Abstract:
A resistive touch screen controller provides two-finger gesture recognition. Current mirror circuitry, coupled to the XP/XN and YP/YN conductors, generates a screen current IL corresponding to X/y plate currents, and a corresponding mirror current IL/N. A variable resistor receives mirror current IL/N, and a resistance controller sets the resistance value R 1  of the variable resistor, and monitors a variable resistor voltage VR 1  based on IL/N*R 1 . A processor determines calibration voltages for the X and Y plates corresponding to the mirror current IL/N for X/Y voltage values of VR 1  for a no touch condition, and X/Y offset voltages VOFS and HOFS of VR 1  for a two touch condition. For a two touch condition, the processor determines touch resistance relative to no touch, and generates an adjusted X/Y plate resistance ΔX/ΔY based on VOFS/HOFS, and based on X/Y, determines a distance and angle between the two touches.

Description:
PRIORITY 
     This Application claims priority to U.S. Provisional Application No. 61/663,888, filed Jun. 25, 2012, entitled “Dual Touch Gesture That It is Substantially Simultaneous”, which is incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This Application is directed, in general, to recognition of a touch gestures and, more specifically, to recognition of touch gestures on a flexible resistive screen. 
     BACKGROUND 
     Touch screen controllers (“TSC”) are used in a multitude of commercial products, such as “smart” mobile phones, and can also be found in iPhones® or iPads®. TSC can be used either on resistive touch screens or capacitive touch screens. Capacitive TSCs can generate such information as multi-finger placement on a touch screen. However, capacitive touch screens can also be prohibitively expensive. Therefore, resistive touch screens are sometimes used as a less-expensive alternative. 
     U.S. Patent Publication No. 2010/0277417 A1 to Sarasmo, entitled “Resistive Touch Screen Apparatus, A Method and a Computer Program” is one example of a prior art multi-touch resistive touch screen. 
     FIGS.  1 Ai- 1 Aii illustrate the Sarasamo resistive TSC approach. F Referring to FIG.  1 Ai, a voltage (“V 1 ”) is measured across an internal reference resistance  120 , as a function of a voltage division between a sensor resistor  110  and the internal reference resistance  120 . The prior art TSC recognizes that, for a certain reference voltage V 1 , a “no touch situation” is indicated, as the voltage V 1  is measured as being at a given threshold. 
     In FIG.  1 Aii, in an event of a “single touch”, the sensor resistor  110  is bisected or “split” into a first sensor resistor  112  and second sensor resistor  114 , and a contact is made at a bottom resistor plate, and the bottom resistor plate is “split” into a first bottom resistor  122  and a second bottom resistor  124 . A measurement of voltage V 1  is then made over reference resistor  120 ; this voltage would typically decrease. This decrease in the voltage V 1  measured at the reference resistor indicates a “single touch.” An amplitude of the reference voltage position of the “single touch” can be used to determine a position of a “single touch.” 
     In FIG.  1 Aiii, in an event of a “dual touch”, a second part of a resistive screen is touched, represented by a second resistive bisection with a top sensor resistor  132  and  134 , and a bottom sensor resistor  142  and  144 . This again further lowers a voltage measured across internal sense resistor  120  indicating a “dual touch.” Moreover, the voltage measured at the internal reference voltage  120  can indicates a position and orientation of the “dual touch”. 
     The above can be better appreciated in  FIG. 1B , an illustration of a prior art method  150  for determining finger positioning. 
     In  FIG. 1B , in a step  160 , it is determined whether the reference voltage is above a first, higher threshold (“T 2 ”). If it is, in a step  165 , it is determined that no touch has occurred, and the method  150  stops. 
     In a step  170 , it is determined whether the voltage is above a second, lower threshold (“T 2 ”). If it is, in a step  175 , it is determined that a “single touch” has occurred, and the reference voltage, and the voltages across the first bottom resistor  122  and the second bottom resistor  124  are measured, and the method  150  stops. 
     Alternatively, in a step  180 , it is then determined that a dual touch has occurred, and the reference voltage, and voltages v 2  and v 3 , which are used for distance of the two fingers input and the orientation of the fingers, are measured. 
       FIG. 1C  illustrates various relationships representing dual finger position and orientation. 
     In  FIG. 2A , a current is measured between a V cc  and a ground for a prior art single touch. However, as is illustrated, characteristics of the bottom plate are not measured only a current through the top plate. For purposes of explanation, a single touch does not affect a measured current. 
     However, in  FIG. 2B , two fingers are used, with two different contact positions, and resistor R 2  is in series with resistors R 3 , thereby increasing current, as a parallel current path through R 2  in series with R 3  in parallel to R 1  has been created as used in a prior art dual touch circuit. 
       FIG. 3A  illustrates prior art calculations that can be made regarding location of two fingers. 
       FIG. 3B  illustrates that for a single touch, a current magnitude of “I”, such as through R 2 , is constant and does not change. For a dual touch, however, current magnitude “I” through R 2  is in proportion to a distance between two fingers, but not in proportion to the absolute position of the two fingers. 
       FIGS. 4A and 4B  illustrate a prior art circuit  400  for measuring an x position that combines both a single touch measurement and a dual motion measurement of a dual touch. In the circuit  400 , a voltage is measured across a sense resistor, such as Rx 2 , to determine an x position of a single touch. Please note that if the current through the resistor Rx 2  is below a given threshold, the touch is deemed a dual touch, and a different analysis applies. For a single finger, this lowers voltage across resistor Rx 2 . 
     In  FIGS. 4A and 4B , coordinates of a single touch is measured by divided resisters of X/Y plate. In other words, where there is a single touch, Rx 1  and RX 2  are divided. These resistances are measured, and a ratio is generated. A distance between two touches is also measured by resistors of X/Y plate, although these resistors themselves change value. 
     Rx 1  and Rx 2  represent a flexible top plate that is touchable, and Ry 1  and Ry 2  represent a bottom plate. Moreover, these Rx and Ry resistors are oriented in a perpendicular orientation. 
     In other words, when there are two touches, the values of each of the resistances change, as well as the ratios between the resistances (due to perpendicular orientation). The distance between two touches is calculated based on a difference between a no touch resistance and two touch resistance for these values. In  FIGS. 4A and 4B , R c  represents the resistance that is created when part of a circuit is shorted, as is illustrated in  FIG. 3B . 
     However, there are certain drawbacks associated with the above prior art. For example, it can be expensive and cumbersome to have additional, external circuitry for the two finger measurement in a resistive prior art TSC, such as Sarasmo. 
     Therefore, there is a need for an improved approach to dual gesture recognition. 
     SUMMARY 
     A first aspect provides an apparatus, comprising: a plurality of resistive screen being an upper screen and a lower screen; a configurable resistor coupled to the plurality resitive screens, and a processor coupled to the resistive screens and the resistor, the processor configured to set a resitive value of the resistor as a function of a measured current on the resistive screens through comparing: no touch; single touch; and dual touch. The processor further configured to determine a position of two touches on a screen; and the processor further configured to determine a change of position of at least one of the two fingers, the processor employs a deriviative of the change of current on at least one of the plates over time to determine a characteristic of a change of position. 
     The apparatus may further comprise at least one of (a) a current mirror coupled to said processor to measure a change of current through said touch screen, (b) an input output device coupled to a bus, the bus also coupled to both the current mirror and the resistor, wherein the processor further configured to calculate an absolute position of a single finger on the touch screens, and (c) setting the resistor at a higher resistance if a single touch is determined than if a dual touch is determined. 
     A second aspect provides a method, comprising: measuring a current on a top and bottom touch screen, wherein the top touch screen is not being touched; measuring a current on a top and bottom touch screen, wherein the top touch screen is being touched by one finger; measuring a current on a top and bottom touch screen, wherein the top touch screen is being touched by two fingers; calculating a one and a two finger threshold on the touch screens, wherein, if the touch is a two finger touch: calculating an orientation of the two finger touch; and calculating a change of position of at least one finger of the two finger touch, wherein the calculating employs a deriviative of the change of current on at lest one of the plates over time to determine a characteristic of a change of position. 
     The second aspect may further include calculating the change of position of the two fingers through a slope of a change from a previous position of the two fingers, and wherein the change of positions is selected from the group consisting of: an expansion of the two fingers, a pinching of the two fingers, and a rotation of the two fingers, wherein the position of the two fingers includes an angle between the two fingers, wherein the distance between the two fingers is calculated through a measurement of the change of resistance between the two parallel plates. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS.  1 Ai- 1 Aiii illustrate a prior art resistive TSC. 
         FIG. 1B  illustrates a prior art method of determining finger positions in the prior art resistive TSC. 
         FIG. 1C  is an illustration of calculation factors for finger positions in the prior art resistive TSC. 
         FIGS. 2A and 2B  are an example of prior art single and dual-touch on a four-wire resistive touch panel. 
         FIGS. 3A-3B  illustrate prior art calculations that are made with regard to a prior art dual placement  FIGS. 4A-4B  illustrate prior art equivalent circuits for location of dual position of two coordinates, which can then be differentiated to determine gesture significance. 
         FIG. 5  illustrates a dual gesture motion example. 
         FIGS. 6A and 6B  illustrate equivalent circuits that determines both a position and a vector of a dual touch gesture. 
         FIG. 6C  illustrates an example functional embodiment of a circuit used to determine a touch and a direction of a touch. 
         FIG. 7  illustrates a method of calibration and use for a touch and gesture detection circuit of  FIG. 6 . 
         FIG. 8  illustrates a method of a step of a measurement mode of  FIG. 7 . 
         FIG. 9  illustrates a method of a step of dual touch processing of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     Generally, for a resistive Touch Screen Controller (TSC), which employ dual sets of coordinates to determine a simultaneous two finger touch, the present inventors have recognized that, if one is willing to forego a determination of absolute dual finger position on a resistive TSC, but instead employ information that is related to both the distance between the fingers and the motion of at least one of those fingers, a significant simplification of circuitry can be achieved in recognizing motion of dual touch on a screen, according to the principles of the present Disclosure. 
     The inventors have also recognized that by utilizing only information from a top plate, and disregarding information from a bottom plate, that a differential of the measured current “I” can be used, wherein the differential of the measured current “I” is a function of a change of distances of the two finger contacts. Recognition of the usefulness of employment of this differential allows a gesture recognition. 
       FIG. 5  illustrates a motion of a dual gesture that can be interpreted by a resistive touch screen of the present Disclosure. As is illustrated, there can be a two finger expansion and a two finger pinch. As understood by the present inventors, a current that is made when at least one touch is moved in relation to another creates a differential of the current. This differential of current can then be measured and used to calculate a dual touch gesture, as will be described in connection with  FIGS. 6-9 . 
       FIGS. 6A-6B  illustrate an equivalent circuit  600  for measuring either one finger position ( FIG. 6A ) or, a two finger position and motion ( FIG. 6B ). 
     For one finger touch, the current is greater than a two two finger touch. Therefore, if the current is above a certain level, a one finger touch has been determined, and position and gesture motions occur at that point. However, if the current drops below the two finger threshold, then a two finger touch is detected, with the key parameter being current loss. Once two finger touch is determined, the distance and movement are determined and used to interpolate gestures. 
     The equivalent circuit in  FIG. 6B  can be used to determine if either a single touch has occurred if a first current sensor determines that the current is above the first threshold, or determine that a dual touch has occurred if the first current sensor determines that the current is below the first threshold and the second current determines that the current is above the second threshold. If it is determined that a dual touch has occurred, a differential of the current is used to determine at least one direction of motion of at least one member of the dual touch. That is, if I 1  is greater than I 2 A+I 2 B, then there is a single touch. 
       FIG. 6C  illustrates an equivalent circuit for implementing a single or dual according to this Disclosure. 
     As is illustrated, a CPU  617  and an input/output/display device  618  are coupled to a bus  650 . The bus  650  is coupled to a resistance touch screen controller  640  (RTSC_MR) which controls current mirror  634 . The bus  650  is coupled to a variable resistance controller (RTSC_R 1 )  642 . The RTSC_R 1  (resistance controller)  642  is coupled to a variable resistor  636 . Coupled between the current mirror  634  and the variable resistor  636  is a capacitor  638 . Current mirror  634  is coupled through various NMOSs to the touch screen  610 . 
     The circuit can work as follows. The current mirror is monitored by the RTSC_MR  640 . This information is passed to the CPU  617 . The CPU  617  then determines if a one finger touch or a two finger touch has occurred. If a two finger touch, resistor R 1  is set to a lower value than for a two finger touch, by RTSC_R 1   642 , such as 1K ohms versus  10   k  ohms. 
     If the touch is a one touch, then the RTSC_MR  640  monitors the current, and based upon characteristics of the current, determines the motion of a finger, as will be discussed below. 
       FIG. 7A  illustrates a calibration method  700  for a gesture detection circuit, such as that of  FIG. 6 . 
     In a step  710 , the method  700  enters a panel calibration mode. Measurements of the x and y current are made with no touches occurring. 
     Step  710  advances to a step  715  and  720  in parallel, wherein  720  is a two finger calibration mode. Here, the two finger threshold current is calculated. This can be at a preset distance, such as one centimeter. 
     In a step  720 , the two finger position calculation is performed to determine a value of offset voltages VOFS and HOFS, which are the differences between the x and y offset coordinate of the two fingers. The absolute value of measurement is taken of the resistances by comparing values off of the X and Y plates. A determination of a two finger touch condition can be found by using the lookup calibration table  715 . 
     In a step  730 , a measurement mode is entered into. This measures the currents on the X and Y plates. 
     In a step  740 , resistance is measured in relation to the two finger threshold. The step  740  determines if the resistance is less than the two finger threshold. If not, then it advances to a step for dual touch processing  745 . If it is less than for a two finger threshold, then the method advances to a step  750  for one finger touch processing. 
     In step  745 , the x/y coordinates of a one finger touch are reported, which will later on include gesture recognition. In step  750 , dual touch processing occurs for the stationary finger positions. 
       FIG. 8  correlates to  FIG. 7 , step  730 , in which measurement mode determines that dual touch condition has occurred. 
     In a step  810 , a position in the X plate is measured by using a reference voltage over a total voltage. There VMR of current mirror  634  and the voltage of the bottom panel of display  610  is used to create a current mirror. In this step, a VMR mirror current ratio  634  is generated based on this current. A current flows from current mirror  634  through capacitor  638  to ground, and from current mirror  634  through variable resistor  636  to ground. An MR signal, along with a value of the selectable resistor  636 , is determined by dividing the one current into the other (i.e., from bottom layer of  610  to ground, and between capacitor  638  to ground, 
     In a step  820 , a position in the Y plate is measured analogously. 
     In a step  830 , a calculation of a change of resistance in the x plate is made. In this step, the current measurement minus “no touch measurement”, is change of resistance. 
     In a step  840 , a calculation of a change of resistance in the y plate minus the initial “no touch measurement” for yΔ, is change of resistance. 
     In a steps  850  and  860 , an adjustment of a change in resistance of X/Y plates are made based on the offset voltages VOFS/HOFS. In other words, determining the absolute position of each finger, not just relative to each other. 
     In a step  870 , a calculation of distance of two fingers occurs. This calculation of the distance the change of resistivity measured in the X and Y plate between initial measurement, and with both fingers on the touch plates. 
     In a step  880 , the angle of orientation of two fingers is calculated. 
     In  FIG. 9 , correlates to  FIG. 7 , step  745750  for of dual touch processing. In step of  955 , a previous measurement of x and y resistances, determined from X and Y plate currents ( FIG. 7 , step  740 ), are compared to a present resistance on the X and Y plates. In one embodiment, the processor employs a deriviative of the change of current on at lest one of the plates over time to determine a characteristic of the position. 
     In a step  960 , it is determined if a change has occurred between a resistance value, but no change in the calculated angle. If yes, step  960  advances to a step  970 . If not the method step  960  advances to a step  965 . The change of resistance can be positive for an expanding position in the relation of the x and y directions. The slope of this change is the percentage change. Moreover, the x and y measurements are compared to each other to determine direction. 
     In a step  965 , it is determined if a change has occurred between a resistance value, but no change has occurred in the calculated angle. This is done by comparing the x and y coordinates, and changes in values of x and y coordinates. If true, step  965  advances to a step  980 . If false the step  965  advances to a step  985 . 
     In a step  970 , it is determined whether a gesture is an expansion or a pinch. 
     In a step  980 , it is determined whether a two finger rotation has occurred. 
     In a step  985 , it is determined whether one or more other gestures have occurred. 
     In a step  990 , a gesture, two-finger distance, and orientation are reported) through the I/O device  618  in  FIG. 6 ) based on measurements from the previous steps  960 ,  965 ,  970 ,  980 ,  985 . 
     U.S. Patent Publication No. 2010/0277417 A1 to Sarasmo, entitled “Resistive Touch Screen Apparatus, A Method and a Computer Program” (“Sarasmo,”) is hereby incorporated by reference in its entirety. 
     Those skilled in the art to which this application relates will appreciate that other and further additions, deletions, substitutions and modifications may be made to the described embodiments.