Abstract:
A projected capacitive touch panel that can detect touch pressure. The cover layer of projected capacitive touch panel has protrusions with gaps that fill up partially when finger is pressed, thereby registering a large change in projected capacitance. A keyboard using such device with optional mechanical switches underneath the touch surface for tactile feedback. Haptic feedback is coupled to detection of touch pressure. Reconfigurable keyboard and trackpad regions on a touch panel sensitive to touch pressure with tactile feedback from underlying mechanical switches. A mouse with left and right click support using projected capacitive touchpad with pressure detection for mouse click. Human finger based mimicking of mouse operation in combination with touch pressure detection. Supporting gestures that use touch pressure. Providing a visual feedback in an underlying display when touch pressure is detected. Providing an audio feedback when touch pressure is detected.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Patent Provisional Application No. 61/654,957, filed Jun. 4, 2012, and titled “PRESSURE SENSITIVE PROJECTED CAPACITIVE TOUCH SENSING,” which is herein incorporated by reference in its entirety. 
         [0002]    The present application is related to U.S. Pat. No. 8,139,035 B2, dated Mar. 20, 2012, for TOUCH SENSITIVE KEYPAD WITH TACTILE FEEDBACK, included by reference herein. 
         [0003]    The present application is related to United States patent application US 2010/00860593 A1, published Mar. 11, 2010, for PHASE COMPENSATION FOR MULTI-STIMULUS CONTROLLER, included by reference herein. 
     
    
       [0004]    Validation of a 3-D Finite Element Human Fingerpad Model Composed of Anatomically Accurate Tissue Layers, by Matt B. Wagner, Gregory J. Gerling, and Jacob Scanlon, Department of Systems and Information Engineering, University of Virginia, USA 
         [0005]    Italian National Research Council website at http://niremf.ifac.cnr.it/tissprop/htmlclie/htmlclie.htm 
       FIELD OF THE INVENTION 
       [0006]    This invention relates generally to projected capacitive touch-sensitive devices, particularly those that rely on an electrical coupling between a user&#39;s finger and a touch device, with particular application to such devices that are capable of detecting multiple touches applied to different portions of the touch device at the same time. 
       BACKGROUND 
       [0007]    Projected capacitive touch panels are used very widely today in mobile devices like smartphones, tablets etc. While they enable a display area to be reused for touch, they do not offer the same user experience of a pressure sensitive keyboard with tactile feedback to the finger. 
         [0008]    For dedicated keyboards, in U.S. Pat. No. 8,139,035 B2 titled “TOUCH SENSITIVE KEYPAD WITH TACTILE FEEDBACK,” a touch sensitive surface is placed on top of a mechanical keyboard switch arrangement that provides tactile feedback, while the switch arrangement itself has electrical connectivity for indicating touch. 
         [0009]    Very low profile mechanical keyboards have a limited electrical contact life though the tactile life of each key can be significantly larger. It is expensive to replace these keyboards in notebook PCs. 
         [0010]    United States patent application US 2010/00860593 A1, published Mar. 11, 2010, for PHASE COMPENSATION FOR MULTI-STIMULUS CONTROLLER, describe the operation of a projected capacitance touch panel. It is referenced for the description of prior art regarding the operation of the projected capacitance touch panel. 
       SUMMARY 
       [0011]    In view of the foregoing, a projected capacitive multi-touch sensing method is disclosed for detecting touch pressure, and for offering tactile or haptic feedback. While only the details of the panel itself had been described, it is assumed to include a suitable touch controller IC with associated firmware. A capacitive touchpad has unlimited life in terms of equivalent electrical connectivity of keyboard switches, and with a combination of pressure sensitivity and tactile or haptic feedback, the user experience can be significantly improved, and a dedicated mechanical keyboard can be replaced by a much lower profile touch-based keyboard with tactile feedback. 
         [0012]    An embodiment of the patent includes a pressure sensitive projected capacitive touch panel. In one embodiment of the patent, a haptic feedback is given whenever a pressed condition is detected by the pressure sensitive projected capacitive touch panel. In another embodiment of the patent, a projected capacitive touch surface that is sensitive to touch pressure, is placed on a dummy low-profile keyboard switch that is only used for tactile feedback. The low-profile keyboard switch could be dedicated to each alphanumeric key, or to a region of the keyboard or to the entire keyboard. In another embodiment of the patent, a dedicated pressure sensitive touch enabled keyboard is reused as a trackpad. In another embodiment, the trackpad is a fixed extension of the keyboard, while in another embodiment the trackpad can be extended from under the keyboard. In another embodiment, a passive mouse technology is used on the pressure sensitive touch enabled trackpad, while in yet another embodiment the human fingers double as a mouse on the pressure sensitive touch enabled trackpad. In another embodiment of the patent, a pressure sensitive touch enabled keyboard comprising of virtual keys are redefined either completely or in sections for different applications like gaming, mouse and trackpad combination, special drawing enabled trackpad region that can for example automatically straighten lines and draw smooth curves with zoom in and zoom out based on touch. 
     
    
     
       DRAWINGS 
         [0013]      FIG. 1  is a cross section of a projected capacitive touch panel and it illustrates a projected capacitance electric field lines under no-touch conditions, according to prior art. 
           [0014]      FIG. 2  illustrates the cross-section of the human finger including the skin. 
           [0015]      FIG. 3  is a cross section of a projected capacitive touch panel and it illustrates a projected capacitance electric field lines under touch conditions in presence of a human finger, according to prior art. 
           [0016]      FIG. 4  illustrates the cross-section of a projected capacitive Pressure sensitive touch panel according to an embodiment of this patent. It is shown for the no-touch condition, and shows protrusions in the top layer according to an embodiment of this patent. 
           [0017]      FIG. 5  illustrates the cross-section of a projected capacitive Pressure sensitive touch panel according to an embodiment of this patent. It is shown for the touch condition in presence of a human finger, and shows protrusions in the top layer according to an embodiment of this patent. It is shown for the non-pressed condition. 
           [0018]      FIG. 6  and  FIG. 7  illustrate the cross-section of pressure sensitive projected capacitive touch panel based on other embodiments of this patent relating to the placement of the upper electrode. 
           [0019]      FIG. 8  illustrates the cross-section of a projected capacitive Pressure sensitive touch panel according to an embodiment of this patent. It is shown for the touch condition in presence of a human finger, and shows protrusions in the top layer according to an embodiment of this patent. It is shown for the pressed condition. 
           [0020]      FIG. 9  illustrates the cross-section of a pressure sensitive projected capacitive touch panel using dummy mechanical switches under it for tactile feedback. The dummy switches are just mechanical contraptions without electrical connections, but optionally could also have electrical connections for pressed-touch detection, for robustness. 
           [0021]      FIG. 10  shows a single piece low-profile keyboard and trackpad combination, using pressure sensitive projected capacitive touch panel according to an embodiment of this patent. The trackpad can double as a mouse pad that can also work with a passive mouse. The passive mouse is another embodiment of the patent. 
           [0022]      FIGS. 11 ,  12  and  13  show a construction of a passive mouse according to an embodiment of this patent. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    In the following description of preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which it is shown by way of illustration specific embodiments in which the invention can be practiced. It is to be understood that other embodiments can be used and structural changes can be made without departing from the scope of the embodiments of this invention. 
         [0024]    Furthermore, although embodiments of the invention may be described and illustrated herein in terms of double-sided Indium Tin Oxide (DITO) touch sensor panels, it should be understood that embodiments of the invention are also applicable to other touch sensor panel configurations, such as configurations in which the drive and sense lines are formed on different substrates or on the back of a cover glass, and configurations in which the drive and sense lines are formed on the same side of a single substrate. 
         [0025]      FIG. 1  is a cross section of a flat projected capacitive touch panel  250  and it illustrates a projected capacitance electric field lines under no-touch conditions, according to prior art.  200  is a sense electrode,  201  is a drive electrode,  202  is a dielectric separating sense and drive electrodes,  203  is a top-layer dielectric material usually comprising of a uniformly thick cover glass sheet, and  204  are exemplary traces of electric field lines between drive and sense electrodes. While  FIG. 1  shown only one sense  200  electrode and one drive  201  electrode in the cross section view of a projected capacitive touch panel  250 , the panel  205  comprises a plurality of drive  201  electrodes and a plurality of sense  201  electrodes. The sense electrodes  200  are orthogonal to the plane of the cross section i.e. to the plane of  FIG. 1 , while the drive electrodes  201  are tangential to the plane of the cross section. All sense  200  electrodes are parallel to each other, and all drive  201  electrodes are parallel to each other, within the plane of the panel  250 . The flat projected capacitive touch panel  250  is placed above a flat electronic display panel that is usually an LCD or AMOLED display panel (not shown). In a projected capacitive touch panel, as shown in  FIG. 1  for the cross-section, the drive electrodes  201  injects signal onto the sense electrodes  200 . These two sets of electrodes are orthogonal and separated by a dielectric layer  202 . The sense electrode  200  as shown in  FIG. 1 , is intruded into the dielectric material  202 . A cover glass  203  is used to cover the sense electrodes. The electric field lines  204  as shown in  FIG. 1  are for the no-touch condition. The sense electrodes  200  are at virtual ground potential, while the drive electrodes  201  carry a drive signal. 
         [0026]      FIG. 2  illustrates the cross-section of a human finger  300  including the skin. The outer layer of the skin called the epidermis, has a thick layer  301  which has a high dielectric constant but low conductivity. The inner layer of the skin  302  called the dermis, has high conductivity and provides the grounding effect to the touch panel when the panel is touched. In table 1 of the reference “Validation of a 3-D Finite Element Human Fingerpad Model Composed of Anatomically Accurate Tissue Layers,” by Matt B. Wagner, Gregory J. Gerling, and Jacob Scanlon, Department of Systems and Information Engineering, University of Virginia, USA, the mean thickness of the outer epidermis layer is about 0.37 mm.  FIG. 3  in this reference shows that a 1 mm displacement of the skin from a sharp edge results in 50% return to normal at a distance of 1.5 mm from the sharp edge. However with a hard press, the 50% return to normal would occur at a much shorter distance. This property of the human skin is used in this patent to define the height of ridges and the separation of these ridges for pressure detection, as described later. From the Italian National Research Council website at http://niremf.ifac.cnr.it/tissprop/htmlclie/htmlclie.htm, the dielectric constant of skin is shown to be extremely high between 1100 and 15000, while the conductivity is extremely low in the range of 0.00045 to 0.0066. This high value of the dielectric constant combined by the low conductivity helps in increasing the projected mutual capacitance when the skin is in close proximity between the sense electrode and drive electrode of the touch panel. 
         [0027]      FIG. 3  is a cross section of a projected capacitive touch panel and it illustrates a projected capacitance electric field lines under touch conditions in presence of a human finger, according to prior art.  FIG. 3  shows the electric field lines  204  of a projected capacitive touch panel under touch conditions i.e. when the human finger layer  301  is touching the uniformly thick cover glass  203 . Due to a large external capacitive coupling between the human body and the touch panel&#39;s system ground that is normally a conductive layer much below the transmit ( 201 ) and sense ( 200 ) electrodes, the finger is at the same AC ground potential as a sense electrode  200  that is maintained at a virtual AC ground by a sensing electronic circuit. Because of this, some of the electric field  204  lines between the driver  201  and sense  200  electrodes are terminated on the human finger layers  301  and  302  instead of being terminated on the sense electrode  200 . This reduces the capacitance between the sense  200  and the drive  201  electrodes, and this change in capacitance is used to decode the touch information. However this method is not able to decode the pressure information of the touch unless it results in a large increase of the touch area under the finger. This increase in area is unreliable and dependent on the position of the human finger. 
         [0028]      FIG. 4  illustrates the cross-section of a projected capacitive Pressure sensitive touch panel according to an embodiment of this patent. It is shown for the no-touch condition, and shows protrusions in the top layer cover glass according to an embodiment of this patent. The cover glass  203   b  instead of being uniformly thick, has ridges or protrusions running parallel to the sense electrodes, as shown in this figure by the varying thickness of this layer, compared to the uniform thickness of  203  in  FIG. 3 . The ridges are formed by reducing the thickness of the cover glass from around 0.7 mm to about 0.1-0.2 mm typically between the ridges, while maintaining the thickness of the ridges at 0.5-0.7 mm. 
         [0029]      FIG. 5  illustrates the cross-section of a projected capacitive Pressure sensitive touch panel according to an embodiment of this patent. It is shown for the touch condition in presence of a human finger, and shows protrusions in the cover glass  203  according to an embodiment of this patent. It is shown for the non-pressed condition. Under normal touch as shown in  FIG. 5 , some of the electric field lines  204  that terminate on the sense electrode  200 , are stolen by the finger layers  301  and  302 , thereby reducing the capacitance between the sense  200  and drive  201  electrode during touch i.e. when finger layer  301  touches cover glass  203 . During normal touch there is an air gap  205  between the finger layer  301  and the non-uniformly thick cover glass  203 . This capacitance reduction effect is the same as in prior art. However, during a pressed condition as shown in  FIG. 8 , the outer region of the epidermis layer  301  of the finger covers the gaps ( 205  in  FIG. 5 ) between the ridges that would normally have been an air gap under non-pressed touch conditions. The effect of filling up the air gaps between the ridges of the cover glass  203  is to significantly increase the effective thickness of the cover glass, with a huge increase in the dielectric constant of this layer, largely determined by that of epidermis layer  301 . It results in a large increase in electric fields  204  that terminate on the sense electrode  200 , thereby increasing the capacitance between the driver  201  and sense  201  electrodes instead of reducing it. Whereas a regular touch decreases this capacitance, a pressed condition increases the capacitance. Therefore, both regular touch and pressure can be detected by determining whether capacitance has decreased or increased. In regular touch panel the pitch of the drive and sense electrodes is approximately 5 mm. However this is extremely wide for pressure sensing since the finger could fill the void between the ridges even without significant pressure. In order to make the pressure sensing work i.e. for the air gaps between the ridges of cover glass  203  to fill up with the epidermis layer  301  of the finger only under reasonable pressure, the spacing of the ridges has to be reduced to a pitch of 2-3 mm. The pitch of the sense  200  traces and the drive  201  traces can also be optionally maintained at this range of value instead of a typical 5 mm value. 
         [0030]      FIG. 6  and  FIG. 7  are other embodiments of the patent showing the cross section of projected capacitive touch panel. In  FIG. 6 , the dielectric layer  202  between the drive  201  and sense  200  electrodes are much thinner than that of the cover glass  203  of a projected capacitive touch panel  251 . This is typically the case for mobile cellular phone devices. According to this patent, the cover glass  203  in not uniformly thick, but has ridges or protrusions on the top outer surface, running parallel to either sense  200  electrodes or to drive  201  electrodes or to both.  FIG. 7  is the case for a projected capacitive touch panel printed circuit board  251  that is used for a keyboard and trackpad. The sense electrode  200  are copper traces covered with a scratch resistance smooth insulating material  203  like Teflon etc. The dielectric material  202  is usually made of FR4 material for printed circuit boards, and separates the sense  200  and drive  201  electrodes. The ridges or protrusions in the cover layer  203  comprises the material  203  above sense electrodes  200 , and also the material in the sense electrode  200 . 
         [0031]    According to another embodiment of the patent, instead of having ridges in the cover glass that run parallel to only the sense electrodes, dummy parallel ridges could also be included to run in a perpendicular direction to the sense electrodes for better touch experience. These electrodes would run in parallel to the drive electrodes and would ideally be placed at the border between the drive electrodes. The cover glass refractive index can optionally be suitably graded so that the ridges do not create significant optical distortions. 
         [0032]      FIG. 9  shows an embodiment of the patent for tactile feedback.  FIG. 9  illustrates the cross-section of a pressure sensitive projected capacitive touch panel  251  using dummy mechanical switches under it for tactile feedback. The dummy switches are just mechanical contraptions without electrical connections, but optionally could also have electrical connections for pressed-touch detection, for robustness. The pressure sensitive projected capacitive touch panel  251  is made flexible, and sits on top of mechanical switches comprising of movable part  207  and fixed part  206  that provide the tactile feedback when pressed. The fixed part  206  is attached to a rigid base layer  205  that could be part of a printed circuit board and could optionally be made of FR4 material. The dummy switches comprising of  206  and  207  need not have any electrical contacts, but in another embodiment of the patent, could also have them in order to indicate through their electrical contacts closure a positive touch pressure for improved robustness. There could be one electrical or dummy mechanical switch for every alphanumeric position of the keyboard, or several virtual keys could share one electrical or dummy mechanical switch, or the entire keyboard could have just one electrical or dummy mechanical switch, which could optionally rock in different directions. There could be LED or LCD under the alphanumeric numbers that light up when the corresponding key is pressed. 
         [0033]    For a transparent cover glass with ridges running along the columns, the touch panel is intended to be used with the display underneath. A haptic feedback can be given whenever pressed condition is detected, for improved user experience. An audio feedback could also be given, and the area under the pressed key could also be made to change color. In another embodiment of the patent, LCD, LED, AMOLED or suitable display under the touch panel can be used to visually indicate through suitable means of highlighting or color change or animation, the region or text or key where finger is touching or hovering, and a different visual indication could be given when touch pressure is detected. This could be combined with an audio indication e.g. a click sound could be given to indicate detection of pressure. 
         [0034]      FIG. 10  shows a single piece low-profile keyboard  300  and trackpad  303  combination  300 , using pressure sensitive projected capacitive touch panel. The trackpad can double as a mouse pad that can also work with a passive mouse. The passive mouse is another embodiment of the patent. Also shown is a ground layer  301  that helps to improve the ground coupling of the keyboard  302  with the human body or hand (nor shown). The keyboard can use low-profile mechanical switches comprising of movable part  207  and fixed part  206  of  FIG. 9  for tactile feedback, or could use haptic feedback. The drive electrodes could run horizontally covering the keyboard  300  and trackpad  303 , while the sense electrodes could run vertically, as an example. The trackpad  300  can be used to operate a virtual mouse using just the human fingers. For example, the index finger of the right-hand could be used for the mouse operation, and pressing it could indicate the left mouse click, while pressing the middle finger while simultaneously touching the index finger, could indicate the right mouse click. Various other gestures can be incorporated by including pressure information for improved user experience, according to an embodiment of this patent. 
         [0035]      FIGS. 11 ,  12  and  13  show a construction of a passive computer mouse according to an embodiment of this patent. While a regular computer mouse works on a passive surface, the passive mouse according to an embodiment of this patent, works on a trackpad that comprises a projected capacitive touch panel and serves as a mouse pad. The trackpad  303  of  FIG. 10  can be used as a mouse pad with a passive mouse  400  that is shown in  FIG. 11  for the bottom view,  FIG. 12  for the top view and  FIG. 13  for the side view. The bottom surface of the passive mouse is flat and has three conductive surfaces  401 ,  402  and  403  as shown in  FIG. 11 . It also has two low-friction surfaces  404  for aiding smooth movement of the passive mouse on a trackpad, The top surface of the passive mouse is curved and includes a conductive layer, and a side view cross section is depicted in  FIG. 13 . The front part of the top surface includes two switch surfaces  403   b  and  403   a  as shown in  FIG. 12 , for left-click and right click of the mouse respectively. The placement of the conductive discs  401 ,  402  and  403  relative to the left-click and right click switch surfaces are also depicted in  FIG. 12  by the shaded regions.  FIG. 11  shows the bottom surface of the passive mouse that sits on top of the trackpad  303  of  FIG. 10 . The position of the mouse is tracked by the circular conductive disk  401  which creates a touch on the said trackpad  303 . As shown in  FIG. 13 , the circular disk  401  is connected to the top outer curved shell  406  of the mouse which is conductive and is in close proximity with a human hand and therefore at the same potential as the human body. This connection to  406  is depicted in  FIG. 13  as a triangular electrical “ground” symbol at one end of a wire with the other end connecting to  401 . Also used are smaller circular conductive disks  402  and  403  for the mouse clicks. Circular disks  403  and  402  do not normally extrude out of the bottom surface  400 , but are pushed out by the left and right click switches  403   b  and  403   a  of the mouse respectively using a conductive piston arrangement as shown in  FIG. 13  as a line joining  402  and  403  to  406  with a pivoting mechanical connection of this line to  406  shown by a shaded region just below  406  and on top of this line. The conductive piston is electrically connected to  406  using a wire. One end of this wire connects to the line depicting the piston in  FIG. 13 , while the other end of this wire is connected to  406 , with this connection depicted in  FIG. 13  as a triangular electrical “ground” symbol. The left click  403   b  and right click  403   a  switches rest on individual springs  407  as depicted in  FIG. 13 , for tactile feedback and for “normally off” switch operation.  403   a  and  403   b  are hinged to the mouse body at the contact region  405  as shown in  FIG. 13 . The protrusions  404  at the two ends of the lower surface of the mouse have low friction and are used for gliding the mouse smoothly on the projected capacitive trackpad  303  based mouse pad. The circular discs  402  and  403  could optionally have a soft surface to mimic the mushy human finger in order to detect pressed condition, according to another embodiment of this patent. 
         [0036]    In another embodiment of the patent, circular discs  402  and  403  are permanently attached to the bottom flat surface, and are electrically connected to the top curved shell  406  whenever the corresponding left mouse click  403   b  and right mouse click  403   a  button is pressed. The click buttons close an electrical switch each, when pressed.