United States Patent r191
`Young et al.
`
`11111111111111111 1111
`
`US005708460A
`[111 Patent Number:
`[451 Date of Patent:
`
`5,708,460
`Jan. 13, 1998
`
`[54] TOUCH SCREEN
`
`[57]
`
`ABSTRACT
`
`[75]
`
`Inventors: Thomas M. Yowig. Oakland; WIDiam
`Martin Becker, San Carlos; Joseph
`Shamash, Orinda. all of Calif.
`
`[73] Assignee: AVI Systems, Inc., Oakland, Calif.
`
`[21] Appl. No.: 460,647
`Jun. 2, 1995
`[22] Filed:
`Int. CL6 ....................................................... G09G 5/eO
`[51)
`[52] U.S. Cl .............................. 345/173; 345/174; 178/18
`[58] Field of Search ..................................... 345/173, 174;
`178/18. 19
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`8/1991 Flowers et al .......................... 345/173
`5,038,142
`7/1994 Hashimoto et al ..................... 345/173
`5,327,163
`5,463,388 10/1995 Boie et al. . ............................. 345/174
`
`Primary Examiner-Mark R. Powell
`Assistant Examiner-Matthew Luu
`Attome)> Agent; or Fimr-Steinberg Raskin & Davidson
`P.C.
`
`A touch screen or touch panel wherein there is a monitcring
`of relative distribution of force via one or more, preferably
`symmetrically positioned, sensors such as strain gage sen(cid:173)
`sors. The strain gage sensors are positioned such that bend(cid:173)
`ing strain on the touch screen. engendered by touch. is
`detected by the one or more strain gages and accurately
`measured by an electronic controller. connected to the strain
`gage(s). The electronic controller. or associated hardware. is
`programmed to relate relative bending force to a unique
`position on the screen and is a charge balancing and mul(cid:173)
`tiplying analog-to-digital converter which provides accurate
`position determination, even with very low forces and with
`very minor differentiation in position related forces. A sum
`and divide analog-to-digital converter uses charge balancing
`and integration. with the balance charge coming from the
`plus and minus sum of the comers (wherein four sensors are
`positioned at the corners of a square or rectangular display).
`and the input signal is the difference between two sides of
`the display panel. This, in effect. results in the input signal
`being divided by the sum signal and the sum of charge
`counts over a fixed interval, resulting in the ouq,ut value and
`unique position determination. A unique mounting structure
`for flat panel displays includes using the flat panel as the
`bending beam and wherein a circuit board mounted behind
`the flat panel transmits forces to sensors mounted on the
`circuit board.
`
`18 Claims, 5 Drawing Sheets
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`U.S. Patent
`U.S. Patent
`
`Jan. 13, 1998
`Jan. 13, 1998
`
`Sheet 1 of 5
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`5,708,460
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`U.S. Patent
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`Jan. 13, 1998
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`Sheet 2 of 5
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`U.S. Patent
`U.S. Patent
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`Jan. 13, 1998
`Jan. 13, 1998
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`U.S. Patent
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`U.S. Patent
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`Jan. 13, 1998
`Jan. 13, 1998
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`Sheet 5 of 5
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`2
`FIG. 2 is a cross section view taken along line 2-2 of
`FIG. 1;
`FIG. 3 is a cross section view taken along line 3--3 of
`FIG. 1.
`FIG. 4 is a block schematic of the position determining
`means with charge balancing and multiplying analog-to(cid:173)
`digital converter of the present invention;
`FIG. 5 is a circuit drawing of the position determining
`means of the block schematic of FIG. 4; and
`FIG. 6 is a schematic side view depiction of a support
`structure for a flat panel display.
`
`5
`
`IO
`
`1
`TOUCH SCREEN
`FIELD OF THE INVENTION
`This invention relates to touch screens for computer
`applications and particularly to touch screens having accu-
`rate touch location identification by means of force sensors
`which identify position based on relative touch force exerted
`on the screen.
`BACKGROUND OF THE INVENTION
`Touch screens used in computer applications. such as cash
`register-inventory control devices. CRTs and flat panel
`displays, as well as POS (point of sale), kiosks, restaurants,
`gaming systems, industrial control. telephone, control
`devices and general pwpose computers; have included 15
`sophisticated and costly electronics. In resistive touch
`screens finger placement on specific areas of the screen
`completes a circuit. with a message having been sent thereby
`to computer means for processing. Each area on the screen
`is micro-wired on a grid. with unique circuit characteristics. 20
`whereby the particular area which is touched is identifiable.
`Since each area is wired by a grid, the wide area, with direct
`contact. increases the possibility of grid breakage, under
`touch pressure, with possible resultant malfunction. Other
`touch screens include those of the capacitive type (using 25
`capacitive sensors) which put out a low AC voltage field
`across the surface of the screen. When a finger touches the
`sensor area, the capacitive properties of the finger draws
`current to the point touched. which is then registered by the
`system. Accordingly such system will not respond to touch 30
`with a glove or a non-capacitive stylus.
`In another type of touch screen, surface acoustic wave
`sensors (SAW) on a glass transmit waves across a screen
`area. which when touched, creates a disturbance in the wave
`pattern which allows the system to determine area being 35
`touched. However, such devices are subject to permanent
`touch spots and moisture on the surface can inadvertently set
`it off.
`IR (infra red) touch screens operate with beams in a grid
`form which are broken to determine a signal position.
`However these devices are subject to low resolution.
`Recently, touch screens have been described, wherein
`strain gages, with force sensing means, are utilized to
`measure unique strain or forces at different finger touch
`locations, in order to identify areas and to provide operabil(cid:173)
`ity for indicated commands at such locations, as described in
`U.S. Pat. No. 5,241.308. These strain gages emit signals
`which are unique for different positions being touched on the
`panel. However, because the forces involved are very low,
`high accuracy of force sensing means is required for proper
`operation. Primarily foil gages have been used but such
`technology has been essentially abandoned because of prob(cid:173)
`lems resulting from creep, low signals and signal to noise
`ratio, as well as calibration problems.
`It is accordingly, an object of the present invention to
`provide an economical and accurate touch screen with force
`sensing means.
`It is another object of the present invention to provide
`such touch screen with reliable operation wherein exerted
`force is indirectly measured.
`These and other objects, features and advantages of the
`present invention will become more evident from the fol(cid:173)
`lowing discussion and drawings in which:
`SHORT DESCRIPTION OF THE DRAWINGS
`FIG. 1 depicts four strain gages, as corner mounted with
`brackets, on a touch screen of the present invention;
`
`60
`
`SUMMARY OF THE INVENTION
`Generally the present invention comprises a touch screen
`or touch panel (referred to hereinafter collectively as ''touch
`screen") wherein there is a monitoring of relative distribu(cid:173)
`tion of force via one or more and preferably at least three,
`preferably symmetrically positioned. sensors such as strain
`gage sensors, acoustic wave sensors, capacitive sensors and
`the like. The sensors. such as strain gage sensors are
`positioned such that bending strain on the touch screen,
`engendered by touch, is detected by the one or more strain
`gages and accurately measured by position determining
`means comprising. for example, an electronic controller.
`connected to the strain gage(s). The electronic controller, or
`associated hardware, is programmed to relate relative bend(cid:173)
`ing force to a unique position on the screen. Both the
`composition and structure of the screen being touched are
`adapted to provide a unique relative force at each touch
`zone. whereby the touch zone is identifiable by such force.
`In accordance with the present invention the position
`determining means comprises a charge balancing and mul(cid:173)
`tiplying analog-to-digital converter which provides accurate
`position determination, even with very low forces and with
`very minor differentiation in position related forces. A sum
`and divide analog-to-digital converter uses charge balancing
`and integration similar to the front end of a sigma delta
`converter. The balance charge comes from the plus and
`40 minus sum of the comers (wherein four sensors are posi(cid:173)
`tioned at the comers of a square or rectangular display). The
`input signal is the difference between two sides of the
`display panel. This, in effect, results in the input signal being
`divided by the sum signal and the sum of charge counts over
`45 a fixed interval. resulting in the output value.
`In order to provide such accurate determinations with
`very low forces and minor differentiation in position related
`forces, it is desirable to further minimize noise generation by
`effective filtration out of resonant effects. It is also desirable
`50 to maximize resonant frequency of the touch screen by
`constructing the touch screen with a stiff, low mass structure
`with a wide dynamic range being generated. Stiffness, as
`required for the screen of the present invention is of a degree
`which permits for detectable and reproducible bending
`55 movement of the screen under exerted touch forces. The
`degree of mass particularly that of low mass is such that
`there is little if any damping effects which may interfere with
`the detection of the magnitude of the force or touch related
`bending movement.
`
`DEfAilED DESCRIPTION OF THE
`INVENTION
`There are basically two types of touch screen platforms
`(CRT displays and flat panel displays, "FPD") currently
`65 extant and each requires a somewhat different structural
`configuration for operability in accordance with the present
`invention.
`
`

`

`5,708,460
`
`4
`the use of a combination of touch. sound and pressure
`sensitivity. utilization of the touch screen can be made sight
`independent Appropriate pressure as detected by the strain
`gage sensors. may be utilized to provide variations in
`5 commands and interpretation. e.g.. 10 points of pressure
`may be indicative of a "yes" response or command, whereas
`a recognizably distinct 50 points of pressure is indicative of
`a "no" response or command. Alternatively. a single com(cid:173)
`mand or interpretation is effected at a pressure site. but with
`10 variations in pressure providing variations thereof. e.g ..
`color variations at clifferent pressures (pink/red/maroon).
`with higher pressures being indicative of deeper colors.
`Differently language equivalents may also be differentiated
`by degree of pressure as well. Touch/sound/pressure on this
`15 and other systems which provide this combination can also
`utilize other features:
`(a) different sound effects through pressure (e.g .. tones.
`chords. etc.);
`(b) controlling video responses through this system of
`different layers of touch pressure. via sound signals;
`(c) identification and retrieval use, such as "you selected
`"product name", press harder to "retrieve", or play
`music or movie at different pressures; and
`(d) an interface which allows for a universal language or
`standard on computer screens or control panels.
`
`3
`With a CRf display. a metal stand is used to support the
`CRf display or the touch screen glass. Strain gage sensors.
`(highly improved over the foil strain gages of the prior art.
`whose use has been essentially abandoned) as described in
`co-pending application Ser. No., entitled DIRECT ADHER(cid:173)
`ING POLYSil.lCON BASED STRAIN GAGE, filed on
`May 26. 1995. the disclosure of which is incorporated herein
`by reference thereto. are placed on the stand in a back to
`back configuration and a flex circuit is utilized to intercon(cid:173)
`nect the sensors at shield positions peripheral to the CRT
`display. In such configuration, the stand mechanically
`directly or indirectly supports the touch glass which is
`sandwiched between the CRf and the front bezel (bolted on
`the four corner ears thus requiring no additional ( or minimal
`modification of existing CRf display designs. In such
`embodiment. sensors are affixed to the metal stand at the
`corners to read touch forces on the glass, via forces trans(cid:173)
`mitted through the adjacent metal of the stand to the sensor
`connected thereto. The sensors are solid silicon beams with
`half bridge on top and bottom respectively and wherein there 20
`is a direct edge attachment of the silicon to the circuit board
`with solder such as with use of invar clips and the like.
`In flat panel applications. the sensors may be supported
`directly on the electronic circuit board positioned behind the
`display. used as the touch screen surface. This type of 25
`utilization is similar to that of weight sensing scales which
`detect a single force to measure weight Alternatively, the
`sensors are embedded directly in the glass surface, which
`allows the area at the sensor perimeter to become active. In
`a further embodiment. the sensors, when positioned in the 30
`circuit board behind the flat panel display, are enclosed
`within a ceramic housing and wherein the housing is sol(cid:173)
`dered to the circuit board. to eliminate any creep effect
`resulting from adhesive attachment or from temperature
`changes.
`In further embodiments. the corner mounts previously
`described, may be replaced by foil torsion beams and an
`intermediate controller board can be used as the bending
`beam. With the use of the foil torsion beams, there is created
`a simple strain topology in the sensor. Any surface, not just 40
`glass may be utilized as the touch panel, provided it has the
`requisite characteristics of stiffness, low mass and high
`frequency. Materials for the touch panel include wood,
`plastic. metal, etc., which are selected for the requisite
`characteristics. Non-transparent materials are utilizable as
`separate touch pads independent of the visible screen sur(cid:173)
`face. By using these materials, the touch panel can be used
`as a measuring or pointing device such as in scales or joy
`
`:!;n~1!~h::~eq(:: : : : : : !::i::n~ :es~~z 50
`
`configuration.
`Sealing of the CRT and the FPD to housings must be
`effected without negating the measurable strain resonance.
`Accordingly. with CRf's. sealing is effected by means of a 55
`non-contact dust lip. In addition and particularly with flat
`displays or surfaces. ferro fluids are used to this effect. as a
`method to achieve low contact pressure sealing on the flat
`surface of the FPD.
`Appropriate software provides the requisite interrelation
`between detected forces and command processing. The
`software also provides signal filtering to enhance signal
`processing for the command processing.
`In preferred embodiments of the present invention, pres(cid:173)
`sure on a single point of the touch screen is utilized to also 65
`provide sound responses to simulate tactile and communi(cid:173)
`cation feedback effects (i.e .. button pushing feel). Through
`
`35
`
`45
`
`DEfA.Il..ED DESCRJPTION OF THE DRAWINGS
`AND THE PREFERRED EMBODIMENT
`With reference to the drawings, four strain gages lOa-d
`are depicted as being placed on a touch screen 20 in FIGS.
`1 with glass touch screen panel 20 being closely retained by
`four corner brackets 14a-d. As shown in FIG. 2. with a cross
`section view of bracket 14b, the corner of the glass panel 20
`is closely retained within metal clip 15b of bracket 14b and
`epoxy bonded thereto. The strain gage sensor 10b is soldered
`with solder 16 between metallized areas thereon (not
`shown). and the mounting stand of bracket 14b. As a result
`the strain gage sensor 10b (with a c-shape configuration)
`sandwiches a section of the mounting bracket 14b, adjacent
`the metal clip 15b, with retained glass of touch panel 20.
`Strain engendered by a touching of the glass panel at a
`particular position of the surface thereof. causes a measur(cid:173)
`able deflection of the glass, which is in turn transmitted
`through the metal of the bracket to gage sensor 10b (similar
`transmissions occur to the remaining gages 10a, 10c and
`10d). The gages are electrically interconnected and con(cid:173)
`nected to external elements for translation of measured
`strain, via resistance level changes in the polysilicon strain
`gage, to events or measurements. As shown in F1GS. 1 and
`3, wires 40a-d effect such electrical connection and inter-
`connection. The strain gages l0a-d are protected from
`exterior elements by front bezel 30 which peripherally
`encloses the edges of panel 20.
`As shown in the block diagram of FIG. 4, of an analog to
`digital converter of the present invention, input A represents
`the input from the two left hand sensors 10a and 10d and
`input B represents the input from the two right hand sensor
`lOb and 10c. When a point is touched on touch screen 20,
`60 at any place along line 50 ( equidistant from left and right
`side edges 20a and 20b of the panel 20), the values of A and
`B are equal. Touching of the screen closer to one side
`increases the value input from nearer sensors and decreases
`the value input from the farther sensors.
`In operation, for example, if a point on line 50 is touched,
`the values of A and Bare equal, e.g .. with 1 volt from each
`being summed at voltage summer 51. The difference is
`
`

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`5,708.460
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`5
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`10
`
`5
`obtained at voltage difference element 52, with respective
`output values of 2 volts and 0 volts respectively. Voltages of
`+2 and -2 (negative voltage is obtained through inverter 53)
`pass through resistors R 1 and R2 to switches S1 and S2•
`respectively. Since there is zero voltage at R3 , in order to
`keep the summing junction 54 at an overall zero value, it is
`necessary to close switches S 1 and S2 for equal amounts of
`time (S /S 2 is 50%150%) during the duty cycle.
`If a point at left hand edge 20a is touched, the input value
`from A is 1 volt and the input value from B is zero volts.
`Thus the values at resistors R 1, R2 and R3 are+ L -1, and+ 1
`respectively. The logic to keep the summing junction 54 at
`an overall zero value requires that S2 be closed at all times
`and S 1 remain open at all times during the duty cycle.
`Different points on the screen have proportional logic
`values for the relative percentages of open and closed times
`for switches S 1 and S2. Vertical position on the screen is
`similarly determined by a top input of gages 10a & 10b
`relative to the bottom input of gages 10c and 10d. Switches
`S3 and S4 are preset to cancel the junction, prior to touch.
`The zero summing junction for the block diagram shown
`in FIG. 4 is O=S 1.(A+B)-S2.(A-B)+(A-B)+5v.S3-5v.S4.
`The X position=( duty of S2)-( duty of S 1) and it ranges from
`+1.0 to -1.0, and is represented in accordance with block
`diagram in FIG. 4 as X=A-B/A+B.
`FIG. 5 is the overall circuit diagram for the system with
`separated inputs A', B', C, and D' from sensors 10d (lower
`left), 10a (upper left), l0b (upper right) and 10c (lower right)
`respectively and with logic switches Si', S2', S3 ', and S4'.
`In FlG. 4>. a flat panel display 100 is utilized as the
`bending beam. The display 100 is mounted on mechanical
`stand members 101 and held in place by frame 102. The
`mechanical stand members 101 are sandwiched between the
`flat panel display 100 and the circuit board 103, with the
`latter also being held by frame 102. Sensors 104, affixed to
`the circuit board 103 directly measure torsion forces trans(cid:173)
`mitted thereto from the flat panel display. Alternatively the
`sensors can be housed in ceramic packages which function
`as a load cell or transducer and/or support for the display, in
`lace of the circuit board.
`It is understood that the above description, the drawings
`and discussion of specific embodiments of the present
`invention are not to be construed as limitations thereof.
`Changes in circuit. arrangement of elements. the nature of
`the elements. including different sensor means and the like,
`are possible without departing from the scope of the present
`invention as defined in the following claims.
`What is claimed is:
`1. A touch screen comprising sensors for monitoring
`relative distribution of force thereon, said sensors being
`positioned relative to the touch screen such that bending
`strain on the touch screen, engendered by touch, is detected
`by the sensors, wherein said sensors transmit one or more
`input signals to a charge balancing and multiplying analog
`to digital converter configured to relate bending force to an
`identifiable unique position on the screen, the charge bal(cid:173)
`ancing and multiplying analog to digital converter compris-
`ing a sum and divide analog-to-digital converter using
`charge balancing and integration, wherein said sensors pro(cid:173)
`vide sensing and valuation of touch forces on said screen,
`from opposite sides of said screen. with conversion of the
`valuation of the touch forces from opposite sides of the
`screen to separate proportional charge signals, whereby a
`balance charge comes from the plus and minus sum of the 65
`sensing of touch forces on said screen from opposite sides
`thereof. and means for converting the balance charge to a
`
`6
`position on the screen. wherein said screen is quadrilateral
`and wherein said sensors include at least four sensors
`positioned at the four corners of the quadrilateral screen.
`wherein an input signal is the difference between propor-
`tional charge signals from two opposite sides of the screen
`and wherein the input signal is divided by the sum signal and
`the sum of charge counts over a fixed interval. resulting in
`an output value used by the means for converting the balance
`charge to a position on the screen.
`2. The touch screen of claim 1, wherein the screen is
`comprised of a relatively stiff, low mass material, wherein
`the relative stiffness is such that it permits for detectable and
`reproducible bending movement of the screen under exerted
`touch forces, and the mass is such that damping effects.
`15 which may interfere with the detection of the magnitude of
`the bending movement, is minimized.
`3. The touch screen of claim 2. wherein the screen is
`fixedly held in position by a metal stand, with the screen
`being held by metal brackets at the corners of the screen, and
`20 wherein said metal brackets transmit the bending forces
`exerted on said screen to said sensors.
`4. The touch screen of claim 3. wherein said sensors
`comprise strain gages integrated with said brackets.
`5. The touch screen of claim 4, wherein pairs of strain
`25 gages at opposite sides of the quadrilateral provide input
`signals for both horizontal and vertical position determina(cid:173)
`tion on said screen.
`4>. The touch screen of claim 1. wherein said screen
`comprises a arr.
`7. The touch screen of claim 1. wherein said screen
`comprises a touch panel.
`8. The touch screen of claim 1. further comprising touch
`pressure sensing means whereby pressure on a single point
`of the touch screen is detected by said pressure sensing
`35 means to provide sound responses to simulate tactile and
`communication feedback effects.
`9. The touch screen of claim 1. further comprising touch
`pressure sensing means whereby degree of pressure on a
`single point of the touch screen. having operational instruc-
`40 lions associated therewith, is detected by said pressure
`sensing means to provide variations in commands and
`interpretation.
`10. The touch screen of claim 8. wherein one range of
`pressure causes said pressure sensing means to provide a
`45 "yes" response or command. whereas a recognizably distinct
`second pressure range causes said pressure sensing means to
`provide a "no" response or command.
`11. The touch screen of claim 10, wherein the touch
`screen is part of a flat panel display and wherein the flat
`so panel display functions as the bending beam when touched.
`wherein said display is mounted on at least one mechanical
`stand member and peripherally held in place by a frame
`member, with the mechanical stand member being sand(cid:173)
`wiched between the flat panel display and a force transmit-
`55 ting member, held in stationary relation to the flat panel
`display, said force transmitting member having force sensors
`affixed thereto for detecting touch pressure exerted on said
`flat panel display.
`12. The touch screen of claim 11. wherein said force
`60 transmitting member comprises a circuit board.
`13. The touch screen of claim 11. wherein said force
`transmitting member comprises a housing for said force
`sensors.
`14. A touch screen device comprising:
`a first sensor and a second sensor positioned relative to
`opposing sides of a touch screen. such that bending
`strain on the touch screen, engendered by touch, is
`
`30
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`

`5.708,460
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`7
`detected by the first and second sensors, the first and
`second sensors outputting respective first and second
`sensor signals; and
`a charge balancing and analog to digital converter having
`a difference signal input. a positive charge sum input.
`and a negative charge sum input. said difference signal
`input coupled to a difference of the first and second
`sensor signals. the positive charge sum input coupled to
`a sum of the first and second sensor signals. the
`negative charge sum input coupled to a negative sum of
`the first and second sensor signals. the charge balancing
`analog to digital converter relating a bending force
`applied to the touch screen to an identifiable position on
`the display screen as a function of the first and second
`sensor signals.
`
`8
`15. The touch screen device according to claim 14,
`wherein the charge balancing and analog to digital converter
`further comprises an integrator having an integrator input.
`the integrator input and the difference signal input being
`5 coupled to a common node. the positive charge sum input
`and negative charge sum input being selectively coupled to
`the common node to provide a balance charge to the
`common node.
`16. The touch screen device according to claim 14.
`wherein the touch screen is a display screen.
`17. The touch screen device according to claim 14.
`wherein the touch screen is a flat panel display.
`18. The touch screen device according to claim 14,
`wherein the touch screen is a measuring device.
`
`10
`
`* * * * *
`
`