TOUCH FORCE ESTIMATION IN AN FTIR-BASED PROJECTION-TYPE TOUCH-SENSING APPARATUS

• US 20150317036A1
• Filed: 07/14/2015
• Published: 11/05/2015
• Est. Priority Date: 09/11/2012
• Status: Active Grant

• Current Assignee: FlatFrog Laboratories AB
• Original Assignee: FlatFrog Laboratories AB
• Inventors: OHLSSON, Nicklas, JOHANSSON, Andreas
• Granted Patent: US 10,088,957 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• 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

A device implements a method for estimating the application force of a touching object onto a touch surface in an FTIR-based projection-type touch-sensing apparatus. The apparatus generates projection signals representing radiation that has propagated on a plurality of propagation paths by total internal reflection (TIR) inside a transmissive panel beneath a touch surface of the transmissive panel such that a touching object on the touch surface causes attenuation (frustration) of at least one of the projection signals. The device generates a time series of force values, which represent the application force, based on a time series of magnitude values, which represent a magnitude of a peak in two-dimensional interaction patterns generated by image reconstruction processing of the projection signals, the peak corresponding to the touching object on the touch surface. The force estimation may involve one or more corrections.

Claims

1. A method of data processing in relation to an FTIR-based projection-type touch-sensing apparatus, wherein the touch-sensing apparatus is operable to generate projection signals representing radiation that has propagated on a plurality of propagation paths by total internal reflections inside a transmissive panel beneath a touch surface of the transmissive panel such that a touching object on the touch surface causes attenuation of at least one of the projection signals, said method comprising:

obtaining a time series of magnitude values representing a magnitude of a peak in two-dimensional interaction patterns generated by image reconstruction processing of the projection signals, the peak corresponding to a touching object on the touch surface; and

generating, as a function of the time series of magnitude values, a time series of force values representing the application force of the touching object onto the touch surface.

2. The method of claim 1, wherein a current force value in the time series of force values is generated as a function of a current magnitude value among the magnitude values and a current speed of the touching object.

3. The method of claim 2, further comprising:

detecting, based on the current speed, that the touching object is in a low speed state, and applying a duration-based modification function to the current magnitude value so as to counteract a gradual increase in attenuation with time for touching objects in the low speed state.

4. The method of claim 3, further comprising:

associating the touching object with an age counter which is incremented with the duration of the touching object in the low speed state, wherein the duration-based modification function operates on the age counter and the current magnitude value.

5. The method of claim 4, further comprising:

applying an increment to the age counter that decreases with the current speed while the touching object is in the low speed state.

6. The method of claim 4, further comprising:

applying a decrement to the age counter when the touching object has left the low speed state.

7. The method of claim 6, wherein the decrement is increased with increasing current speed of the touching object.

8. The method of claim 1, further comprising:

operating a low-pass filter on at least one of the time series of force values and the time series of magnitude values.

9. The method of an claim 8, further comprising:

decreasing a cut-off frequency of the low-pass filter with increasing current speed of the touching object.

10. The method of claim 9, further comprising:

selectively delaying an increase in cut-off frequency of the low-pass filter when the touching object is deemed to approach a stand-still on the touch surface.

11. The method of claim 1, further comprising:

applying a speed-based modification function to the current magnitude value so as to counteract a decreasing attenuation with increasing speed of the touching object.

12. The method of claim 1, further comprising:

obtaining a time series of size values representing a size measure of the peak in the two-dimensional interaction patterns; and

applying a size-based modification function to the current magnitude value so as to counteract an increasing attenuation with increasing size of the peak.

13. The method of claim 1, wherein the step of obtaining the time series of magnitude values comprises, repeatedly:

obtaining current values of the projection signals, processing the current values by image reconstruction to generate a current interaction pattern for the touch surface, identifying a peak associated with the touch in the current interaction pattern, and computing a magnitude value for the peak.

14. The method of claim 1, wherein the magnitude represents a degree of attenuation or transmission of radiation at the location of the touching object on the touch surface.

15. A computer readable medium comprising computer instructions which, when executed by a data-processing system, are configured to carry out the method of claim 1.

16. A device for data processing in relation to an FTIR-based projection-type touch-sensing apparatus, wherein the touch-sensing apparatus is operable to generate projection signals for radiation that has propagated on plurality of propagation paths by total internal reflections inside a transmissive panel beneath a touch surface on the transmissive panel such that a touching object on the touch surface causes attenuation of at least one of the projection signals, said device comprising a signal processor configured to:

obtain a time series of magnitude values representing a magnitude of a peak in a time series of two-dimensional interaction patterns generated by image reconstruction processing of the projection signals, the peak corresponding to the touching object on the touch surface; and

generate, as a function of the time series of magnitude values, a time series of force values representing the application force of the touching object onto the touch surface.

18. An FTIR-based projection-type touch-sensing apparatus, comprising:

a transmissive panel configured to conduct radiation from a plurality of incoupling points to a plurality of outcoupling points by total internal reflection inside the transmissive panel, thereby defining a plurality of propagation paths beneath a touch surface on the transmissive panel between pairs of incoupling and outcoupling points such that a touching object on the touch surface causes the radiation on at least one of the propagation paths to be attenuated by frustration of the total internal reflection;

at least one signal generator coupled to the incoupling points to generate the radiation;

at least one signal detector coupled to the outcoupling points to detect the radiation on the plurality of propagation paths and generate corresponding projection signals; and

a device according to claim 16.

17. A device for data processing in relation to an FTIR-based projection-type touch-sensing apparatus, wherein the touch-sensing apparatus is operable to generate projection signals for radiation that has propagated on plurality of propagation paths by total internal reflections inside a transmissive panel beneath a touch surface on the transmissive panel such that a touching object on the touch surface causes attenuation of at least one of the projection signals, said device comprising:

means for obtaining a time series of magnitude values representing a magnitude of a peak in a time series of two-dimensional interaction patterns generated by image reconstruction processing of the projection signals, the peak corresponding to the touching object on the touch surface; and

means for generating, as a function of the time series of magnitude values, a time series of force values representing the application force of the touching object onto the touch surface.