Improved stylus identification

{
  "publication_number": "US2018356940A1",
  "country": "US",
  "kind": "A1",
  "title": "Improved stylus identification",
  "abstract": "An optical IR touch sensing apparatus configured to determine, based on output signals of light detectors, a light energy value for each light path across a touch surface, and generate a transmission value for each light path based on the light energy value. A processor is then configured to operate an image reconstruction algorithm on at least part of the thus-generated transmission values and determine a position of a touching object on the touch surface, and an attenuation value corresponding to the attenuation of the light resulting from the object touching the touch surface. Using these values, the processor is configured to identify the type of object.",
  "claims": [
    "1. A touch sensing apparatus, comprising: a touch surface, a set of emitters arranged around the periphery of the touch surface to emit beams of light such that an object touching the touch surface causes an attenuation of the light; a set of light detectors arranged around the periphery of the touch surface to receive light from the set of emitters on a plurality of light paths, wherein each light detector is arranged to receive light from more than one emitter; and a signal processor configured to: determine, based on output signals of the light detectors, a light energy value for each light path; generate a transmission value for each light path based on the light energy value; operate an image reconstruction algorithm on at least part of the thus-generated transmission values so as to determine; a position of the object on the touch surface, and an attenuation value corresponding to the attenuation of the light resulting from the object touching the touch surface, and determine a type of the object in dependence on the attenuation value. 2. The touch sensing apparatus of claim 1, wherein the image reconstruction algorithm is an algorithm for transmission tomography. 3. The touch sensing apparatus of claims 1, further comprising a light transmissive panel defining the touch surface and an opposite surface, wherein the emitters are configured to introduce light into the panel for propagation by internal reflection between the touch surface and the opposite surface, and the detectors are configured to receive the light propagating in the panel. 4. The touch sensing apparatus of claims 1, wherein the emitters are configured to transmit the beams of light above the touch surface and the detectors are configured to receive said beams of light travelling above the touch surface. 5. The touch sensing apparatus of claim 1, wherein a determination of an interaction area between an object and touch surface is determined in dependence on the attenuation value. 6. The touch sensing apparatus of claim 4, wherein the beams of light transmitted by the emitters and received by the detectors extend no further than 5 mm from the touch surface. 7. The touch sensing apparatus of claim 1, the signal processor further configured to store a plurality of object IDs, each having an associated attenuation value range. 8. The touch sensing apparatus of claim 7, the signal processor further configured to identify an object ID with an attenuation value range corresponding to the attenuation value of the object and associating the object ID with the object 9. The touch sensing apparatus of claim 8, wherein the identifying step is not performed by the signal processor until the attenuation value is determined to be stable. 10. The touch sensing apparatus of claim 9, wherein the attenuation value is determined to be stable when the rate of change of the attenuation value is below a predefined threshold. 11. The touch sensing apparatus of claim 9, wherein the attenuation value is determined to be stable when the rate of change of the attenuation value is determined to rise above a first threshold and then subsequently drop below a second threshold, wherein the second threshold is lower than the first threshold. 12. The touch sensing apparatus of claim 1, the attenuation value is generated in dependence on the attenuation of the light resulting from the object touching the touch surface and a compensation value. 13. The touch sensing apparatus of claim 12, wherein the compensation value is a function of at least the position of the object on the touch surface. 14. The touch sensing apparatus of claim 12, the compensation value being the value at a position on a compensation map corresponding to the position of the object on the touch surface. 15. The touch sensing apparatus of claim 12, wherein object has an object axis and wherein the compensation value is a function of at least an angle of the object axis relative to the normal of the touch surface. 16. The touch sensing apparatus of claim 15, wherein object has a flat end and wherein the angle of the object axis relative to the normal of the touch surface is determined as a function of the transmission value and geometry of each light path intersecting with object. 17. The touch sensing apparatus of claim 15, wherein the angle of the object axis relative to the normal of the touch surface is determined as a function of the ratio between the minimum amount of attenuation and maximum amount of attenuation for the light paths intersecting the stylus. 18. The touch sensing apparatus of claim 12, wherein the compensation value is a function of at least the speed of the object across the touch surface. 19. The touch sensing apparatus of claim 18, wherein the compensation value is proportional to the speed of the object across the touch surface. 20.- 26. (canceled) 27. A method of determining a type of object in contact with a touch surface of a touch sensing apparatus, said touch sensing apparatus comprising: a touch surface, a set of emitters arranged around the periphery of the touch surface to emit beams of light such that an object touching the touch surface causes an attenuation of the light; a set of light detectors arranged around the periphery of the touch surface to receive light from the set of emitters on a plurality of light paths, wherein each light detector is arranged to receive light from more than one emitter; and said method comprising the steps of: determining, based on output signals of the light detectors, a light energy value for each light path; generating a transmission value for each light path based on the light energy value; operating an image reconstruction algorithm on at least part of the thus-generated transmission values so as to determine; a position of the object on the touch surface, and an attenuation value corresponding to the attenuation of the light resulting from the object touching the touch surface, and determining a type of the object in dependence on the attenuation value."
  ],
  "cpc": [
    "G06F 3/0421",
    "G06F 2203/04109",
    "G06F 3/03545",
    "G06F 3/0416",
    "G06F 3/04162",
    "G06F 3/04166",
    "G06F 3/04186",
    "G06F 3/042",
    "G06F 3/0428",
    "G06T 11/005",
    "G06T 12/10"
  ],
  "assignees": [
    "FLATFROG LAB AB"
  ],
  "filing_date": "2016-12-07",
  "publication_date": "2018-12-13",
  "priority_date": "2015-12-09",
  "application_number": "US-201615781690-A",
  "family_id": "59013880",
  "citations": [
    "US2010073327A1",
    "US2013342490A1",
    "US2015199071A1",
    "US2015293600A1",
    "US2016062549A1"
  ]
}