EP0001882B1 - Touche à pression sans contact utilisable dans un clavier électronique - Google Patents

Touche à pression sans contact utilisable dans un clavier électronique Download PDF

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Publication number
EP0001882B1
EP0001882B1 EP19780300393 EP78300393A EP0001882B1 EP 0001882 B1 EP0001882 B1 EP 0001882B1 EP 19780300393 EP19780300393 EP 19780300393 EP 78300393 A EP78300393 A EP 78300393A EP 0001882 B1 EP0001882 B1 EP 0001882B1
Authority
EP
European Patent Office
Prior art keywords
piezoconductive
key
conductors
force
pair
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
EP19780300393
Other languages
German (de)
English (en)
Other versions
EP0001882A1 (fr
Inventor
Franco Dr. Varesio
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Telecom Italia SpA
Original Assignee
Ing C Olivetti and C SpA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ing C Olivetti and C SpA filed Critical Ing C Olivetti and C SpA
Publication of EP0001882A1 publication Critical patent/EP0001882A1/fr
Application granted granted Critical
Publication of EP0001882B1 publication Critical patent/EP0001882B1/fr
Expired legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H13/00—Switches having rectilinearly-movable operating part or parts adapted for pushing or pulling in one direction only, e.g. push-button switch
    • H01H13/70—Switches having rectilinearly-movable operating part or parts adapted for pushing or pulling in one direction only, e.g. push-button switch having a plurality of operating members associated with different sets of contacts, e.g. keyboard
    • H01H13/78—Switches having rectilinearly-movable operating part or parts adapted for pushing or pulling in one direction only, e.g. push-button switch having a plurality of operating members associated with different sets of contacts, e.g. keyboard characterised by the contacts or the contact sites
    • H01H13/785—Switches having rectilinearly-movable operating part or parts adapted for pushing or pulling in one direction only, e.g. push-button switch having a plurality of operating members associated with different sets of contacts, e.g. keyboard characterised by the contacts or the contact sites characterised by the material of the contacts, e.g. conductive polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C10/00—Adjustable resistors
    • H01C10/10—Adjustable resistors adjustable by mechanical pressure or force
    • H01C10/106—Adjustable resistors adjustable by mechanical pressure or force on resistive material dispersed in an elastic material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H13/00—Switches having rectilinearly-movable operating part or parts adapted for pushing or pulling in one direction only, e.g. push-button switch
    • H01H13/70—Switches having rectilinearly-movable operating part or parts adapted for pushing or pulling in one direction only, e.g. push-button switch having a plurality of operating members associated with different sets of contacts, e.g. keyboard
    • H01H13/702—Switches having rectilinearly-movable operating part or parts adapted for pushing or pulling in one direction only, e.g. push-button switch having a plurality of operating members associated with different sets of contacts, e.g. keyboard with contacts carried by or formed from layers in a multilayer structure, e.g. membrane switches
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H2201/00—Contacts
    • H01H2201/022—Material
    • H01H2201/032—Conductive polymer; Rubber
    • H01H2201/036—Variable resistance
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H2207/00—Connections
    • H01H2207/008—Adhesive means; Conductive adhesive
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H2227/00—Dimensions; Characteristics
    • H01H2227/002—Layer thickness
    • H01H2227/012—Conductive rubber
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H2227/00—Dimensions; Characteristics
    • H01H2227/002—Layer thickness
    • H01H2227/012—Conductive rubber
    • H01H2227/014—Conductive particles

Definitions

  • This invention relates to a depressible contactless key for generating electric signals in an electronic keyboard, e.g. for data processing equipment comprising a piezoconductive element formed of a matrix of insulating elastomeric material polymerized with a magnetic, metallic, conductive powder dispersed therein, the element having a flat shape with a pair of parallel large surfaces and extending between a pair of conductors, the key when depressed causing a compression spring to generate a force perpendicular to the said surfaces.
  • Elastomeric materials are known which are rendered conductive by adding materials such as carbon black or metal powders to the mix or composition.
  • Some compositions and processes for producing conductive rubbers are given in the book: Conductive Rubbers and Plastics, by R. H. Norman - Elsevier, Amsterdam, London, New York, 1970.
  • Elements of conductive rubber are used as contact materials in some known types of keyboard.
  • piezoconductive rubbers are more interesting, that is those rubbers which become conductive under the effect of applied pressure, because they allow keyboards without contacts exposed to oxidation to be obtained, inasmuch as contact takes place within the piezoconductive material.
  • Some piezoconductive elastomers are used for producing fixed contacts. In the known materials the piezoconductive effect disappears after a few thousand actuations of the elastomeric element, for which reason these materials are not suitable for use in keyboards.
  • a keyboard using such a piezoconductive rubber is known from the German Patent Specification 1,939,642, where the deformable piezoconductive element bridges two stationary contacts and is compressed through a spring urged member, upon depressing the key, to establish the electric connection of the two contacts.
  • a keyboard with such a piezoconductive material is however not reliable for the reasons stated above.
  • the object of this invention is to provide a contactless keyboard wherein the piezoconductive element is very sensitive to the depression and release of the key and preserves its characteristics over a very high number of actuations.
  • Fig. 2 shows a key 10 which uses a patch 11 of piezoconductive elastomer and can be employed to replace a normal contact-type key as an input device for a data processing apparatus, with an interface towards semiconductor electronic circuits of high input impedance.
  • a housing 12 of the key rests on a printed circuit board 13 on which there is formed an island 14 with a diameter of 8 mm and connected to one end of the contact circuit of the key.
  • the other end of this circuit is connected to another island 15 to which there is soldered a flexible metal plate 17 having a circular end 16 with a diameter of 8 mm.
  • the patch 11 of piezoconductive material which has a diameter of 8 mm and a thickness of 0.6 mm, is fixed by means of conductive adhesive between the island 14 and the circular end 16 of the flexible plate 17.
  • the force exerted is transmitted through the spring 18 and the end 16 of the flexible plate 17 to the patch 11 of piezoconductive rubber, reaching a value of about 10° when the button 21 strikes the top of the housway 12 of the key. Under the effect of the applied force, the patch 11 becomes conductive, ensuring a path of low resistivity between the islands 14 and 15.
  • the patch 11 For use of the key in a data entry keyboard, it is required that the patch 11 behave as a practically perfect insulator until the pressure applied reaches a predetermined value of about 80 g and to assume a low resistance when this pressure is exceeded, and then to reacquire the insulating properties on release of the key, presenting a certain hysteresis, but with a negligible delay. It is moreover essential that the patch preserves these characteristics for at least 100,000 operations of the same key, with a contact resistance always below 10,000 ohms.
  • the preferred metal material is a nickel powder consisting of spherical grains and having the maximum hardness compatible with preservation of the magnetic characteristics. More particularly, good results have been obtained with a nickel powder known by the trade name of Alloy 79 GS, supplied by the Baudier Company, of Liancourt (France).
  • the powder consists of 93.94% of nickel, 3.5% of silicon, 1% of iron, 1.6% of boron and 0.05% of carbon and has a Rockwell C hardness of 18-22; the spherical granules have a diameter between 100 and 150,u.
  • a preferred composition of the piezoconductive elastomer is constituted by:
  • Preparation of the piezoconductive elastomer requires careful mixing of the powder and silicone rubber, addition of the hardener, a first degassing of the mix under vacuum and casting in the mould followed by a second degassing under vacuum and introduction into the magnetizer, which applies a magnetic field with a direction perpendicular to the faces of the sheet during the polymerization of the binder.
  • the thickness of the sheet or film of piezoconductive elastomer may vary from 0.4 to 0.8 mm, preferred thickness being 0.6 mm.
  • the intensity of the magnetic field during the polymerization is not critical, provided that the field reaches an intensity of at least 500 oersteds. Above this value no appreciable variations are found in the results.
  • the magnetic flux is maintained throughout the time of polymerization of the elastomer by the current flowing in two windings 34 and 35.
  • the elastomer is kept at room temperature. Under these conditions, complete polymerization requires about 18 hours.
  • the time required for preparing the piezoconductive elastomeric material can be reduced to 10 minutes, still in a magnetic field, if the temperature of the mould 31 is brought to 100°C.
  • Fig. 5 shows a simple circuit used for detecting the characteristics of the key of Fig. 2, comprising a DC voltage generator 41 producing 5 V and a 50 KQ limiting resistor 42 in series with the key 10.
  • Fig. 4 is a graph of the voltage drop detected across the terminals 43 and 44 of the resistor 42 as a function of the force F applied to the key. The phenomenon of hysteresis between actuation and release of the key is obvious from the graph.
  • FIG. 3 An alternative embodiment of a keyboard employing the piezoconductive rubber is shown in Fig. 3.
  • a single sheet 24 of piezoconductive material produced in a magnetic field is used, instead of individual patches of piezoconductive elastomer as in the key of Fig. 2.
  • the sheet 24 is stuck by means of a conductive adhesive to islands 26 of a printed circuit board 25 which constitute one of the contact terminals of the keys 27.
  • a second, flexible, printed circuit board 28 is stuck by means of conductive adhesive on top of the sheet 24 of piezoconductive material at islands 29 in line with the islands 26.
  • the islands 26 and 29 constitute contact terminals of the keys 27.
  • Fig. 3 which is functionally equivalent to the modular solution of Fig. 2, is more convenient for producing keyboards with a large number of keys inasmuch as it drastically reduces the number of parts.
  • the maximum value of the actuating force applied to the keys a maximum value of 100 g is required. Since it has been verified that the number of operations which can be obtained before the occurrence of irregularities increases with the value of the force applied, the maximum number of operations in keyboards employing the piezoconductive elastomer according to the invention can be further increased if, instead of the actuating force being obtained directly from the key, it is obtained from a lever system which presses on the piezoconductive rubber with a force higher than, for example double, that applied to the key, with a proportionally smaller stroke.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Dispersion Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Push-Button Switches (AREA)

Claims (4)

1. Une touche enfonçable sans contact pour engendrer des signaux électriques dans un clavier électronique, comprenant un élément piézo-conducteur (11) formé par une matrice en une matière élastomère isolante polymérisée dans laquelle une poudre métallique, magnétique, conductrice est dispersée, l'élément ayant une forme plate comportant une paire de grandes surfaces parallèles et s'étendant entre une paire de conducteurs (14, 16), la touche lorsqu'elle est enfoncée provoquant la production par un ressort de compression (18) d'une force perpendiculaire auxdites surfaces, caractérisée en ce que l'élément piézo-conducteur est rendu anisotrope avec des propriétés piézo- conductrices prédominantes dans une direction perpendiculaire auxdites grandes surfaces par l'action d'un champ magnétique qui lui est appliqué pendant la polymérisation de la matière élastomère, l'élément piézo-conducteur ayant l'une des grandes surfaces en contact avec un premier conducteur fixe (14) de ladite paire et l'autre grande surface en contact avec l'autre des conducteurs (16) qui est déformable ou déplaçable sous la force engendrée par le ressort de compression (18) pour comprimer l'élément piézo-conducteur dans ladite direction de telle sorte que la connexion électrique des conducteurs est très sensible à l'enfoncement de la touche.
2. Une touche selon la revendication 1, caractérisée en ce que la poudre est une poudre de nickel dur formée de granules approximativement sphériques ayant un diamètre compris entre 100 et 150 µm et un pourcentage en volume dans la matière élastomère compris entre 15% et 27%.
3. Une touche selon la revendication 1 ou 2, caractérisée en ce qu'il est prévu une série d'éléments piézo-conducteurs, au moins l'un des conducteurs de la paire de conducteurs étant propre à chacun des éléments, la force étant agencée de façon à comprimer simultanément la série d'éléments.
4. Une touche selon la revendication 1 ou 2 dans laquelle l'élément est sous forme d'une feuille, caractérisée en ce que la feuille a une épaisseur constante et est comprimée par ladite force sur une surface limitée prédéterminée, le premier des conducteurs étant porté par un circuit imprimé rigide, le second conducteur étant porté par un circuit imprimé flexible, la feuille étant emprisonnée entre les deux circuits imprimés.
EP19780300393 1977-11-07 1978-09-18 Touche à pression sans contact utilisable dans un clavier électronique Expired EP0001882B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IT6948677A IT1091947B (it) 1977-11-07 1977-11-07 Materiale elastomerico conduttore sotto pressione
IT6948677 1977-11-07

Publications (2)

Publication Number Publication Date
EP0001882A1 EP0001882A1 (fr) 1979-05-16
EP0001882B1 true EP0001882B1 (fr) 1981-12-09

Family

ID=11312229

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19780300393 Expired EP0001882B1 (fr) 1977-11-07 1978-09-18 Touche à pression sans contact utilisable dans un clavier électronique

Country Status (3)

Country Link
EP (1) EP0001882B1 (fr)
DE (1) DE2861435D1 (fr)
IT (1) IT1091947B (fr)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5641618A (en) * 1979-09-14 1981-04-18 Nissan Motor Picture display switch
JPS5846532A (ja) * 1981-09-16 1983-03-18 東レ株式会社 透明面状スイツチ構造体およびスイツチ装置
DE3543890C2 (de) * 1985-12-12 1994-11-17 Thomson Brandt Gmbh Eingabetastatur
US5216316A (en) * 1989-12-18 1993-06-01 Ralph Ipcinski Piezo electric transducer
US5455556A (en) * 1991-08-20 1995-10-03 Key Tronic Corporation Single station cursor device suitable for keyboards

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1298089A (en) * 1969-02-24 1972-11-29 William Barber Sudduth Electric switch made of conducting elastomer
DE1939642B2 (de) * 1969-08-04 1975-01-09 Standard Elektrik Lorenz Ag, 7000 Stuttgart Auf linearem Druck basierender Schalter für prellfreies Schalten
CH547007A (de) * 1972-04-06 1974-03-15 Wifo Forschungsinst Ag Druckempfindlicher elektrischer schalter, insbesondere fuer schwach- oder signalstrom.
CH553066A (fr) * 1972-04-26 1974-08-30 Battelle Memorial Institute Procede de fabrication d'un ruban a conductivite electrique anisotrope.
US4292261A (en) * 1976-06-30 1981-09-29 Japan Synthetic Rubber Company Limited Pressure sensitive conductor and method of manufacturing the same

Also Published As

Publication number Publication date
IT1091947B (it) 1985-07-06
EP0001882A1 (fr) 1979-05-16
DE2861435D1 (en) 1982-02-04

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