United States Patent 5)
`Duwaer
`
`CACAOTRA
`5,231,381
`Jul, 27, 1993
`
`US005231381A
`11) Patent Number:
`
`[45] Date of Patent:
`
`{54] DATA PROCESSING SYSTEM WITH A
`TOUCH SCREEN ANDA DIGITIZING
`TABLET, BOTH INTEGRATEDIN AN INPUT
`DEVICE
`
`4,933,544 6/1990 Tamaru ......cccccessessesseceeseees 340/712
`4,977,397 12/1990 Kuoetal. ........
`.
`5,038,142
`8/1991 Flowerset al.
`..
`:
`4,7775,765 10/1988 Kimura et al. ou... 178/18
`
`
`
`{75]
`
`Inventor: Arne L. Duwaer, Eindhoven,
`Netherlands
`
`[73] Assignee: U.S. Philips Corp., New York, N.Y.
`[21] Appl. No.: 590,985
`{22] Filed:
`Oct. 1, 1990
`[30]
`Foreign Application Priority Data
`Oct. 2, 1989 [EP]
`European Pat. Off.
`........ 89202473.8
`
`FOREIGN PATENT DOCUMENTS
`
`.
`0256327 2/1988 European Pat. Off.
`.
`0297557
`1/1989 European Pat. Off.
`. 0039232
`3/1985 Japan on...eeccscesececenteeeeeene 340/712
`
`Primary Examiner—Ulysses Weldon
`Assistant Examiner—Matthew Luu
`Attorney, Agent, or Firm—Jack D. Slobod
`
`[57]
`ABSTRACT
`TSE] nt, (1S on ceeessseeseeeesesseseeceeees G09G 3/02
`A data processing system includes a multipurpose data
`
`[52] US. Ch. ceecccseeesenen
`ww. 340/712; 340/706;
`input device formed by a touch screen andadigitizing
`178/18; 178/19
`tablet integrated with one another whichare activatable
`[58] Field of Search .............00. 178/18, 19; 340/712,
`independently of each other by proper stimuli. The
`340/708, 706; 367/907, 129; 341/34
`input device is integrated with a flat panel display in
`order to establish a visual feedback to the user or to
`References Cited
`present information pertaining to the entered data after
`U.S. PATENT DOCUMENTS
`processing. The flat panel display, touch screen and
`digitizing tablet take a variety of forms anda variety of
`techniquesare utilized to determine whichof the touch
`screen and digitizing tablet is activated at any time.
`
`[56]
`
`1/1986 Moore et al. vcccscscssee 178/18
`4,564,079
`. 178/19
`4,645,870 2/1987 Adler ww...
`
`8/1987 Greaniaset al.
`ws 178/19
`4,686,332
`
`4,786,896 11/1988 Harte occ cccccecsssesceseneeveee 340/712
`
`8/1989 Taniishi .......ccccccssscneeeee 340/706
`4,853,496
`4,916,308 4/1990 Meadows ....ccssussseesere 340/712
`
`23 Claims, 5 Drawing Sheets
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`a
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`10
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`210
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`TABLET
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`DIGITIZING
`12
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`.
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`Valve Exhibit 1072
`Valve Exhibit 1072
`Valve v. Immersion
`Valve v. Immersion
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`U.S. Patent
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`DATA PROCESSING SYSTEM WITH A TOUCH
`SCREEN AND A DIGITIZING TABLET, BOTH
`INTEGRATED IN AN INPUT DEVICE
`
`2
`by a surface moreorless coinciding with the area to be
`written upon. The known touch screens requiring an
`actual contact
`for activation will
`register simulta-
`neously the contact of the stylus with the screen and the
`contact of the writer’s hand with the screen without
`discriminating between the two impressions. The
`knowntouch screensthat are activatable by manipulat-
`ing an object, like the user’s finger, in front of the screen
`cannot discriminate between the stylus and the user’s
`handeither. For example, both the hand and the stylus
`intercept the light beams ofthe grid that couples a plu-
`rality of light transmitters with a plurality of associated
`light detectors, or both enable a capacitive coupling
`towards ground.
`-
`Also the touch screen and the digitizing tablet oper-
`ate with mutually different resolutions on stimuli, since
`the accuracy of a touch depends on the dimensions of a
`finger (order of magnitude: 1 cm) and the accuracy of a
`data entry with a stylus depends on the dimensions of
`the cooperative part of the stylus (order: 1 mm or even
`smaller).
`
`BACKGROUND OF THE INVENTION
`1, Field of the Invention
`The invention relates to a data processing system
`including an input device with a touch screenfor input-
`ting data into the system by meansof touch,anda digi-
`tizing tablet for inputting data into the system by means
`of manipulation of a stylus near a tablet area, wherein
`the touch screen area and the tablet area are at least
`partly overlapping.
`2. Description of the Related Art
`Systems employing a touch screen as a data input
`device are widely known. By touching the touch screen
`at a predetermined position with a finger, or with an
`object having a similar operation with respect to the
`touch screen, data are selected that are indicative of that
`particular position. Thereupon the associated data are
`introduced into the system and are processed, A touch
`screen may be combined with a display for selecting
`data according to the zones shown onthedisplay, such
`It is therefore an object of the invention to provide a
`as virtual buttons. Also, the display may function as a
`data processing system with a compact data input de-
`means for providing visual feedback to the user by
`vice enabling the entering of data into the system by
`showing the information pertaining to the data after
`touching the touch screen with a finger or the like as
`processing. Onthe basis of the mechanismforactivating
`well as by writing, drawing or accurate pointing on the
`the touch screen several types of touch screens can be
`screen by means of an appropriate stylus as desired.
`distinguished. Touch screens of a first type are those
`A data processing system according to the invention
`that require for activation an actual contact between the
`is therefore characterized in that the touch screen com-
`finger of the user or another object and the screen. An
`prises a first sensing means for convertingafirst stimu-
`example of such a touch screen employsthe localization
`lus representative of a touch presence and location into
`of the absorption of surface acoustic waves propagating
`a first signal for the data handling means, and that the
`in a front-panel,
`the absorption occurring as conse-
`digitizing tablet comprises a second sensing means for
`quence of the contact between the panel and a soft
`converting a second stimulus representative of a pres-
`tissue such as the user’s finger. Another example of a
`ence and location of the stylys into a second signal, the
`touch screen of the first type is a screen wherein the
`first and second sensors being physically distinct and
`reaction-forces and reaction-moments, occurring in the
`their outputsignals being fed out in parallel.
`suspension of the screen when it is touched, are regis-
`Physically distinct sensing means, that is, two sepa-
`tered for deriving the location of the contact.
`rate conversion mechanisms, where components in-
`For touch screens of a second type the presence ofan
`volved in converting a stimulus into a signal are allo-
`object, such as the user’s finger, in the proximity of the
`cated to either the first or the second sensor, have the
`screen is sufficient for enabling the activation of the
`advantage that they are easier to manufacture, because
`touch screen without an actual contact. An example of
`the two distinct sensing devices can be manufactured
`such a touch screen uses a grid of light beams(infrared)
`separately and added successively to the system. It is
`in front of and parallel to a front-panel. The presence of
`also convenientin use, because the outputsignals can be
`an object at a particular location in the grid is detected
`fed out in parallel leaving the data handling means the
`upon the blocking of lightbeams associated with that
`option to handle the outputs in parallel or one by one.
`particular position.
`In another example of a touch
`Thus, the two sensing meanswill not interfere with one
`screen of the second type the user’s finger in the prox-
`imity of the touch screen establishes a capacitive cou-
`another and do not need to contend for shared sensing
`pling towards ground, which coupling can be detected
`means, which allowsfor simplicity and flexibility in the
`and localized.
`design of application programsutilizing such a com-
`bined touch screen and tablet.
`Therefore, the term “touch”in this text will incorpo-
`rate: “manipulating an object in the detection range of”,
`A compact input device is realized by integrating a
`in addition to: “establishing an actual contact with”.
`touch screen and a digitizing tablet with one another.
`It is a disadvantage of the conventional systems that
`Asboth are activatable independently of one another,
`these are not suitable for both a data-input by means of
`the touch screen will only respond to a touch and the
`touching the touch screen at predetermined zones, like
`digitizing tablet will only respond to the stylus. The
`virtual buttons, with a finger or a similar object suitable
`touch screen and the digitizing tablet are integrated on
`for pointing, and a data-input by means of writing,
`the organizing level, that is employing a data handling
`drawing or accurate pointing on the screen with a suit-
`meansthatis commonto both. The data handling means
`able stylus. In other words, the touch screens of the
`handles the data originating in the touch screen as well
`knownsystems cannotrepresent a virtual control panel
`as the data originating in the digitizing tablet.
`with buttons, or a keyboard as well as a digitizing tablet.
`Several types of separate digitizing tablets are known.
`Writing or drawing in an ergonomically justified way
`In.a first example, the stylus radiates ultrasonic waves.
`implies that the writer’s or drawer’s hand is supported
`Forinstance by meansofat least two receivers a cross-
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`SUMMARYOF THE INVENTION
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`bearing then indicates the momentary position of the
`stylus. In a second example, the stylus emits electro-
`magnetic waves that
`induce currents in two sets of
`oblong conductors thatlie in mutually different orienta-
`tions in two parallel planes. The inductive currents in
`the pair of crossing conductors that overlap the area of
`the momentary position of the stylus are detected for
`localization of the stylus. In a third example,the digitiz-
`ing tablet comprises a conductive sheet that conducts
`alternating currents in such a way, that the phase or
`amplitude of the resulting electromagnetic field, mea-
`sured at a predetermined location of the sheet, is indica-
`tive of said location. Via a capactive coupling thestylus
`detects the associated electromagnetic field exhibiting
`the particular phase or amplitude. The information con-
`tained by the phase or amplitude can then be transmit-
`ted to the system and thereupon be processed as an ~
`indication of the stylus’ momentary position. In a fifth
`example the digitizing tablet comprises a resistive sheet
`wherein the radiating stylus induces currents. By mea-
`suring the aggregated currents in two anti-parallel di-
`rections a quantity can be derived indicative of the
`aggregated resistance that the currents have overcome.
`The ratio of the resistances that correspond to the ag-
`gregated currents in two anti-parallel directions is asso-
`ciated with the ratio of distances the currents have had
`to travel through the sheet. By deriving these ratios for
`two mutually independent directions the area can be
`located at which the currents originated,that is the area
`in the nearest proximity of the radiating stylus.
`Atthis pointit will be clear for the man skilled in the
`art that a plurality of combinations of touch screen and
`digitizing tablet both integrated within the same com-
`pact input device will be possible, dependent on the
`screen’s and the tablet’s activation mechanismsor ac-
`cessability in view of their position relative to each
`other.
`Several combinations are possible. The touch screen
`and the digitizing table can be integrated contiguously
`within substantially the same area of the front panel of
`the input device. This set up enables a cooperation be-
`tween the touch screen and the digitizing tablet, the
`touch screen functioning for example as an input device
`for selecting a particular operating mode by means of
`soft keys of the digitizing tablet as a data-receiver. The
`touch screenand thedigitizing tablet need not be copla-
`nar. For instance, the touch screen part may be inte-
`grated in a raised border of the input device under a
`substantial angle with the plane digitizing tablet for
`ergonomic reasons. Also the touch screen andthe digi-
`tizing tablet may occupyareas ofsubstantially different
`proportions. In another embodiment the touch screen
`and thedigitizing tablet are stacked permitting the input
`device to have limited dimensions. Again, the touch
`screen and the digitizing tablet may occupy areas of
`substantially different proportions. Preferably, a selec-
`tion means,like a toggle switch, is provided for alternat-
`ingly turning on oroff either part of the input device in
`order to prevent an unintentional data entry form oc-
`curring, for example from a hand resting on the input
`surface while it manipulates the stylys. As an alterna-
`tive, such an undesired touch signal can be avoided by
`using a data processing system comprising touch dis-
`abling means for disabling touch location sensing in
`response to stylus presence detection.
`Preferably, the structure containing the touch screen
`and the digitizing tablet itself is integrated with a dis-
`play for the visual feedback towardsthe user. In view of
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`the dimensions of this laminated composition the dis-
`play preferably is of the so-called flat panel type.
`Within the technical field of the flat panel displays,
`one can differentiate between self-emitting (or active)
`panels and non-self-emitting (or passive) panels. An
`exampleof an active panelis a thin film electro-lumines-
`cent display (ELD). Such a display comprises a matrix
`of capacitors, each whereof has a dielectric layer be-
`tween twoelectrodes. With a sufficiently high, alternat-
`ing electrical field across the dielectric layer, containing
`for instance ZnS and Mn, hole-electron pairs will be
`generated that wil! cause the radiation upon recombina-
`tion.
`
`Another example of an active flat panel display is a
`plasma display panel (PDP) based on localized vapour
`discharge.
`An example of a passive flat panel display is a liquid
`crystal display (LCD). In a LCD the polarization of
`light by liquid crystals can be varied under control of an
`electric field, giving rise to the modulation of the
`amountoflight transmitted when appropriate polarizers
`are used. In view oftherelatively low powerdissipation
`and ofthe relatively low cost price, the LCD prevails
`over the other types. LCD’s suitable for integration
`with the touch screen and the digitizing tablet may be
`the Twisted Nematic LCD’s, with an active matrix with
`a switching element(e.g. a transistor or a diode-ring) for
`each pixel, the Super Twisted Nematic LCD’s without
`an active matrix, or a Ferro-Electric LCD comprising a
`memory inherent in the display itself.
`Preferably, the data processing system according to
`the invention comprises mouse means coupled to the
`input device in order to enable all current ways of data
`entry. For instance, the “mouse” is operated via the
`touch screen by indirect pointing, that is by touching
`with a finger a particular sector of a segmented com-
`pass-card that is shown on the touch screen resulting in
`relative displacements of the cursor, or via the digitiz-
`ing tablet by direct pointing and cursor-contro! for
`dragging. Thus, the invention provides a data process-
`ing system that is compact, portable, and multi-func-
`tional with respect to data entry. Also, within this con-
`text reference is made to Dutch Patent Application
`8901805 of the same Applicant wherein means are dis-
`closed for converting a touch screen into a keyboard
`which permits professionaly high data-entry speed by
`wayofa tactile feedback towards the user.
`Preferably,
`in case at least the touch screen or the
`digitizing tablet is activatable in an electrical way, the
`input device comprises a conductive sheet at a fixed
`potential for protecting the touch screen or the digitiz-
`ing tablet against electromagnetic radiation originating
`in the control circuitry of the data processing system,
`for instance due to the control of the display. In a
`stacked embodimentthere may be provided a transpar-
`ent conductive layer between the digitizing table and
`the touch screen on the one hand and the radiating
`circuitry part of the display on the other hand.
`Ashas been stated previously,it will be clear to the
`manskilled in the art what kind of touch screen digitiz-
`ing tablet and, display can be integrated within a single
`panel. The usefulness of a particular combination will
`depend among others on the activation mechanisms of
`the touch screen and ofthe digitizing tablet, the possi-
`bility of realizing transparent embodimentsofsaid latter
`parts, and the insusceptibility of the various parts consti-
`tuting the panel to each other’s operation.
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`pact laminated device. The touch screen 10 operates on
`BRIEF DESCRIPTION OF THE DRAWING
`the basis of surface acoustic waves (SAW), radiated by
`Various embodimentsof an input device comprising
`transmitters 16 and 18 into the front panel 20 along
`particular combinations of a touch screen,a digitizing
`respective series of reflective elements 22 and 24 in
`tablet and a flat panel display for use in a data process-
`order to spread the transmitted waves across the panel
`ing system according to the invention will be illustrated
`20. The panel is further provided with receivers 26 and
`by way. of non-limitative examples with reference to
`28 that receive the wavesafter they have beenreflected
`drawing, wherein:
`by respective otherseries of reflective elements 30 and
`FIG. 1 is an exploded isometric view of a first dia-
`32. A SAW-pulse transmitted by transmitters 16 or 18
`grammatic example of an input device containing as
`will be received retarded.and broadenedby receivers 26
`integral parts thereof: a touch screen based on the use of
`or 28. In case a soft tissue, like the user’s finger 34,
`surface acoustic waves, a digitizing tablet based on a
`contacts the panel 20, some of the energy of the SAW-
`capacitive coupling between the tablet and an appropri-
`pulse will be absorbed by thetissue, resulting in a de-
`ate stylus, and a LCD,asa display;
`creased amplitude of the pulse components 36 and 38
`FIG. 2 is an exploded isometric view of a second
`passing throughthe location of contact 40. The moment
`diagrammatic example containing a touch screen and a
`of the receipt of said reduced components,related to the
`display as in FIG. 1 and using a digitizing tablet based
`momentoftransmission,is indicative of the momentary
`on an inductive coupling between the tablet and an
`position 40 at which the absorption occurs. In order to
`appropriate stylus;
`avoid mutual interference, transmitters 16 and 18 may
`alternate transmission.
`FIG.3 is an isometric view of a third diagrammatic
`example using a touch screen andadisplay as in FIG. 1
`The digitizing tablet 12 is situated below touch screen
`and comprising a digitizing tablet based on localizing
`10. The tablet 12 comprises an electrically resistive
`the position of an appropriate stylus by a cross-bearing
`homogeneous sheet 42 of a transparant, electrically
`of ultrasonic waves;
`conductive substance, for instance Indium-Tin-oxide.
`FIG.4 is an isometric view of a fourth diagrammatic
`Along its circumference sheet 42 is provided with a
`example employing a touch screen, that registers the
`plurality of series of highly conductive, uniformly dis-
`forces and movements in the suspension of the screen
`tributed electrodes 44, 46, 48 and 50 for establishing
`for determining a place of contact, and a digitizing
`electrical contacts with the resistive sheet 42. Each
`tablet integrated on a surface of a LCD,the tablet’s
`series of electrodes is connectable to or disconnectable
`Operation being based on ultrasonic-wave-cross-bear-
`from an associated conductor 52, 54, 56 and 58, by
`ing;
`meansofan associated series of switches 60, 62, 64 and
`FIG.5 is an isometric view of a fifth diagrammatic
`66. The switches 60 and 64 are operated simultaneously.
`example of an input device employing a touch screen
`Also the switches 62 and 66 are operated simulta-
`and a digitizing tablet, both based on a capacitive cou-
`neously. The pairs of switches 60/64 and 62/66 are
`pling with the input device, while using a force-thre-
`connected alternately with their associated conductors
`shold for determining the activation of the touch screen;
`52/56 and 54/58, respectively. This basic arrangement
`and
`may be used in various ways.
`FIG.6 is an isometric view of a sixth diagrammatic
`In a first appliance the stylus 68 may comprise a
`example of an input device wherein the display is sand-
`source for generating electromagnetic radiation that
`wiched between the touch screen and the digitizing
`couples capacitively with sheet 42 and an area 70
`tablet, and
`.
`through panel 20 for thereupon inducing currents in
`FIG.7 is a generalized schematic diagram of a data
`sheet 42. These currents will spread over sheet 42 and
`processing system in accordance with the invention.
`will be gathered by conductors 52/56 or 54/58 at zero
`potential, that have been connected to sheet 42. Now,
`the current in each conductoris indicative ofthe aggre-
`gated resistance between area 70 and the relevant con-
`ductor. Since the sheet is homogeneous, this aggregated
`resistance is a quantity that corresponds with a respec-
`tive distance between an area 70 and the respective
`conductor. Therefore, by sensing the aggregated cur-
`rents in both pairs of conductors connected to sheet 42
`the area 70 can be accorded coordinates that corre-
`spond to the stylus’ 68 momentarily position. For sens-
`ing the aggregated currents each conductorthatis con-
`nected to sheet 42 is coupled with a detector (not
`shown) which may contain: a current-to-voltage con-
`verter operating at zero potential (“virtual ground”), an
`amplifier, an ac-to-de converter, an analog-to-digital
`converter and a microcontroller with appropriate soft-
`ware for calculating the coordinates and for possibly
`adjusting for any deviation between calculated coordi-
`nates and physical position of the stylus 68 due to the
`particular embodiment of the shown input device.
`In a second appliance a time-varying electromagnetic
`field is established across sheet 42 which field has alocal
`phasethatis indicative of a position within the field. To
`this end conductors 54 and 58 may supply synchro-
`nously varying simple harmonic voltages to sheet 42,
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`Referring first to FIG..7, the data processing system
`200 of the present invention is seen to generally com-
`prise a touch screen 10 for receiving a touch as by a
`user’s finger 34, a digitizing tablet for interacting with a
`stylus 68 proximate thereto,first sensing means 202 for
`sensing the presence and location of the touch within
`the area of touch screen 10, and second sensing means
`for sensing the presence of stylus 68 abovedigitizing
`tablet 68 and its location within the tablet’s area. The
`first and second sensing means generate respective sig-
`nals 206, 208 and feed them in parallel to data handling
`means 210.
`the Figures same reference numerals
`Throughout
`with designate identical or corresponding parts.
`In FIG. 1 there is showna first diagrammatic exam-
`ple of an input devicefor use in a data processing system
`according to the invention. The input device comprises
`a layered structure with the touch screen 10 at the top,
`the digitizing tablet 12 in the middle and a liquid crystal
`display (LCD)14 at the bottom.For clarity the compo-
`nents constituting the layered structure have been
`drawn spaced out. In practice, the structure is a com-
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`which voltages have a predetermined mutual phase
`difference, like for instance a sine and a cosine time-
`dependence. By first sensing the phase by a probe (not
`shown) in stylus 68 while conductors 54 and §8 are
`active, and then sensing the phase by the probein stylus
`68 when conductors 52 and 56 carry the time-dependent
`voltages, the location of the stylus can be derived from
`the registered phases.
`The digitizing tablet 12 is disposed on top ofa flat
`panel display 14 of the LCD type. As both the touch
`screen 10 and the digitizing tablet 12 are transparant the
`display 14 can be viewed through these devices, for
`instance in order to provide visual feedback to the user
`while writing or drafting with stylus 68 within the
`range ofdigitizing tablet 12 or in order to select data to
`be processed on thebasis of information shown on LCD °
`14 by touching touch screen 10 at a predetermined
`position associated with said data.
`As has been stated above.the figure presents an ex-
`ploded view of a data input device for use in a data
`processing system according to the invention. Thelay-
`ered structure may in practice be realized as a very
`compact device, for instance by using the upper surface
`of a same panel 20 for depositing a pattern thereupon
`constituting the reflective elements 22, 23, 38 and 32,
`and by using the downfacing surface for depositing
`thereupona layerofresistive material constituting sheet
`42 preferably of Indium-Tin-oxide forits transparancy.
`In another embodiment
`the features constituting the
`reflective elements 22, 24, 30 and 32 and the sheet 42
`may be integrated within one of the polarizers 140 of a
`LCD,the reflective elements at the one surface for
`accessability, the resistive sheet 42 at the other surface
`of the respective polarizer. In a further embodiment the
`digitizing tablet 12 and the touch screen 10 each may
`comprise a separate associated panel like panel 20 in
`view of convenient manufacturing said devices.
`Since both the touch screen 10 and the digitizing
`table 12 utilize different activation mechanisms, (the
`touch screen 10 is activated mechanically, the digitizing
`lablet 12 is activated electrically) the input data trans-
`ferred into the data processing system via the input
`device shownin FIG. 1 are distinguishable. In order to
`feed input data selectively into the data processing sys-
`tem,
`the system may be provided with a selection-
`switch to enable either the touch screen 10 orthe digi-
`tizing tablet 12. In the alternative, stylus 68 may incor-
`porate either a (piezo-ceramic) pressure sensor with
`appropriate processing or simply a pressure-sensitive
`switch for turning-off the touch screen 10 and turning
`on the digitizing tablet 12 upon contacting the surface
`of the input device.
`In FIG. 2 a second example is shown of a disassem-
`bled input device for use in a data processing system
`according to the invention. The example in this FIG. 2
`discloses the LCD 14 to havea polarizer 140 forming an
`isolating panel as a part of the digitizing tablet 12. The
`digitizing tablet comprises two sets of oblong conduc-
`tive loops that lie in a mutually perpendicular orienta-
`tion in two parallel planes separated by an electrically
`isolating polarizer 140. For clarity only two crossing
`loops 80 and 82 have been drawn. By manipulating a
`stylus 68 having a tip 84 that radiates electromagnetic
`waves inductive currents occur in the loops 80 and 82
`that overlap the projection onto the digitizing tablet 12
`ofan area 86 at the surface ofthe input device, in which
`area 86 the stylus tip 84 is maintained.
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`By sensing those inductive currents the momentary
`location ofthe stylus’ tip 84 is determined. Preferably
`the stylus is provided with a pressure sensitive switch at
`tip 84 for radiating only when contacting the surface of
`the input device upon sensing a pressure exceeding a
`predetermined threshold. Preferably,
`the conductive
`loops are made of a transparent material, for instance
`Indium-Tin-Oxide. As in FIG. 1 input data are discrimi-
`nated onthebasis of the different physical characters of
`the stimuli, the touch screen 10 being susceptible to
`mechanically draining the energy of the surface acous-
`tic waves, the digitizing tablet being activated electri-
`cally by inducing currents in sets of crossing loops.
`In FIG. 3 a third exampleis shownof an input device
`for use in a data processing system according to the
`invention. The digitizing tablet 12 and the touch screen
`10 now both have been integrated on oneofthe polariz-
`ers 140 of LCD 14. The touch screen 10 is of the sur-
`face-acoustic-wave type already described with refer-
`ence to FIG.1. At the same surface the digitizing tablet
`12 is realized, the operation thereof being based upon
`ultrasonic waves propagating acrossthe polarizer in the
`air. The surface is provided with two ultrasonic receiv-
`ers 90 and 92 for determining the position of a source of
`ultrasonic pulses at the tip 74 ofstylus 68, for instance
`by means of cross-bearing. Preferably, more than two
`ultrasonic receivers are employed in order to ensure
`that position decoding is always possible in spite of the
`presence of the user’s hand that may obstructtheultra-
`sonic waves.
`FIG. 4 discloses an input device wherein the opera-
`tion of the touch screen part 10 employs the registering
`of the reaction forces and -moments in the suspension of
`the device and wherein the digitizing tablet 12 uses the
`capacitive coupling between the tablet and a special
`stylus as has been described previously with reference
`‘to FIG. 1. The touch screen part is established by sus-
`pending the LCD 14 byfour elastic devices 104, 106,
`108 and 110, that are attached to a rigid frame 112. Each
`elastic device comprises a strain gauge, for instance a
`piezo resistive strain gauge printed on an aluminum
`substrate, like gauges 114, 116, 118 and 120. Each gauge
`incorporates several resistances that, for example, are
`connected in Wheatstone bridge configurations (not
`shown) in order to derive from the various reaction-
`forces and -movements in the suspension, occurring
`whenan external force is applied to the upper surface of
`the input device, the location whereto the external force
`is applied.
`Filter means may be provided forfiltering out reac-
`tion forces and moments, that are due to the input de-
`vice’s inertia when it is moved and therefore bear no
`relation with any intended activation. For instance, the
`filter means may be realized in software for discriminat-
`ing signals that have predetermined characteristics rep-
`resenting an intended activation by touching the input
`device with a finger or a stylus in a specified, ergonomi-
`cal way.
`The use of the gauges may be restricted to measure
`the force in order to compare it with a threshold for
`ergonomic reasons. This will be clarified by way of
`FIG. §, which is similar to the previous FIG. 4 to a
`large extent. Now, the homogeneouselectrically resis-
`tive sheet 10 and 12 plays a part in both thedigitizing
`tablet 12 and the touch screen 10. In order to function as
`a touch screen for being activated by the proximity of
`finger 130 appropriate electronic circuitry (not shown)
`is provided for detecting a capacitive coupling from
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`sheet 10 and 12 towards earth via finger 130 and for
`thereupon deriving the finger’s 130 position. This item
`is well knownin the art. In order to function as a digitiz-
`ing tablet cooperating with stylus 68 other appropriate
`electronic circuitry (not shown) is incorporated for
`determining the stylus’ 68 momentary position in the
`way as has already been described with reference to
`FIG.1. In this particular embodiment the stimuli that
`represent the finger’s 130 touch or the presenceofstylus
`68 for activating the touch screen part or the digitizing
`table part, respectively, are of a same physical character
`(a signal detected capacitively).
`The aggregated force measured by the gauges 114,
`116, 118 and 120 is compared with a threshold by a
`comparator (not shown) for determining when the
`touch screen should be activated. Preferably,
`the
`threshold corresponds with a force of 60-80 gram asso-
`ciated with the pressing of a key in a conventional alfa-
`numerical keyboard of a typewriter. Only when the
`applied force exceeds the predetermined threshold the
`touch screen will be activated. Therefore, the use of
`gauges makes an adjustment of the touch screen part
`possible with respect to the required force to be applied
`for activating the touch screen.
`Within this context it should be mentioned that the
`use of gauges as a touch-force thresholding means may
`be of particular advantage for ergonomic reasons in
`respect ofa tactile feedback when employing a touch
`screen of the kind,
`that does not require an actual
`contactfor activation, for instance the capacitive touch
`screen discussed above and the touch screen based on
`obstructing light beams that form a grid in front of a
`front panel.
`In all examples given thus far, the digitizing tablet
`part hadto be transparent becauseofits location in front
`of the display. An exampl