TOUCH DETERMINATION WITH IMPROVED DETECTION OF WEAK INTERACTIONS

• US 20160070415A1
• Filed: 02/19/2013
• Published: 03/10/2016
• Est. Priority Date: 02/21/2012
• Status: Active Grant

• Current Assignee: FlatFrog Laboratories AB
• Original Assignee: FlatFrog Laboratories AB
• Inventors: CHRISTIANSSON, Tomas, OHLSSON, Nicklas
• Granted Patent: US 9,811,209 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06F 2203/04104 Multi-touch detection in digitiser, i.e. details about the simultaneous detection of a plurality of touching locations, e.g. multiple fingers or pen and finger
• CPC Class Codes: G06F 2203/04109 FTIR in optical digitiser, i.e. touch detection by frustrating the total internal reflection within an optical waveguide due to changes of optical properties or deformation at the touch location
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/0421 by interrupting or reflecting a light beam, e.g. optical touch-screen

Abstract

Touch sensitivity is enabled using a touch system that comprises a panel configured to conduct signals, e.g. by TIR, along detection lines across a touch surface. A signal processor operates to obtain observed values for the detection lines, and identify an interaction pattern on the touch surface as a solution to an optimization function that comprises an aggregation of differences, for each detection line, between the observed value and a projected value, which is given by a projection function that defines a functional relation between the interaction pattern and the projected value for each detection line. The signal processor implements a normalization to ensure that the interaction pattern indicates weak touches even in the presence of strong touches. The normalization involves computing a respective normalization value for each of the differences as a function of the observed value for the respective detection line; and applying the respective normalization value so as to normalize the respective difference in the optimization function.

Claims

1. A method of enabling touch determination based on an output signal from a touch-sensitive apparatus, the touch-sensitive apparatus comprising a panel configured to conduct signals from a plurality of incoupling points to a plurality of outcoupling points, thereby defining detection lines that extend across a surface portion of the panel between pairs of incoupling and outcoupling points, at least one signal generator coupled to the incoupling points to generate the signals, and at least one signal detector coupled to the outcoupling points to generate the output signal which is indicative of interaction between one or more touching objects and one or more of the detection lines, wherein the method comprises the steps of:

receiving the output signal;

processing the output signal to obtain observed values for the detection lines; and

identifying an interaction pattern for the surface portion as a solution to an optimization function that comprises an aggregation of differences between the observed value and a projected value for each of the detection lines, the projected value being given by a projection function that defines a functional relation between the interaction pattern and the projected value for the respective detection line;

said method further comprising the steps of;

computing a respective normalization value for each of the differences as a function of the observed value for the respective detection line; and

applying the respective normalization value so as to normalize the respective difference in the optimization function.

2. The method of claim 1, wherein the respective normalization value is computed to be relatively larger when the observed value corresponds to a strong interaction compared to a weak interaction.

3. The method of claim 1, wherein the interaction pattern is generated to indicate changes in interaction on the surface portion, and wherein the respective normalization value is computed as a function of a nominal difference between the observed value for the respective detection line and a nominal projected value for the respective detection line, the nominal projected value being given by the projection function when the interaction pattern indicates that there are no changes in interaction on the surface portion.

4. The method of claim 3, wherein the respective normalization value is computed as a function of a positive offset value and the nominal difference.

5. The method of claim 4, wherein the step of computing the respective normalization value comprises adding a positive offset value to a non-negative value obtained as a function of the nominal difference.

6. The method of claim 4, wherein the positive offset value is set to exceed an estimated noise level of the output signal.

7. The method of claim 1, wherein the step of estimating the interaction pattern comprises:

finding the solution that causes a gradient of the optimization function for each interaction value in the interaction pattern to be essentially zero.

8. The method of claim 7, wherein the optimization function comprises a first part that represents a likelihood distribution, which is a function of the aggregation of differences, and a second part that represent a prior distribution, which is configured to penalize variations between neighboring interaction values in the interaction pattern.

9. The method of claim 8, wherein the prior distribution is a function of an aggregation of second differences between each individual interaction value in the interaction pattern and its neighboring interaction values in the interaction pattern, wherein each of the second differences is normalized by a respective second normalization value that represents a local interaction strength at said individual interaction value.

10. The method of claim 9, wherein the local interaction strength is computed as a function of said individual interaction value.

11. The method of claim 9, wherein the second normalization value is computed by adding a positive second offset value to the local interaction strength.

12. The method of claim 11, wherein the positive second offset value is set to exceed an estimated noise level in the interaction pattern.

13. The method of claim 1, wherein the step of processing the output signal comprises identifying a measurement value for each detection line, and generating the observed value to represent a relative change of the measurement value to a reference value for the respective detection line.

14. The method of claim 13, wherein the observed value is given as a logarithm of the relative change.

15. The method of claim 13, wherein the reference value for the respective detection line is computed as a function of the measurement value for the detection line in the output signal at a calibration time without said interaction between said one or more touching objects and said one or more of the detection lines.

16. The method of claim 13, which operates in a sequence of repetitions to identify the measurement value for each detection line, generate the observed values for the detection lines, and estimate the interaction pattern, wherein the reference value for the respective detection line is intermittently updated based on the output signal such that the interaction pattern indicates changes in interaction with respect to a preceding repetition in the sequence of repetitions.

17. The method of claim 1, wherein the interaction pattern is representative of changes in one of attenuation and transmission.

18. A computer program product comprising computer code which, when executed on a data-processing system, is adapted to carry out the method of claim 1.

19. A device for enabling touch determination based on an output signal from a touch-sensitive apparatus, the touch-sensitive apparatus comprising a panel configured to conduct signals from a plurality of incoupling points to a plurality of outcoupling points, thereby defining detection lines that extend across a surface portion of the panel between pairs of incoupling and outcoupling points, at least one signal generator coupled to the incoupling points to generate the signals, and at least one signal detector coupled to the outcoupling points to generate the output signal which is indicative of interaction between one or more touching objects and one or more of the detection line, said device comprising:

an input for receiving the output signal, and

a signal processor configured to receive the output signal;

process the output signal to obtain observed values for the detection lines; and

identify an interaction pattern for the surface portion as a solution to an optimization function that comprises an aggregation of differences between the observed value and a projected value for each of the detection lines, the projected value being given by a projection function that defines a functional relation between the interaction pattern and the projected value for the respective detection line;

said signal processor being further configured to;

compute a respective normalization value for each of the differences as a function of the observed value for the respective detection line; and

apply the respective normalization value so as to normalize the respective difference in the optimization function.

21. A touch-sensitive apparatus, comprising:

a panel configured to conduct signals from a plurality of incoupling points to a plurality of outcoupling points, thereby defining detection lines that extend across a surface portion of the panel between pairs of incoupling and outcoupling points;

means for generating the signals at the incoupling points;

means for generating an output signal based on detected signals at the outcoupling points; and

the device for enabling touch determination according to claim 19.

20. (canceled)