Touch sensing apparatus and method of operating the same
A touch sensing apparatus includes a group of emitters arranged to emit light to illuminate at least part of the touch surface, a light detector arranged to receive light from the group of emitters, and a processing element. Each emitter is controlled to transmit a code by way of the emitted light such that the code identifies the respective emitter. The codes may at least partly be transmitted concurrently. The codes may be selected such that a value of an autocorrelation of each code is significantly higher than a value of a cross-correlation between any two codes of different emitters. The processing element processes an output signal from the light detector to separate the light received from the individual emitters based on the transmitted codes, and to determine the position of the object/objects based on the light received from the individual emitters.
1. A touch sensing apparatus, comprising:
a touch surface;
a group of emitters arranged to emit light to illuminate at least part of the touch surface, each respective emitter in the group of emitters configured to transmit a linearly independent binary value by way of the emitted light, the linearly independent binary value identifying the respective emitter;
a group of light detectors arranged to receive light from the group of emitters, the group of light detectors configured to generate an output signal; and
at least one processor configured to separate light signals received from individual emitters from the output signal based on the linearly independent binary values, and to process the light signals based on an algorithm for transmission tomography to determine a position of one or more objects interacting with the touch surface; wherein
the algorithm for transmission tomography generates a two-dimensional model of an interaction between the one or more objects and the touch surface.
2. The touch sensing apparatus of claim 1 , wherein a value of an autocorrelation of each linearly independent binary value is greater than a value of a cross-correlation between any two linearly independent binary values of different emitters.
3. The touch sensing apparatus of claim 1 , wherein the linearly independent binary values are transmitted concurrently.
4. The touch sensing apparatus of claim 1 , wherein at least two emitters in the group of emitters are controlled to emit light simultaneously during transmission of the linearly independent binary values.
5. The touch sensing apparatus of claim 1 , wherein the linearly independent binary value from each respective emitter is embedded in the emitted light by modulation.
6. The touch sensing apparatus of claim 5 , wherein
the modulation is amplitude modulation; and
each linearly independent binary value includes a sequence of binary values, each of the binary values represented by an energy of the emitted light.
7. The touch sensing apparatus of claim 5 , wherein
the modulation is amplitude modulation according to a basic periodic function; and
each linearly independent binary value is represented by a unique modulation frequency of the basic periodic function.
8. The touch sensing apparatus of claim 1 , wherein the linearly independent binary value from each respective emitter is embedded in the emitted light by on-off-modulation of the respective emitter.
9. The touch sensing apparatus of claim 8 , wherein the linearly independent binary values are selected such that approximately 50% of emitters in said group of emitters emit light simultaneously.
10. The touch sensing apparatus of claim 1 , wherein
each linearly independent binary value includes a sequence of binary values;
said linearly independent binary values form columns of a modulation matrix M; and
the at least one processor is further configured to operate an inverse M −1 of the modulation matrix M on the output signal to separate the light signals received from the individual emitters.
11. The touch sensing apparatus of claim 10 , wherein the modulation matrix M is a Hadamard matrix or a Sylvester matrix derived from a Hadamard matrix.
12. The touch sensing apparatus of claim 1 , wherein each respective emitter is configured to emit a diverging beam of light.
13. The touch sensing apparatus of claim 1 , further comprising:
a total set of light detectors and a total set of emitters, wherein
each light detector is configured to receive light from one or more groups of emitters, and
each respective emitter in the total set of emitters is included in at least one group.
14. The touch sensing apparatus of claim 13 , wherein the total set of emitters and the total set of light detectors are arranged around a periphery of the touch surface.
15. The touch sensing apparatus of claim 14 , wherein
emitters in the total set of emitters are arranged to illuminate a space immediately above the touch surface; and
the at least one processor is further configured to
identify occlusions in the light received from each of said emitters, and
determine the position of said one or more objects based on the identified occlusions.
16. The touch sensing apparatus of claim 1 , further comprising:
a light transmissive element that defines the touch surface;
wherein said light propagates inside the light transmissive element to illuminate the touch surface such that the one or more objects interacting with the touch surface cause an attenuation of the light propagating inside the light transmissive element; and
wherein the at least one processor is further configured to
identify attenuations in the light received from each respective emitter, and
determine the position of said one or more objects based on the identified attenuations.
17. The touch sensing apparatus of claim 1 , wherein the touch surface is polygonal, and at least one emitter is arranged at a corner of the touch surface.
18. A method of operating a touch sensing apparatus, the touch sensing apparatus including a touch surface, a group of emitters arranged to emit light to illuminate at least part of the touch surface, and a group of light detectors arranged to receive light from the group of emitters, the group of light detectors configured to generate an output signal, said method comprising:
controlling each respective emitter in the group of emitters to transmit a linearly independent binary value by the emitted light, the linearly independent binary value identifying the respective emitter;
separating light signals received from individual emitters from the output signal based on the linearly independent binary values; and
processing the light signals based on an algorithm for transmission tomography to determine a position of one or more objects interacting with the touch surface; wherein
the algorithm for transmission tomography generates a two-dimensional model of an interaction between the one or more objects and the touch surface.
19. A non-transitory computer readable storage medium storing processing instructions that, when executed by at least one processor, cause the at least one processor to perform the method according to claim 18 .