Keyboard venting.

Field of the Invention

0001This invention relates to keyboard systems. More parti­cularly, this invention relates to keyboard systems for elec­tronic devices such as calculators.

Background of the Invention

0002There are many types of keyboard systems in use in vari­ous types of electronic devices such as calculators. Some of these keyboard systems, such as are found in some portable calculators, involve the use of a dome sheet over a printed circuit which is in turn supported or carried on a relatively rigid substrate.

0003The dome sheet includes a plurality of domes in a prede­termined pattern which is in registry with a pattern of switch locations on the printed circuitry. When a dome is depressed or collapsed by finger pressure it causes a corresponding con­nection to be made in the underlying switch in the printed circuitry. This may be effected by finger pressure directly on the dome or indirectly by finger pressure on a key button positioned over the dome.

0004When the components are clamped together or bonded during manufacture, air is trapped under each dome. This air must be vented in some manner to enable the dome to be depressed or collapsed when striking a key. Venting is also required to allow the air pressure to equalize (e.g., when changing alti­tude such as on an airplane). Venting prevents mushiness and improves the tactile feel of a key when it is depressed.

0005Previous keyboards of this type have included a spacer sheet between the dome sheet and the printed circuitry. A series of slots were die cut in the spacer sheet to allow for air to be forced out from beneath a dome when the dome is depressed or collapsed.

0006However, on a large multi-keyed keyboard, the presence of numerous slots causes the spacer sheet to be flimsy and diffi­cult to handle and assemble with the other components.

0007Another type of keyboard which is used includes membrane switches which comprise spaced-apart parallel conductors at each switch site. When the upper conductor is deflected down­wardly to contact the lower conductor an electrical connection is made. The air which is present between the two conductors should be vented in some manner to prevent mushiness of key action.

0008The present invention provides a system which represents an improvement in venting techniques in a keyboard such as is used in a calculator, for example.

Summary of the Invention

0009In accordance with the present invention there is pro­vided an improved keyboard comprising in one embodiment: <ul id="ul0001" list-style="none"><li>(a) a rigid base member including an upper surface and a plurality of channels;</li><li>(b) electrical circuitry on a support carried by the upper surface of the base member, the circuitry defining a plurality of open switches in a predeter­mined pattern of switch sites;</li><li>(c) a plurality of flexible, resilient domes covering said circuitry and being in registry with the pat­tern of switch sites; wherein the underside of each dome includes a conductive surface which is capable of completing an electrical connection at a switch when the dome is deflected downwardly against the circuitry.</li></ul>

0010Each switch site communicates with at least one of the chan­nels in a manner such that air present under a dome is forced into one of the channels when the dome is deflected downward­ly.

0011The provision of channels in the upper surface of the base member avoids the need for die cutting a spacer sheet. In fact, the spacer sheet could be left out, if desired. Even where the spacer sheet is used, there is no need to cut slots in it.

0012In another embodiment the electrical circuitry includes membrane switches comprising spaced-apart parallel conductors at each switch site. When the upper conductor is deflected downwardly to contact the lower conductor, the air present between the two conductors is forced into a channel in the base member via an aperture. A dome may also be positioned over, and in registry with, each switch site.

0013If desired, a key button may also be positioned over each switch site. Finger pressure is then applied to the key button.

0014Other advantages of the venting system of the invention will be apparent from the following detailed description.

Brief Description of the Drawings

0015The invention is described in more detail hereinafter with reference to the accompanying drawings wherein like reference characters refer to the same parts throughout the several views and in which: <ul id="ul0002" list-style="none"><li>FIGURE 1 is a cross-sectional view of one embodiment of keyboard system of this invention;</li><li>FIGURE 2 is a cross-sectional view of the embodiment of Figure 1 in which the dome over the switch has been depressed or collapsed to make a connection and close the switch;</li><li>FIGURE 3 is a top view illustrating a common form of switch used in a keyboard;</li><li>FIGURE 4 is a top view illustrating interconnected chan­nels in the keyboard;</li><li>FIGURE 5 is a cross-sectional view of another embodiment of keyboard of the invention which includes venting to the atmosphere through the base member;</li><li>FIGURES 6 and 7 are cross-sectional views illustrating another embodiment of keyboard of the invention which utilizes membrane switches.</li></ul>

Detailed Description of the Invention

0016In the drawings there is illustrated a keyboard embodi­ment 10 of the type which is useful, for example, in a port­able calculator or any other electronic device including switches and a keyboard.

0017The keyboard includes a rigid base member 12 which may be, for example, metal, plastic, etc. It is dimensionally stable and may vary in thickness so long as it retains its shape and provides a firm support.

0018The base member 12 includes a pattern of channels 14 which may all be interconnected to provide a pathway for air movement when a dome is depressed or collapsed, as described in more detail hereafter. Each switch site on the printed circuit communicates with at least one such channel. If desired, all of the channels may interconnect with each other. The channels may have varying cross-sectional configurations so long as they are capable of allowing air to move there­through when a dome is depressed.

0019Preferably there are at least three switch sites communi­cating with a single channel in the base member when there is no venting to the atmosphere so that the air from one of the switch sites can be adequately dispersed when such switch is actuated by pressing the dome downwardly. Of course, by making the volume of each channel greater, it is easier to alleviate the extent of air compression when a single switch is actuated.

0020As another alternative, a chamber may be provided in the base member into which air may be forced when a switch is actuated. If the base member is thin, however, this may not be entirely satisfactory.

0021As illustrated in the drawings, the channels are provided in the upper surface of the base member. It is possible for the channels to be located below the upper surface so long as there is an appropriate aperture communicating between each switch site and a channel.

0022The printed circuitry comprises a thin dielectric layer 16 on which the required conductive paths are located. The thickness of the layer 16 may vary, but it preferably is thin and flexible. At each switch site there may be a plurality of interdigitated, spaced conductive fingers 17 and 17A, as illustrated in Figure 3.

0023Although the width of each such finger may vary, a width of about 0.005 to 0.020 inch is common. Similarly, the spacing between adjacent fingers may vary, although a spacing of about 0.005 to 0.020 inch is also common.

0024Other arrangements of conductors may also be used at each switch site. All that is required is that there be two or more spaced conductors present which will complete an electri­cal connection when contacted with another conductor. For example, the conductors may be in parallel, spaced arrangement or in a spiral arrangement, etc. Three pole switches may also be used if desired.

0025Overlying the printed circuitry there is preferably included a spacer member 18. This spacer is preferably in the form of a sheet having a uniform thickness and having openings or cut-outs in a pattern which corresponds with the locations of the switch sites.

0026The spacer member is preferably a dielectric material, and it preferably has a thickness in the range of about 0.005 inch. A typical spacer member is polyester film (which may be rigid or flexible). Alternatively, the spacer member may be conductive so long as it is electrically insulated from the printed circuitry.

0027Positioned over the spacer member is the dome sheet 20. This sheet includes a pattern of raised domes 24 which are in registry with the switch sites on the printed circuitry. When the sheet is dielectric material the bottom surface of each dome includes a thin conductive layer or coating 22. For example, layer 22 may comprise a conductive ink or conductive particles in a polymerized coating.

0028Each dome may be formed in the dome sheet by means of heat and pressure, for example, when the sheet is plastic. The dome sheet is flexible and resilient so that each dome can be depressed or collapsed by means of finger pressure and will then return to its original shape and position when the finger pressure is released.

0029The size of each dome is normally the same. Preferably each dome is circular and has a diameter of about 0.25 inch. Other sizes may, of course, be used in this invention.

0030When finger pressure is used to depress or collapse a dome (e.g., as illustrated in Figure 2) the conductive layer 22 on the underside of the dome comes into contact with the interdigitated fingers 17 and 17A on the printed circuitry at a switch site. At the same time the air present under dome 24 is forced through aperture 14A and into channel 14. This allows the air to dissipate through the channel system. If desired, there may also be included a vent aperture 14B com­municating between channel 14 and the atmosphere, as illus­trated in Figure 5. This is not required, however, and could allow moisture to enter the keyboard.

0031The spacer sheet 18 is optional, It's presence is pre­ferred, however, because it increases the distance which the dome can travel as it is being depressed or collapsed. This provides a better "feel" to the key being operated.

0032The domes may be integral with a sheet as illustrated in the drawings, or the domes may be individual components posi­tioned over and in registry with the switch sites. The dome sheet may be dielectric (e.g., plastic) or it may comprise a thin metal sheet (e.g., cold rolled stainless steel). As another alternative, there may be provided strips which each include a plurality of domes.

0033The dome sheet may be bonded to the top of the circuitry (or to the top of the spacer member, if present) or it may be clamped in place.

0034In Figure 6 there is illustrated another embodiment of keyboard 30 of the invention which includes spaced-apart, parallel conductors 34 and 35 as a membrane switch on base member 37. A spacer member 33 is positioned between the con­ductors 34 and 35 except in the area of the switch site. A dome sheet 31 having dome 31A may be positioned on top of the structure, as illustrated, with a spacer member 32 positioned between the dome sheet and the upper conductor 34, except in the area of the switch site.

0035The upper surface of the base member includes a channel 36 which communicates with the air space between the conduc­tors 34 and 35 via aperture 36A in the lower conductor 35. This allows air present between the conductors to exit and enter the channel 36 when the conductor 34 is deflected down­wardly to contact conductor 35 and actuate the switch. If desired, conductor 34 may also include an aperture to enable air present under the dome to enter into the channel when the dome is depressed or collapsed.

0036Layers 34 and 35 are thin and may comprise metal or, alternatively, may comprise plastic or other such dielectric material with a conductive matter on the opposing surfaces of layers 34 and 35.

0037Dome sheet 31 may be metal or plastic. Because the elec­trical connection for the switch is made when layer 34 con­tacts layer 35, it is not necessary for the underside of dome 31A to be conductive.

0038Figure 7 illustrates another embodiment of keyboard 40 of the invention which includes membrane switches. One such mem­brane switch is illustrated. It includes spaced-apart paral­lel layers 42 and 43 which are separated by spacer member 41 except in the area of the switch site. When the upper layer 42 is depressed or deflected downwardly to contact layer 43, air present between the two layers is forced out through aper­ture 46A in layer 43 into channel 46 in the upper surface of base member 44. If desired, the channel may communicate with the atmosphere.

0039Other variants are possible without departing from the scope of the present invention.