Patent Application
20090322701
This invention relates generally to touchscreen systems and more particularly to resistive touchscreen systems.
Resistive touchscreens are used for many applications, including small hand-held applications such as mobile phones and personal digital assistants. Unfortunately, when a user touches the resistive touchscreen with two fingers simultaneously, creating two touches or dual touch, the specific locations of two touches cannot be determined. Instead, the system reports a single point somewhere on the line segment between the two touches as the selected point, which is misleading if the touch system cannot reliably distinguish between single-touch and multiple-touch states.
However, the detection and use of two simultaneous touches is desirable. A user may wish to interact with data being displayed, such as graphics and photos, or with programs such as when playing music. The ability to use two simultaneous touches would increase the interactive capability the user has with the resistive touchscreen system.
Therefore, a need exists for the detection of two simultaneous touches on a resistive touchscreen.
In one embodiment, a resistive touchscreen system comprises a substrate having a first conductive coating that has a first resistance and a coversheet having a second conductive coating that has a second resistance. The substrate and coversheet are positioned proximate each other such that the first conductive coating faces the second conductive coating. The substrate and coversheet are electrically disconnected with respect to each other in the absence of a touch. A first set of electrodes for establishing voltage gradients in a first direction are formed on the substrate and a second set of electrodes for establishing voltage gradients in a second direction are formed on the coversheet. A controller is configured to bias the first and second sets of electrodes in two different cycles. The controller senses a bias current associated with at least one of the first resistance and the second resistance. The bias current has a reference value associated with no touch. An increase in the bias current relative to the reference value indicates two simultaneous touches.
In another embodiment, a method for detecting two simultaneous touches on a resistive touchscreen system comprises biasing a resistive touchscreen to generate voltage gradients along a first direction and a second direction. A first bias current associated with the first direction is detected. The first bias current is associated with a non-zero first reference value that is representative of a bias current along the first direction when no touch is present on the resistive touchscreen. A second bias current associated with the second direction is detected. The second bias current is associated with a non-zero second reference value that is representative of a bias current along the second direction when no touch is present on the resistive touchscreen. Two simultaneous touches are determined to be present on the resistive touchscreen when one of the first and second bias currents is greater than the first and second reference values, respectively.
The foregoing summary, as well as the following detailed description of certain embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. To the extent that the figures illustrate diagrams of the functional blocks of various embodiments, the functional blocks are not necessarily indicative of the division between hardware circuitry. Thus, for example, one or more of the functional blocks (e.g., processors or memories) may be implemented in a single piece of hardware (e.g., a general purpose signal processor or random access memory, hard disk, or the like). Similarly, the programs may be stand alone programs, may be incorporated as subroutines in an operating system, may be functions in an installed software package, and the like. It should be understood that the various embodiments are not limited to the arrangements and instrumentality shown in the drawings.
As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property.
First and second conductive coatings 106 and 108 are formed on the two surfaces of the coversheet 102 and substrate 104, respectively, facing the air gap. The first and second conductive coatings 106 and 108 may be transparent and may be formed of materials such as indium tin oxide (ITO), transparent metal film, carbon nanotube containing film, conductive polymer, or other conductive material. At right and left sides (or opposite sides) 130, 132, respectively, of the first conductive coating 106 are provided a first set of electrodes 110 and 112. Similarly, second conductive coating 108 is provided at opposite sides 134, 136 with a second set of electrodes 120 and 122 that are perpendicular with respect to the first set of electrodes 110 and 112. In another embodiment, the first and second sets of electrodes may be positioned at other angles with respect to each other. Each of the first and second conductive coatings 106 and 108 has an associated resistance measured between the electrodes of the respective conductive coating. For example, a resistance associated with the first conductive coating 106 may be measured between the first set of electrodes 110 and 112, and a resistance associated with the second conductive coating 108 may be measured between the second set of electrodes 120 and 122. In one embodiment, the resistances of the first and second conductive coatings 106 and 108 may be in the range of 400 to 600 ohms, depending on the aspect ratio. In another embodiment, different materials and/or different thicknesses of the same or different materials may be used to form the first and second conductive coatings 106 and 108 to achieve different resistance values.
To detect X coordinates associated with one or two touches, first and second voltages from voltage source 114 are applied to electrodes 110 and electrode 112, respectively, thus establishing a voltage gradient across first conductive coating 106 in a first direction 118. One of the voltages may be ground or ground potential. The voltage on first conductive coating 106 at the touch location on a touch sensing area 116 is transmitted to second conductive coating 108 and hence to electrodes 120 and 122. The controller 138 measures the X coordinate by measuring the voltage at either electrode 120 or 122. To detect Y coordinates associated with the one or two touches, third and fourth voltages from voltage source 114 are applied to electrode 120 and electrode 122, respectively, thus establishing a voltage gradient across second conductive coating 108 in a second direction 126. Again, one of the voltages may be ground potential. In addition, the first and second directions 118 and 126 may be formed perpendicular or at other angular positions with respect to each other. The voltage on second conductive coating 108 at the touch location on touch sensing area 124 is transmitted to the first conductive coating 106 and hence to electrodes 110 and 112. The controller 138 measures the Y coordinate by measuring the voltage at either electrode 110 or 112. The touch sensing areas 116 and 124 may be the same with respect to each other. In one embodiment, the voltage sources 114 and 128 may be the same voltage source and in another embodiment the voltage sources 114 and 128 may be different voltage sources. However, the coversheet 102 and the substrate 104 are electrically disconnected with respect to each other in the absence of a touch, and thus there is no hard-wired connection between the coversheet 102 and the substrate 104.
During operation, a controller 138 biases the first set of electrodes 110 and 112 in a first cycle and the second set of electrodes 120 and 122 in a second cycle. A touch causes the coversheet 102 to deflect and contact the substrate 104 thus making a localized electrical connection between the first and second conductive coatings 106 and 108. The controller 138 measures one voltage in one direction in the first cycle and another voltage is measured in the other direction in the second cycle. These two voltages are the raw touch (x,y) coordinate data. Various calibration and correction methods may be applied to identify the actual (X,Y) display location within the touch sensing areas 116 and 124. For example, corrections may be used to correct linear and/or non-linear distortions.
The resistance of the first conductive coating 106 of coversheet 102 and the resistance of the second conductive coating 108 of the substrate 104 do not change when there is no touch and when there is one touch. When two touches are present, however, the resistance of one or both of the first and second conductive coatings 106 and 108 decrease. For example, if two touches are currently deflecting the coversheet 102 to create electrical contact with the substrate 104 in two different touch locations simultaneously, a portion of the conductive coating of the non-biased sheet between the two touches is in parallel with the resistance of the conductive coating of the biased sheet. In other words, when two touches are present, the resistance of one or both of the first and second conductive coatings 106 and 108 of the coversheet 102 and substrate 104, respectively, decreases. Furthermore, as the distance between the two points increases, the resistance decreases.
When the resistance decreases, the current increases. The current flowing between electrodes 110 and 112 and the current flowing between electrodes 120 and 122 may be referred to as “bias currents”, as the currents are induced by a bias voltage to produce voltage gradients for coordinate measurements. In some embodiments, the bias currents change based on the axial separation or distance between the two simultaneous touches. Therefore, by either measuring the change in resistance or the change in bias current, the controller 138 can determine that two touches are present, can identify that the returned coordinates when two touches are present are of a point located on a line between two actual touch coordinates, and also can detect movement of one or both of the touches with respect to the other touch. At least some of the embodiments herein describe systems and methods for measuring the changes in bias currents.
To measure bias current, current sensing resistors 140 and 142 may be placed in series with the voltage detection circuits (i.e. within the controller 138) of each of the coversheet 102 and substrate 104, respectively). The resistors 140 and 142 have a relatively small value so as not to negatively impact the coordinate sensing capability of the controller 138, such as by increasing voltage offsets in the calibration correction. The resistors 140 and 142 may be provided within the controller 138. In one embodiment, the resistors 140 and 142 may each be a traction of the resistances of the associated first and second conductive coatings 106 and 108, such as approximately 10 percent.
During the first cycle, when the controller 138 biases the X direction by placing a voltage across the coversheet 102, the controller 138 may read a voltage drop across the resistor 140, such as at points A and B. The controller 138 may then calculate a bias current Ix based on the voltage drop. When no touch is present and when one touch is present, the bias current Ix is a reference value (as shown in
Therefore, when calculating X and Y coordinate values, the controller 138 may also sense the bias current to determine whether the bias current has changed. An increase in one or both of the bias currents from the reference values may indicate that two touches are detected while a decrease in the bias current back to the reference values may indicate that a single touch or no touch has been detected.
In one embodiment, an A/D converter (not shown), such as within the controller 138, may be used to sense the voltage drop across the resistors 140 and 142. However, the voltage drop across the resistors 140 and 142 may be low compared to the operational range of the A/D converter. Therefore, amplification circuits 144 and 146 may be provided to amplify the voltage drop so that changes in the voltage drop may be more easily determined. The controller 138 may then read the amplified voltage levels at points C and F, for example.
As discussed previously, the position of the two touches with respect to each other impacts the level of bias current. The farther apart the two touches are, the greater the bias current because the resistance decreases as the two touches are moved farther apart. Therefore, if a user is touching the coversheet 102 at points indicated as first and second touches 148 and 150 and moves at least one of the touches 148 and 150 closer to the other, such as by pinching two fingers together, at least one of the X and Y bias currents decreases. Two finger gestures may thus be determined based on bias current values or changes in the bias current values.
The controller (not shown) alternately pulses the X and Y directions as shown, using voltage source 332, and measures the bias current with current meter 334. When a user presses on the coversheet 326 at two different locations, first and second touches 336 and 338 result. The controller senses the change in bias current, such as through the current meter 334 or through current sensing resistors (not shown) or other current or voltage sensing methods and apparatus, and determines that two touches are present.
Turning to the circuit 320, the resistance of the substrate 324 is illustrated as Rsubstrate 340 and is connected on either side to voltage source 342 and current meter 344. Contact resistance between the substrate 324 and the coversheet 326 is illustrated as first and second variable Rcontact 346 and 348. The resistance of the coversheet 326 between the first and second touches 336 and 338 is illustrated as Rcoversheet 350. The length of Rcoversheet 350 depends on the position of the first and second touches 336 and 338 relative to each other.
As contact resistances between the substrate 324 and coversheet 326 increase, such as by decreasing pressure, the resistances of both first and second conductive coatings 106 and 108 also increases. If the pressure of one or both of the first and second touches 336 and 338 varies, resulting in variations of one or both of the bias currents, erroneous detection of gestures may result. In one embodiment, if the conductive coating on the coversheet 326 is formed of a material that is not ITO but rather thin transparent metallic film, the contact resistance (the first and second variable Rcontact 346 and 348) is very small. By reducing the contact resistance, the pressure of the first and second touches 336 and 338 has little or no effect on the detection of gestures.
In other embodiments, to prevent erroneous detection of gestures, the controller 138 may filter out rapid fluctuations in the bias currents that may be due to changes in contact resistance. In another embodiment, the controller 138 may respond based on an overall trend of the bias current, such as over a minimum time period or for the duration of the two finger touch. In yet another embodiment, at least one pressure sensor may be mounted on the substrate 324 to detect changes in an aggregate finger pressure (i.e. pressure at one or more touches). Returning to
For the coversheet 102, a current sensing resistor 160 and a switch 162 are placed between the voltage source 114, which may be within the controller 138, and the coversheet 102. Also, a current sensing resistor 164 and a switch 166 are placed between the voltage source 128 and the substrate 104. It should be understood that the resistor and switch may together be positioned on the other side of the coversheet 102 and substrate 104, and/or may be within the controller 138.
To sense the X coordinate, the controller 138 connects the switch 162 to line 168 and to sense the Y coordinate, the controller 138 connects the switch 166 to line 170. During the third cycle, the controller 138 may alternately connect the switch 162 to line 172 and the switch 166 to line 174. Therefore, during one third cycle, the controller 138 may sense the voltage drop across the resistor 160 and in the next third cycle, the controller 138 may sense the voltage drop across the resistor 164. The controller 138 may determine the bias currents based on the voltage drops as discussed above.
Because the bias current is being sensed during a cycle other than when the X and Y coordinates are being sensed, the values of the resistors 160 and 164 may be larger than the values of the resistors 140 and 142 of
In another embodiment, one or more additional cycle(s) may be added to sense the bias currents. For example, the controller 138 may detect the X and Y coordinates in the first and second cycles, then detect the first and second bias currents in third and fourth cycles. Therefore, a detection frame may have 4 or 5 total cycles. In yet another embodiment, once two touches are detected, the controller 138 may no longer detect the X and Y coordinates and may only detect the first and second bias currents.
In yet another embodiment, a virtual ground may be used as a current sink without losing the ability to measure current. All current through the coversheet 102 and substrate 104 (as shown in
At 202, the controller 138 determines the X and Y coordinates, and at 204 the controller 138 measures the X arid Y bias currents Ix and Iy as discussed above. Therefore, 202 and 204 may be accomplished during the same or different cycles. At 206 the controller 138 compares the bias currents Ix and Iy to the reference values IX Ref and IY Ref, respectively. If neither of the bias currents Ix and Iy is greater than the respective reference value IX Ref and IY Ref, a single touch or no touch has been detected and the method passes to 208. The controller 138 may then report the X and Y coordinates to the operating system (not shown) of the touchscreen system 100. The controller 138 may also save the X and Y coordinates as a first coordinate (X1,Y1). However, if no coordinates were detected, then no coordinates are reported or stored and the first coordinate (X1,Y1) may be cleared. If the single set of X and Y coordinates is detected, the controller 138 may clear or zero the contents of a second coordinate (X2,Y2). The second coordinate (X2,Y2) may have been generated during a previous detection of two simultaneous touches but is no longer valid. The second coordinate (X2,Y2) is further discussed below.
Returning to 206, if either of the bias currents Ix and Iy is greater than the respective reference value IX Ref and IY Ref, two touches have been detected. It should be noted that if both of the touches are anywhere along a voltage line of equipotential in one of the X and Y directions, the bias current will not increase in that direction. At 210 the controller 138 determines whether the currently detected X and Y coordinates were detected in a detection cycle immediately following the detection of (X1,Y1). A lapse in time has occurred if the currently detected X and Y coordinates are not detected immediately after (X1,Y1), indicating that the previously stored coordinate (X1,Y1) may not correlate to a current touch. Therefore, the touchscreen system 100 has detected two new touches within the same detection cycle and the method passes to 212. Because there are two touches, the currently detected X and Y coordinates are of a point (X,Y) located along a line between the actual touches. At 212 further processing may be accomplished to attempt to determine the actual locations of the two touches, however, in some embodiments the coordinates of the two touches may not be resolved. In one embodiment, the controller 138 may use the coordinates of the point (X,Y) in applications as discussed below that may not require the identification of the particular coordinates. In other embodiments, an error may be generated or the controller 138 may ignore the input, returning to 202 to continue to detect X and Y coordinates.
Returning to 210, if the controller 138 determines that the currently detected X and Y coordinates (X,Y) were detected in a detection cycle immediately following the detection of (X1,Y1), indicating that (X1,Y1) is still a valid coordinate, the method passes to 214 where the controller 138 may determine if values are stored in (X2,Y2). If yes, in 216 further processing, such as gesture recognition as discussed below in
The gestures discussed in
Turning to
At 232, the controller 138 determines whether at least one of the bias currents Ix and Iy is increasing over time while neither is decreasing over time. If yes, this indicates that the two touches are moving away from each other and the method passes to 234. The controller 138 may report a zoom-in gesture to the operating system. In response the operating system may perform a zoom-in operation based on information, characters, pictures and the like that are currently displayed beneath the touchscreen system 100 corresponding to the centroid coordinates (Xcentroid,Ycentroid) and/or the first and second coordinates (X1,Y1) and (X2,Y2). As discussed previously, the gesture associated with the increasing bias current(s) may be a gesture other than zoom-in. Also, the application associated with the information on the touchscreen that correlates to the coordinates may determine the gesture response.
Returning to
Returning to
If the response at 240 is no, the method passes to 246 where the controller 138 determines whether one of the bias currents Ix and Iy is increasing over time while the other is decreasing over time. If yes, the gesture may be a rotate gesture and the method passes to
Due to the sinusoidal nature of the changes in the X and Y separation distances when making the rotate gesture, opposing changes in the bias currents can occur even when the distance between the two touches remains the same. Therefore, during a rotation the controller 138 may detect an increase in the bias current Ix and a decrease in the bias current Iy. As the rotation continues, or during a different rotation, the controller 138 may detect an increase in the bias current Iy and a decrease in the bias current Ix. The change in bias current may be within a predetermined percentage or range, or may be tracked over a predetermined period of time to determine that the rotate gesture is being indicated. If yes, this indicates that the two touches are rotating with respect to each other.
Some ambiguity exists for determining whether the rotation is in the clockwise (CW) or counter-clockwise (CCW) direction.
Turning to
At 402, the controller 138 determines whether the first and second touches 440 and 446 are in the second and fourth quadrants 434 and 438. If yes, the method passes to 404, where the controller 138 determines whether the bias current Ix is increasing and the bias current Iy is decreasing. If yes, the method passes to 406 where a CCW rotate gesture is reported to the operating system. The amount of rotation may be dependent on the application. For example, if the application is displaying photos, the amount of rotation may be 90 degrees in the selected direction. Other applications may use smaller or larger amounts of rotation.
Returning to 404, if the response is no, the method passes to 408 where the controller 138 determines whether the bias current Ix is decreasing and the bias current Iy is increasing. If yes, the method passes to 410 where a CW rotate gesture is reported to the operating system.
Returning to 402, if the first and second touches 440 and 446 are in the first and third quadrants 432 and 436, the method passes to 412 where the controller 138 determines whether the bias current Ix is decreasing and the bias current Iy is increasing. If yes, the method passes to 406 and a CCW rotate gesture is reported to the operating system. At 414, the controller 138 determines if the bias current Ix is increasing and the bias current Iy is decreasing. If yes, the method passes to 410 and a CW rotate gesture is reported to the operating system.
Zoom-out signal traces 364 and 366 are indicated during time duration 460. The controller 138 may detect a start time 370 of the two-finger state, a time of a signal maximum 372 and 374 for each of the signal traces 364 and 366, and an end time 376 of the two-finger state when at least one of the bias currents returns to below the threshold levels 368 and 369. Therefore, for the zoom-out signal traces 364 and 366, a signature of signal timing is that the time difference between each of the signal maximums 372 and 374 and the start time 370 is less than the time difference between the signal maximums 372 and 374 and the end time 376. For zoom-in signal traces 378 and 380 indicated during tune duration 462, signal maximums 382 and 384 are closer to end time 386 than start time 388. For rotate signal traces 394 and 396 indicated during time duration 464, one signal maximum 398 is closer to start time 388 while the other signal maximum 399 is closer to the end time (not shown).
The controller 138 may determine the gesture based on signal profiles of the X and Y signal traces. For example, the controller 138 may detect the start and end times of the two-finger state. The controller 138 may then compare the X and Y signal traces to predetermined profiles that represent different gestures. Alternatively, the controller 138 may analyze the X and Y signal traces, such as to determine a time relationship between the signal maximum and each of the start and end times.
The dual touch sensing and gesture recognition discussed herein is applicable to resistive touchscreens other than 4-wire. In each of the configurations of 3-, 4-, 5-, 7-, 8-, and 9-wire touchscreens, the bias currents IX and IY through the drive lines increase when two touches are simultaneously present. The 4-wire touchscreen of
The coversheet is provided with one wire (not shown) for connection to voltage sensing circuitry of a controller (not shown). In a 5-wire touchscreen, in addition to the wire to the coversheet, four wires 292, 296, 298 and 294 connect the controller to corner electrical interconnection points 1283, 1285, 1297 and 1289 respectively. In a 9-wire touchscreen, wires 300, 304, 306 and 302 also connect the controller to corner interconnection points 1283, 1285, 1287 and 1289, respectively, so as to provide separate drive and sense lines to each corner. However, these extra four wires are not present in the 5-wire touchscreen. During X coordinate measurement, a bias voltage is applied between the pair of right corner interconnection points 1285 and 1287 and the pair of left corner interconnection points 1283 and 1289. A voltage, for example 3.3 Volts, applied to the right pair of corner interconnection points 1285 and 1287 is transmitted via electrode structure 288 to the right side of the conductive coating. Similarly, a voltage, say 0 Volts, applied to the left pair of corner interconnection points 1283 and 1289 is transmitted via electrode structure 190 to the left side of the conductive coating. Such an X bias voltage (difference) between the right and left sides induces a voltage gradient in the conductive coating. Associated with this X bias voltage is a corresponding X bias current IX and hence, via Ohm's Law, an X bias load resistance. Similarly when a Y coordinate is being measured there is an Y bias voltage applied between the pair of corner interconnection points 1283 and 1285 and the pair of corner interconnection points 1287 and 1289, resulting in Y bias current IY and corresponding Y bias load resistance.
The 3-wire touchscreen is similar to the 5-wire touchscreen. In a 3-wire touchscreen, one wire connects to the coversheet and only two wires connect to the substrate 282 shown in
It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. While the dimensions and types of materials described herein are intended to define the parameters of the invention, they are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third.” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. §112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure.
