the clips 9 relative to the plate 3 is facilitated by slots 90 formed in the plate on each side of each clip 9 as seen in Figure 1.

The plunger 7 has a flange 12 projecting from its lower end such that upward movement of the plunger is limited by engagement of the flange with the plate 3. V-section grooves 13 are provided in the upper surface of the flange 12 and are arranged to mate with cooperating projections 113 (as seen in Figure 3) from the underside of the plate 3 thereby providing positive positional location of the plunger - 7 -

relative to the housing 2 at the upper extreme of the plunger travel.

The plunger 7 has a central axially extending channel 14 which is keyed to receive a switch cover (not shown) . The collar 5 has a recess 128 to captively locate a co l spring (not shown) which optionally may be placed coaxially around the collar and arranged to provide additional spring bias if so required. Each recess 128 has an associated hole 129 formed in the plate 3 by the moulding tool used to form the recess.

A leaf spring 15 of a first type is located within the housing 2 beneath the plunger 7 and is arranged to bias the plunger into a rest position as shown in Figure 3 in which the plunger is fully raised with the flange 12 in abutment with the plate 3 of the housing 2.

The leaf spring 15 is formed of a resilient metal and has a flat strip portion 16 connected to a flat cut-out portion 17 by a ϋ-bend portion 18. The flat strip 16 ends in a crimped edge portion 19 which is received in a horizontal slot 20 formed in the housing adjacent the lower end of the post 10 such that the edge portion 19 remains fixed in position relative to the housing.

The cut-out portion 17 has a cut-out or aperture 22 adjacent its free eϊid portion 21 and the leaf spring 15 is assembled with the housing 2 such that the post 10 extends through the aperture. The aperture 22 is formed by cutting a rectangular portion of the metallic material on three sides to form a tongue 23 which is bent out of the plane of the cut-out portion 17 through an acute angle with the free edge 24 of the tongue being rolled over to form a cam follower portion 25 adapted for sliding contact with the post 10. - 8 -

The post 10 has a generally vertical cam surface 26 against which the cam follower portion 25 rests.

In the rest position of the plunger 7 as shown in Figure 3 the flat strip 16 of the leaf spring 15 extends upwardly from the edge portion 19 at an angle of about 30° to the horizontal. The U-bend portion 18 connects the flat strip 16 to the cut-out portion 17 which extends horizontally back towards the post 10. A central projection 27 formed on the underside of the plunger 7 makes contact with the cut-out portion 17 at a location 28 along the length of the leaf spring 15. The projection 27 is flat bottomed with chamfered flanks 127 such that the U-bend portion 18 is able to extend slightly above the horizontal level of the cut-out portion. This allows the radius of the U-bend portion to be maximised and in the present example is maintained at a radius not less than 1 mm. The leaf spring 15 is formed so as to have a shape memory which provides upward spring bias against the plunger 7 in the rest position as shown in Figure 3.

The free end portion 21 of the leaf spring 15 in Figures 1 to 5 is shown more clearly in Figure 6 where it can be seen that a detent 29 projects centrally from the cam follower portion towards the aperture 22. A corresponding recess 30 is formed in the post 10 so as to extend centrally the length of the cam surface 26, the detent 29 being formed so as to extend only partially into the recess 30 so that sliding contact is normally made between side portions 31 of the cam follower portion 25 and corresponding smoothly profiled side portions 32 of the cam surface 26. As seen in Figure 8, the recess 30 includes an outwardly extending projection 33 located - 9 -

intermediate the upper and lower extremities of the cam surface 26. The projection 33 has upper and lower ramp surfaces 34 and 35 respectively such that the projection is of triangular cross-section as seen in the upper portion of Figure 6.

The housing 2 and plunger 7 are assembled with the first type of spring 15 when switch apparatus 1 is required to exhibit tactile response.

In use a user manually depresses the plunger ₇ such that it begins to travel downwards with respect to the housing 2. Spring bias exerted by the lea_f spring 15 against the plunger 7 at location 28 is overcome by the manually applied depressive force such that the leaf spring is deformed by bending localised at the U-bend portion 18. The cut-out portion 17 is moved downwards by this depression and is retained in a generally horizontal attitude by the flat bottomed projection 27 of the plunger so that the cam follower portion 25 is also moved downwards. Sliding contact between the cam surface 26 and the cam follower portion 25 thereby results and almost immediately the detent 29 encounters the upper ramp surface 34 within the recess ₃₀. Ramp action urges the cam follower portion 25 away from the cam surface 26 with the result that the tongue 23 flexes to an increased angle relative to the horizontal. Reaction from the upper ramp surface 34 provides a vertical force component acting upwardly on the cam follower portion 25 and which is transmitted through the leaf spring 15 to the plunger 7. Consequently the total spring bias acting on the plunger 7 is enhanced throughout this movement while the detent 29 "climbs" the upper ramp surface 34. After further travel of the plunger 7 the detent 2₉ surmounts the peak of the projection ₃₃ and encounters the lower ramp surface 35. Reaction from - 10 -

the lower ramp surface 35 provides a vertical force component acting downwardly on the cam follower portion 25 and which is transmitted to the leaf spring 15 thereby partially cancelling the spring bias exerted on the plunger by the leaf spring.

The projection 33 is finally cleared by the detent and continued travel of the plunger is accompanied by sliding contact between the side portions 31 of the cam follower portion 25 and the side portions 32 of the cam surface 26. The cam surface 26 is arranged to be smoothly varying such that the spring bias increases linearly with plunger travel both before and after the projection is encountered by the cam follower portion 25. The travel of the plunger 7 is arrested by contact between downwardly projecting stand-off portions 37 of the plunger against the flat strip 16 of the leaf spring 15 as shown in Figure 5 where it is seen that in this bottom position the cut-out portion 17 continues to extend horizontally and is spaced above the flat strip 16. The flat strip 16 is wider than the cut-out portion 17 to enable the stand off portions 37 to straddle the cut-out portion and make contact with the flat strip without contacting the printed circuit board.

During downward travel of the plunger the flat strip 16 flexes very slightly but remains sufficiently rigid such that the U-bend portion moves in an arc centred on the fixed edge portion 19. Consequently an increasing horizontal pull is exerted on the free end portion 21 which is increasingly biassed towards the post 10. The tongue 23 is therefore progressively flexed to an increased angle relative to the horizontal, thus providing a degree of lateral movement of the cut-out portion 17 away from the post 10. Friction between the cut-out - 11 -

portion 17 and the projection 27 is minimal because the chamfered shape of the projection provides a small area of contact. The cam surface 26 is also made slightly curved so as to moderate the extent of flexure of the tongue 23 as the travel progresses. This is useful in avoiding seizure of the tongue 23 relative to the surface 26 which might otherwise occur.

The cam surface 26 (including the detent 29) , the cam follower portion 25 and the projection 33 together comprise a cam means which controls the spring bias exerted on the pl nger 7 at each point along its travel. The profile of the side portions 32 of the cam surface 26 is smoothly varying so as to provide spring bias which varies linearly with travel. The detent 29 within the recess 30 however provides a feature of the cam means resulting in non-linear spring bias characteristics. In particular, when the detent 29 surmounts the peak of the projection 33, it conveys a negative tactile response to the user. The user is thereby made aware by sense of touch that sufficient travel of the plunger has taken place without having to look at the switch apparatus 1. This is particularly important where the switch apparatus is incorporated in a keyboard as in the case of a typewriter or word processor.

The switch apparatus 1 provides electrical switch action by means of capacitive coupling between the flat strip 16 and the printed circuit board 11.

An insulating layer such as lacquer is applied to one or other of the leaf spring 15 and the printed circuit board 11 such that direct electrical contact does not take place. Switch action by capacitive coupling occurs typically during the first half of plunger travel and is synchronised with the tactile response when using apparatus 1 as described above which include the first type of spring 15.

The switch apparatus 1 may alternatively be assembled including an alternative second type of leaf spring 38 of similar construction except that it does not include a detent corresponding to detent 29 of Figures 6 and 8. The alternative leaf spring 38 of Figures 7 and 12 is described with reference to the same reference numerals as those used for leaf spring 15 where appropriate. In the absence of any such detent the sliding contacts between the cam follower portion 25 of the alternative leaf spring 38 and the cam surface 26 is confined to the side portions 31 and 32 respectively. The characteristic of spring bias is thereby linear as a function of plunger travel throughout the entire travel of the plunger.

The use of such an alternative second type of leaf spring 38 in effect provides switch apparatus having a cam means with a cam surface profile providing entirely linear spring bias characteristics.

Such an alternative leaf spring 38 would be useful for example in a keyboard where particular keys such as shift keys were not required to exhibit any tactile response. It would nevertheless be possible to assemble a keyboard from components in which the same type of housing and plunger were used throughout and the spring bias characteristics of each individual key being selected during assembly by choosing either the spring of Figures 1 to 6 or the spring of Figures 7 and 12.

A second embodiment of the invention is shown in Figure 9 where corresponding reference numerals to those appearing in Figure 1 were used where appropriate. Switch apparatus 150 as shown in

Figure 9 is modified to reduce the likelihood of dust - 13 -

and other debris entering the housing 2 from above. Unlike the switch apparatus 1 which includes recesses 128 and associated holes 129 the apparatus 150 has a collar 5 joined continuously to the plate 3 without any such recess or hole being formed.

The apparatus 150 also includes slots 151 formed on each side of the clips 9, the slots 151 extending only partially through the plate 3 such that dust is prevented from entering the slots by a thin membrane 152 formed over each respective slot. Continued reliable operation of the apparatus

151 is therefore enhanced by excluding dust and debris.

A further alternative housing 151 is shown in Figure 10 where corresponding reference numerals to those of previous Figures are used where appropriate for corresponding elements. The housing 151 includes a plate 3 in which is formed a score line

152 delineating a corner portion 153 of the plate. The score line 152 constitutes a zone of weakness enabling the corner portion 153 to be readily broken from the housing 151 to create an aperture into which a light emitting diode (not shown) can be inserted. This enables the housing 151 to be illuminated if required.

The housing 151 also includes a clip 154 located on the plate 3 and adapted to comprise a bearing for a torsion wire (not shown) which may for example be required to bias a space bar in a keyboard. In Figure 11 an alternative leaf spring 160 is shown engaging the post 10 of the housing 2, reference numerals corresponding to those of previous Figures being used where appropriate to denote corresponding elements. Leaf spring 160 has a tapered tongue 161 terminating in a cam follower portion 25 which is - 14 -

sufficiently narrow to extend into the recess 30 formed in the cam surface 26. The cam follower portion 25 of tongue 161 therefore follows a path defined by a portion 162 of the cam surface 26 lying within the recess 30 and makes contact with the projection 33 to provide tactile linear response as described above with reference to spring 15.

The cam means incorporated in switch apparatus in accordance with the present invention can be readily adapted for example by choice of shape given to the projection 33. If for example the projection 33 is given a part cylindrical profile then the resulting tactile response will be noticeably different, i.e. smoother, than that provided by a triangular profile.

Other forms of actuator may be used for example in a rocker switch in which a pivoted arm is used in place of a plunger.

Claims

- 15 -CLAIMS :

1. Switch apparatus (1) comprising a housing (2) , a switch means (16) , an actuator (7) reciprocatably movable in the housing to actuate the switch means, spring means (15^38) providing spring bias of the actuator into a rest position and cam means (25,26,33) operable between the spring means and the housing to control the spring bias as a function of actuator travel from the rest position, the cam means comprising a cam follower portion (25,29) of the spring means co-operating with a cam surface (26,34,35) of the housing, characterised in that the housing and plunger are selectively assemblable with either one of a first and second springs (15 and 38) having different first and second cam follower portions (25,29 and 25) respectively co-operable with different portions (26,34,35 and 26) of the cam surface, th selected first or second spring constituting the spring means to provide distinct first and second characteristics of spring bias as a function of actuator travel, whereby the required characteristic is selectable by selection of the first or second springs during assembly.

2. Switch apparatus as claimed in claim l wherein the profile of the cam surface includes a smooth profiled portion (26) and a projection (33) co-operable with the cam follower portion (25,29) of the spring means when constituted by the first spring (15) to provide a non-linear variation in the spring bias of the actuator during a predetermined portion of the actuator travel so as to produce a tactile response to a user manually depressing the actuator.

3. Switch apparatus as claimed in claim 2 wherein the cam follower portion (25) of the spring means when constituted by the second spring engages only the smooth profiled portion of the cam surface such that the spring bias is substantially linearly dependent on the actuator travel thereby providing a substantially linear response to a user manually depressing the plunger.

4. Switch apparatus as claimed in either of claims 2 or 3 wherein the cam surface has a recess

(30) in the smooth profiled portion defining a recessed surface portion of the cam surface and the projection is formed on the recessed surface portion, the cam follower being biassed into sliding contact with the smooth profiled portion.

5. Switch apparatus as claimed in claim 4 wherein the first spring comprises a leaf spring (15) which includes a detent (29) normally extending into the recess such that the detent engages the projection at the predetermined portion of actuator travel and wherein the second spring comprises a leaf spring (38) which does not include such a detent.

6. Switch apparatus as claimed in claim 4 wherein the cam follower portion of the spring means when constituted by the first spring extends into the recess continuously throughout travel of the actuator and follows a path defined by a portion of the cam surface within the recess.

7. Switch apparatus as claimed in claim 6 wherein the cam follower portion of the spring means when constituted by the second spring is shaped such that it cannot extend into the recess and contacts only the smooth profiled portion of the cam surface. - 17 -

8. Switch apparatus as claimed in any preceding claim wherein the switch means comprises a capacitive switch of which an electrically conductive portion (16) of the spring means comprises a conductor movable into and out of proximity with at least one fixed conductor to make and unmake the capacitive switch respectively.

9. Switch apparatus as claimed in claim 8 wherein the or at least one of the fixed conductors is formed on a circuit board (11) on which the housing is mounted in use.

10. Switch apparatus as claimed in any preceding claim wherein the actuator is a plunger (7) longitudinally slidable in the housing, wherein the spring means comprises a leaf spring having one end portion (19) fixed relative to the housing and a free end portion (21) movable in response to plunger movement and wherein the plunger is engaged by the leaf spring at a contact location (28) intermediate the fixed and free end portions of the leaf spring.