CA1196985A - Touch sensitive switches - Google Patents
Touch sensitive switchesInfo
- Publication number
- CA1196985A CA1196985A CA000415528A CA415528A CA1196985A CA 1196985 A CA1196985 A CA 1196985A CA 000415528 A CA000415528 A CA 000415528A CA 415528 A CA415528 A CA 415528A CA 1196985 A CA1196985 A CA 1196985A
- Authority
- CA
- Canada
- Prior art keywords
- cell
- liquid crystal
- capacitance
- touch
- change
- 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
Links
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
- H03K17/96—Touch switches
- H03K17/962—Capacitive touch switches
Abstract
ABSTRACT OF THE DISCLOSURE
A touch sensitive switch comprises a liquid crystal cell and means for measuring capacitive changes when the cell is deformed by touch. The cell comprises a layer of a liquid crystal material between slides bearing electrodes, Capacitive changes are detected for example by a comparator or by a bridge circuit which includes one or more cells. Touching one cell unbalances the bridge. The area of cell that is touched may be coincident with or separate from a display area. For some types of cell extra sensitivity is achieved by maintaining a voltage across the cell between a critical and saturation value.
A touch sensitive switch comprises a liquid crystal cell and means for measuring capacitive changes when the cell is deformed by touch. The cell comprises a layer of a liquid crystal material between slides bearing electrodes, Capacitive changes are detected for example by a comparator or by a bridge circuit which includes one or more cells. Touching one cell unbalances the bridge. The area of cell that is touched may be coincident with or separate from a display area. For some types of cell extra sensitivity is achieved by maintaining a voltage across the cell between a critical and saturation value.
Description
~.g~
TOUCH SENSITIVE SWITCHES
The invention relates to touch sensitive switches.
There are many touch sensitive s~Jitches. Some rely on sensing a change in capacitance when touched by a human finger.
Examples of these are four~ in lifts (elevators) etc. ~.K. Patent Specification 1,553,563 describes a liquid crystal display having a front outer electrode that is touched by the operator to switch the display ON and OFF. The action of touching the front electrode chan~es the capacitance of circuits connected thereto.
This touch switch has the feature that the touched area also displays information, useful where a large number of switches are employed.
Another t~pe of touch switch uses a resilient upper sheet that i8 slighly deformed b~ touch. The flexible sheet carri~s rows of spaced electrodes separated from orthogonally arranged column electrodes on a fi~ed ba~e sheet. The two sets of electrodes form a matri~. On depressing the flexible sheet local contact 20' i9 ~ade between a row and a column electrode. With suitable materials small deflection~ of the fle~ible sheet are ~uEficient to cause contact between the two electrode~. U.~. Patent Specification No. 2,033,6~2 A describes ~uch a switch~ A
featu~e of this switch is that it is separated from any display it contrGl~ e.g~ an air traffic control cathode ray tube consol.
~$
TOUCH SENSITIVE SWITCHES
The invention relates to touch sensitive switches.
There are many touch sensitive s~Jitches. Some rely on sensing a change in capacitance when touched by a human finger.
Examples of these are four~ in lifts (elevators) etc. ~.K. Patent Specification 1,553,563 describes a liquid crystal display having a front outer electrode that is touched by the operator to switch the display ON and OFF. The action of touching the front electrode chan~es the capacitance of circuits connected thereto.
This touch switch has the feature that the touched area also displays information, useful where a large number of switches are employed.
Another t~pe of touch switch uses a resilient upper sheet that i8 slighly deformed b~ touch. The flexible sheet carri~s rows of spaced electrodes separated from orthogonally arranged column electrodes on a fi~ed ba~e sheet. The two sets of electrodes form a matri~. On depressing the flexible sheet local contact 20' i9 ~ade between a row and a column electrode. With suitable materials small deflection~ of the fle~ible sheet are ~uEficient to cause contact between the two electrode~. U.~. Patent Specification No. 2,033,6~2 A describes ~uch a switch~ A
featu~e of this switch is that it is separated from any display it contrGl~ e.g~ an air traffic control cathode ray tube consol.
~$
2 --A s~itch according to this inventio~ utilises the capacitive change~ in a liquid crystal cell when deformed by touch. When appropriate voltages are applied to the cell it is very 3ensitive to phyaical changes in layer thickness.
A liquid cry~tal cell comprise~ a thin layer of a liquid crystal ~aterial contained between two walls carrying electrode struct~re~
on their inner faces. This forms a capacitor due to the highl~
resistive liquid crystal material bet~een opposing electrodes.
Local deformation of the walls by touching causes a change i~
capacitance. This arises for two reason~. Capacitance i~
proportional to layer thickness i.e. ~all ~eparation and therefore changes in layer thiclc~es~ give rise to cha~ges in capacitance.
More ~ignificant capacitsnce changes are causes by the ~low and change of alignment of liquid crystal molecules in the deformed srea. For some types of displayq this flow o~ liquid crystal material gives an observable change in optical transmis~ion.
Since the capacitance change is due to a physical movement of the molecules and cell walls it i9 immaterial ~hether or not sn operator's hand is gloved. Thi~ contrasts ~ith some prior art devices where a good electric contact with an operator is ~ecessaryl A capacitance change also occurs when the capacitance re~erts to it9 origisl value on removal of the deforming pressure~
According to this inventio~ a touch s~itch COmDrises a liquid cry~tal cell and m2ans for detectiDg a change in cell capacitance whe~ the cell is deformed, the cell comprising a layer of a liquid crystal material cvntained between walls bearing opposing electrode structures.
-~- 2 --The liquid crystal material may be nematic or cholesteric with a positive or ne~ative dielectric anisotropy. The cell walls inner sur~ace may be treated to give homogeneous molecular alignment (molecules parallel to wal~ sur-face) in a single direction e.g. by oblique evaporation of magnesium, fluoride or silicon monoxide at a gra~ing angle of 15 to 45 . Alternatively the walls may be unidirectionally rubbed e.g. with a soft tissue or coated with a layer of poly vinyl alcohol and rubbed to give a Molecular tilt of about 2 at the wall surface. Oblique evaporation at an angle o~ less than 15 may ~lso be used ~c give high molecular tilt (e.g. 30 ) plus alignment. Such alignment techniques are described in U.K~ Patent Specification No. 1,472,247.
The cell walls may be treated to give homeotropic align~ent (molecules perpendicular to cell walls) e.gO by cleaning followed by dipping in a surfactant such as lecithin.
Using these alignmen~ techniques various well-known type~
oY display cells may be constructed e.g. the ~listed nematic ~here the homogeneous alig~ent directions are orthogonal t or parallel nematic where the homogeneous aiignment directions are parallel. Both these cells use nematic material with positive dielectric anisotropy ~ith or without dyes and may include an amount of cholesteric material.
Additionally the display cell may operate as a phase cha~ge device with long or short pitch cholesteric material, or a dynamic scattering device. Dyes may be added to the ~0 material.
The change in capacitance may be measured by any suit-able capacitance instrument e.g. a capacitance meter, capacitance bridge, lock in amplifier, or bridge with reference capacitor~
In this latter case a voltage is supplied -to -the display cell and a reference capaci-tor in series, The voltage developed across -the display cell is a measure of its capacitance.
When using displaysemploying high surface tilt e.g. 30 the voltage level across the cell is not critical, However for lower tilt angles e.g, below 10 the cell capacitance is much more sensitive to deformation if the voltage across the cell is above a threshold value and below an upper limit.
The detected change may be used to switch a liquid cry-stal display cell ON or OFF, used to switch a light source, switch a sound source, or switch any other electrically swltch-able device.
The display cell and touch switch may be separate cells, different parts of one cell or the same cell.
In accordance with this invention, there is provided a touch sensitive swi-tch comprising a liquid crystal cell formed by a layer of liquid crystal material contained between two walls spaced apart and bearing electrode structures on their inner faces, means for detecting a change in cell capacitance between opposing electrodes when the cell is deformed by an operators touch, and locally reduces the thickness of the liquid crystal layer, means for increasing capacitance sensi-tivity to deformation of the cell by tilting liquid crystal molecules away from being near parallel to the walls, and means for producing a signal indicating a de-tec-ted capacitance change.
I'he invention will now be described by way of e~ample only with reference to the accompanyiny drawinys of which:-Figures 1 and 2 are respectively front an~ cross sec-tional views of a combined touch switch and display cell;
Figure 3 is a front view of a multi-function display cell haviny separate touch areas;
Figure 4 is a circuit diagram with separate touch switch and display cells; and Figure 5 is a graph showing cell capacitance variation with applied voltage for different cell temperatures.
Figures 6, 7 are front and side view of an alternative touch switch cell having four touch areas forming a bridge circuit.
Figure ~ is a circuit diagram of Figures 6, 7.
.;~`' ri ~AY -~a--- 5 ~
As shown in Figures 1, 2 a liquid crystal cell 1 comprises two 2mm thick glass walls 2, 3 spaced 12 ~ apart by a spacer ring ~.
Electrode structure3 5, 6 e.g. a layer of tin oxide, forrning a seven bar for~at 7 are formed on the inner faces of thes~ walls 2, 3. Bet~leen -the walls 2, 3 is a layer 8 of ne1natic ]iquid crystal material. It may also contain a sMal] amount of cholesteric material and or dye. Prior to assembl~ the ualls 2, 3 inner surface is treated e.g. by unidirectional rubbing with a soft tissue or oblique evaporation of MgF2.
On assembly the rubbing (alig~lent) directions are arranged to be orthogonal. As a result the liquid crystal molecule~ are surface aligned ~1ith the rubbing direction ~1ith a progressive 90 twist across the layer 8 thickness. ~his is known as a twisted nematic cell. Polariser 9, 10 are located either side the cell 1 uith their optic axis parallel to the rubbing direction on the adjacent ~all. With such an arrangement light from a souh-ce 11 is transmitted through the CQll 1 when it is an OFF, zero applied voltage, state. Alternatively the polarisers 9, 10 may be arran~ed with their optical axis parallel to anothe~ and to one alignment direction. In this case no light is transmitted through the cell 1 in its OFF state.
~hen a suitable voltage is applied to the cell electrode 5, 6 light is transmitted where the liquid crystal molecules allgn themselves parallel to the applied electric field. This light transmission occurs only at electrodes to which the voltage is applied so that numerals O to 9 can be displayed by selective application of voltages to the seven bar electrode structure 7.
Alignment techniques for lo-~ and high surface molecular tilt are described in UoK~ Patent Specifications Nos~ 1,472,247 and 1,47~ 9 592.
Liquid crystal cells employing ef:Eects other than the twisted nernatic effect have a simi]ar construction but different surface alignment and different liquid crystal materials which may include dissolved dyes. For some oE these efects one or even no polarisers are used.
Examples of materials and dyes are described in the following patent s,pecifications :-United Kingdom Patent No. 1,433,130 United Kingdom Patent No. 1,441,571 United Kingdom Patent No. 1,452,826 United Kingdom Patent No. 1,555,955 United Klngdom Patent Application No. 2,011,940 A, published July 18, United Kingdom Patent Application No. 2,0~3,097 A, published October 1, United Kingdom Patent Application No. 2,082,196 A, published March 3, Canadian Patent Application No. 396,957, filed February 24, 1982.
The liquid crystal material may be E7 or E43, with CB 15 (all available from BDli Chemicals Ltd.~ Poole, Dorset) and the dyes may be Dl, D2, D16, D35, D80, D81, D82.
L9~?~
~7 has tho composition 5 11 { ~ CN 515~ by weight C7X15~ ~ CN 25~ by weight 8 17 ~ CN 16~ by weight 5 11 ~ CN ~ by weight One suitable dye has the structure:
oH o OH
(CH3~2CH CH2. ~ CH~C~CH3)~
112N ~ 2 _ _ .._................... .?
The display cell of Figures 1, 2 is used as both a switch component and display cell. That is, the same area that displays information, the seven-bar format, is also pressed by an operator's finger 12.
The display of Figure 3 is a multi-function display capable of displaying three functions marked A, B, and C in different areas of a single large cell 15. Beneath each function A, B, C
is a touch area 16, 17, 18 which may be of a different texture to assist night time location. Each function A, B, C and touch area 16, 17, 18 is defined by electrode patterns on the inner faces of the cell and independently and selectively supplied with appropriate voltage signals.
In large area displays accurate spacing of the walls over the whole cell may be achieved using short lengths, e.g. 50 µm diameter glass fibres. These fibre spacers are arranged over the whole area of walls. Since the touch areas 16, 17, 18 must be capable of wall deflection spacers are not used in these parts of the display. Spacers are preferably used between adjacent touch areas 16, 17, 18 to provide isolation.
Each touch area 16, 17, 18 is a separate seitch element.
Figure 4 shows a circuit diagram of a touch s~ritch. It comprises a liquid crystal cell 20, e.g. as Figure 2, with sp~ced electrodes 21, 22 and a layer 23, of liquid crystal material. A reference capacitor 24 is connected in series with the cell 20. A voltage source 25 of e.g, 100 Hz frequency is a-Dplied to the reference capacitor 24 and cell 20.
The voltage developed between the reference capacitor and cell VLc is fed into a comparator 26 also supplied with a reference voltage Vref. Output from the comparator 26 is to a control logic 27 that switches voltage to a liquid crystal display 28 e.~. ~igure 1 or appropriate parts of Figure 3, as required. The reference capacitor 24 may be adjustable in capacitance value and may be around 100 times the value of the cell 20 element capacitance. For exa~ple C f may be 105pF and the cell CLc ~ lO~p~.
~he capacitanc~ of and optical transmission through a liquid crystal cell h2ving lo~ surface tilt angles e.g. below 15 varies with applied vo]tage as sho~rn in Figure 5. For low applied voltages capacitance remains constant until a critica] value Vc is reached. ~his corresponds to the point at which liquid crystal molecules start to turn towards their ON state. Above Vc capacitance increases. The cu~e is displaced to the left for increasing liquid crystal temperature and to the right for decreasing temperature. The point Vsat is the value giving a fully optically ON cell. Norm211y displays are switched on by a voltage above V t and turned OFF by voltages below Vc preferably zero voltage.
The value of the voltage supply 25 Fi~ure 4 is adjusted 30 that the voltage VLc across the oell 20 i~ between Y and V t.
For display cells having low e.g. 2 molecular tilt at the cell ~lalls the value of V~c is preferably between Vc and 5 Vc.
For hi,~,her tilt values VLc may be between zero and 5 V . The value of Yref is adJusted to equal VLc. In this condition the output of the comparator 26 is zero and the liquid crystal display 28 remains in its set state e.g. OFF state.
_ g _ ~6~
~en finger pressure is applied to the centre of the ~ront ~Jall of the switcn cell 20 it bends, bringing the opposing electrode~ 21, 22 closer together, displacing some liquid crystal material and changing the align~ent of th~ molecules.
As a result -the capacitance chan~es and V~c changes. The comparator 26 gives an output to the control logic which alter~
the state o~ the display 28 e.g. switches it ON. On re~oval of pressure the cell 20 revert3 back to its original shape and capacitance. The comparator 26 output is ~ero and the di~play remains in its ON state. ~urther finger pressure on the switch cell 20 cau~es the display 28 to s~itch to 0~.
A capacitance change occur~ when the deforming pressure is re~oved.
~hus two capacitive changes are associated with touch. Either change may be used by the logic 27 i.e. one change is ignored.
Alternatively both changes may be used, e.g. a double change i8 reouired to provide an output fr~m tha logic 27.
Other s~itching e,fects are possible dependiDg on the comple~ity of display 28 and control logic 27~ ~or example it may be arranged that continued pressure on the switch cell 20 inde~e3 the display 20 e.g. from displaying zero to nine etc. until pressure is released.
~5 Visual confirmation of a switching action may be arranged by flashing of a light behind the touched area e.g. area~ 169 17, 18 of Figure 3~ Alternatively audible confirmation of switching may be arranged.
For di~plays operating o~er a wide ambient temperat~re range, ~emperature compensation may be used~ Such compensation may adjust Vref and/or the Yoltage ~wupply 25 to maintain YLC between VC and Vsat when the s~itch cell 20 i8 undeformed.
- 10 ~
~ 6~
One method of` temperature compensation i5 described in U.X.
Patent Specifieation ~o. 2,012,09~ ~. A voltage is applied across a fi~ed capacitor ~ld a liquid crystal cell in series.
This is similAr to the arrangement of Figure 4. The voltage developed across the cell is a measure of liquid crystal temperature and is used to adjust the voltage level applied to drive adjacent liquid crystal displays.
Thus in the present case the voltage YLC developed across one area of display cell, near a touch area/ could be used to vary the voltage source and Vref. Additionally or altern&tively the temperature measurement could be used to control cell heaters.
Twisted nematic cells using high surface tilt angles, e.g. 30, are sensitive to finger pressure for values of applied voltages below YcO In this case it is not necessary to arrange VLc to lie between Vc and VsAT.
Greater sensitivity can be provided by thinner glass front walls or even flexible plastic such as polyester, polyacrylate, polyurethene, etc.
As an alternative to, or in addition to, the temperature compensation described above a band pass filter may be incorporated in the supply to the comparator 26. This filter may attenuate very low frequency changes in voltage 7 e.g. caused by temperature fluc-tuations, and also higher frequency changes e.g caused by vibrations such as experienced in the dashboard of a carO
6~
Figures 6, 7, and 8 show an alternative touch switch arranged aa a bridge cîrcuit~ This re~o~es the nece~sity to use a reference capacitor 2~ ~nd ref`erence ~oltage.
The cell 30 comprises two 2mm thick glass slides ~1, 32, enclosing a 12 ~lm thick liquid crystal layer 3~. A 3pacer ring 34 and partitions S5 maintain the slide separation where required~ ~he top slide 31 carries two parailel ~trip el ~trodes 36, 3'7 ~hilst the bottom slide 32 carries two parallel ~trip electrodes 38, 39 1U orthogonal to the top electrodes. Material and slide surface treatment are as desc~ibed zbove. Thi~ arran~ement providc-s four electrode intersections marked rl, X, Y, g. ~hese four intersectiolls W! X, Y, Z form four capacitors arranged in a bridge as shown in Fig~e 8. A voltage supply 25 e.g. of 100 ~z frequency is supplied between ths top electrodes 38, 39 at a value between Vc and Vsa~ e.g. 1 to 12 volts or more depending on material and thickness etc. An output is taken between the bottom electrodes 36, 37 to control logic 27 which cortrols a display 40 or other ele~trically operated device.
In use as a touch s~itch the output of the bridge circuit is zero because all four capacitors W, X, Y, Z have equal value. ~his situation remains substantially true for all reasonable temperatures and with cell ageing. When any one capacitors W, X, Y, or g is touched its capacitance changes and the bridge is unbalanced. A
~oltage tnen appears betwDen the bottom electrodes 36, 37 and is used b,y the control logic 27 as required.
The capacitors W3 X~ Y, Z can take any shape but should haYe the ~0 same capacitance. Since only one capacitor needs to be touched the others may form part of a non-touch display.
, . _, . _ . . . .
The arrangement of Figures 6, 7, 8 may be modified to use just t~o liquid cry~tal capacitive areas conDected to re~i~tor~ to form the bridge. ~'or example capacitor3 Y, Z may be replaced by a centre tapped re~i~tor. The precise point of tapping i~
adjustable to balance the bridgeO An advantage of thi3 arrangement over that of Figure 4 is A balance over a full operating te~perature range.
A liquid cry~tal cell comprise~ a thin layer of a liquid crystal ~aterial contained between two walls carrying electrode struct~re~
on their inner faces. This forms a capacitor due to the highl~
resistive liquid crystal material bet~een opposing electrodes.
Local deformation of the walls by touching causes a change i~
capacitance. This arises for two reason~. Capacitance i~
proportional to layer thickness i.e. ~all ~eparation and therefore changes in layer thiclc~es~ give rise to cha~ges in capacitance.
More ~ignificant capacitsnce changes are causes by the ~low and change of alignment of liquid crystal molecules in the deformed srea. For some types of displayq this flow o~ liquid crystal material gives an observable change in optical transmis~ion.
Since the capacitance change is due to a physical movement of the molecules and cell walls it i9 immaterial ~hether or not sn operator's hand is gloved. Thi~ contrasts ~ith some prior art devices where a good electric contact with an operator is ~ecessaryl A capacitance change also occurs when the capacitance re~erts to it9 origisl value on removal of the deforming pressure~
According to this inventio~ a touch s~itch COmDrises a liquid cry~tal cell and m2ans for detectiDg a change in cell capacitance whe~ the cell is deformed, the cell comprising a layer of a liquid crystal material cvntained between walls bearing opposing electrode structures.
-~- 2 --The liquid crystal material may be nematic or cholesteric with a positive or ne~ative dielectric anisotropy. The cell walls inner sur~ace may be treated to give homogeneous molecular alignment (molecules parallel to wal~ sur-face) in a single direction e.g. by oblique evaporation of magnesium, fluoride or silicon monoxide at a gra~ing angle of 15 to 45 . Alternatively the walls may be unidirectionally rubbed e.g. with a soft tissue or coated with a layer of poly vinyl alcohol and rubbed to give a Molecular tilt of about 2 at the wall surface. Oblique evaporation at an angle o~ less than 15 may ~lso be used ~c give high molecular tilt (e.g. 30 ) plus alignment. Such alignment techniques are described in U.K~ Patent Specification No. 1,472,247.
The cell walls may be treated to give homeotropic align~ent (molecules perpendicular to cell walls) e.gO by cleaning followed by dipping in a surfactant such as lecithin.
Using these alignmen~ techniques various well-known type~
oY display cells may be constructed e.g. the ~listed nematic ~here the homogeneous alig~ent directions are orthogonal t or parallel nematic where the homogeneous aiignment directions are parallel. Both these cells use nematic material with positive dielectric anisotropy ~ith or without dyes and may include an amount of cholesteric material.
Additionally the display cell may operate as a phase cha~ge device with long or short pitch cholesteric material, or a dynamic scattering device. Dyes may be added to the ~0 material.
The change in capacitance may be measured by any suit-able capacitance instrument e.g. a capacitance meter, capacitance bridge, lock in amplifier, or bridge with reference capacitor~
In this latter case a voltage is supplied -to -the display cell and a reference capaci-tor in series, The voltage developed across -the display cell is a measure of its capacitance.
When using displaysemploying high surface tilt e.g. 30 the voltage level across the cell is not critical, However for lower tilt angles e.g, below 10 the cell capacitance is much more sensitive to deformation if the voltage across the cell is above a threshold value and below an upper limit.
The detected change may be used to switch a liquid cry-stal display cell ON or OFF, used to switch a light source, switch a sound source, or switch any other electrically swltch-able device.
The display cell and touch switch may be separate cells, different parts of one cell or the same cell.
In accordance with this invention, there is provided a touch sensitive swi-tch comprising a liquid crystal cell formed by a layer of liquid crystal material contained between two walls spaced apart and bearing electrode structures on their inner faces, means for detecting a change in cell capacitance between opposing electrodes when the cell is deformed by an operators touch, and locally reduces the thickness of the liquid crystal layer, means for increasing capacitance sensi-tivity to deformation of the cell by tilting liquid crystal molecules away from being near parallel to the walls, and means for producing a signal indicating a de-tec-ted capacitance change.
I'he invention will now be described by way of e~ample only with reference to the accompanyiny drawinys of which:-Figures 1 and 2 are respectively front an~ cross sec-tional views of a combined touch switch and display cell;
Figure 3 is a front view of a multi-function display cell haviny separate touch areas;
Figure 4 is a circuit diagram with separate touch switch and display cells; and Figure 5 is a graph showing cell capacitance variation with applied voltage for different cell temperatures.
Figures 6, 7 are front and side view of an alternative touch switch cell having four touch areas forming a bridge circuit.
Figure ~ is a circuit diagram of Figures 6, 7.
.;~`' ri ~AY -~a--- 5 ~
As shown in Figures 1, 2 a liquid crystal cell 1 comprises two 2mm thick glass walls 2, 3 spaced 12 ~ apart by a spacer ring ~.
Electrode structure3 5, 6 e.g. a layer of tin oxide, forrning a seven bar for~at 7 are formed on the inner faces of thes~ walls 2, 3. Bet~leen -the walls 2, 3 is a layer 8 of ne1natic ]iquid crystal material. It may also contain a sMal] amount of cholesteric material and or dye. Prior to assembl~ the ualls 2, 3 inner surface is treated e.g. by unidirectional rubbing with a soft tissue or oblique evaporation of MgF2.
On assembly the rubbing (alig~lent) directions are arranged to be orthogonal. As a result the liquid crystal molecule~ are surface aligned ~1ith the rubbing direction ~1ith a progressive 90 twist across the layer 8 thickness. ~his is known as a twisted nematic cell. Polariser 9, 10 are located either side the cell 1 uith their optic axis parallel to the rubbing direction on the adjacent ~all. With such an arrangement light from a souh-ce 11 is transmitted through the CQll 1 when it is an OFF, zero applied voltage, state. Alternatively the polarisers 9, 10 may be arran~ed with their optical axis parallel to anothe~ and to one alignment direction. In this case no light is transmitted through the cell 1 in its OFF state.
~hen a suitable voltage is applied to the cell electrode 5, 6 light is transmitted where the liquid crystal molecules allgn themselves parallel to the applied electric field. This light transmission occurs only at electrodes to which the voltage is applied so that numerals O to 9 can be displayed by selective application of voltages to the seven bar electrode structure 7.
Alignment techniques for lo-~ and high surface molecular tilt are described in UoK~ Patent Specifications Nos~ 1,472,247 and 1,47~ 9 592.
Liquid crystal cells employing ef:Eects other than the twisted nernatic effect have a simi]ar construction but different surface alignment and different liquid crystal materials which may include dissolved dyes. For some oE these efects one or even no polarisers are used.
Examples of materials and dyes are described in the following patent s,pecifications :-United Kingdom Patent No. 1,433,130 United Kingdom Patent No. 1,441,571 United Kingdom Patent No. 1,452,826 United Kingdom Patent No. 1,555,955 United Klngdom Patent Application No. 2,011,940 A, published July 18, United Kingdom Patent Application No. 2,0~3,097 A, published October 1, United Kingdom Patent Application No. 2,082,196 A, published March 3, Canadian Patent Application No. 396,957, filed February 24, 1982.
The liquid crystal material may be E7 or E43, with CB 15 (all available from BDli Chemicals Ltd.~ Poole, Dorset) and the dyes may be Dl, D2, D16, D35, D80, D81, D82.
L9~?~
~7 has tho composition 5 11 { ~ CN 515~ by weight C7X15~ ~ CN 25~ by weight 8 17 ~ CN 16~ by weight 5 11 ~ CN ~ by weight One suitable dye has the structure:
oH o OH
(CH3~2CH CH2. ~ CH~C~CH3)~
112N ~ 2 _ _ .._................... .?
The display cell of Figures 1, 2 is used as both a switch component and display cell. That is, the same area that displays information, the seven-bar format, is also pressed by an operator's finger 12.
The display of Figure 3 is a multi-function display capable of displaying three functions marked A, B, and C in different areas of a single large cell 15. Beneath each function A, B, C
is a touch area 16, 17, 18 which may be of a different texture to assist night time location. Each function A, B, C and touch area 16, 17, 18 is defined by electrode patterns on the inner faces of the cell and independently and selectively supplied with appropriate voltage signals.
In large area displays accurate spacing of the walls over the whole cell may be achieved using short lengths, e.g. 50 µm diameter glass fibres. These fibre spacers are arranged over the whole area of walls. Since the touch areas 16, 17, 18 must be capable of wall deflection spacers are not used in these parts of the display. Spacers are preferably used between adjacent touch areas 16, 17, 18 to provide isolation.
Each touch area 16, 17, 18 is a separate seitch element.
Figure 4 shows a circuit diagram of a touch s~ritch. It comprises a liquid crystal cell 20, e.g. as Figure 2, with sp~ced electrodes 21, 22 and a layer 23, of liquid crystal material. A reference capacitor 24 is connected in series with the cell 20. A voltage source 25 of e.g, 100 Hz frequency is a-Dplied to the reference capacitor 24 and cell 20.
The voltage developed between the reference capacitor and cell VLc is fed into a comparator 26 also supplied with a reference voltage Vref. Output from the comparator 26 is to a control logic 27 that switches voltage to a liquid crystal display 28 e.~. ~igure 1 or appropriate parts of Figure 3, as required. The reference capacitor 24 may be adjustable in capacitance value and may be around 100 times the value of the cell 20 element capacitance. For exa~ple C f may be 105pF and the cell CLc ~ lO~p~.
~he capacitanc~ of and optical transmission through a liquid crystal cell h2ving lo~ surface tilt angles e.g. below 15 varies with applied vo]tage as sho~rn in Figure 5. For low applied voltages capacitance remains constant until a critica] value Vc is reached. ~his corresponds to the point at which liquid crystal molecules start to turn towards their ON state. Above Vc capacitance increases. The cu~e is displaced to the left for increasing liquid crystal temperature and to the right for decreasing temperature. The point Vsat is the value giving a fully optically ON cell. Norm211y displays are switched on by a voltage above V t and turned OFF by voltages below Vc preferably zero voltage.
The value of the voltage supply 25 Fi~ure 4 is adjusted 30 that the voltage VLc across the oell 20 i~ between Y and V t.
For display cells having low e.g. 2 molecular tilt at the cell ~lalls the value of V~c is preferably between Vc and 5 Vc.
For hi,~,her tilt values VLc may be between zero and 5 V . The value of Yref is adJusted to equal VLc. In this condition the output of the comparator 26 is zero and the liquid crystal display 28 remains in its set state e.g. OFF state.
_ g _ ~6~
~en finger pressure is applied to the centre of the ~ront ~Jall of the switcn cell 20 it bends, bringing the opposing electrode~ 21, 22 closer together, displacing some liquid crystal material and changing the align~ent of th~ molecules.
As a result -the capacitance chan~es and V~c changes. The comparator 26 gives an output to the control logic which alter~
the state o~ the display 28 e.g. switches it ON. On re~oval of pressure the cell 20 revert3 back to its original shape and capacitance. The comparator 26 output is ~ero and the di~play remains in its ON state. ~urther finger pressure on the switch cell 20 cau~es the display 28 to s~itch to 0~.
A capacitance change occur~ when the deforming pressure is re~oved.
~hus two capacitive changes are associated with touch. Either change may be used by the logic 27 i.e. one change is ignored.
Alternatively both changes may be used, e.g. a double change i8 reouired to provide an output fr~m tha logic 27.
Other s~itching e,fects are possible dependiDg on the comple~ity of display 28 and control logic 27~ ~or example it may be arranged that continued pressure on the switch cell 20 inde~e3 the display 20 e.g. from displaying zero to nine etc. until pressure is released.
~5 Visual confirmation of a switching action may be arranged by flashing of a light behind the touched area e.g. area~ 169 17, 18 of Figure 3~ Alternatively audible confirmation of switching may be arranged.
For di~plays operating o~er a wide ambient temperat~re range, ~emperature compensation may be used~ Such compensation may adjust Vref and/or the Yoltage ~wupply 25 to maintain YLC between VC and Vsat when the s~itch cell 20 i8 undeformed.
- 10 ~
~ 6~
One method of` temperature compensation i5 described in U.X.
Patent Specifieation ~o. 2,012,09~ ~. A voltage is applied across a fi~ed capacitor ~ld a liquid crystal cell in series.
This is similAr to the arrangement of Figure 4. The voltage developed across the cell is a measure of liquid crystal temperature and is used to adjust the voltage level applied to drive adjacent liquid crystal displays.
Thus in the present case the voltage YLC developed across one area of display cell, near a touch area/ could be used to vary the voltage source and Vref. Additionally or altern&tively the temperature measurement could be used to control cell heaters.
Twisted nematic cells using high surface tilt angles, e.g. 30, are sensitive to finger pressure for values of applied voltages below YcO In this case it is not necessary to arrange VLc to lie between Vc and VsAT.
Greater sensitivity can be provided by thinner glass front walls or even flexible plastic such as polyester, polyacrylate, polyurethene, etc.
As an alternative to, or in addition to, the temperature compensation described above a band pass filter may be incorporated in the supply to the comparator 26. This filter may attenuate very low frequency changes in voltage 7 e.g. caused by temperature fluc-tuations, and also higher frequency changes e.g caused by vibrations such as experienced in the dashboard of a carO
6~
Figures 6, 7, and 8 show an alternative touch switch arranged aa a bridge cîrcuit~ This re~o~es the nece~sity to use a reference capacitor 2~ ~nd ref`erence ~oltage.
The cell 30 comprises two 2mm thick glass slides ~1, 32, enclosing a 12 ~lm thick liquid crystal layer 3~. A 3pacer ring 34 and partitions S5 maintain the slide separation where required~ ~he top slide 31 carries two parailel ~trip el ~trodes 36, 3'7 ~hilst the bottom slide 32 carries two parallel ~trip electrodes 38, 39 1U orthogonal to the top electrodes. Material and slide surface treatment are as desc~ibed zbove. Thi~ arran~ement providc-s four electrode intersections marked rl, X, Y, g. ~hese four intersectiolls W! X, Y, Z form four capacitors arranged in a bridge as shown in Fig~e 8. A voltage supply 25 e.g. of 100 ~z frequency is supplied between ths top electrodes 38, 39 at a value between Vc and Vsa~ e.g. 1 to 12 volts or more depending on material and thickness etc. An output is taken between the bottom electrodes 36, 37 to control logic 27 which cortrols a display 40 or other ele~trically operated device.
In use as a touch s~itch the output of the bridge circuit is zero because all four capacitors W, X, Y, Z have equal value. ~his situation remains substantially true for all reasonable temperatures and with cell ageing. When any one capacitors W, X, Y, or g is touched its capacitance changes and the bridge is unbalanced. A
~oltage tnen appears betwDen the bottom electrodes 36, 37 and is used b,y the control logic 27 as required.
The capacitors W3 X~ Y, Z can take any shape but should haYe the ~0 same capacitance. Since only one capacitor needs to be touched the others may form part of a non-touch display.
, . _, . _ . . . .
The arrangement of Figures 6, 7, 8 may be modified to use just t~o liquid cry~tal capacitive areas conDected to re~i~tor~ to form the bridge. ~'or example capacitor3 Y, Z may be replaced by a centre tapped re~i~tor. The precise point of tapping i~
adjustable to balance the bridgeO An advantage of thi3 arrangement over that of Figure 4 is A balance over a full operating te~perature range.
Claims (7)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A touch sensitive switch comprising a liquid crystal cell formed by a layer of liquid crystal material contained between two walls spaced apart and bearing electrode structures on their inner faces, means for detecting a change in cell capacitance between opposing electrodes when the cell is deformed by an operators touch, and locally reduces the thickness of the liquid crystal layer, means for increasing capacitance sensitivity to deformation of the cell by tilting liquid crystal molecules away from being near parallel to the walls, and means for pro-ducing a signal indicating a detected capacitance change.
2. The switch according to claim 1 wherein the cell is arranged to change displayed information in at least a part of the cell area.
3. The switch according to claim 2 wherein the part of the cell displaying information is arranged to be deformable by an operator's touch.
4. The switch according to claim 2 wherein that part of the cell displaying information is separate from that part deformable by an operator's touch.
5. The switch according to claim 1 wherein the means for detecting a change in capacitance includes a balanced bridge circuit which is unbalanced on deformation of the cell which forms a part of the bridge.
6. The switch according to claim 5 wherein a plurality of cells are connected into the bridge circuit.
7. The switch according to claim 1 wherein the means for detecting a change in capacitance includes means for supplying a voltage across the cell and a reference capacitor in series, and a comparator for comparing the voltage developed across the cell with a reference voltage.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8134496 | 1981-11-16 | ||
| GB8134496 | 1981-11-16 | ||
| GB8206709 | 1982-03-08 | ||
| GB8206709 | 1982-03-08 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1196985A true CA1196985A (en) | 1985-11-19 |
Family
ID=26281280
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000415528A Expired CA1196985A (en) | 1981-11-16 | 1982-11-15 | Touch sensitive switches |
Country Status (3)
| Country | Link |
|---|---|
| US (1) | US4529968A (en) |
| EP (1) | EP0079711A3 (en) |
| CA (1) | CA1196985A (en) |
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| GB2093861B (en) * | 1981-02-09 | 1984-08-22 | Canning Materials W Ltd | Bath for electrodeposition of chromium |
| JPS6066298A (en) * | 1983-09-21 | 1985-04-16 | キヤノン株式会社 | Information processor |
| JPS60105348A (en) * | 1983-11-14 | 1985-06-10 | Kyocera Corp | Multi-function key input device |
| EP0203914B1 (en) * | 1984-01-30 | 1989-10-18 | Touch Display Systems Ab | Touch controlled display device |
| JPS60175077A (en) * | 1984-02-22 | 1985-09-09 | 株式会社日立製作所 | Information holder |
| JPS61290520A (en) * | 1985-06-19 | 1986-12-20 | Nippon Texas Instr Kk | Electronic equipment |
| US4738514A (en) * | 1986-01-16 | 1988-04-19 | Rca Corporation | Crystal variation compensation circuit for liquid crystal displays |
| US5016982A (en) * | 1986-07-22 | 1991-05-21 | Raychem Corporation | Liquid crystal display having a capacitor for overvoltage protection |
| WO1988000719A1 (en) * | 1986-07-22 | 1988-01-28 | Raychem Corporation | Liquid crystal display with capacitor connected in series |
| US5159323A (en) * | 1987-02-19 | 1992-10-27 | Semiconductor Energy Laboratory Co., Ltd. | Liquid crystal display |
| US4836786A (en) * | 1987-08-07 | 1989-06-06 | Joseph Leeb Enterprises, Inc. | Demonstration calculator |
| FR2632793B1 (en) * | 1988-06-08 | 1994-04-15 | Jaeger | IMPROVED BUTTON EXPLOITING THE PROPERTIES OF A LIQUID CRYSTAL |
| DE3907671A1 (en) * | 1989-03-09 | 1990-09-13 | Stefan Weller | Method of making passive displays addressable for touching, with the capability of controlling displayed or otherwise established operating functions or parameters on their surface |
| US5087825A (en) * | 1990-02-15 | 1992-02-11 | Nartron Corporation | Capacity responsive keyboard |
| US5153572A (en) * | 1990-06-08 | 1992-10-06 | Donnelly Corporation | Touch-sensitive control circuit |
| US5164609A (en) * | 1990-06-08 | 1992-11-17 | Donnelly Corporation | Controllable power distribution system |
| US5189417A (en) * | 1990-10-16 | 1993-02-23 | Donnelly Corporation | Detection circuit for matrix touch pad |
| US5239152A (en) * | 1990-10-30 | 1993-08-24 | Donnelly Corporation | Touch sensor panel with hidden graphic mode |
| US5084801A (en) * | 1991-02-19 | 1992-01-28 | General Electric Company | Liquid crystal variable capacitor and high intensity discharge lamp ballast employing same |
| JP2837578B2 (en) * | 1992-05-20 | 1998-12-16 | シャープ株式会社 | Image input / output device and method |
| US5572205A (en) * | 1993-03-29 | 1996-11-05 | Donnelly Technology, Inc. | Touch control system |
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| US6310611B1 (en) | 1996-12-10 | 2001-10-30 | Touchsensor Technologies, Llc | Differential touch sensor and control circuit therefor |
| US5942815A (en) * | 1997-10-03 | 1999-08-24 | Sheldahl, Inc. | Programmable capacitive horn switch |
| US7528508B2 (en) * | 1998-10-09 | 2009-05-05 | Azoteq Pty Ltd. | Touch sensor user interface with compressible material construction |
| US7906875B2 (en) | 1999-01-19 | 2011-03-15 | Touchsensor Technologies, Llc | Touch switches and practical applications therefor |
| US6320282B1 (en) | 1999-01-19 | 2001-11-20 | Touchsensor Technologies, Llc | Touch switch with integral control circuit |
| DE10011645A1 (en) * | 2000-03-10 | 2001-09-13 | Ego Elektro Geraetebau Gmbh | Touch switch with an LC display |
| WO2003079176A2 (en) * | 2002-03-15 | 2003-09-25 | Koninklijke Philips Electronics N.V. | Touch sensitive display device |
| US7154481B2 (en) * | 2002-06-25 | 2006-12-26 | 3M Innovative Properties Company | Touch sensor |
| US7388571B2 (en) * | 2002-11-21 | 2008-06-17 | Research In Motion Limited | System and method of integrating a touchscreen within an LCD |
| FR2847996B1 (en) * | 2002-11-28 | 2005-10-07 | Thales Sa | DEDICATED DISPLAY DEVICE WITH PROXIMITY DETECTION |
| US20040189612A1 (en) * | 2003-03-27 | 2004-09-30 | Bottari Frank J. | Touch sensor using light control |
| US7708437B2 (en) * | 2003-11-19 | 2010-05-04 | Lear Corporation | Instrument panel system having concealed switches |
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| TWI304471B (en) * | 2005-10-14 | 2008-12-21 | Hon Hai Prec Ind Co Ltd | The touch sensing apparatus |
| KR101328387B1 (en) * | 2006-08-25 | 2013-11-13 | 삼성디스플레이 주식회사 | Method of touch position detecting |
| TWI399672B (en) * | 2008-08-26 | 2013-06-21 | Au Optronics Corp | Method for controlling touch screen apparatus |
| TWI376623B (en) * | 2008-11-19 | 2012-11-11 | Au Optronics Corp | Touch panel and touch display panel |
| US20110036164A1 (en) * | 2009-07-27 | 2011-02-17 | Touchsensor Technologies, Llc | Level sensing controller and method |
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|---|---|---|---|---|
| GB1172222A (en) * | 1965-08-05 | 1969-11-26 | Mini Of Technology | Touch Displays |
| FR1586612A (en) * | 1967-07-27 | 1970-02-27 | ||
| US3815127A (en) * | 1973-03-20 | 1974-06-04 | Control Data Corp | Data entry device |
| GB1553563A (en) * | 1976-07-06 | 1979-09-26 | Secr Defence | Touch sensitive electrical switches |
| CH607872B (en) * | 1976-11-04 | 1900-01-01 | Centre Electron Horloger | WATCH EQUIPPED WITH A MANUAL CONTROL DEVICE. |
| US4224615A (en) * | 1978-09-14 | 1980-09-23 | Texas Instruments Incorporated | Method of using a liquid crystal display device as a data input device |
| GB2033632B (en) * | 1978-09-22 | 1982-07-21 | Secr Defence | Touch-sensitive switch units |
| US4313108A (en) * | 1978-12-07 | 1982-01-26 | Casio Computer Co., Ltd. | Electric apparatus for displaying a plurality of key symbols on a single passive display |
| US4290061A (en) * | 1979-08-23 | 1981-09-15 | General Electric Company | Electrically integrated touch input and output display system |
-
1982
- 1982-10-29 EP EP82305767A patent/EP0079711A3/en not_active Withdrawn
- 1982-11-10 US US06/440,590 patent/US4529968A/en not_active Expired - Lifetime
- 1982-11-15 CA CA000415528A patent/CA1196985A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| US4529968A (en) | 1985-07-16 |
| EP0079711A2 (en) | 1983-05-25 |
| EP0079711A3 (en) | 1984-10-03 |
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| Date | Code | Title | Description |
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| MKEX | Expiry |