»
`United States Patent 15
`Stein et al.
`
`U
`$005365461A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,365,461
`Nov. 15, 1994
`
`[54] POSITION SENSING COMPUTER INPUT
`DEVICE
`
`[75]
`
`Inventors: Robert A. Stein, Bridgewater, Mass.;
`James D, Logan, Windham,N.H.;
`Charles A. Woringer, Catumet, Mass.
`[73] Assignee: MicroTouch Systems, Inc.,
`Wilmington, Mass.
`[21] Appl. No.: 860,054
`:
`[22] Filed:
`Apr. 30, 1992
`
`Tint, C15 oo...ccsecscnerceeetsnencearacseneceeeeres G01B 7/00
`[5 1]
`
`[52] U.S. Cl.
`...
`
`[58] Field of Search.............--+-0- 364/350; 178/19
`[56]
`References Cited
`U.S. PATENT DOCUMENTS
`4,659,874 4/1987 Landmeier .......secs 178/19
`4,680,429
`7/1987 Murdocket al. ........-eeeee 178/19
`
`4,686,332
`8/1987 Greanias et al. oi. 178/19
`
`«- 178/19
`4,788,384 11/1988 Bruere-Dausonetal.
`«» 178/19
`1/1989 Yamazaki ........
`4,795,858
`
`.. 178/19
`4,806,708
`2/1989 Yahagi ..........0.
`4,848,496 7/1989 Murakamiet al... 178/19
`Primary Examiner—Jack B. Harvey
`Assistant Examiner—Thomas Peeso
`Attorney, Agent, or Firm—Kirk Teska; Joseph S.
`Tandiori
`anczorio
`ABSTRACT
`[57]
`a .
`.
`.
`.
`A position sensing computer input device including a
`sensor with a sensing surface including a conductive
`sheet on which a human touch and the touch of an
`inanimate object may both be sensed. The deviceis able
`to discriminate between the two types of touch for
`allowing input with at least one of an inanimate object
`and a human touch.
`
`31 Claims, 3 Drawing Sheets
`
`
`
`Valve Exhibit 1075
`Valve Exhibit 1075
`Valve v. Immersion
`Valve v. Immersion
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`

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`U.S. Patent
`
`Nov. 15, 1994
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`Sheet 1 of 3
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`5,365,461
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`CONVERTER
`€ CONTROLLER
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`POSITION
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`OUTPUT
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`120 122 124
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`FIG. SA
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`5,365,461
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`U.S. Patent
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`Nov.
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`15
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`, 1994
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`Sheet 2 of 3
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`US.
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`Patent
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`Nov.
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`315
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`1994
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`Sheet 3 of 3
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`5,365,461
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`1
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`5,365,461
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`POSITION SENSING COMPUTERINPUT DEVICE
`
`FIELD OF INVENTION
`
`This invention relates to a position sensing computer
`input device which is responsive to both human and
`stylus touch and which discriminates between the two
`types of touch for allowing input in either manner with
`a single sensor device.
`BACKGROUND OF INVENTION
`
`10
`
`There are many types of touch sensitive computer
`input devices currently used for the purpose ofdigitiz-
`ing touch on or in conjunction with computer displays.
`Such devices measure the position of a stylus or finger
`touch on the sensor surface. The position is used to
`generate coordinates for the purpose of interacting with
`the computer, for example in pointing to icons on the
`display, picking menu items, editing computer gener-
`ated images, and feedback for input of hand-drawn
`characters and graphics.
`Such devices which sense a human touch may sense
`using any numberof technologies, including capacitive
`sensing, resistive sensing using a conductive overlay
`sheet, infrared sensing, acoustic wave sensing, and pi-
`ezoelectric force sensing. Digitizers which use corded
`handheld styli such as pens or pucks typically use elec-
`tromagnetic sensing, electrostatic sensing,
`resistive
`sensing, or sonic pulse sensing.
`Devices responsive to human touch are typically
`used for cursor control application, for example point-
`ing to display icons and picking menu items. Devices
`that are responsive to styli (usually a corded pen) are
`used to create or trace drawings, blueprints, or original
`art. These devices are also used for character or hand-
`writing recognition.It is desirable that the device have
`a pen and paper feel so that it’s use is intuitive to most
`users. It is therefore desirable that the sensor reproduce
`the trace of the pen below the stylus by some visual
`means so that the user has visual feedback.
`Someof these devices are responsive to both human
`touch and stylus touch, thereby providing the conve-
`nience of stylus-based input, for example when writing
`on the screen, as well as the ease of human touchinput,
`which does not require the user to find the stylus and
`pick it up to use it. However, because these sensors
`cannotdistinguish between human and stylus touch, the
`user may not touch the screen while using the stylus, or
`vice versa. Accordingly, in the use of these sensors the
`operator must take great care, which detracts from their
`desirability.
`Somesuch devices are used as computer input tablets
`which, rather than being placed on the faceof a display,
`are placed on the desk top next to the computer, similar
`to a mouse. Such sensor devices are commonly em-
`ployed for handwriting recognition, in which they are
`used as a writing tablet. However, when using such
`tablets, the operator must painstakingly avoid touching
`the screen with his finger or hand while writing with
`the stylus. Accordingly, these devices are rather awk-
`ward to use.
`One system that has the capability of sensing both
`stylus and human touch is disclosed in U.S. Pat. No.
`4,686,332 (Greanias et al., Aug. 11, 1987). The device
`uses an X-Y array of discrete conductors in spaced
`planes to electrostatically detect the position of the
`stylus; finger touch position is determined by detection
`of a change in capacitance of the conductors closest to
`
`2
`the finger. The two large arrays of closely spaced con-
`ductors required for good resolution, however, is diffi-
`cult to fabricate, requiring etching of two layers of
`conductive material into parallel conductor patterns,
`and then careful placement of the layers one over the
`other to accomplish the spaced X-Y conductor array.
`Having two layers of conductors over the display also
`interferes significantly with light transmittance, making
`the device uncomfortable to use. In addition, each con-
`ductoror pair of conductors requires discrete electronic
`components to make the capacitance measurements,
`making the device compiex and costly. Finally,
`the
`requirement of driving the conductors individually
`results in relatively slow digitization response, unless
`expensive high-speed drive and sensing circuitry is
`used.
`
`SUMMARYOF INVENTION
`
`It is therefore an object of this invention to provide a
`position sensing input device which discriminates be-
`tween a human and inanimate object touch.
`It is a further object of this invention to provide such
`a device which allowsthe user to place his hand on the
`input tablet while writing thereon with a stylus.
`It is a further objectof this invention to provide such
`a device which allowsthe display of the stylus trace on
`the input device.
`It is a further object of this invention to provide such
`a device in which the sensoris virtually transparent.
`It is a further object of this invention to provide such
`a device with relatively simple and inexpensive cir-
`cuitry.
`It is a further object of this invention to provide such
`a device that has fast response.
`It is a further objectof this invention to provide such
`a device that can digitize up to 200 touch points per
`second.
`It is a further object of this invention to provide such
`a device that does not require discrete drive and sense
`components for pairs of conductors.
`It is a further object of this invention that it provide
`a pen and paperfeel.
`This invention results from the realization that a sim-
`ple to use, intuitive computer input device may be ac-
`complished by sensing both human and inanimate-
`object touch, and discriminating between the two, so
`that the user does not have to meticulously avoid touch-
`ing the screen when using a stylus, or vice versa.
`This invention features a position sensing input de-
`vice which includes a sensor with a sensing surface that
`includes a conductive sheet, means for detecting both a
`human touch and the touch of an inanimate object on
`the surface, and means for discriminating between the
`twotypes of touch to allow input with at least one of an
`inanimate object and a human touch.
`The means for detecting a human touch mayinclude
`means for supplying current, preferably time-varying,
`to the conductive surface coating, and may further
`include means for determining the current flow to the
`conductive surface responsive to the touch. The de-
`tected current may be out of phase with the supply
`voltage. The input device may further include means
`for determining the human touch location on the sur-
`face and means for determining the inanimate touch
`location on the surface. In one embodiment, the inani-
`mate object is conductive and may be a cordedstylus.
`In that case, the touch of the conductive object may be
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`electrode pattern has leading from it a wire connected
`to one of four phase-sensitive current devices 14
`through 17 in series with the four corner wires. Time
`varying voltage source 13 is alternately applied to the
`surface of sensor 12 and to stylus 22 through switch 18
`as described below.
`For sensing the position of a human touch operation
`is as follows. Time varying voltage source 13 applies a
`voltage to the surface of sensor 12 through switch 18
`being in position “a”. When person 28 touches the
`screen, a small amount of current
`is conducted to
`ground via the equivalent capacitance Cg. Current de-
`tectors 14 through 17, under control of controller 20,
`are enabled to detect the current flow to each of the
`four corners of sensor 12, 90° leading the phase of volt-
`age source 13. The equivalent circuit for such touch
`sensing is shown in FIG. 2A, described below.
`Forsensing the position of a stylus on the surface of
`sensor 12, the operation is as follows. Time varying
`voltage source 13 applies a voltage to stylus 22. Switch
`18 is set
`in position “b” and current detectors 14
`through 17 are enabled by controller 20 to detect cur-
`rent flowing out of the four corners of sensor 12,
`through the current detectors, to ground. The detection
`is in phase with voltage source 13. The equivalent cir-
`cuit is shown in FIG. 2B, described below.
`Converter and controller 20 receives as its input the
`current values sensed by each of the four phase sensitive
`current detectors 14 through 17, labelled i, through ig.
`Circuit 20 then employs the following algorithm to
`compute the X and Y position of the touch or stylus on
`the surface of sensor 12:
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`detected by supplying a current to the object and deter-
`mining the current flow through the object into the
`conductive coating and in phase with the supply volt-
`age responsive to the touch on the sensor surface.
`In one embodiment, the device discriminates between
`a human andinanimate object touch by alternately en-
`abling the means for detecting a human touch and
`means for detecting an inanimate object touch; this may
`be accomplished with a switch either under control of
`the operator or the system. The operator controlled
`switch may be a manual switch mounted on the stylus,
`a stylus attitude-indicating switch, a finger-sensing
`switch on the stylus, or a stylus-sensing switch in a
`stylus holder, for example. Preferably, the touch of the
`inanimate object is enabled when that touch is concur-
`rent with a humantouch to establish touch priority to
`the inanimate object touch.
`BRIEF DESCRIPTION OF DRAWINGS
`
`Other objects, features and advantages will occur to
`thoseskilled in the art from the following description of
`a preferred embodiment and the accompanying draw-
`ings, in which:
`FIG.1is a simplified schematic diagram of a position
`sensing input device according to this invention;
`FIGS. 2A and 2B are equivalent circuits for touch
`and stylus sensing, respectively;
`FIG. 3 is a more detailed schematic diagram of the
`device of FIG.1;
`FIG.4 is a flow chart of the software algorithm for
`the sensor of FIG.1;
`FIG.5Ais a side view of a sensor construction of the
`device of this invention showing a manual switch for
`switching between stylus touch-based sensing;
`FIG. 5B is a cross sectional view of a stylus holder
`used for stylus storing according to this invention and
`FIG.5Cis a partly cross-sectional view ofan alterna-
`tive sensor construction showing additional switching
`schemes.
`
`DISCLOSURE OF PREFERRED EMBODIMENT
`
`This invention may be accomplished in a position
`sensing input device which includes a sensor having a
`resistive sheet sensing surface on which may be de-
`tected a human touch andthe touch of an inanimate
`object. The device then is able to discriminate between
`the two types of touch to allow input with at least one
`of an inanimate object and a human touch.
`There is shown in FIG.1 position sensing input de-
`vice 10 accordingto this invention. Device 10 includes
`sensor 12 made of a glass substrate, typically in the
`shape ofthe display device over whichit fits, to which
`is applied over the front surface a continuousor discon-
`tinuous conductive coating; the discontinuous coating
`may take the form of an etched “waffle pattern” as is
`knownto those skilled in the art. The conductive sheet
`maybe protected from scratching with a thin protective
`coating that still provides for electrical “touching” of
`the conductive coating. Around the perimeter of sensor
`12 is an electrode pattern for conducting current to and
`from the conductive coating of sensor 12 through the
`four sensor corners. The construction of the sensor,
`including the conductive coating and the electrode
`pattern for the coating, is knownto thoseskilled in the
`art, as established for example in U.S. Pat. Nos.
`4,071,691, 4,129,747, 4,198,539, 4,293,734, 4,302,011,
`and 4,371,746, all by Pepper, Jr., and incorporated
`herein by reference. Each of the four corners of the
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`Device 10 is thus able to sense the touch of an inani-
`mate object as well as a human touch; the device dis-
`criminates between those two types of touch as follows.
`First, controller 20 may be enabled to convey to output
`26 information relating to the state of switch 18, which
`indicates whetherthe touchor stylus sensing is enabled.
`Then, when a touch point is found, the type of touch is
`known. Preferably, the device prioritizes stylus sensing
`over human touch sensing so that the operator may rest
`his hand on the sensor while using the stylus as the input
`device, as commonly occurs in handwriting or charac-
`ter recognition.
`Alternatively, the system may output virtually simul-
`taneously for both the stylus and touch by rapidly oper-
`ating switch 18 at approximately 200 times per second,
`which is sufficient for most digitization applications,
`including handwriting recognition. For handwriting
`recognition, however, it is preferable to sense only the
`stylus.
`The above description contemplates employing ca-
`pacitive sensing technology in digitizing the stylus and
`finger touch location. However,this is not a limitation
`of the invention as any of the appropriate digitization
`technologies may be employed. For example, sensor 12
`could employ capacitive type sensing for sensing the
`human touch and resistive sensing for the stylus with
`appropriate sensor and signal drive configurations. As
`an example, a human touch sensor using any available
`technology, for example surface acoustic wave, light
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`beam, or capacitive sensing, could be physically laid
`over an electromagnetic digitizer tablet to form a fin-
`ger/stylus sensing assembly. As long as the two layers
`were carefully aligned to maintain touch-point digitiza-
`tion accuracy, such a combined assembly would be
`practical.
`An alternative sensor arrangement could employ
`discrete portions of sensor conductor for providing
`touch sensitivity in only selected portions of the device.
`Such an arrangement would be preferred for a touch-
`sensitive keyboard or keypad arrangement.
`FIG. 2A illustrates the circuit equivalent to that of
`FIG.1 for sensing a human touch;the current sensed by
`detector 24 is 90° leadingofthe voltage source 13a. The
`equivalent circuit for stylus sensing is shown in FIG.
`2B. In this mode, the sensed currentis in phase with the
`voltage source.
`FIG. 3 shows in greater detail an embodiment of
`device 10a in which buffer 38 is employed as a source of
`current to the lower left (LL) corner of sensor 12 for
`sensing human touch (touch mode), and as a current
`sink from the same sensor corner when operating to
`detect a stylus (stylus mode). In touch mode, switch 18
`is in the position shown, and buffer 38 acts as a current
`source for supplying current to the lower left corner of
`sensor 12. When sensor 12 is touched, current is con-
`ducted to groundat the point of touch. Component 30
`would include three parallel duplicates of converter
`circuit 21 and buffer 38 to supply the samesignal toall
`four corners for capacitive-type sensing of a finger
`touch; only one circuit 21 is shown for clarity. Con-
`verter and controller 20a includes lowerleft converter
`circuit 21 comprising current to voltage converter 40,
`which determines the current flow to the lowerleft
`corner. Phase detector 42 allows the processor 36 to
`sample the input signal at various phase angles as appro-
`priate. Analog filter 44 enables A/D converter 34 to
`sample a stable signal. Analog multiplexer 32 enables
`processor 36 to switch between the four input channels
`so that it may determine the touch location from the
`current flow into each of the four corners of sensor 12.
`In the stylus mode, switch 18 is moved by digital
`processor 36 to ground, and the current is supplied to
`stylus 22. Buffer 38 then acts as a current sink for allow-
`ing the measurement of in-phase current flow from the
`stylus to each of the four corners of sensor 12 before
`digitizing the stylus touch location.
`Undercontrol of processor 36, the device may be
`enabled to sense only human touch, only stylus touch,
`or both at virtually the same time by operating switch
`18 at up to 200 cycles per second. By switching rapidly
`between the two types of sensing modes, the touch and
`stylus can both be detected. Preferably, only one posi-
`tion is digitized and outputted to enable a very fast
`report rate to allow accurate and timely computer input
`using the sensor. If both a touch and stylus are in
`contact with sensor 12 at the same time, processor 36
`preferably reads only the stylus position to enable the
`user to rest his hand on the sensor while writing with
`the stylus.
`FIG.4 details flow chart 80 of the software algorithm
`for operating the device in either the stylus, touch, or
`automatic mode, in which both the stylus and human
`touch can be used for input. After initialization, step 82,
`andif the automatic modeis chosen either by the opera-
`tor or by the system (for example as a default), step 84,
`the hardware is switched to stylus mode first, step 86,
`and if a stylus touch is detected, step 88, the system
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`reports the stylus coordinates to the host computer, step
`90, for use as desired. Operation would then return to
`step 84. If a stylus touch is not detected, the hardware
`switches to touch mode,step 92, and if a touch is de-
`tected, step 94, the system reports the touch coordinates
`to the host computer, step 96, and operation returns to
`step 84. If a touch was not detected, operation returns to
`step 84. Alternatively, to sense both stylus and finger
`touching at virtually the same time, operation after step
`90 could proceed to step 92. This would allow the user
`to use both the stylus and a finger to operate the com-
`puter, for example to allow the user to select a menu
`item with a finger while writing, without the needto lift
`the stylus from the sensor surface.
`If auto modeis not chosen and touch modeis chosen,
`step 98, operation proceedsto step 92 for detection of a
`touch. If the touch mode was not chosen the hardware
`switches to stylus mode, step 100, and when the stylusis
`detected, step 102, the stylus coordinates are reported
`to the host computer, step 104, and operation returns to
`step 84.
`Manypersons using the device in a computer hand-
`writing tablet will tend to rest their hand on the sensor
`surface as they use the stylus to write. Since the hand
`contact interferes with signal
`transmission from the
`stylus, through the sensor conductive coating, and into
`the edge electrodes, touching the sensor while using the
`stylus will cause the computerto resolve a stylus touch
`point that is somewhere between the stylus tip and the
`hand contact area, thereby decreasing the digitization
`accuracy.
`To overcomethis loss of accuracy, the device ofthis
`invention may be enabled to use the perceived stylus
`position in conjunction with the resolved handposition
`determined with the stylus signal off (touch mode), to
`calculate the true stylus position. In effect, the true hand
`position is subtracted from the perceived stylus position
`(stylus plus hand position) to resolve the true stylus
`position.
`The following software algorithm can be used to
`correct inaccuracies due to sensor/display misalign-
`ment, rescale the active sensor area to the display area,
`or correct offset errors in the sensor/analog hardware.
`The algorithm can be executed separately for touch or
`pen modeto eliminate accuracy differences between the
`two modes. Theuser is required to touch the lowerleft
`and upper right display to “‘rescale” the reported coor-
`dinates to these points.
`Xcorrected==Nx(X—X11)/(Kur—-X1 rN)
`Yeorrected=Nv -Y) p/(Yur— Yi 1)
`Where:
`X,Y—Calculated via algorithm set forth above.
`Nx,Ny=X and Y Axis resolution.
`X11,¥11 = Coordinates reported at lowerleft touch.
`XunYur=Coordinates reported at upper
`right
`touch.
`The software could also enable the system to desig-
`nate selected screen portions to detect only touch, or
`only the stylus. This could be accomplished by report-
`ing touch digitization points only in areas designated for
`touch sensing, and doing the same for stylus sensing.
`This feature would be especially useful as a simple
`means of rejecting touch in an area (potentially the
`entire screen) designated for handwriting input using
`the stylus, in order to allow the user’s hand to rest on
`the sensor surface while writing.
`FIGS. 5A and 5Billustrate two alternate embodi-
`ments for accomplishing switching between stylus and
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`finger sensing. Manual switch 71 FIG. 5A, which may
`be a slide switch, may be mounted on stylus 22 for
`manual operation by the user. Switch 22 would in this
`embodiment
`replace machine-controlled switch 18,
`FIG.1, to provide user selection of sensing mode. Al-
`ternatively, stylus holder 150, FIG. 5B maybe used for
`stylus storage, in receiving slot 152, and microswitch
`154 or anotherstylus-sensing means such as a light beam
`may be employed within slot 152 to detect the presence
`of stylus 22a in holder 150, interpreted by the system as
`a user selection of touch mode sensing.
`Alternative means of providing for switching be-
`tween stylus and touch modes are shown in FIG. 5C.
`Stylus-mounted external finger sensors such as capaci-
`tive-sensing metal bands 120, 122, and 124 maybe used
`to detect when the stylus is being held near the tip to
`automatically switch to the stylus sensing mode. Alter-
`natively, spaced resistive contacts 126 and 128, short-
`ened by a user’s finger, may be used for the same pur-
`pose. Lastly, position-sensitive switch 132 may be used
`to detect the relative attitude of stylus 22b; when the
`stylus is vertical or close to vertical, operation is
`switched to stylus mode, and whenthestylusis horizon-
`tal or close to it, operation is switched to touch mode.
`Switch 132 may be a mercury switch in which contacts
`139 and 140 are mounted close to one end ofvial 134
`containing mercury 136 so that mercury 136 creates a
`conductive path between the contacts whenthestylusis
`held near vertical. Switching may also be provided by
`software under user control, for example by use of key
`strokes on the computer keyboard.
`Although specific features of the invention are shown
`in some drawingsand notothers, this is for convenience
`only as each feature may be combined with anyorall of
`the other features in accordance with the invention.
`Other embodiments will occur to those skilled in the
`art and are within the following claims:
`Whatis claimedis:
`1. A position sensing input device, comprising:
`a sensor having on analog sensing surface and includ-
`ing a single layer of one or more conductive sheets;
`means for detecting without electromagnetic radia-
`tion either a human touch or the touch of an inani-
`mate object or both on said sensor; and
`means for discriminating between the two types of
`touch for allowing input with at least one of an
`inanimate object and a human touch.
`2. The input device of claim 1 in which said sensor
`includesan insulative substrate with a single conductive
`surface coating.
`3. The input device of claim 1 in which said means for
`detecting a human touch includes meansfor supplying
`current to each said conductive sheet.
`4. The input device of claim 3 in which said means for
`detecting a human touch further includes means for
`determining the current flow to each said conductive
`sheet responsive to the human touch.
`5. The input device of claim 3 in which said currentis
`time-varying.
`6. The input device of claim 2 in which said inanimate
`object is conductive.
`7. The input device of claim 6 in which said means for
`detecting an inanimate object touch includes means for
`supplying a current to said inanimate object.
`8. The input device of claim 7 in which said means for
`detecting an inanimate object touch further includes
`means for determining the current flow through said
`inanimate object into said conductive surface coating
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`responsive to the inanimate object touch on said sensing
`sensor surface.
`9. The input device of claim 1 in which said meansfor
`discriminating includes means for alternately enabling
`said means for detecting a human touch and said means
`for detecting an inanimate object touch.
`10. The input device of claim 1 in which said means
`for discriminating includes means for detecting the in-
`animate object touch when that touch is concurrent
`with a human touch to establish touch priority to the
`inanimate object touch.
`11. The input device of claim 1 further including
`means for determining the inanimate touch location on
`said surface.
`12. The input device of claim 9 in which said means
`for alternately enabling includes a switch.
`13. The input device of claim 12 in which said switch
`is mounted on the inanimate object for operator control.
`14. The input device of claim 9 in which said means
`for alternately enabling includes means for resolving
`human touch on the inanimate object.
`15. The input device of claim 14 in which said means
`for resolving includes one or more capacitive sensors.
`16. The input device of claim 14 in which said means
`for resolving includes a pair of resistive contacts.
`17. The input device of claim 9 in which said means
`for alternately enabling includes means for determining
`the relative attitude of said inanimate object.
`18. The input device of claim 17 in which said means
`for determining the relative attitude includesa tilt-sensi-
`tive switch for said inanimate object.
`19. The input device of claim 9 in which said means
`for alternately enabling includes a sensor in an inani-
`mate-object holding device.
`20. The input device of claim 1 further including
`means for determining the human touchlocation on said
`surface.
`21. The input device of claim 5 in which said means
`for determining the current flow includes means for
`detecting current out of phase with the voltage.
`22. The input device of claim 8 in which said means
`for determining the current flow includes means for
`detecting current in phase with the voltage.
`23. The input device of claim 1 in which said means
`for detecting includes a phase-sensitive detector.
`24. The input device of claim 1 further including
`means for allowing human or inanimate object touch
`selection of discrete portions of said sensor for provid-
`ing preestablished touch-sensitive areas.
`25. The input device of claim 1 in which said means
`for detecting includes separate human touch and inani-
`mate object touch sensors aligned to accurately report
`touch prints.
`26. The input device of claim 1 further including
`means for calibrating touch position of both a human
`touch and an inanimate-object touch.
`27. A position sensing input device, comprising:
`an insulative substrate with a single conductive sur-
`face coating;
`means for supplying time-varying current to said
`surface coating;
`meansfor resolving current flow to said surface coat-
`ing out of phase with the supply voltage responsive
`to a human touch on said surface coating for de-
`tecting the human touch;
`a conductive stylus;
`means for supplying time-varying current to said
`stylus;
`
`

`

`5,365,461
`
`9
`means for resolving current flow from said stylus to
`said surface coating in phase with the supply volt-
`age responsiveto stylus touch onsaid surface coat-
`ing for detecting the stylus touch; and
`means for discriminating between the human and
`stylus touch for allowing input with at least one of
`said stylus and a human touch.
`28. The input device of claim 27 in which said means
`for supplying time-varying current to said surface coat-
`ing and said means for resolving current flow from said
`stylus to said surface coating includes a current buffer.
`29. A position sensing input device, comprising:
`an insulative substrate with a single conductive sur-
`face coating;
`means for supplying time-varying current
`surface coating;
`meansfor resolving current flow to said surface coat-
`ing out ofphase with the supply voltage responsive
`to a human touch on said surface coating for de-
`tecting the human touch;
`a conductive stylus;
`means for supplying time-varying current to said
`stylus;
`meansfor resolving current flow from said stylus to
`said surface coating in phase with the supply volt-
`
`to said
`
`10
`age responsive to stylus touch on said surface coat-
`ing for detecting the stylus touch; and
`means for alternately enabling said means for resolv-
`ing current flow to said surface coating responsive
`to a human touch and said means for resolving
`current flow from said stylus to said surface coat-
`ing for discriminating between the two types of
`touch.
`30. The input device of claim 29 in which said means
`for alternately enabling includes means for detecting
`stylus touch whenthat touch is concurrent with human
`touch to establish touch priority to the stylus touch.
`31. A position sensing input device, comprising:
`a sensor having an analog sensing surface;
`an input stylus;
`means for detecting without electromagnetic radia-
`tion either a human touch or a stylus touch or both
`on said sensor;
`means for determining whenthestylus is being used;
`and
`means, responsive to said means for determining, for
`reporting only stylus touch points when said stylus
`is being used, to allow the user to physically touch
`the sensing surface while using the stylus.
`%
`*
`*
`*
`*
`
`10
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`60
`
`65
`
`