Touch sensing using shadow and reflective modes
A touch panel is described which uses at least one infrared source and an array of infrared sensors to detect objects which are in contact with, or close to, the touchable surface of the panel. The panel may be operated in both reflective and shadow modes, in arbirary per-pixel combinations which change over time. For example, if the level of ambient infrared is detected and if that level exceeds a threshold, shadow mode is used for detection of touch events over some or all of the display. If the threshold is not exceeded, reflective mode is used to detect touch events. The touch panel includes an infrared source and an array of infrared sensors.
1. A method of operating a touch panel system for detecting one or more objects in proximity with a touchable surface of a touch panel, the method comprising:
scanning at least a portion of the touch panel to measure a level of ambient infrared radiation using at least one infrared sensor;
switching to a shadow mode of operation if a level of ambient infrared radiation exceeds a first threshold;
switching to a reflective mode of operation if the level of ambient infrared radiation does not exceed both the first threshold and a second threshold;
determining that a battery level is below a predetermined limit while the level of ambient infrared radiation exceeds the second threshold and not the first threshold;
switching to the shadow mode of operation after the battery level drops below the predetermined limit; and
switching to the reflective mode of operation after the battery level rises above the predetermined limit.
2. A method according to claim 1 , wherein scanning at least a portion of the touch panel further comprises:
scanning different portions of the touch panel dependent upon time and upon signals from the infrared sensors.
3. A method according to claim 1 , wherein the first threshold is higher than the second threshold.
4. A method according to claim 1 , wherein the touch panel system further comprises a plurality of infrared sources configured to illuminate the objects with infrared radiation through the touchable surface, the method further comprising, in reflective mode of operation:
scanning the touch panel; and
on detection of a touch event at an infrared sensor, illuminating those infrared sources in proximity to said infrared sensor.
5. A method according to claim 1 , further comprising, in reflective mode of operation:
illuminating the touchable surface with infrared radiation of a first wavelength;
detecting infrared radiation reflected from an object at said first wavelength; and
repeating the illuminating and detecting steps at a second wavelength.
6. A method according to claim 1 , further comprising, periodically recalibrating the touch panel system based on the scanning at least the portion of the touch panel.
7. A touch panel system for detecting one or more objects in proximity with a touchable surface of the touch panel system, the touch panel system comprising:
a touch panel having integrated therein infrared sensors distributed throughout the touch panel parallel to the touchable surface;
at least one infrared source configured to illuminate objects through the touchable surface; and
a control element arranged to:
scan at least a portion of the touch panel to measure a level of ambient infrared radiation;
switch to a shadow mode of operation if a level of ambient infrared radiation exceeds a first threshold;
switch to a reflective mode of operation if the level of ambient infrared radiation does not exceed both the first threshold and a second threshold;
determine that a battery level is below a predetermined limit while the level of ambient infrared radiation exceeds the second threshold and not the first threshold;
switch to the shadow mode of operation after the battery level drops below the predetermined limit; and
switch to the reflective mode of operation after the battery level rises above the predetermined limit.
8. A touch panel system according to claim 7 , wherein the control element comprises:
a processor; and
a memory arranged to store executable instructions arranged to cause the processor to monitor signals from the infrared sensors and switch between the reflective mode of operation and the shadow mode of operation for at least a portion of the touch panel based on the monitored signals.
9. A touch panel system according to claim 8 , further comprising an array of infrared sources, wherein the memory is further arranged to stored executable instructions arranged to cause the processor, in the reflective mode of operation, to:
scan the touch panel; and
on detection of a touch event at an infrared sensor; to illuminate those infrared sources in proximity to said infrared sensor.
10. A touch panel system according to claim 7 , wherein the object comprises a wavelength selective tag or label which can be read using different wavelengths of IR that enables the object to be distinguished from another object.