Method for operating a resistive touchscreen

Abstract

Method for operating a resistive touchscreen (1), wherein the coordinates of a touch point (25) on the touchscreen (1) are connected to a circuit arrangement, - wherein the circuit arrangement comprises a resistive touchscreen (1) with a resistive first layer (2) and a resistive second layer (3) arranged in parallel to each other, - wherein the voltage dividers (U1, U2) of the first and second layers (2, 3) formed by touching the touchscreen (1) are extended by electrical resistors (8, 11, 14, 17) arranged at the edges (4, 5, 6, 7) of the first and second layers (2, 3), characterized in that determined positions of the touch point (25) outside the operating area of ​​the touchscreen (1) are recognized as an error of a control circuit of the touchscreen (1).

Description

Field of invention

[0001] The invention relates to a method for operating a resistive touchscreen. Background of the invention

[0002] For operating medical imaging devices, so-called "touch panels" (control panels) with a resistive touchscreen (touch-sensitive screen) could also be used. These must comply with, among other things, the safety requirements of the European medical safety standard EN60601.

[0003] Resistive touchscreens respond to pressure, which locally connects two electrically conductive layers. These layers form a voltage divider, and the electrical resistance across this divider is measured to determine the position of the pressure point. Such touchscreens consist of an outer polyester layer and an inner glass or plastic disc, separated by spacers. The surfaces facing each other are coated with indium tin oxide, a transparent semiconductor.

[0004] To determine the position of the pressure point, a DC voltage is applied to one of the conductive layers. The voltage decreases uniformly from one edge of the layer to the opposite edge. At the pressure point, the voltage of both layers is equal because they are connected there. The second conductive layer connects this point to the outside. Two voltages can be measured between the edge of this second layer and the two opposite edges of the first layer. If the two voltages are equal, the pressure point is exactly midway between the two edges of the first layer. The higher one voltage is relative to the other, the further the pressure point is from the respective edge.

[0005] A second such measurement must always be performed with the roles of the two layers reversed, so that the distances to the other two edges can be determined. Only then is the position on the surface established. To capture both dimensions, the DC voltage is therefore applied alternately in a crisscross pattern.

[0006] Faults in the touchscreen's control electronics can lead to incorrect position readings on the screen, which can ultimately cause dangerous situations with a medical imaging device. For example, there are faults in the control circuitry that cause a position at the very edge of the touchscreen to be measured incorrectly instead of the correct position.

[0007] Patent application US 2013 / 0063365 A1 discloses a circuit arrangement for a resistive touchscreen in which additional resistors are intended to limit the current. Summary of the invention

[0008] The object of the invention is to provide a method for operating a touchscreen that distinguishes whether a measured position at the edge of the touchscreen corresponds to an actual touchscreen operation or is the result of an error.

[0009] According to the invention, the stated problem is solved using the method of the independent claim. Advantageous further developments are specified in the dependent claims.

[0010] To distinguish whether the measured position of a touchscreen operation corresponds to an actual operation or is the result of a fault in a control circuit, the touchscreen's user interface is virtually extended according to the invention. For this purpose, an electrical resistor is arranged both before and after the conductive layers of the touchscreen. This extends the voltage divider of the resistive touchscreen. This addition to the circuit arrangement corresponds to a virtually extended touchscreen.

[0011] In this extended circuit arrangement, voltages are measured in the area of ​​the touchscreen's internal voltage divider when the touchscreen is operated. Errors in the control circuit, which in a non-extended circuit arrangement lead to voltages corresponding to positions at the edge of the touchscreen, lead in the circuit arrangement according to the invention to voltages corresponding to positions outside the operating area, namely in the area of ​​the virtually extended touchscreen surface.

[0012] The invention claims a method for operating a resistive touchscreen, wherein the coordinates of a touch point on the touchscreen are determined with a circuit arrangement described below, and determined positions of the touch point outside the operating area of ​​the touchscreen are recognized as errors in a control circuit of the touchscreen.

[0013] Until now, the use of touchscreens has been limited to non-safety-related applications, as the required safety integrity cannot be achieved with conventional commercial touch-sensitive screens. By adding resistors according to the invention, fault disclosure can be ensured directly for a significant proportion of faults in a control circuit. Touchscreens for safety-related applications allow the advantages of touchscreens to be utilized in areas where their use was previously prohibited.

[0014] The circuit arrangement comprises: an electrical first resistor with a first and a second terminal, wherein the first terminal is electrically connected to a first edge of the first layer; an electrical second resistor with a third and a fourth terminal, wherein the third terminal is connected to a second edge of the first layer opposite the first edge; an electrical third resistor with a fifth and a sixth terminal, wherein the fifth terminal is connected to a third edge of the second layer oriented at ninety degrees to the first edge; and an electrical fourth resistor with a seventh and an eighth terminal, wherein the seventh terminal is connected to a fourth edge of the second layer opposite the third edge.

[0015] In another embodiment, the circuit arrangement has a current source that is optionally connected between the second and fourth terminals or the sixth and eighth terminals.

[0016] In a further development, the first layer can be designed in such a way that a uniformly progressing first voltage drop occurs between the first and second edges when current flows.

[0017] Furthermore, the second layer can be designed in such a way that a uniformly decreasing second voltage drop occurs between the third and fourth edges when current flows.

[0018] In a further embodiment, the circuit arrangement includes a high-impedance voltage measuring device configured to detect a third voltage drop between a contact point on the first layer and the second terminal and a fourth voltage drop between the fourth terminal and the contact point, wherein the contact point is formed by locally short-circuiting the first layer with the second layer.

[0019] Furthermore, the voltage measuring device can be configured to detect a fifth voltage drop between the point of contact and the sixth terminal and a sixth voltage drop between the eighth terminal and the point of contact.

[0020] Further features and advantages of the invention will become apparent from the following explanations of several exemplary embodiments with reference to schematic drawings.

[0021] They show: Fig. 1: a block diagram of a medical imaging device, Fig. 2: a block diagram of a circuit arrangement with a touchscreen, Fig. 3: a block diagram of another circuit arrangement with a touchscreen and Fig. 4: A circuit diagram of a touchscreen showing the voltage curves. Detailed description of several exemplary implementations

[0022] Fig. Figure 1 shows a block diagram of a medical imaging device 24, for example, an X-ray angiography unit or a computed tomography scanner, with a control panel 22. The control panel 22 has a resistive touchscreen 1, also referred to as a touch-sensitive screen, for inputting commands. The touch-sensitive surface is virtually extended by means of additional resistors connected to the edges of the layers of the touchscreen 1. Details are given in the Fig. 2 to Fig. 4 is shown and described in more detail below.

[0023] Fig. Figure 2 shows a block diagram of a circuit arrangement with a rectangular, resistive touchscreen 1 on the left. A top view of the touchscreen 1 is shown on the right. To determine the position of a touch point (pressure point) on the screen, current is sent through either the resistive first or the resistive second layer 2, 3 of the touchscreen 1 using a current source 20. This causes a voltage drop in the two layers 2 and 3, which can be detected at the touch point by a short circuit with the second layer 3. The y-direction for determining the y-axis position of the pressure point is shown. To determine the x-axis position (not shown), the current source 20 is connected to the second layer 3 in a crosswise direction, specifically to the edges rotated by 90°.

[0024] To detect faults in the control electronics, which typically simulate a voltage drop from maximum voltage or zero, or near maximum voltage or near zero, thus falsely indicating a touch at the edge of the touchscreen 1, the first layer 2 is connected with resistors. The first layer 2 has a first edge 4 in the y-direction and a second edge 5 opposite it. An electrical first resistor 8 has a first electrical terminal 9 and a second electrical terminal 10. The first terminal 9 is conductively connected to the first edge 2. The second terminal 10 is connected to ground. An electrical second resistor 11 has a third and a fourth electrical terminal 12, 13. The third terminal 12 is conductively connected to the second edge 5. The fourth terminal 13 is conductively connected to the power source 20.

[0025] The additional circuitry with the first and second resistors 8, 11 creates a virtually extended contact area 27, which is larger than the real, haptically perceptible contact area 26.

[0026] Layers 2 and 3 can also be round, in which case edges 4 to 7 are each semicircular.

[0027] Fig. Figure 3 shows the measurement of the voltage drop when touching the touchscreen 1 in one dimension, illustrated in a block diagram. At the touch point 25, the first layer 2 of the touchscreen 1 is short-circuited with the second layer 3 of the touchscreen 1. The two layers 2 and 3 are superimposed and spaced apart from each other. The two resistors 8 and 11 are connected to the edges 4 and 5 of the first layer 2 via their terminals 9 and 12, respectively. The other terminals 13 and 10 of the two resistors 8 and 11 are connected to the current source 20 and ground, respectively. By inducing a current in the resistive first layer 2, a voltage drop occurs between the first edge 4 and the second edge 5. A voltage drop also occurs across the first resistor 8 and the second resistor 11.

[0028] The resistive second layer 3 has edges 6 and 7 that are rotated 90° relative to edges 4 and 5. The third resistor 14 is conductively connected to the third edge 6 via a fifth terminal 15. The fourth resistor 17 is conductively connected to the fourth edge 7 via a seventh terminal 18. The voltage drop between the contact point 25 and the second terminal 10, between the sixth terminal 16 (third resistor 14) and the second terminal 10, is measured using the high-impedance voltage measuring device 21. Knowing the length of the first layer 2 in the current flow direction and the values ​​of resistors 8 and 11, and assuming a uniform voltage drop in the first layer 2, the position of the contact point 25 in the current flow direction can be determined.In the perpendicular direction, the position of the contact point 25 can be determined analogously by connecting the current source 20 to the second layer 3 and connecting the voltage measuring device 21 to the first layer 2.

[0029] Fig. Figure 4 shows the voltage dividers and voltage drops of the circuit arrangement according to Fig. 3. Links in Fig. Figure 4 shows the voltage divider 28 formed by contact in the resistive first layer 2. The first and second resistors 8 and 11 are connected to the voltage divider 28. The current source 20 induces a current in the resistors 8 and 11 and in the voltage divider 28. A first voltage drop U1 occurs in the first layer 2. The third voltage drop U3 occurs between the first resistor 8 and the point of contact. The fourth voltage drop U4 occurs between the second resistor 11 and the point of contact. The voltage drops U3 and U4 can be determined using the voltage measuring device 21. The measurement of the fourth voltage drop U4 is shown.

[0030] Right in Fig.Figure 4 shows the voltage divider 29 of the resistive second layer 3 formed by contact. The third and fourth resistors 14 and 17 are connected to the voltage divider 29. The current source 20 induces a current in resistors 14 and 17 and in the voltage divider 29. A second voltage drop U2 occurs in the second layer 3. The fifth voltage drop U5 occurs between the third resistor 14 and the point of contact. The sixth voltage drop U6 occurs between the fourth resistor 17 and the point of contact. The voltage drops U5 and U6 can be determined using the voltage measuring device 21. The measurement of the sixth voltage drop U6 is shown.

[0031] Although the invention has been illustrated and described in detail by the exemplary embodiments, the invention is not limited by the disclosed examples and other variations can be derived from them by a person skilled in the art without departing from the scope of protection of the invention. In particular, the invention can also be used in non-medical applications. Reference symbol list 1 Touchscreen (touch-sensitive screen) 2 first shift 3 second shift 4 first edge 5 second edge 6 third edge 7 fourth margin 8 electrical first resistance 9 electrical first connection 10 electrical second connection 11 electrical second resistance 12 electrical third connection 13 electrical fourth connection 14 electrical third resistance 15 electrical fifth connection 16 electrical sixth connection 17 electrical fourth resistance 18 electrical seventh connection 19 electrical eighth connection 20 Power source 21 Voltage measuring device 22 Control panel 24 medical imaging devices 25 Point of contact 26 Contact area 27 extended contact area 28 voltage dividers 29 voltage dividers U1 first voltage drop U2 second voltage drop U3 third voltage drop U4 fourth voltage drop U5 fifth voltage drop U6 sixth voltage drop

Claims

[1] Method for operating a resistive touchscreen (1), wherein the coordinates of a touch point (25) on the touchscreen (1) are connected to a circuit arrangement, - wherein the circuit arrangement comprises a resistive touchscreen (1) with a resistive first layer (2) and a resistive second layer (3) arranged in parallel to each other, - wherein the voltage dividers (U1, U2) of the first and second layers (2, 3) formed by touching the touchscreen (1) are extended by electrical resistors (8, 11, 14, 17) arranged at the edges (4, 5, 6, 7) of the first and second layers (2, 3), characterized by , that determined positions of the touch point (25) outside the operating area of ​​the touchscreen (1) are recognized as an error of a control circuit of the touchscreen (1). [2] Method according to claim 1, characterized by , that the first and second layers (2, 3) are rectangular in shape. [3] Method according to claim 1 or 2, characterized by : - an electrical first resistor (8) with a first and a second terminal (9, 10), wherein the first terminal (9) is electrically connected to a first edge (4) of the first layer (2), - an electrical second resistor (11) with a third and a fourth terminal (12, 13), wherein the third terminal (12) is electrically connected to a second edge (5) of the first layer (2) opposite the first edge (4), - an electrical third resistor (14) with a fifth and a sixth terminal (15, 16), wherein the fifth terminal (15) is electrically connected to a third edge (6) of the second layer (3) oriented at ninety degrees to the first edge (4), and - an electrical fourth resistor (17) with a seventh and an eighth terminal (18, 19), wherein the seventh terminal (18) is electrically connected to a fourth edge (7) of the second layer (3) opposite the third edge (6). [4] Method according to claim 3, characterized by : - a power source (20) that is connected either between the second and fourth terminals (10, 13) or the sixth and eighth terminals (16, 19). [5] Method according to claim 3 or 4, characterized by , that the first layer (2) is designed such that a uniformly increasing first voltage drop (U1) is generated between the first and the second edge (4, 5) when current flows. [6] Method according to any one of claims 3 to 4, characterized by, that the second layer (3) is designed such that a uniformly progressive second voltage drop (U2) is generated between the third and the fourth edge (6, 7) when current flows. [7] Method according to any one of claims 3 to 6, characterized by : - a high-impedance voltage measuring device (21) configured to determine a third voltage drop (U3) between a contact point (25) on the first layer (2) and the second terminal (10) and a fourth voltage drop (U4) between the fourth terminal (13) and the contact point (25), wherein the contact point (25) is formed by locally short-circuiting the first layer (2) with the second layer (3). [8] Method according to claim 7, characterized by, that the voltage measuring device (21) is configured to determine a fifth voltage drop (U5) between the contact point (25) and the sixth terminal (16) and a sixth voltage drop (U6) between the eighth terminal (19) and the contact point (25).

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