METHOD FOR DETERMINING A POSITION OF A CONTACT ON A CAPACITIVE SENSOR FIELD

• US 20140002418A1
• Filed: 12/08/2011
• Published: 01/02/2014
• Est. Priority Date: 12/08/2010
• Status: Active Grant

• Current Assignee: TRW Automotive Electronics & Components GmbH & Co. KG
• Original Assignee: TRW Automotive Electronics & Components GmbH & Co. KG
• Inventors: Backes, Ulrich, Reise, Wulf
• Granted Patent: US 9,342,197 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• CPC Class Codes: G06F 3/0354 with detection of 2D relative movements between the device, or an operating part thereof, and a plane or surface, e.g. 2D mice, trackballs, pens or pucks
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/044 by capacitive means

Abstract

In a method of determining a position of a touch on a capacitive sensor field having a grid of a plurality of discrete electrodes (12), contacted electrodes are determined by measuring a capacitance value for each of the electrodes and by checking for each of the electrodes for the measured capacitance value whether this value is above a predefined threshold value. A rough touch position (B_g) is calculated by weighting the electrode position with the measured capacitance value. A touch diameter (14) is calculated from the measured capacitance values, and a final touch position (B_e) is calculated from the rough touch position (B_g) and the calculated touch diameter (14) using a value table in which correction values that were determined empirically or by means of simulation are stored for possible rough touch positions (B_g) and given touch diameters (14).

Claims

1-11. -11. (canceled)

12. A method of determining a position of a touch on a capacitive sensor field having a grid of a plurality of discrete electrodes (12), wherein:

(a) touched electrodes are determined by measuring a capacitance value for each of the electrodes and checking for each of the electrodes for the measured capacitance value whether this value is above a predefined threshold value;

(b) a rough touch position (B_g) is calculated by weighting the electrode position with the measured capacitance value;

(c) a touch diameter (14) is calculated from the measured capacitance values; and

(d) a final touch position (B_e) is calculated from the rough touch position (B_g) and the calculated touch diameter (14) using a value table in which correction values (k) that were determined empirically or by means of simulation and are dependent on the rough touch position (B_g) and the touch diameter (14) are stored for possible rough touch positions (B_g) and given touch diameters (14).

13. The method according to claim 12, characterized in that the correction values (k) are stored for discrete relative positions with a higher resolution than the electrode grid.

14. The method according claim 12, wherein the electrodes (12) for which the measured capacitance value is above the threshold value are combined into at least one group (E1-E4) of neighboring electrodes, in particular of four electrodes, the centers of which constitute the corners of a rectangle, and the rough touch position (B_g) is determined for each group of electrodes by a division of the sum of the products of the electrode positions of the group with the measured capacitance values by the sum of all measured capacitance values of the group.

15. The method according to claim 14, wherein symmetries in two directions (x, y) orthogonal to each other in relation to a center (M) of the group of electrodes (E1-E4) are assumed for the correction values.

16. The method according to claim 15, wherein:

a difference value (d_x) in the first direction (x) is determined in that

based on the component (B_x) of the rough touch position (B_g) in the first direction (x) in relation to the center (M), an x-proportion (d_x1) is defined which originates from a first group of values (x, y_a, k) of the correction values (k) for a predetermined coordinate (y_a) along the second direction (y);

based on the component (B_y) of the rough touch position (B) in the second direction (y) in relation to the center (M), a y-proportion (d_x2) is defined which originates from a second group of values (x_a, y, k) of the correction values (k) for a predetermined coordinate (x_a) along the first direction (x); and

the difference value (d_x) is calculated as a sum of the x-proportion (d_x1) and the y-proportion (d_x2);

a difference value in the second direction (y) is determined in that

based on the component (B_y) of the rough touch position (B) in the second direction (y) in relation to the center (M), a y-proportion (d_y1) is defined which originates from a third group of values (x_b, y, k) for a predetermined coordinate (x_b) along the first direction (x); and

based on the component (B_x) of the rough touch position (B) in the second direction (x) in relation to the center (M), an x-proportion (d_y2) is defined which originates from a fourth group of values (x, y_b, k) for a predetermined coordinate (y_b) along the second direction (y);

the difference value (d_y) is calculated as a sum of the y-proportion (d_y1) and the x-proportion (d_y2); and

the final touch position (B_e) is formed from the sum of the rough touch position (B) and the difference values (d_x, d_y).

17. The method according to claim 16, wherein on the basis of the symmetry of the correction values (k) in relation to the center (M), the groups of values in the first and second directions (x, y) are each reduced to half the electrode distance.

18. The method according to claim 12, wherein the touch diameter (14) is determined from the measured capacitive values of the electrodes (12) by means of a linear relationship.

19. The method according to claim 12, wherein the electrodes (12) are spaced from each other.

20. The method according to claim 12, wherein a diameter of the electrodes (12) or a distance of the centers (M) of the electrodes (12) amounts to approx. 5-15 mm.

21. The method according to claim 12, wherein the capacitive value of each electrode (12) is measured against ground.