GB2332395A - Magnetic keyboard with sealed Hall effect sensor - Google Patents

Abstract

The keyboard 1 comprises: spring biased keys 7; a magnet 17 mounted on the base of each key and movable therewith; a conductive non-magnetic housing 5 having an internal chamber 11 sealed from the external environment; and a respective Hall effect sensor 30 within the chamber. A movement of a key and its associated magnet towards the sensor results in an electrical signal indicative of the movement being produced by the sensor.

Description

2332395 1 KEYBOARD This invention relates to keyboards.

Keyboards are widely used to perform a variety of different functions in a variety of different applications. For example, keyboards are widely used for word-processing, computer programming, data entry and for the control of various types of equipment.

Conventional keyboards for domestic or commercial use typically comprise an outer guard and an inner support upon which a set of keys are mounted. The keys each typically have a support post about which a spring is provided to enable the keys to be depressed to a position where the base of the post abuts against a respective mechanical switch provided beneath each of the keys. A microcontroller is typically provided within the keyboard to scan for key depressions and to obtain digital codes from a look-up table, for example, corresponding to the particular key that has been depressed. These digital codes are then output to the equipment to which the keyboard is connected for the control thereof.

Whilst these conventional keyboards are adequate for home or commercial usage, it has been noted that problems can arise if dirt should migrate between the keys to a position where it can impair either key depression or the proper operation of the mechanical switch provided therebelow. Whilst this problem can be mitigated with regular cleaning, it is difficult to ensure that the keyboard has been properly cleaned without taking it to pieces. Furthermore, the relatively large amount of time required properly to clean a keyboard is inconvenient as the keyboard cannot be used during that time. If moisture or a liquid should migrate into the keyboard, then the electronics contained therein can be permently damaged and the keyboard can become useless.

A variety of so-called rugged keyboards have been proposed which attempt to address the problems associated with the ingress of dirt, moisture or 2 the like into a keyboard. Rugged keyboards have a common aim in that they attempt to seal the interior workings of the keyboard from the external environment.

German Patent Specification No. 19522773 discloses a rugged keyboard that has an alloy steel protective top plate and a plurality of keys set into apertures of the plate. Each key has a projecting shaft that fits in a bore in a bush and is movable against contacts on a mat beneath the keys. An elastic sealing gasket is provided between the shaft of the keys and the protective top plate to n seal the interior of the keyboard from the exterior environment.

United States Patent No. 5197178 discloses a computer terminal keyboard that is sealed by a moulded elastomeric top cover that is shaped to conform to the housing and keys of the keyboard. The top cover is shaped to provide a planar surface on the top plate with elevated individual key covers integrally formed in the top cover. Portions of the top cover extending over the top face and sides of the keyboard housing are formed in a first thickness sufficient to provide a durable covering. Portions of the top cover immediately adjacent and between the individual key covers, and the sides of the key covers, are formed in a reduced, second thickness to allow for flexure as the keys are depressed.

Whilst both of these keyboards adequately protect the internal workings of the keyboard from the external environment, they suffer from the disadvantage that the seal can degrade or become damaged thereby causing the internal workings of the keyboard to be vulnerable once more. Damage to the seal can be 0 caused in a variety of ways. For example, if the seal should come into contact with a sharp object, then the seal can tear. Similarly, if a caustic substance, for example, is spilt on the keyboard, then the substance can penetrate between the keys and destroy the seal. Finally, repeated flexing of the seal upon operation of the keys can cause the seal to wear and degrade over time.

A further problem associated with these previously proposed keyboards is 30 that they can emit electromagnetic radiation (EM) (typically radio frequency C1 1 3 radiation (RF)) which can cause interference in associated equipment. This EM interference generally results from the microcontrollers employed within the keyboard to scan for key depressions. As the microcontrollers are clocked,, so they emit a characteristic EM signal which can cause interference in associated equipment. As a'result of this, the above described keyboards are not suitable for use in EM sensitive environments.

In addition to generating interfering signals, the keyboards are also unduly sensitive to external EM interference that can cause errors in the keyboard. These problems are particularly, but not exclusively, pertinent when the keyboards are being used with sensitive military equipment (whereby stray EM radiation from the keyboard can cause interference in sensitive equipment) or where they are being used in an environment with a high ambient EM radiation level.

There is an need in the art, therefore, for a keyboard which mitigates some or all of the problems associated with the prior art.

In accordance with the invention, there is provided a keyboard comprising: a plurality of resiliently biased keys mounted for reciprocal movement upon depression against the resilient bias; magnet means attached to each of said keys and moveable therewith; an electrically conductive nonmagnetic housing having an internal chamber that is sealed from the external environment; respective sensing means provided within said internal chamber, movement of one of said keys and associated magnet means towards a respective one of said sensing means causing the respective sensing means to output an electrical signal indicative of the movement of the associated key and magnet means.

The keyboard according to the invention is advantageously not reliant upon a sealing member that is repeatedly stressed, such as a gasket or elastic seal, to seal the internal workings of the keyboard from the external environment. Thus the present invention alleviates the problems of the prior an associated with the degradation of seals. Furthermore, the keyboard according to the invention 4 advantageously has its sensitive internal components enclosed within a housing that acts, at least partly, as a shield against ambient EM radiation.

Means may be provided within said internal chamber for scanning for electrical signals outputted by said sensing means and for outputting an 5 identification signal to identify which of said keys has been depressed.

Preferably, the sensing means each comprise a hall effect sensor. It is also preferred that the magnet means each comprise a permanent magnet.

The keyboard may comprise an outer guard fittable over the housing and having one or more apertures therein through which a respective one of said keys extends. The keys may be supported from the underside of said guard.

Alternatively, a key mounting plate may be provided by means of which said keys are supported, the mounting plate being provided between the housing and the auard.

t:- Preferably, the housing comprises a base plate, and a top plate having side panels depending from each edge thereof, the side panels each terminating in a lip to which the base plate is secured. Preferably, a sealing gasket is provided between the side panel lips and the base plate.

Preferably, the housing is of a non-magnetic metal. The housing may be of aluminium or stainless steel. Alternatively, the housing may be of an 20 electrically conductive non-magnetic plastic material.

Preferably, each of said keys comprises a key head and a key stem locatable on a post, the resilient biasing means being provided about the post.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic cross-sectional representation of a keyboard.

Figure 1 shows a cross-sectional view through a keyboard 1. As shown, the keyboard 1 has an outer guard 3 3 and a housing 5. A plurality of keys 7 are provided (one of which is shown) which are mounted on a key support plate 4 between the housing and outer guard. The keys are reciprocally movable through apertures 9 in the outer guard. The outer guard may be of a tough material such 1 as high density plastics or metal. The keys may alternatively be supported from the underside of the guard 3, in which case the support plate 4 may be dispensed with.

The keyboard's EM sensitive components (not shown) are housed within the housing 5 and mounted on a printed circuit board 6 (PCB). The housing has an internal chamber 11 therewithin. The chamber is sealed from the exterior environment in use, but may have a removable or openable lid or base to facilitate assembly or repair of the keyboard. The housing is preferably of an electrically conductive non-magnetic material such as stainless steel, aluminium or the like. Alternatively, the base may be permenantly attached to the housing in which case, the base may be welded or otherwise joined to the housing.

In the preferred embodiment, the housing comprises a base plate 20 and a top plate 22. The top plate has side panels 24 which depend therefrom and which have a lip 26 to which the base plate 20 may be abutted to seal the housing. The base plate is joined to the lips 26 of at least one of the side panels 24 to form a lid and a sealing gasket 28 is provided between the lid and the remainder of the housing.

Each key 7 of the keyboard 1 is conventional in that they each comprise a head 13 and a stem 15. The stem 15 of each key is mounted on a post 16 provided with resilient biasing means 14 to return the key to its rest position after it has been depressed and subsequently released. The resilient biasing means may comprise a spring wound about or provided about the post 16, one end of the spring bearing against the underside of the key stem 13 and the other bearing against the topside of the housing 5 or against part of the outer housing 3. The tn key heads each have a letter, numeral or other indication applied thereto to indicate the designation of each key.

As mentioned above, there are currently a very large number of keyboards available which all have very similar keys and internal components. Accordingly, the structure of the keys and internal components will not be 30 described in detail herein.

6 Each of the keys 7 is provided with a magnet 17 mounted on the base of the stem. Sensing means 30 are provided within the housing, one for each key. Each sensing means comprises, in the preferred embodiment, a hall effect sensor which detects movement of the magnet attached to the end of the key stem and 5 outputs an electrical signal in response thereto.

In this preferred embodiment, depression of the key 7 causes the magnet 17 mounted on the base of the stem 15 to be moved towards the associated hall effect sensor. As the magnet 17 approaches the hall effect sensor 30, so the C sensor detects the magnet and outputs an electrical signal to scanning means (not shown) which is employed to scan for key depression. Thresholding means may be provided so that a signal is output only once the key has been depressed by more than a predetermined amount. Once the scanning means detects depression of a key, it refers to a code store (not shown), such as a look-up table, to determine a digital code relating to that key. The digital code is then outputted to an output where it can be transferred to the equipment with which the keyboard is being used. The exact operation of the scanning means and code store is conventional and will not be ftu-ther described herein.

It can be seen therefore that the present arrangement alleviates the problems associated with the prior art devices by providing a keyboard wherein the internal components are totally sealed from the external environment. Furthermore, as the housing is completely sealed, so there is no possibility of dirt, moisture or the like migrating into the keyboard as a result of an external seal failure. In addition, as the housing is conductive it provides an effective shield against EM radiation (both incoming and outgoing), and is particularly effective against RF radiation. Thus, the present arrangement is particularly well suited for use with sensitive electronic components. The keyboard according to the present arrangement could even be used underwater.

It will be understood, of course, that the invention has been described herein by way of example only and that modifications may be made within the scope thereof.

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Claims (15)

1. A keyboard comprising: a plurality of resiliently biased keys mounted for reciprocal movement upon depression against the resilient bias; magnet means attached to each of said keys and moveable therewith; an electrically conductive non- magnetic housing having an internal chamber that is sealed from the external environment; and respective sensing means provided within said internal chamber, movement of one of said keys and associated magnet means towards a respective one of said sensing means causing the respective sensing means to output an electrical signal indicative of the movement of the associated key and magnet means.

2. A keyboard according to Claim 1, comprising means provided within said internal chamber for scanning for electrical signals outputted by said sensing means and for outputting an identification signal to identify which of said keys has been depressed.

A keyboard according to Claim 1 or Claim 2, wherein said one or more sensing means each comprise a hall effect sensor.

4. A keyboard according to any of Claims 1 to 3), wherein said one or more magnet means each comprise a permanent magnet.

5. A keyboard according to any of Claims 1 to 4, comprising an outer guard fittable over the housing and having one or more apertures therein through which a respective one of said keys extends.

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6. A keyboard according to Claim 5, wherein said keys are supported from the underside of said guard.

7. A keyboard according to Claim 5, comprising a key mounting plate by means of which said keys are supported, the mounting plate being provided between the housing and the guard.

8. A keyboard according to any preceding claim,. wherein the housing R comprises a base plate, and a top plate having side panels depending from each edge thereof, the side panels each terminating in a lip to which the base plate is secured.

9. A keyboard according to Claim 8, comprising a sealing gasket provided between the side panel lips and the base plate.

10. A keyboard according to any preceding claim, wherein the housing is of a non-magnetic metal.

A keyboard according to Claim 10, wherein the housing is of aluminium.

12. A keyboard according to Claim 10, wherein the housing is of stainless steel.

1 3).A keyboard according to any of Claims 1 to 9, wherein said housing is of an electrically conductive non-magnetic plastic material.

14. A keyboard according to any preceding claim, wherein each of said keys comprises a key head, and a key stem locatable on a post, the resilient biasing means being provided about the post.

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15. A keyboard substantially as hereinbefore described with reference to the accompanying drawings.