GB2193378A

GB2193378A - A push button switch actuator

Info

Publication number: GB2193378A
Application number: GB08616960A
Authority: GB
Inventors: Remond Johannes Putzeys
Original assignee: Access Keyboards Ltd
Current assignee: Access Keyboards Ltd
Priority date: 1986-07-11
Filing date: 1986-07-11
Publication date: 1988-02-03
Also published as: GB8616960D0

Abstract

The present invention provides a switch actuator particularly of a kind applicable to the keys of a keyboard. The switch actuator comprises a housing (12) and a plunger (14) for reciprocating movement within the housing (12). The housing (12) has an upper guidance chamber (16) and a lower guidance chamber (18). The plunger (14) has an upper guidance surface (22) and a lower guidance surface (28). The guidance surfaces (22, 28) cooperate with the respective guidance chamber (16, 18) so as to restrain the plunger (14) from lateral movement within the housing (12). The lower guidance chamber (18) is laterally more extensive than the upper guidance chamber (16) whereby improved resistance to lateral movement of the plunger (14) within the housing (12) is provided. The upper guidance chamber (16) is preferably of cylindrical shape and the lower guidance chamber (18) preferably has the shape of a truncated cross. <IMAGE>

Description

SPECIFICATION A switch actuator The present invention relates to a switch actuator particularly of a kind applicable to the keys of a keyboard.

A key for use in a keyboard usually consists of a key top, an actuator and a switching element. It is known to combine the key top and actuator to form a single component and it is also known to combine the actuator and switching element to form a single component. However, the perceived quality of a keyboard key depends upon its 'feel'. A desirable feel is usually obtained by ensuring that when operated the key top moves linearly against a smoothly increasing resistance. Any significant tendency for one component of the key to tilt relative to another will impair smooth operation of the key by increased resistance to movement and possible jamming. A corresponding reduction in lifespan also results.

Reduction in the height of the keys of a keyboard, such as in 'low-profile' keyboards, causes difficulty in maintaining the required "feel" of the keys because of an increased tendency for tilting as the key is operated.

This often arises because of the reduced depth of the switch actuator. It is known for the manufacture of low-profile keyboards to include key switching elements comprising two spaced apart electrodes which are operably interconnected by a contact normally held apart from the electrodes by a rubber support.

One difficulty encountered in the design of keyboards is related to the use of key tops which span more than one key space. With such enlarged key tops the force applied to operate the key is often applied at a location laterally spaced from the centre of the key with the result that the key top has an increased tendency to tilt. The tilting of the key top detracts from the "feel" of the key and significantly increases the wear on the arrangement which guides movement of the key top, usually the switch actuator. The use of "turret" keys has been proposed to mitigate this problem. Such keys consist of a flat plate with a central projection having the shape and size of a normal single key top. An additional or alternative arrangement has been the use of torsion wires provided beneath the key top, which solves the problem but adds an extra cost.

With a view to providing an improved arrangement, the present invention provides a switch actuator comprising a housing and a plunger for reciprocating movement within the housing, the housing having an upper guidance chamber and a lower guidance chamber and the plunger having an upper guidance surface and a lower guidance surface which guidance surfaces cooperate with the respective guidance chambers so as to restrain the plunger from lateral movement within the housing, the lower guidance chamber being laterally more extensive than the upper guidance chamber whereby improved resistance to lateral movement of the plunger within the housing is provided.

Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 illustrates the components of a switch actuator in accordance with the present invention, Figure 1 A showing a housing and Figure 1B showing a plunger, and Figure 2 is a vertical section through an assembled key showing the actuator of Figure 1 in place with a key top and a switching element, Figure 2A showing the key in its quiescent state and Figure 2B showing the key when the switch is closed.

As illustrated in the drawings, the switch actuator 10 comprises a housing 12 and a plunger 14. The housing 12 has an upper guidance chamber 16 and a lower guidance chamber 18. Upper guidance chamber 16 is provided by an open ended cylinder and lower guidance chamber 18 has, in plan view, the shape of a truncated cross. Lower guidance chamber 18 is laterally more extensive than upper guidance chamber 16. The cylinder defining the upper chamber 16 is located centrally in the square defined by the intersection of the truncated limbs 20 of the cross shape of the chamber 18. Although the components of the housing 12 have been described separately, as the open ended cylinder and the truncated cross, the whole of the housing 12 is formed as an integral unit-usually by the injection moulding of a plastics material.

The shape and configuration of the plunger 14 corresponds to the shape and configuration of the housing 12. Plunger 14 has a cylindrical neck portion 22 and a base 24 consisting of a plate 26 having the truncated cross shape of the base of housing 12. The depth of the base 24 of plunger 14 is defined by four uprights 28 which constitute respective end faces of the limbs of the truncated cross shape of the base. Apart from the uprights 28, the sides of the base 24 are left open. As with housing 12, although the shape of the upper and lower portions of the plunger 14 have been described separately, the plunger is formed as an integral unit normally by injection moulding of a plastics material.

The top of the cylindrical neck 22 of plunger 14 is closed by a surface 30 which has a recess with two longitudinal slots 32 provided therein. Slots 32 receive retaining pegs 35 of a keytop 34 (shown in Figure 2).

One of the uprights 28 of the base of plunger 14 is divided into two sections by a verti cal recess 36 which also forms a notch 37 which extends into plate 26. Recess 36 cooperates with a key 38 (shown in Figure 2) thus requiring a unique orientation of plunger 14 within housing 12.

Figure 2 of the drawings shows a vertical section through an assembled key of a keyboard, the key including the actuator 10 illustrated in Figure 1. The key comprises a switching element 40, the actuator 10 and a keytop 34.

Switching element 40 is of known construction commonly referred to as an elastomer rubber dome switch, such switches being known for use with low-profile keyboards.

Two spaced apart electrodes 42 are associated with each switching element 40. The electrodes 42 are located on the printed circuit board 44 by which the key is supported.

Electrodes 42 are covered by a rubber support 46 which has an electrical contact 48 depending from the underside of the support 46 and positioned above the electrodes 42.

Plunger 14 is positioned within housing 12 with plate 26 of the plunger being held against the underside of the top of the base 12 by the rubber support 46. The housing 12 sits on the feet of the support 46 which is normally a continuous sheet provided over the whole of the base of the keyboard.

Keytop 34 is retained on plunger 14 by a snap fit of pegs 35 with appertures 32. The keytop 34 has the conventional concave upper surface 50 which assists in~directing an operators finger to apply an operating force centrally to the key. The present invention provides such improved resistance to tilting of the key mechanism that the keytop 34 has the same lateral extent as housing 12. This can be important where it is desirable to reduce the spacing between adjacent keys. This also enables the housing 12 to be retained in a keyboard by a single plate which clamps the base of the housings between the plate and the circuit board.

Neck 22 of plunger 14 has a sliding fit within the guidance chamber 16 and the uprights 28 have a sliding fit within the chamber 18. The plunger is thus restrained to reciprocate linearly within the housing. If forces applied to keytop 34 tend to tilt the keytop, the tilting motion is transmitted to plunger 14 and is resisted by the sliding fit of the plunger within the housing. Any lateral motion of the external surface of neck 22 would be accompanied by a significantly larger movement of the uprights 28 because the base 24 is laterally more extensive than neck 22. Contact between uprights 28 and the housing 12 also significantly increase the area over which any tilting forces are transmitted by the plunger to the housing. That is, there is an improved bearing surface distribution.There is a consequent reduction in wear as compared with transmission of such forces by the neck 22 alone.

The key is shown in its quiescent state in Figure 2A and is shown with the switch actuated or closed in Figure 2B. When the key top 34 is pressed, plunger 14 slides within housing 12 against the resistance provided by the support 46. The sliding fit of the plunger within the housing also contributes to the resistance. Prior to the limit of travel of plunger 14, contact 48 makes an electrical connection between the electrodes 42, thus operating the switch. The rubber dome collapses further, until the uprights 28 of the plunger strike the rubber sheet and base. When the operating force is removed from the keytop 34 the resilience of support 46 propels the plunger 14 back to its original position. There is a positive stop at the limit of travel of the key mechanism. The arrangement enhibits desirable characteristics such as the avoidance of switch "bounce".More importantly, the arrangement provides good resistance against lateral forces which would otherwise tend to result in tilting of the keytop.

The present invention provides a sufficient improvement in resistance to tilting of the key mechanism that it has been found to be acceptable to avoid the use of previously required levelling mechanisms with keytops which span upto two key spaces.

Effectively, the invention provides two guidance systems. The particular shape of the base of the housing and plunger as illustrated in the drawings can be considered as providing eight points of guidance, that is one at each end of each upright 28, distributed as far as possible from the switch centre.

While one embodiment of the invention has been described in detail, it will be apparent to those skilled in the art that various modifications can be made without departing from the scope of the appended claims. For example.

one particular shape of the base of housing 12 and plunger 14 has been illustrated and described but it is immediately apparent that other shapes may be used.

Claims

1. A switch actuator comprising a housing and a plunger for reciprocating movement within the housing, the housing having an upper guidance chamber and a lower guidance chamber and the plunger having an upper guidance surface and a lower guidance surface which guidance surfaces cooperate with the respective guidance chambers so as to restrain the plunger from lateral movement within the housing, the lower guidance chamber being laterally more extensive than the upper guidance chamber whereby improved resistance to lateral movement of the plunger within the housing is provided.

2. A switch actuator as claimed in claim 1, wherein the upper guidance surface of the plunger is provided by the external surface of a cylinder.

3. A switch actuator as claimed in claim 1 or 2, wherein the lower guidance chamber is of rectalinear shape.

4. A switch actuator as claimed in claim 3, wherein the lower guidance chamber has the shape of a truncated cross.

5. A switch actuator as claimed in any preceding claim, wherein the lower guidance surface of the plunger is formed by four separate guidance faces each of rectangular shape.

6. A switch actuator substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

7. A keyboard containing one or wore switch actuators of the form claimed in any preceding claim.

CLAIMS Amendments to the claims have been filed, and have the following effect: Claims 1 and 3 above have been deleted or textually amended.

New or textually amended claims have been filed as follows: Claims 2 and 4-7 above have been re-numbered as 4,2,3,5,6 and their appendancies corrected.

1. A switch actuator comprising a housing and a plunger for reciprocating movement within the housing, the housing having an upper guidance chamber and a lower guidance chamber and the plunger having an upper part and a lower part each part having a respective guidance surface which guidance surfaces cooperate with the respective guidance chambers so as to restrain the plunger from lateral movement within the housing, the lower guidance chamber being laterally more extensive than the upper guidance chamber, the lower part of the plunger being that part of the plunger which is housed fully within the lower chamber and the lower guidance surface extending for substantially the whole depth of the lower part of the plunger whereby improved resistance to lateral movement of the plunger within the housing is provided.