Patent Publication Number: US-10318083-B1

Title: Touch screen display with tactile feedback using transparent actuator assemblies

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The instant application is a continuation of U.S. application Ser. No. 13/293,686, filed Nov. 10, 2011, entitled “TOUCH SCREEN DISPLAY WITH TACTILE FEEDBACK USING TRANSPARENT ACTUATOR ASSEMBLIES”, now issued U.S. Pat. No. 9,746,968, issued Aug. 29, 2017, which claims priority to provisional application No. 61/412,171, filed Nov. 10, 2010, entitled “Multiple Touch Screen with Tactile Feedback Using Transparent Actuator Assemblies”, the entire contents of which are incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present patent disclosure relates to a touch screen for a display device and, more particularly, to a touch screen that is capable of both multiple touch sensing and high resolution tactile feedback. 
     BACKGROUND OF INVENTION 
     The touch screen of the Apple iPhone is recognized as a user interface breakthrough and, at least at the time of the device&#39;s introduction in 2007, was seen as somewhat radical in that the iPhone does not have any keypad or keyboard at all. The new multi-touch screen could detect multiple fingers touching the screen, was well integrated into the phone&#39;s operating system and featured in many applications. Regarding the absence of a keyboard, the market success of the iPhone demonstrates a form of market acceptance of requiring the user to enter phone numbers by touching a flat screen&#39;s displayed keypad or to enter text by typing on a displayed QWERTY keyboard. However, typing on an image of a QWERTY keyboard displayed on a flat surface is generally considered to be somewhat problematic when compared to using a real keyboard. 
     As discussed by Michael Kwan,  Pros and Cons of Touchscreen Cell Phones, Mobile Magazine , August 2008, the absence of tactile feedback is a problem: “There&#39;s just something to be said about hitting a physical button. For the life of me, I just can&#39;t type as fast on something like the Samsung Instinct or Apple iPhone as I can on something with a physical QWERTY keyboard like the LG enV2 or HTC Touch Pro. I also find that it&#39;s a lot easier dialing on a conventional numeric keypad than it is on a virtual keypad. Some handsets have tried to rectify this with haptic feedback, but it&#39;s just not the same.” 
     The author goes on to point out that ‘having to look to touch’ is a definite additional safety issue if a cell phone user is driving a motor vehicle and that a main attraction of a button on a ‘regular phone’ is that you know you pressed it. 
     More recently, Matt Braga in “ How Haptic Feedback Brings Sensation to Touchscreens ”, Tested, May 2010, speaks similarly to the touch screen typing problem then surveys today&#39;s attempts at a solution: 
     “It&#39;s for that reason that haptic feedback technology has become all the rage in recent years. Usually with the aid of a motor, haptic feedback aims to simulate the feeling of physical interaction while using a touch screen device. We&#39;ve seen companies like RIM implement the technology with their Storm line of BlackBerries, while Motorola devices like the Droid have followed a similar approach. However, none of them feel quite right, so to speak. A vibration does little to simulate so-called ‘natural’ interaction, and that&#39;s a problem the latest haptic feedback technology is hoping to fix. The problem, however, is that the resulting vibrations are far from precise. Anything you touch seems to produce a similar, repetitive result, doing little to replicate the tactile sensation of a physical input.” 
     Toshiba&#39;s plan, announced May 2010, is to use Senseg&#39;s electrical haptic technology which modulates an electrical field to directly stimulate the touch sensors in the user&#39;s fingers. This approach is not only described in U.S. Patent Application 2009/0109007 assigned to Senseg a Finnish company founded in 2006, but also, in U.S. Patent Application 2010/0152794 assigned to Nokia, another Finnish company. The primary problem with this direct stimulation of the touch receptor approach is making the sensation that it produces recognizable to the user, for example like the feeling of a key on a keyboard. 
     Inventive efforts at Apple Inc. on haptic feedback for touch screens are evident in published U.S. Patent Applications 2009/0156818 and 2010/0156818. The latter application,  Multi Touch with Multi Haptics , employs a phased array of haptic actuator/vibrators to create localized vibration feedback that appears to be an advance in comparison to the non-localized motor generated vibration feedback described above, but retains the problem of being a vibration. The former application,  Multi - touch Display Localized Tactile Feedback , is closest to the present invention but focuses on how an application program would use such a technology with little contribution to actually creating the technology. 
     What is needed is a multiple touch screen with a dynamic tactile surface that can provide haptic feedback of sufficient fidelity that, for example, it can replicate the experience of using a physical keyboard. A transparent multi-touch sensing and tactile feedback screen assembly and an associated controller are desired that together are capable of providing both multi-touch input and local tactile response. Given the existing mutual capacitance technology for multiple touch detection and given the emerging capacitance-based technology of carbon nanotube actuators, what is needed is a means for combing the two technologies to provide a multi-touch screen with tactile feedback. Both of these technologies either use, or can use, a grid of x and y line electrodes in the screen assembly to provide localization. As a consequence, a specific need is for a touch and tactile screen controller system and method that allow the x and y line electrodes that are used for multi-touch sensing to also and simultaneously be used for localized actuator-based tactile feedback. 
     SUMMARY OF INVENTION 
     The present invention provides a module or system and a method that uses an assembly containing multiple electrodes that act as both sensors and actuators to provide a multi-touch screen with a dynamic tactile surface. Prior art multi-touch screen controllers are not concerned with simultaneously exciting actuators that produce a dynamic tactile surface. The present invention provides a transparent multi-touch sensing and tactile feedback screen assembly and an associated controller that provide both the desired multiple touch sensing input and the desired tactile feedback response. An example embodiment of the present invention may include a method of detecting user initiated touch. The method may include sensing the user initiated touch via an electrode layer laid beneath a transparent touch screen having form lines laying in a same direction under the transparent touch screen, and sensing the user initiated touch via an actuator layer laid beneath the electrode layer by providing a tactile surface responsive to the user initiated touch. Another example embodiment of the present invention may include a user initiated touch sensitive apparatus. The apparatus may include an electrode layer laid beneath a transparent touch screen and configured to sense the user initiated touch via form lines laying in a same direction under the transparent touch screen. The apparatus may also include an actuator layer laid beneath the electrode layer and configured to sense the user initiated touch and provide a tactile surface responsive to the user initiated touch. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  depicts an example implementation of a two layer, orthogonal electrode line grid with a battery that can be connected between the electrodes of the two layers; 
         FIG. 1B  depicts an example implementation of a two layer, orthogonal electrode line grid with a battery that is connected between two line electrodes, one on each of the two layers; 
         FIG. 2A  depicts a side view of an assembly that contains a two layer, orthogonal electrode line grid of  FIG. 1A  with an inactive actuator layer between the electrode layers in accordance to an embodiment of the present invention; 
         FIG. 2B  depicts a side view of an assembly that contains a two layer, orthogonal electrode line grid of  FIG. 1B  with an activated actuator layer between the electrode layers in accordance to an embodiment of the present invention; 
         FIG. 2C  depicts a side view of the assembly that contains a two layer, orthogonal electrode line grid with an activated actuator layer between the electrode layers and an activation voltage profile along the upper electrode layer in accordance to an embodiment of the present invention; 
         FIG. 3  depicts an electrode controller and a top view of the assembly that contains the two layer, orthogonal electrode line grid in accordance to an embodiment of the present invention; 
         FIG. 4  depicts a side view of an assembly that contains a two layer, orthogonal electrode line grid with a dielectric layer between the electrode layers in accordance with prior art mutual capacitance multi-touch sensor technology; 
         FIG. 5  depicts a block diagram of certain processes performed by a touch screen controller in accordance with prior art mutual capacitance multi-touch sensor technology; 
         FIG. 6  depicts a diagram of an example embodiment of an individual channel in the charge amplifier array of a touch screen controller in accordance with prior art mutual capacitance multi-touch sensor technology; 
         FIG. 7  depicts a side view of an assembly that contains a two layer, orthogonal electrode line grid with an activated actuator layer between the electrode layers in accordance with an embodiment of the multiple touch and tactile feedback system of the present invention; 
         FIG. 8  depicts a block diagram of certain processes performed by a multi-touch sensing and tactile feedback screen controller in accordance with an embodiment of the multiple touch and tactile feedback system of the present invention; 
         FIG. 9  depicts a diagram of an example embodiment of an individual channel in the charge amplifier/driver array of a multi-touch sensing and tactile feedback screen controller in accordance with an embodiment of the multiple touch and tactile feedback system of the present invention; 
         FIG. 10  shows a diagram of certain processes performed by an example implementation of the processor in the multi-touch sensing and tactile feedback screen controller of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a module or system and a method that includes: 1) a transparent screen assembly containing an actuator layer lying between two layers of transparent multiple line electrodes, where one electrode layer of forms lines in the x-direction layer and the other electrode layer forms lines in the y-direction; and 2) a controller that is connected to these electrodes. The system and method of the present invention provides: 1) multiple touch sensing on or near a surface of the transparent screen and 2) simultaneous high resolution tactile feedback across the same surface. 
       FIG. 1A  depicts an example implementation of a two layer, orthogonal line electrode grid assembly  110  with a battery  140  that can be connected between the electrodes of the two layers in accordance to an embodiment of the present invention. As shown, the y-direction line electrodes  130  and  132  are on the bottom layer and the x-direction line electrodes,  120 ,  122  and  124 , are on the top layer. The line electrodes may be individually connected to the battery  140  by means of the switchable connections  150  and  152  for the y-direction electrodes and switchable connections  160 ,  162  and  164  for the upper x-direction electrodes. The ellipses in  FIG. 1A  indicate there may be many electrodes, in both the x and y directions. For the touch screen application of the present invention the electrode grid assembly should be transparent. 
     A touch screen may contain a transparent conductor pattern consisting of 10 columns of 1 millimeter (mm) wide indium tin oxide (ITO) spaced 5 mm apart on one side of a glass sheet and 15 rows of 5 mm high ITO with 37 micrometer (μm) deletions between them on the other side. The space between the 10 columns is filled with unconnected ITO in order to maintain uniform optical appearance. 
     The shape details of the line electrodes in the present invention are not restricted to the plain line shapes drawn in  FIG. 1A . For example, line electrodes designed with the “line of diamonds” pattern are well known to those skilled in the art of touch screens and can also be used here. In general, it is desirable for the line electrodes to be designed with a linear pattern that optimizes the performance of the touch screen. 
     In the present invention, the orthogonal line electrodes, e.g.  120  and  130 , can be ITO electrodes but in some embodiments are preferably formed from a transparent carbon nanotube composite coating or structure. 
     SWNT and SWCNT are acronyms for “single walled carbon nanotube” molecular structures; as opposed to MWNT and MWCNT which are acronyms for “multiple walled carbon nanotube” molecular structures. Most single-walled nanotubes (SWNT) have a diameter of close to 1 nanometer, with a tube length that can be many millions of times longer. Carbon nanotubes are highly anisotropic with axial properties very different than trans-axial properties and can have the highest tensile strength and the highest axial electrical and thermal conductivities. If they are constructed slightly differently, i.e., different carbon bond angles on the tube surface relative to the tube axis, carbon nanotubes are semiconductors instead of metallic conductors. 
     In the present invention, the orthogonal line electrode grid assembly  110  has electrodes that may be composed of transparent carbon nanotube material instead of the traditional indium tin oxide (ITO) material. ITO is widely used for transparent electrode assemblies in touch screens and display technologies including liquid crystal displays (LCD) and plasma displays. Carbon nanotube electrodes may be preferred in embodiments of the present invention where the electrodes are used as part of, to integrate into, or at least interface with, a carbon nanotube based actuator. Note that in the present invention, this actuator electrode function is in addition to the use of the electrodes as traditional capacitive sensors in the manner required for multi-touch detection. 
       FIG. 1B  depicts the orthogonal line electrode grid assembly  110  under the condition that the y-direction line electrode  130  has been connected to the negative terminal of battery  140  by switch closure on conductor/connector  150  and the x-direction line electrode  122  has been connected to the positive terminal of battery  140  by switch closure on conductor/connector  162 . This results in an electrical field between electrodes  122  and  130  at the square  170  that is defined by the intersection of these two electrodes as viewed from above and is indicated by an “X” in  FIG. 1B . 
       FIGS. 2A, 2B and 2C  depict cross-sectional views of an example touch screen embodiment of the present invention. Relative to the electrode grid assembly of  FIGS. 1A and 1B , this cross-sectional view is defined by the view of the eye  180  in  FIG. 1B  toward the components of the example touch screen embodiment along a plane that contains line  182  in  FIGS. 1B  and is normal to the x and y directions of the line electrode grid. 
       FIG. 2A  depicts a cross-sectional view of an example touch screen embodiment of the present invention and shows cross-sections of lower y-direction line electrode  130 , and the upper x-direction electrodes  120 ,  122  and  124 .  FIG. 2A  also shows the upward projecting display unit  230 , which provides a hard and fixed support surface for the lower y-direction electrodes.  FIG. 2A  also shows a flexible, transparent top surface  210  that rests on, is stretched over, or is attached to, the upper x-direction electrodes.  FIG. 2A  also shows a touch screen and display enclosure support  240  and  242 , wherein 242 is shown as providing an access path or hole for the connecting conductor (wire)  150  to the lower y-direction electrode  130 . 
     In the example touch screen embodiment of the present invention diagrammed in  FIG. 2A , the lower y-direction line electrodes, e.g., electrode  130 , and the upper x-direction electrodes, e.g.,  120 ,  122  and  124 , are separated by material layer  220  which is a transparent, multiple electrode actuator assembly. In a preferred embodiment, multiple electrode actuator assembly  220  is a transparent composite assembly of carbon nanotubes. 
     In an example preferred embodiment, the transparent, multiple electrode, carbon nanotube composite actuator assembly  220  is based on a dry SWNT-Nafion composite. The present invention anticipates further development in the field of transparent, macro-scale carbon nanotube actuators, e.g., actuators that do not use Nafion, and includes all such developments in the intended embodiments. 
     The present invention also includes embodiments that use transparent piezoelectric composites for the transparent, multiple electrode actuator assembly  220 . 
       FIG. 2B  depicts a cross-sectional view of an example touch screen embodiment of the present invention wherein the y-direction electrode  130  and x-direction line electrode  162  are connected to the battery  140  as in indicated in  FIG. 1B . These connections result in an electrical field between electrodes  122  and  130  and the electric field stimulates a local actuator response  252  in the example transparent, multiple electrode, and carbon nanotube composite actuator assembly  220 . Given the hard and fixed support surface provided by the display unit  230  and the flexible top surface  210 , the local actuation response  252  locally raises the surface  210  of the touch screen by a displacement indicated by the arrows and the displacement line  260 . In the present invention this electrode-activated local displacement provides the touch screen a means of providing tactile feedback. 
       FIG. 2C  depicts a cross-sectional view of an example touch screen embodiment of the present invention wherein all three of the illustrated x-direction line electrodes,  160 ,  162  and  164 , are activated to produce the displacement indicated by the arrows and the displacement line  260 . For the purpose of illustration, the local actuation response is shown as being composed of three individual responses,  250 ,  252  and  254 . This example depicts the general requirement, according to the present invention, of a multiple electrode activation profile that drives the multiple electrode actuator assembly  220  so that it produces a desired multiple x-y coordinate displacement profile on the surface of the touch screen. 
       FIG. 3  shows a diagram of an embodiment of the present invention which contains a multi-touch sensing and tactile feedback screen controller system or module  310  that is electrically connected to each of the lower y-direction electrodes via connector assembly  320  and each of the upper x-direction electrodes via connector assembly  330 . One function of the multi-touch sensing and tactile feedback screen controller module  310  in the present invention is to provide the x and y electrodes of the orthogonal line electrode grid assembly  110  with the electrode activation profile that drives the multiple electrode actuator assembly  220  to produce a desired multiple x-y coordinate displacement profile on the surface of the touch screen. A second desired function of the multi-touch sensing and tactile feedback screen controller module  310  in the present invention is to use the x and y electrodes of an orthogonal line electrode grid assembly to provide a sensing capability for multiple touch user input to the device containing the touch screen of the invention. 
     It is well known that the projected, mutual capacitance technique can provide multiple touch sensing using an electrode grid assembly, for example assembly  110 . 
       FIG. 4  depicts a cross-sectional view of an example touch screen wherein the nearby presence of a finger  410  is being sensed using the mutual projected capacitance technique. In  FIG. 4  the layer  420  between the lower y-direction line electrodes, e.g.,  130 , and the upper x-direction electrodes, e.g.,  160 ,  162  and  164 , is a dielectric (insulator) such as a suitable glass or plastic. The dielectric layer  420  and the electrode line grid assembly  110  (see  FIG. 3 ) create a matrix of x-y electrode pair mutual capacitances C x,y  which are approximately equal in the absence of the finger and, most importantly, decrease in the nearby presence of the finger allowing the location of the finger  410  to be sensed. Excitation of individual lower y-direction electrode  130  results in an electric field induced charge in the upper x-direction electrodes. The induced charge is lessened in the x-direction electrodes that are near the finger since a finger is an effective grounding object that lessens the electric field connecting the x and y electrodes. The finger&#39;s lessening of the induced electric charge on ‘sensing’ electrodes  120  and  122  is indicated by the sensing arrows  430  and  420 , respectively. This mutual capacitance technique can detect multiple simultaneous finger touches (i.e., more than one finger) since induced charges are measured for all of the x electrodes when each individual y electrode is activated; the process being repeated until all y electrodes have been activated. This produces an independent x-y coordinate sensing capability. 
       FIG. 5  is a block diagram of certain processes performed by known example embodiments of a touch screen electrode controller capable of detecting multiple touches using the electrode line grid assembly  110  depicted in  FIGS. 3 and 4 . The controller contains a processor  510  which provides control signals and a capacitance-sensing excitation waveform data  515  to a capacitance-sensing excitation waveform generator/driver circuitry  520 , which provides a low impedance output  525  to a multiplex-out module  520 . The multiplex-out module  520  connects via an output connection assembly  320  to the plurality of lower y-direction, driving electrodes which are sequentially driven with the excitation waveform. An excited lower y electrode, e.g., electrode  130  in  FIG. 4 , induces charge in each of the upper x-direction sensing electrodes, e.g.,  160 ,  162  and  164  due to the presence of an x-y electrode pair mutual capacitance C x,y . These induced charges are converted to voltages by the charge amplifier array  530  which has as one amplifier channel for each x-direction sensing electrode. The voltage output of the entire charge amplifier array  540  may be simultaneously sampled and then sequentially multiplexed  550  into an analog-to-digital converter (ADC)  560  which provides a digitized sample  565 , for each x sensing electrode (snapshot of the sensing x-electrodes) to the processor  510 . The capacitance excitation driver  520  and the multiplexer-out  530  then excite the next y driving electrode and the snapshot of the x sensing electrodes is repeated; until all of the y electrodes have been excited. At this point the processor has received mutual-capacitance-induced-charge measurements for all x-y coordinates of the electrode line grid assembly  110 . The presence of a finger near an x-y coordinate is indicated by a change in the induced-charge measurement at that coordinate. The processor executes signal/image processing algorithms that enhance the induced-charge measurement data to detect multiple touch events and gestures of interest and to report these touch detections  580  to the host application. 
       FIG. 6  is a diagram of an example embodiment of an individual charge amplifier channel in the charge amplifier array  540  according to known prior art. The operational amplifier  610  has a feedback capacitor C FB    620  that determines a charge-to-voltage gain as the ratio of C x,y  to C FB  and a feedback resistor R FB    630  that determines the direct current (d.c.) input resistance and allows the operational amplifier to hold d.c. voltage of the input to V REF . The inverse product of R FB  and C FB  determines the corner frequency of the amplifier&#39;s filter characteristic. The reference voltage V REF  may be set to zero to reduce the effects of stray capacitances to ground. Feedback resistor R FB    630  is omitted in some embodiments with the closing the reset switch  640  between scans providing a unity-gain amplifier that clears the induced charges in Cx,y from the last measurement. Various implementations of analog circuitry  650  are known that provide driver-electrode-dependent gain and offset compensation and that use the capacitance excitation (CE) waveform to improve the signal-to-noise ratio of the output to the multiplexer-in module  550 . 
       FIG. 7  depicts a cross-sectional view of an example touch screen that is a preferred embodiment of the present invention wherein the multiple electrode actuator assembly  720  is a transparent assembly of carbon nanotube composites. The carbon nanotube actuators are capacitors with an electrolyte dielectric matrix. The multiple electrode carbon nanotube actuator/capacitor assembly  720  together with a novel touch and tactile electrode controller allows the same electrode line grid assembly  110  (see  FIG. 3 ) to: 1) sense nearby fingers using the above mutual capacitance technique and 2) simultaneously produce high resolution, local tactile feedback using the above multiple electrode actuator technique. 
       FIG. 8  is a block diagram of certain processes performed by an example embodiment of the present invention of a multi-touch sensing and tactile feedback screen controller  810  that is capable of both detecting multiple touches and providing local tactile feedback using the electrode line grid assembly  110  depicted in  FIG. 3  and the multiple electrode carbon nanotube actuator assembly  720  in  FIG. 7 . The processor  510  receives tactile commands  805  from and provides touch detections  580  to a host processor application. The processor  510  also provides control signals and a high frequency capacitance-sensing excitation waveform data  515  to the high frequency capacitance-sensing excitation waveform generator  520 . The processor  510  also provides control signals and low frequency actuator excitation waveform data  815  to the low frequency actuator excitation multiple-waveform generator  820 . To generate a desired tactile surface given a set of tactile commands  805 , there is generally a plurality of actuator excitation waveforms required to drive a plurality of lower y-electrodes and a plurality of actuator excitation waveforms required to drive a plurality of upper x-electrodes. 
     In a preferred embodiment of the multi-touch sensing and tactile feedback screen controller  810  in  FIG. 8 , the frequency domain spectral power densities of the high frequency capacitance-sensing excitation waveform and the low frequency actuator excitation waveforms do not overlap. This driving-waveform-frequency-separation condition greatly simplifies the signal processing that is required to extract the touch-sensing capacitative-coupling signals on all x-electrode connections in connection assembly  330 . These signals are in response to the capacitance driving signal that is sequentially imposed on individual y-electrodes in connection assembly  320 . The signal processing that is required for the touch-sensing capacitative-coupling signals on the x-electrodes must take into account that any number of x-electrodes and any number of y-electrodes are being driven with actuator excitation waveforms. In an example preferred embodiment, a driving-waveform-frequency-separation condition restricts the high frequency capacitance-sensing excitation waveform to frequencies above 100,000 Hertz (100 KHz); a condition that is known to be feasible to those skilled in the art of mutual capacitance touch sensing measurements for touch screen devices. An example high frequency capacitance-sensing excitation waveform that has frequency components above 100 KHz is an infinite train of 50% duty cycle pulses where the time between the leading edge of adjacent pulses is 1/200 KHz or 5 microseconds. Restricting this pulse train to at least 10 pulses provides an acceptable approximation to the driving-waveform-frequency-separation condition of the present invention. Those skilled in the art know that other high-frequency-only pulse waveforms such as pseudo-random pulse sequences can be used to support signal enhancement techniques, such as cross-correlation of the response and driving signals. Given the actuator response times are generally slower than 1 millisecond; it follows that the actuator excitation driving waveforms can occupy frequencies below 10 KHz, which together with above pulse train example of an above 100 KHz capacitance excitation waveform, indicates that the proposed driving-waveform-frequency-separation condition of the present invention can be readily achieved in practice. 
     Referring to  FIG. 8 , the capacitance-sensing excitation waveform signal  823  is input to a multiplexer-out module  830  which connects the signal to one of the y-electrode signal paths  835  that are output from the multiplexer-out module  830  and input to the adder array  840 . The other input to the adder array  840  is the actuator excitation signals  835  for the y-electrodes that are output from the actuator excitation multiple-waveform generator  820 . The array adder  840  can be described as a vector summing module where the input vectors are the analog signal busses  825  and  835 , the output vector is the analog signal bus  845 , and the elements of the vectors are defined by the individual, corresponding y-electrode signals in each analog signal bus. The y-electrode signals in analog signal bus  845  are input to the driver array  850  which contains as many driver amplifier channels as there are y-electrodes with each amplifier being connected to a y-electrode via the output connection/wiring assembly  320 . The actuator excitation multiple-waveform generator  820  also outputs the x-electrode actuator excitation signals  827  that are received by the charge amplifier/driver array  860 . 
       FIG. 9  is a diagram of an example embodiment of the present invention of an individual charge amplifier/driver channel in the charge amplifier/driver array  860 . By connecting the x-electrode actuator excitation signal  910  to the positive input of the operational amplifier  920  the x-electrode can be driven with the actuator signal at frequencies below the feedback RC characteristic frequency of F c =2*π/(R FB *C FB ). For example, F c  can be on the order of 10 KHz, based on the above discussion of example capacitance excitation and actuator excitation waveforms. Compared to the operational amplifier  610  in  FIG. 6 , the operational amplifier  920  has an additional output power requirement that allows it to drive the x-electrode. This operational amplifier output requirement should be consistent with the driving requirements of the multiple electrode carbon nanotube actuator/capacitor assembly  720  in  FIG. 7 . The touch-sensing induced-charge signal of interest  950  is obtained by subtracting  940  a scale adjusted actuator excitation signal  918  from the output  925  of the operational amplifier  920 . A multiplier  915  scales the actuator excitation signal  910  by the actuation compensation parameter K A    912  that is provided by the processor  510  for that particular x and y electrode combination. K A  compensates for the changes in low frequency y-to-x electrode impedance with changes in the level of local actuator activation. As discussed earlier, known analog circuitry  650  can provide gain and offset compensation and use the capacitance excitation (CE) waveform to improve the signal-to-noise ratio of the induced-charge measurement that is output to the multiplexer-in module  550  in  FIG. 8 . 
       FIG. 10  shows a diagram of certain processes that are performed by an example implementation of processor  510  of the multi-touch sensing and tactile feedback screen controller  810  of  FIG. 8  that controls the multi-touch sensing and tactile feedback assembly of  FIG. 7 , all of which are of the present invention. The frequency separation of the capacitance-sensing excitation signal and the actuator excitation signals, from waveform generators,  520  and  820 , respectively, together with the design of the charge amplifier/driver array  860  has the result that the touch-sensing and tactile-feedback software processing modules in processor  510  are separable, i.e., they can operate independently of each other, as shown in  FIG. 10 . This independence is highly desirable since it means the new tactile feedback processing can simply be added to the processor  510 , while retaining existing prior art processing for multi-touch sensing which typically has already been reduced to practice and performance optimized. 
     Referring to  FIG. 10 , according to the present invention, the processor receives  1010  tactile commands  805  from a host processor software application and determines the desired series of x-y surface displacements  1020  that satisfy the tactile command, where the displacement refers to the z-axis orthogonal to the x-y surface of the screen assembly. The desired x-y surface displacements  1020  and the current x-y surface displacement  1030  and are input to a dynamic model of the multiple-electrode actuator  1040 . The dynamic model of the multiple electrode actuator  1040  is used to determine the series of actuator excitation waveforms  1050  that will produce these displacements, using, for example, numerical inversion techniques of applied control theory. The actuator excitation waveforms are output  815  to the low frequency actuator-excitation, multiple-waveform generator  820 . The x-y dependent K A  compensation parameters for the charge amplifier/driver array  860  are determined  1060  based on the state of the dynamic model  1040 . Note the K A  compensation data may in general vary with the x-y coordinate and time because it is dependent on the state of the multiple-electrode actuator as expressed in the dynamic model  1040 . The processor  510  outputs the K A  compensation data to the compensation data memory  570 . The dynamic model  1040 , the actuator waveforms  1050  and the K A  compensation data  1060  can preferably be reset to a known ‘flat surface’ state using a reset command  1015  from the host processor application. The ‘flat surface’ reset command  1015  mitigates errors in the tactile feedback that may accumulate due to modeling errors in the dynamic model of the multiple electrode actuator  1040 . 
     Referring to  FIG. 10 , the processor can receive induced charge data  1015  from the ADC  560  that is x-y coordinate indexed and perform processing that includes multi-touch signal enhancement, detection and tracking  1090  and output the resultant touch detection information  1095  to the host software application(s). The capacitance excitation waveform data is output  1080  to the high frequency capacitance-sensing excitation waveform generator  520  and to the compensation data memory  570  of  FIG. 9 . The offset and gain compensation data is also output  1070  to the compensation data memory  570 .