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EP0001882A1 - Depressible contactless key for generating electric signals in an electronic keyboard - Google Patents

Depressible contactless key for generating electric signals in an electronic keyboard Download PDF

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Publication number
EP0001882A1
EP0001882A1 EP78300393A EP78300393A EP0001882A1 EP 0001882 A1 EP0001882 A1 EP 0001882A1 EP 78300393 A EP78300393 A EP 78300393A EP 78300393 A EP78300393 A EP 78300393A EP 0001882 A1 EP0001882 A1 EP 0001882A1
Authority
EP
European Patent Office
Prior art keywords
piezoconductive
key
force
magnetic field
elastomer
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.)
Granted
Application number
EP78300393A
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German (de)
French (fr)
Other versions
EP0001882B1 (en
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.)
Olivetti SpA
TIM SpA
Original Assignee
Olivetti SpA
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 Olivetti SpA, Ing C Olivetti and C SpA filed Critical Olivetti SpA
Publication of EP0001882A1 publication Critical patent/EP0001882A1/en
Application granted granted Critical
Publication of EP0001882B1 publication Critical patent/EP0001882B1/en
Expired legal-status Critical Current

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    • 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 an elastomeric material which is conductive under pressure and suitable for use in keyboards of data processing equipment.
  • Elastomeric materials which are rendered conductive by adding materials such as carbon black or metal powders is the mix or composition.
  • Some compositions and processes for poducing conductive rubbers are given in the book: Conductive Rubbers as Plastics, by R. H. Norman - Elsevier, Amsterdam, London, New York, 100.
  • Elements of conductive rubber are used as contact materials in 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.
  • piezoconductive elastomers are used for producing fixed contact.
  • 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.
  • the ject of the invention is to provide an elastomer which becomes conductive under the effect of pressure and preserves this characteric for a number of operations of the order of at least some hundreds of nousands.
  • Fig. 2 shows a key 10 which uses a path 11 of piezoconductive elastomer according to the invention 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.
  • 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 spnerical 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 tron, 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 ⁇ .
  • 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, the 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 K ⁇ 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 according to the invention is shown in Fig. 3.
  • a single sheet 24 of piezoconductive material produced in a magnetic field in accordance with the invention 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.

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

Abstract

An elastomeric material conductive under pressure is suitable for use in a keyboard. When not compressed the material is insulating. When a key (21) is depressed, the pressure renders the material (11) conductive and completes a circuit (14, 11, 16, 17, 15). In order to prolong the life of the material when it is repeatedly compressed, a magnetic field is used during polymerization of an elastomer in which magnetic powder is dispersed. The material becomes piezoconductive in a preferred direction parallel to the applied field.

Description

  • This invention relates to an elastomeric material which is conductive under pressure and suitable for use in keyboards of data processing equipment.
  • Elastomeric materials (rubbers) are known which are rendered conductive by adding materials such as carbon black or metal powders is the mix or composition. Some compositions and processes for poducing conductive rubbers are given in the book: Conductive Rubbers as Plastics, by R. H. Norman - Elsevier, Amsterdam, London, New York, 100.
  • Elements of conductive rubber are used as contact materials in
    Figure imgb0001
    known types of keyboard.
  • For application in keyboards, 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.
  • Figure imgb0002
    piezoconductive elastomers are used for producing fixed contact. 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.
  • The ject of the invention is to provide an elastomer which becomes conductive under the effect of pressure and preserves this characteric for a number of operations of the order of at least some hundreds of nousands.
  • This prolem has been solved by means of the piezoconductive elastomerionterial according to the invention, as claimed in claim 1.
  • The invention will be described in more detail, by way of example, with reference to the accompanying drawings in which:
    • Fig. 1 is a front view of an apparatus for preparing an elastomer according to the invention;
    • Fig. 2 shows a key employing the piezoc:nductive elastomer according to the invention;
    • Fig. 3 shows a detail of a keyboard employing the elastomer according to the invention;
    • Fig. 4 is a graph relating to the key of Fig. 2;
    • Fig. 5 is a diagram of a measuring cirotit used for the graph of Fig. 4.
  • Fig. 2 shows a key 10 which uses a path 11 of piezoconductive elastomer according to the invention 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.
    Figure imgb0003
  • 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.
  • According to the known literature (B. E. Spingett: Conductivity of a system of metallic particles dispersed in an insulating medium - J. A. Phys., Vol. 44, No. 6, June 73, pp. 2925 - 26, and C. H. Kuist: Anisotropic conduction in elastomeric composites - Proc. 7 Am. Conn. Symposium, June 1974, pp. 203 - 209), on varying the percentage of metal powder in a matrix of insulating elastomer the conductivity of the whole shows a distinct transition from insulating material to conductive material for a well-defined percentage by volume (V ) of metal powder close to 0.2 and dependent to a certain extent on the grain size and on the shape of the metal granules, presenting piezoconductive characteristics for percentages by volume of metal powders a little lower than V . m
  • In particular in the article by C. H. Kuist, percentages of metal (nickel) powder by volume ranging between 0.08 and 0.18 are suggested for the piezoconductive rubbers.
  • It is known that the application of a magnetic field during the polymerization of rigid epoxy plastics materials containing metal powders (see the said book Conductive Rubbers and Plastics, page 82) brings a considerable increase in the conductivity of the whole in the direction of the magnetic field; it could therefore be expected from this that also with elastomers the application of a magnetic field during the polymerization would lead to a lowering of the transition percentage V m between the piezoconductive condition and the conductive condition in the preferred direction established by the magnetic field.
  • Surprisingly, it has been found that on dispersing nickel powders in a matrix of elastomeric binder, for example of the type Silastic E manufactured by Dow Corning, and maintaining the composition under the effect of a magnetic field during the polymerization of the binder, the rubber proves to be insulating in the absence of pressure even with percentages of powder between 15 and 27%, which greatly exceed the indicated limit values. On the other hand, the endurance of the piezoconductive characteristics improves decisively and passes from a few thousand operations of the key to several hundreds of thousands before irregularities of operation not tolerated by noraml electronic utilization circuits are encountered.
  • It has also been found that on exceeding these percentages, the riezoconductive characteristics become worse again and that the optimum value is found for percentages around 21%.
  • The preferred metal material is a nickel powder consisting of spnerical 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 tron, 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 150µ.
  • A preferred composition of the piezoconductive elastomer is constituted by:
    • Silastic E silicone rubber from Dupont: by weight: 30 parts;
    • 79 GS nickel powder from Baudier: 70 parts;
    • Silastic E hardener from Dupont: 3 parts.
  • 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, the 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 apparatus used for preparing the elastomer is shown diagrammatically in Fig. 1, in which a mould 31 of non-magnetic material, in which the elastomer mix 36 is cast, is between two pole pieces 32 and 33 a magnetizer 37 which are interconnected by an external magnetic circuit (not shown). The magnetic flux is maintained throughout the time of polymerization of the elastomer by the current flowing in two windings 34 and 35. During the polymerization, 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.
  • All the samples tested have exceeded the prescribed minimum life of 100,000 operations, with peaks of more than 1,000,000 operaticns.
  • 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 KΩ 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.
  • An alternative embodiment of a keyboard employing the piezoconductive rubber according to the invention is shown in Fig. 3.
  • In.the keyboard 23, a single sheet 24 of piezoconductive material produced in a magnetic field in accordance with the invention 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..
  • Springs 30, in combination with the movement of buttons 22, transmit the force applied to the buttons 22 to the piezoconductive sheet 24, causing locally the formation of passages of relatively low resistivity between the islands 26 and 29, while the material of the piezoconductive sheet 24 interposed between the keys 27 and not subjected to pressure maintains its insulating properties. The solution of 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.
  • Figure imgb0004
  • With this solution, it is possible to construct keys which simultaneously close a plurality of independent circuits by using a plurality of separate and insulated patches of piezoconductive material according to the invention or acting simultaneously on different points of the same sheet of piezoconductive material by means of actuating elements insulated from one another.
  • It is possible to make numerous variations in the solutions exemplified here as regards the type of elastomer and of magnetic conductive material, the form of the key, the level of modularity, that is the manner of grouping the keys, the actuating mechanism, and the production of contact between the piezoconductive material and the encoding circuit, without departing from the scope of the invention as claimed.

Claims (7)

1. Piezoconductive elastomeric material containing a magnetic metal powder dispersed in a matrix of polymerized elastomer, characterised in that the material is subjected to the action of a magnetic field during the polymerization, whereby it becomes piezoconductive in a preferred direction parallel to the direction of the magnetic field.
2. Material as in claim 1, characterised in that the percentage by volume of the powder is between 15% and 27%.
3. Material as in claim 1 or 2, characterised in that the
magnetic metal material is substantially a hard nickel powder with spherical granules having a diameter between 100 and 150µ.
4. Key for data processing equipment without movable contacts, characterised in that the force of actuation of the key acts on a piezoconductive material according to any one of the preceding claims.
5. Key as in claim 4, characterised in that the force of actuation acts on a patch of piezoconductive material.
6. Key as in claim 5, characterised in that the force of actuation acts to establish a contact at a predetermined point of a sheet of piezoconductive material.
7. Key as in claim 5 or 6, characterised in that the said force of actuation acts simultaneously on a plurality of patches of piezoconductive material or at a plurality of predetermined points of the sheet of piezoconductive material, cl7.osing a plurality of independent electric circuits.
EP19780300393 1977-11-07 1978-09-18 Depressible contactless key for generating electric signals in an electronic keyboard Expired EP0001882B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IT6948677A IT1091947B (en) 1977-11-07 1977-11-07 ELASTOMERIC MATERIAL CONDUCTOR UNDER PRESSURE
IT6948677 1977-11-07

Publications (2)

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

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Family Applications (1)

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EP19780300393 Expired EP0001882B1 (en) 1977-11-07 1978-09-18 Depressible contactless key for generating electric signals in an electronic keyboard

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EP (1) EP0001882B1 (en)
DE (1) DE2861435D1 (en)
IT (1) IT1091947B (en)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3034523A1 (en) * 1979-09-14 1981-03-19 Nissan Motor SWITCH AND DISPLAY DEVICE
EP0088132A4 (en) * 1981-09-16 1985-11-07 Toray Industries Transparent planar switch structure and switch unit.
DE3543890A1 (en) * 1985-12-12 1987-06-19 Thomson Brandt Gmbh Input element
WO1993004491A1 (en) * 1991-08-20 1993-03-04 Key Tronic Corporation. Inc. Single station cursor device suitable for keyboards
US5216316A (en) * 1989-12-18 1993-06-01 Ralph Ipcinski Piezo electric transducer

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2006176B2 (en) * 1969-02-24 1973-04-19 Sudduth, William B., Gloucester, Mass. (V.StA.) ELECTRIC SWITCH ARRANGEMENT
FR2182099A1 (en) * 1972-04-26 1973-12-07 Battelle Memorial Institute
CH547007A (en) * 1972-04-06 1974-03-15 Wifo Forschungsinst Ag PRESSURE-SENSITIVE ELECTRIC SWITCH, IN PARTICULAR FOR LOW CURRENT OR SIGNAL CURRENT.
DE1939642B2 (en) * 1969-08-04 1975-01-09 Standard Elektrik Lorenz Ag, 7000 Stuttgart Switch based on linear pressure for bounce-free switching
DE2729959A1 (en) * 1976-06-30 1978-01-05 Japan Synthetic Rubber Co Ltd PRESSURE SENSITIVE MANAGER

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2006176B2 (en) * 1969-02-24 1973-04-19 Sudduth, William B., Gloucester, Mass. (V.StA.) ELECTRIC SWITCH ARRANGEMENT
DE1939642B2 (en) * 1969-08-04 1975-01-09 Standard Elektrik Lorenz Ag, 7000 Stuttgart Switch based on linear pressure for bounce-free switching
CH547007A (en) * 1972-04-06 1974-03-15 Wifo Forschungsinst Ag PRESSURE-SENSITIVE ELECTRIC SWITCH, IN PARTICULAR FOR LOW CURRENT OR SIGNAL CURRENT.
FR2182099A1 (en) * 1972-04-26 1973-12-07 Battelle Memorial Institute
DE2729959A1 (en) * 1976-06-30 1978-01-05 Japan Synthetic Rubber Co Ltd PRESSURE SENSITIVE MANAGER

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
JOURNAL OF APPLIED PHYSICS, vol. 44, no. 6, June 1973, B.E. SPRINGETT: "Conductivity of a system of metallic particles dispersed in an insulating medium", pages 2925 to 2926 *
SEVENTH ANNUAL CONNECTOR SYMPOSIUM PROCEEDINGS, October 1974, Camden, New Jersey, (USA) CH. KUIST: "Anisotropic Conduction in Elastomeric Composites, pages 203 to 209 *

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3034523A1 (en) * 1979-09-14 1981-03-19 Nissan Motor SWITCH AND DISPLAY DEVICE
EP0088132A4 (en) * 1981-09-16 1985-11-07 Toray Industries Transparent planar switch structure and switch unit.
DE3543890A1 (en) * 1985-12-12 1987-06-19 Thomson Brandt Gmbh Input element
US5216316A (en) * 1989-12-18 1993-06-01 Ralph Ipcinski Piezo electric transducer
WO1993004491A1 (en) * 1991-08-20 1993-03-04 Key Tronic Corporation. Inc. Single station cursor device suitable for keyboards

Also Published As

Publication number Publication date
EP0001882B1 (en) 1981-12-09
DE2861435D1 (en) 1982-02-04
IT1091947B (en) 1985-07-06

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