Abstract:
Systems and methods that allow the user to rest their fingers on a touch-sensitive surface and make selections on that surface with a pressing action. Touch capacitance sensors that typically provide X and Y location data associated with a user&#39;s touch are also used to discern finger pressure in the Z direction. This allows the user to make an actuation on the touch screen by simply pressing harder at a location where they may already be resting their finger(s).

Description:
PRIORITY INFORMATION 
     The application claims priority to provisional application Ser. No. 61/472,799 filed Apr. 7, 2011 and is incorporated herein by reference. 
     FIELD OF INVENTION 
     The present invention relates to input devices for electronics and, more particularly, to a touch sensitive input surface especially suited to smartphones, tablet computers, touch sensitive keyboards, input panels, medical equipment, or any other device that uses a touch-sensitive panel or display. 
     BACKGROUND OF THE INVENTION 
     With the advent of touch-sensitive interfaces on the screen of computing devices, it has become necessary to find alternative human-computer interfaces to the traditional keyboard and mouse. Many of these devices, often referred to as tablet computers, smart phones, and smart screens, don&#39;t support the traditional input paradigms of an external keyboard and mouse. Rather, they rely on the direct input of the user through human touch. 
     Besides this type of computing device, there are also other touch-interface devices that use a similar mode for user input. One such example is that of a touch-sensitive computer keyboard that is made up of a solid touch-sensitive surface that can be easily wiped for cleaning purposes. 
     Traditionally, these touch sensitive surfaces respond immediately to the user&#39;s touch (or release). The paradigm is simple: point, touch, select. While this works well for many applications, it is problematic in situations where the user desires to rest their hands and/or fingers on the surface. A touch sensitive keyboard (onscreen or stand-alone) is a good example of such a situation; a trained ten-finger touch typist relies on resting their fingers on the home row of the keyboard and then pressing keys to initiate an action. On traditional touch surfaces, this isn&#39;t possible because as soon as the user touches the surface to rest their fingers, an action is initiated. These solutions don&#39;t take into account the need for the user to rest their hands/fingers on the surface. 
     There are many methods for detecting the touch of a human user, including sensors based on capacitance, infrared light, resistance, surface acoustic waves, and force sensors. Each of these methods have their respective advantages and disadvantages. But the vast majority of today&#39;s touch-based systems have standardized on using touch capacitance. 
     An example of one of the first uses of a touch capacitance for computer input is described in U.S. Pat. No. 5,305,017 to Gerpheide. This approach has become the standard for providing a cursor-pointing alternative to a computer mouse in the form of a touchpad, commonly included in most laptop computers. The method decodes touches in two dimensions, offering offsets in the horizontal (x) direction and vertical (y) direction as the user moves their finger across the touchpad surface. However, no consideration is given to user assertions in the vertical (−z) direction. 
     This approach to sensing human touch using changes in capacitance is commonly employed in the industry. Electronic chips are readily available to perform these functions, such as the QT60486 from Quantum Research Group and the AT32UCL3L from Atmel Corporation. These chips, and others like them, are used by hundreds of companies to sense human touch. 
     Others have taken the concept of touch capacitance input further to include decoding user gestures and assigning functions to them. U.S. Pat. No. 7,470,949 by Jobs et al. teaches how gestures using simultaneous touches on a capacitive surface such as “pinching”, rotating, and swiping can be used to manipulate onscreen elements. While this approach allows for multiple fingers touching the surface at one time, it is not for the purpose of allowing the user to “rest” their fingers on the surface, but rather for a specific intended action to be performed. 
     The object coming into contact with the touch sensitive surface may not always be a human finger. For example, other forms of touch sensors such as resistive, surface acoustic wave, and infrared allows passive objects such as a plastic stylus to be used to make selections on the touch surface. It is possible to also apply this concept using capacitive sensors, by designing input objects with capacitive properties similar to a human finger. For example, in U.S. Pat. No. 5,488,204 Mead et al. describe a paintbrush-like input device that is capable of creating brush-like strokes on a display screen. Mead further teaches using X and Y sensor data to determine a Z-value representing finger pressure. Mead&#39;s teachings build on the teachings of Miller et al. in U.S. Pat. No. 5,374,787. This method, however, is targeted toward a single input (of either a single finger, stylus, or paintbrush-like input device) and is focused on a touchpad rather than a touch surface that is part of a display or graphical surface. It doesn&#39;t apply the concept to the problem of multiple fingers resting directly on the touch surface on which are displayed actionable regions, as disclosed in the present invention. 
     There are numerous other devices that use force sensors to detect pressure in the Z direction. For example, in U.S. Pat. No. 8,026,906 Molne et al. describe using force-sensing resistors (FSR&#39;s) to measure downward pressure on a touch screen, wherein the FSR&#39;s are placed between the touch sensitive surface and supporting posts (or feet at all four corners). In U.S. Pat. No. 5,241,308 Young et al. describe a similar method wherein pressure is detected by the deformation between two panels closely spaced apart, or by providing force-sensing means located at each of the spaced apart support. These devices measure the forces transmitted by the touch surface to a fixed frame at multiple points (see also U.S. Pat. No. 3,657,475 to Peronneau et al. and U.S. Pat. No. 4,121,049 to Roeber). These methods detect pressure by a means that is separate from the means to detect touch, whereas the present invention detects touch, resting, and pressing all through the same touch capacitive means. 
     SUMMARY OF THE INVENTION 
     The present invention provides systems and methods that allow the user to rest their fingers on a touch-sensitive surface and make selections on that surface by pressing. Touch capacitance sensors that typically provide X and Y location data associated with a user&#39;s touch are also used to discern finger pressure in the Z direction. This allows the user to make an actuation on the touch screen by simply pressing harder at a location where they may already be resting their finger(s). 
     In one aspect of the invention, the process discerns between the actions of tapping on the surface, resting on the surface, and pressing on the surface. It does so using, in part, thresholds for the touch signal (which may be dynamically altered to accommodate the touch signatures of different users). The process also takes into account the rate of the rising edge of the touch signal to discern between a tap, a resting action, and a press. 
     It is desirable to allow a human user to rest their hands and/or fingers on a touch surface without causing an actuation, yet still allow other actions issued by the user through touch, such as a press, to be interpreted as commands by the system. 
     One such method takes into account the vibration caused by the user “tapping” on keys and is described in U.S. Patent Publication No. 20090073128 (Marsden et al.) all of its teaching are hereby incorporated by reference. This method accounts for the common user action of striking, or “tapping” a key to actuate it. The present invention furthers this teaching by also allowing a press action on the surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred and alternative examples of the present invention are described in detail below with reference to the following drawings: 
         FIG. 1  is a block diagram of an exemplary system formed in accordance with an embodiment of the present invention; 
         FIG. 2  is a graphical representation of a state machine, detailing the states of resting and pressing; 
         FIG. 3  is a data flow diagram of exemplary processes performed by the system shown in  FIG. 1 ; 
         FIGS. 4A  and B are plots of waveforms representing the touch signal value in the time domain for various press actions; 
         FIG. 5  illustrates the disruption of an electrical field caused by the capacitance of a lightly touching finger; 
         FIG. 6  illustrates the disruption of an electrical field caused by the capacitance of a finger being pressed strongly into the surface; and 
         FIGS. 7A ,  7 B, and  7 C are waveform plots of a tap selection, a rest, and a press action, all in the time domain. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows a block diagram of an exemplary device  100  for providing a touch interface that can discern between tapping, resting, and pressing. The device  100  includes one or more touch sensors  120  that provide input to a CPU (processor)  110 . The touch sensors  120  notify the processor  110  of contact events when a surface is touched. In one embodiment, the touch sensor(s)  120 , or the processor  110 , include a hardware controller that interprets raw signals produced by the touch sensor(s)  120  and communicates the information to the processor  110 , using a known communication protocol via an available data port. The processor  110  generates an image that is presented on a display  130  (touch surface) or alternatively, the display may be static. The processor  110  is in data communication with a memory  140 , which includes a combination of temporary and/or permanent storage, and both read-only and writable memory (random access memory or RAM), read-only memory (ROM), writable nonvolatile memory, such as FLASH memory, hard drives, floppy disks, and so forth. The memory  140  includes program memory  150  that includes all programs and software such as an operating system  151 , press detection software component  152 , and any other application software programs  153 . The memory  140  also includes data memory  160  that includes System Settings  161 , a record of user options and preferences  162 , and any other data  163  required by any element of the device  100 . 
     The device  100  allows the user to perform at least three interactions on the touch screen: a touch-and-release selection (or a “tap”), a resting action wherein they rest two or more fingers simultaneously on the touch surface, and a pressing action. Being able to distinguish between these three actions significantly improves the flexibility and usefulness of the user interface of the device  100 . For example, the touch surface can be used as a keyboard, allowing the user to rest their fingers on it as they would while touch-typing on a traditional keyboard. 
       FIG. 2  is a state diagram that illustrates how a press state is determined by the processor  110 . The system is initialized in  200  and then enters the idle state  205  where no touch is detected. When a touch signal is detected, the system begins to measure the accumulation of the signal. When the accumulation reaches a pre-defined threshold called the Binary Rest Threshold in  206 , the system proceeds to the Plateau State  210 . In the Plateau State  210 , the user is deemed to be resting their finger(s) on the touch surface. If the user removes their finger(s) from the surface and the Slope Accumulation drops below the Binary Rest Threshold in  211  then the system returns to Idle State  205 . From the Plateau State  210  a user may press their finger harder into the surface causing the Slope Accumulation to continue to increase past a pre-defined Positive Press Threshold  212 , upon which the system proceeds to the Positive Press Detect State  215  and asserts a press action. As long as the user maintains the pressure while in the Positive Press Detect State  215 , the system maintains the press assertion (similar to holding down a key on a traditional keyboard). Once in the Positive Press Detect State  215 , the user may lift their finger(s) from the surface causing the Slope Accumulation to decrease below the Binary Rest Threshold in  217  and the system returns once again to the Idle State  205 . However, while in the Positive Press Detect State  215 , the user may reduce the pressure of the pressing action without completely removing their finger. In this case, a negative inflection point occurs where the touch signal decreases to a point and then either levels out or begins to increase again (ie. where the slope of the touch signal curve is zero as it passes from negative to positive). When a negative inflection point is detected the system determines if the Slope Accumulation has decreased below a Negative Press Threshold point in  216 , at which point the system advances to the Negative Press Detect State  220  and the press action is released. Note that the Negative Press Detect State  220  is similar to the Plateau State  210  in that the user is deemed to be resting. However, the absolute value of the touch signal may be quite different between the two states. When in the Negative Press Detect State  220  the system watches for a maximum inflection point (where the slope of the curve is zero as it passes from positive to negative). When a max inflection point takes place and the Slope Accumulation exceeds the Positive Press Threshold in  221 , the system returns to the Positive Press Detect State  215  and asserts a press action. Alternatively, while in the Negative Press Detect State  220 , if the Slope signal falls below the Binary Rest Threshold in  222  then the user is deemed to have lifted their finger off the surface and the system returns to the Idle State  205 . 
       FIG. 3  is a data flow diagram that shows how the CPU  110  measures, stores, and analyzes the touch signal. In block  300  the system acquires the raw sensor data from an analog to digital convertor (ADC). The signal is then passed through a low-pass filter in block  305  in order to smooth out any high frequency noise that may be present in the signal. The result is then stored in a Cache (2) in block  310 . The slope of the signal is then analyzed in block  315 , followed by detection of the minimum and maximum inflection points of the signal in block  320 . In block  325  the system accumulates the slope changes and stores the result in Cache (1) in block  330 . This calculation determines the amplitude difference between the min and max inflection points. In block  335 , the rate of change of the signal is determined and stored in Cache (1) in block  340 . The rate of change of the signal is helpful in determining the difference between a tap selection, a resting set-down action, and a press (as illustrated in  FIGS. 7A ,  7 B, and  7 C. In block  345  of  FIG. 3 , the system determines the current press state. 
       FIGS. 4A and 4B  are representations of the touch signal going through a number of conditions resulting in press actions being issued by the system. In  FIG. 4A  the system follows a very simple process of using fixed threshold values to determine the different between a resting action and a press. The user touches the surface at  4000  causing the touch signal to rise above the pre-defined Rest Threshold  4050 , as which point the signal levels off at  4010  causing an inflection point and putting the system into the Plateau State  210 . Some time later, the user presses harder on the surface causing the touch signal to increase above the Press Threshold  4055  to a local maxima value at  4020  at which point the system asserts a press action (indicated by the black circle). The system continues looking for maxima and minima inflection points. The inflection points found at  4025  and  4030  are ignored since they occur above the Press Threshold, meaning the press asserted at  4020  continues to be asserted. At  4035  the system detects a minima inflection point that falls above the Rest Threshold  4050  and below the Press Threshold  4055  at which point it asserts a press release action (indicated by the hollow circle). The user then presses again causing the touch signal to increase past the Press Threshold. The system detects the maxima inflection point at  4040  and assets another press action. The user then completely lets go, causing the touch signal to fall back to zero. Although no inflection point is detected, at  4045  the system recognizes that the touch signal has fallen below the Rest Threshold  4050  and assets a press release action. 
     The method described in the above paragraph associated with  FIG. 4A  is straight-forward, but fails to discern the possible press action that takes place between  4025  and  4030 . When a user performs multiple presses in quick succession, the touch signal often remains above the Press Threshold even on the press release action. In order to remedy this short-coming an embodiment is illustrated in  FIG. 4B . 
     Referring to  FIG. 4B , the user touches the surface at  4100  causing the touch signal to rise above a pre-defined Rest Threshold  4150 , at which point the signal levels off at  4110  causing an inflection point which the system discerns as a Rest assertion and places the state machine into the Plateau State  210 . Some time later, the user presses harder on the surface causing the touch signal to increase to a local maximum value at  4120 . The relative change in the signal from  4110  to  4120  is compared with another threshold called the Press Assertion Delta Threshold. If the increase in signal between  4110  and  4120  is greater than the Press Assertion Delta Threshold then a press action is asserted by the system at  4120  (indicated by the solid black circle). Following this assertion, the user decreases the touch pressure between  4120  and  4125  but then once again increases the pressure between  4125  and  4130 . At  325 , the system detects a minimum inflection point and measures the change in the touch signal between  4120  and  4125  which is then compared with yet another threshold called the Press Release Delta Threshold. If the absolute value of the decrease in the touch signal between  4120  and  4125  is greater than the Press Release Delta Threshold then a release action is asserted by the system (indicated by the hollow circle). A similar process takes place between  4130 ,  4135 , and  4140  only with different amplitudes and rate of change in the signal. Finally, the user stops pressing at  4140  but keeps their finger in contact with the surface in a resting action at  4145 , at which point the system asserts a press release action. After some amount of time, the user then removes their finger from the touch surface and the signal quickly falls to zero. As the signal decreases through the Rest Threshold the system asserts a Rest release action at  4150 . 
     In one embodiment the two methods described in  FIG. 4A  and  FIG. 4B  may be selectively combined. 
       FIG. 5  illustrates one of many possible embodiments in how a touch-sensitive surface can be implemented using capacitance. A touch-sensitive surface  500  is made up of one or more sensors in which an electrode  510  emits an electrical signal forming an electrical field  530 ,  540 , and  570 . An adjacent electrode  520  couples with a portion of the formed electrical field  570 . The coupled signal at the adjacent electrode  520  is detected and measured by the system. As a human finger  550  touches the surface  500 , a portion of the electrical field  540  couples with the finger, resulting in less of the electrical field  570  coupling with the second electrode  520 . The processor  110  receives a digital representation of the analog voltage measurement obtained from the second electrode  520  then detects the change of the signal at the second electrode  520  and determines a touch has taken place. The degree to which the electrical field  540  couples with the human finger  550  is dependent, in part, on the amount of surface area  560  with which the finger comes in contact. A “light” touch is shown in  FIG. 5  where the finger  550  is just making contact with the touch surface  500 . A relatively lower amount of the electrical field  540  is disrupted by the light touch. 
       FIG. 6  illustrates the effects of a stronger press on the touch capacitance signals. A touch-sensitive surface  600  is made up of one or more sensors in which an electrode  610  emits an electrical signal forming an electrical field  630 ,  640 , and  670 . An adjacent electrode  620  couples with a portion of the formed electrical field  670 . The coupled signal at the adjacent electrode  620  is detected and measured by the system. As a human finger  650  presses hard on the surface  600 , a relatively larger portion of the electrical field  640  couples with the finger, resulting in less of the electrical field  670  coupling with the second electrode  620 . The processor  110  receives a digital representation of the analog voltage measurement obtained from the second electrode  620  then detects the change of the signal at the second electrode  620  and determines a press has taken place. The degree to which the electrical field  640  couples with the human finger  650  is dependent, in part, on the amount of surface area  660  with which the finger comes in contact. A “heavy” touch, or press, is shown in  FIG. 6  where the finger  650  makes strong contact with the touch surface  600  causing the finger to flatten out at  660 . A relatively larger amount of the electrical field  640  is disrupted by the pressing action. 
       FIGS. 7A ,  7 B, and  7 C illustrate the three actions of a tap selection, a resting set-down action, and a set-down press action respectively. Both the amplitude of the touch signal and the slope of the leading edge of the signal are used to determine which action is being initiated by the user. In  FIG. 7A  the user quickly taps on a key causing the signal to exceed a pre-defined first threshold indicating a valid touch has taken place. The rising slope of the signal is steep, as is the falling edge, and it peaks between the First Threshold and the Second Threshold (the conditions for a “tap” selection).  FIG. 7B  illustrates the signal that meets the conditions for a resting set-down action. In this case, the rising edge of the touch signal is relatively slow (as compared to a tap signal) and the amplitude of the signal stabilizes between the First and Second Thresholds.  FIG. 7C  illustrates the signal that meets the conditions for a set-down press action. In this case, the rising edge of the touch signal is relatively slow as compared to the tap signal, but similar in slope to the rising edge of a rest set-down action. However, the amplitude of the signal continues beyond the Second Threshold indicating the user has pressed harder than a normal touch. The slower rise time, but higher amplitude indicates a set-down pressing action has taken place. 
     Being able to distinguish between a tap selection, a set-down resting action, and a pressing action is critical in allowing the user to rest their fingers on a touch surface. Further, using the same sensors to detect all three actions has the advantages of keeping the cost of the system relatively lower and simpler. 
     While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.