SWITCH MATRIX KEYBOARD

Technical Field

The present invention is directed to a switch matrix keyboard and more particularly to a keyboard for use in data terminal devices which provides lead-through operation of the keys. Such lead-through operation provides instructions for an operator of the keyboard which key to depress next in a transaction.

Background Art

In order to reduce the overall cost of terminal devices, low cost membrane-type keyboards have been developed for use with terminal devices. This type of keyboard includes a plurality of substrates assembled to provide a compact structure with the top substrate having portions forming the keys of the keyboard. This type of keyboard is well suited where the keyboard is required to have a large number of keys. Where the circuit elements associated with the keyboard are small in structure and the number of keys are limited such as found in ten key keyboards, such circuit elements are easily secured to the rear surface of the keyboard. When the keyboard has a large number of key positions and the circuit elements are large, such as in the case of capacitors or other types of large circuit elements, it has been the procedure to locate these elements adjacent the keyboard within the terminal. The keyboard is connected to these circuits elements by the use of a ribbon cable. This type of construction lends itself to operating problems such as EMC interference due to the required use of the ribbon cable while also increasing the cost of the keyboard. Because of the membrane-type construction of the keyboard, it has been difficult to provide a lighting arrangement for lead-through operation of the keyboard.

GB-A-1542 558 describes a membrane-type construction of a keyboard with hight emitting diodes monted on a printed circuit board to provide selective illumination of the keyboard.

Disclosure of the Invention

It is an object of this invention to provide a keyboard in which the above disadvantages are alleviated.

Thus, according to the invention, there is provided a switch matrix keyboard for use in a data terminal device, including a keyboard cover means for supporting a switch matrix assembly and including a plurality of actuating members adapted for movement to a position engaging an associated portion of said switch matrix assembly, said switch matrix assembly being arranged to generate electrical signals in response to the movement of an actuating member to a position engaging the associated portion of said switch matrix assembly, and said switch matrix assembly includes first support means having a plurality of illuminating devices mounted therein and respectively aligned with said actuating members, each of said illuminating devices being operable to illuminate the associated one of said actuating members, and said switch matrix assembly serving to cause one of said illuminating devices to be operated in response to actuation of one of said actuating members, characterized by rotatably mounted switch means cooperatively associated with said switch matrix assembly and selectively rotatable to one of a number of predetermined possible positions relative to said switch matrix assembly, the setting of said switch means determining which of said illuminating devices is operated in response to actuation of one of said actuating members.

The advantage of the keyboard according to the invention is that, while it is capable of housing a large number of operating keys and a plurality of large circuit elements, it is compact, low in cost and provides for a lead-through operation of the keys.

In a preferred embodiment of the invention, a keyboard assembly is provided which includes a printed circuit switch matrix unit comprising a rigid printed circuit (P.C.) board together with all of the circuit elements associated with the operation of the keyboard mounted to the underside of the P.C. board. A layer of copper mounted on the top surface of the P.C. board is etched to provide a matrix of first electrical conductors forming one portion of the operating circuit of the keyboard assembly. A first insulating substrate having a plurality of apertures located therein is bonded to the electrical conductors. A second sheet of insulating material having a matrix of second electrical conductors secured to its underside is bonded to the first insulating substrate forming the other portion of the operating circuit. The switch matrix unit is mounted within a cover member which includes a transparent sheet of flexible material mounted on the cover member having printed thereon a plurality of key tip positions. Slidably mounted within a recessed portion of the cover member is a plastic sheet having key tip indicia printed thereon. Light-emitting diodes mounted on the underside of the P.C. board, within holes extending through the P.C. board, are selectively operated to illuminate selected key tip positions providing a lead-through operation of the key board assembly. Plated-through holes filled with an electrical conducting material are located in the P.C. board for interconnecting the circuit elements mounted on the lower surface of the P.C. board with the matrix of electrical conductors embedded in the top surface of the P.C. board. This arrangement provides an electrical path from the electrical conductors to the circuit elements upon depression of a key tip position of the insulating sheet. A key operated switching member mounted in the keyboard assembly is operated in conjunction with a plurality of light-emitting members for controlling various operating conditions of the keyboard assembly. A support member formed of a plastic material having a configuration to accommodate the switching member and the circuit elements is secured to the lower surface of the P.C. board for supporting the keyboard assembly within a data terminal device.

Brief Description of the Drawings

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

• Fig. 1 is an exploded view of a switch matrix keyboard in accordance with the present invention;
• Fig. 2 is a top view of the keyboard of the present invention;
• Fig. 3 is a partial side view of the keyboard of the present invention showing the mounting of circuit elements to the underside of a P.C. board and a portion of a supporting structure;
• Fig. 4 is a plan view of the lower surface of the keyboard of Fig. 1 showing the location of some of the surface mounted circuit elements, light-emitting diodes and associated electrical conductors;
• Fig. 5 is an enlarged exploded cross-sectional view of a portion of the keyboard of Fig. 1 with a portion of the printed circuit board removed;
• Fig. 6 is a partial cross-sectional view of the keyboard mounted in a data terminal cabinet;
• Fig. 7 is a partial side view of a key-actuated switch mechanism;
• Fig. 8 is a partial side view of an alternative key tip construction.

Best Mode for Carrying Out the Invention

Referring now to Fig. 1, there is shown an exploded view of the keyboard of the present invention, generally indicated by the numeral 18, which includes a flexible key tip sheet 20 fabricated of any type of transparent plastic material such as plasticized polyvinyl-chloride or urethane secured to the top portion of a cover member 22. The sheet 20 includes a plurality of key tips 24 printed thereon. As will be described more fully hereinafter, depression of any of the key tips 24 will result in the generation of binary signals representing a predetermined numerical value in a manner that is well known in the art. An alternative arrangement of a key tip construction is an array of raised key members 25 (Fig. 8) formed as part of sheet 20.

The keyboard assembly 18 further includes an indicia sheet 26 which is inserted within a recessed portion 27 (Figs. 5 and 6) of the cover member 22 (Figs. 1, 5 and 6) beneath the sheet 20. The sheet 26 can be of any type of flexible plastic sheet construction such as polyethylene upon which a plurality of information bearing indicia 28 can be printed. When inserted within the cover member 22, each of the printed indicia 28 will be positioned beneath an associated key tip 24, which, being transparent, will be identified with the indicia. It is obvious that by inserting other sheets 26 within the recess portion 27 of the cover member 22, each with a different set of indicia printed thereon, a wide variety of key operations can be programmed using a single keyboard of the terminal device.

The keyboard assembly 18 also includes a matrix switch unit, generally indicated by the numeral 29, mounted within the cover member 22 which includes a rigid printed circuit (P.C.) board 30, having a plurality of longitudinally extending conductors 32 (Figs. 5 and 6) embedded in the upper surface 31 of the P.C. board 30, a sheet 34 of insulating material such as mylar positioned adjacent the conductors 32, the sheet 34 including a plurality of apertures 36 each aligned with a key tip 24 in the sheet 20. The switch unit 29 further includes a flexible transparent plastic sheet 38 positioned between the sheets 26 and 34 which includes a plurality of longitudinally extending electrical conductors 40 embedded in the lower surface of the sheet 38 and extending at right angles to the conductors 32 in the P.C. board 30. In order to waterproof the matrix switch unit 29 from liquids spilled on the keyboard assembly, the switch unit 29 itself or at least the edges thereof may be sealed with a plastic or other type of waterproof material when mounted to the cover member 22 so as to prevent any liquid from entering into the area within the matrix switch unit where the conductors 32 and 40 would be exposed to the liquid's corrosive influence.

In a manner that is well known in the art, portions of conductors 32 and 40 located adjacent the same aperture 36 will make contact when the conductor 40 is moved through the aperture 36 by the depression of a key tip 24 aligned with the aperture 36. This contact generates binary signals representing the key tip 24 depressed.

Referring now to Fig. 2, there is shown, in dotted lines, a plan view of a data terminal device 42 which includes the keyboard 18 and a display 44. The keyboard 18 is mounted to the top cabinet surface 46 of the terminal device 42 in any conventional manner such as by hinge members 47.

As shown more clearly in Figs. 3, 4 and 5, mounted to the lower surface 48 of the printed circuit board 30 are a plurality of circuit elements 50 which form part of the operating circuit of the keyboard assembly which includes the conductors 32 and 40. also secured to the lower surface 48 of the printed circuit board 30 are a plurality of stand-off members 52 which mate with the cabinet structure 54 (Fig. 6) of the terminal device 42 to locate the keyboard within the terminal device 42. As shown in Figs. 4 and 5, the circuit elements 50 are connected to the ends of plated-through holes 56 located in the printed circuit board 30 by electrical conductors 58 which are formed by etching a layer of copper applied to the lower surface 48 of the printed circuit board 30. The plated-through holes 56 are filled with electrical conducting paste 60 and make contact with the electrical conductors 32. The paste 60 consists of a silver filled silicone material which is commercially available from the Tecknict Co. of Santa Barbara, California.

As shown in Figs. 4 and 5, the plated-through holes 56 may be located adjacent the circuit elements 50 or connect directly with the leads 51 of the circuit elements 50. As shown in Figs. 1 and 4, the P.C. board 30 further includes a plurality of apertures 60, each positioned adjacent one of the conductors 32 and in alignment with one of key tips 24 in sheet 20. Mounted in each of the apertures 60 is a light-emitting diode 62 (Fig. 5) which extends through and adjacent to the lower surface 48 of the P.C. board 30. The diodes 62 are connected to the circuit elements 50 by the conductors 63 and 58. When energized, each diode 62 will illuminate its associated key tip 24 to provide a lead-through operation of the keyboard assembly.

As shown in Fig. 1, located in each of the sheets 20, 38 and 34, and the P.C. board 30 are corresponding aligned apertures 64-70 inclusive in which is mounted a switch member 72 (Fig. 7), which may be key-actuated. Secured to the lower end of the switch member 72 by means of a screw 74 is an arm member 76 which is selectively positioned adjacent one of four infrared transmitter-receiver members 78 mounted to the lower surface 48 of the P.C. board 30. Each of the members 78 is connected to one of the circuit elements 50 by the conductors 58 (Fig. 4). When a key member 80 (Fig. 7) is inserted into the switch member 72, the arm 76 may be positioned in one of a number of predetermined positions adjacent one of the members 78 to reflect the infrared energy beam emitted from the member 78 back towards the member 78 enabling the member 78 to generate an electrical signal which controls the mode of operation of the terminal device. The signals generated by transmitter-receiver members 78 may, for example, turn the power supplied to the terminal device on or off or put the terminal device in a diagnostic or programming mode. This will determine which of the key tips will be illuminated for head-through operation. The transmitter-receiver member 78 is commercially available from the Optoelectronics Division of General Instrument Corp. of Palo Alto, California as Part. No. MCA7.

In mounting the keyboard 18 to the terminal device 42 (Fig. 1), a plastic support member 82 (Fig. 6) is secured to the lower surface 48 of the P.C. board 30 which includes recessed portions 84 formed to accommodate the exterior dimensions of each of the circuit elements 50 mounted to the lower surface 48 of the printed circuit board 30 in addition to the arm 76 of the switch member 72. The support member 82 together with the stand-off members 52 (Figs. 3 and 4) provides stiffness to the keyboard 18 when mounted to the cabinet structure 54 of the terminal device 42. The plastic material forming the support member 82 is commercially available from the General Electric Corp. of Selkirk, New York as Part No. PC180.

It will be seen that there has been provided a compact waterproof keyboard structure which provides lead-through operation of the keyboard by means of illumination devices working in cooperation with a key operated switch member controlling various operations of the keyboard. This structure does not require any external connecting wiring thus eliminating any electromagnetic interference with the operation of the keyboard.