PYROELECTRIC KEYBOARD

Abstract: Non-contact electrical keyboard switch (10) apparatus which is immune to effects of cross-talk and unaffected by the presence of any EMI radiation. The apparatus includes at least one heat source, preferably IR (24). The heat energy from the heat source (24) is directed onto a selected pyroelectric polymeric film (30) which generates a coded or uncoded signal in response to the heat energy applied to the film when a key (14) is depressed. Means (26) are described for directing the heat energy from the heat source (24) to selected pyroelectric films (30).

Description: Pyroelectric Keyboard Stat ment of the Invention This invention relates to keyboard applications which utilize the pyroelectric properties of poled polymeric films possessing piezoelectric and pyroelectric properties. Background and Summary of the Invention A key switch is capable of generating a voltage sign l when an instant force is applied to the switch. The resultant voltage signal may be employed in applications involving computers, alphanumeric keyboards, kitchen appliances, intrusion detectors and numerous other electroni devices. Conventional metal contact key switches become unreliable after extended periods of usage. For example, contact resistance tends to increase with age, and poor contact at the contact points produce undesirable chattering and/or bounce. In an effort to overcome the general unreliability of metal contact key switches, Hall effect key switches employing magnetic resistance elements, or capacitive key switches have been developed, each requiring elaborate or complicated parts and/or controlling circuits. Mora recently, poled polymeric piezoelectric films functioning as the pressure sensing component have been developed, which films substantially overcome the deficiencies of metal contact key switches, as well as the deficiencies inherent in piezoelectric ceramics, which are hard, brittle, easily broken, difficult to machine into complex shapes, and often generate spurious voltage signals from sound waves bouncing off their surfaces. Generally, polymeric materials are non-piezoelectric. Polyvinylidene fluoride (PVDF) however, may be made piezoelectric. PVDF is approximately 50% crystalline and 50 amorphous. The principal crystalline forms of PVDF are the highly polar β form and the non-polar a form. High piezo an # pyro response is associated with the polar β form. By._ . carefully controlling process steps to polarize the film, including mechanical orientation and treatment in an intense electric field, a highly piezoelectric and pyroelectric film results. Such a film is commercially available under the trademark KYNAR®, a product of Pennwalt Corporation, Philadelphia, PA. , assignee of the presen invention. Copolymers of vinylidene fluoride, and copolymerizable comonomers such as tetrafluoroethylene and trifluoroethylene for example, may also be advantageously employed as the pyroelectric film material of the present invention. It is essential that keyboards provide a definite, reproducible and recognizable signal at each key site. Attempts to create these signals by means of stress applied to the film, i.e., utilizing the piezo properties 7 thereo.f, often result in faulty signals being generated when keys are non-uniformly depressed by fingers, each of the stressed films being supported at its respective- key well. Similarly, if the film is secured with greater or lesser tension on the key wells, signals derived ma be erratic. If,, however, the pyroelectric properties of the film ar utilized, film tension is not a critical factor. In U.S. Pat. No. 3,539,723, means are disclosed for generating coded electrical signals when light is reflected from code markings on- a type* bar, the reflected coded markings being sensed by photoelectric means. Such apparatus requires expensive photoelectric code-sensing elements, a plurality of threshold circuits as well as keying circuits. The present invention requires non of the above, and makes use of inexpensive poled pyroelectri polymeric film capable of generating reliable signals even after being exposed to millions of bursts or pulses of heat energy from a controlled heat source. Briefly, the present invention discloses a pyroelectric keyboard which is unaffected by the presence of EMI radiatio and is immune to the effects of cross-talk. The pyroelectri film associated with the keyboard generates signals when hea energy, preferably from an IR source, is reflected from a selected portion of a key shaft, or the heat energy is redirected through channeled guides provided in the key shaft, preferably square in cross-section, onto the pyroelectric polymeric film, suitably -electrically connected Since- the film is not physically contacted by the key mechanisms and is therefore not stressed or flexed, the film should be capable of constant usage over very extended periods. Brief Description of the Drawings FIG. 1 is a fragmentary plan view of the keyboard of th present invention, a portion of the key p-late being cut away to show the location of the heat sources. FIG. 2 is a sectional view of the device of FIG. 1 take 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 ±s a sectional view of a portion of the device o FIG. 2 illustrating a key in operative position. FIG. 5 is a sectional view similar to FIG. 2 showing modified key shafts, one in operative position; and FIG. 6 is a sectional view similar to FIG. 5, showing coded intelligence being reflected onto the pyroelectric fil from a depressed key. Detailed Description of the Invention In FIG. 2 a fragment of a keyboard of an alphanumeric computer 10, for example, is provided with rows of keys 12. Keys 12 have key caps 14 for identifying a key with a particular letter, number, control code, and the " like. The mechanism for permitting- the individual keys 12 to be depressed and returned to their original undepressed position, as well as means for support of the keys, are conventional and well known, and may readily be adapted by one skilled to the operation of the key mechanism used in th present invention. Referring additionally to FIGS. 2 and 3, each key 12 _ includes a key shaft 16, preferably square or rectangular in cross-section. Key shafts 16 are depressable within square or rectangular vertically disposed bores 18 formed throug -.a- key plate 20. Plate 20 is provided with a plurality of aligned rows of circular passageways 22 corresponding to row of keys 12 (FIG. 1). A source of heat energy 24, typically infra-red, is disposed within or adjacent to each passageway 22. Thus, 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 (FIG. 2) Each of key shafts 16 is provided with circular connecting channels, i.e., horizontally disposed channels 26 and vertically disposed channels 28, the former communicatin with heat passageways 22 while the latter communicate with pyroelectric film members 30 secured on keypad 32. Pyroelectric film members 30 are provided with conventional metallic film coatings 34 and 36 at their upper and lower surfaces respectively, the upper surfaces conveniently led t a common ground and the lower surfaces conventionally connected to electrical connectors (not shown) associated with the keyboard or other ' application. Passageways 22 are preferably slightly larger in diameter than channels 26 and 28. Plate 20 is provided with recesses 40 at its upper surface in order to partially receive key caps 14 therein to aid in maintaining vertical alignment of key shafts 16 and t limit their downward movement. When a key 12 is depressed a shown in FIG. 4, IR hea ' energy 25- from source 24 flows through passageway 22 to enter channels 26 and 28 to be directed onto pyroelectric film 30, the rather abrupt temperature change thereof, even though slight, creating a minute increase in the volume of the pyroelectric polymeric film 30 with a concomitant distortion of its dipole alignmen altering the electric field therewithin, with the resultant generation of a signal voltage therefrom. Passageway 22, shown to the right of key shaft 16 of FIG. 4, is unstippled indicating an absence of heat energy flowing therethrough when key shaft 16 is in its depressed or operative position. In FIG. 5, heat energy 25 from IR source 24 is directed longitudinally through plate 20 by means of passageways 22 until it strikes angled reflecting surface 42, suitably a mirror, provided at a bottom portion of the key shaft 16 which is depressed, i.e., the key disposed intermediately th three keys illustrated. The heat energy 25 is directed onto pyroelectric film 30. - " In the embodiments illustrated in FIGS. 2, 4 and 5 of the drawings, since only uncoded intelligence or messages ar transmitted, each key site must be continually scanned by conventional scanners or central processing units seeking on-off switches, i.e., voltages at certain sites. The embodiment illustrated in FIG. 6 however requires n key site scanning since each key shaft includes an angled surface 44 wherein strips or patterns of heat absorbing material (typically black) are printed or otherwise provided on a heat reflecting surface (typically a mirror) to yield a coded message or intelligence 46 which identifies the depressed key. Since the messages are coded, each may readily be fed into a common guide or channel for processing The metallic film coatings 34 and 36 for the ground electrodes and signal generating or detecting electrodes respectively may be conveniently deposited on the polymeric film by a conventional silk screening process, for example. The pyroelectric film 30 -may have a thickness ranging betwee about 6μ to HOμ , and preferably 16 to 50μ . Thicknesses for electrodes 34 and 36 may typically be about 5 to 7μ . The ground electrode 34 may, of course, contact key pad 32 rathe than the negative or detecting, electrode 36. Keys 12, comprising key caps 14 and key shafts 16, as well as key plate 20 and key pad 32 may be made from a suitable plastic material. Key- pad 32 is provided with supporting feet 48 and may include registration pins (not 5 ' shown) for maintaining the key pad in proper registration with key plate 20. Pyroelectric film 30 is placed physically close to the redirected or reflected heat energy, especially in the embodiment illustrated in FIG. 6, in order to minimize any 1.0 loss of definition of the reflected coded intelligence. Heat energy from. IR heat source 24 may.be regulated by well known means, as by a potentiometer, for example. Controlling the heat output from source 24 insures that the * pyroelectric films farthest removed from the source will be 15- subjected to adequate heat pulses or energy to generate the desired signals. In lieu of separate heat sources 24, a single heat source may be employed with branches diverting therefrom to provide substantially uniform heat energy to each row of 20 keys. Heat source 24 is not limited to an IR emitter. Heat from any suitable source that is capable of being absorbed b the coatings and polymeric film may be used. It is appreciated that the gradual heating and cooling 25 of the poled pyroelectric film generates no signals. Thus, typical ambient temperature variations or dissipated heat from source 24 present no barriers to the successful operation of the present apparatus.

Claims: I CLAIM: 1. A.non-contact electrical keyboard switch apparatus for heat sensitive applications comprising a keyboard including a plurality of rows of aligned key devices, at least one source of heat energy proximate to said keyboard, means for directing heat energy from said heat source t each of said key devices, a keypad supporting a plurality of poled pyroelectric polymeric films, each of said films in spaced registration with one of said key devices, each of said key devices having means for redirecting heat energy .directed thereto from said heat source, and other means for generating an output signal by said pyroelectric film when said key device is depressed and said redirected heat energy is directed onto said film. 2. Apparatus of claim 1 wherein said keyboard is associated with a key plate, said key plate having spaced bores therethrough, said key devices including a key shaft each being vertically depressable within one of said bores, said key shafts having means for redirecting heat energy directed thereto onto said pyroelectric film 3. Apparatus of claim 1 wherein one of said heat sources i provided for each row of said key devices. 4. Apparatus of claim 2 further characterized by said key plate being substantially horizontally disposed and having horizontally disposed passageways therethrough, each of said passageways registering with a respective one of sai rows of said key shafts and bores associated therewith, each of said passageways intersecting each of said bores associated, with respective one of said rows of said key shaf s. 5. Apparatus of claim 4 wherein said key shafts are square or rectangular in cross-section and said bores throug said key plate are matingly configured. 6-. Apparatus of claim 5 wherein said means for redirecting heat energ directed to each of said key shafts onto said pyroelectric film comprises a heat energy channel guide within said key shaft, said channel guide permitting * * » heat energy to be directed from a passageway onto said pyroelectric film when said key shaft is in a depressed position. 7. Apparatus of claim 5 wherein said means for redirecting heat energy directed to each of said key shafts onto said pyroelectric film comprises a pair of interconnected channels within said key shaft, one of said channels being horizontally disposed in communication with a passageway and other of said channels being vertically disposed and communicating with said pyroelectric film. 8 ' . Apparatus of claim 5 wherein said means for redirecting heat energy directed to each of said " key shafts onto said pyroelectric film comprises .a heat reflecting surface. 9. Apparatus of claim 8 ' wherein said heat reflecting surface comprises a mirror. 10. Apparatus of claim 8 wherein said heat reflecting surface comprises a mirror with stripes or patterns of heat absorbing material provided thereon wherein heat energy reflected therefrom comprises coded intelligence. 11. A. non-contact electrical keyboard switch apparatus for- heat sensitive applications, said keyboard being immune to the effects, of cross-talk and unaffected by the presence of EMI radiation, said apparatus comprising a keyboard including a plurality of rows of aligned key devices having key shafts associated therewith, at least one source of IR heat energy proximate to said keyboard, means for permitting heat energy from said heat source to be directed to each of said key shafts, a keypad supporting a plurality of poled pyroelectric polymeric films thereon, each of said films in spaced registration with each of said key shafts, each of said key shafts having means for redirecting heat energy directed thereto from said heat source, and other means for generating an output signal by said pyroelectric film when a key shaft is in a depressed position permitting said redirected heat energy- to be directed onto said pyroelectric film.

Inventors: RADICE PETER F, RADICE, PETER, F.
Applicants: RADICE PETER F, RADICE, PETER, F.
Application year: 1986
Main classification: H03K17
IPC codes: H03K17