WO2012073261A1

WO2012073261A1 - Improved method for determining multiple touch inputs on a resistive touch screen

Info

Publication number: WO2012073261A1
Application number: PCT/IT2010/000476
Authority: WO
Inventors: Andrea Celani; Pastore Nicolo'
Original assignee: Haptyc Technology S.R.L.
Priority date: 2010-11-29
Filing date: 2010-11-29
Publication date: 2012-06-07

Abstract

The present invention concerns a method for determining multiple touch inputs on a resistive touch screen, such screen having a first layer (2A) and a second layer (2B) with a first axis (2C) and a second axis (2D) orthogonal to each other, being definable thereat, and wherein said first layer is designed to be touched, the method including the steps of touching said first layer (2A) at a first touch point (Pl), while also touching said first layer (2A) at a second point (P2); powering the first layer (2A) with a voltage value (Vcc), while said first layer (2A) is touched at said first point (Pl) and said second point (P2) respectively; detecting a first value of current (I2,x) circulating in said first layer (2A), when the latter is powered with said voltage value (Vcc); processing said first current value (I_2,x) to calculate a first value (Δx) that represents the coordinate difference along an axis (2C) of the first layer (2A) between the coordinates of said first touch point (Pl ) and said second touch point (P2); obtaining the first coordinate (POxc) of a midpoint (PO) relative to the coordinates of said first point (Pl) and said second point (P2); processing said first value (Δx) and the first coordinate (POxc) of said midpoint (PO) to determine the coordinates (Plx,P2x) of said first touch point (Pl) and said second touch point (P2) along said axis (2C) of the first layer (2A). It is characterized in that the step of obtaining said first coordinate (POxc) of a midpoint (PO) provides detection of a first read voltage (Vl) and a second read voltage (V2) of the second layer (2B) and processing of a first read voltage (Vxc), which is an average value between said first read voltage (Vl) and said second read voltage (V2) to obtain said first coordinate (POxc) of a midpoint (PO).

Description

Improved method for determining multiple touch inputs on a resistive touch screen

Related art

The contents of patent application PCT/IT2009/000239 by the Applicants hereof is incorporated herein by reference

Technical field

The present invention relates to an improved method for determining multiple touch inputs on a resistive touch screen.

Background art

Patent application PCT/IT2009/000238 discloses a method for determining multiple touch inputs on a resistive touch screen. Particularly, the method teaches to read the value of a current that flows in one of the two layers of the resistive screen when that layer is simultaneously touched at two distinct points PI and P2 and is powered with a voltage equal to the power-line voltage. For example, the coordinates X of the touch points P I and P2 are used to process the current value and obtain a modulus value Δχ, representative of the difference along the x axis of the first layer between the coordinates of the first touch point PI and the second touch point P2. Once the modulus value Δχ has been obtained, and knowing the coordinates POxc of the midpoint PO with respect to the x coordinates of the two touch points, the x coordinates of the two points PI e P2 may be calculated by addition or subtraction of the modulus value Δχ to or from the coordinates POxc of the midpoint PO.

The modulus value Ay, representative of the difference along an axis perpendicular to the first axis within the first layer, is obtained likewise; once the modulus value Ay has been obtained, the y coordinates for the two points PI and P2 may be calculated by addition or subtraction of the modulus value Ay to or from the coordinates POyc of the midpoint PO.

It will be understood that the precision of the x axis and y axis coordinates of the two touch points P I and P2 is affected by the precision with which the circuitry returns the coordinates POxc, POyc of the midpoint PO.

In patent application PCT/IT2009/000238, also referring to Figure 1 , the coordinates of the midpoint PO are estimated by detecting the read voltage from a reading terminal V I or V2 of one of the two links defined by the resistors Rl 1 , R12 and R3 and the resistors R7, R8 and R3 respectively, when the screen is simultaneously touched at the two points PI and P2.

This estimate simplifies the method of PCT/IT2009/000238, but introduces an error caused by the influence of one of the two touch points with respect to the reading terminal. Technical problem

Therefore, the need is highly felt for detection of multiple high-precision touch inputs in resistive touch screens to implement features that might not otherwise find application in a common resistive touch screen.

Hence, the present invention is based on the problem of providing a method that has such functional features as to fulfill the above need, while obviating the above prior art drawbacks.

Technical solution

This problem is solved by a method for determining multiple touch inputs on a resistive touch screen as defined in claim 1.

Advantageous effects

With the present invention, a method is provided for determining the coordinates of each touch point without changing the construction of a common resistive touch screen, such as of the 4- wire, 5-wire or 8-wire screen.

The present invention may particularly find application in a variety of electronic apparatus such as ATMs (Automated Teller Machines), kiosks, POS (Points of Service) apparatus, but especially in electronic devices such as PDAs (Personal Digital Assistants), mobile phones, notebooks, laptops, MP3 readers, etc.

Brief description of the drawings

Further features and advantages of the method of the present invention will result from the following description of one preferred embodiment thereof, which is given by way of illustration and without limitation with reference to the accompanying figures, in which:

- Figure 1 shows a diagrammatic view of the panel when it is touched at two points with the coordinates of the points being determined along an axis, according to the present invention;

- Figure 2 shows a different diagrammatic view of the panel of Figure 1 , in which the centering problem is identified;

- Figure 3 shows the same diagrammatic view as the panel of Figure 2, with the coordinates of the points being determined along an axis, according to the present invention;

- Figure 4 shows a diagrammatic view as the panel of Figure 2, with the coordinates of the points being determined along another axis, according to the present invention;

- Figures 5 and 6 show a different diagrammatic view of the panel of Figure 1 , in which the ambiguous orientation problem is identified; Detailed description

Centering issue

Referring to the description of PCT/IT2009/000238 and to Figure 1 , which shows a circuit model of a resistive touch screen, if pressure is exerted, for instance by fingers, at two points PI and P2, the latter being shown for simplicity to have a x coordinate equal to that of the touch point PI and, if only one layer of the two layers that form the screen is powered, and the other is held floating, then the current 12 that flows in the powered layer increases with respect to the condition in which the touch screen is touched at a single touch point.

Particularly, in Figure 1 the layer that is powered with the voltage Vcc is, for instance, the layer representative of the y coordinates, whereas the layer that is held floating is, for instance, the one representative of the x coordinates.

The current 12 that flows in the powered layer (i.e., in the particular case of Figure 1 , the layer representative of the y coordinate) increases as compared to the one that would be obtained if the screen were touched at a single touch point. Such increase is caused by the fact that by touching the first screen layer at two points, a parallel path is introduced in the lower panel, (here representing the x coordinate).

Particularly, the current 12 also flows through the links defined by the resistors Rl 1 , R12, R3 and the resistors R7, R8 and R3 respectively.

In PCT/IT2009/000238, the coordinate of the midpoint P0 is estimated by evaluating one of the two possible read voltages VI and V2 provided by common resistive touch screen control circuitry.

This estimate simplifies the method for determining multiple touch inputs on a resistive touch screen, but introduces an error caused by the influence of one of the two touch points PI or P2 with respect to the selected reading terminal VI or V2.

With the above in mind and referring to Figure 2, the present inventors found that the touch point PI , i.e. the one placed, for instance, at the top right, will "influence" more the reading terminal V 1 , whereas the touch point P2, placed for instance at the bottom left, will "influence" more the reading terminal V2.

This different influence on the reading terminals VI , V2 is caused by the fact that the average voltage evaluated in one of the two reading terminals VI or V2 is obtained by weighting the two touch voltages by their impedance to the reading terminal.

Considering the reason for the different influences on the reading terminals VI , V2, in the method for determining multiple touch inputs on a resistive touch screen with improved precision, also referring to Figure 3 (for the Y coordinates of the points PI and P2), and Figure 4 (for the X coordinates of the points PI and P2), the step of obtaining the coordinates P0xc,P0yc of the midpoint P0 is carried out by first detecting a first read voltage VI (reading terminal VI) and a second read voltage V2 (reading terminal V2) and then by processing a read voltage Vxc, Vyc that equals an average value between the first read voltage VI and the second read voltage V2 (by appropriately changing the power nodes and the read nodes) to obtain said coordinates POxc, POyc of the midpoint P0.

It shall be noted that reference can be made to PCT/IT2009/000238, incorporated herein, for calculation of modulus values Δχ and Ay of the two touch points PI and P2 relative to the coordinates of the midpoint P0 as well as the coordinates x,y of said two touch points PI and P2, as shown by the block diagrams of Figures 3 and 4.

For the purposes of the present invention it shall be noted that the modulus value Δχ (and likewise the modulus value Ay) is calculated by powering the first layer 2A (e.g. the flexible outer layer) with a voltage value Vcc, while such first layer 2A is touched in the first point PI and the second point P2 respectively; by detecting a first current value I2,x for the current flowing in the first layer 2A, i.e. the layer powered with the voltage value Vcc; by processing the first current value I2,x to determine a first modulus value Δχ representative of the coordinate difference along the axis 2C (e.g. the x axis) of the first layer 2A between the coordinates of the first touch point PI and those of the second touch point P2.

The method may include, also with reference to Figure 3, averaging of the read voltages VI and V2 to obtain an estimate of the average voltage Vyc, representative of the coordinate POyc of the midpoint P0, which is more accurate than the estimate that can be obtained by traditional methods.

For instance, the average voltage Vyc may be calculated using the following formula:

a * V\ + B * V2

Vyc = — — in which a and β are two parameters that account for the impedance with which the two touch points PI and P2 control the related voltages VI and V2.

These two parameters a and β may be obtained iteratively, may be calculated by a complex model of the resistive panel, or may be also saved in a previously prepared look-up table.

Likewise, also referring to Figure 4, a more accurate estimate of the coordinate POxc of the midpoint PO consists in averaging the read voltages V I and V2 using weights γ, δ, i.e. according to the following formula:

^' * V\ + S * V2

Vxc =

2

in which γ are δ are two weights or parameters that account for the impedance with which the two touch points PI and P2 control the related voltages VI and V2.

Also in this case, the two parameters γ and δ may be obtained iteratively, may be calculated by a complex model of the resistive panel, or may be also saved in a previously prepared look-up table.

A more precise estimate of the read voltages Vyc,Vxc will also provide a more precise estimate of the x, y coordinates of the two touch points P 1 , P2.

Thus, once the modulus value Ax and the modulus value Ay have been obtained (as described in PCT/IT2009/000238), and knowing the coordinates POxc, POyc of the midpoint PO from the average read voltage Vxc, Vyc, the x and y coordinates of the two points PI e P2 may be calculated by addition or subtraction of the modulus value Ax, Ay to or from the coordinates xc, yc of the midpoint PO.

Once an estimate of the voltage Vxc, Vyc of the midpoint PO has been obtained, the spatial coordinates POxc and POyx may be obtained by the method in a conversion step, for converting such voltage values Vxc, Vyc, in proportion to the size of the resistive panel, into the coordinates POxc and POyc.

Such conversion step requires knowledge of the size of the resistive panel (e.g. its pixel size according to the graphic display with which the touch screen panel is coupled, or the size in meters, etc.).

Preferably, the conversion step of the method is based on pixel conversion. This ensures direct use of the coordinates by the graphic processing system that actively controls the graphic display mounted with the resistive panel.

Characteristic parameters of the resistive panel are known by the skilled person to be, for instance, the y axis dimension Height_pj_xei,y or the x axis dimension Height_pj_xe of the pixel graphic display.

Once the Height_Pj_xei_,y and Height_pj_xei_iX values are known, the coordinates POxc and POyc may be calculated, e.g. using the following formulas:

- for the coordinate POyc of the midpoint PO: VI + V2

2

- for the coordinate POxe of the midpoint P0:

wherein:

- Vcc is the voltage supplied to the panel or more generally the potential difference between one terminal of the panel and the other terminal of the panel with which the voltage reference is connected (ground reference of the circuit).

Ambiguity issue

Nevertheless, also with reference to Figures 5 and 6, the electronic circuitry of the resistive touch screen can identify two pairs of touch points ε and λ, using the acquired information (i.e. the coordinates P0xc,P0yc of the midpoint P0, Ay and Δχ, see Figure 5).

Particularly referring to Figure 6, it can be noted that both pairs of touch points ε and λ have the same coordinates P0xc,P0yc, the same value Ay and the same value Δχ as the midpoint

P0.

Each pair ε or λ, unless they have identical x or y coordinates, is oriented along a diagonal of a hypothetical Cartesian reference plane. Each pair is also in specular orientation with respect to the other.

In other words, the electronic circuitry of the resistive touch screen cannot determine, with the acquired information, whether the two touch points PI and P2 are oriented in the direction of extension of the pair of touch points ε or in the direction of extension of the pair of touch points λ, as both pairs ε and λ fulfill the reading conditions.

Therefore, the circuitry has to solve the problem of ambiguous orientation of the two touch points PI and P2, which may cause wrong interpretation of the x and/or y coordinates of the two touch points.

Particularly, as shown by way of example in Figure 6, the pair of touch points ε may extend along a top right to bottom left diagonal (i.e. the first and third quadrants of a Cartesian reference system centered in the midpoint P0xc,P0yc ) whereas the pair of touch points λ may extend along a top left to bottom right diagonal (i.e. the second and fourth quadrants of a Cartesian reference system centered in the midpoint P0xc,P0yc) or vice versa.

In order to obviate the problem of ambiguous orientation of the two pairs, referring to the situation as shown in Figure 6, the method may comprise the step of monitoring the difference between the potential at the reading terminal V I and the potential at the reading terminal V2, to determine the orientation of the axis that joins the two touch points PI and P2 with respect to the supply axis.

The present inventors found from experimental tests that the reading terminals V I and V2 are controlled with a different impedance, proportional to the distance from each of the two touch points P I and P2.

Particularly, still considering the diagram as shown by way of example in Figure 6, since the point PI is closer to the reading terminal V I , it has a lower impedance than the touch point P2. The touch point PI controls the terminal VI with a lower impedance than the touch point P2, that controls it with a higher impedance. The touch point PI will force a voltage close to that of the point PI , which is higher (according to the voltage supply of the panel) than that of the touch point P2.

Once this has been determined concerning the pair of touch points ε, the method may advantageously comprise a step of checking whether the voltage of the reading terminal VI is higher than the voltage of the reading terminal V2 of the first layer 2A (see Figure 3), and if it is, determining the coordinates Ply of said first touch point PI along the axis 2D (i.e. the y axis) of the layer 2B by summing half the value Ay to the coordinate POyc of the midpoint P0 for such axis 2D of the layer 2B of the panel 1.

In other words, the y coordinate of the touch point PI of the pair ε can be calculated using the following formula: y 2

where POyc is the y coordinate of the midpoint PO.

Likewise, the y coordinates may be determined for the second touch point P2, by checking whether the read voltage VI is higher than the read voltage V2 of the layer 2 A and, if it is, determining the coordinates P2y of the touch point (P2) along the axis 2D of the layer 2B by subtracting half of said second value Ay from the coordinate POyc of the midpoint PO for such axis 2D of the layer 2B of the panel 1.

In other words, the y coordinate of the touch point P2 of the pair ε can be calculated using the following formula: P2_; ^:,/^C

The same method also applies to the x coordinate of the touch points P I and P2 and the x coordinate of the touch point PI of the pair ε may be calculated using the following formula:

Ax

P\ , = POxc +—

. 2

where POxc is the x coordinate of the midpoint P0,

whereas the x coordinate of the touch point P2 of the pair ε can be calculated using the following formula:

Ax

P2 = P0xc

2

In other words, if the read voltage VI is higher than the read voltage V2, then the pair of touch points PI , P2 is oriented along a diagonal that passes through the first and third quadrants of a Cartesian reference system centered in the midpoint P0xc,P0yc and hence with respect to the coordinates of the midpoint P0.

This is caused by the fact that, if the touch points are oriented as a pair ε, then the touch point at the top right (i.e. PI as shown in Figure 6) will be closer to the reading terminal VI whereas the touch point at the bottom left (i.e. P2 as shown in Figure 6) will be closer to the reading terminal V2.

In this context, the two touch points PI , P2 have different potentials along the supply axis and the top right touch point (i.e. PI as shown in Figure 6) will have a higher potential than the bottom left touch point (i.e. P2 as shown in Figure 6).

This potential difference, in the conditions of the pair ε causes the potential of the reading terminalNl to be higher than the potential of the reading terminal V2.

Concerning the pair of touch points λ, the method advantageously comprises checking whether the voltage of the reading terminal VI is lower than the voltage of the reading terminal V2 of the first layer 2 A and if it is, determining the coordinates Ply of the first touch point PI along the axis 2D of the second layer 2B by summing half the value Ay to the y coordinate POyc of the midpoint P0 for the axis 2D of the second layer 2B.

In other words, the y coordinate of the touch point PI of the pair λ can be calculated using the following formula:

where POyc is the y coordinate of the midpoint P0.

Likewise, the y coordinates may be determined for the second touch point P2, by checking whether the read voltage VI is lower than the read voltage V2 of the layer 2A and, if it is, determining the coordinates P2y of the touch point P2 along the axis 2D of the layer 2B by subtracting half of said second value Ay from the coordinate POyc of the midpoint PO for such axis 2D of the layer 2B of the panel 1.

In other words, the y coordinate of the touch point P2 of the pair λ can be calculated using the following formula:

P2 = P0yc - ^- 2

The same applies to calculation of the x coordinate of the touch points PI and P2. Particularly, the x coordinate of the touch point PI of the pair λ can be calculated using the following formula:

P\ = P0xc -—

2

whereas the x coordinate of the touch point P2 of the pair λ can be calculated using the following formula:

Ax

P2 = P0xc +—

2

It shall be noted that the method as described above may be used in any time discretization situation, both when the time distance between the first touch point PI and the second touch point P2 is lower than the time resolution of the electronic circuitry of the resistive touch screen panel 1 and when the time distance between the event of the first touch point PI and the second touch point P2 is higher than the time resolution of the resistive touch screen panel 1.

In other words, the method as described above is applicable either when the screen is touched at the two touch points PI and P2 substantially at the same time, or when the touch points PI and P2 are touched one after the other slow enough to allow detection by the control circuitry.

In the method, if the two touch inputs PI and P2 are made in such a manner as to allow time discrimination thereof by the acquisition electronics (i.e. within its time resolution), the coordinate of the first touch input made on the panel may be stored, until the second touch input occurs, Δχ, Ay (Δχ, Ay being calculated with the technique as described in PCT/IT2009/000238) and the coordinates P0xc,P0yc of the midpoint PO (the coordinates P0xc,P0yc of the midpoint PO being calculated with the method as described in the present application or the technique as described in PCT/IT2009/000238) are acquired, to calculate an absolute value of the distance between the stored coordinate of the first touch input made on the panel and all the assumed coordinates determined after the touch input P2, and to determine the x,y coordinate at zero distance from those that have been stored.

Particularly, in addition to storing the coordinate of the first touch point, e.g. the coordinate Plxm, Plym if the first touch point is PI, and waiting until the panel has not been touched at a second touch point, the method includes the steps of:

- calculating all possible coordinates for all the quadrants with the formulas

P\_{v t}=yc + ^ Pl, _t=xc ₊ - P2_{y £}=yc-^ P2 _=JCC_^ P\_{y JL}=yc ₊ ^ y_c 2 2 ' ^y- 2 ' ~ 2 ' 2 '

Ax ₀_ Ay _n. Ax

P\_x , =xc P2_v , =yc-— P2_X , =xc +—

- calculating the distance between the stored coordinates PlxJPly of the single touch point PI and all the calculated coordinates Ply_s, Ρΐχ ε, P2y_s, Ρ2χ_ε, Ρ1ν_λ, Ρ1χ_λ, Ρ2γ_λ, Ρ2χ_λ, i.e.:

dl_l=Plxm-Plx_e

d2_l=Pl m-PlxJ.

d3_l=Plxm-P2x_e

d4_l=Plxm-P2x_

or:

d-_2=Plym-Ply_s

d2_2=Plym-PlyJ.

d3_2=Plym-P2y_e

d4_2=Plym-P2y_X

or as a geometric distance:

d4 =^(P\xm-P2_{y Λ}) +(p\ym-P2_v

The minimum distance value between the calculated coordinates Ply_s, Ρ1χ_ε, P2y_s, Ρ2χ_ε, Ρ^_λ, Ρ1χ_λ, ?2y_X, Ρ2χ_λ and the stored coordinates Plxm,Plym defines the point that is closest to the single touch point PI, in a single touch condition. Assuming that the first touch position is not considerably displaced between the single-touch input time and the multi- touch input time, then the determination of the multi-touch input coordinate that is closest to the single-touch input coordinate determines the quadrants of the axis of the two touch inputs.

Gestures issue

For improved usability of ATMs (Automated Teller Machines), kiosks, POS (Points of

Service) apparatus, but especially in electronic devices such as PDAs (Personal Digital Assistants), mobile phones, notebooks, laptops, MP3 readers, gestures are typically used whereby pressure at the two touch points PI and P2 quickly and easily triggers functions (such as zoom, rotation, etc.) that would be otherwise only available through pressure of one or more special keys or through exploration of menus of said electronic devices.

Magnification

Advantageously, the information concerning the current I_2x, I_2y (see Figures 3 and 4) circulating in the resistive touch screen 1 as a result of two touch inputs PI , P2 may be related to a magnification factor K of an object displayed on a screen, such as a text, an image, a vector figure, etc.

Particularly, measurement of currents in orthogonal panels at successive times provides the magnification factor Kz of the object on the screen.

It shall be noted that the magnification factor Kz can be defined for both the axis 2C (defined as Kz, x) and the axis 2D (defined as Kz,y), i.e. for x axes and y axes respectively.

Particularly, to obtain the factor Κζ,χ, the method comprises:

- detecting, at a first time tl , a first value of current I_2x circulating in said first layer 2A when the latter is powered with said preset voltage value Vcc while said first layer 2A is being touched at said first point PI or at two points PI and P2;

- subtracting a first threshold value I_thd from said first current value I_2x to generate a first processed current value I_{2x t}i at said first time tl ;

- detecting, at a first time t2 (with t2 > tl), a second value of current Ι_2χ· circulating in said first layer 2A when the latter is powered with said preset voltage value Vcc while said first layer 2A is being touched at said first point PI or at two points PI and P2;

- subtracting said first threshold value I_thd from said second current value Ι_2χ· to generate a second processed current value I_2x,i2 at said second time t2;

- defining a first magnification factor Κζ,χ along a first reference axis x using the formula

J It shall be noted that the current value I_thdx is a predetermined value that is preferably equal to the value of the current that circulates in the first powered layer 2A, when such first layer 2A is touched at one point only.

Similar results are reached by the method when it obtains the factor Kz,y along a second reference axis 2D (i.e. the y axis) perpendicular to the first reference axis 2C (i.e. the x axis), using the formula:

- where I_2x,ti and I_2y,ti represent the currents as measured in the screen 2A and the layer 2B at the time tl respectively, with the threshold values I_thdx and Udy subtracted therefrom respectively (see Figures 3 and 4);

- where I₂x.t2 and I_2y,t2 represent the currents as measured in the screen 2A and the layer 2B at the time t2 respectively, with the threshold values I_thdx and I_thd_y subtracted therefrom respectively (see Figures 3 and 4).

An overall magnification factor z may be also determined, using the following formula:

Once the magnification factor Kz has been found, the text, image, vector figure on the screen may be magnified by modulating it with such a modulation factor μ that:

a) x-axis and/or y-axis proportions of the original text, image, vector figure are maintained using the following formulas:

X_sc = * K_z * X_img b) x-axis and/or y-axis proportions of the original text, image, vector figure are not maintained, using the following formulas: Υ,_::' = μ * Κ_{: :} * Χ^

where μ is a parameter that may be constant or depend, for instance, on the rate of increase of current I_2x and/or I_2y according to this possible formula: μ ^ a - a a ~ t\

or with the formula:

Rotation

As an alternative or in combination with zoom gestures, the measure of the angle 9_current between the orthogonal current components I_2x, I_2y may be related to a rotation factor 9₀bj_ect of an object as it appears on the screen (text, image , costruzione vettoriale ecc.) in a relative or absolute manner.

Particularly, if the angle 9_current between the orthogonal current components I_2x, I_2y is defined as:

/,,,

#™ = arctgij-)

* 2x

and its variation A6_current is defined as:

Δ =

then the rotation factor 9₀bject can be defined in an absolute manner, using the following formula:

Θ = Ύ

nbjiicl * θ current

and in a relative manner, using the following formula: where χ is a constant parameter or depends on the rate of increase of current, according to the following relation:

where AI_2y = I_{2y l2} - I_{2y l} and AI_2l = I_{2x 2} - I_{2x n}

or on the rate of increase of the angle, according to the following relation:

__ t AG current

-ti

As clearly shown in the above description, the method of the present invention fulfills the above mentioned need and also obviates prior art drawbacks as set out in the introduction of this disclosure.

Those skilled in the art will obviously appreciate that a number of changes and variants may be made to the above method, still within the scope of the invention, as defined in the following claims.

Claims

1. A method for determining multiple touch inputs on a resistive touch screen, such screen having a first layer (2A) and a second layer (2B) with a first axis (2C) and a second axis (2D) orthogonal to each other, being definable thereat, and wherein said first layer is designed to be touched, the method including the steps of:

- touching the first layer (2 A) at a first touch point (PI), while also touching said first layer (2A) at a second point (P2);

- powering the first layer (2A) with a voltage value (Vcc), while said first layer (2A) is touched at said first point (PI) and said second point (P2) respectively;

- detecting a first value of current (I_2,x) circulating in said first layer (2A), when the latter is powered with said voltage value (Vcc);

- processing said first current value (I₂,_x) to calculate a first value (Δχ) that represents the coordinate difference along an axis (2C) of the first layer (2A) between the coordinates of said first touch point (PI ) and said second touch point (P2);

- obtaining the first coordinate (POxc) of a midpoint (P0) relative to the coordinates of said first point (PI ) and said second point (P2);

- processing said first value (Δχ) and the first coordinate (POxc) of said midpoint (P0) to determine the coordinates (Plx,P2x) of said first touch point (PI ) and said second touch point (P2) along said axis (2C) of the first layer (2A);

characterized in that said step of obtaining said first coordinate (POxc) of a midpoint (PO) includes:

- detecting a first read voltage (VI) and a second read voltage (V2) of the second layer

(2B);

- processing a first read voltage (Vxc), which is an average value between said first read voltage (VI ) and said second read voltage (V2) to obtain said first coordinate (POxc) of a midpoint (PO).

2. A method for determining multiple touch inputs on a resistive touch screen as claimed in claim 1 , wherein in said step of processing the average value of the first read voltage (Vxc) said average voltage is processed as a function of the impedance with which said first touch point (PI) and said second touch point (P2) control the first read voltage (VI ) and the second read voltage (V2) respectively.

3. A method for determining multiple touch inputs on a resistive touch screen as claimed in claim 1 or 2, comprising a step of converting said first read voltage (Vxc) in proportion to the size of the resistive panel, to obtain the coordinate (POxc) of said midpoint (P0).

4. A method for determining multiple touch inputs on a resistive touch screen as claimed in any preceding claim, comprising the step of:

- checking whether said first read voltage (VI ) is higher than said second read voltage (V2) of the second layer (2B) and if it is, determining the coordinate (P lx) of said first touch point (P I ) along said axis (2C) of said first layer (2A) by adding half of said first value (Δχ) to said first coordinate (POxc) of the midpoint (P0) for said axis (2C) of said first layer (2A).

5. A method for determining multiple touch inputs on a resistive touch screen as claimed in any preceding claim from 1 to 3, comprising the step of:

- checking whether said first read voltage (V I ) is higher than said second read voltage (V2) and if it is, determining the coordinate (P2x) of said second touch point (P2) along said axis (2C) of said first layer (2A) by subtracting half of said first value (Δχ) from said first coordinate (POxc) of the midpoint (PO) for said axis (2C) of said first layer (2A).

6. A method for determining multiple touch inputs on a resistive touch screen as claimed in any preceding claim from 1 to 3, comprising the step of:

- checking whether said first read voltage (VI) is lower than said second read voltage (V2) of the second layer (2B) and if it is, determining the coordinates (Plx) of said first touch point (PI ) along said axis (2C) of said first layer (2A) by subtracting half of said first value (Δχ) from said first coordinate (POxc) of the midpoint (PO) for said axis (2C) of said first layer (2A).

7. A method for determining multiple touch inputs on a resistive touch screen as claimed in any preceding claim from 1 to 3, comprising the step of:

- checking whether said first read voltage (VI) is lower than said second read voltage (V2) and if it is, determining the coordinates (P2x) of said second touch point (P2) along said axis (2C) of said first layer (2A) by adding half of said first value (Δχ) to said first coordinate (POxc) of the midpoint (PO) for said axis (2C) of said first layer (2A).

8. A method for determining multiple touch inputs on a resistive touch screen as claimed in any preceding claim, comprising the step of:

- powering the second layer (2B) with said voltage value (Vcc), while said first layer (2A) is touched at said first point (P I) and said second point (P2) respectively;

- detecting a second value of current (I_2,y) circulating in said second layer (2B), when the latter is powered with said voltage value;

- processing said second detected current value (I2,y) to calculate a second value (Ay) that represents the coordinate difference of the distance between the coordinates of said first touch point (PI ) and said second touch point (P2), said coordinate difference being calculated along an axis (2D) of the second layer (2B), which is orthogonal to said axis (2C) of the first layer (2A);

- processing said second' value (Ay) and a second coordinate (POyc) of said midpoint (PO) to determine the coordinates (P ly,P2y) of said first touch point (P I) and/or said second touch point (P2) along said second axis (2D) of said second layer (2B);

- processing a second read voltage (Vyc), which is an average value between said first read voltage (V I ) and said second read voltage (V2) to obtain said second coordinate (POyc).

9. A method for determining multiple touch inputs on a resistive touch screen as claimed in claim 8, wherein in said step of processing the average value of the second read voltage (Vyc) said average voltage is processed as a function of the impedance with which said first touch point (P I ) and said second touch point (P2) control the first read voltage (VI) and the second read voltage (V2) respectively.

10. A method for determining multiple touch inputs on a resistive touch screen as claimed in claim 8 or 9, comprising a step of converting said second read voltage (Vyc) in proportion to the size of the resistive panel, to obtain the coordinate (POyc) of said midpoint (PO).

11. A method for determining multiple touch inputs on a resistive touch screen as claimed in any preceding claim from 8 to 10, comprising the step of:

- checking whether said first read voltage (VI ) is higher than said second read voltage (V2) of the first layer (2 A) and if it is, determining the coordinates (Ply) of said first touch point (PI ) along said second axis (2D) of said second layer (2B) by adding half of said second value (Ay) to said second coordinate (POyc) of said midpoint (PO) for said second axis (2D) of said second layer (2B).

12. A method for determining multiple touch inputs on a resistive touch screen as claimed in any preceding claim from 8 to 10, comprising the step of:

- checking whether said first read voltage (VI ) is higher than said second read voltage (V2) of the first layer (2A) and if it is, determining the coordinates (P2y) of said second touch point (P2) along said second axis (2D) of said second layer (2B) by subtracting half of said second value (Ay) from said second coordinate (POyc) of said midpoint (P0) for said second axis (2D) of said second layer (2B).

13. A method for determining multiple touch inputs on a resistive touch screen as claimed in any preceding claim from 8 to 10, comprising the step of:

- checking whether said first read voltage (V I ) is lower than said second read voltage (V2) of the first layer (2A) and if it is, determining the coordinates (P l y) of said first touch point (P I ) along said second axis (2D) of said second layer (2B) by adding half of said second value (Ay) to said second coordinate (POyc) of said midpoint (PO) for said second axis (2D) of said second layer (2B). ·

14. A method for determining multiple touch inputs on a resistive touch screen as claimed in any preceding claim from 8 to 10, comprising the step of:

- checking whether said first read voltage (VI) is lower than said second read voltage (V2) of the first layer (2A) and if it is, determining the coordinates (P2y) of said second touch point (P2) along said second axis (2D) of said second layer (2B) by subtracting half of said second value (Ay) from said second coordinate (POyc) of said midpoint (PO) for said second axis (2D) of said second layer (2B).

15. A method for determining multiple touch inputs on a resistive touch screen as claimed in any preceding claim, comprising the step of:

- storing the coordinates (Plxm, P lym) of said first touch point (PI) until a touch input is made at said second touch point (P2);

- calculating the coordinates of said first touch point (PI ) and said second touch point (P2) as claimed in any claim from 8 to 14;

- calculating the absolute value of the distance between the stored coordinate (P l xm,P l ym) of said first touch point (P I ) and all the coordinates that have been calculated after said input at said second touch point (P2) to determine a coordinate (x,y) at zero or minimum distance from said stored coordinates (Plxm, P lym) .