.
`
`United States Patent [19]
`Gerpheide
`
`lllllllllllllllllllllllllllIlllllllllllllllllllllllllllllllllllllllllllllll
`[11] Patent Number:
`5,305,017
`[45] Date of Patent:
`Apr. 19, 1994
`
`USO05305017A
`
`.
`
`[54] METHODS AND APPARATUS FOR DATA
`INPUT
`
`[76] Inventor: George E. Gerpheide, 3481 S. Monte
`Verde Dr., Salt Lake City, Utah
`84109
`
`[21] Apple NO-= 914,043
`-
`_
`[22] Filed"
`
`Jul- 13’ 1992
`
`4,476,463 10/1984 Ng et a]. .
`4,495,485 l/1985 Smith .................................. .. 341/33
`4,550,221 10/1985 Mabusth .
`4,587,378 5/1986 Moore ................................. .. 178/18
`4,639,720 l/ 1987 Rympalski et a1. .
`4,672,154 6/1987 Rodgers et a1. .
`4,680,430 7/1987 Yoshikawa .
`4,736,191 4/1988 Matzke et al. .................... .. 340/709
`4,740,781 4/1988 Brown ............. ..
`341/33
`4,743,895 5/1988 Alexander ........................... .. 341/33
`
`Related US. Application Data
`
`[63]
`
`Continuation of Ser. No. 754,329, Sep. 4, 1991, which
`is a continuation of Ser. N0. 394,566, Aug. 16, 1989.
`
`Prim"? Examiner-WW5“ Weldon
`Assistant Examiner-M. Fatahiyar
`~ _
`Am" "2}" Agem' 0’ Fm" Thorpe North 8‘ Western
`
`56
`l
`1
`
`ABSTRACT
`[57]
`[51] Int. c1.5 ............................................. .. G09G 3/02
`Methods and apparatus for data input. Devices are pro
`[52] US. Cl. ............................ .. 345/174; 345/168
`vided in accordance with this invention which utilize
`[58] Field of Search ............. .. 340/706, 709, 710, 712;
`capacitive coupling of an object to the device to sense
`341/20, 23; 178/18, 19; 345/ 173, 174, 168
`the object’s position. The devices are comprised of a
`R f
`Ci d
`plurality of electrode strips which form virtual elec
`e erences
`te
`trodes. The virtual electrodes are selectively connected
`U.S. PATENT DOCUMENTS
`to form virtual dipole electrodes which are responsive
`3 886 311 5/1975 Rodgers a a1‘ .
`4,071,691 l/l978 Pepper, Jr. .......................... .. 341/20 m ‘he oblect’s P0519011
`4,l03,252 7/1978 Bobick .
`4,246,452 l/ 1981 Chandler ............................. .. 341/20
`
`17 Claims, 13 Drawing Sheets
`
`/ 30
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`
`EXHIBIT 2011
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`

`

`U.S. Patent
`US. Patent
`
`Apr. 19, 1994
`Apr. 19, 1994
`
`Sheet 1 of 13
`Sheet 1 of 13
`
`‘ 5,305,017
`‘
`5,305,017
`
`EXHIBIT 201 1
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`EXHIBIT 2011
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`U.S. Patent
`US. Patent
`
`Apr. 19, 1994
`Apr. 19, 1994
`
`Sheet2 of 13
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`EXHIBIT 201 1
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`EXHIBIT 2011
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`

`US. Patent
`
`. Apr. 19, 1994
`
`Sheet 3 of 13
`
`5,305,017
`
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`US. Patent
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`Apr. 19, 1994
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`EXHIBIT 2011
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`

`

`U.S. Patent
`
`Apr. 19,1994
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`5,305.,017
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`EXHIBIT 201 1
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`EXHIBIT 2011
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`

`

`US. Patent
`
`Apr. 19, 1994
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`Sheet 6 of 13
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`EXHIBIT 2011
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`

`

`US. Patent
`
`Apr. 19, 1994
`
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`EXHIBIT 2011
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`

`

`US. Patent
`
`Apr. 19,1994
`
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`5,305,017
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`
`EXHIBIT 2011
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`

`

`US. Patent
`
`Apr. 19, 1994
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`Sheet 9 of 13
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`5,305,017
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`EXHIBIT 2011
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`US. Patent
`
`Apr. 19,1994
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`EXHIBIT 2011
`
`

`

`US. Patent
`
`Apr. 19,
`
`1994
`
`Sheet 11 of 13'
`
`5,305,017
`
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`
`EXHIBIT 2011
`
`

`

`US. Patent
`
`Apr. 19,
`
`1994
`
`Sheet 12 of 13
`
`5,305,017
`
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`
`EXHIBIT 2011
`
`

`

`US. Patent
`
`Apr. 19,1994
`
`Sheet 13 of 13
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`
`5,305,017
`
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`
`EXHIBIT 2011
`
`

`

`1
`
`METHODS AND APPARATUS FOR DATA INPUT
`
`This application is a continuation of U.S. application
`Ser. No. 07/754,329, ?led Sep. 4, 1991, which is a con
`tinuation of prior application Ser. No. 07/394,566, ?led
`on Aug. 16, 1989, by George E. Gerpheide for METH
`ODS AND APPARATUS FOR DATA INPUT.
`
`FIELD OF THE INVENTION
`This invention relates generally to methods and appa
`ratus for data input. More speci?cally, this invention
`relates to touch sensitive input devices for data input to
`computers and other instruments.
`
`l0
`
`15
`
`25
`
`30
`
`20
`
`5,305,017
`2
`tric ?eld from the tip of a conductive pen cartridge. The
`pen tip is capacitively coupled to a digitizer tablet hav
`ing an X-Y coordinate system. The pointing device
`disclosed in the second Rodgers et al. patent may also
`function as a mouse. See column 1, lines 65 through 68.
`Both the stylus embodiment and the mouse embodiment
`disclosed 'in the second Rodgers et al. patent are both
`_ active devices which emit electrostatic ?elds that inter
`face with the digitizer tablet.
`The Rodgers et a1. patents disclose digitizing styluses
`and mouse pointing devices which require a separate
`rolling surface. Furthermore, both of these patents dis
`close devices which are active and emit electrostatic
`?elds to interact with the digitizing tablet in order to
`input data to a computer. Since the devices disclosed in
`both Rodgers et al. patents are active, the stylus is either
`attached to the tablet by a wire or contains a replaceable
`power source such as a battery. In either case, the user
`is required to grasp a bulky item in order to_ use the
`device. Thus, the devices disclosed in the Rodgers et al.
`patents do not satisfy a long-felt need in the art for
`pointing and input devices which can be conveniently
`and ef?ciently used for a variety of portable and desk
`top applications.
`It has been known in the art to use tactile sensing
`devices to provide data input. See U.S. Pat. No.
`4,680,430, Yoshikawa et al. The Yoshikawa et a1. patent
`discloses a coordinate detecting apparatus for determin
`ing the coordinate position data of a point on a plane
`indicated by the touch of a ?nger tip or other load.
`Yoshikawa et al. teaches an analog type apparatus
`which uses a resistive ?lm through which the coordi
`nate position of a point is detected. The point’s coordi
`nate position is indicated by applying a load impedance
`to the position. See column 3, lines 8 through 22.
`Tactile devices such as those disclosed in Yoshikawa
`et al. exhibit a signi?cant disadvantage since they re
`quire electrical contact between the ?nger tip and the
`device. When individuals possess long ?ngernails or
`have other objects about the ?ngers and hands, good
`electrical contact is prevented and the device does not
`function properly.
`Other analog tactile devices also exist in the art. See,
`e.g., U.S. Pat. No. 4,103,252, Bobick. The Bobick patent
`discloses electrodes located on the boundaries of a sens
`ing region. Human touch on an edge of an electrode
`produces a capacitive charge to vary the time constant
`of an RC network which is part of an oscillator. The
`variation in capacitance of the sensor changes the time
`constant of the RC network and results in a change in
`frequency in the output signal of the oscillator. See
`column 2, lines 8-20.
`U.S. Pat. No. 4,736,191, Matzke, discloses a touch
`activated control device comprising individual conduc
`tive plates which form sectors of a circle. A user’s touch
`on the dielectric layer overlaying the plates is detected
`by individually charging and discharging each of the
`sectors in the plates in a sequential manner to determine
`the increased capacitance of the sector. See column 2,
`lines 26 through 40.
`Display devices which are touch sensitive have also
`been utilized in the art. See U.S. Pat. No. 4,476,463, Ng
`et al. The Ng et al. patent discloses a display device
`which locates a touch anywhere on a conductive dis
`play faceplate by measuring plural electrical imped
`ances of the faceplate’s conductive coating. The imped
`ances are at electrodes located on different edges of the
`faceplate. See column 2, lines 7 through 12. The touch
`
`BACKGROUND OF THE INVENTION
`Input devices for computers are well known in the
`art. There are several types of input devices, such as the
`familiar “mouse", which have been utilized and are
`generally useful in providing “user friendly” computer
`systems for both technical and non-technical applica
`tions. The popularity which these devices have
`achieved in the art can be given large credit for foster
`ing the explosive growth of the personal computer
`industry since they provide a simple means for users to
`input data to computers for users.
`Currently, about 95% of all input devices or “point
`ing devices” are mice. A mouse generally requires a
`free-rolling surface on which it can interface. Depend
`ing upon the particular mouse which is used, the device
`couples to the free-rolling surface and translates move
`ment across the surface as an input to a computer. Thus,
`the mouse is unsuitable for any input application which
`cannot provide space for a rolling surface. The current
`and growing popularity of “laptop” computers thus has
`created a signi?cant problem for mouse type technolo
`gies which require a rolling surface. Laptops are gener
`ally used in small con?ned areas such as, for example,
`airplanes, where there is insuf?cient room for a rolling
`surface. Therefore, a long-felt need in the art exists for
`non-mouse pointing solutions for computers and other
`instruments.
`A further long-felt need in the art exists for input and
`pointing devices which are simple to use and which can
`be easily integrated with current computers. This long
`felt need has not been solved by previous mechanical
`ball or shaft rolling technologies, such as, for example,
`track balls. Furthermore, new pointing devices should
`be reliable and rugged, with the ability to be transported
`to a variety of locations. Current track ball devices do
`not satisfy these long-felt needs and are also quite cum
`bersome since they require practiced dexterity by the -
`user as he interacts with the device.
`Other types of pointing or input devices have been
`employed in the art. U.S. Pat. No. 3,886,311, Rodgers et
`al., discloses a writing pen for detecting time varying
`electrostatic ?eld components. The writing pen dis
`closed in Rodgers et al. is used in conjunction with a
`writing tablet which generates an electrostatic ?eld.
`The Rodgers et a1. patent discloses an X-Y grid having
`a writing surface overlaying the grid and an active
`stylus which writes on the grid in the same manner as a
`ball point pen. See column 2, lines 63, through column
`3, line 7.
`Other examples of stylus-type or “tablet” input de
`vices are disclosed in U.S. Pat. No. 4,672,154, also to
`Rodgers et al. The second Rodgers et al. patent dis
`closes a cordless stylus which emits a directional elec
`
`40
`
`45
`
`50
`
`60
`
`65
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`EXHIBIT 2011
`
`

`

`20
`
`5,305,017
`4
`3
`Methods of measuring an object's position are further
`sensitive devices disclosed in Ng et al. are generally
`provided in accordance with the present invention. The
`designed to overlay a computer display and provide
`methods comprise the steps of providing an electrically
`positioning information.
`sensitive pad comprising insulator means having ?rst
`The tactile input devices disclosed in the Bobick,
`and second sides for providing an insulating substrate to
`Matzke et al. and Ng et al. patents do not satisfy a long
`the apparatus, ?rst electrode means electrically coupled
`felt need in the art for tactile input devices which accu
`rately and ef?ciently provide data input for computers
`to the ?rst side of the insulator means for establishing an
`electromagnetic ?eld, second electrode means electri
`and other instrumentation. The devices disclosed in the
`cally coupled to the second side of the insulator means
`aforementioned patents fail to satisfy this long-felt need
`for further establishing the electromagnetic ?eld in
`since they effectively only measure position as a frac
`cooperation with the ?rst electrode means, synthesis
`tion of the distance between electrodes located on the
`means operatively coupled to the ?rst electrode means
`boundaries of a sensing region. This leads to measure
`and the second electrode means for selecting ?rst elec
`ment inaccuracies since the distance between electrodes
`is relatively large, thereby causing small errors in the
`trode means and second electrode means to repeatedly
`synthesize virtual dipole electrodes. The steps of the
`measured fraction to result in large position errors.
`methods further comprise measuring electrical balances
`Still other tactile sensing devices utilize a grid of
`electrodes to digitally determine an object’s position
`between the plurality of ?rst electrode means and the
`somewhere on the grid. See U.S. Pat. No. 4,550,221,
`second electrode means, calculating the object's coarse
`Mabusth, and U.S. Pat. No. 4,639,720, Rympalski et al.
`position based on at least one target index, calculating
`The Mabusth patent discloses a touch sensitive control
`the object’s ?ne position based on the measured bal
`device which translates touch location to output signals
`ances between the plurality of ?rst electrode and sec
`and which includes a substrate that supports ?rst and
`ond electrode means, and calculating the object’s net
`second interleaved, closely spaced, non-overlapping
`position.
`conducting plates. The plates are aligned in rows and
`BRIEF DESCRIPTION OF THE DRAWINGS
`columns so that edges of each ‘plate of an array are
`proximate to, but spaced apart from, the edges of plates
`FIG. 1 is a block diagram of a touch sensitive control
`of the other array. The ?rst and second arrays are peri
`device provided in accordance with this invention.
`odically connected in a multiplexed fashion to a capaci
`FIG. 2 shows a touch sensitive control device pro
`tance measuring circuit which measures the change in
`vided in accordance with this invention interfaced with
`capacitance in the arrays. In effect, the Mabusth patent
`a computer keyboard.
`discloses a grid of pixels which are capacitively cou
`FIG. 3 illustrates synthesis of virtual electrodes.
`pled.
`FIG. 4 shows synthesis of virtual dipole electrodes
`Similarly, the Rympalski et al. patent discloses an
`from virtual electrodes.
`electronic sketch pad which contains a graphics input
`FIG. 5(a) illustrates a simple virtual dipole electrode.
`pad having an array of transparent capacitive pixels, the
`FIG. $(b) illustrates a simple virtual dipole electrode
`capacitance characteristics of which are changed in
`wrapped around.
`.
`response to the passing of a conductive tipped stylus
`FIG. 6 illustrates cyclic virtual dipole electrodes.
`over the surface of the pad. The change in capacitance
`FIG. 7 is a block diagram of a virtual electrode pad
`is sensed by buffers disposed along the columns of the
`and row and column synthesis circuitry.
`pixel matrix as the rows are scanned at a prescribed
`FIG. 8(a) shows an elevation view of a virtual elec
`scanning rate.
`trode pad provided in accordance with this invention.
`Neither the Mabusth patent nor the Rympalski et al.
`FIG. 8(b) is a plan view of a virtual electrode pad
`patent satisfy a long-felt need in the art for tactile input
`taken along the 8(b) line of FIG. 8(a).
`devices which exhibit good position resolution of an
`FIG. 9 is a block diagram of row and column synthe
`object. Since the aforementioned patents teach devices
`sis circuitry.
`which utilize a grid of electrodes and which operate in
`FIG. 10(0) illustrates object position sensing with a
`a “binary" mode, i.e., measure position by examining
`touch sensitive control device provided in accordance
`each electrode and determining that an object is located
`with this invention.
`or is not located at a point on the grid, the resolution of
`FIG. 10(b) shows object position sensing taken along
`the position measurement is limited to, at best, a few
`the 10(b) line of FIG. 10(a).
`times the grid resolution. This requires an extremely
`FIG. 11 is a graph of electrical balance versus posi
`?ne pattern of electrodes to achieve acceptable position
`tion for a sensed object.
`resolution. However, a ?ne pattern of electrodes is
`FIG. 12 illustrates a preferred embodiment of the
`extremely expensive and, in most cases, not practical.
`electrical balance measurement circuit of FIG. 1.
`Therefore, the Mabusth and Rympalski et al. patents do
`FIG. 13 is a virtual dipole electrode pad on which a
`not satisfy a long-felt need in the art for tactile sensing
`single row virtual dipole electrode and two column
`devices which can input data to computers or other
`‘virtual dipole electrodes are synthesized.
`instruments.
`FIG. 14 is a graph of balances versus object position
`SUMMARY OF THE INVENTION
`for the arrangement of FIG. 13.
`FIG. 15 shows target and base virtual dipole elec
`The aforementioned long-felt needs are met by meth
`trode extent with indices updated reflecting sensed ob
`ods and apparatus provided in ‘accordance with this
`ject position.
`invention. An apparatus for data input is provided. The
`FIG. 16 is a preferred embodiment of a ?ow chart of
`apparatus comprises pad means for sensing at least one
`a control algorithm provided in accordance with this
`object’s position, the pad means having electrical bal
`invention.
`ances responsive to the object’s position, and measure
`FIG. 17 is a flow chart to determine the proximity of
`ment means operatively coupled to the pad means for
`an object to a virtual dipole electrode pad.
`measuring the electrical balances in the pad means.
`
`25
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`FIG. 18 is a ?ow chart to determine the x position of
`an object.
`FIG. 19 is a flow chart to determine the y position of
`an object.
`FIG. 20 is a flow chart to accomplish x position index
`updating.
`FIG. 21 is a ?ow chart to accomplish y position index
`updating.
`DETAILED DESCRIPTION OF PREFERRED
`EMBODIMENTS
`Referring now to the drawings wherein like numerals
`refer to like elements, FIG. 1 is a touch sensitive input
`device provided in accordance with this invention,
`comprised of a virtual electrode pad 20, electrical bal
`ance measurement circuit 30, balance ratio determina
`tion circuit 40, and control circuit 50. In preferred em
`bodiments, virtual electrode pad 20 is in the shape of a
`sheet. In further preferred embodiments, the virtual
`electrode pad 20 is capable of forming “virtual elec
`trodes” at various positions on its top and bottom sur
`faces. The electrodes are denoted as “virtual elec
`trodes” since separate conductive strips on the two
`sides of pad 20 are used to form single elements denoted
`“virtual electrodes.” The virtual electrodes are con
`nected to electronic circuitry capable of measuring the
`electrical balance between selected top virtual elec
`trodes and selected bottom virtual electrodes.
`In still further preferred embodiments, balance ratio
`determination circuit 40 is provided to determine the
`ratio of one balance measurement to another. Control
`circuit 50 selects appropriate electrodes for balance
`measurement and ratio determination. The control cir
`cuit 50 responds to balance ratios to calculate position
`information of the sensed object 60. This information
`may include position along 1 or 2 axes parallel to the
`electrode pad surface. Additional “proximity” informa
`tion along an axis perpendicular to the surface of elec
`trode pad 20 may also be determined from an appropri
`ate balance measurement.
`Position information determined by control circuit 50
`is provided to a utilization means 70 which may be any
`of a variety of electronic or computer devices.
`A finger 60 is shown located with its tip in close
`proximity to the top surface of electrode pad 20. The
`position of the ?nger tip over some region in the x and
`y directions may be sensed, as may its proximity in the
`z direction by virtual electrode pad 20. The sensed
`object 60 could also be a thumb tip, or any other con
`ductive object. The coordinate axis 80 is shown for
`reference.
`Referring to FIG. 2, a touch sensitive input device 90
`provided in accordance with the present invention may
`provide information indicative of an operator’s ?nger
`position to a computer, as an alternative to the function
`commonly performed by a computer mouse. An opera
`tor may draw, select commands, or manipulate graphi
`cally portrayed objects on a computer with touch sensi
`tive input devices provided in accordance with this
`invention. The device 90 may be a separate pad which
`could be held in the hand, placed on a desktop, or in
`preferred embodiments built into a computer keyboard
`100 positioned below the space bar 110 so an operator
`can manipulate it with his or her thumbs. In other pre
`ferred embodiments, the electrodes and insulator might
`be constructed from transparent materials for attach
`ment to the viewing surface of a computer display
`screen.
`
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`The device 90 provides ?nger position information to
`any type of electronically controlled equipment. An
`operator could control the volume of a stereo, tempera
`ture of an oven, time for a cycle of an appliance, selec
`tion of a vending machine item, a “video game” elec
`tronic entertainment game, or the functions of elec
`tronic test or measuring equipment, for example, an
`oscilloscope. If a l-axis form of the device is desired for
`an application, the electrode pad may be of a straight
`linear geometry. It could also be circular or cylindrical,
`having an operation like a common dial or potentiome
`ter knob.
`In preferred embodiments, the sensed object may be
`any substantially conductive object. With an electrode
`pad constructed on an appropriate scale, the device
`could sense the position of a nearby hand, person, auto
`mobile, or piece of machinery. The touch sensitive
`control devices provided in accordance with this inven
`tion could be further adapted for use as an “electronic
`blackboard.”
`Referring to FIG. 3, virtual electrode 120 is com
`prised of a number of electrode strips 130 deployed over
`an area. An electrode strip is a sheet conductive region.
`The strips are separated by insulating spaces 140 but are
`electrically connected together by electrode synthesis
`circuit 150. The area over which the connected strips
`130 are deployed, including the area between strips 140,
`is defined as the area of the virtual electrode.
`As defined and used throughout, the notation A B
`means A modulo B, that is, the remainder when A is
`divided by B. Square brackets are used to enclose indi
`ces, typically selecting one of a number of similar ob
`jects or points. For example, C[i] denotes the “i-th col
`umn”. All indices are to be taken with respect to an
`understood row or column modulus. For example, if
`there are M “columns”, then C[i+ 1] is to be interpreted
`as C[(i+l) M].
`FIG. 4 shows a preferred embodiment of virtual elec
`trode pad 20 with two “row” virtual electrodes 160 on
`the top side of the sheet and two “column” virtual elec
`trodes 170 on the bottom side. In further preferred
`embodiments, each virtual electrode is rectangular in
`shape. The virtual electrodes have a “length” and a
`“width”. The width of the row electrodes 160 are in the
`y direction with respect to the coordinate system 80,
`while the width of the column electrodes 170 are in the
`x direction. The two row virtual electrodes 160 form a
`row “virtual dipole electrode” (V DE) labelled R?] at
`180. A column VDE labelled C[i] at 190 is also formed.
`In still further preferred embodiments, a VDE con
`sists of two virtual electrodes of equal area located
`along side each other. A virtual electrode extending to
`the pad edge may “wrap around” to the opposite side’s
`edge. The component virtual electrodes of the VDE are
`referred to as the “positive” and “negative” halves of
`the VDE. The location (along the axis in the width
`direction in the present example is greater for the posi
`tive half than for the negative half of the VDE. The
`positive half of C[i] is denoted by C[i]<p> at 200 and
`the negative half by C[i]<n> at 210. C[i]<p> is con
`nected to wire CP at 220 and C[i]<n> to wire CN at
`230. Similarly, R?]<p> at 240 is connected to RP at
`250 and R?]<n> 260 to RN at 270.
`The “location” of a VDE is de?ned as the coordinate
`in the width direction of a location line, i.e., equidistant
`between the two component virtual electrodes. Column
`VDEs C[O] . . . C[M—~ l] are located at x[0] . . . x[M- 1],
`respectively. Row VDEs R[0] . .
`. R[N- l] are located
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`at y[0] . . . y[N-1], respectively. The "VDE spacing" is
`the distance between adjacent row (or column, as ap
`propriate) VDE locations. Typically, VDE width is
`greater than VDE spacing and therefore VDEs may
`overlap at adjacent locations.
`Referring to FIGS. 5(a) and 5(b), a preferred embodi
`ment of two simple column VDEs as described above is
`shown. There is a single location line 280 with a nega
`tive VDE half 290 on the left and a positive half 300 on
`the right. Each VDE covers essentially the entire vir
`tual electrode pad 20. In FIG. 5(1)), the location line is
`not in the center of the pad. The <n> virtual electrode
`290 extends to the left edge of the pad and wraps around
`to the right edge at 310. In other preferred embodi
`ments, a VDE may have only a positive half wherein
`the area of the negative half and any mutual capacities
`to the negative half are defined to be zero.
`FIG. 6 illustrates another preferred embodiment of a
`VDE called a “cyclic” column VDE. A cyclic VDE
`20
`consists of a "fundamental” VDE and additional VDEs
`located periodically along the axis. All the <n > virtual
`electrodes 290 are electrically connected together to the
`CN wire 230. Similarly, all <p> virtual electrodes 300
`are connected to C? at 220. Thernumber of component
`VDEs-(including the fundamental VDE) in a cyclic
`VDE is de?ned as the “multiplicity”. The multiplicity is
`three for the example shown. The location 280 of the
`fundamental VDE is taken to be the location of the
`entire cyclic VDE. This location has the lowest coordi
`nate of all the component VDEs. Simple and cyclic row
`VDEs are analogous to the column VDEs described
`here.
`Simple VDEs can be considered to be a special case
`of cyclic VDEs having multiplicity equal to one. The
`advantage of using higher multiplicity is increased accu
`racy compared to a virtual electrode pad of the same
`size and same number of cyclic VDEs but lower multi
`plicity. Assume the former has multiplicity A and the
`latter multiplicity B, where A is greater than B. The
`VDE spacing of the former will be the fraction B/A of
`the latter. Greater accuracy can be realized with the
`former due to the smaller VDE spacing.
`Multiplicity greater than one implies the sensed ob~
`ject’s absolute position can not be determined unambig
`uously. Position can be determined relative to the loca
`tion of one component VDE, but there is no way to
`determine which component VDE. In many cases only
`relative position (that is, a change in position) needs to
`be sensed. With multiplicity greater than one, position
`should be measured frequently enough that the sensed
`object never moves more than half the VDE spacing
`from one measurement to the next. In this fashion, rela
`tive position change can be unambiguously determined.
`A multiplicity of one may be used if absolute position
`must be measured. Another solution is to use two differ
`ent periodic VDEs with different VDE spacings.
`Referring to FIG. 7, virtual electrode pad 20 com
`prises a substrate 320 and a plurality of electrical strips
`130 on both sides of the substrate 320. In preferred
`embodiments, substrate 320 is an insulator. Electrode
`synthesis circuit 150 comprises row synthesis circuit 330
`and column synthesis circuit 340. In further preferred
`embodiments, electrode pad 20 is connected to row
`synthesis circuit 330 through lines A1 through A8,
`shown generally at 350. Similarly, electrode pad 20 is
`connected to column synthesis circuit 340 through lines
`B1 through B8, shown generally at 360. In still further
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`preferred embodiments, there are eight electrode strips
`on the top side of pad 20.
`On command from control means 50, the electrode
`synthesis circuit 150 connects selected electrode strips
`to wires CN, CP, RN and RP to form one row and one
`column VDE on respective sides of the virtual elec~
`trode pad. A signal, S, from control means 50 is input to
`row synthesis circuit 330 and column synthesis circuit
`340 and commands the virtual electrode pad 20 to select
`one row VDE and one column VDE. The location of
`each VDE is varied according to the requirements of a
`control algorithm. Both halves of each VDE are con
`nected to the electrical balance measurement means 30.
`This connection is via wires RN and RP connected to
`the positive and negative halves, respectively, of the
`row VDE; and via wires CN and CP connected to the
`positive and negative halves of the column VDE. In
`preferred embodiments, the electrical measurement
`accomplished is a capacitive measurement between the
`electrode strips.
`FIGS. 8(a) and 8(b) show virtual electrode pad 20.
`Referring to FIG. 8(a), ?at electrode strips 130 are
`present on the top and bottom of separator insulating
`substrate, shown generally at 370. On the top surface of
`electrode pad 20 is a thin overlay insulator 380 which
`prevents a sensed object from making electrical contact
`with electrode strips 130 and substrate 370. It also pro
`tects the electrode strips from corrosion and wear.
`In further preferred embodiments, pad 20 has overall
`dimensions of about 1.0 inch high by 3.5 inches wide by
`0.08 inch thick. Overlay insulator 380 is a 0.02 inch
`thick MYLAR sheet, and separator insulator 370 is a
`0.06 inch thick epoxy-glass printed circuit board mate
`rial. Electrode strips 30 are 0.04 inch wide copper traces
`on 0.2 inch centers fabricated on both sides of the sepa
`rator insulator using standard printed circuit board
`techniques. Dimensions may be varied considerably
`while still achieving good functionality. The width of
`the traces, spacing between the traces, and thickness of
`the circuit board insulator and overlay insulator may be
`selected for the particular application and object being
`sensed. The above-mentioned dimensions give good
`results for a human finger tip.
`Referring to FIG. 8(b), there are eight electrode
`strips on the top side of the separator insulator 370
`perpendicular to the y axis. Wires labelled A0 through
`A7 are attached to these 8 electrode strips. In still fur
`ther preferred embodiments, there ar