# US 2014/0152624 A1 · Optical Touch Tomography

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- Number: US 2014/0152624 A1
- Document ID: US20140152624A1
- Status: Published application
- Kind: A1
- Application number: 14/092,850
- Filed: 2013-11-27
- Published: 2014-06-05
- Earliest claimed: 2012-11-30
- Assignees: Rapt Touch, Inc.
- Applicants: Rapt Touch, Inc.
- Inventors: Julien Piot; Mihailo Kolundzija; Danil Korchagin; Ivan Dokmanic; Martin Vetterli; Owen Drumm
- Web page: https://patentgrep.com/patent/US20140152624A1

## CPC

- G06F 3/0421: {by interrupting or reflecting a light beam, e.g. optical touch-screen}
- G06F 3/04166: {Details of scanning methods, e.g. sampling time, grouping of sub areas or time sharing with display driving (Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally G06F3/04184)}
- G06F 3/042: by opto-electronic means
- G06F 2203/04104: Multi-touch detection in digitiser, i.e. details about the simultaneous detection of a plurality of touching locations, e.g. multiple fingers or pen and finger
- 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
- G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N)

## Abstract

An optical touch-sensitive device has the capability to determine touch locations of multiple simultaneous touch events. The touch events disturb optical beams propagating across the touch sensitive surface. With multi-touch events, a single beam can be disturbed by more than one touch event. In one aspect, a non-linear transform is applied to measurements of the optical beams in order to linearize the effects of multiple touch events on a single optical beam. In another aspect, the effect of known touch events (i.e., reference touches) is modeled in advance, and then unknown touch events are determined with respect to the reference touches.

## Claims

### Claim 1

A method of resolving a multi-touch event occurring at a plurality of touch regions on a touch sensitive surface, the method comprising a computer processor executing the steps of:
receiving a plurality of beam measurement values bn resulting from the multi-touch event, wherein different beam measurement values bn result from different optical beams transmitted across the touch sensitive surface and the multi-touch event disturbs optical beams in a vicinity of the touch region;
determining binding value estimates p′i from the beam measurement values bn, the binding value estimates p′i estimating optical beam disturbance at corresponding locations Li of the touch-sensitive surface, wherein determining the binding value estimates p′i is based on modeling a transfer function from binding values pi to the beam measurement values bn as a linear transfer function; and
determining the touch regions for the multi-touch event from the binding value estimates p′i.

### Claim 2 (depends on 1)

The method of claim 1, wherein the linear transfer function is described by:
b=Mp,
where:
b is a column vector of the beam measurement values bn,
p is a column vector of the binding values pi, and
M is the linear transfer function, and each column n of the matrix M is the beam measurement values bn resulting from a reference touch at location Li, said reference touch corresponding to a binding value pi=1.

### Claim 3 (depends on 2)

The method of claim 2, wherein determining binding value estimates p′i comprises applying an inversion process to b=Mp.

### Claim 4 (depends on 2)

The method of claim 2, wherein determining binding value estimates p′i comprises evaluating
p′=Rb,
where:
p′ is a column vector of the binding value estimates p′i, and
R is an inverse matrix of the linear transfer function M.

### Claim 5 (depends on 4)

The method of claim 4, wherein R is a sparse matrix.

### Claim 6 (depends on 4)

The method of claim 4, wherein R is zero for elements for which a touch at location Li does not disturb an optical beam for the beam measurement value bn.

### Claim 7 (depends on 2)

The method of claim 2, wherein b=Mp is overdetermined.

### Claim 8 (depends on 2)

The method of claim 2, wherein the number of beam measurement values bn is greater than the number of locations Li.

### Claim 9 (depends on 2)

The method of claim 2, wherein each column n of the matrix M is at least 50% zeroes.

### Claim 10 (depends on 2)

The method of claim 2, wherein the reference touch occupies a finite area of less than 100 square millimeters and each column n of the matrix M contains zeroes for elements outside the finite area.

### Claim 11 (depends on 10)

The method of claim 10, wherein the reference touch occupies a constant area.

### Claim 12 (depends on 10)

The method of claim 10, wherein the reference touch occupies a variable area.

### Claim 13 (depends on 2)

The method of claim 2, wherein reference touches at adjacent locations Li overlap.

### Claim 14 (depends on 2)

The method of claim 2, wherein reference touches occupy at least 1000 locations Li.

### Claim 15 (depends on 2)

The method of claim 2, wherein reference touches at adjacent locations Li do not overlap.

### Claim 16 (depends on 2)

The method of claim 2, wherein each column n of the matrix M contains elements less than zero.

### Claim 17 (depends on 1)

The method of claim 1, further comprising:
receiving optical measurements of optical beams from emitters to detectors, wherein an optical measurement is a non-linear function of touch events along the optical beam; and
calculating the beam measurement values bn from the optical measurements by applying a non-linear function.

### Claim 18 (depends on 17)

The method of claim 17, wherein the non-linear function is a log function.

### Claim 19 (depends on 17)

The method of claim 17, wherein the non-linear function is a log function of an optical transmittance of optical beams from emitters to detectors.

### Claim 20 (depends on 17)

The method of claim 17, wherein the non-linear function is a linearized approximation of a log function of an optical transmittance of optical beams from emitters to detectors, the linearized approximation representing an optical loss coefficient of the optical beams.

### Claim 21 (depends on 1)

The method of claim 1, wherein the locations Li are located on a rectangular grid.

### Claim 22 (depends on 1)

The method of claim 1, wherein the locations Li are located on a regular grid.

### Claim 23 (depends on 1)

The method of claim 1, wherein the locations Li are irregularly spaced.

### Claim 24 (depends on 1)

The method of claim 1, wherein the locations Li are at least 2 mm apart from each other.

### Claim 25 (depends on 1)

The method of claim 1, wherein determining the touch regions for the multi-touch event comprises applying a threshold to the binding value estimates p′i, and identifying candidate touch regions based on which binding value estimates p′i exceed the threshold.

### Claim 26 (depends on 1)

The method of claim 1, wherein determining the touch regions for the multi-touch event comprises applying a threshold to a local feature based on the binding value estimates p′i, and identifying candidate touch regions based on which local features exceed the threshold.

### Claim 27 (depends on 1)

The method of claim 1, wherein determining the touch regions for the multi-touch event comprises using more than one binding value estimate p′i to determine each touch region.

### Claim 28 (depends on 27)

The method of claim 27, wherein determining the touch regions for the multi-touch event comprises interpolating between binding value estimates p′i to determine each touch region.

### Claim 29 (depends on 1)

The method of claim 1, wherein the touch regions can be determined to an accuracy that is smaller than the spacing between adjacent locations Li.

### Claim 30 (depends on 1)

The method of claim 1, wherein the linear transfer function is determined a priori.

### Claim 31 (depends on 1)

The method of claim 1, further comprising:
automatically calibrating to compensate for changes in the linear transfer function.

### Claim 32 (depends on 1)

The method of claim 1, wherein the optical beams are transmitted between emitters and detectors arranged around a periphery of the touch sensitive surface.

### Claim 33 (depends on 1)

The method of claim 1, wherein multiple optical beams are simultaneously received by detectors.

### Claim 34 (depends on 1)

The method of claim 1, further comprising determining physical attributes for touch events in the multi-touch event from the binding value estimates p′i.

### Claim 35 (depends on 34)

The method of claim 34, wherein determining physical attributes for a touch event comprises determining one or more of: a touch pressure, a pressure gradient, a spatial pressure distribution, and an optical transmission property associated with the touch event.

### Claim 36 (depends on 34)

The method of claim 34, further comprising identifying one or more objects causing the multi-touch event based on the determined physical attributes for the touch events of the multi-touch event.

### Claim 37 (depends on 1)

The method of claim 1, further comprising determining spatial properties for the touch regions of the multi-touch event from the binding value estimates p′i.

### Claim 38 (depends on 37)

The method of claim 37, wherein determining spatial properties for the touch regions comprises determining one or more of: a dimension, a boundary, a perimeter, an area, and a geometric shape, associated with the touch regions.

### Claim 39 (depends on 37)

The method of claim 37, further comprising identifying one or more objects causing the multi-touch event based on the determined spatial properties for the touch regions of the multi-touch event.