CA1277003C - Touch control arrangement for graphics display apparatus - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A system for recognizing touch positions along a predetermined coordinate axis on a surface of a touch panel display apparatus comprises a substrate having a surface capable of propagating surface acoustic waves and is so characterized that a touch on that surface causes amplitude damping of a surface wave passing through the region of touch. An input surface wave tranducer, coupled to the substrate surface launches a burst of surface waves on the surface in a first direction parallel to the aforesaid axis. An output surface wave transducer is also coupled to the substrate. A first surface wave reflecting means derives wave components from the launched wave and reflects them across the display surface to a second wave reflecting means that redirects the reflected components in a second direction opposite to the aforesaid first direction.
The first and second reflecting means causes wave components to traverse the display surface orthogonally to the coordinate axis along a progression of paths associated with different positions along the coordinate axis. Circuit means coupled to the input and output transducers initiate surface wave bursts across the surface as well as detect touch-induced damping of the received waves. The circuit means further includes means for developing an electrical signal representative of the time occurrence of the damping and thus an indication of which of the plurality of paths was traversed by the touch-damped wave and thereby the location of the touch on the display surface.

Description

~277~3 The present invention relates to touch panel systems.
It is known to use surface acoustic wave (SAW) energy for touch control. Prior art U.~S. patent 3,134,099-Woo, issued May 19, 1964, teaches an arranqement in which a plurality of piezoelectric transducers, electrically connected in parallel, is disposed along each of two adjacent edges of a sheet of glass. The transducers are coupled to the sheet and, in response to a control signal, create surface waves which propagate across the surface of the glass sheet. A writi~g pen, embodying a pie20electric component, is placed in contact with the glass sheet to sense a propagating disturbance and then issue an appropriate signal to a control unit which measures the elapsed time interval hetween the time the control siqnal was applied to the transducer that initiated the disturbance and the time the signal was received by the pen.
It is of siqnificance that, in the Woo arranqement, a plurality of piezoelectric transducers is required for each of two adjacent sides of the glass panel. Further, the Woo system requires the use of a special touch stylus capable of sensing surface acoustic waves traveling across the panel.
U.S. ~atent 3,653,031-Hlady~ et al, issued March 28, 1~72, is addressed to a touch sensitive position encoder also employing elastic surface wave generating transducers positioned along the edges of a sheet of transparent glass.
The transducers function as radiators, as well as sensors, and thus serve to launch surface waves across the glass sheet, as well as to receive such waves. In operation, a finger or stylus placed at a particular position on the ~lass sheet serves to reflect the surface waves encountered. A reflected wave that is detected is applied to timing circuitry associated with the sensors, which circuitry determines the geometric coordinates of the position of the finger or stylus. Again, as in Woo, two arrays, or banks, of transducers are required to create the surface waves that propaqate across the glass sheet.
U.S. Patent 3,673,327-Johnson, et al, issued June 27, 1972, describes still another SAW-type touch responsive panel assembly comprising a panel positioned over the face-., ' . , . . ~.. ..
~!~ r. i -2 ~7'~3 plate of a CRT and having a first plurality of transmitters positioned along a first ed~e of the panel for ~enerating a like plurali-ty of Rayleigh (surface) beams that propagate across the surface of the panel in an X direction and a like plurality oE detectors positioned along the edge of -the panel opposite said firs-t ed~e for individually receiviny an assi~ned one of said plurality of beams. In like fashion, a second plurality of transmitters is positioned along a second ed~e of the panel, adjacent the first edge, for simultaneously ~enerating a second plurality of Raylei~h wave beams that propagate across the panel in a Y direction, perpendicular to the X direction. A like second plurality of detectors is positioned along the edqe of the,panel opposite said second edge for receiving an assigned one of said second plurality of beams. Accordingly r to establish this ~-Y ~rid of wave beams, a transmitter is re~uired for each wave beam and a separate detector is required for each such transmitter.
Each transmitter, upon actuation, launches a beam of Raylei~h surface waves along the surface of the panel. There-after, when a`finger or other object is pressed~against the panel, acoustical wave energy is absorbed, thereby interrupting its transmission to its assigned detector. The absence or reduction of the normal signal at a specific detector constitutes a touch indication which i9 applied to a computer.
However, a principal drawback of the Johnson et al touch contro~ system like that of its optical counterpart, resides in the requirement of a multiplicity of transmitters and detectors to es:tablish the intersecting wave ~nergy paths that form the ~rid overlying the panel. The mechanical considerations, and cost, involved in the practice of utilizing dual pluralities of transmitters and detectors, all of which must be separately wired, are obvious short-comings.
Other U.S. patents in the touch control art are set forth below:

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Patent No. Inventor Issue Date 3,775,560 Ebeling et al. Nov. 27/73 3,808,364 Veith Apr. 30/74 3~916,099 Hlady Oct. 28/75 3,956,745 Ellis May 11/76 4,198,623 Misek et al. Apr. 15/80 4~254,333 Bergstrom Mar. 3/81 4,286,289 Ottesen Aug. 25/81 4,346,376 Mallos Aug. 24/82 Additionally, art in the field of surface acoustic waves which was considered included U.S. patents:
3,883,831 Williamson et al. May 13/75 4,403,165 Ballato et al. Sept. 6/83 "Use of Apodized Metal Gratings in Fabricating Low Cost Quartz RAC Filters" by G.W. Judd and J.L. Thoss.
Proceedings of the IEEE 1980 Ultrasonics Symposium, p. 343.
It is a feature of the invention to provide an improved touch responsive graphics display apparatus.
It is another feature of the invention to provide an improved touch responsive arrangement for, or for use with, a graphics display CRT.
It is also a feature of the invention to provide a touch responsive arrangement for use with graphics display apparatus which imposes but minimal limitations on cabinet and escutcheon designs.
It is another feature of the invention to provide such a touch responsive arrangement characterized by minimal rn/

~27'7~3 mechanical and electrical complexity and reduced cost of manufacture.
Specifically, the invention relates to a system for recognizing touch positions along a predetermined coordinate axis on a surface associated with a touch panel apparatus.
The system comprises: a substrate having a surface capable of propagating surface acoustic waves and being so characterized that a touch on the substrate surface causes a perturbation of a surface wave propagating through the region of the lo touch. Surface acoustic wave scanning means, including input surface wave transducer means are coupled to said substrate surface, for effecting scanning of said surface with a timed succession of surface wave bursts directed in a plurality of substantially parallel overlapped paths across the substrate surface transversely to the coordinate axis, the plurality of paths being respectively associated with different positions along the coordinate axis on the substrate surface. Output surface wave transducer means are coupled to the subskrate surface for receiving the bursts of surface waves; and circuit means are coupled to the input and output transducer means for initiating the time succession of surface wave bursts on the substrate surface and for detecting touch-induced perturbations of received wave bursts. The circuit means include means coupled to the output transducer means for developing an electrical amplitude characteriæation of the perturbation and thus determining which of the plurality of paths was transversed by the touch-perturbed wave burst rn/J ~-:,, ~277C~C3 3 5a and thereby the location of the touch along the coordinate axis of the substrate surface.
Brief Description of the Drawing The features of the present invention believed to be novel are set forth with particularity in the appended claims. The invention together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:
Figure 1 illustrates, partially in schematic form, a graphics display apparatus embodying the invention;
Figure 2 is a plan view of the Figure 1 touch responsive display panel depicting, in some detail, reflective grating construction and placement, Figure 3 is a graphical plot representative of received surface acoustic wave energy traversing one coordinate of the touch panel of Figure 2;
Figure 4 is a graphical plot representative of received surface acoustic wave energy traversing a second, orthogonal, coordinate of the touch panel of Figure 2;
Figure 5 is a schematic representation of a reflection grating and a series of reflected wave components developed by that grating;

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iL2'7~ 3 Figure 6 illustrates the waveform developed by an output transducer responding to the reflected wave components shown in Figure 5;
Figure 7 illustrates the waveform developed by an output transducer responding to an elongated series of reflected wave components;
Figure 8 is a schematic representation of a rectified version of the output signal of an output transducer employed in a touch panel display apparatus constructed in accordance with the invention.
Figure 9 is a schematic representation of a reflective array in which the pattern of elements results from "finger withdrawal";
Figure 10 is a schematic representation of a reflective array in which individual elements are fragmented in a patterned fashion;
Figure lOA is a schematic representation of a reflective array in which the length ~f individual elements increases in the direction away fromm the adjoining transducer;
Figure 11 is a schematic representation of a touch panel arrangement in which a single device is utili~ed as the input and output transducers;
Figure 12 is a schematic representation of a touch panel arrangement utilizing an output transducer coextensive with one coordinate of the panel;

~277~3 Figure 13 is a schematic representation of a touch panel arrangement in which the surface wave reflective grating comprises discrete gxoups of reflective elements;
Figure 14 depicts the pulse-type waveform developed by an output transducer responding to the burst component~ develvped by the Figure 13 em~odime~t;
Figure 15 depicts a variation of th~ waveform shown in Figure 14; and Figure 16 is a schematic representation of another embodiment of the invention featuring an angular coordinate system.
Figure 1 shows a graphics display apparatus 10 comprising a graphics controller 12 and a display device 14 having a display surface 16. A CRT may be employed to display graphics and the subject invention will be described in that environment.
However, it is to be appreciated that the invention is readily applicable to other display devices, e.g., electroluminescent or liquid crystal devices, or even displays as simple as an elevator number display, any of which can be employed in lieu of a CRT. In some applications, a separate panel i5 disposed over the faceplate of the display device.
The faceplate, or panel, is commonly designated a "touch control panel" since graphics, or other information may be ordered up for display from controller 12 in response to an operator's command which can take the form of a touching of a particular area of a menu associated with the touch control panel. The display surface 16, whether it be a CRT faceplate or a separate panel, constitutes a substrate the surface of which is capable of propagating surface acoustic waves. As will be shown, the act of touching serves to interrupt or reduce wave energy directed along one or more paths that form a grid ~277~3 overlying the panel. Detection and analysis of such interruption serves to identify the X, Y, or other coordinates of the touched area, which informat~on, in turn, is determinatiYe of the graphics to be delivered up for display or other response of the device.
To this end, apparatus 10 further includes a computer 22 for rendering an interface circuit 24 operative in a predetermined sequence so that when a perturbation, or interruption of acoustic wave energy is detected, converted to an electrical signal and fed back to the computer, via interface circuit 24, the location of the interruption is identifiable by the computer. Graphics controller 12 comprises the drive electronics for CRT 14 and, to that end, serves to amplify and otherwise condition the output of computer 22. ~o achieve its functions, the computer comprises a clock (source of timing signals), a source(s) of video information, as well as sources of horizontal and vertical sync pulses. The output of contxoller 12 is coupled to the control electrodes of CRT 14, as well as to the CRT's deflection windings, to display, under the direction of computer 22, selected graphics. Accordingly, when the computer identifies the location, or address, of wave interruptions, it will then output the appropriate information to controller 12 to change the video display to graphics associated with the address touched by the operator.
As shown in Figure 1, interface circuit 24 has input terminals coupled, via a buss 30, to receiver transducers R1, R2 and output terminals coupled to transmitter transducers Tl, T2 via the buss 32. Circuit 24 has additional input and output terminals coupled to computer 22 for interacting therewith. Circuit 24, in response to timing signals from computer 22, outputs firing signals that stimulate transducers ~77~3 Tl, T2 in a timed sequence so that the location of a subsequent interruption of a surface wave is identifiable.
Inpu~ transducers ~1, T2, which are more particularly described below, are mounted upon substrate surface 16 adjacent to edges 18 and 20, respectively, of Figure 2. A source 25 in interface circuit 24 serves to apply input signals Sl, S2, via buss 32, to respective transducers Tl, T2, which transducers, in response thereto, individually launch a burst of acoustic surface waves along first and second paths Pl, P2, respectively on surface 16.
Also as shown in Figure 2, first and second output transducers Rl, ~2, are mounted upon substrate surface 16 adjacent to respective edges 18, 20 that is, the edges close to their associated input transducer Tl, T2. In a manner to be detailed below, transducers Rl, R2, upon receipt of the surface waves launched by their associated input transducers develop respective output signals S3, S4 which, upon analysis, will exhibit a characteristic of the launched surface wave, e.g.
a change in amplitude, attributable to a perturbation of a received surface wave burst.
A first reflective grating Gl comprising an array of reflective elements el-en is disposed along path Pl with each of the aforesaid elements effectively arranged~ preferably, at like angles of incidence to the longitudinal axis of path Pl.
Desirably, the angles of incidence of the reflective elements, relative to the axis of path Pl, are approximately 45 degrees.
Additionally, the longitudinal axis of path Pl is preferably disposed parallel to the upper edge of substrate surface 16, as viewed in Figures 1 and 2.
Reflective elements el-en serve to extract from the initially launched surface wave burst a multiplicity of wave components and to direct such wave burst components across substrate surface 16 along a like multiplicity of paths pv each ~77~3 disposed at an angle to the axis of path Pl. As depicted in Figures 1 and 2, these multiplicities of paths are each disposed at 90 degrees to the axis of path Pl.
A second reflecti~e gYating G 2 likewise comprises an array sf reflective elements e'l- e'n which are disposed along path P3 and are effectively arranged at like angles of incidence to the longitudinal axis of path P3 for intercepting the wave components extracted from the wave traversing path Pl and directed across substrate surface 16 along the paths pv. Grating G2 intercepts the wave burst components arriving along paths pv and redirects them along path P3 toward receiving transducer Rl which converts the wave energy in a received burst to an electrical output signal S3. In a fashion complementary to that of the first reflective grating Gl, the elements of grating G2 are disposed at 45 degrees to the longitudinal axis of path P3 to facilitate interception and redirecting of wave components arriving from grating Gl.
The abcve-described transducer pair Tl, Rl and gratin~s Gl, G2 serve to establish one portion of a grid of surface wave burst paths pv which are disposed across substrate surace 16.
A second portion of that grid is established by a second pair of transducers T2, R2 and associated gratings G3, G4. In a manner similar to that described above, transducer T2, in response to a firing signal S2 from source 25 in interface circuit 24, launches a burst of acoustic surface waves along the pa'h P2, which path is disposed perpendicular to the previously described paths Pl, P3. The third reflective grating G3 comprises an array of reflective element ell-enn which are disposed along path P2 with the elements effectively arranged at like angles of incidence to the axis of path P2. Grating G3 serves to extract from the surface wave launched by transducer T2 a multiplicity of wave burst components and to direct such 1~

~'77~3 wave burst components across ~ubstxate surface 16 along a multiplicity of paths ph each disposed at a 90 degree angle to the axi 5 of path P2.
A fourth xeflective grating G4, comprising an ar~ay of reflective elements e'll- e'nn is disposed along path P4, each element being arranged at a 45 degree angle to the longitudinal axis of path P4. The reflective elements of grating G4 intercep~
the wave components directed thereto by the elements of grating G3 along paths ph and ~edirect these intercepted wave burst components along path P4 to receiving transducer R2.
Since transducers Tl, T2 additionally launch surface acoustic waves along paths Pl, P2 in directions opposite from their respective adjoining gratings Gl, G3, it is desirable to provide means for arresting such wave energy. Accordingly, a pair of absorbers 33, 35, which can be formed of a soft epoxy, are mounted upon the display surface immediately behind respective transducers Tl and T2.
In the manner just described, and as depicted in Figure 2, display surface 16 is now provided with an overlying grid comprising a multiplicity of intersecting paths of acoustlc surface wave bursts which surface waves are conined to predetermined paths, one series ph being disposed parallel to what may be termed the horizontal or major axis of display surface 16 while a second, intersecting series of paths pv are disposed parallel to the vertical or minor axis of the display surface. In this fashion intersecting wave energy paths traverse.
the surface of the display device, forming a grid that overlies display surface 16.
As described above, means, in the form of interface circuit 24 and buss 32, are coupled to the inpu~ transducers Tl, T2 for initiating the launching of bursts of surface waves along paths ~27~7~3~3 :
Pl, P2. The application of ~ignals Sl, S2 to transd~cers Tl, `~ T2 serve to generate and launch across surface 16 elastic (ultrasonic) surface waves having a ~ubstantia~ly planar wavefront with unior~ ~mplitude and phase along lines parallel to the initiating transducerO Transducers ~1, T2, ~as well a~
Rl and R2) typically, are piezoelectric transducers comprised of a lead zirconate-titanate ceramic mounted upon a prism o~
lower velocity material, e.g., Lucite* which effects an efficient electro-mechanical coupling to substrate surface 16.
The generated surface waves launched along paths Pl, P2 are eventually received by transducers Rl, R2, respectively, and converted to electrical signals S3, S4. Means comprising a signal processing circuit 23, included in interface circuit 24, see Figure 1, is coupled to the outputs of receiving transducers Rl, R2 for determining, by an analysis based on the transit time of the perturbed surface wave bu~st, which of paths ph, pv the touch-perturbed wave traversed and thereby establish the location of the touch along two coordinates of the display surface. In one coordinate system, for example, in order to identify the X coordinate for the location of the path of a perturbed wave burst along the horizontal axis, as viewed in Figure 2, the determining means is arranged to make a time analysis of the surface wave burst received by transducer Rl. To this end, the determining means analysis commences at the instant input signal Sl is applied to transducer Tl to launch a surface wave. On the time scale of Figure 3 there is plotted the earliest time an acoustic wave burst from transmitter Tl could ~rrive at receiver Rl.
Assuming that the dimensions of the grid overlying display surface 16 are approximately 8" x 11", and assuming ~urther that the transit time required for a surface wave burst to reach the * trade-~ark first reflective element el on path Pl is approximately 2 microseconds, as is the transit time reguired for the surface wave burst to travel to receiver Rl from el~ment e'l; to this is added the transit time of the surface wave from reflective element el across the display surface 16 to element en, which is approximately 64 microseconds~ Accordingly, the detector will ignore any disturbance arriving within the first 64 microseconds immediately following the triggering of transmitter Tl. Assuming for the moment, that no disturbance or perturbation of the instant surface wave launched by Tl is experienced, the output of transducer R2 might exhibit the solid line response shown in Figure 3. Depicted therein is a waveform having a relatively constant amplitude extending for approximately 176 microseconds. This response is established by virtue of the fact that for a period commencing at to surface wave energy is continually received by the d~tector Rl for 176 microseconds that is until time tn. The 176 microsecond interval is the approximate time reguired for a surface wave to traverse the entire length of reflective grating Gl and return al~ng the length of reflective grating G2. In the absence of a perturbation the output of receiver transducer R2, when analyzed by interface circuit 22, will supply a signal to computer 22 which is indicative of the fact that an uninterrupted burst of surface waves traversed substrate surface 16 without interference. The computer relays this information to controller 12 which, in turn, maintains the graphics display on the CRT
undisturbed.
Assuming now that an operator wished to select a graphic other than that being displayed. A menu, such as a chart or other type of directory, would indicate which particular area of display surface 16, should be touched to call up the desired ~2~

graphic~ Accordingly, assuming that the particular area is that designated Al in Figure 2, the operator then inserts his finger into the grid of inter~ecting surface waves by touching the display surface at Al, which action causes a portion of the acoustic surface wave energy traversing the touched area to be absorbed. This act of touc~ing is ~est explained, and manifested, by reference again to Pigure 3 which depict~ the effect upon the output waveform of Rl attributable to a perturbation of the sur$ace waYe traversing the display surface in the vicinity of area Al. This effect is manifested in the waveform as a dip Dl along the time axis which corresponds to the point where the operator touched the panel. L~t us assume that the point of touch occurred approximately one-fourth of the distance along the major axis of the display surface commencing from the left side, as viewed in Figure 2. As previously noted, it was assumed that the time entailed for a surface wave to travel the length of grating Gl wa~ 88 microseconds. One-fourth of that time would be 22 microseconds.
Adding to that number the 64 microseconds required for the wave to traverse the paths parallel to the minor axis of the surface, the 22 microseconds entailed in traversing a corresponding portion of array G2, and finally adding the 4 microseconds (2 + 2) initial and terminal transit timesl the detector, output waYeform would indicate ~hat a perturbation of the wave burst transmitted by Tl and subsequently received by Rl, occurred approximately 112 microseconds (2 + 2 + 64 + 22 ~ 22) after the transmitter Tl launched the surface wave under consideration~
This 112 microsecond interval is ~nalyzed by computer 22 which informs the controller 12 $hat a perturbation was detected by receiver Rl at a particular instant i~ the time domain.

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~L~7~
Preferably, a short time later, a ~urface wave burst is lau~ched by transmi~ter T2 and reflected by gratinqs G3 and G4 to return the components of that wave to receiver R2. ~n the manner described above with ~eference ~o a perturbation detected ~y ~1, the ~ur~ace wave components now traversing a path ph parallel to the ma~ox axis of the display surface are detected by R2 which e~a~lishes, in like fashion, the occurrence and time when the aforementioned perturbation ~f the wave, mani~ested in Figure 4 as dip D2, was experienced along the Y-axis.
Applying this time-related information to that developed relative to the other axis, the computer informs controller 12 of the coordinates of the pert~r~ation (touching Al) so that the controller may deliver for display upon the CRT screen the particular graphics associated or assigned to the location at which the touching occurred.
It is recognized that simultaneous operations to identi~y both coordinates are possible, but the preferred mode of operation is to alternate between the two. The latter prac~ice eliminates crosstalk problems and makes it possible to economize by switching certain circuit elements (eOg. a tuned amplifier) between coordinate identifying channels, instead of duplicating such elements.
In an embodiment successfully reduced to practice the above-descibed gratings Gl-G4 were formed by resort to a silk-screening technique in which a frit (solder glass) material was deposited in the pattern depicted in Figure 2. More particularly, the actual configuration and spa~ing of the srating element pattern was computer generated utili~ing the finger-withdrawal method. Consider first a basic reflectivç
linear array comprising a multiplicity of surface wave reflecting fingers ~elementsl of equal width, equally spaced and 1~

~27~3 collectively disposed at 45 degrees to the longitudinal axis of the path they define. Desirably, the spacingr or pitch, between adjacent elements should be one wavelength of the frequency of the burst of acoustic waves launched by the transmitting transducer. An acoustic wave traversing such an array in which the reflecting ~ingers ~re uniformly spaced will exp~rience an exponenti~l attenua~ion of power with distance so that little!, if any, ae~uStic wave energy is available for reflection at ~he terminus of the array. Moreover, a uniform array of the type advertea to results, of necessity, in exponentially decreasing power density with distance in the reflected acoustic wave components directed across ~he display surface. In other words, the power density of the initially reflected wave components will be significantly greater than that of subsequently reflected wave components. Desirably, the reflected wave components traversing the display surface should be characterized by a substantially constant power density, as graphically depicted in Figures 3 and 4, otherwise those plots would depict an exponentially decreasing amplitude.
The desirea constant power density of the reflected waves is achieved, in an execution thàt has been reduced to practice, by a patterned deletion of a grating's reflective elements in which the percentage of deleted elements decreases gradually ~ from the launch point to the terminus of the grating. This results in a progressively increasing coefficient of reflectivity culminating in the sought for constant power density.

i A reflective yrating tailored for the above-mentioned I execution was designed from an initial array of approximately 300 equally spaced elements having a pitch lin the direction of wave propagation) of one wavelength of a four MHz acoustic ;

~ wave. In practice elements are selectively deleted to ~he end ~7~0q:~3 .hat th~ spacing between remaining adjacent elements in the grating is a multiple of the above-mentioned one wavelength.
In the subject execution array elements were selectively deleted in accordance with the following formula:
f C e~
In the above expression, ~ is equal to the density of elements at coordinate x, wheze x is the distance measured from the far end of the array back toward the launch end. When x equals zero, element density is unity, which is the case for a uniform array with no elements deleted. C and L are constants, the values of which are determined by recourse to experimental data and depend upon the material properties of $he display panel and the reflective elements, the length, width and thickness of the reflective elements, etc. The resulting grating comprised an array of approximately 130 elements having a pattern determined by the above formula and in which individual elements were .7" long and .011" wide.
Having described a preferred embodiment of the invention, a number of the principles underlying the invention and variants of the preferred embodiment will be discussed~ Whereas the preferred embodiment of the invention is illustrated as providing for touch position detection in Cartesian coordinates, it should be understood that the principles of the invention are applicable in devices having angular or other coordinate systems, or in devices having a single coordinate axis.
The preferred embodiment has been described in the context of a system for launching a burst of surface waves into a reflective array or grating from which is derived a plurality of burst components. The array redirects these components across the display surface. In a broader sense, the invention may be thought of as surface acoustic wave scanning means including ~IL2770~ 3 input surface wave transducer means coupled to a surface wave propagating substrate for sca~ning the surface in the direction of the coordi~at~ axis with a timed succession of surface wave bursts directed in substantially para~el paths across the surface transversely to the said coordina~e a~i~. The plurality of paths are respectively associated with different positions along the coordinate axis of the display surface. As the touch position information is developed by timing the ~urface wave burst component which is perturbed, the starting time of each of the succession of surface wave bursts which are directed across the panel must be carefully controlled. In the aforesaid preferred embodiment, the timing is inherent in the propagation velocity of the surface wave burst as it travels through the reflective grating. Other embodiments are contemplated wherein the launching of the bursts of surface waves or wave components along parallel paths across the panel is determined by other than the natural propagation velocity of surface waves on the display surface, For e~ample, in the embodiment wherein a reflective array such as is shown in Figure 2 is used to launch the surface wave burst components across the panel, the reflective array may be formed on a separate strip composed of a material having a different wave propagation velocity, such as a different glass or a metal, which is adhered to the display surface. Care must be taken to insure an efficient transition of the waves from the reflective grating onto the display surface, as by feathering the interfacing edge of the strip.
The wave reflective array may be formed on a separate strip for other reasons also, such as ease or economy of manufacturec In a broad sense, ~he invention may also be thought of as n absorption ranging system, quite unlike the above-discussed l/,S, reflection-type ranging system shown in the prior art~Patent No. 3,653,031~ In the present invention, the absence of wave energy or the presence of wave energy at a reduced level, as results when a finger, ~r a stylus reasonably capable of absorbing acoustic $urface wave energy, damps the amplitude of a surface wave burst propagating through the region of the touch, is sensed and the timing of that information is utilized to determine which of the plurality o~ burst propagation paths has been perturbed, and thus the location of the touch. One will note that in the preferred embodiment, the time required for the surface wave burst components to propagate across the panel is constant for all burst paths. However, the time re~uired for the surface wave burst launched by the input transducer to propagate to the point at which it is again redirected across the panel, and from the point at which it is redirected to the output transducer, varies along the coordinate axis along which the touch may occur. It is this varying distance, and the surface wave propagation time associated therewith, which is used in the present invention to ocate the position of a touch along the coordinate axis.
Unlike prior art systems which have a fixed number of emitters along one side of the touch panel and a corresponding fixed number of detectors along the opposed side thereof and which detect the position of a touch by determining which of the emitter-detector pairs have been triggered, the present invention teaches the formation of a continuous succession of surface wave bursts which sweep across the panel and develop at the output an analog output signal. With the present invention, a touch panel system designer has a free choice, by detection circuit design, to pick touch panel specifications conforming to the specifications of a device driven by the display -- a computer, for example -- without making mechanical ~27t7~C~3 changes. This subject will be treated at length belowO
Figure 5 will further an understanding of certain principles underlying the present invention, and certain desired optimizations. Whereas other means may be devised for redirecting a burst of surface waves launched by the input transducer across the display surface, as in the preferred embodiment described above, Figure 5 shows a reflective grating 40 for this purpose. The grating is shown as comprising reflective elements El, E2, E3, E4, and E5 arranged in the direction of the touch coordinate axis 41. In practice, the grating would comprise additional elements as shown in Figure 2, however, in the interest of clarity of illustration, only five elements are shown. An input signal 42 for application to the schematically represented input transducer 44 i5 shown as comprising a five cycle signal burst, here depicted as a sine wave having cycles Cl, C2, C3, C4 and C5.
Application sf input signal 42 to the input transducer 44 results in a burst of equal-amplitude surface waves from the transducer 44. The wavelength of the cycles Cl-C5 is selected to be equal to the period of the grating 40. ~he first cycle C1 of signal 42 generates a first surface wave which is partially reflected from the first element El of grating 40, here shown by way of example as being oriented at 45 degrees to axis 41.
The reflected surface wave propagates at 90 degrees to the direction of travel of the launched surface wave. The first reflected surface wave is labeled in Figure 5 as ClEl, signifying the first surface wave developed by input signal cycle Cl, as reflected from grating element E1~
The same first wave reflected from grating element E2 is shown in Figure 5 at ClE2. The surface waves reflected from elements E3 E5 are labeled ClE3, ClE4 and ClE5, respectively.

~n ~Z770~3 Similarly, the second cycle C2 of the input siqnal 42 develops a second surface wave which lags the first surface wave by one period, producing a second pattern of surface waves of exactly the same configuration as the pattern of waves produced by the first cycle Cl of the input signal, but lagging in time by one cycle. Similarlyt input signal cycles C3-C5 produce three more surface wave patterns. Thus, the application of input signal 42 results in a burst of surface waves from the input transducer 44 which propagate through the reflective grating 40. A
plurality of surface wave burst components are derived from the grating 40 which propagate across the display surface. As used herein, ClEl, C2El,C3El, C4El, C5El constitutes one burst component. Another would be ClE2, C2E2, C3E~, C4E2, C5E2. It is preferred that the burst components be heavily overlapped to produce at the output a smooth analog signal, as will be discussed at length below.
The output developed by an output transducer ~5, positioned as shown in Figure 5, will take the form shown schematically in Figure 6 wherein the amplitude of the detected signal will rise to a peak and then decay to zero. This can be easily understood from Figure 5 wherein it can be seen that the burst of surface waves is led by single wave ClEl, which is followed by a double wave ClE2, C2El in turn followed by a triple wave, and so on. After the peak is reached, the number of surface waves which add at the output progressively decreases until the burst has passed and the detected wave energy falls to zero.
It has been discovered that i signal/noise ratio is considered, there exists an optimum relationship of surface wave burst length to input transducer width (or more precisely, width of gratings Gl,G2 etc.). Specifically, in a preferred execution of the present invention, the duration of the input surface wave ~2770~3 burst ("T") emerging from the input transducer should be in the range of 1.0 w/c to 2.0 w/c where "w~ i5 the above-mentioned width and "c" is the ve~ocity of propag~ion o~ ~urfac0 waves on the conducting substrate.
~ he implications of the above can be better understood by reference to Figure 8 which is a highly schematic representation of a rectified version of the wave form of a signal which might be produced at the output of the output transducer in touch panel display apparatus according to the present invention. Eigure 8 is a schematic illustration corresponding to Fi~ures 3 or 4 discussed above. Using an optimized configuration, as described above, an output signal 48 results in which the amplitude dip 49 resulting from a damping of a burst of surfaee waves in a particular burst path has substantial amplitude. The signal to noise ratio of the signal 48 is adequate. The dip 49 in the waveform of the rectified signal 48 corresponding to the detected damping of the wave has a well-defined bottom which can be j located with extreme precision, as will be discussed below.
¦ If the length of the input burst of surface waves is substantially above the optimum range, the output transducer will develop an output signal having an envelope with an excessively elongated trapezoidal shape, as shown schematically in Figure 7. In Figure 8, the waveform 50 represents the type of rectified output which would result -- namely an output signal having a dip 51 asso~iated with the perturbation which has a poorly defined bottom and thus poor touch resolution.
Conversely, if the input burst of surfase waves (the duration of the input signal 42) is significantly shorter than the optimum length, a weak signal will result such as shown in Figure 8 at 52, with lower signal-to-noise ratio and thus a signal whose reliability and touch resolution is poor. It is the ~L277~3 signal-to-noise ratio of the signal developed at the output transducer which determines the limiting touch resolution in the present system.
By way of example, the spacing of the grating elements and the wavelength of the surface waves which make up the surface wave ~ursts may, for example, be thirty mils (.030"). In determining the optimum inp~t burst length in accordance with the present invention, one factor which must be taken into account is the distance the surface waves wi}l travel across the panel without significant spreading due to diffraction effects. As a rule of thumb, a surface wave will propagate from its launching transducer a distan~e roughly equal to the square of the width of the transducer, measured in number of wavelengths, without excessive spreading. By way of example, to launch a surface wave across a fifteen inch wide panel, the input transducer should be about twenty-four wavelengths wide.
Assuming a thirty mil wavelength, the surface wave burst will travel approximately 576 wavelengths or about seventeen inches before significant spreading occurs. In practice/ however~ it has been found that for a fifteen inch panel width, the transducer need only be about 16 wavelengths (.48 inches) wide;
this favorable finding is explained by the simultaneous acti~n of two gratings (e.g. Gl and G2) in determining the wave paths across the display surface. Now, if the surface wave velocity on the display surface is 120 mil per microsecond ~=3000 meter/second), then w/c equals 4 microseconds, and conse~uently the optimum burst duration is between 4 and 8 microseconds, corresponding to the range of 16 to 32 cycles. The fre~uency corresponding to these figures, determined by the quotien~ of velocity c and wavelength, equals 4 Megahertz.

~L~7700~ 1 It is important to note that with bursts as long as 32 cycles passing through the grating, maintaining the correct relationship between the transmitted frequency and the mutual spacing S of the Ieflecting ~trips is important. In the embodiment described so far, the strips are or;ente~ at 45 degrees to the direction of the incident wave, and the proper spacing for this case is one wavelength or an integral number of wavelengths; the correct frequency is f= ~S or an integral multiple thereof, and the transmitted frequency should be very close to the theoretical value; for shorter bursts, i.e. those containing fewer cycles, frequency tolerance is proportionately wider. Power reflectivity, to be defined later, mus~ also be determined at the correct frequency. For the same reasQn, it is important that the chosen value of S be accurately maintained constant along the entire grating, with the exception that integral multiples of S are allowed.
As intimated above, the present invention is distinquished from other touch panel systems, in its preferred form, in its particular utilization o an analog output signal~
In accordance with an aspect of this invention, circuit means are provided which are coupled to the input and output transducer means for initiating a timed succession of surface wave bursts, or burst components, on the display surface and for detecting touch-induced perturbations of received wave bursts, the circuit means including means for rectifying the output from the output transducer means to develop an electrical characterization of the perturbation and for developing an output representing the timing of said characterization of said perturbation~ From that output, it is determined which of the plurality of paths was traversed by the touch-perturbed wave burst and thereby the location of the touch along the coordinate axis of the display ~2~ 3 surface.
A number of arrangements are contemplated for analyzing the output signal to deter~ine the timing of the wave burst ~r~vQ,~ ~f~ /-C perturbation. In a preferred embodiment,~means are pxovided for sampling the amplitude of the rectifiea output from the output transducer at a plurality of time spaced points. Means are provided for storing the amplitude samples for future reference. During a touch of the display surface, means are provided for again sampling the amplitude of the output transducer output and comparing the developed touch-related amplitude samples with the stored reference samples. Means are provided for developing a signal representing the point of greatest difference, or if desired the greatest ratio, between the amplitudes of the reference samples and the touch-related samples and thus the timing of the touch-perturbed wave burst.
As mentioned above, a designer utilizing the present invention has a free choice in tailoring the touch panel specification to the standards of a device driven by the panel That is, ~he sampling means can be adiusted and designed to sample at any selected time interval to correspond to the standards of the driven device. For example, if the touch panel apparatus drives a computer, the sampling frequency may desirably be selected to correspond to every character or every other character for which the computer is programmed. Typical computers today have 640 matrix points along a horizontal line, corresponding to 80 characters. One would like to have touch resolution elements that have some integral relationship to the number 640, if the driven computer has 640 horizontal matrix points. There is nothing inherent in the output signal developed in accordance with the present invention that needs to be changed if one wishes to drive a computer having, instead, 512 matrix 2~

~2~7~
points (64 characters) along its horizontal axis. All that is required is that the timing of the electronic sampling signal be changed. This is not true of prior art fixed emitter systems because they cannot readily be changed to meet a different standard. Thus, in such p~ior art systems, a physically different touch panel would have to be provided for every standard desired to be met. With the present invention, only the timing of the sampling signal need be changed to accommodate a variety of different standards in the driven devices.
Yet another approach to analyzing the output from the output transducer to determine the timing of the pert~rbed wave burst is to provide differentiating means for differentiating the rectified output of the output transducer means. The zero ~rossing of the resulting signal represents the timing of the touch-perturbed wave burstu While the differentiating approach has the advantage that relatively inexpensive electronics can be utilized, the ~ratings employed in such a system must be very carefully tailo-ed to insure that the burst components issuing from and intercepted by them will enable the output transducer to produce a s~bstantially flat output signal. Moreover, the differentiating approach is vulnerable to interpreting the presence of a contaminant (e.q., grease on the display surface) as a "touch".

~27~3 The above described preferred embodiment (Figure 2) is shown as having reflective gratings Gl, G2, G3 and G4, the elements of which are non-uniformly spaced. As alrea~y noted, in a practical embodiment this is desirable since a grati~g whose elements are uniformly spaced would reflect uniformly and thus produce an exponential fall-~ff in radiated power along its length. That is to say, if for each unit of length along the fixed grating, a fixed percentage of the power incident thereupon is radiated sideways, a smaller residue of power remains. If the same fixed percentage of that power is radiated in the succeeding section, it can be seen that the power decreases in a geometrical progression.
By way of review, desirably, a flat response such as is shown in Figures 3, 4 or 8 is preferred. In accordance with an aspect of this invention, the reflectivity of the reflective elements constituting the reflective grating or ~ratings which adjoin the input transducer is weighted such that the initial elements have a relatively low reflectivity and the succeeding elements have increasing reflectivity. Stated in another way, the reflective array has an increasing coefficient of reflection in the direction away from the adjoining transducer so as to compensate for the fall-off in wave amplitude which results from the continuing diversion of wave energy into paths across the panel. It should be understood that the reflective array adjoining the input transducer should have increasing reflectivity in the direction of wave propagation, but for the array adjoining the output transducer, the array should ha~e a corresponding decrease in reflectivity in the direction of wave propagation. Thus, in both cases, the reflectivity should increase in the direction away from the adjoining transducer.
This desirable attribute is realizable in the Figure 2 embodiment ~ 27~ 03 by virtue of the depicted non-uniform spacing of the reflective elements constituting each of gratings Gl-G4.
For perfect uniformity of the transversely radiated surface wave power, and assuming no power loss by aissipatiOn anywhere in the array, the power along the array must decrease linearly with distance. For this to occur, the p~wer re~lectivity must increase inversely with the distance remaining to the point beyond the array where the linearly decreasing power would drop to zero. IAs used herein, reflectivity is the fraction of the longitudinally incident power diverted transversely per unit length.) In other words, power reflectivity K must increase with the distance x from the transducer in accordance with K= -~ _ ~ t y~ where Ke is the maximum reflectivity actually used at the far end where x=G, the symbol G representing the length of the grating. Note that K and Ke have the dimension of a reciprocal length (fraction of power diversion per unit length).
There are a number of ways the reflectivity of the grating can be increased in the direction away from the adjoining transducer so as to flatten out the output waveform of the output transducer. One way would be to increase the thickness of the reflective elements in the direction away from the adjoining transducer, as the power reflectivity is proportional to the square of the thickness of the reflective elements. This could be done, in theory, by screen printing or etching (where grooves are used), however in practice this approach might prove to be difficult to execute.
A second, more practical, approach is to remove selected ones of the reflective elements in accordance with a ormula which yields the desired increase in reflectivity along the array See Figure 9, also Figure 2 and the earlier discussion ~27~3 concerning tailoring a reflective grating. For example, if one wished to cover a range of power reflecti~ity variation of 9 to 1 (an amplitude ratio of about 3 to 1~, ~ne would eliminate two of every three strips at the be~inning of the array. Strips would be grad~ally adde~ Ifewer strips eliminated) along the length of the array until at the end of the array, no strips would be eliminated. This is a practical method and has been reduced to practice successfully.
Yet another method involves weighting the reflectivity of each of the individual reflective element~, as shown schematically in Figure 10 by fragmenting individual elements of an array G'l. The elements have greater interruptions ~which may be produced according to a random formula) at the end of the array nearest the transducer (input or output) than at the opposite end of the array.
In yet another embodiment (Figure lOA), the reflective array G"l has array elements whose individual length increases in the direction away from the adjoining transducer and whose individual position in a direction along the length of the element is varied within the side boundaries of the array. ~ith all these methods, the reduction in element length~ corresponds to an equal reduction in amplitude of the reflected burst, and the power reduction, above referred to as K/Ke, equals ~ 2.
The same technique can be used, that is, weighting the reflective elements according to a prescribed reflectivity shading formula, to compensate for eneryy dissipation in the reflective array or other factors for which compensation may be desirable. The equation previously mentioned in connection with the preferred embodiment allows for uniform dissipation.
Various other applications of the principles of the present invention will now be discussed.

~9 2~
Whereas the preferred embodiment is des~ribed as having separate input and output transducer means and means redirecting a burst of surface waves launched from an input transducer to a different output transducer, it is contemplated that the input transducer may also be the output transduc~r. See Fiyure 11 wherein a reflector 60 is employed to reflec~ the wave~ launched by the common input/~utput transducer 61 back across the panel where they are redirected by a grating 62 back to the input/output transducer 61.
The reflector 60 may consist of a seri~s of` half-wavelength spaced reflecting elements -- either raised or depressed grooves -- as is well known in the surface wave art.
Figure 12 illustrates ye. another embodiment of the invention comprising a substrate 64 to which is coupled an input transducer 66 for launching a buræt of surface waves on the surfac~e of the ~;ubstrate 64. Surface wave redirecting means includes a grating 68 of the character of the gratings desGribed above for redi,-ecting surface wave burst components derived therefrom across the surface of the substrate 64 to output transducer means 70 along a plurality of paths of different lengths which are respectively associated with different positions along a coordinate axis on the display surface.
The Figure 12 embodiment differs from other embodiments described in that the output transducer means 70 extends in the direction of the coordinate axis 69 and is of such length as to intercept each of the plurality of burst component paths.
Circuit means ~not shown) may be provided for initiating surface wave bursts on the surface and for detecting touch-induced perturbations of received wave burst components. It will be understood that unlike the other embodiments described, the varying component of the transit time of each of the surface wave burst co~ponents will only be half that in the aforedescribed embodiments~ In the aforedescribed embodiments the variable part of the transit time of the surace wave burst component had an ~utgoing component and a returning ~mpo~ent, whereas in the Figure 12 embodiment, the sur~ace wave burst component tlansit time has only an outgoing component. It is, of course, understood that the functions of input and output transducer may be interchanged.
Yet another embodiment of the invention is shown schematically in Figure 13. Whereas in each of the aforedescribed embodiments, the wave redirecting means, or reflective grating, is continuous, producing an analog output signal, in the Figure 13 embodiment the wave redirecting means comprises discrete groups of wave reflective elements, two of which groups are shown at 72 and 74. The groups are spaced in the direction of the coordinate axis such that the paths of the surface wave burst components, shown schematically at 76, 78, are discrete and non-overlapping.
The output of the output transducer (not shown), rather than being an analog signal as shown for example at 43 in Figure 8, will have a pulse characteristic as shown, for example, in Figure 14. In Figure 14 the pulses 80 have a height which defines an envelope corresponding to the wave form 48 in Figure 8. In Figure 14, a pulse 82 of reduced height corresponds in time to the timing of a surface wave burst component which has been perturbed by its passage through a touched region on the surface of the touch panel apparatus.
In the Figure 13 embodiment, circuit means (not shown~
includes processing means for processing the pulses and may develop a waveform such as shown in Figure 15 consisting of a serles of pulses 84 wherever the pulse height exceeds a _ .

predetermined threshold and a pulse void 86 corresponding to the missing pulse 82 (less than the threshold). The circuit means aforedescribed for initiating surface wave bursts on the surface and for detecting touch-induced perturbations of received wave burst components may include means for determining, by an analysis based on the timin~ of the detected pulse void associated with a pe~turbed wave burst component or by counting the pulses precedins the void, which of the plurality of paths was traversed by the touch perturbed wave burst component and thus the location of the touch along the coordinate axis of the display surface.
Figure 16 illustrates yet another embodiment of the invention in which the coordinate axis is not lineax, but rather is angular. Such a one-coordinate system (angle only) could be used, for example, on the cover of a conventional meter to initiate an action in response to the meter reading. The Figure 16 embodiment, which shows such a system in highly schematic form, comprises a display substrate 88 coupled to which is an input transducer 90 for launching circular surface waves which radiate outwardly across a display surface having angular coordinate markings 92 from the apparent center point of the angular coordinate system. Surface wave redirecting means in the form of a series of discrete reflectors 94 redirect the wave components derived from the burst to an output transducer 96 along a plurality of paths of different lengths which are respectively associated with different angular positions on the display surface. Circuit means similar to that described above, coupled to the input and output transducer means 90, 96 for initiating surface wave bursts on the surface of the substrate 88 may be provided. As for the above described embodiment, the circuit means includes means for determining by an analysis of ~'77~3 the transit time of a detected perturbed wave burst component, which of the plurality o~ radial paths was traversed by the touch-perturbed wave ~urst component, and thus the angular location of the touch along the angular axis of the display surface.
The Figure 16 embodiment illustrates that the pxinciples of the invention may be employed in a system iD which the redirecting means does nvt redirect the surface waves across the display surface for detecting a touch, but rather intercepts the surface waves after they have traversed the display (touch) surface. It is, however, unders~ood that the functions of input and output transducers may be interchanged, and if that is done, the redirecting means 94 functions to redirect the surface waves, now generated by transducer 96, onto radial paths across the display surface toward transducer 90. As in each of the above embodiments, an output signal will be developed which reveals a perturbation associated with a touch of the display surface, and the timing of which perturbation signifies, or can be processed to signify, the position of the touch on the panel along the predetermined coordinate axis.
Still other embodiments and implementations of the present invention are contemplated and are within the spirit and scope of this invention.

Claims (32)

1. For use with a touch panel apparatus, a system for recognizing touch positions along a predetermined coordinate axis on a surface associated with said apparatus comprising:
a substrate having a surface capable of propagating surface acoustic waves and being so characterized that a touch on said substrate surface causes a perturbation of a surface wave propagating through the region of the touch;
surface acoustic wave scanning means, including input surface wave transducer means coupled to said substrate surface, for effecting scansion of said surface with a timed succession of surface wave bursts directed in a plurality of substantially parallel overlapped paths across said substrate surface transversely to said coordinate axis, said plurality of paths being respectively associated with different positions along said coordinate axis on said substrate surface;
output surface wave transducer means coupled to said substrate surface for receiving said bursts of surface waves, and circuit means coupled to said input and output transducer means for initiating said timed succession of surface wave bursts on said substrate surface and for detecting touch-induced perturbations of received wave bursts, said circuit means including means coupled to said output transducer means for developing an electrical amplitude characterization of said perturbation and thus determining which of said plurality of paths was transversed by the touch-perturbed wave burst and thereby the location of the touch along said coordinate axis of said substrate surface.

2. The system defined by Claim 1 wherein said circuit means includes comparator means for:
a) rectifying the output from said output transducer b) sampling the amplitude of said rectified output from said output transducer means at a plurality of time spaced points, c) storing the amplitude samples for future reference, d) during a touch of the apparatus, again sampling the amplitude of the said output transducer output and comparing the developed touch-related amplitude samples with the stored reference samples, and e) developing a signal representing the point of greatest difference between the amplitudes of said reference samples and said touch-related samples and thus the timing of said touch-perturbed wave burst.

3. The system defined by Claim 1 wherein said circuit means includes differentiating means for differentiating the output from said output transducer means, the zero crossing of resulting signal representing the timing of said touch-perturbed wave burst.

4. For use with a touch panel apparatus, a system for recognizing touch positions along a predetermined coordinate axis on a surface associated with said apparatus comprising:
a substrate having a surface capable of propagating surface acoustic waves and being so characterized that a touch on said substrate surface causes a perturbation of a surface wave propagating through the region of the touch;
input surface wave transducer means coupled to said substrate surface for launching a burst of surface waves on said surface;
output surface wave transducer means coupled to said substrate;
surface wave redirecting means for redirecting surface wave burst components derived from said surface wave burst across said substrate surface and to said output transducer means along a plurality of paths of different lengths which are respectively associated with different positions along said coordinate axis on said substrate surface; and circuit means coupled to said input and output transducer means for initiating surface wave bursts on said substrate surface and for detecting touch-induced perturbations of received wave burst components, said circuit means including means for determining, by an analysis based on the transit time of the detected perturbed wave burst component, which of said plurality of paths was traversed by the touch-perturbed wave burst component and thus the location of the touch along said coordinate axis of said substrate surface.

5. The system defined by Claim 1 wherein the surface wave burst initiated by said circuit means has a duration T in the range of 1.0 w/c to 2.0 w/c where "w" is the width of said input transducer means and "c" is the velocity of propagation of surface waves on said substrate.

6. For use with a touch panel apparatus, a system for recognizing touch positions along a predetermined coordinate axis on a surface associated with said apparatus comprising:
a substrate having a surface capable of propagating surface acoustic waves and being so characterized that a touch on said surface causes a perturbation of a surface wave propagating through the region of the touch;
input/output surface wave transducer means coupled to said substrate surface for launching a burst of surface waves on said surface and for receiving said burst and developing an output therefrom;
surface wave redirecting means including first means for redirecting surface wave burst components derived from said surface wave burst across said substrate surface and reflective means for reflecting them back to said input/output transducer means along a plurality of paths of different lengths which are respectively associated with different positions along said coordinate axis on said substrate surface, and circuit means coupled to said input/output transducer means for initiating surface wave bursts on said substrate surface and for detecting touch-induced perturbations of received wave burst components, said circuit means including means for determining, by an analysis based on the transit time of the detected perturbed wave burst component, which of said plurality of paths was traversed by the touch-perturbed wave burst component and thus the location of the touch along said coordinate axis of said substrate surface.

7. The system defined by Claim 6 wherein said reflective means includes an array of half-wave spaced grooves or deposits of wave-reflective material.

8. For use with a touch panel apparatus, a system for recognizing touch positions along a predetermined coordinate axis on a surface associated with said apparatus comprising:
a substrate having a surface capable of propagating surface acoustic waves and being so characterized that a touch on said surface causes a perturbation of a surface wave propagating through the region of the touch;
input surface wave transducer means coupled to said substrate surface for launching a burst of surface waves on said surface;

output surface wave transducer means coupled to said substrate;

surface wave redirecting means for redirecting surface wave burst components derived from said surface wave burst across said substrate surface and to said output transducer means along a plurality of paths of different lengths which are respectively associated with different positions along said coordinate axis on said substrate surface, said output transducer extending in the direction of said coordinate axis and being of such length as to intercept each of said plurality of paths; and circuit means coupled to said input and output transducer means for initiating surface wave bursts on said substrate surface and for detecting touch-induced perturbations of received wave burst components, said circuit means including means for determining, by an analysis based on the transit time of the detected perturbed wave burst component, which of said plurality of paths was traversed by the touch-perturbed wave burst component and thus the location of the touch along said coordinate axis of said substrate surface.

9. For use with a touch panel apparatus, a system for recognizing touch positions along a predetermined coordinate axis on a surface associated with said apparatus comprising:
a substrate having a surface capable of propagating surface acoustic waves and being so characterized that a touch on said substrate surface causes an amplitude reduction of a surface wave propagating through the region of the touch:
input surface wave transducer means coupled to said substrate surface for launching a burst of surface waves on said surface;
output surface wave transducer means coupled to said substrate;
surface wave redirecting means including a reflective array for deriving surface wave burst components from said surface wave burst and redirecting them across said substrate surface and to said output transducer means along a plurality of paths of different lengths which are respectively associated with different positions along said coordinate axis on said substrate surface, said reflective array having an increasing reflectivity in a direction away from said input transducer means, to at least partially compensate for the fall-off in wave amplitude with increasing wave path length;
circuit means coupled to said input and output transducer means for initiating surface wave bursts on said substrate surface and for detecting touch-induced amplitude damping of received wave burst components;
said circuit means including means for determining, by an analysis based on the transit time of the detected amplitude-damped wave burst component, which of said plurality of paths was traversed by the touch-damped wave burst component and thus the location of the touch along said coordinate axis of said substrate surface.

10. The system defined by Claim 9 wherein said reflective array has, in said direction away from said input transducer means, selected array elements eliminated in progressively decreasing proportion to effect said increasing reflectivity.

11. The system defined by Claim 9 wherein said reflective array has, in said direction away from said input transducer means, the reflectivity of the individual array elements increasing.

12. The system defined by Claim 9 wherein said reflective array has array elements whose individual length increases in said direction away from said input transducer means, and whose individual position in a direction along the length of the element is varied within the side boundaries of the array.

13. The system defined by Claim 9 wherein said circuit means includes means for rectifying the output from said output transducer means to develop an electrical amplitude characterization of said perturbation and for developing an analog signal representing the timing of said characterization of said perturbation.

14. The system defined by Claim 9 wherein the surface wave burst initiated by said circuit has a duration T in the range of 1.0 w/c to 2,0 w/c where "w" is the width of said input transducer means and "c" is the velocity of propagation of surface waves on said substrate.

15. For use in a touch panel apparatus, a system for recognizing touch positions along a predetermined coordinate axis on a surface associated with said apparatus comprising:
a substrate having a surface capable of propagating surface acoustic waves and being so characterized that a touch on said surface causes a perturbation of a surface wave propagating through the region of the touch;
input surface wave transducer means coupled to said substrate surface for launching a burst of surface waves on said surface;
output surface wave transducer means coupled to said substrate surface;
surface wave redirecting means for redirecting surface wave burst components derived from said surface wave burst across said substrate surface and to said output transducer means along a plurality of paths of different lengths which are respectively associated with different positions along said coordinate axis on said substrate surface, said surface wave redirecting means comprising discrete groups of wave-reflective elements spaced in the direction of said coordinate axis such that said paths are non-overlapping and the output of said output transducer means consists of pulses whose respective transit times are directly proportional to the lengths of the paths traversed by the pulses over said substrate surface; and circuit means coupled to said input and output transducer means for initiating surface wave bursts on said substrate surface and for detecting touch-induced perturbations of received wave burst components, said circuit means including means for determining, by an analysis based on the timing of the pulse or pulse void associated with a perturbed wave burst component, which of said plurality of paths was traversed by the touch-perturbed wave burst component and thus the location of the touch along said coordinate axis of said substrate surface.

16. For use in a touch panel apparatus, a system for recognizing touch positions along a predetermined coordinate axis on a surface associated with said apparatus comprising:
a display substrate having a surface capable of propagating surface acoustic waves and being so characterized that a touch on said surface causes an amplitude damping of a surface wave propagating through the region of the touch;
input surface wave transducer means coupled to said substrate surface for launching a burst of surface waves on said surface in a first direction parallel to said coordinate axis;
output surface wave transducer means coupled to said substrate;
first surface wave reflecting means for deriving surface wave burst components derived from said surface wave burst and reflecting said burst components across said display surface, and second surface wave reflecting means for redirecting said surface wave burst components reflected across said display surface to said output transducer means in a second direction opposite to said first direction, said first and second reflecting means causing said wave burst components to traverse said display surface substantially orthogonally to said coordinate axis along a progression of paths which are respectively associated with different positions along said coordinate axis on said display surface;
circuit means coupled to said input and output transducer means for initiating surface wave bursts across said surface and for detecting touch-induced dampings of the received waves, said circuit means including means for determining, by an analysis based on the transit time of the detected damped wave, which of said plurality of paths was traversed by the touch-damped wave and thus the location of the touch along said coordinate axis of said display surface.

17. The system defined by Claim 16 wherein the surface wave burst initiated by said circuit has a duration T in the range of 1.0 w/c to 2.0 w/c where "w" is the width of said input transducer means and "c" is the velocity of propagation of surface waves on said substrate.

18. For use in a touch panel apparatus, a system for recognizing touch positions along a predetermined coordinate axis on a surface associated with said apparatus comprising:
a display substrate having a surface capable of propagating surface acoustic waves and being so characterized that a touch on said surface causes an amplitude damping of a surface wave propagating through the region of the touch;
input surface wave transducer means coupled to said substrate surface for launching a burst of surface waves on said surface in a first direction parallel to said coordinate axis;

output surface wave transducer means coupled to said substrate;
first surface wave reflecting means for deriving surface wave burst components derived from said surface wave burst and reflecting said burst components across said display surface, and second surface wave reflecting means for redirecting said surface wave burst components reflected across said display surface to said output transducer means in a second direction opposite to said first direction, said first and second reflecting means causing said wave burst components to traverse said display surface substantially orthogonally to said coordinate axis along a progression of paths which are respectively associated with different positions along said coordinate axis on said display surface, said first reflecting means having an increasing reflectivity, and said second reflecting means having a corresponding decreasing reflectivity, in the direction of wave propagation to at least partially compensate for the fall-off in wave amplitude with increasing path length; and circuit means coupled to said input and output transducer means for initiating surface wave bursts across said surface and for detecting touch-induced dampings of the received waves, said circuit means including means for rectifying the output from said output transducer means to develop an electrical amplitude characterization of said perturbation and thus an indication of which of said plurality of paths was traversed by the touch-damped wave and thereby the location of the touch along said coordinate axis of said display surface.

19. The system defined by Claimed 18 wherein said circuit means includes comparator means for:
a) sampling the amplitude of the rectified output from said output transducer means at a plurality of time spaced points, b) storing the amplitude samples for future reference, c) during a touch of the apparatus, again sampling the amplitude of the said output transducer output and comparing the developed touch-related amplitude samples with the stored reference samples, and d) developing a signal representing the point of greatest difference betweeen the amplitudes of said reference samples and said touch-related samples and thus the timing of said touch-perturbed wave burst.

20. The system defined by Claim 18 wherein said circuit means includes differentiating means for differentiating the rectified output for said output transducer means, the zero crossing of resulting signal representing the timing of said touch-perturbed wave burst.

21. The system defined by Claim 18 wherein the surface wave burst initiated by said circuit has a duration T in the range of 1.0 w/c to 2.0 w/c where "w" is the width of said input transducer means and "c" is the velocity of propagation of surface waves on said substrate.

22. For use in a touch panel angular coordinate display apparatus, a system for recognizing touch positions at different angles on a display surface of said apparatus, comprising:
a substrate having a surface capable of propagating surface acoustic waves and being so characterized that a touch on said surface causes a perturbation of a surface wave propagating through the region of the touch;
input surface wave transducer means coupled to said substrate surface for launching a burst of circular surface waves which radiate outwardly across the display surface from the apparent center point of the coordinate system;
output surface wave transducer means coupled to said substrate;
surface wave redirecting means located beyond the display surface for redirecting surface wave burst components derived from said surface wave burst to said output transducer means along a plurality of paths of different lengths which are respectively associated with different angular positions on said display surface; and circuit means coupled to said input and output transducer means for initiating surface wave bursts on said surface and for detecting touch-induced perturbations of received wave burst components, said circuit means including means for determining, by an analysis based on the transit time of the detected perturbed wave burst component, which of said plurality of paths was traversed by the touch-perturbed wave burst component and thus the angular location of the touch on said display surface.

23. For use with graphics display apparatus, an arrangement for recognizing and locating a momentary, intentional absorption of acoustic wave energy propagating along at least one of a multiplicity of paths, said arrangement comprising:
a substrate having a surface capable of propagating surface acoustic waves;
an input transducer coupled to said substrate surface and responsive to an input signal for launching acoustic surface waves along a first path on said surface;
a first reflective grating comprising an array of reflective elements disposed along said first path, with said elements effectively arranged at like angles of incidence to the longitudinal axis of said first path, for extracting from said surface wave a multiplicity of wave components and for directing said wave components across said substrate surface along a like multiplicity of paths each disposed at an angle to said axis of said first path;
an output transducer, for developing an electrical output signal upon receipt of surface acoustic wave energy, also coupled to said substrate surface at the terminus of a second path on said surface;
a second reflective grating comprising an array of reflective elements disposed along said second path and effectively arranged at like angles of incidence to the longitudinal axis of said second path for intercepting said wave components and for redirecting said intercepted wave components along said second path toward said output transducer; and means coupled to said output transducer for utilizing a change in amplitude of said output signal, attributable to an intentional absorption of energy from at least one of said extracted wave components, to identify a coordinate for the location of said intentional absorption.

24. An arrangement of the type set forth in Claim 23 in which said substrate comprises an isotropic medium.

25. An arrangement of the type set forth in Claim 24 in which said substrate is formed of a sheet of transparent glass.

26. An arrangement of the type set forth in Claim 23 in which said second path is disposed parallel to said first path.

27. An arrangement of the type set forth in Claim 26 in which said angles of incidence of said reflective elements to their respective paths are approximately 45 degrees.

28. An arrangement of the type set forth in Claim 23 in which said multiplicity of paths are disposed at approximately 90 degrees to said axis of said first path.

29. An arrangement of the type set forth in Claim 23 in which the configuration of said second reflective grating is a mirror image of the configuration of said first reflective grating.

30. An arrangement of the type set forth in Claim 29 in which the spacing between adjacent ones of said elements of said gratings is a multiple of one wavelength of the frequency of said acoustic surface waves.

31. A touch panel system having a predetermined coordinate axis on a touch surface comprising:
a substrate having a touch surface capable of propagating surface acoustic waves and being so characterized that a touch on said surface damps the amplitude of a surface wave propagating through the region of the touch;
input surface wave transducer means coupled to said substrate surface for launching a burst of surface waves on said surface;
output surface wave transducer means coupled to said substrate;

surface wave redirecting means for redirecting surface wave burst components derived from said surface wave burst across said surface and to said output transducer means along a plurality of paths of different lengths which are respectively associated with different positions along said coordinate axis on said touch surface; and circuit means coupled to said input and output transducer means for initiating surface wave bursts across said surface and for detecting touch-induced amplitude damping of received wave burst components, said circuit means developing an output signal having a first wave-timing-related characteristic indicative of which of said plurality of paths was traversed by the touch-damped wave burst component and thus the location of the touch along said coordinate axis of said surface, said output signal having a second charactristic indicative of the touch-pressure-induced damping of said wave burst component propagating on said surface through the region of the touch.

32. For use with touch-controllable apparatus having a predetermined coordinate axis on a surface associated with said apparatus, comprising:
a substrate having a surface capable of propagating surface acoustic waves and being so characterized that a touch on said surface causes a perturbation of a surface wave propagating through the region of the touch, the magnitude of said perturbation being related to touch pressure;
surface acoustic wave scanning means including input surface wave transducer means coupled to said substrate surface for effecting scansion of said surface with a timed succession of surface acoustic wave bursts directed in a plurality of substantially parallel overlapping paths across said surface transversely to said coordinate axis, each of said plurality of paths being respectively associated with a different position along said coordinate axis on said substrate surface;
output surface wave transducer means coupled to said substrate surface for receiving said bursts of surface waves; and circuit means coupled to said input and output transducer means for initiating said timed succession of surface wave bursts on said substrate surface and for detecting touch-induced perturbations of received wave bursts;
said circuit means including means coupled to said output transducer means for developing an output signal having a first characteristic representative of the timing of a touch perturbed received burst and thus determinative of which of said plurality of paths was traversed by said touch-perturbed wave burst and thereby the location of the touch along said coordinate axis of said substrate surface;
said output signal having a second characteristic representative of the magnitude of the perturbation occasioned by the touch pressure-induced perturbation of the waves passing through the region of the touch.