(IR 2813)

Cross-Reference to Related Applications This application is a con tinuat ion-in-part of co pending U.S. Serial No. 789,268, filed on October 18, 1985 The speci ication, drawings and claims of U. S. Serial No 789,268 are incorporated herein by reference as if se forth in full.

Background of the Invention The present _t , invent ion is directed toward th application and use of pyroelectric transducers i alphanumeric keyboards, and in particular, pyroelectri transducers made of Kynar® piezo film. Specifically, th invention is directed toward overcoming the problem associated with three conventional keyboard configurations conventional contact switches; photoelectric detectors; an piezoelectric pressure contacts.

Pyroelectricity is the phenomenon by which a electric potential is produced across certain crystals o polymers by the application of thermal energy. Th resulting electric potential produced is directl proportional to the rate of change in temperatur experienced by the crystal or polymer. Pyroelectri transducers typically have the following properties: large pyroelectric coefficient; high volume resistivity low dielectric constant; low dielectric loss; low specifi heat; low density; and a broad usable temperature range Good pyroelectric materials also exhibit response times o the order of nanoseconds, and are largely immune t electromagnetic interference.

Kynar ^® piezoelectric film, a commercially available product of Pennwalt Corporation, Philadelphia, PA. , assignee of the present invention, has been found to possess excellent pyroelectric properties and can be fabricated into a pyroelectric transducer. Copolymers o polyvinylidene fluoride, and copolymerizable comonomers such as tetraf luoroe thylene and trif luoroethylene , fo example, may also be advantageously employed as suitabl pyroelectric films. The small heat capacity of Kynar piezo film provides a rapidly responding linear therma detector for infrared and millimeter waves. Pyroelectri transducers composed of Kynar® film also exhibit tim responses on the order of several nanoseconds

Pyroelectric transducers composed of Kynar ^® film i keyboard applications have advantages over conventional ke switches and contacts. Conventional metal contact ke switches, long an industry standard, become unreliabl after extended periods of usage. Typically, the contac resistance of the switch tends to increase with age, an poor contact at the contact points can produce undesirabl chattering or bounce. In an effort to overcome the genera unreliability of metal contact key switches. Hall effec switches, employing magnetic resistance elements, an capacitive key switches have been developed. However, Hal effect switches and capacitive key switches generall require elaborate and complicated parts and/or contro circuits.

Attempts to create reliable key signals by mean of piezoelec ic pressure sensitive films, while substantial improvement, have not always proved successful Piezoelectric pressure films occasionally produce fault signals when the keys are non-uniformly depressed by th user. Similarly, if the film is secured with greater o lesser tension on the key wells, the signals produced ma be erratic. Pyroelectric transducers, on the other hand have the advantage over contact switches and piezo pressur films of not relying upon direct mechanical contact betwee parts.

Photoelectr ic sensors have been incorporated into keyboards to generate coded electrical signals upon the inci ence of reflected or direct light. hile photoelectric keyboards represent an improvement over metal contact switches, photoelectric sensors require expensive photoelec ric code-sensing elements, a plurality of threshold circuits and keying circuits. In addition, photoelectric sensors generate a single voltaic output upon the incidence of light energy. Accordingly, they have typically required complex switching and timing mechanisms in order to produce digitized signals. Pyroelectric transducers, by contrast, provide output signals of varying amplitudes based upon the rates of change in incident temperature, and no output signal when temperature is constant. This feature of pyroelectric transducers simplifies the engineering problem of digitizing and decoding signals, and facilitates the application of pyroelectric transducers in keyboards.

It is an object of the present invention to overcome the problems associated with conventional keyboards and to incorporate the features and properties of Kynar ^® pyroelectric film in order to create a keyboard which is activated by thermal radiation, and which is capable of generating reliable signals even after being exposed to millions of bursts or pulses of heat energy from a controlled heat source.

It is another object of the present invention to provide a pyroelectric keyboard which is unaffected by the presence of electromagnetic radiation and is immune to the effects of cross-talk.

It is still another object of the present invention to provide a keyboard in which the pyroelectric film associated with the keyboard can generate individualized pyroelectrically produced signals which are representative of the respective key being struck, and can be decoded utilizing conventional decoding circuitry.

Summary of the Invention

The present invention comprises a pyroelectric keyboard. The keyboard has plurality of key devices, at least one source of heat energy proximate to said keyboard, means for directing heat energy from said heat source to each of said key devices, and means for supporting a plurality of poled pyroelectric polymeric films. Each of the films is in registration with one of the key devices. The key devices each have means for redirecting heat energy directed thereto from the heat source onto the poled pyroelectric polymeric films, so as to generate an output signal. In one embodiment of the invention, the redirected heat energy generates a characteristic waveform. Brief Description of the Drawings

FIG. 1 is a partial plan view of a pyroelectric keyboard, a portion of the key plate being cut away to show the location of the heat sources.

FIG. 2 is a sectional view of the keyboard of FIG. 1 taken along line 2-2 thereof.

FIG. 3 is a sectional view of the key shaft of FIG. 2 taken along line 3-3 thereof.

FIG. 4 is a sectional view of a portion of the device of FIG. 2 illustrating a key in operative position.

FIG. 5 is a sectional view of a second embodiment i which IR radiation is reflected onto a pyroelectri transducer by a reflective beveled surface.

FIGS. 6-8 display a time-lapse sequence of th operation of the keyboard of another embodiment of th disclosed invention.

FIG. 9 is an enlarged view of the operation of th pyroelectric key shown in Fig. 7.

FIG. 10 is a bottom plan view of the beveled edg taken along line 10-10 of Figure 9.

Detailed Description of the Invention

Referring to FIG. 1, a fragment of a keyboard 1 according to the invention is provided with rows of key 12. Keys 12 have key caps 14 for identifying a key with a

particular legend (e.g., a letter, number, control code, o the like) . Referring now to FIGS. 2 and 3, each key 1 includes a key shaft 16 which is preferably square o rectangular in cross-section. Key shafts 16 ar depressible within square or rectangular verticall disposed bores 18 formed through a key plate 20. Keys 12, comprising key caps 14 and key shafts 16, as well as ke plate 20 may be made from a plastic material.

The mechanism for permitting the individual keys 1 to be depressed and returned to their original undepresse position, as well as means for support of the keys, ar conventional and well known, and ^' may readily be adapted b one skilled to the operation of the key mechanism used i the present invention. Electrical circuitry may b utilized to automatically depress the keys at a constan velocity.

Plate 20 is provided with a plurality of aligned row of circular passageways 22 corresponding to rows of keys 1 (FIG. 2). A source of heat energy 24, typically infra-re (IR) radiation, is disposed within or adjacent to eac passageway 22. V7hen no key is in a depressed position, heat energy 25, represented by stippled markings , continuously flows through passageways 22 until it passe out into the atmosphere at 22A. Heat energy from IR hea source 24 may be regulated by well-known means, such as b a potentiometer. Controlling the heat output from sourc 24 insures that the pyroelectric films situated farthes from source 24 will be subjected to adequate heat pulses o energy.

In lieu of separate heat sources 24, a single hea source may be employed, for all passageways 22, wit branches diverting therefrom to provide substantiall uniform heat energy to each row of keys. In addition, hea source 24 is not limited to an IR emitter. Heat from an suitable source that is capable of being absorbed by th coatings and polymeric film may be used.

Each of key shafts 16 is provided with circula connecting channels, i.e., horizontally disposed channel

26 and vertically disposed channels 28. The former are i communication with heat passageways 22 while the latter ar in communication with pyroelectric film members 30 secure on keypad 32. Passageways 22 are preferably slightl larger in diameter than channels 26 and 28.

Pyroelectric film members or transducers 30 ar provided with conventional metallic film coatings 34 and 3 at their upper and lower surfaces, respectively. The uppe surfaces are connected to a common ground and the lowe surfaces ^" are connected to electrical connectors (no shown). The metallic film coatings 34 and 36 for th ground electrodes and signal generating or detectin electrodes respectively may be, for example, deposited o the polymeric film by a silk screening process.

The pyroelectric film or transducer 30 should have thickness ranging from between about 6 to 110 microns and preferably 16 to 50 microns. Thicknesses fo electrodes 34 and 36 should typically be about 5 to microns. The ground electrode 34 may contact key pad 3 rather than the negative or detecting electrode 36.

Plate 20 is further provided with recesses 40 at it upper surface in order to partially receive key caps 1 therein to aid in maintaining vertical alignment of ke shafts 16 and to limit their downward movement. When a ke 12 is depressed as shown in FIG. 4, IR heat energy 25 fro source 24 flows through passageway 22 to enter channels 2 and 28 and onto pyroelectric film 30. This creates minute increase in the temperature of the pyroelectri polymeric film 30 with the resultant generation of a signa voltage therefrom. Passageway 22, shown to the right o key shaft 16 of FIG. 4, is unstippled indicating an absenc of heat energy flowing therethrough when key shaft 16 is i its depressed or operative position.

FIG. 5 illustrates an embodiment in which heat energ 25 from IR source 24 is directed longitudinally throug plate 20 by means of passageways 22 until it strikes beveled reflecting surface 42, for example a mirror provided at a bottom portion of each key shaft 16. T

heat energy 25 is directed onto pyroelectric film 30 when a key is depressed (for example, the center key in FIG. 5) , which generates an electrical impulse.

In each of the embodiments illustrated in FIGS. 2, 4 and 5 of the drawings, only uncoded intelligence or messages are created by depressing a key. Each key site mus therefore continually be scanned by conventional scanning circuitry or by a microprocessor or central processing unit in order to determine which key has been activated according to its position on a matrix. Such circuitry is well known to those skilled in the art.

Referring to FIGS. 6 through 10, a time lapse illustration of a keyboard having individually decodable elements is disclosed. In the previously disclosed keyboards, the pyroelectric element produced an identical signal upon key depression. The particular key depressed was identified by scanning circuitry and then decoded. In the embodiment disclosed in FIGS. 6 through 10, each individual key can be identified according to an individualized signature waveform, and scanning is unnecessary.

Referring to FIG. 6, the keyboard of this embodiment comprises keys 12' with square or circular key shafts 16' as disclosed hereinabove, except that each key has a beveled edge 42' similar to that shown and described in FIG. 5. The beveled edge 42' contains alternating horizontal strips or regions of infrared absorptive material 48 interposed between infrared reflective strips 50. The disposition of the alternate strips or regions is more clearly visible on the bottom plan view of the beveled surface ( FIG. 10) .

The heat reflective strips 50 can consist of a material such as aluminum. The strips extend perpendicular to the direction of key depression. In most applications, the strips will extend horizontally. The key shafts are depressible within square or rectangular vertically disposed bores 18' formed through key plate 20 'as described hereinabove.

Plate 20' is provided with a plurality of aligned rows of circular passageways 22' corresponding to rows of keys 12. A source of heat energy 24", typically infra-red, is disposed within or adjacent to each passageway 22" . When no key is in a depressed position, heat energy 25", represented by stippled markings, continuously flows through passageways 22' until it passes out into the atmosphere at 22A' . Pyroelectric film members o transducers 30' are provided as already described.

In operation, IR source 24' directs heat energy 25' longitudinally through plate 20' by means of passageway 22'. When a key is depressed, the beveled reflectin surface 42' breaks the plane of passageway 22' and come into contact with the stream of IR energy 25' . As th first reflective strip 50 located on beveled edge 42' come into contact with the stream of IR energy 25' , a beam of I 25'A i's reflected onto the pyroelectric transducer. Thi ge erates an electric signal corresponding to h instantaneous increase in the rate of temperature change a shown in FIG. 6A.

As the descent of the beveled key continues ove time, the second reflective strip breaks the plane passageway 22' and comes into contact with the stream of I energy 25*. This causes a second stream of 'IR 25' B t reflect onto the transducer, thereby instantaneousl increasing the rate of change of temperature of th. transducer. This results in the generation of a secon electronic pulse as shown in FIGS. 7A and 9.

As the key descends over time to a final, full depressed position, the third reflective strip breaks th plane of the incident IR radiation 25* transmitted i passageway 22'. This reflects a third stream of IR 25 ' onto the pyroelectric transducer, thereby furthe increasing the rate of change in temperature of th transducer. Thus, a third and final voltage step signal a shown in FIG. 8A is generated. (Naturally, an individua key can have more or less than three reflective strips.) When the key is released and returns to its origina

position, the respective reflected IR beams ar sequentially withdrawn from the poled polymeric transducer. The temperature of the transducer therefore drops linearl as each IR stream (25'A, 25'B, 25'C) is withdrawn. The ke is thus prepared for a subsequent depression. As with th previous embodiments, conventional electrical circuitry ma be utilized to automatically depress the key at a constan velocity.

The resulting waveform is , in e f fect , characteristic signature of the key which has bee depressed and the use of conventional rectifying an decoding circuitry known to those skilled in the art can b employed to decode the signals (FIGS. 6A , 7A, 8A) t produce a DC waveform centered at zero (FIGS. 6B , 7B an 8B) . As will be readily apparent to those skilled in th art, by varying the respective placement, widths, an position of the various reflective strips, a plurality o keys having unique key signature waveforms can b constructed . The rapid response time of Kynar pyroelectric transducers coupled with s ate-of-the-a decoder circuitry permits the construction of an entir keyboard composed of keys having unique signatur waveforms .

Further, the reflective material need not comprise a alternating series of horizontal reflective strips. A those skilled in the art will readily recognize, an configuration of alternating regions of reflective- mate ia which is capable of producing a signature waveform, wil fulfill the function of the invention.

The present invention may be embodied in othe specific forms without departing from the spirit o essential attributes thereof, and, accordingly, referenc should be made to the appended claims, rather than to th foregoing specification, as indicating the scope of th invention.