Method for determining the locations of one or more impacts or touches on a surface of an object including two or more transducers
View Patent ↗The invention relates to a method for determining the locations of one or more impacts or touches on a surface of an object including two or more transducers which improves the precision of localisation even for low signal to noise ratios and furthermore provides the possibility to identify multi touch or multi impact situations. To achieve these objects the method comprises the steps of: a) receiving a signal, in particular an acoustic signal, from each one of the transducers, wherein the signals correspond to at least one impact at least one location on the surface; b) determining a representative value based on the signals received in step a) and predetermined properties, in particular acoustic properties, of the object at a given location on the surface of the object; and c) deciding whether the at least one impact at the at least one location on the surface of step a) corresponds to the given location on the surface based on a comparison of the representative value and the corresponding value of the at least two signals.
1. A method for determining one or more impact locations on an object's surface, the method comprising:
receiving acoustic signals from at least two transducers, wherein the acoustic signals correspond to at least one impact location on the object's surface;
determining a representative value based on a reconstructed excitation source signal, wherein the reconstructed excitation source signal is based on an algorithmic transformation of (i) the acoustic signals and (ii) predetermined acoustic properties of the object at a given location on the object's surface;
removing background noise around a maximum of the reconstructed excitation source signal in a time domain, wherein the removing comprises:
transforming the reconstructed excitation source signal in the time domain:
determining a time (t max ) at which the transformed reconstructed excitation source signal has a maximum amplitude;
filtering a time window around t max to obtain a modified reconstructed source signal corresponding to a given impact at the given location on the object's surface; and
transforming the modified reconstructed source signal into a frequency domain; and
deciding whether the at least one impact location corresponds to the given location on the object's surface based on a comparison of the representative value and a corresponding value of the acoustic signals.
2. The method according to claim 1 , wherein the determining the representative value further comprises:
determining at least two reconstructed acoustic signals for the given location based on the reconstructed excitation source signal and the predetermined acoustic properties of the object at the given location.
3. The method according to claim 2 , further comprising:
determining an error energy using the expression:
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wherein e 1 (f k ) and e 2 (f k ) represent algorithmic transformations of the acoustic signals forming the corresponding values, e 1 ′(f k ,i) and e 2 ′(f k ,i) represent the at least two reconstructed acoustic signals based on the reconstructed excitation source signal at a given location i on the object's surface, and the summation is over frequencies of interest, k, comprising frequencies for which the predetermined acoustic properties of the object are present.
4. The method according to claim 1 , further comprising:
repeating the receiving, determining, and deciding for a plurality of locations on the object's surface.
5. The method according to claim 1 , wherein the removing is triggered for locations close to a location of a real impact.
6. The method according to claim 3 , further comprising:
determining a signal energy of the acoustic signals using the expression:
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wherein k represents a number of values in a frequency domain, and e 1 (f k ) and e 2 (f k ) represent algorithmic transformations of the acoustic signals; and
the deciding is based on a ratio between the signal energy and the error energy.
7. The method according to claim 3 , further comprising:
deciding that the given location corresponds to one location of an impact when the error energy represents a minimum value compared to an error energy of neighboring locations.
8. The method according to claim 6 , further comprising determining at least one of:
a minimum value of the error energy by: analyzing locations i on the object's surface for which predetermined acoustic properties have been determined, or comparing a value for a given location with a value of a previously analyzed location and keeping a smaller value error energy; and
a maximum value of the ratio by: analyzing locations i on the object's surface for which predetermined acoustic properties have been determined, or comparing a value for a given location with a value of a previously analyzed location and keeping a larger value ratio.
9. The method according claim 1 , wherein amplitude and phase information of the acoustic signals are used in the determining the representative value.
10. The method according to claim 1 , further comprising:
determining at least two modified reconstructed acoustic signals corresponding to the acoustic signals for the given location based on the modified reconstructed source signal and the predetermined acoustic properties of the object at the given location.
11. A non-transitory computer program product comprising one or more non-transitory computer readable media having computer-executable instructions stored therein for execution by a processor to perform operations for determining one or more impact locations on an object's surface comprising:
receiving acoustic signals from at least two transducers, wherein the acoustic signals correspond to at least one impact location on the object's surface;
determining a representative value based on a reconstructed excitation source signal, wherein the reconstructed excitation source signal is based on an algorithmic transformation of (i) the acoustic signals and (ii) predetermined acoustic properties of the object at a given location on the object's surface;
removing background noise around a maximum of the reconstructed excitation source signal in a time domain, wherein the removing comprises:
transforming the reconstructed excitation source signal in the time domain;
determining a time (t max ) at which the transformed reconstructed excitation source signal has a maximum amplitude;
filtering a time window around t max to obtain a modified reconstructed source signal corresponding to a given impact at the given location on the object's surface; and
transforming the modified reconstructed source signal into a frequency domain;
and
deciding whether the at least one impact location corresponds to the given location on the object's surface based on a comparison of the representative value and a corresponding value of the acoustic signals.
12. The non-transitory computer program product according to claim 11 , further comprising:
determining at least two reconstructed acoustic signals for the given location based on the reconstructed excitation source signal and the predetermined acoustic properties of the interaction surface at the given location.
13. The non-transitory computer program product according to claim 11 , further comprising:
determining an error energy using the expression:
∑
k
(
e
1
(
f
k
)
-
e
1
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f
k
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k
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-
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2
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k
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wherein e 1 (f k ) and e 2 (f k ) represent algorithmic transformations of the acoustic signals forming the corresponding values, e 1 ′(f k ,i) and e 2 ′(f k ,i) represent the at least two reconstructed acoustic signals based on the reconstructed excitation source signal at a given location i on the object's surface, and the summation is over frequencies of interest, k, comprising frequencies for which the predetermined acoustic properties of the object are present.
14. The non-transitory computer program product according to claim 13 , further comprising:
determining a signal energy of the acoustic signals using the expression:
∑
k
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1
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f
k
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2
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wherein k represents a number of values in a frequency domain, and e 1 (f k ) and e 2 (f k ) represent algorithmic transformations of the acoustic signals; and
the deciding is based on a ratio between the signal energy and the error energy.
15. The non-transitory computer program product according to claim 13 , further comprising:
deciding that the given location corresponds to one location of an impact when the error energy represents a minimum value compared to an error energy of neighboring locations.
16. A touch sensitive device comprising:
an interaction surface;
at least two transducers coupled to the interaction surface; and
a control unit coupled to the at least two transducers and configured to:
receive acoustic signals from at least two transducers, wherein the acoustic signals correspond to at least one impact location on the interaction surface;
determine a representative value based on a reconstructed excitation source signal, wherein the reconstructed excitation source signal is based on an algorithmic transformation of (i) the acoustic signals and (ii) predetermined acoustic properties of the interaction surface at a given location on the interaction surface;
remove background noise around a maximum of the reconstructed excitation source signal in a time domain, wherein to remove the background noise, the control unit is configured to:
transform the reconstructed excitation source signal in the time domain;
determine a time (t max ) at which the transformed reconstructed excitation source signal has a maximum amplitude;
filter a time window around t max to obtain a modified reconstructed source signal corresponding to a given impact at the given location on the object's surfaces and
transform the modified reconstructed source signal into a frequency domain; and
decide whether the at least one impact location corresponds to the given location on the interaction surface based on a comparison of the representative value and a corresponding value of the acoustic signals.
17. The touch sensitive device according to claim 16 , wherein the control unit is further configured to:
determine at least two reconstructed acoustic signals for the given location based on the reconstructed excitation source signal and the predetermined acoustic properties of the interaction surface at the given location.
18. The touch sensitive device according to claim 17 , wherein the control unit is further configured to determine an error energy at the given location on the interaction surface based on the representative value based on the at least two reconstructed acoustic signals, and the corresponding value of the acoustic signals.
19. The touch sensitive device according to claim 18 , wherein the control unit is further configured to determine at least one of:
a minimum value of the error energy at a plurality of locations on the interaction surface; and
a maximum value of a ratio between a signal energy of the acoustic signals and the error energy at the plurality of locations on the interaction surface.
20. The touch sensitive device according to claim 16 , wherein to remove the background noise, the control unit is configured to remove background noise for locations at or near a real impact.