This patent application is assigned to
The following quote was obtained by the news editors from the background information supplied by the inventors: "Capacitive touch panel devices are widely used to allow user interaction with electronic devices. In particular, a transparent touch panel can be used on top of a display device to allow a user to interact with the electronic device via a graphical user interface presented on the display device. Such touch panels are used in for example mobile phones, tablet computers, and other portable devices.
"A known touch panel for use with such devices comprises a glass plate provided with a first electrode comprising a plurality of first sensing elements on one face of the glass plate, and a second electrode on an opposite face of the glass plate. The core operating principle is that the touch panel is provided with means for determining (changes in) the capacity between any of the first sensing elements of the first electrode and the second electrode. Such change in capacitance is attributed to a touch event, sometimes also called a gesture or touch gesture. By determining the location of the sensing element where the change in capacitance is maximized, the central location of the touch event is determined.
"In coplanar touch panels the sensors are located in one single (Indium Tin Oxide, ITO) layer and each sensor has its own sense circuitry. Coplanar touch technology uses differential capacitance measurements in combination with a coplanar touch sensor panel. The sense circuit measures the charge that is required to load the intrinsic capacitance of each individual sensor and in addition (if applicable) the finger-touch-capacitance for those sensors that are covered/activated by the touch event. The intrinsic capacitance of the sensor depends on the sensor area, distance to a reference (voltage) layer and the dielectric constant of the materials between sensor and this reference layer. Assuming that the intrinsic capacitance is stable and constant over time, this is accounted for during the tuning/calibration procedure. The variation of sensor capacitance due to a touch event will then be the discriminating factor revealing where the touch is located.
"The accuracy performance of a touch panel is the most important characteristic of the functionality of a touch panel as it shows the capability of recognizing a touch event on the same location as the actual spot location of the physical touch. Next to this, a high accuracy will improve the ability of determining the shape and size of the touch event. Moreover, a high spatial accuracy performance of a touch display will enable to correctly recognize stylus input (i.e. touches with a relative small impact diameter
"In general, the accuracy of a touch panel with a fixed size will increase by enlarging the sensor density i.e. the total number of active touch sensors per display area. With a larger sensor density per area, not only the location, but also the shape and size of the touch can be detected with more accuracy. For a typical touch application of a pixelated display panel, (in which as a response of the touch event, part of the display will be activated/selected), the ultimate touch sensor dimension will be equal to the display pixel sensor or in other words: the maximum accuracy can be achieved when the touch sensor density is equal to the Pixels-Per-Inch (PPI) value of the display.
"For various reasons, such as costs, design and process capability (track/gap capabilities) and display form factor (e.g. availability for track/routing layout) the number of I/O lines of the touch driver/controller will be limited. Consequently, the number of touch sensors of a touch panel of a display module will, in general, be much smaller than the actual number of display pixels which will have its negative impact on the achievable accuracy. Normally, for stylus input (i.e. with only a small area touching the surface,
"FIG. 3 illustrates a so-called 'centroid' method in which known touch panel devices calculate the touch location based on the detected touch sensor values. A touch location is here defined as a location on a touch panel sensing a touch of an object like a finger or a stylus. FIG. 3 shows a part of a touch panel comprising sensors 10 arranged in a diamond shape. The panel is touched at touch location 21 (the center of the x-y coordinates used in FIG. 3) by an object having a touch spot area A indicated by the circle around central touch location 21. The values (or 'counts') detected by each capacitive sensor 10 are indicated with S.sub.1, S.sub.2, . . . S.sub.9, and graphically represented in the form of an area. A larger area means a relatively higher count. The count is proportional to the part of area A that overlaps with the sensor cell. The 5th sensor measures the largest count (S.sub.5), while neighbouring 4th, 8th, and 7th sensors measure decreasing values. The touch location [x, y] may be determined by evaluating the following formula:
"[ x , y ] = i S i P _ i i S i ( 1 ) ##EQU00001##
"In this formula, vector P.sub.i represents the center location [x.sub.i,y.sub.i] of the ith sensor. The calculated location [x, y] is thus a weighted average of the center locations [x.sub.i,y.sub.i], wherein the sensor counts are the weights. In the present example, the location indicated by 20 in FIG. 3 is calculated, which is a little below the true touch location 21. This is due to the fact that the distant center of cell 7, which does not actually overlap with touch spot A, effectively 'drags' the estimated touch location down along the negative y-axis.
"The centroid method thus gives an [x, y] location that has a theoretically higher resolution than the resolution of the sensor grid. However, the centroid method only gives an approximation of the true touch location. The direction and magnitude of the error varies depending on the true location. For example, if the sensor 10 is touched exactly in the middle, the centroid method will give an exact result. If the true touch location is off-center, there is a varying error.
"This varying error is particularly evident when the user tracks or draws a straight line across the sensor panel, as illustrated in lines a through e of FIG. 4a. These straight lines a, b, c, d, and e are 'translated' by the centroid method into the wobbly lines a', b', c', d' and e' of FIG. 4b. In FIG. 4b, only the wobble inside a single sensor 10 is shown. However, as the sensors form a regular grid, the wobble will also be regularly repeated across the length of the drawn straight line a-e.
"It is an object of the disclosure to provide a method and apparatus for determining a touch location that reduces this wobble effect."
In addition to the background information obtained for this patent application, VerticalNews journalists also obtained the inventor's summary information for this patent application: "The disclosure provides a method for determining a touch location on a touch panel comprising a plurality of sensors, the method comprising obtaining a first estimate for the touch location, determining a correction vector by applying at least one predetermined mapping, using the first estimate as input for said mapping, and combining the first estimate and the correction vector to obtain corrected location values.
"The first estimate may advantageously be a low-complexity method, such as weighted average or centroid method. The mapping is pre-determined to map results of the first estimate to a correction vector, so that the combination of a the first estimate vector and the correction vector yields a close approximation of the true touch location. Thereby, the 'wobble error' of the estimation is effectively reduced or removed altogether. The pre-determined mapping may be dependent on the detected touch spot size, that is, different mappings are used for smaller or larger touching objects (e.g. stylus point, fingertip, etc).
"Here a mapping is understood to be any function that takes a number of input variables (e.g. one or more coordinate components corresponding to a touch location) and outputs one or more variables (e.g. one or more components of a correction vector) depending on the input variables. A mapping can be implemented in many different ways. To name but a few: it can implemented in hardware, in software, or a combination of both. The mapping can be numerically evaluated or approximated by means of a polynomial approximation, a series expansion, a Fourier series, a function fitted to empirical data, or by a (interpolated) lookup table comprising empirical or modeled data. According to an embodiment of the disclosure, the mapping can be implemented as a two-dimensional mapping, taking an two-dimensional estimate vector as input and yielding a two-dimensional correction vector. The two-dimensional mapping can be implemented as a two-dimensional lookup table (LUT). The mapping could also take three input variables, where the third variable is the touch spot size, and yield two correction vector components as output variables dependent on the input estimation components and the spot size.
"The mapping can also be implemented as a combination of two one-dimensional mappings, where a first one-dimensional mapping takes a first component of the estimate vector as input yielding a first component of the correction vector, and a second one-dimensional mapping takes a second component of the estimate vector as input yielding a second component of the correction vector. The one-dimensional mappings may be implemented as one-dimensional lookup tables (LUTs). The mapping could also take two input variables, one estimation component and the touch spot size, and return a correction vector component dependent on the estimation component and the spot size.
"The disclosure also provides a location determination module arranged to perform the above described method. To that end, the module may comprise an estimator unit for generating a first location estimate. The module may comprise a processor for controlling the units and performing calculations. The module may comprise one or more evaluation units implementing the above described mappings.
"The disclosure also provides a touch sensor system comprising a touch sensor panel having a plurality of sensors and a touch location determination module as described above. The module may be arranged to receive touch sensor measurement values from the touch sensor panel.
"The disclosure further provides a computer program product storing a computer program adapted to, when run on a processor, perform a method as described above.
BRIEF DESCRIPTION OF THE FIGURES
"The disclosure will be further explained in reference to figures, wherein
"FIG. 1 schematically shows a top view of an electronic device comprising a touch panel device according an embodiment of the disclosure;
"FIGS. 2a-2c schematically show cross section of touch panel device variants according an embodiment of the disclosure;
"FIG. 3 schematically illustrates the centroid method for determining a touch location on a touch panel;
"FIGS. 4a and 4b schematically illustrate the wobble effect
"FIGS. 5a-5e schematically illustrate a method for determining a touch location according to an embodiment of the disclosure for various forms of sensors;
"FIGS. 6a-6b schematically illustrate correction functions used in a method according the disclosure;
"FIGS. 7a-7b schematically illustrate a method for determining a touch location according to an embodiment of the disclosure;
"FIG. 8 illustrates a touch location determination module according to an embodiment of the disclosure."
URL and more information on this patent application, see: Hekstra, Gerben. Method for Determining Touch Location on a
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