Abstract:
An actuator for a switch, the actuator being movable between on and off positions against an adjustable resilient bias to provide a first signal when said actuator is in said on position and a second signal when said actuator is in said off position.

Description:
FIELD OF THE INVENTION 
     This invention relates to actuators for switches, and more particularly—but not exclusively—to actuators for switches for use in computer systems. 
     BACKGROUND OF THE INVENTION 
     Over the last few decades, the use of computers has become widespread in business, education and at home. Modern computers are controllable by way of graphical user interfaces (GUIs) which allow a user to control the computer simply by manipulating a cursor to select commands from lists of alternatives displayed in pull-down menus on the screen of the computer. 
     The cursors employed in GUIs are designed to be controlled by a pointing device rather than a keyboard, although in practice control is often duplicated on the keyboard so that the computer can still be controlled if the pointing device should fail. Various pointing devices have been developed for control of a cursor in a GUI environment. The pointing devices are also typically provided with one or more switches or buttons for user selection of system functions. Separate switching modules may also be provided. 
     All of these previously proposed pointing devices may easily be manipulated by an able-bodied user to control a cursor in a GUI, and thus to control a computer. These modern computers can be controlled to perform a large number of functions such as speech replication and global communication through the internet and through modern to modern connections. 
     Given the great utility of modern computers, it would be highly desirable if they could be effectively utilised by mentally and physically disabled persons to perform a variety of different functions. To this end, various pointing devices have been developed which cater for the special needs of disabled users. These devices provide improved mechanisms for the control of an on-screen cursor, but they typically do not address the problems associated with the user selection of computer system functions. 
     For example, some mental and physical disabilities are such that the disabled person is incapable of illustrating the fine motor control necessary to depress keys of a keyboard or to depress buttons on a conventional pointing device to select functions of, or perform tasks on, a computer system. Other disabled persons suffer from problems associated with hand shake, for example, that cause a repeated depression of a button when they only wanted to press the button once. As a consequence of this, these disabled persons can be unable to effectively operate modern GUI-driven computers. 
     SUMMARY OF THE INVENTION 
     In accordance with an aspect of the invention, there is provided an actuator for a switch, the actuator being movable between on and off positions against an adjustable resilient bias to cause said switch to provide a first signal when said actuator is in said on position and a second signal when said actuator is in said off position. 
     This aspect of the invention alleviates these problems by providing an actuator wherein the resilient bias is adjustable to allow the resistive force against which the actuator is depressed to be varied to take account of the particular disability of the user. For example, for those users who lack sufficient strength to effectively utilise conventional switches, the resistive force (i.e. the resilient bias) can be decreased so that a lesser pressure is required. Similarly, for those persons who suffer from hand shake, for example, the resistive force (i.e. the resilient bias) can be increased so that a definite depressive movement is required to activate the switch and so that relatively small hand movements, caused by a hand tremor for example, do not cause the switch to be activated. 
     Preferably, said resilient bias is adjusted by rotating said actuator. Preferably, said resilient bias is provided by a resiliently flexible elongate arm. The actuator may be movable to bear upon said elongate arm to flex the same. The resilient bias may be adjusted by varying a distance between at least two support points of a resiliently flexible elongate arm that provides said bias. 
     Preferably, increasing the distance between the support points decreases the resilience of the flexible arm. More preferably, decreasing the distance between the support points increases the resilience of the flexible arm. 
     Preferably, the support points each comprise a body having a cam follower that is fittable into and moveable in a cam track formed in a supporting plate. The cam track may be a spiral cam track. 
     Preferably, the support points are each movable in a respective radial slot formed in a top plate that is mountable over said supporting plate, rotation of said top plate causing said cam followers to move along said cam track to increase or decrease the distance between said support points. 
     The thickness of said arm may vary along its length. End portions of said arm may be thinner than a central portion thereof. 
     Preferably, said actuator is moveable to bear upon said arm, whereupon said arm bears upon switching means to activate and/or deactivate the same. The switching means may comprise a microswitch. 
     A second aspect of the invention provides a switch comprising an actuator as described herein. 
     A third aspect of the invention provides an actuator for a switch comprising: a button moveable upon the application of a force from a first position to a second position, and means for providing a resilient bias capable of acting against said force, said bias providing means being adjustable to vary the force required to move said button from said first position to said second position. 
     A fourth aspect of the invention provides a switch comprising: a button moveable upon the application of a force from a first position to a second position; resilient bias providing means for providing a resilient bias acting against movement of said button from said first position to said second position; and switching means operable to provide an output signal when said button is moved, or once said button has been moved, from said first position to said second position, wherein means are provided for adjusting said resilient bias thereby to vary the force required to move said button from said first position to said second position. 
     A fifth aspect of the invention provides an actuator for a switch comprising: a button moveable against a resistive force from a first position to a second position, means for providing said resistive force, and means for adjusting said resistive force. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional view through a switch according to an aspect of the invention; 
         FIGS. 2   a  to  2   c  show various views of a component of the switch of  FIG. 1 ; and 
         FIGS. 3   a  and  3   b  show various views of another component of the switch of  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to  FIG. 1 , a switch  1  comprises a housing  3  and an actuator  5  mounted for movement with respect to the housing  3 . 
     The housing  3  comprises a base plate  7 , a cam plate  9  and a top plate  1 . The cam plate  9  is secured to the base plate  7 , and the top plate  11  is fitted over the cam plate  9  and is rotatable with respect thereto. The base plate  7  is provided with a cavity  13  and a microswitch  15  is fitted therein. The top plate  11  is attached, preferably releasably, to the actuator  5 , and the top plate  11  and actuator  5  are rotatable with respect to the base plate  7  and cam plate  9 . The microswitch could be connected to a computer system, and the switch  1  could be used to select functions of, or perform tasks or, that system. The actuator  5  is preferably connected to the top plate by a series of complementary interengaging hooks, wherein the hooks on the actuator  5  engage with hooks on the top plate  11  to securely hold the one to the other. This arrangement is particularly advantageous as the hooks also act as a pivot point when pressure is applied to an edge portion of the actuator. 
       FIGS. 2   a  to  2   c  show various views of the top plate  11 . As can be seen from these figures, the top plate  11  comprises an annular body having an elongate central channel  17  and an outer peripheral wall  19  extending substantially in parallel to the wall of the channel  17 . The free end of the peripheral wall  19  is provided with a lug  21  which is fittable, possibly snap-fittable, in a co-operating groove  23  in the cam plate  9  (see  FIG. 3   b ). 
     The top plate  11  is provided, in this embodiment, with a pair of slots  25 —one either side of the channel  17 . The slots  25  each provide a guide for a respective support  27 ,  29  movably located therein. One end of each support is provided with a cam follower  31  that is fittable into a preferably spiral cam track  33  formed in the cam plate  9 . The other end of each support  27 ,  29  is provided with a supporting projection that abuts against an elongate arm  35  provided on the underside of the actuator  5 . The elongate arm  35  is resiliently deflectable against a resilient bias that differs in degrees in dependence upon the distance between the supports  27 ,  29 . If the distance between the supports  27 ,  29  is increased then the resilient bias against which the actuator is deflected will decrease. Similarly, if the distance between the supports  27 ,  29  is decreased then the resilient bias against which the actuator is deflected will increase. In the preferred construction, depression of the actuator causes a projection on the underside thereof to bear against the elongate arm  35 , which bears in turn upon the microswitch  15  to activate the same. Releasing the actuator releases the microswitch  15  and deactivates the same. In an alternative construction, the microswitch could remain in a given state until the actuator is depressed a second time to cause the microswitch to change to another state. 
     Whilst the cam track shown in the drawings and described herein is formed as a spiral, it will be appreciated that the cam track may have alternative forms. For example, the cam track could simply comprise a radially inwardly extending groove for each of the cam followers. 
     The elongate arm  35  may be of varying thicknesses and is preferably thicker in the middle portion than at end portions. Such a construction aids the operation of the device as the thicker portion is more difficult to flex than the thinner portions. Thus, the force required to flex the elongate arm is further increased as the distance between the supports is reduced. The elongate arm rests upon the supports  27 ,  29  in use and the ends of the arm are moveable within the actuator  5 . 
       FIG. 3   a  is a plan view of the cam plate  9  showing the spiral cam track  33  formed therein, and  FIG. 3   b  is a lateral cross-sectional view of the cam plate  9 . The groove  23  with which the lug  21  on the free end of the peripheral wall  19  co-operates is clearly visible in  FIG. 3   b.    
     To assemble the switch  1 , the cam followers of the supports  27 ,  29  are first located in appropriate points of the cam track  33  in the cam plate  9 . Preferably, the cam followers are inserted at diametrically opposite points on either side of the channel  17  so that the elongate arm  35  is evenly supported. The top plate  11  is then fitted over the cam plate  9  to allow at least supporting projections of the supports  27 ,  29  to project through respective ones of the slots  25 . The top plate  11 , cam plate  9  and supports  27 ,  29  are then fitted onto the base plate  7 , and the cam plate  9  is secured to the base plate  7 . The top plate  11  and supports  27 ,  29  are then freely rotatable about the cam plate  9  and base plate  7 . The elongate arm  35  is then mounted on the supports  27 ,  29 , and the actuator  5  is fitted to the top plate  11  (by way of the interengaging hooks described above) so that the elongate arm  35  abuts against a protrusion formed on the underside of the actuator  5 . The actuator  5  is not rotatable with respect to the top plate  11 , and thus a rotation of the actuator  5  will cause the actuator  5 , elongate arm  35 , top plate  11  and supports  27 ,  29  to rotate about the cam plate  9  and base plate  7 . The actuator  5  is, of course, movable towards and away from the top plate  11 . 
     If, as mentioned above, the actuator  5  is rotated, then the cam followers of the supports  27 ,  29  will follow the spiral cam track  33  and the supports will move radially outwards or radially inwards depending upon the direction of actuator rotation. Radially inward or outward movement of the supports will vary the ease with which the actuator may be deflected against the resilient bias provided by the elongate arm  35 . 
     Thus, it may be seen that the degree of resistance to actuator deflection may easily be adjusted to take account of the user&#39;s particular disability. For example, for those users with poor physical strength the resilience can be adjusted (by rotating the actuator and connected components) to increase the distance between the supports and thus to decrease the resistance to actuator deflection. Similarly, for those users with handshake or poor motor control, the resilience can be adjusted (by rotating the actuator and connected components) to decrease the distance between the supports. Decreasing the distance between the supports will increase the resistance to actuator deflection to such a point where a definite movement is required, thereby alleviating problems caused by accidental switch activation. 
     The actuator described herein is particularly well suited for use with a switch in a computer system to select functions of, or to perform tasks on that system. However, it will be appreciated that the switch could alternatively be used in a variety of different circumstances. Accordingly, the disclosure given herein is not to be interpreted as being limited to an actuator of a switch exclusively for use in a computer system. 
     The actuator described herein may be effectively retrofitted to existing switch units. 
     It will be understood that the invention has been described herein by way of example only and that modifications may be made within the scope thereof. 
     For example, the above disclosure has described a switch employing a pair of supports each located in a respective slot. It will be appreciated that a greater number of supports and slots may be provided if desired. 
     The cam track may also be formed such that the resiliency of the actuator is not freely adjustable. In such an arrangement, the resiliency of the actuator would be adjustable between predetermined graduated levels. 
     In addition, whilst the above described switch employs a microswitch that is directly acted upon by the elongate arm, it will be appreciated that alternative arrangements are feasible. For example, the switch could be an optical switch, with the arm having a blanking plate mounted thereon that is moveable to make or break a beam of light to an appropriate detector. Alternatively, the arm could indirectly act upon the switch by one of a number of different means.