United States Patent 5
`5,053,757
`[11] Patent Number:
`Oct. 1, 1991
`(45) Date of Patent:
`Meadows
`
`
`[54] TOUCH PANEL WITH ADAPTIVE NOISE
`REDUCTION
`
`Inventor: Robert D. Meadows, Portland, Oreg.
`{75}
`.
`[73] Assignee:
`Tektronix, Inc., Beaverton, Oreg.
`[21] Appl. No.: 455,892
`(22] Filed:
`Dec. 27, 1989
`
`4,698,461 10/1987 Meadowset al. ww 178/19
`
`4,707,845 11/1987 Krein et ab. cecsccssssssesenen 178/19
`4,723,299
`2/1988 Kobayashi oes 178/18
`
`OTHER PUBLICATIONS
`
`.
`Thomas Malzbender, ‘““Permuted Trace Ordering Al-
`lows Low-Cost, High Resolution Graphics Input,”
`Hewlett-Packard Journal, Jun. 1987, pp. 4-7.
`
`[63]
`
`[56]
`
`ae
`Primary Examiner—Jeffery A. Brier
`Related U.S. Application Data
`Assistant Examiner—Richard Hjerpe
` Continurtion of Ser. No. 58,320, Jun. 4, 1987, aban-
`Attorney, Agent, or Firm—John D. Winkelman; Mark
`doned..
`M. Meininger
`
`(S2] Unt. C15 oe
`estenseetereenseeseeeenees G09G 5/00
`[57]
`ABSTRACT
`[52] U.S. Che eeeeeeeteccsetsessetseeeeees 340/712; Sess
`A touch panel has panel scanning signals selectively
`[58] Field of Search
`340/706, 712, 825.34:
`applied to the four sides of a touch sensing surface of the
`178/18, 19 20:84/1.22, 1.24,
`| 26 273/85 G.
`panel so as to establish alternating current voltage gra-
`yoo
`"341/22, 33, 34: 307/116
`dients in desired directions across the touch sensing
`yore’
`surface. When the panelis touched, touchsignals result
`References Cited
`and are utilized by a touch location circuit in determin-
`U.S. PATENT DOCUMENTS
`ing the location of touch. The impedance touch current
`resulting from a user’s touch may also be determined
`te seteeenesresenvesneaenees
`34
`.
`.
`:
`3.995.178
`3/1976 Warfel
`340/825.
`and used. The touch panel circuit automatically filters
`4,205,199
`5/1980 Mochizukioeeeeseeteaes 178/18
`4,213,367
`7/1980 Moog vseeseseee
`84/1.22
`the touch signals to an extent which varies depending
`4,221,975
`9/1980 Ledniczki et al.
`307/116
`upon the rate of movementof touch from onelocation
`
`4,344,347
`8/1982 Faulkner ......ceccseeeeessees 84/1.26
`on the touch sensing surface to a subsequent location.
`pera Novtog Pepper,Jr. ”
`aohpael
`Filtering is decreased with the increasing rates of move-
`1476,
`getalh ou...
`wee
`
`1/1986 Blanchard .....
`4.567.480
`340/712
`ment. The touch panel thereby minimizes the effects of
`4,680,429
`7/1987 Murdocketal.
`178/19
`noise on touch location determination.
`4,686,331
`8/1987 Burgess........
`w 178/19
`4,698,460 10/1987 Krein et al. we. 178/19
`
`21 Claims, 12 Drawing Sheets
`
`190,
`
`88
`
`O
`
`PANEL
`SUPPLY
`
`
`
`INTERFACE
`
`120
`
`98
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`199
`OSC. EN.
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`REFERENCE
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`CONVERTER
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`AMPLIFIER
`
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`
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`Valve Exhibit 1066
`Valve Exhibit 1066
`Valve v. Immersion
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`ANALOG TO
`
`

`

`U.S. Patent
`
`Oct. 1, 1991
`
`Sheet 1 of 12
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`5,053,757
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`U.S. Patent
`
`Oct. 1, 1991
`
`Sheet 2 of 12
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`5,053,757
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`U.S. Patent
`
`Oct. 1, 1991
`
`Sheet 3 of 12
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`U.S. Patent
`
`Oct. 1, 1991
`
`Sheet 4 of 12
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`5,053,757
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`

`U.S. Patent
`
`Oct. 1, 1991
`
`Sheet 5 of 12
`
`5,053,757
` PANEL
`
`
`SUPPLY
`AMPLIFIER
`
`
`QUADRATURE
`OSCILLATOR
`
`
`
`
`
`
`

`

`U.S. Patent
`
`Oct. 1, 1991
`
`Sheet 6 of 12 5,053,757
`
`> @o°o
`
`INIT. FREQ.|482
`(FIG.10)
`
`484
`
`486
`
`X,¥=0
`_ Z*FFh
`
`OUTPUT
`[x,Y,Z]
`
`
`
`SET OLD
`[x,¥,Z]=[x,y,Z]
`
`‘FILTER
`
`FIG.9
`
`
`READ
`POSITION
`
`
`(FIGS. 13,14)
`1
`
`
`496
`
`QUTPUTEL
`
`
`
`502
`
`IN
`H ON BREAR>*
`MODE
`
`504
`
`
`iS OLO
`Z#FFh AND
`
`Z=FFh
`
`
`506
`
`Y_,|
`
`OUTPUT OLD
`[x,¥Z]
`
`
`ON ?
`
`
`508
`
`Y
`
`.
`
`510
`
`DELAY
`(i.e. ONE TSECOND)
`
`

`

`U.S. Patent
`
`Oct. 1, 1991
`
`Sheet 7 of 12
`
`5,053,757
`
`
`
`5i2
`
`5/4
`
`534
`
`FREQ.*7Fh
`
`516
`
`Feonst=0
`OLD Feonst =FFh
`
`518
`
`520
`
`COUNT = 10
`
`536
`
`532
`
`/
`
`OLD Z*Z
`
`538
`
`MEASURE Z
`. (FIG. 12)
`
`522
`
`INIT. NULL
`(FIG. 1)
`
`5452
`
`Y
`
`FREQ.s
`FREQ.+|
`
`
`COUNT =
`
`
`
`
`
`
`COUNT- 1
`SSuej
`FIG. 10
`
`
`
`
`
`
`> N
`
`526
`
`FREQ.=FREQ.+10
`
`

`

`U.S. Patent
`
`Oct. 1, 1991
`
`Sheet 8 of 12
`
`9,053,757
`
`
`
`INET.
`NULL[Xx,Y,Z]
`(FROM
`FIG. 10)
`
`
`550
`
`552
`
`LAST NULL *FALSE
`
`592
`
`SET PANEL STATE
`
`554
`
`SET NULL STATE
`
`594
`
`596
`
`598
`
`600
`
`602
`
`604
`
`556
`
`NULL® NULL+BIT
`
`558 VALUE =
`
`MEASURE[X,Y,Z]
`(FIG. 12)
`
`DISCHARGE
`INTEGRATOR
`
`A/D OFFSET =DIGITIZED
`INTEGRATOR OUTPUT
`
`INTEGRATE
`
`VALUE= DIGITIZED -
`INTEGRATOR
`OUTPUT
`
`FOR [Max mn
`
`2 gain
`
`
`
`VALUE ®
`(VALUE-A/D OFFSET)
`
`SWITCHES OFF
`
`SET PANEL
`STATE TO ALL
`
`606.
`
`608
`
`FIG. 12
`
`MEASURE[X,Y,Z]}
`(FIG. 12)
`OFFSET|x,Y,Z)=|
`MEASURED|X,Y,Z]
`
`568
`
`22°
`
`FIG. ||
`°
`
`582
`
`

`

`U.S. Patent
`
`Oct. 1, 1991
`
`Sheet 9 of 12
`
`5,053,757
`
` FIG. IS
`
`612
`
`
` SHUT DOWN;
`X=OLDX Y=OLDY Z#0
`LAST NULL = FALSE
`
`
` UPDATE
`OFFSETS
`LZ MEASURE
`Z=(2Z)
`(FIG.15)
`X,Y £X,ZY
`GAIN=GAIN +]
`
`
`
`
`

`

`U.S. Patent
`
`Oct. 1, 1991
`
`Sheet 10 of 12
`
`5,053,757
`
`
`
`
`
`
`
`
`FROM
`UPDATE
`FIG.13
`
`FREQ.
`READ
`
`
`(FROM
`
`POSITION
`FIG.15)J690
`CONT.
`
`
`
`
`692
`
`f,(Foftset,UPDATE NULL
`
`
`
`
`
`is
`1s
`
`
`Feonst>OLD
`
`
`Foffset >MAX.
`EX-N ersgain
`
`Foffset
`Fconst
`
`
`
`
`?
`
`696
`N
`.
` _ufYoffset
`PY a a]
`sos
`702 OLD Fconst =
`
`
`raw|FIG.IG
`
`UX
`
`2
`
`642
`
`LY=
`
`694
`
`700
`
`Fconst=
`Foonst + |
`
`Fmod=-Fmod
`
`Feonst
`
`Fconst=0
`Foffset = O
`
`offset (X,Y, Z]=0
`
`706
`
`708
`
`TIO
`
`FREQ.
`FREQ.+Fmod
`
`712
`
`648
`
`650
`
`652
`
`FIG.14
`
`

`

`U.S. Patent
`
`Oct. 1, 1991
`
`Sheet 11 of 12
`
`5,053,757
`
`
`
`660
`
`662
`
`UPDATE NULL®=
`FALSE OLOZ=Z
`
`682
`
`. MEASURE Y
`OLDYsY
`
`684
`
`LAST NULL®*
`TRUE
`
`686
`
`UPDATE NULL2 TRUE
`
`668a
`
`670a
`
`Xnull=Xnull -1
`
`6784
`
`Xoffset>MIN.
`
`Xnulls Xnull+]
`
`
`
`iS
`668
`
`Zoffset > MAX.
`
`Zoffset
`?
`
`Zoffset =
`
`f, (Zoffset, OLDZ)
`
`
`
`
`
`
`iS
` Zoffset =O
`LAST CYCLE A
`NO TOUCH
`
`
`Xoffset =
`f, (Xoffset, OLDX)
`
`680
`MEASURE X
`
`
`OLDX=xX
`
`
`
`
`
`Xoffset
`
`
`
`
`? Yoffset=0
`
`UPDATE FREQ.
`(FIG. 16)
`
`666b
`
`Yoffset =
`f, (Yoffset, OLDY)
`
`688
`
`Xoffset =O
`UPOATE NULL = TRUE
`
`
`
`668b
`
`670b
`
`FIG.15
`
`Yoffset
`
`UPDATE NULL=TRUE
`
`

`

`U.S. Patent
`
`Oct. 1, 1991
`
`Sheet 12 of 12
`
`5,053,757
`
`
`
`FILTER
`POSITION
`
`
`
`(FROM
`
`FIG. 17
`
`
`RETURN\ sg
` SET NUMBER OF
`SAMPLES N
`OF MOVEMENT
`
`FIG.18
`
`726
`
`30
`
`| |
`
`LOCATION
`
`612
`
` DETERMINE RATE
`
` DETERMINE K
`
`N = [Ff (gain)] + [1/k]
`
`
`
` DETERMINE
`
`724
`
`RATE OF
`MOVEMENT
`
`

`

`1
`
`3,053,757
`
`TOUCH PANEL WITH ADAPTIVE NOISE
`REDUCTION
`
`.
`
`This is a continuation of application of Ser. No.
`07/058,320 filed June 4, 1987 and now abandoned.
`
`2
`touch screen by
`a switch closure on a transparent
`switching current between X and Y axes of the touch
`screen. Current which has been passed tnrough the
`various switches of the touch screen is converted to
`voltage and then from analog X/Y signals to digital
`X/Y position coordinates. In such a membrane switch
`type device, the membranes are subject to scratching.
`Also, the multiple layers used in these devices tend to
`This invention relates to a touch panel having a touch
`havea high reflectance,a relatively low light transmis-
`sensing surface and also to a touch panel device having
`sion and a relatively low resolution.
`It is known to detect and to locate the touch on a
`circuitry for determining the location, which may in
`essence be any location, at which the touch sensing
`touch panel by providing an array of optical sources
`surface of the device is touched. In addition, the inven-
`and detectors about the periphery of the touch panel.
`tion relates to the use of adaptive or variable noise re-
`Alternatively, an array of ultrasonic generators and
`duction methods and apparatus in a touch panelto en-
`ultrasonic detectors are provided aboutthe periphery of |
`hance the accuracy of touch location determination.
`the panel. In each instance, the sources and detectors
`The invention. may be used with a wide variety of
`are connected with an electronic system that responds
`to and locates the disturbance which touch causesin the
`display devices of the type which display information
`from which a user makes a selection. One exampleis a
`signals delivered from the sources to the detectors.
`lap held tablet in which a user selects and touches the
`Another capacitive touch detection device is dis-
`device to, for example, indicate a response to a question.
`closed in Ng,et al. U.S. Pat. No. 4,476,463. This partic-
`A further exampleis user selection of information items
`ular device utilizes an electrically conductive touch
`sensitive coated surface with four elongatedelectrically
`displayed on the screen of a display terminal, such as a
`conductive bar electrodes connected to the coating.
`cathode-ray tube (CRT) terminal, which is connected
`to a computerized information processing system.
`One of these electrodes is provided along each side of
`Cathode-ray tube display terminals are known which
`the touch sensitive coating. As described in this patent,
`employ a touch panel with a set pattern of touch sec-
`measurements are made of the changein electrical im-
`tions over a terminal display screen. The termina! re-
`pedance which a capacitive touch introducestoaresist-
`sponds to touch at any section in the prescribed pattern
`ance-capacitance (R-C) circuit. which includes the
`and identifies the location of the touched section. Such
`touch sensing surface. The impedance measurement
`examines the electrical time constant of the R-C circuit
`a system typically employs a capacitive sensing tech-
`nique. That is, a controller continually transmits a scan-
`with the measurementbeing performed repeatedly from
`ning signal across the touch panel and samplesthe sec-
`each end of each of two intersecting linear axes. The
`tions until a touch is detected. When oneofthe sections
`resultant measures are combined to determine the posi-
`tion of the touch. In one embodiment set forth in the
`is touched by a user, the capacitance of the user’s body
`is added to the circuit. The controller senses the result-
`Ng,et al. patent, an alternating current measuring signal
`ing change in capacitance and identifies the touched
`is applied to an electrode and the voltage waveform
`section from this change.
`generated in response to the applied signal is monitored
`One example of such a touch responsive terminal is
`at this electrode. The frequency of this measuring signal
`40
`manufactured by RGB Dynamics of Salt Lake City,
`is varied until the monitored voltage waveform attainsa-
`Utah. In the RGB device, a touch sensitive surface
`selected condition. From the measuring signal
`fre-
`comprises indium tin oxide which is applied to a glass
`quency which yields the selected condition, a determi-
`nation is made of the location of touch from the ener-
`base plate. The coating is patterned in discrete sections
`with conductors coupling each section to an electrical
`gized electrode. In another described embodiment, a
`detection circuit. Such patterning limits the touch reso-
`direct current measuring signal having two successive
`lution to the size of the patterned sections. Also, touch
`selectively-timed values is applied to an electrode. The
`detection is limited by the particular pattern of sections
`touch location relative to the energized electrode is
`employed. In addition, a complex wiring arrangementis
`determined from the voltage at the electrode resulting
`required to make electrical contact with each of the
`from the applied direct current signals. That is, the first
`patterned sections. Such complex connection schemes
`measuring signal charges any capacitance coupled to
`are more proneto failure and more costly than simpler
`the touch sensing coating, including the capacitance
`arrangements.
`due to touch, to a knownlevel. The second signal then
`Another known practice employs a pattern of trans-
`partially discharges the capacitance through theresis-
`parent mechanical switches over a display. Sierracin-
`tance of the touch sensing coating. The voltage remain-
`/Intrex Products of Sylmar, Calif. markets Transflex
`ing on the electrode following this partial discharge
`identifies the location of touch from that electrode. The
`(TM) brand switchesof this type. Morespecifically, this
`particular type of device employs membrane sheets
`circuits described in the Ng, et al. patent have certain
`undesirable complexities, such as the need to apply
`which are pressed together at the touch of a user to
`make electrical contact. When the films are pressed
`signals of varying frequencies or direct current signals
`together at a location, current flowsin a specific circuit
`of two successively-timed values.
`and identifies the location. Another membrane type
`Still another touch panel device with a touch sensing
`touch panel of this type is disclosed in Dorman,etal.
`surface is disclosed in Pepper, Jr. U.S. Pat. No.
`U.S. Pat. No. 4,484,038.
`4,353,552. In the Pepper device, a user touches the
`Also, as described in a product bulletin, Dorman-
`touch sensing surface with a finger, or other body por-
`Bodonoff Corp. of Andover, Mass.hasa priorart Series
`tion, or an electrically conductive stylus. Plural termi-
`1000 touch screen device which utililizes an unpat-
`nations(i.e. the four corners A, B, C and D) of the touch
`terned membrane switch type touch panel. The Series
`sensing surface are simultaneously driven to the same
`1000 touch panel devices have a controller which senses
`instantaneous potential by an oscillator. When the sens-
`
`TECHNICAL FIELD
`
`5
`
`20
`
`25
`
`30
`
`35
`
`45
`
`60
`
`65
`
`

`

`5,053,757
`
`— 0
`
`SUMMARYOF THE INVENTION
`
`3
`ing surface is touched, currents flow throughthe driven
`terminations. The X and Y coordinates of touch are
`determined from these currents independently of the
`impedance of the user’s touch. This approach suffers
`from inaccuracies in touch location determination and
`eliminates impedance information which can be useful
`in certain applications. In one embodiment, Pepperalso
`utilizes pressure sensors, which, for example, sense pres-
`sure at a touchedlocation in excess of a threshold. Upon
`such a determination, discrete action can be controlled,
`such as the firing of a gun during playing of a video
`game.
`The accuracy of a number of these touch panel de-
`vices are adversely affected by noise in the environment
`in which they are used, and in particular by fixed fre-
`quencyinterference spectra, such as from cathode-ray
`tube flyback signals. Moreover, in somedisplay devices,
`the fly-back signal frequency is varied as these display.
`devices are operated. This makesit difficult to compen-
`sate for the effects of such signals.
`Therefore, a need exists for an unpatterned touch
`panel which over overcomesthese and other disadvan-
`tages of the priorart.
`
`4
`with a decreasing rate of movement. In oneillustrated
`embodiment of the present invention, this variable or
`adaptive filtering is accomplished by a processor which
`digitally filters and modifies determined touch locations
`in accordance with the rate of movement. In another
`form of the invention, the number of samples of touch
`signals averaged and processed to determine a touch
`location is varied to accomplish this adaptivefiltering.
`In this approach, the number of samples that are aver-
`aged is increased with a decreasing rate of movement.
`In still another embodimentof the invention, a variable
`analogfilter is controlled by the processorto adjust the
`touch signalfiltering in response to changes in the rate
`of movement.
`Touch locations can also be determined when touch
`is by an electrically conductive stylus in addition to a
`user’s finger. Also, accurate touch location determina-
`tion of touch by a gloved finger results when the glove
`is of an electrically conductive material, or, if not con-
`ductive, is sufficiently thin to allow measurable capaci-
`tive touch currents at the frequency of the panel scan-
`ning signals. Touching mayalso be by any other mecha-
`nism which permits such touch currents. When men-
`tioned herein, touches by a gloved finger or by a stylus
`are to be understood as limited to touches by a glove or
`A touch panel device accordingto the present inven-
`stylus of the type which allows such touch currents.
`tion detects touch, such as a touch by a humanfinger,
`It is accordingly one object of the invention to pro-
`which occurs anywhere on a touchsensitive surface of
`vide an improved touch-responsive display device.
`a touch panel. Circuitry is provided for determining the
`Still another object of the present invention is to
`position of the touch on the touch sensing surface. The
`provide improved circuitry and methods for locating
`position or location of the touchis typically determined
`the position at which a touch sensing surface of a touch
`relative to an X-Y coordinate system with the location
`panel is touched.
`of the touch being accurately pinpointed.
`It is another object of the present invention to pro-
`The touch locations are determined from touchsig-
`vide a touch panel device for locating touch on a touch
`nals or currents generated by selectively applying alter-
`sensing surface thereof with a relatively high degree of
`nating current voltage panel scanning signals to the
`reliability and accuracy.
`touch sensing surface.
`A further object of the present invention is to provide
`In one scanning method, these panel scanning signals
`a touch panel device for locating touch on a touch
`are applied so as to establish an alternating current volt-
`40
`sensing surface thereof whether touch is by a user’s
`age gradientin a first direction fromafirst side of the
`finger or other body part, by a user who is wearing a
`touch sensing surface to a second side of the touch
`glove, or by a stylus.
`sensing surface. When scanned in this manner and the
`Another object of the present invention is to mini-
`touch sensing surface is touched by a user,a first touch
`mize the effects of noise on touch panel device opera-
`current flows through the user andis detected. In addi-
`tion.
`tion, when a commonalternating currentvoltage panel
`These and other objects, features and advantages of
`scanning signal is then simultaneously applied to both
`the first and second sides of the touching sensing sur-
`the present invention will become apparent with refer-
`face, an impedance touch current flows through the
`ence to the following description and drawings.
`user and is detected. The touch location along thefirst
`BRIEF DESCRIPTION OF THE DRAWINGS
`direction is determined from the detected first and im-
`pedance touch currents. Also, an alternating current
`FIG.1 is a block diagram of one embodimentofa
`voltage scanning panel signal may be applied to the
`touch panel device according to the present invention;
`touch sensing surface so as to establish an alternating
`FIG.2 is a front elevational view of a touch panelin
`current voltage gradient in a second direction across the
`accordance with the present invention and also showing
`touch sensing surface from third to fourth sides of the
`one form ofswitching circuitry for applying panelscan-
`surface. When the panel is touched, a second touch
`ning signals a touch sensing surface of the panel;
`current signal flows and is detected. Typically, the first
`FIG. 3A &Bis electrical circuit schematic diagram
`and second directions are normal to one another and
`of a portion ofthe touchlocating circuit utilized in the
`correspond to an X-Y coordinate system. The touch
`embodiment of FIG. 1,
`location is-then determined relative to this coordinate
`FIG.4 is a block circuit diagram of an alternate form
`system from the first, second and impedance touch
`of automatic nulling circuit utilized in the touch panel
`currents Other suitable scanning methods mayalso be
`device of FIG.1,
`used.
`FIG,5 is a block circuit diagram of a further form of
`the touch
`As one aspect of the present invention,
`a automatic nulling circuit;
`signals are filtered to an extent which varies with the
`FIG.6 is a block circuit diagram ofa still further
`rate of movementof touch of the touch sensing surface
`form of automatic nulling circuit;
`from one touch location to a subsequenttouch location.
`FIG. 7 is a block circuit diagram of another form of
`Morespecifically,
`touch signal filtering is increased
`automatic nulling circuit;
`
`20
`
`25
`
`30
`
`35
`
`45
`
`30
`
`35
`
`60
`
`65
`
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`FIG.12 is a flow chart of the touch signal or current
`measuring sequence utilized by the microcontroller of
`FIG.1;
`FIGS.13 and 14are flow chartsof the touch position
`determining sequenceutilized by the microcontroller of
`FIG. 1 in determining totich location from the mea-
`sured touch signals;
`FIG. 15 is a flow chart of a sequence utilized by the
`microcontroller of FIG. 1 for adjusting the nulling of
`touch signals when the touch sensing surface is un-
`touched;
`FIG.16 is a flow chart of a sequence utilized by the
`microcontroller of FIG. 1 for changing the frequency
`of the panel scanning signals during operation of the
`touch panel device;
`FIG.17 is a flow chart of a filter position sequence
`which maybe used by the microcontroller of FIG. 1 to
`adaptively filter the touch signals; and
`FIG. 18 is a modified flow chart block illustrating a
`sequence which may be used to vary the number of
`samples processed in a touch location determination to
`adaptively filter the touch signals.
`DETAILED DESCRIPTION OF PREFERRED
`EMBODIMENTS
`
`5
`6
`FIG.8 is a block circuit diagram ofstill another form
`contacts or electrodes, in this case twenty such contacts
`of automatic nulling circuit;
`A through T. A first set 22 of these contacts,
`that’ is
`FIG.9 is a flow chart of an overall touch location
`contacts P through T,is positioned in a row at one side
`determining sequenceutilized by the microcontroller of
`of the touch sensing surface 18. A second set 24 of
`FIG.1;
`contacts, contacts F throughJ, is positioned in a row at
`FIG. 10 is a flow chart of an initial panel scanning
`the opposite side of the touch sensing surface from the
`signal frequency determination sequenceutilized by the
`first set. That is, the first and second sets 22, 24 are in
`microcontroller of FIG.1;
`rows spaced apart from one anotherinafirst direction
`FIG. 11 is a flow chart of an initial nulling sequence
`across the surface 18. A third set 28 of such contacts,
`—
`0°
`utilized by the microcontroller of FIG. 1 during the
`contacts K through O,is positioned along the lower or
`initial panel scanning frequency determination of FIG.
`third side of the surface 18. In addition, a fourth set of
`9;
`such contacts, contacts A through E,
`is positioned
`along the fourth or upper side of the surface. Thus, the
`third and fourth sets of contacts are spaced apart from
`one another in a second direction across the touch panel
`surface. The contacts may comprise air dried silver
`contact paint spots, approximately 0.2 inches square.
`Respective leads are coupled to the contacts to facilitate
`convenient electrical connection to the contacts. To
`provide strain relief, the portion of each of these leads
`adjacentto its associated contact may be secured, as by
`epoxy, to the edge of the touch panel base plate.
`With this construction, the first and second sets 22, 24
`of contacts are at the opposite horizontally separated
`peripheral side edges of the touch panel. The othersets
`26, 28 of contacts are vertically spaced apart at opposite
`peripheral side edges of the touch panel. Although the
`contacts of each set do not necessarily have to be in a
`line, when colinear and whenthefirst and second direc-
`tions are normal to one another, the contacts define a
`reference coordinate system. Touch locationsare deter-
`mined relative to this coordinate system by the circuitry .
`explained below. Moreover, when the touch panel is
`mounted andcalibrated, the contacts are at known loca-
`tions relative to the terminal screen 14. Therefore, by
`determining a touched location on the touch sensing
`surface 18, a corresponding determination is made of
`the location on the display terminal screen 14. It should
`be noted thatthe inventionis not limited to this particu-
`lar contacting scheme. Moreover, a greater or fewer
`number of contacts may be used along eachside of the
`touch sensing surface.
`The touch locating system illustrated in FIG. 2 uti-
`lizes the two pairs of opposed sets 22, 24 and 26, 28 in
`determining the touch location relative to the two di-
`rections across the touch sensing surface. Only onepair
`of opposedsets is used if single direction touch location
`determination is to be made. Thatis, sets 22 and 24 are
`used to determine touch location in the first or X direc-
`tion. Also, sets 26 and 28 are used to determine touch
`location in the second or Y direction.
`With further reference to FIGS. 1 and 2, a function
`generator or signal source 30 generates an alternating
`current voltage touch panel scanningsignal at an output
`36. A panel driving amplifier 38 receives the panel scan-
`ning signal, amplifies this signal, and applies the resul-
`tant signal on an output 40 to the primary winding 42 of
`a touch panel driving transformer 44. This drives the
`secondary winding 46 of the transformer andestablishes
`an alternating current voltage across the secondary
`winding between its signal plus (SIG-+) output 48 and
`its signal minus (SIG—) output 50. A multiplexer or
`switching circuit 52 applies the panel scanning signals
`from outputs 48 and 50 of the secondary winding to
`selected sets or rows of the touch panel contacts as
`explained below. In response to these scanning signals,
`panel output touch signals or touch current signals are
`
`30
`
`40
`
`45
`
`55
`
`65
`
`Overall Description
`As shown in FIG. 1, a touch panel device in accor-
`dance with the invention has a display unit 12 with a
`display screen 14. Theillustrated display unit comprises
`a cathode-ray tube computer terminal and, accordingly,
`the display screen 14 comprises the face of the cathode-
`tay tube. An optically-transparent touch panel 16 is
`positioned to overlay the screen 14 so that the screen is
`visible through the touch panel. By optically transpar-
`ent, it is meant that it is possible to perceive images on
`screen 14 through the touch panel 16. In other applica-
`tions, the display unit 12 is eliminated. For example, an
`information containing sheet of paper, such as a ques-
`tion and answer sheet, may be positioned underneath
`the touch panel 16 with the touch panel being utilized to
`enter data relating to the question and answersheet. In
`certain applications, the touch panel 16 need not be
`transparent. For example, the touch panel may simply
`be used as a data entry pad with the location touched
`causing the entry of data into a computer or other de-
`vice.
`.
`
`The touch panel 16 has a base plate, which may be of
`glass or other optically transmissive material, with an
`electrically-conductive coating 18 over its outer sur-
`face. The coating 18 may coverthe entire display screen
`14 whenthe touch panelis in place, or only that portion
`of the screen 14 whichis used to display user-selectible
`items.
`As shown in general in FIG. 2, and described in
`greater detail below, the coating 18 comprises a touch
`sensitive or
`sensing surface with plural electrical
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`8
`generated at the center tap 54 of the transformer 44
`nications interface circuit 120. This permits the touch
`whenthe touch sensing surface is touched. These touch
`panel to communicate over a telecommunications net-
`work with remote data processing stations. ‘rypically, a
`current signals are processed by a panel output signal
`processing circuit means 56 to provide an indication of
`serial output 122 is provided from the interface circuit
`120.
`the location of touch and other information.
`In the illustrated panel output signal processing cir-
`Control signals from the microcontroller 108 are
`cuit 56, the touch currentsignals from center tap 54 are
`transmitted at respective MO and M1outputs alonglines
`transmitted along a line 60 to a touch current detector
`124, 126 to the multiplexer 52. These contro! signals
`62, such as a current sensing operational amplifier. The
`cause the multiplexer to route the panel scanningsignals
`output of amplifier 62 correspondsto the touch currents
`to desired sets of contacts. Therefore,
`touch current
`at the center tap 54. The amplifier 62 outputis fed on an
`signals are generated from which touch locations may
`output line 64 through a filter 66 (FIG. 3) and then to
`be determined. Exemplary scanning sequencesare dis-
`cussed below.
`.
`one input 68 of an analog multiplier 69. The signal gen-
`erator 30 has an alternating-current voltage reference
`The FIG. 1 panel output signal processing circuit 56
`output whick is coupled by a line 70 to a multiplier
`also includes a decoder demultiplexer circuit 130. De-
`reference circuit 72. Multiplier reference voltage signals
`coder 130 decodes input signals on lines 132, 134, and
`from the reference circuit are applied on a line 74 to a
`136 from the microcontroller and, in response thereto,
`reference input 76 of the analog multiplier. The refer-
`generates signals which control various functions of the
`ence output signals synchronize the multiplication by
`touch panelcircuitry. For example, decoder 130 gener-
`ates the integration timing signals (INT) fed to line 88.
`multiplier 69 with the alternating current voltage sig-
`nals applied to the touch sensing surface 18.
`Upon receiving these signals, switch 84 closes so that
`The resulting multiplied touch current signals are
`integration commences when touch location determina-
`transmitted along a line 78 to an amplifier and filter
`tions are desired. Integration continues for the duration
`of the INI signal. The decodercircuit also generates the
`circuit 80. The output of circuit 80 is fed on a line 82
`integration capacitor discharge signals (DIS) online 96.
`through an integrator timing switch 84 and to an inte-
`grator circuit 86, which integrates these signals. The
`These signals cause switch 94 to close so that integra-
`integrator timing switch 84 is closed during integration
`tion capacitor 90 is discharged prior to each successive
`time periods in response to integration timing (INT)
`integration. The microcontroller has a synchronization
`signals generated as explained below and applied to an
`input which receives synchronization signals on a line
`integrator timing input 88. When switch 84 closes,sig-
`140 derived from the reference output of signal source
`nals delivered to integrator circuit 86 are integrated
`30. Consequently, integration is synchronized with the
`therein. The integrator circuit includes an integrating
`application of panel scanning signals to the touch sens-
`capacitor 90 in parallel with an amplifier 92. In addition,
`ing surface 18. The decoder circuit also has an output
`an integrating capacitor discharge switch 94is included
`coupled bya line 142 to the analog to digital converter
`for selectively discharging integrating capacitor 90'in
`100 for controlling the delivery of digitized integrated
`response to discharge (DIS) signals on a line 96. These
`touch signals from converter 100 to the microcontroller
`discharge or integrator zero signals are generated as
`108. In addition, decoder 130 generates filter control
`explained below. The integrated touch current signals
`signals (FILT.) fed to line 87 and to dynamicfilter 85.
`are fed on a line 98 to an analog to digital converter
`Asexplained below, the FILT signals control the filter
`circuit 100 which digitizes these signals. These digitized
`85 to vary the filtering of touch signals depending upon
`signals are transferred along data busses 102, 104 to data
`the movement of touch across the touch sensing sur-
`face.
`inputs 106 of a microcontroller 108. The microcon-
`troller, among other functions, computes the touch
`More accurate determination of touch currents and
`location and other desired information from the touch
`touch locations result when the analog to digital con-
`current signals.
`verter is providing an output of a magnitude whichis
`A dynamic or variable frequency low passfilter 85
`within a desired range. If too small, minor variations in
`may be interposed between amplifier and filter 80 and
`touch currents can be overlooked and spurioussignals
`the integrator circuit 86. As explained in connection
`ha