Magnetically snap actuated contact keyboard apparatus

This invention relates to keyboards for alphanumeric and data entry applications in general and specifically to magnetically detented snap actuators and keyboard apparatus incorporating the same.

Magnetic snap actuation keyboards are widely known since the breakaway characteristic of magnetically detented devices has often been exploited in patent literature to provide the sudden snap actuation that is desirable for keyboard applications. The designs have been of two general sorts: either an actuator plate is broken free from a fixed magnet or a movable magnet is broken free from a fixed plate.

Thus, German patent DE-A-3 119 227 describes a snap switch or detented actuator which comprises a pair of stationary separate contacts, a permanent magnet adjacent and laterally spaced from the contacts and an actuator plate of magnetically permeable electrically conductive material which is positioned to lie in contact with the magnet. This actuator plate has a part extending laterally and upwardly therefrom and positioned to be depressed and provide a moment tending to separate the actuator plate from the magnet.

A keyboard using such detented actuators wherein actuator plates are lying in contact with magnet before the depression of the key overcomes the magnetic attraction, is described in the Article "Spring and magnet keyboard actuator" by K. Lennon, published in the IBM Technical Disclosure Bulletin, Vol 24, n° 8, 1982.

But none of these prior arts describes an actuator wherein a wiping action of the contacts is performed during the snapping action.

In view of the foregoing shortcomings in the known prior art, it is an object of the present invention to provide an improved magnetically detented keyboard structure with a minimum of assembly parts and a maximum of shared function structure in which numerous functions are performed by the same element or elements, and in particular a wiping function of the contacts.

The object of the invention is therefore a magnetically detented actuator comprising a circuitboard having a pair of stationary physically separate contacts, a permanent magnet adjacent to the contacts and laterally spaced from them, and an actuator plate of magnetically permeable electrically conductive material positioned to lie in contact and in magnetic attraction with the permanent magnet, the actuator plate having one angled lever arm extending laterally and upwardly therefrom and positioned to be depressed and provide a moment tending to separate the actuator plate from the permanent magnet. The actuator plate has electrically conductive portions being integral spring fingers which are maintained in contact with the stationary physically separate contacts as long as the lever arm is not depressed and the actuator plate is lying in contact with the permanent magnet, and the permanent magnet tends to retain the actuator plate and the integral spring fingers thereof in contact with the permanent magnet as the lever arm is depressed, thereby causing a sliding, wiping action between the physically separate contacts and the integral spring fingers to occur until depression of the lever arm finally overcomes the magnetic attraction between the actuator plate and the permanent magnet in a sudden release that breaks electrical contact between the integral spring fingers and the physically separate contacts.

Another object of the invention is a keyboard comprising a baseplate, a circuitboard having a plurality of pairs of electrical contacts thereon and a plurality of conductor lines thereon connected to the contacts, a plurality of permanent magnets mounted on the circuitboard adjacent to the pairs of electrical contacts, and a plurality of angled magnetically permeable electrically conductive actuator plates each positioned to lie in contact and magnetic attraction with a magnet and having electrically conductive portions in the form of integral spring fingers, each actuator plate having one lever arm extending laterally and upwardly therefrom and positioned to be depressed and provide a moment tending to separate the actuator plate from the magnet. The baseplate has a plurality of upstanding locator posts, and the circuitboard has apertures therein to align it over the locator posts. The electrically conductive portions of the actuator plates are each in contact with one of the electric contacts. Each magnet tends to retain the associated actuator plates and integral spring fingers in contact with the magnet as the angled lever arm is depressed, causing a sliding, wiping action between the physically separate contacts and the integral spring fingers until depression of the lever arm finally overcomes the magnetic attraction between the actuator plate and the magnet in a sudden release that breaks electrical contact between the integral spring fingers and the physically separate contacts, the plates each having an aperture therein for placement over the locator posts.

The invention will be described with reference to preferred embodiments thereof as more fully depicted and explained with reference to the drawings in which:

• Figure 1A illustrates a horizontal cross section schematic through a single magnetically detented key actuator position of a preferred embodiment of the invention.
• Figure 1B illustrates a horizontal schematic cross section of the apparatus depicted in Figure 1A in the actuated condition.
• Figure 2A illustrates a plan view of an individual angled plate actuator. Figure 2B illustrates a side elevation of the angled actuator in Figure 2A.
• Figure 3A illustrates schematically an exploded horizontal view of the various elements in the simplified structure of a second preferred embodiment of the invention.
• Figure 3B illustrates in greater detail the layered assembly approach for the preferred embodiment illustrated in Figure 3A.
• Figure 3C illustrates an enlarged schematic view of a portion of the assembly that results in the embodiment of Figures 3A and 3B.
• Figure 4 illustrates a single key actuator position in enlarged form.
• Figure 5A illustrates an enlarged horizontal schematic of a single key actuator mechanism in the unactuated position.
• Figure 5B illustrates the same mechanism as Figure 5A but in the actuated position.
• Figure 6 (including figures 6A, 6B, 6C and 6D) illustrates an overall electrical schematic diagram of a microprocessor driven scanned keyboard system as a preferred embodiment of the invention.
• Figure 7 illustrates an enlarged partial cross section in schematic form of a third preferred embodiment of the invention.

Turning to Figures 1A and 1B, a schematic enlarged cross section of a first preferred embodiment of the invention in the at rest and in the actuated condition, respectively, are illustrated. In Figure 1A, the positioning or baseplate 1 may be formed of plastic or steel or other material as desired. Steel offers the advantage of electromagnetic radiation shielding, electrical grounding possibilities and high structural integrity but molded and/or plated plastics can offer much the same with the exception of the same high physical strength. A number of individual locator posts 2 of which one appears in Figure 1A may be formed integrally with the baseplate 1 by slitting and stamping in the case of a steel or metallic plate or by molding in the case of plastic. The posts 2 would be spaced at regular intervals correlated with the desired keybutton spacings and positions in the assembled keyboard.

A circuitboard or circuit card 3 of insulating material such as an epoxy laminate, sheet polyamide or the like may be employed. An aperture 4 in the circuit card 3 facilitates registering the circuit card precisely over the locator posts 2 on the baseplate 1. Circuitry 12 in the desired artwork pattern may be formed using well known techniques on the surface of the circuitboard 3. A contact 11 which may be spherical as shown in Fig. 1A or hemispherical or any other generally dome shape may be attached to the circuitry 12 as a contact. Two of these contacts are utilized for each key actuator position, but only one is shown in Figure 1A, lying directly behind it.

A snap actuator 5 in the form of an angled thin spring steel plate comprises a body slit to form two side arms 10 and a central angled tongue or tab 13, leaving an angled end extension or lever arm 6 is illustrated in cross section. The part 2 passes through a slit 14 (Fig. 2A) which forms the tongue or tab 13 which serves as a stop against post 2 when actuator 5 is moved as shown in Figure 1B. The locator post 2 in the slit 14 locates the actuator 5 that the side arms 10 align with the contacts 11 at each key position.

A top frame 9 (part of which only appears in Figs. 1A and 1B) is apertured to receive key buttons 8 (of which only one appears in Figs. 1A and 1B) of which a key stem 7 is arranged to slide in a housing 9 which may form a part of the top frame so that when pressure is applied to the top of a key button 8, the bottom of stem 7 will contact the lever arm 6 of the actuator plate 5. A permanent magnet 16 is placed on top of the circuitboard 3 and overlies the circuitry 12 as shown. The magnet 16 may be a molded plastic permanent magnetic material well known in the industry as flexible plastic strip magnets and it may be adhesively applied to lie between the contact balls 11 and the locator posts 2 in elongated strips (Figures 3A to 3C). By magnetic attraction, the magnet 16 will attract the actuator plate 5 which must be made of a ferromagnetic steel or stainless steel or some other magnetically permeable material. Magnetic type stainless steel is preferred since it resists corrosion and contamination better than ordinary steels.

Contact between the ends 10 of the spring steel actuator plates 5 and the individual contact balls 11 comprising each key location occur when the plate 5 is attracted to the magnet 16 as shown. Because of the spherical nature of the contact 11 bearing against the flattened contact finger 10 which is integrally formed in the end of the magnetic actuator plate 5, high contamination resistance is achieved. In addition, due to the break away characteristic of the magnet and the flexibility of the actuator plate 5, a slight wiping action occurs between the contact portion 10 of the plate 5 and the fixed hemispherical contact 11 on the circuitboard 3. This provides a cleaning action well known in the art.

Figure 1B illustrates the elements of Figure 1A when the key button 8 has been fully depressed to the point that break away of the actuator plate 5 from the magnet 16 has occurred and the stop tongue 13 has been brought into abuttment with the locator post 2. Continued downward pressure on key button 8 will flex lever arm 6 providing the necessary overtravel so desirable in key mechanisms. Eventually, the lever arm 6 will contact the top of the circuitboard and a high resistance to increased deflection will immediately result.

A logic level high voltage such a 5-volt DC is supplied to all of the key positions in a keyboard so that for each key position such as illustrated in Figure 1A, one of the contact balls 11 is supplied with 5-volt potential. The other ball 11 is connected to ground and interconnection between the two balls at each key location is via the actuator plate 5 with its integral contact spring fingers 10. Thus, when the actuator is in the actuated position such as shown in Figure 1B, shorting between the two contact balls 11 is interrupted and the high voltage potential of 5 volts may be scanned by a scanner as will be described later and found to be present at the specific key location which has been actuated.

As is apparent from Figures 1A and 1B, when sufficient force has been applied to the top of key button 8 and transmitted to the actuating lever arm 6 of the actuating plate 5, the magnetic attraction to plate 5 will be broken and the actuator plate will snap to a stop condition where stop post 13 contacts locating post 2. Additional deflection of the arm 6 is also possible as has been previously described.

Turning to Figure 2A, a plan view of an individual actuator plate 5 is shown. It may be seen that the plate is actually one integral piece of material that has been formed by stamping or slitting or chemical machining or other operation of similar sort. A slit 14 frees a tongue or tab portion 13 to be bent upward at an angle from the main body 5 to serve as the stop post as shown in Figure 1A, 1B and 2B. Individual contact spring fingers 10 are formed in the end of the actuator plate 5 as illustrated and the lever arm 6 is formed by bending the plate 5 at location 15 as shown in Figure 2B.

As will be easily understood by those skilled in the art, a total assembly of key positions in a typical keyboard may be easily manufactured utilizing the structure as shown in Figures 1A and 1B for the preferred embodiment. First a baseplate 1 is formed with appropriate locating posts 2. Then a circuitboard with die cut apertures corresponding to the spacing of the locating posts and the baseplate 1 is positioned on top of the baseplate and the magnets 16 are laid in place over the top of the circuitboard. Then, individual actuators 5 are positioned over the locator posts 2 which protrude through the individual slots 14 in each actuator 5. This precisely locates the actuator plates 5 so that the spring fingers 10 will align with the contact balls 11 at each key position. Then a keyboard frame top 9 containing numerous key buttons can be placed over the entire structure and assembly is complete. The actuator 5 is made from a single piece of material and formed by stamping or slitting or chemical machining and the like.

An even more simplified embodiment is illustrated in Figure 3A through 3C.

Figure 3A illustrates a schematic horizontal exploded section of a second preferred embodiment of the invention. In Figure 3A, the base plate 1 is made of molded plastic material that can be sensitized and have plated directly on it the entire circuit pattern and contacts 11 and 12. Individual strip magnets 16 can then be laid down adjacent the locator posts 2 and the actuator plates 5 put in position as previously disclosed. The overall unitary top cover and frame 9 with individual key actuator buttons 8 can then be dropped in place and located over locating and snap fit posts 17 to complete the assembly.

Figure 3B illustrates pictorially the assembly steps and dramatically illustrates the simplicity of structure and manufacturing steps involved for this embodiment. It will be observed that the baseplate 1 is actually the lower housing of the overall keyboard and has integrally molded with it the contacts 11, the locating posts 2, and the circuitry 12 interconnecting the various contacts as necessary. The form of the individual strip magnets is shown and the individual actuator plates 5 in a typical key button array are also shown. The upper housing and frame portion 9 holds the individual tops of key 8 as depicted.

Figure 3C illustrates an enlarged partial pictorial view of a section of the assembled structure from Figures 3A and 3B. It may be observed that the individual locator posts 2 serve the purpose of providing a registration point for registering the magnet 16 as well as providing the location points for the individual actuators 5 (not shown in Figure 3C). The individual circuit lines 18 making up the printed circuit 12 are plated directly in place on the base plate or frame 1 as are the individual contacts 11 associated with each key position. Only one contact at each key position is supplied with a conductor 18, the other contact 11 being connected to ground through a common connection to the base of frame 1 (not shown).

Turning to Figure 4, an enlarged pictorial view of one assembled actuator plate 5 in position over a locator post 2 and having spring finger contacts 10 engaging the contacts 11 when the plate 5 is attracted to magnet 16 is illustrated.

Figures 5A and 5B illustrate diagramatically the structure as shown in Figure 4 in two stages of actuation. In Figure 5A, the actuator is in its rest position and spring finger contacts 10 are in electrical and physical contact with the individual contacts 11 that are connected as previously described to the circuitry 12, not shown. The actuator plate 5 is attracted by magnet 16 and the stop post 13, preferably bent upward at an angle of approximately 55°, is out of contact with the locator post 2. The angled upward lever arm 6 which is an integral part of the actuator plate 5 may be supported at its fulcrum point as shown or may be fulcrummed on the post 2.

In Figure 5B, a downward force has been applied to arm 6 and contact between the contacts 10 and 11 has been interrupted since force applied to arm 6 has been depicted as great enough to have caused breakaway to have occurred between the magnet 16 and the actuator plate 5. Magnetic adhesion always exists between the angled plate and the fulcrum. This allows the mechanism to function when completely inverted. The magnetic attraction dampens bounce to the point of virtual non-existence. Also, the keyboard is significantly less susceptible to vibration The stop post 13 is in position against the locator post 2 and further deflection of arm 6 is possible to provide an overtravel feel that is desirable in the art.

As is evident from the discussion so far, beam spring or spring finger actuators of the type depicted in the figures can be formed either with flat fingers 10 or with a dome portion in the end of each finger 10. If the end of the fingers 10 is formed into a hemispherical pad, the keyboard may be made with flat contact pads 11 on the circuitboard 3. While this has not been illustrated, its variation will be apparent to those of skill in the art. The hemispherical contact on the circuitboard, which is the alternative illustrated in the figures, has some desirable attributes beyond that of a flat contact 11 in that actual contact point is elevated above the substrate of the frame or circuitboard so that any contamination in the form of dust, dirt, or liquid has a chance to run off from the actual contact points.

A wiping action is achieved during actuation by making the height of the actual contact point slightly greater than the thickness of a magnet 16. This causes a slight deflection in the spring finger ends 10 of the actuator 5 as depicted in the figures. Overall assembly is greatly simplified since the base plate or positioning plate 1 can have the locator post 2 integrally formed in it by stamping or molding. The steel actuators 5 can be located over the posts as can the circuitboard 3 and the actuators will be held in place by the magnet strip 16 so that the unfinished assembly may be easily handled from station to station and have the entire top cover or frame 9 with individual buttons 8 and return springs (not shown) dropped in place. Alternatively, the spring lever arm 6 of individual actuator plates 5 may serve as the key button return spring.

When an individual key button 8 is depressed sufficiently, a force is exerted on the actuator plate 5 sufficient to cause breakaway from the magnet 16 which interrupts the circuit that has been completed between the contacts 11 via the integral spring contact fingers 10 in plate 5. This will be registered in a scanning microprocessor as will be described briefly below. The operator pushing key button 8 experiences a touch sense of instantaneous snap action that is very desirable for keyboard applications. The actuator plate 5 actually lifts off of magnet 16 initially and is followed by the spring fingers 10 which forms a wiping action on lift-off that is repeated in reverse upon closure of the contacts. The self-wiping feature results in high reliability contacts as will be appreciated by those skilled in the art. In addition, the magnetic attractive forces between the actuator plates 5 and the magnetic strip 16 greatly reduce contact bounce upon closure. The magnetic damping action upon release is also effective. The overall result is that the contacts are self-cleaning, wiping and have a high anti-tease function because of the sudden breakaway that is achieved in the irreversible fashion due to the stored energy of the spring arm 6.

The overall design is also suited to an overlay style of keyboard if the baseplate 1 is used actually as a top cover and the tabs or posts 2 are bend downward. Using this technique, with appropriate spacers and overlays, a nomenclature sheet can be placed over the arm 6 of the actuator plates 5 as is depicted in Figure 7.

In Figure 7, for example, an overlay sheet 50 with individual nomenclature 51 that can be supported on a top plate 52 having an aperture 53 aligned with the lever arm 6 of an actuator plate 5 attracted to a magnet 16 on a circuitboard 3 can be built. The contact arm 10 is shown of the formed spring finger type to make contact with a flat contact 11 on the circuitboard 3. A spacer post 54 keeps the top plate 52 at the desired spacing above the baseplate or circuitboard 3.

As will be apparent to those skilled in the art, the touch or sense of feel provided can be easily varied by varying the width of the actuator plates 5 that are in contact with the magnet 16. Alternatively, the size of the magnetic strip 16 can be modified to offer a menu of different key touch and sense options for an individual preferred result, i.e., high, medium or low force keyboard actuation. Alternatively, the contacts 10 and 11 can be made between the stop post 13 and the locator post 2 to form a normally opened switch structure instead of a normally closed one such as that illustrated in the foregoing figures.

The second preferred embodiment described above with relation to Figures 3A through 3C and Figure 4 illustrates an embodiment in which the manufacture or assembly is made most convenient and the number of parts employed is greatly reduced as will be appreciated by those skilled in the art.

Turning now to Figure 6, an overall electrical schematic generically applicable to any of the physical embodiments of the present invention is shown.

In Figure 6, individual switch contacts 11 are schematically shown with normally closed switches comprising actuators 5 and spring fingers 10 as schematically illustrated. Individual ground conductors 18 are commonly connected together and to ground so that voltages applied on the supply lines 18A for each switch position will be shunted to ground through the normally closed switch contacts.

In the embodiment of the circuitry illustrated in Figure 6, a control microprocessor 19 directs the overall scanning of the key locations in a manner well known in the art. The microprocessor may be, for example, an Intel type 8048 or its equivalent, many of which have been commercially available for a number of years. Similar microprocessor based keyboard scanners exist for both capacitive and resistive circuitry and are commercially available. Hence, no great detail is indulged in at this time and the overall embodiment will only be briefly described.

An interface plug 20 supplies 5-volt DC, an electrical ground and the data and clock input/output ports to the keyboard. The 5-volt DC potential is labeled 29 as it appears at numerous points within Figure 6. The microprocessor 19 has an internal crystal oscillator that may be trimmed or regulated with the leads 22 connected to a tank oscillator circuit 23 as schematically depicted.

In operation, the microprocessor 19 steps continuously through a sequence of operations in which a specific drive code is applied on lines 24 to select one of the six illustrated 16 to 1 decoder selector chips 25. All that is required is that an individual port P10 through P15 be activated by the processor 19 to strobe an individual decoder selector chip 25 to determine whether any keys connected to its inputs have been actuated. The individual decoder selector chips may be the Texas Instrument type SN54150 16 to 1 data selectors multiplexors that are well known in the industry.

These chips are constructed in such a fashion that an input on any one of the 16 possible inputs will be gated to an output when the appropriate selection code is applied at ports A, B, C, and D.

The selection code is produced by the processor 19 as a key scan and sense code appearing at ports P20 through P23 and outputted on lines 26. Inverter amplifiers are connected in these lines to produce on lines 27 the select signals A, B, C and D that are applied in common to each of the six decoder selectors 25. However, only that decoder 25 that has its decode select on from one of the lines 24 will actually decode the lines A, B, C and D. If a key has been depressed on a decoder that has been selected, and a match finally occurs between the A, B, C, D code produced by the key scan and sense output applied to the A, B, C, D inputs to the decoder selector chip 25 to which that key is connected, a 5-volt DC signal will be outputted to the OR inverter gates 31 or 30 to which the individual decoder selector chips 25 are connected. This level will be inverted in an inverter 32 or 33 and applied to a common OR gate 34 to supply an input on line 28 to the processor 19 indicating that an activated key has been found at the particular decoder 25 selected at this time by one of the lines 24 and at a key location identified by the key sense code A, B, C, D appearing on lines 26. The processor 19 can then output the appropriate data from a stored memory table associated with the given key that has been found to be actuated and this data appears on line 21 at the output from the processor 19.