Patent Publication Number: US-9836149-B2

Title: Method and apparatus for tomographic tough imaging and interactive system using same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority and benefit of previously filed Argentinean Patent Application No. 20070105651 filed on Dec. 17, 2007, in the name of Victor Manuel Suarez Rovere, which is here incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to a method and apparatus for tomographic touch imaging sensor and interactive system using same. More particularly, the invention relates to a method and apparatus for touch sensitive devices for computing systems or for controlling actions of associated devices or equipment, and still more particularly, to devices that detect and/or process simultaneously multiple touch interactions (by fingers or other objects) at distinct locations on a touch-sensitive surface. 
     Prior Related Art 
     Many types of input devices are presently available for performing operations in a computing system, such as buttons or keys, mice, trackballs, touch panels, joysticks, touch screens and the like. Touch screens, in particular, are becoming increasingly popular because of the ease and versatility of operation, as well as, their declining price. Touch screens can include a touch panel, which can be a clear panel with a touch-sensitive surface. The touch panel can be positioned in front of a display screen so that the touch-sensitive surface covers the viewable area of the display screen. Touch screens can allow a user to make selections and move a cursor by simply touching the display screen via a finger or stylus. In general, the touch screen can recognize the touch and position of the touch on the display screen, and the computing system can interpret the touch and thereafter perform an action based on the touch event. 
     One limitation of many conventional touch panel technologies is that they are only capable of reporting a single point or touch event, even when multiple objects simultaneously come into contact with the sensing surface. That is, they lack the ability to track multiple points of contact at the same time. Thus, even when two points are touched, these conventional devices can only identify a single location, which is typically the average between the two contacts (e.g. a conventional touchpad on a notebook computer provides such functionality). This single-point identification is a function of the way these devices provide a value representative of the touch point, which is generally by providing an average resistance or capacitance value. 
     Another limitation of most touch panels is that, besides being incapable of reporting a plurality of touch points that occurs simultaneously, is that they provide information about just touch coordinates. Most known touch panels cannot provide a complete representation of the details of all shapes contacting the panel, because the methods of detection often include just triangulation of touch points. Thus, a need exists for providing a better and fuller representation of touch interactions. The present invention proposes to provide a method and apparatus for achieving, for example, by providing a pixilated image representative of all the touch areas and theft shapes. This ability of providing a full representation of all touch interactions is sometimes called “true-touch”. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a principal object of my invention to provide a method and apparatus for tomographic touch imaging and interactive system using same, especially for computing systems but also usable to control actions of other devices, and still more particularly, to devices that detect and/or process simultaneously multiple touch interactions (by fingers or other objects) at distinct locations on a touch-sensitive surface. The foregoing is accomplished by combining a touch panel with a tomograph in a unique way, and by using this combination as a touch imaging sensor and/or as an interactive system in a computer system. 
     The present invention applies techniques from tomography field of science, but instead of using it for medical purposes, the tomographic techniques are used for making a computer input device. Specifically, the input device is a touch device capable of multi-touch operations, oriented to control the forthcoming new generation of software applications that propose a new paradigm for Human Computer Interaction. 
     Since tomography is used to determine inner information from the borders of a panel, and because invisible signals are used, it is possible to make a transparent touch panel with almost perfect light transmission properties. The transparent properties make the touch sensor useful to work with a display, as a touch screen. Other such input devices need to put complex elements on a panel that obstruct vision. As these other such input devices need to have at least some transparency, but not 100%, this requirement makes it difficult to manufacture, affecting costs. 
     The present invention can be implemented with a very clear and homogeneous material, like a simple sheet of acrylic. Also, because the panel can be very thin, a slim and small system including a flat display can be made, thus enabling the system to be portable. 
     Several objects and advantages of my invention are listed as follows. 
     a) To provide a device that is sensitive to touch and able to detect objects when they are making a subtle pressure. If the object touching is a finger of an user the invention can provide a tactile feedback. This is in contrast to proximity sensors which can be activated when the user isn&#39;t touching anything.
 
b) To provide a touch sensitive device that can provide a digital representation of nearly all areas where there is a touch interaction available. This is in contrast to devices that provide location information of just a few touch interactions simultaneously.
 
c) To provide a touch sensitive device that can be thin, thus having a large relative surface area with respect to volume.
 
d) To provide a touch sensitive device that can have a transparent touch panel so that it can include a display visible through the panel.
 
e) To provide a touch sensitive device that can be interactive by providing output information related to touch interactions.
 
f) To provide a thin touch sensitive device that can be flat, or non-planar (e.g. domed) in 3-dimensional space.
 
g) To provide, in some embodiments, a touch sensitive device that can detect a zero-pressure contact.
 
h) To provide, in some embodiments, a touch sensitive device that can discriminate regarding more than one level of pressure on possible different touch interactions that occurs simultaneously.
 
i) To provide, in some embodiments, a touch sensitive device that can be robust to some external unwanted interfering signals.
 
j) To provide, in some embodiments, a touch sensitive device that can have a transparent touch area of quite low absorption with respect to visible light, useful to make the power requirements of a possibly attached display less demanding.
 
k) To provide, in some embodiments, a touch sensitive device that can be constructed with elements relatively easy to manufacture.
 
     Further object and advantages of my invention will become apparent from the following detailed description of preferred embodiments of the invention when taken in conjunction with the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  show, respectively, a top view of the basic tomographic touch device of the present invention, and a cross sectional view taken along line A-A of  FIG. 1A . 
         FIG. 1C  shows selected imaginary or notional regions or areas of the touch panel shown in  FIGS. 1A and 1B  illustrating where touch interactions may occur or be estimated. 
         FIG. 2  shows an annular shape representing a particular “test” touch interaction made on a rectangular touch panel. 
         FIG. 3  shows components of a typical tomograph as used in the present invention. 
         FIG. 4A  shows one simple way of defining geometries for the tomography apparatus according to the invention. 
         FIG. 4B  shows a very useful way of defining geometries for the tomograph. 
         FIGS. 5A and 5B  show, respectively, a top plan view and a cross sectional view of a touch device taken along line BB of  FIG. 5A  that includes a display and a computer as part of an interactive system according to the present invention. 
         FIGS. 6A to 68  show, respectively, a top view of a similar touch device combined with an electrical impedance tomograph and a cross sectional view taken along line C-C of  FIG. 6A . 
         FIG. 7  shows an embodiment of the present invention that uses just an air gap to optically couple emitters and detectors to a panel, and the effect of signal reflection on a panel&#39;s edge. 
         FIG. 8  shows two typical emission patterns and its associated detectors, and the signal alteration level measured on each detector after passing through an annular phantom. 
         FIG. 9  illustrates a flowchart of the operation of an embodiment of the touch device as part of an interactive system. 
         FIG. 10A  illustrates a flow chart of the tomographic touch sensor operation. 
         FIG. 10B  illustrates a flow chart of the tomographic touch screen operation. 
         FIG. 11  illustrates a flow chart of the interactive system using a tomographic touch sensor, a data processing element, and an output device. 
         FIG. 12  illustrates a flow chart showing an example embodiment for the acquisition of a tomogram representative of touch interactions. 
         FIG. 13  illustrates a flow chart showing an example embodiment for the acquisition of an unreconstructed tomogram representative of touch interactions. 
         FIG. 14  illustrates a flow chart showing an example embodiment for the reconstructed tomogram calculation. 
         FIG. 15  illustrates a flow chart showing an example embodiment for the definition of parameters for tomogram acquisition. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
     Referring now to the drawings, and particularly to the embodiment of the present invention, a touch device is illustrated in  FIG. 1A  (top view) and  FIG. 1B  (cross sectional view). The touch device, as shown, consists of a thin, flat, circular panel  10  of light conductive material, such as a suitable plastic material known for this purpose. The panel  10 , due to its properties is adapted to conduct signals, introduced into the borders of the panel, through the panel. The panel can be opaque or transparent and can be rigid or flexible. The panel can also be resilient and/or compressible. The signals may be any radiation or wave energy that can pass through the panel from border to border or edge to edge including without limitation, light waves in the visible or infra-red or ultraviolet regions of the spectrum, electrical energy, electromagnetic or magnetic energy, or sonic and ultrasonic energy or vibration energy. In the following description, light passing through the panel will be described as a preferred embodiment. The light signals  20  are introduced through the edge or border  22  of the panel  10 , as shown in  FIG. 1B . The shape of the panel  10  is not limited to any particular shape and may be irregular or regular, such as, circular, elliptical, square, rectangular or polygonal. The panel has a refraction index greater than air so it can act as a waveguide by the effect of TIR (Total Internal Reflection). Touch interactions at discrete locations on the panel surface  12  can interfere with, disrupt or frustrate the TIR effect so that a portion of the signal (light) is lost by escaping the waveguide of the panel. This is indicated in  FIG. 1B  by the reference numeral  14  showing the light exiting form the panel, i.e. light loss. Thus, the light conductive properties of the panel are altered in those places where the touch interactions occurs, as indicated by reference numeral  16  in  FIG. 1A . 
     Surrounding the conductive panel  10 , there is an optical tomograph  30 . In the context of the present invention, “tomograph” means, as usually defined, a device that can image from the borders. The tomograph is controlled to emit light signals  20  by light emitters  34 , through signal flow ports, which also detects light signals by detectors  32 . 
     The term “signal flow port” refers to both emitters and receivers (detectors), and the signal flow port physically acts either as emitter or receiver. For example, an electrode in the electrical part of the embodiment can be a unique device that could serve both purposes emitter and/or receiver. Also an optoelectronic device like a LED can be used as a detector, although with less performance. So a signal flow port here isn&#39;t anything material and thus, isn&#39;t either an element that can house an emitter or detector. In the context of this invention, a signal flow port is a term used to refer interchangeably to an emitter, or to a detector, or to a device that may accomplish both roles. Thus, the port houses an emitter and/or detector and may be virtual or real. 
     The signal flow ports (emitters and detectors) are positioned at the edge  22  of the panel  10 . The light signals  20  introduced into the panel  10  by emitters  34  at their associated signal flow ports penetrate or pass through the panel  10 , in the manner described, and are detected by detectors  32  at theft associated signal flow ports after circulating or passing through the panel  10 . The tomograph  30  generates a tomogram representative of the panel conductivity, which is a two dimensional representation of the calculated or estimated conductivity on many imaginary or notional regions  40  defined on the panel surface  12 , as shown by the array on  FIG. 1C  (top view). The resulting tomogram is thus a calculation or an estimative representation of the touch interactions, including its shapes and details. The tomogram may be calculated to represent the conductivity change produced by touch interactions, by comparing it with the conductive properties of the panel when no touch interactions occur. The resulting tomogram can be provided as digital information aimed to control or operate a digital device. The digital device may include an output device, such as a display, and a processing element to transform the tomogram and provide output to a user as feedback of touch interactions, thus forming an interactive device. 
     An exemplary shape  50  of an interesting and quite challenging touch interaction is shown on  FIG. 2  (top view). Shown is an annular shape that could be an approximation of the contact area produced by the palm of a hand touching a rectangular touch panel. As will be appreciated, the resulting tomograph can represent any complex figure or shape depending on the touching interactions. As a parallelism with medical X-ray tomography, the annular shape shown could be an approximation of the cross section of a hollow bone. It will be appreciated that CT or computerized tomography is a well known technology and is understood by those of ordinary skill in the art. 
     The tomograph  30  of the touch device as illustrated on  FIG. 3  may typically comprise a set of signal flow ports  18 . Each signal port may be an emitter and/or a detector for the signals, where the signal flows through the port. An emitter  34  is typically an electronic device, for example an R LED (Infrared Light Emitting Diode) or other light emitting device. A detector  32  is typically an electronic device, such as a phototransistor, photodiode, Charge Coupled Device (CCD) and other like devices. The signal flow ports are typically located around the periphery or perimeter (edges  22 ) of the conductive panel  10  and spaced apart, usually at regular intervals. The emitters  34  are optically coupled to the panel, in a way that at least a portion of the emitted signal penetrates the conductive panel  10  and circulates or passes through by effect of TIR. The detectors  32  are optically coupled to the panel  10  in a way that each detector  32  receives the emission signals  20  emanating from one or more of the emitters  34  via signal flow ports  18 . The ports may be coupled to the conductive panel by via a coupling object that may be optical glue, or just direct contact, or a waveguide like an optical fiber, a diffuser or just an air gap, or by any other known means provided the light from the emitters  34  is introduced properly into the panel  10  and the light is detected by the detectors  32 . Although by using an air gap  92 , see  FIG. 7 , total reflections could occur on the border of a polished panel, before reaching a detector close to the point of reflection, as shown in  FIG. 7 , anyways the reflected signal may approach another detector, thus tomographic reconstruction still could be accomplished. 
     The tomograph  30  also includes an emission pattern controller  60  operatively coupled to each emitter  34 , for example, using any conventional set of communication channels  62 , shown in  FIG. 3  as wires. The tomograph  30  further includes a signal sampler  64  operatively coupled to each detector  34 . Also the tomograph  30  includes a data processor  66  operatively coupled to the pattern controller  60 , and to the signal sampler  64 . 
     The emission pattern controller  60  can energize, upon requirement or according to any predetermined program, any desired combination or set of said emitters  34 . Each emitter  34  can be energized at any desired emission level of at least two possible values. The configuration of a set of emitters and its levels defines an emission pattern. A representative emission pattern, according to the invention, can be to have one determinate or preselected emitter  34  active while leaving the rest inactive, and then serially process through the emitters  34 , one at a time. 
     The signal sampler  64  can measure, upon requirement or according to any predetermined program, the signal level received on each detector  32 . A representative signal sampler  64 , according to the invention, can have one or more Analog to Digital Converters (ADC) and also may have one or more analog and/or digital multiplexers. 
     The data processor  66  can be incorporated in any known computer system, and is adapted to command the emission pattern controller  60  to energize the emitters  34  using a desired sequence of patterns. Also the emission pattern controller  60  and/or signal sampler  64  may function based on a determinate or preselected program, without being commanded by the data processor, for example a digital logic circuit. 
     By operating the emission pattern controller  60  and the signal sampler  64 , an unreconstructed tomograph can be acquired. 
     To operate emission controller  60 , a set of emission patterns has to be defined, for example, a sequence of patterns may be to activate, in turn or serially, different emitters  34 . Each emission pattern is active at different times, forming a sequence. While each emission pattern is in effect, an associated set of detectors  32  have to be defined to measure the effects of the active emissions. Then, the data processor  66  acquires from the signal sampler  64 , the measured values from the associated set of detectors  32 , the set being typically all or a substantial subset of the detector  32 . The measured values form part of the unreconstructed tomogram. Thus after applying all emission patterns and obtaining measurements from the detectors, the unreconstructed tomogram is obtained. An example of two emission patterns, its associated detectors, and a representation of the signal alterations, shown in graph of  FIG. 8 , received for the annular phantom, is shown also in  FIG. 4B . 
     The data processor  66  may be a microcontroller, microprocessor, FPGA, ASIC or special purpose electronic circuit or even part of a complete computer system. Although it may be desirable for the data processor  66  to include a data memory containing a computer program, it is possible to practice the invention performing most computations with just a digital logic circuit. For example, a tomographic reconstruction calculation, as known in the art, can be executed just with an integrated circuit. That integrated circuit can lack a specific “memory”, because computation can be hardwired. The invention contemplates a model using a programmable logic circuit (FPGA) that has a memory, but without any “computer program” as such stored in the memory. 
     In a typical embodiment, the data processor  66  commands the emission pattern controller  60  to activate one determinate emitter  34 , then, acquires measurements from all detectors  32 , then, repeating these steps serially for the rest of the emitters  34 , one by one. Thus, if the number of emitters  34  is N e  and the number of detector ports is N d , a vector of N e  by N d  elements is acquired. One can call this vector the projection vector, or one can call it a measurements vector, or just “b”. This acquired vector, not to be confused with a matrix, is sometimes called in the context of Computer Tomography (CT) the “unreconstructed tomogram” or sometimes “sinogram”. 
     Having the unreconstructed tomogram with N e  by N d  potentially independent values, the amount of available information to make reconstruction can be thus in quadratic relation with respect to number of signal flow ports. So the number of potentially independently recognized touch interactions regions can be in accordance to that quadratic relation, and not in linear relation with respect to number of emitters  34  or detectors  32 . Thus, that number of potentially discriminated regions can be quite large or big. Hence, the foregoing is a sample of the potential of the present invention of being able to discriminate not just a few simultaneous touch coordinates, but many. 
     Having the unreconstructed tomogram, a reconstructed tomogram can be calculated by the use of a Tomographic Reconstruction algorithm. The reconstructed tomogram, or just tomogram, is the representation of the features of the tomographed “phantoms”, a phantom being a particular “test” or “active” touch interaction. 
     In a tomographic reconstruction algorithm, a linear or nonlinear model of the tomographic system may be used to transform the unreconstructed tomogram. If a linear model is chosen, the system may be modeled by matrix equations and solved by linear matrix operations in a known manner. 
     A typical equation used to model tomographic systems is Ax=b, where A corresponds to the “system matrix”, as is sometimes called, x corresponds to the reconstructed tomogram and is a vector that represents the regions conductivity values, not to be confused with a matrix just because regions are usually a grid. The variable b is the unreconstructed tomogram, a vector containing the measured projection values reaching the detectors  32  for each emission pattern. The system matrix, in the context of CT, represents the transformation that the typical linear tomograph system accomplishes to generate the projection data. A typical linear tomograph thus works by transforming b into x taking into account matrix A as a transformation operator. 
     To be able to calculate a two-dimensional tomogram adequately, one needs to have defined appropriate locations to each emitter  34  and detector  32 , which are typically surrounding the panel  10  on its edge(s). Also, one needs to define imaginary or notional locations and shapes of a set or array of regions  40  on the surface  22  of the panel  10 , where an estimation of conductivity is going to be calculated. The regions  40  are sometimes called “reconstruction regions”. In a typical embodiment, the regions  40  are rectangular and are disposed next to each other in an appropriate imaginary or notional grid of pixels. 
     Also, to be able to calculate an adequate tomogram, the regions have to be geometrically defined in a way that each region is affected by more than two non-parallel line integrals; each line integral being defined as the path of an actually measured signal between a determined pair of emitter  34  and detector  32 . This is to accomplish, for each region, adequate “angle density” as is usually called. In a diffusion tomograph the concept of line integrals may be geometrically not similar to a line, but to a sort of “field” as shown on  FIG. 6A . 
     A determinate signal corresponding to a line integral may be altered in more than one point of its path without being substantially obstructed by a single touch, as depicted in  FIG. 1B . That physical property of the panel with respect to conduction of signals is an important factor determining ability of permitting adequate tomographic reconstruction. For example if the touch interaction substantially would obstruct the signal, and another touch in other part of the signal path wouldn&#39;t further alter the signal, the annular phantom as shown on  FIG. 2  would be easily confused, by that hypothetic system, with a filled circle, because that system would be unable to adequately estimate the interior properties of the phantom. That property of possible successive alterations of the signal along a line integral, configures an “integral function” as sometimes is called. Also, to be able to adequately measure the possible effects of touches over an emitted signal, measurements by the use of analog to digital conversion techniques are important. 
     Those skilled in the art will understand that the requirements of high angle density for each region and existence of an integral function to do tomographic reconstruction has support in the Projection Slice Theorem, which is related to the Radon Transform. Basically, the projection-slice theorem tells us that if one had an infinite number of one-dimensional projections of an object taken at an infinite number of angles, one could perfectly reconstruct the original object, f(x,y). Note the need of multiple angles (as much as possible in a non-theoretical device) and the need of “projection” (ie. integration data) along the line. However, the present invention is not limited by this theorem. 
     It&#39;s well known that a finger interacting with a waveguide like in the presented embodiments makes better and broader optical contact as more pressure is applied. This effect is because, together with other causes, the skin on the fingerprints gets more deformed, so the average contact area per unit area and thus, average conductivity gets altered in a higher level. This higher change of conductivity could be interpreted as more pressure and used to take distinctive actions. For example an icon of a user interface can be selected with a light pressure but activated with more pressure. 
     Also, as in any measurement instrument, repeated measurements over time can be done to have a time-varying measurement, so taking a series of tomographs over time is useful to determine how touch interactions changes over time, and that information may be used to detect touch events or gestures, with algorithms well known in the art. 
     Another embodiment of the touch device, as illustrated in  FIGS. 5A and 5B  (top plan and cross sectional view, respectively) may include a display  70  beneath the touch panel  10  preferably transparent, to form a touch screen. The touch panel  10  is bent at its edges and the signal flow ports incorporating the emitters  34  and the detectors  32  are arrayed around the bent down perimeter of the device. Light rays  20  pass through the touch screen as described. The touch screen may make available the information related to touch interactions generated by the tomograph, to be interpreted by a digital system, and then the digital system may control the display to show information related to the touch interactions, to be seen through the clear panel. The panel  10  could be convexly curved, and that curved panel could serve to house the display  70  and also to permit the ports to be easily put or mounted on a substrate like a printed circuit board (PCB). 
     Another embodiment of the touch device, as illustrated on  FIG. 5B , may include the output device  70  operatively coupled to the data processor  66  or to an alternative data processor to form an interactive system. The interactive system transforms the tomogram information representative of touch interactions produced by a user, into information to be represented in the output device  70  as feedback to touch interactions. Touch user interactions in the interactive system may be used to modify the state of the software running in the processor, and when the software reflects its modified state in an output device, such as a display, the user receives feedback related to the touch interactions. The typical embodiment of the interactive system may be a cell phone including the touch sensitive area and displaying the images on its user interface. 
     The transformation of the information representative of touch interactions into information for the output device may be of the type commonly used in Graphical User Interfaces (GUI). For example, the transformation could be to show an icon on the display with an alternative color when a touch interaction event is detected on an area inside the icon, so a user can have the sensation of touching the icon. 
     The output device  70  may typically be a display such as a Liquid Crystal Display (LCD). A device with a display behind a transparent panel to form an interactive system is one of the main objectives of the invention. However, the touch sensor could be used without a display, for example, just to generate sounds. 
     The tomograph representative of regions where touch interactions occur may be like a pixilated image representing the conductivity on each region, but an event based GUI may be designed to just accept coordinates of touch interactions or more complex gestures instead of level of activity on determinate regions. So an algorithm to translate activity on each region to coordinates of touch interactions or gestures is useful and contemplated by the invention. The algorithm for determination of touch events often called “Blob Detection and Tracking” and is well known in the art. It is used by some systems that calculate and track touch locations by first using computer vision over an image of the touch regions, and using the image captured with a video camera. 
     In another embodiment of the touch device according to  FIG. 6A  (top view) a conductive panel  80  may be rendered electrically conductive using the signal flow ports, which can be simple electrodes  82 , and the signals  84  may be electric currents. The electrically conductive panel  80  may be of a material as shown in U.S. Pat. No. 4,448,837, which is conductive and transparent. Another way to implement the electrically conductive panel  80  is by depositing a thin film of transparent conductive material over a non-conductive transparent substrate, so the touch of a finger makes some part of the currents normally circulating on the panel, to circulate through the skin thus lowering the resistance on the contact points. A display is mounted beneath the touch screen as previously described. 
     In another embodiment of the touch device the panel may be of a material acting as a dielectric, and the tomograph may be a Capacitance Tomograph, where the touch of a finger or other object can after the dielectric properties of the panel. 
     In another embodiment of the touch device the panel may be of a material acting as a vibration conducting medium, and the tomograph may have acoustic or piezoelectric transducers as ports, in a similar way as an ultrasonic tomograph for pregnancy is implemented. The acoustic impedance of the panel can be altered by the touch of a finger or other object. 
     Operation 
     The operation of the touch screen device included in an embodiment of an interactive device (the method of the invention) is shown in the flow chart of  FIG. 9  and is described as follows. 
     Steps S 1  to S 7  carried out as described in the blocks of  FIG. 9  define and calculate parameters for posterior tomograph acquisition and reconstruction. These parameters can be calculated during the interactive operation of the system or device, or optionally the information can be calculated and stored in memory for later recall. 
     Steps S 8  to S 22  carried out as described in the blocks of  FIG. 9  are a group of steps that repeats indefinitely while a user is interacting with the interactive device. Steps S 9  to S 14  obtain an unreconstructed tomogram; steps S 15  to S 17  calculate a reconstructed tomogram representative of detected or sensed touch interactions. This is carried out by a suitable algorithm as detailed in the blocks of  FIG. 9  for achieving tomographic reconstruction, but other well known algorithms for tomographic reconstruction can be used. Some of these algorithms are well explained in the book “Principles of Computerized Tomographic Imaging” by Kak and Slaney, available on the web, see http://www.slaney.org/pct/pct-toc.html. 
     Step S 18  to S 22  are carried out as described in the blocks in  FIG. 9  for processing touch information to control an application and provide feedback to the user. 
     Step S 1  is for defining positions and shapes of the imaginary or notional reconstruction regions over the sensitive surface. The regions forms typically a pixilated grid but each region can have its own shape, that can be polygonal, or inclusive defining a surface of more than one disjoint shape. 
     Step S 2  is for defining the set of emission and detector ports to be involved in unreconstructed tomogram acquisition, and also for selecting its positions. The port positions may be typically the surroundings of the sensitive panel, for example alternating an emitter with a detector at regular intervals. Also, the positions may be near just some portions of the panel&#39;s surroundings, for example on just a subset of edges of a polygonal panel. Where there are not ports, the panel may have reflective materials so signals can bounce there (be reflected) and reach other ports. 
       FIG. 4A  (top view) is a quite unuseful way of define regions  40  and port  18  locations. If all emitter  34  ports  18  are disposed just on the left of a square panel  10 , all detector  32  ports  16  disposed just on the right, measurements done along just horizontal paths, and reconstruction regions  40  are all vertical rectangles that span from top to bottom, the two dimensional reconstruction that could be done would not produce very interesting results. This example shows that some awkward ways of defining geometries lead to difficulties on tomographic reconstruction. Anyways, the most intuitive and easily defined geometries lead to good results. For example, as shown in  FIG. 4B  simply disposing alternating emitter and detector ports around the panel, measuring from a substantial subset of the possible emitter-detector pairs, and selecting a pixilated grid for the reconstruction regions in an amount in quadratic relation with number of emitters and detectors, good results can be achieved. 
     Step S 3  is for defining a sequence of emission patterns, where the sequence typically contains a linear independent set of emission patterns, for example, the activation in sequence of just one emitter. Another set of patterns may include patterns interpreted as a matrix that has a substantially high rank so different emission patterns can be discriminated. Matrix rank is well known to those of ordinary skill in the art. Another example of patterns can be Code Sequences as normally used for COMA, a well known technique for multiplexing. The objective is to permit multiplexing and adequate discrimination of the different patterns. 
     Step S 4  is for defining for each emission pattern a set of associated detector ports. Once an emission pattern is active, the signal reaches a set of detector ports and some of them are selected for measurement. The set of ports associated with an emission pattern may be selected taking into account the level of the signal normally received. 
     Step S 5  is for taking a reference unreconstructed tomogram that will be used as reference to calculate the differences on conductivity when any touch is occurring. The panel has default conductivity when no touch is affecting its conductivity, and the measurements are for determining the changes produced by touch interactions. 
     Step S 6  is for calculating the system matrix A, assuming a linear model of the tomographic system. A possible way of calculating the system matrix to be further used to calculate the tomogram may be by making X an identity matrix, on equation AX=B, being B a matrix of measurements, a set of unreconstructed tomogram acquisition. So if X is the identity, thus A=B, thus the way of calculating A may be to touch in sequence each reconstruction region with corresponding shape and “unit pressure”, and measuring in each touch step the projection, so to construct B, and thus this set of measurement results in the system matrix A. This procedure, as explained above, will be readily evident to a person of ordinary skill in the art. 
     Step S 7  is for calculating its pseudoinverse A′ by using a Truncated Singular Value Decomposition (TSVD) algorithm. A typical algorithm for pseudoinverse calculation is provided by the function pinv of the MATLAB software from MathWorks. The parameter that controls the truncation may be used to adjust the results provided by the reconstruction algorithm, for example to make a better estimation of the conductivity values by reducing resulting reconstruction noise by the use of that truncation parameter. A way of estimating the truncation parameter may be to simulate the system with respect to its noise performance, and optimizing the parameter trying to minimize the noise figure. 
     The definition of parameters for tomographic reconstruction, that includes the definition of regions, position of ports, and sequence of emission patterns with its associated detectors, needs to be selected in a way to permit adequate reconstruction. A way of evaluating suitability of parameters, is by calculating the associated system matrix A, assuming a linear model of the tomographic problem, and then evaluating characteristics of the matrix A. For example, a criterion could be to evaluate if the matrix rank is close to number of defined regions, and with a condition number that characterizes a “well-conditioned” problem. If after evaluating suitability of tomographic parameters, they don&#39;t meet the defined criteria, the parameters can be redefined until the criteria are met. For example, less and bigger regions may be defined. Conditions number, rank, and matrix conditioning are concepts well understood to those skilled in the art. 
     Step S 8  represents the actions of a user that perform control operations through one or more touch interactions that can occur simultaneously over the sensitive surface. 
     Step S 9  is for initializing a vector b for holding the posterior acquired unreconstructed tomograph. 
     Step S 10  is for energizing emitter ports by configuring the pattern controller with an emission pattern. In each step of the loop, each emission pattern is selected, in sequence, from the set of defined emission patterns and applied. 
     Step S 11  is for measuring the signal levels reaching the set of detector ports associated with the active emission pattern. To measure signal levels having some rejection to possible interfering signals, for example external light on the optical embodiment, a double reading can be done. For example, the signal levels reaching detectors with all emitters off can be subtracted from the value measured when emission pattern is active. 
     An embodiment can discard some of the acquired values with a criterion, or just not measure the value. For example, emitting from a determinate emitter and measuring from a detector in close proximity, may be of little use. Other criteria to discard measurements may include discarding emitter-detector combinations that involves a weak signal between them, because, for example, their relative angle of incidence. Most emitters and receivers respond weakly to signals at high angles with respect to the perpendicular. Also, the measured values can be weighted by associating weighting factors with each measured value, being that operation useful to reduce overall reconstruction noise. 
     Step S 12  is for subtracting to this value, the corresponding reference values taken from vector b 0 . So when no touch is active, the resulting value will be zero plus the possible measurement noise. And in Step  13 , the obtained values are appended to the vector b. As shown on Step S 14 , the steps from S 10  to S 13  are repeated until unreconstructed tomograph is completely acquired. 
     Step S 15  is for preprocessing the unreconstructed tomogram, for example to linearize it by applying for example a nonlinear operation, in a similar way that most X-ray tomography devices first apply a logarithm to linearize the cumulative effect of successive attenuations that tissue imposes to X-rays. Step S 16  is for calculating the reconstructed tomograph x by solving the equation x=A′ b, where A′ is the pseudoinverse of system matrix and b is the unreconstructed tomograph. Step S 17  is for post processing the reconstructed tomogram, for example with a noise gate that assign zero to values that are below some threshold. The threshold can be set just above normal peak noise values. 
     Step S 18  is for recognizing touch interactions taking into account the reconstructed tomogram and generate touch events. To recognize events, a set of previously acquired tomograms may be also used. Algorithms of recognition of touch events and gestures are well known in the art and are sometimes called “blob tracking and detection”, and may be based on algorithms such as the Watershed algorithm. The kind of events recognized can be a new touch appearing, a touch disappearing, an existing touch moving, or other gestures. A gesture can be a “pinch” gesture that is produced by touching the panel in two locations, and separating apart the fingers. That pinch gesture can be used for example to control the zoom factor in a map application. A touch event can be associated with a coordinate that can have more resolution than the provided by the reconstructed tomogram. A set of values around an area where the touch is occurring, can be processed to obtain a sub-pixel coordinate. For example, having a 3×3 pixels area, the coordinate of each pixel center on that area can be averaged by weighting its coordinate with the value associated with each pixel, obtaining a coordinate similar to each pixel but with sub-pixel resolution. 
     Alternatively, another embodiment of the touch device operations may skip touch the events detection and generation, transforming the reconstructed tomogram by DSP algorithms or other methods to control the output device. For example the output device may be a sound generation device. The application to be controller may be a synthesizer, using touch interactions to after synthesizer parameters. As an example, interactions on the horizontal axis may be mapped to pitch and interactions on the vertical axis, to harmonics levels, thus forming a multi spectral instrument. 
     Step S 19  is for modifying the state of a user interface program in response to the touch events. For example if the user interface has a model of a virtual button, that button state becomes active if a touch interaction is detected on the area within the virtual button perimeter. 
     Step S 20  is for generating the output information representative of the altered state of the UI program. For example, in the virtual button case, the output information is one that maps to different colors according to the button activation state. 
     Step S 21  is for showing output information on the display adapted to that information through a transparent implementation of the touch sensitive panel. 
     Finally, the output of Step  21  is passed to Step  22 , which is the user interface receiving feedback of the touch control operations. The user sees the results on the display. Further interactions from the user can be processed by repeating steps from S 8  to S 22 . 
       FIG. 10A  illustrates a flowchart of tomographic touch sensor operation. In step  100 A a tomogram representative of touch interactions over the sensitive surface of the panel is acquired from a tomograph, using as an example the embodiment in  FIG. 12 . In step  100 B the tomogram output of step  100 A is made accessible as digital information used to control a digital device as a result of the touch interactions. 
       FIG. 10B  illustrates a flow chart of tomographic touch screen operation in which step  105 A acquires, when needed, a tomogram representative of touch interactions over the sensitive surface from a tomograph and provide it to a computer using possible embodiment in  FIG. 12 , and in step  105 B access, when needed, image information generated by the computer, and display result, to be seen through the sensitive surface as feedback of touch interactions. 
       FIG. 11  is a flow chart of an Interactive system using a tomographic touch sensor, a data processing element, and an output device. In step  110 A a data processor accesses the tomogram representative of touch interactions produced by a user over the sensitive surface. In step  110 B the tomogram is processed with DSP algorithms. In step  110 C a decision is taken whether it is an events-based interactive system? If YES, the program advances to step  110 D where touch interactions from the tomogram are recognized and touch events are generated. In step  110 F, the touch events in step  100 D are received and a user-interface software program running in the data processor modifies is state in response to the touch events. If NO, the program advances to step  110 E where a user-interface software program running in the data processor transforms the tomogram and modifies its state. The output of steps  110 E and  100 F feed to step  110 G where the user interface software provides information representative of its modified state to the output device as feedback of the touch interactions. 
       FIG. 12  is a flow chart showing an example embodiment for the acquisition of a tomogram representative of touch interactions. In step  120 A, parameters are defined for tomogram acquisition, including emission pattern sequence, set of detector ports associated with each emission pattern, and amount, position and shape of each reconstruction region, using possible embodiment in  FIG. 15 . In step  120 B an unreconstructed tomogram representative of the touch interactions over the sensitive surface is acquired by estimating and measuring the ports around the sensitive surface, using possible embodiment in  FIG. 13 . In step  120 C the reconstructed tomogram is calculated by transforming the unreconstructed tomogram with a tomographic reconstruction algorithm, using possible embodiment in  FIG. 14 . 
       FIG. 13  is a flow chart illustrating an example embodiment for the acquisition of an unreconstructed tomogram representative of touch interactions. In step  130 A configure a pattern controller with an emission pattern selected in turns from the set of defined emission patterns to energize emitter ports. In step  130 B access through a signal sampler, to the measurement values from the set of detector ports associated with the selected emission pattern. In step  130 C append the measurement values to the partially acquired unreconstructed tomogram. The output is put to a decision in step  130 D regarding is any pattern of the set of defined emission patterns not yet applied to have complete the unreconstructed tomogram acquisition? If YES, then the program jumps or loops back to step  130 A; if NO, the program outputs. 
       FIG. 14  illustrates a flowchart for an example embodiment for the reconstructed tomogram calculation. In step  140 A the system provides matrix A, obtains its pseudoinverse A′ by truncated SVD. In step  140 B the unreconstructed tomogram is optionally preprocessed. In step  140 C x=A′b is calculated, where x is the reconstructed tomogram and b is the unreconstructed tomogram. In step  140 D the unreconstructed tomogram is optionally post-processed. 
       FIG. 15  illustrates a flowchart of an example embodiment for the definition of parameters for tomogram acquisition. In step  150 A the amount, positions, and shapes of imaginary or notional reconstruction regions on the sensitive surface are defined. In step  150 B amount of emission ports to be involved in unreconstructed tomogram acquisition is defined, and positions selected. In step  150 C a linearly independent set of emission patterns is defined. In step  150 D amount of detector ports to be involved in unreconstructed tomogram acquisition is defined, and positions selected. In step  150 E for each emission pattern a set of associated detector ports is defined. In step  150 F the system matrix A is calculated assuming a linear model of the tomographic system. The output of step  150 F is passed to a decision in step  150 G, namely, is the rank and condition number of the system matrix A enough to allow an adequate posterior reconstruction? If the answer is YES, the signal is output; if the answer is NO, the signal is looped back to step  150 A. 
     The best mode contemplated for practicing the present invention, as of the filing of this application, is an interactive system with the optical FTIR-based embodiment. This embodiment permits the use of a panel with almost perfect light transmission properties, the detection of touch interactions with zero-pressure and also with above-zero pressure, and the use of a very low-cost panel, and other manufacturing advantages, like ease of mounting. This embodiment is detailed as follows. 
     A conventional LCD display is used as an output device. On top of the display, there&#39;s a clear panel made of a sheet of acrylic of less than a few millimeters thick, where infrared light passes from the borders. The objective is to make the screen visible through the panel. The panel is in mechanic contact with the screen by using two-sided tape put on the borders of the screen top, out of its active visible area. To prevent the display making unwanted TIR effect frustration on the panel&#39;s bottom surface, the tape is reflective or mirror-like. The tape is thick so if mechanic deformation occurs when pressure is applied with the fingers, the panel doesn&#39;t touch the screen. The panel shape is similar to a rectangle, but octagonal with short diagonal corners similar to the panel shown on  FIG. 5A . The panel borders are unpolished so to prevent total reflections on the borders and also to provide some diffusion when light enters or exits the panel&#39;s border. 
     Surrounding all panel perimeter, there are infrared LEDs used as emitters and photo transistors used as detectors, touching the panel&#39; borders, so infrared light can enter and exit from the panel. The LED and photo transistors are alternating, each emitter between two detectors and vice versa. The emitters and detectors are spaced apart at regular intervals on each panel edge, separated by about one millimeter. The emitters and detectors are soldered on different Printed Circuit Boards, one for each panel edge. 
     The emitters are connected to a circuit that works similar to a LED Matrix controller that permits to activate any LED. The possible activation levels for each LED are two: no current or the maximum current allowed for the emitters. Taking into account each LED is active just a short period of time, more than the nominal continuum rate of emission is possible, like in conventional LED Matrices. 
     The photo transistor detectors have infrared filters matching the emission spectrum of emitters. Each phototransistor makes its current flow through a resistance to convert the current in voltage. The detectors are grouped in groups of eight elements, and each group connected to an 8-to-1 analog multiplexer. 
     Each analog multiplexer is associated with a 14-bit Analog to Digital Converter, and each digital output of the ADCs are connected to a digital multiplexer, so each ADC conversion value can be addressed. The digital multiplexer is a bus-based one, so each non-selected ADC is in high impedance state while the addressed one ADO is in low impedance with respect to the bus. 
     The LED matrix controller and the digital multiplexer are connected to a FPGA that controls them and is able to execute a Tomographic Reconstruction Algorithm. 
     The FPGA is connected to a CPU adapted to be able to run an application with a User Interface. The CPU is also connected to the display. 
     On the panel&#39;s top surface a pixilated matrix is defined. The total area matches the screen&#39;s visible area. The pixels are square with a side size matching emitter and detectors separations. A vector representing an unreconstructed tomogram is acquired by energizing in turn each emitter, and while each emitter is active, taking a measurement from all detectors. To optimize acquisition time, all ADC are commanded in parallel to take the measurement using a selected multiplexer channel, repeating this for the eight acquisition channels. The measurements are sent to the FPGA through the bus. 
     Each time an emitter is energized and measurements are taken, another set of measurements is taken but with all emitters deactivated. This measurement is to read ambient light interference level to be subtracted from the measurement with the emission pattern active. That measurement is taken many times because ambient light can be varying, for example most light bulbs oscillates at 120 Hz. To estimate the interference level at the time of measurement with the emitter active, an average with previous and past interference measurement is calculated. This takes into account the fact that photo transistors are not as fast as other optoelectronic devices like PIN photo diodes, so before measurement a delay is inserted to account for phototransistor time response. 
     With the tomogram acquisition as described, a base measurement representative of the tomogram acquired when no touch interactions occurs, is taken at factory and stored with the device on a provided memory. That base measurement is called b 0 . This measurement is taken in every touch device produced, to account possible variations on each specific device properties. For example, not all LED in a batch produces the same level of light emission for same conditions. So this measurement accounts for that possible variation. 
     A linear model of the tomographic system is assumed. The system matrix A is also calculated at factory by methods used to achieve Algebraic Reconstruction Methods. Each column of matrix A is the unreconstructed tomogram taken when a determinate “unity” touch interaction is in effect. This unreconstructed tomogram is the change with respect to the base tomogram b 0 . The “unity” touch interaction is an interaction in a determinate region with a shape and position in accordance with that region. Columns of matrix A are representing each reconstruction region. Each “unity” touch interaction can be made by actually touching the panel with a mechanic arm, or by simulating the effect. Those skilled in the art will know to simulate the effect but a method is proposed anyways. Since the rows of system matrix A represents a determinate pair of emitter-detector, for each emitter-detector pair, the row represents all regions associated with that pair. The regions correspond to a pixilated grid and each region has an associated coefficient, so it can be viewed like a 2D grayscale image canvas. To calculate each coefficient, an anti aliased “white” line is drawn between the emitter and detector on a “black” background, taking into account emitter and detector coordinates. White corresponds to value 1 and black to 0. The “gray” level of each canvas pixel is then associated with the row coefficient. Then each row coefficient is multiplied with the value of the corresponding pair from base tomogram b 0 , to account for actual signal levels involved on the specific device implementation. A rectangular system matrix A is used with more columns that rows, so more measurements are taken than the amount of regions. More measurements than regions are useful to have more precision on tomographic reconstruction. It should be noted that on all steps for tomographic reconstruction, information associated with some pairs of emitter-detector are not taken into account. Some are discarded according to the following criteria: if the dot product of corresponding row on A matrix is below a threshold. The threshold is selected in a way that the rank of A matrix isn&#39;t much below region count. 
     Having the system matrix A, a pseudoinverse A′ is calculated by the Truncated SVD method, by using MATLAB&#39;S pinv function. The tolerance parameter is calculated as follows. A value, say 1, is selected. Then by computer simulation, the reconstruction noise for a set of simulated touch interactions is calculated. Based on the noise properties of simulation results for each region, the value is lowered or incremented, so an optimization algorithm is run. The objective is to have noise lowered and if possible equally distributed for all the regions. A practical value is sometimes around 0.4. The pseudoinverse A′ is also stored on device for later recall. 
     Once all parameters for tomographic reconstruction are calculated, the device enters an interactive loop that runs continuously. 
     A tomogram b is acquired as described, with the base tomogram b 0  subtracted, so if no touch interactions are occurring, the b vector contains zeros or just normal noise values. A reconstructed tomogram x is calculated by solving the equation x=A′ b on the FPGA, by techniques well know to those skilled in the art. The reconstructed tomogram, as represented by vector x, is interpreted as an image representing touch interactions, with each pixel corresponding to each reconstruction region. 
     The tomogram x is transmitted to the CPU, where it is post processed by a noise gate, thus making zero the values below some threshold. The threshold is by default fixed just above normal reconstruction noise. The default threshold value is also calculated at factory but a noise control knob is provided to the user that can run configuration software. 
     On the CPU, a set of current and previous tomograms are analyzed to find touch events and gestures. The software used analyzes the events by executing a Blob Detection and Tracking algorithm. The algorithm can be selected by the user with a configuration application, where adapted versions of the software TOUCHLIB, http://www.nuigroup.com/touchlib/ and OPENTOUCH, http://code.google.com/p/opentouch/ are offered as options. 
     After events or gestures are recognized, they are sent by TUIO protocol to applications adapted to work with that protocol. An example application is a GPS mapping application. 
     The application running on the CPU generates visual information as feedback that is sent to the display to be seen through the panel by the user, thus being that visual response feedback of the control operations introduced by touching the touch device of the present invention. 
     Although the present invention has been described regarding several illustrative embodiments, numerous variations and modifications will be apparent to those skilled in the art that do not depart from the teachings herein. Such variations and modifications are deemed to fall within the purview of the appended claims.