US 12,366,939 B2
Coordinate input apparatus
Akira Sato, Miyagi-ken (JP); Satoshi Nakajima, Miyagi-ken (JP); and Tomohiro Sasaki, Miyagi-ken (JP)
Assigned to Alps Alpine Co., Ltd., Tokyo (JP)
Filed by Alps Alpine Co., Ltd., Tokyo (JP)
Filed on Dec. 21, 2023, as Appl. No. 18/393,383.
Claims priority of application No. 2023-005966 (JP), filed on Jan. 18, 2023.
Prior Publication US 2024/0241601 A1, Jul. 18, 2024
Int. Cl. G06F 3/041 (2006.01); G06F 3/044 (2006.01)
CPC G06F 3/0418 (2013.01) [G06F 3/044 (2013.01)] 5 Claims
OG exemplary drawing
 
1. A coordinate input apparatus comprising:
an insulating substrate;
a capacitance sensor including a plurality of sensor electrodes provided on the insulating substrate, the plurality of electrodes having a plurality of detecting positions;
a top panel covering the plurality of sensor electrodes, the top panel including an operating surface that allows an operation with a pointer, the pointer changing a capacitance of the plurality of sensor electrodes depending on a distance to the operating surface;
a measuring circuit configured to measure the capacitance at each of the plurality of detecting positions, thereby providing a plurality of measured capacitance values; and
a calculating circuit configured to calculate a position of the pointer in two axis directions of the operating surface based on the plurality of measured capacitance values,
wherein the calculating circuit is further configured:
to determine, in each of the two axis directions, a maximum detecting position having a maximum capacitance value among the plurality of measured capacitance values and two adjacent detecting positions on respective sides of the maximum detecting position in the axis direction, and to fit a quadratic curve to the maximum capacitance value and the measured capacitance values of the two adjacent detecting positions, thereby calculating a position of a vertex of the quadratic curve as a position of the pointer in the axis direction, and if the maximum detecting position is an end detecting position closest to an edge of the capacitance sensor in the axis direction, to correct the position of the pointer by shifting the calculated position of the vertex toward the edge of the capacitance sensor in the axis-direction;
to calculate a distance from the operating surface to the pointer based on the maximum capacitance value; and
to set a reference position in a vicinity of the edge of the capacitance sensor in each of the two axis directions, and when the calculated position of the vertex is closer to the edge of the capacitance sensor than the reference position in the axis direction, to calculate a correction distance by multiplying a distance between the reference position and the vertex by a correction factor, thereby correcting the position of the pointer by shifting the calculated position of the vertex toward the edge of the capacitance sensor by the correction distance,
and wherein the correction factor is increased as the maximum capacitance value decreases.