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`(332168816 A 1
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`SPECIFICATION
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`Touch-sensitive position sensor apparatus
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`5 The invention relates to touch~sensitive position
`sensor apparatus for deriving signals which repre-
`sent any position selected by touch in a two-di-
`mensional area. The invention relates more
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`particularly to such apparatus of a type having a
`1D transparent touch-sensitive screen adapted to over»
`lie the display screen of a CRT {cathode ray tube]
`or other display device to enable touch selection of
`any portion of a display produced on the display
`screen.
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`One knOWn form of apparatus of the above type
`has a touch-sensitive screen comprised by a rigid
`transparent plate which fits over a CRT display
`Screen, together with an electrically conductive
`transparent flexible plastic film which is stretched
`20 over the plate and is held out of contact with the
`plate eXcept for, and by, electrically insulating in-
`dentations formed in the plastic film. The surface
`of the plate facing the plastic film has a resistive
`film on it, and means are provided for producing a
`25 voltage gradient across this resistive film. When
`the plastic film is pushed into contact with the
`plate at any point, for instance by finger pressure,
`signals which represent the co-ordinates of the po-
`sition of the point are determined from the voltage
`measured at the point.
`it has been found that this known form of appa-
`ratus is fragile, in that the flexible plastic film can
`be damaged easily. Also. the flexible plastic film
`does not transmit all of the light from the CRT dis—
`35 play screen, so that a slightly fuzzy picture results.
`Another known form of apparatus of the above
`type is disclosed in prior UK patent specification 1
`528 581. in this apparatus, the transparent touch-
`sensitive screen is a transparent rigid sheet which
`is supported over a CRT display screen by four
`load cells located respectively at the corners of the
`sheet. When the sheet is touched at any point, the
`resulting forces at the corners of the sheet are
`measured by the load cells and signals which rep-
`resent the co~ordinates of the position of the
`touched point are determined from these measure-
`ments.
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`A drawback with this latter form of apparatus of
`the above type is its complexity, and thus cost.
`It is an object of the present invention to provide
`a touch-sensitive position sensor apparatus of the
`above type, which is both more robust and less ex-
`pensive than the known apparatuses outlined
`above.
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`55 According to the present invention a touch-sensi-
`tive position sensor apparatus of the above type is
`characterised in that its touch—sensitive screen
`comprises first and second over~lying layers each
`composed of a multiplicity of spaced parallel elec-
`60 trically conductive strips. the strips of one layer
`lying transverse to those of the other layer, to-
`gether with a third layer interposed between said
`first and second layers and composed of electri—
`cally insulating dots which are located respectively
`65 at the intersections formed by the two layers of
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`strips whereby a capacitive coupling is formed be-
`tween the strips at each intersection. the apparatus
`being further characterised by having electronic
`means for detecting a change in the capacitive
`coupling at any intersection and thereby identify
`the intersection as a touched-selected position.
`Said electronic means may comprise pulse gen-
`erator means for applying a pulse to each of the
`strips of the first layer in turn, in a recurrent cycle.
`pulse detector means for detecting a resultant
`pulse, which exceeds a threshold amplitude, on
`any one of the strips of the second layer, and out-
`put means for providing signals which represent
`the intersection formed by the two strips, one in
`each of said first and second layers, to which a
`generated pulse is applied and from which a re-
`sultant pulse is obtained.
`The apparatus then operates to produce a result-
`ant pulse which exceeds the threshold amplitude
`only when touch-selection (by a finger} of a posi-
`tion on the display screen causes an increase in
`the capacitive coupling of the particular intersec-
`tion at or adjacent that position. The capacitive
`coupling at each of the other intersections is insuf»
`ficient for a resultant pulse which exceeds the
`threshold amplitude being produced on any other
`strip of the second layer. Thus, the intersection
`concerned is identified uniquely by the presence,
`respectively, of a generated pulse and a resultant
`pulse of sufficient amplitude on the two strips
`which form the intersection.
`In carrying out the invention, the first and sec-
`ond layers of strips are preferably disposed normal
`to each other. These two layers of strips and also
`the layer of dots would, of course, be formed of
`optically transparent material.
`Preferably, the two layers of strips and the layer
`of dots are formed by respective deposition stages
`onto a rigid transparent substrate, which is suitably
`a glass plate. This construction has the advantage
`of being robust, and no part of it is required to flex
`in operation. Afirst mask leg. of aluminium) hav-
`ing parallel slits formed therein may be used for
`the deposition of the two layers of strips, the mask
`being orientated through 90° for one layer of strips
`relative to the other, whilst a second mask {e.g.
`also of aluminium} having a matrix of small holes
`formed therein may be used for the deposition of
`the layer of dots between the two layers of strips.
`The use of a common mask for the two layers of
`strips reduces cost.
`Known thick or thin film deposition techniques
`can be used for the deposition of the layers. Opti-
`cally transparent electrically conductive strips can
`be formed by these techniques, using indium-tin
`compounds which have a light transmission factor
`greater than 85%. The layer of electrically insulat-
`ing dots can be formed using quartz which has a
`light transmission factor greater than 85%. The use
`of well-established deposition techniques further
`contributes to reducing the cost of manufacture.
`The pulse generator means can include decimal-
`to-binary conversion means for providing binary
`coded signals which identify, respectively, the
`strips of the first layer when generated pulses are
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`being applied to them and, similarly, the pulse de-
`tector means include dacimal-to-binary conversion
`means for providing binary coded signals which
`identify, respectively, the strips of the second layer
`when resultant pulses exceeding said threshold
`amplitude are being detected on them. These two
`binary coded signals can then be latched into the
`output means which combines them to form a
`composite signal which identifies a touch-selected
`position.
`The production of the composite signal in binary
`form has the advantage that it facilitates interfac-
`ing the apparatus with a digital processor or com-
`puter by which the display on the display device is
`controlled.
`in order that the invention may more fully be
`understood, reference will now be made by way of
`example to the accompanying drawing, of which:-
`Figure 1 shows diagrammatically masks which
`are used in a construction touch-sensitive screen of
`apparatus according to the invention;
`Figure 2 shows diagrammatically a fragmentary
`portion of a touch-sensitive screen of a position
`sensor apparatus according to the invention; and
`Figure 3 shows a biock schematic diagram of a
`touch—sensitive position sensor apparatus accord-
`ing to the invention.
`Referring to the drawings, diagram 5 in Figure 1
`shows a mask which is made from an aluminium
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`sheet 1 and has a multiplicity of parallel slits 2
`formed therein. Diagram b in Figure 1 shows the
`same lor a similar} mask which is made from an
`aluminium sheet 1' and has that same number of
`parallel slits 2’ formed therein. The slits of the
`mask in diagram b are orientated 90" relative to the
`slits of the mask in diagram a. Diagram c in Figure
`1 shows a mask which is made from an aluminium
`sheet 3 and has a matrix of small holes 4 formed
`therein.
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`As will be described, the masks shown in Figure
`1 are used to form a touch-sensitive screen using
`deposition techniques. For such a screen which is
`dimensioned to over-lie the display screen of a 9"
`CRT display device, the masks in diagram a and b
`in Figure 1 each have 32 slits which are each 2 mm
`wide and there is a 5 mm gap between adjacent
`slits. The slits are 160 mm long. The mask in dia-
`gram c in Figure 1 has a matrix of 32 x 32 holes
`each of which is 3 mm diameter and there is a 5
`mm spacing between the centres of adjacent holes.
`The aluminium sheets from which the masks are
`made from are 1 mm thick.
`The construction of a touch-sensitive Screen of a
`position sensor apparatus according to the inven-
`tion is illustrated by the fragmentary portion
`thereof shown in Figure 2. The screen comprises a
`glass plate 5 which is to over—lie the display screen
`of the CRT display device. The mask of diagram a-
`Figure 1 is first used to deposit onto the surface of
`the glass plate 5 a layer of strips 6 of electrically
`conducting material. The mask of diagram c—Figure
`1 is next used to deposit on the layer of strips 6 a
`matrix of dots 7 of electrically insulating material.
`Finally, the mask 1’ of diagram b-Figure 1 is used
`to depoeit onto the surface of the glass plate 5 and
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`over the dots 7 a layer of strips 8 of electrically
`conductive material.
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`The deposition of the two layers of strips and the
`layer of dots is effected using known thin or thick
`film deposition techiques. Ail the materials used
`for these deposition stages are optically transpar-
`ent. For instance, indium-tin compounds can be
`used for the layers of strips. These compounds
`have a light transmission factor greater than 85935.
`Quartz having a light transmission factor greater
`than 85% can be used for the layer of dots.
`With the above construction of a touch-sensitive
`screen, there exists a capacitive coupling at each
`intersection formed by the cross-over of two strips,
`one from each layer, and the insulating dot which
`is disposed between the two strips at the intersec-
`tion. Depending on the thickness of the insulating
`dot this capacitive coupling will have a certain
`value. This capacitive coupling wiil, however. be
`increased at any intersection which is at or adja-
`cent to a position on the screen which is touched
`by a finger. it is this change in capacitive coupling
`which is used to provide selection of the touched
`position as will now be described with reference to
`Figure 3.
`The touch-sensitive position sensor apparatus
`show in Figure 3 has a touch-sensitive screen 9
`which is constructed in the manner described
`above. The apparatus also comprises a pulse gen-
`erator 10, a pulse detector 11 and an output circuit
`12.
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`The pulse generator 10 applies a pulse to each of
`the conducting strips 7 of one layer in turn, in a re-
`current cycle ever a set of leads 13. When a gener-
`ated pulse is applied to one of the strips 7, each of
`the strips 8 will have a resultant pulse produced
`thereon due to the capacitive couplings at the rele
`vant intersections between the strip 7 and the
`strips 8. These resultant pulses are applied to the
`pulse detector 11 over a set of leads 14. The pulse
`detactOr 11 operates as a threshold detector to de«
`tect resultant pulses which exceed and threshold
`amplitude. In the quiescent condition of the screen,
`li.e. when it is not being touchedl. the capacitive
`couplings at the intersections are insufficient for
`the amplitude of any of the resultant pulses to ex-
`ceed the threshold amplitude. HoWever, when the
`screen is touched, the capacitive coupling of the
`intersection at {or nearest to] the touched position
`will increase sufficiently-for the amplitude of the
`resultant pulse on the relevant strip 8 to exceed
`the threshold ampiitude, which resultant pulse is
`then detected by the pulse detector 11.
`The pulse generator 10 has associated with it a
`decimal-to-binary converter 15 Which provides bi-
`nary coded signals that identify each of the strips 7
`in turn during the application of generated pulses
`to these strips 7. Similarly, the puise detector 11
`has associated with it a decimalato-binary con-
`verter 16 which provides binary coded signals that
`identify any one of the strips 8 when a resultant
`pulse that exceeds the threshold amplitude is de-
`tected on it.
`The output circuit 12 is connected to receive the
`binary coded signals from the pulse generator 10
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`682168816 A 3
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`terised in that said substrate is a glass plate.
`5. An apparatus as claimed in Claim 3 or Claim
`4, characterised in that the two layers of strips are
`formed using a first mask having parallel slits
`formed therein for the deposition of the two layers
`of strips, the mask being orientated through 90° for
`one layer of strips relative to the other, and in that
`the layer of dots is formed using a second mask
`having a matrix of holes formed therein for the
`deposition of the layer of dots between the two
`layers of strips.
`6. An apparatus as claimed in Claim 3, Claim 4
`or Claim 5, characterised in that known thick of
`thin film deposition techniques are used for the
`deposition of the layers.
`7. An apparatus as claimed in any one of
`Claims 3 to 6, characterised in that optically trans-
`parent electrically conductive strips are formed us-
`ing indium—tin compounds for their deposition.
`8. An apparatus as claimed in any one of
`Claims 3 to 7, characterised in that optically trans-
`parent electrically insulating dots are formed using
`quartz for their deposition.
`9. An apparatus as claimed in Claim 2, or in
`any other Claim as appended directly or indirectly
`thereto. characterised in that the pulse generator
`means include decimal-to-binary coversion means
`for providing binary coded signals which identify,
`respectively. the strips of the first layer when gen-
`erated pulses are being applied to them and, simi-
`larly, the pulse detector means include decimal-to-
`binary conversion means for providing binary
`coded signals which identify respectively, the strips
`of thesecond layer when resultant pulses exceed-
`ing said threshold amplitude are being detected on
`them, the two binary coded signals from the pulse
`generator means and the pulse detector means, re-
`spectively, being latched into the output means
`which combines them to form a composite signal
`which identifies a touched position.
`10. A touch-sensitive position sensor apparatus
`for deriving signals which represent any position
`selected by touch in a two-dimensioned area, sub-
`stantially as hereinbefore described with reference
`to the accompanying drawing.
`
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`Printed in the UK for HMSO, 03813935. Srsfi. 1102.
`Published by The Patent Office. '25 Southampton Buildings. London.
`WC2A 1AY. from which copies may be obtained.
`
`and the pulse detector 11. The former signals are
`applied to the output circuit 12 continually as the
`strips 7 are pulsed, but the latter signals are ap-
`plied only in respect of a strip on which a resultant
`5 pulse of sufficient amplitude had been detected.
`The output circuit 12 can be arranged so as on re-
`ceipt of the latter signals to latch them together
`with the subsisting signals from the pulse genera‘
`tor 1D and to produce a composite signal which
`18 identifies the particular strip 7 and the particular
`strip 8 that form the intersection concerned,
`thereby identifying the touched selected position.
`Given that the touch-sensitive screen 9 has a 32
`x 32 matrix of intersections, then a 5-bit binary
`15 coded signal provides the identification of the
`strips 7 and a 5-bit binary coded signal provides
`the identification of the strips 8. The composite
`signal is then a 10-bit binary coded signal. The
`provision of a binary coded output signal facilitates
`20 direct interfacing of the apparatus with a digital
`processor or computer by which a display device
`for which the apparatus is provided is controlled.
`
`CLAIMS
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`25
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`1. A touch-sensitive position sensor apparatus
`for deriving signals which represent any position
`selected by touch in a two-dimensional area, which
`apparatus comprises a transparent touch-sensitive
`30 screen adapted to over-lie the display screen of a
`display device to enable touch selection of any
`portion of a display produced on the display
`screen. and which apparatus is characterised in
`that its touch-sensitive screen comprises first and
`35 second over-lying layers each composed of a mul—
`tiplicity of spaced parallel electrically conductive
`strips, the strips of one layer lying transverse to
`those of the other layer. together with a third layer
`interposed between said first and second layers
`40 and composed of electrically insulating dots which
`are located respectively at the intersections formed
`by the two layers of strips whereby a capacitive
`coupling is formed betwaen the strips at each in-
`tersection, the apparatus being further character-
`45 ised by having electronic means for detecting a
`change in the capacitive coupling at any intersec~
`tion and thereby identify the intersection as a
`touchvselec‘ted position.
`2. An apparatus as claimed in Claim 1, charac-
`50 terised in that said electronic means comprises
`pulse generator means for applying a pulse to
`each of the strips of the first layer in turn, in a re-
`current cycle, pulse detector means for detecting a
`resultant pulse, which exceeds a threshold ampli-
`55 tude. on any one of the strips of the second layer,
`and output means for providing signals which rep-
`resent the intersection formed by the two strips.
`one in each of said first and second layers. to
`which a generated pulse is applied and from which
`50 'a resultant pulse is obtained.
`3. An apparatus as claimed in Claim 1 or Claim
`2, characterised in that the two layers of strips and
`the layer of dots are formed by respective deposi-
`tion stages onto a rigid transparent substrate.
`4. An apparatus as claimed in Claim 3, charac-
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