Touch screen calibration system and method

• US 6,977,646 B1
• Filed: 11/30/2001
• Issued: 12/20/2005
• Est. Priority Date: 11/30/2001
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Hares, Luke David Ronald, Hauck, Karl P.
• Primary Examiner(s): Shankar, Vijay
• Assistant Examiner(s): DHARIA, PRABODH M
• Application Number:
  US09/998,699
• Time in Patent Office: 1,481 Days
• Field of Search: 345173-179, 345/156, 345/158, 345/162, 345/184, 178 1801- 1807, 178/19, 178/20, 340/712, 341/22
• US Class Current: 345/173
• CPC Class Codes: G06F 3/04186 Touch location disambiguation

Abstract

Disclosed is a touch screen calibration system and method that applies a signal to a the terminals of a touch screen and applies a calibration impedance to those terminals; the effect of the calibration impedance applied to the terminals is sensed; the X, Y position for each terminal is calculated upon application of the calibration impedance and the offset error for each terminal is calculated and applied to obtain the corrected touch position for a measured touch position; in addition the gain error may be calculated for each terminal and applied to obtain the corrected touch position.

Claims

1. A touch screen calibration system comprising:

a touch screen having a plurality of terminals;

a control circuit associated with each of the terminals for applying a signal to the associated terminal and sensing current flowing through the terminals due to a touch on the touch screen;

a switching circuit for applying a calibration impedance to the touch screen; and

a microprocessor configured to calculate offsets upon application of the calibration impedance, to interpolate the offsets as a function of relative X, Y coordinates of a measured touch position determined from ratios of currents flowing through the terminals, the interpolation using error correction equations containing coefficients calculated by solving simultaneous equations derived from a second order Taylor series expansion, and to apply the offsets to the measured touch position thereby obtaining a corrected touch position.

2. A method for calibrating a touch screen comprising:

applying a signal to terminals of a touch screen;

applying a calibration impedance to the terminals;

sensing an effect on the signal of the calibration impedance applied to the terminals;

calculating an X, Y position indicated for each terminal upon application of the calibration impedance;

calculating an error for each terminal;

interpolating the errors as a function of relative X, Y positions of a measured touch position obtained from ratios of currents flowing through the terminals due to a touch to the touch screen, the interpolation using error correction equations containing coefficients calculated by solving simultaneous equations that model the screen errors as a two dimensional Taylor series; and

applying the errors to obtain a corrected touch position from the measured touch position.