U.S. patent application number 13/683173 was filed with the patent office on 2013-03-28 for light-based touch screen.
This patent application is currently assigned to NEONODE INC.. The applicant listed for this patent is Neonode Inc.. Invention is credited to Thomas Eriksson, Magnus Goertz, Joseph Shain.
Application Number | 20130076697 13/683173 |
Document ID | / |
Family ID | 40898745 |
Filed Date | 2013-03-28 |
United States Patent
Application |
20130076697 |
Kind Code |
A1 |
Goertz; Magnus ; et
al. |
March 28, 2013 |
LIGHT-BASED TOUCH SCREEN
Abstract
A light-based touch screen, including a housing for a display
screen, a plurality of infra-red light emitting diodes (LEDs),
fastened on the housing, for generating light beams, at least one
LED selector, fastened on the housing and connected with the
plurality of LEDs, for controllably selecting and deselecting one
or more of the plurality of LEDs, a plurality of photodiode (PD)
receivers, fastened on the housing, for measuring light intensity,
at least one PD selector, fastened on the housing and connected
with the plurality of PD receivers, for controllably selecting and
deselecting one or more of the plurality of PD receivers, an
optical assembly, fastened on the housing, for projecting light
beams emitted by the plurality of LEDs in substantially parallel
planes over the housing, and a controller, fastened on the housing
and coupled with the plurality of PD receivers, (i) for controlling
the at least one LED selector, (ii) for controlling the at least
one PD selector, and (iii) for determining therefrom position and
velocity of an object crossing at least one of the substantially
parallel planes, based on output currents of the plurality of PD
receivers.
Inventors: |
Goertz; Magnus; (Lidingo,
SE) ; Eriksson; Thomas; (Stocksund, SE) ;
Shain; Joseph; (Rehovot, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Neonode Inc.; |
Santa Clara |
CA |
US |
|
|
Assignee: |
NEONODE INC.
Santa Clara
CA
|
Family ID: |
40898745 |
Appl. No.: |
13/683173 |
Filed: |
November 21, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12371609 |
Feb 15, 2009 |
8339379 |
|
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13683173 |
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|
10494055 |
Apr 29, 2004 |
7880732 |
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12371609 |
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Current U.S.
Class: |
345/175 |
Current CPC
Class: |
G06F 3/0425 20130101;
G06F 3/0428 20130101; G06F 2203/04108 20130101; G06F 3/0421
20130101 |
Class at
Publication: |
345/175 |
International
Class: |
G06F 3/042 20060101
G06F003/042 |
Claims
1.-20. (canceled)
21. A touch surface assembly for an electronic device, comprising:
a surface that can be touched by an object from above; a projector
that projects light above said surface; a barrier positioned in
front of said projector, that blocks a portion of the light
projected by said projector, thereby generating a light pattern; a
lens positioned in front of said projector and said barrier, that
spreads the light pattern generated by said barrier, such that the
object, when suitably positioned above the screen, reflects at
least a portion of the light pattern spread by said lens; and a
camera aimed above said surface that captures one or more images of
the light pattern spread by said lens and reflected by the object,
wherein a controller in communication with said camera determines
location of the object relative to said surface by analyzing the
one or more images captured by said camera.
22. The touch surface assembly of claim 21 wherein the controller
identifies a gesture made by the object by analyzing the one or
more images captured by said camera.
23. The touch surface assembly of claim 21 wherein said barrier
comprises a metal plate with shapes etched thereon
lithographically.
24. The touch surface assembly of claim 21 wherein said barrier
comprises a grating.
25. The touch surface assembly of claim 21 wherein said projector
is aimed above said surface at an angle of projection, and wherein
said camera is aimed so as to be substantially aligned with said
projector, so that said camera captures the one or more images at
substantially the angle of projection.
26. The touch surface assembly of claim 21 wherein the location of
the object relative to said surface identified by the controller,
is a two-dimensional location.
27. The touch surface assembly of claim 21 wherein the location of
the object relative to said surface identified by the controller,
is a three-dimensional location.
28. The touch surface assembly of claim 21 wherein the controller
also derives a location on said surface where the object is aimed,
by analyzing the one or more images captured by said camera.
29. The touch surface assembly of claim 21 further comprising: at
least one additional projector that projects light above said
surface; at least one additional barrier positioned in front of
said respective at least one additional projector, that blocks a
portion of the light projected by said respective at least one
additional projector, thereby generating respective at least one
additional light pattern; at least one additional lens positioned
in front of said respective at least one additional projector and
said respective at least one additional barrier, that spreads the
light pattern generated by said respective at least one additional
barrier, such that the object, when suitably positioned above the
screen, reflects at least a portion of the light pattern spread by
said at least one additional lens; and at least one respective
additional camera in communication with said controller, aimed
above said surface, that captures one or more images of the light
pattern spread by said respective at least one additional lens and
reflected by the object, wherein the controller determines the
location of the object relative to said surface by analyzing the
one or more images captured by each camera.
30. The touch surface assembly of claim 21 wherein the light
pattern is a member of the group consisting of a pattern of digits,
a pattern of letters, and a pattern of dots.
31. The touch surface assembly of claim 21 wherein the object is a
member of the group consisting of a finger, a stylus and a pen.
32. A method for operating a touch surface, comprising: projecting
light above a surface, wherein the surface can be touched by an
object from above; blocking a portion of the light projected by
said projecting, to generate a light pattern; spreading the
generated light pattern such that the object, when suitably
positioned above the screen, reflects at least a portion of the
light pattern spread by said lens; capturing one or more images of
the light pattern spread by said spreading and reflected by the
object; and analyzing the one or more images captured by said
capturing, to determine location of the object relative to the
surface.
33. The method of claim 32 comprising further analyzing the one or
more images captured by said capturing, to identify a gesture made
by the object.
34. The method of claim 32 wherein the location of the object
relative to the surface identified by said analyzing, is a
two-dimensional location.
35. The method of claim 32 wherein the location of the object
relative to the surface identified by said analyzing, is a
three-dimensional location.
36. The method of claim 32 comprising further analyzing the one or
more images captured by said capturing to derive a location on said
surface where the object is aimed.
37. The method of claim 32 wherein the light pattern is a member of
the group consisting of a pattern of digits, a pattern of letters,
and a pattern of dots.
38. The method of claim 32 wherein the object is a member of the
group consisting of a finger, a stylus and a pen.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of assignee's
pending application U.S. Ser. No. 10/494,055, filed on Apr. 29,
2004, entitled ON A SUBSTRATE FORMED OR RESTING DISPLAY
ARRANGEMENT.
FIELD OF THE INVENTION
[0002] The field of the present invention is touch screens for
computers.
BACKGROUND OF THE INVENTION
[0003] Conventional touch screens are capacitance-based or
resistance-based. These touch screens provide user interfaces
through which a user enters input to a computing device by touching
a screen at a selected location, with a stylus or with his
finger.
[0004] Conventional touch screens are generally large. When space
is at a premium, such as with small handheld electronic devices,
conventional touch screens are limited to only a few user inputs.
Moreover, these inputs are not accurately interpreted when the user
does not use a stylus.
[0005] Conventional touch screens are also limited as to the types
of user inputs that they can recognize. For example, conventional
touch screens are unable to distinguish between a soft tap and a
hard press. Conventional touch screens are unable to recognize fast
repeated tapping on the same screen locations. Conventional touch
screens are unable to recognize gestures made by a finger or stylus
that moves continuously across a touch screen.
[0006] It would thus be of advantage to produce touch screens that
recognize single soft taps, repeated soft taps, presses, and
gestures, for both large and small screens.
SUMMARY OF THE DESCRIPTION
[0007] Aspects of the present invention relate to touch screens
that operate by measuring light intensities emitted by infra-red
light emitting diodes (LEDs). In distinction from prior art touch
screens, which are resistance-based or capacitance-based,
embodiments of the present invention use light beams.
[0008] LEDs and photodiode (PD) receivers are distributed around
the perimeter of a touch screen. The LEDs are controlled by a
microprocessor to selectively emit light, and the PD receivers are
controlled by the microprocessor to selectively measure light
intensities. The light emitted by the LEDs is projected by a lens
assembly over the touch screen. An object crossing into the
projected light obstructs some of the light from reaching the PD
receivers. The corresponding decrease in light intensities measured
by the PD receivers enables determination of the object's
position.
[0009] In accordance with embodiments of the present invention, the
lens assembly projects light onto parallel planes at multiple
heights over the touch screen. In turn, the light intensities
measured by the PD receivers enable detection of objects that touch
the screen and also objects that are above the screen and nearly
touching the screen. By measuring light intensities over time, the
motion over time of objects that are nearly touching the screen is
also determined. Moreover, determination of motion over time
enables derivation of objects' velocity vectors.
[0010] The touch screen of the present invention is able to
recognize and distinguish still user inputs and motion-based user
inputs made by a user's finger, including inter alia a single soft
tap on the screen, multiple soft taps on the screen, a hard press
on the screen, multiple hard presses on the screen, a directional
gesture, such as a rightward moving swipe on the screen, and a
figurative gesture such as sliding a finger over the screen in the
shape of an "s" or an asterisk "*". The touch screen of the present
invention is also able to recognize positions and motions of more
than one object simultaneously touching the screen.
[0011] The touch screen of the present invention may be used as
both an input device and an output display device. In some
embodiments of the present invention, paths of motion made by an
object on the touch screen are converted to corresponding motion of
a mouse, and input as such to a computer.
[0012] The user touch-based inputs may be logged and post-processed
by a data processor. An application of this is a touch-based
storefront window, whereby touch-based inputs from passersby are
logged and analyzed to derive information about consumer interest
in a storefront showcase display.
[0013] In some embodiments of the present invention, LEDs are
arranged along two adjacent edges of the touch screen, and PD
receivers are arranged along the other two adjacent edges. In other
embodiments of the present invention, four LEDs are positioned at
the corners of the touch screen, and PD receivers are arranged
along the edges.
[0014] In some embodiments of the present invention, the LEDs are
connected as a matrix to LED row drivers that select rows and LED
column drivers that select columns. As such, a designated LED is
activated by appropriately setting its corresponding row and column
drivers. Such a connection significantly reduces the number of IO
connectors required, thereby reducing the cost of materials for the
touch screen. Similarly, the PD receivers may be connected as a
matrix to PD row selectors and PD column selectors.
[0015] Thus the present invention provides touch screens suitable
for both small and large electronic devices. Devices that use touch
screens of the present invention, such as mobile phones, do not
required keypads since the touch screens themselves may serve as
keypads.
[0016] There is thus provided in accordance with an embodiment of
the present invention a light-based touch screen, including a
housing for a display screen, a plurality of infra-red light
emitting diodes (LEDs), fastened on the housing, for generating
light beams, at least one LED selector, fastened on the housing and
connected with the plurality of LEDs, for controllably selecting
and deselecting one or more of the plurality of LEDs, a plurality
of photodiode (PD) receivers, fastened on the housing, for
measuring light intensity, at least one PD selector, fastened on
the housing and connected with the plurality of PD receivers, for
controllably selecting and deselecting one or more of the plurality
of PD receivers, an optical assembly, fastened on the housing, for
projecting light beams emitted by the plurality of LEDs in
substantially parallel planes over the housing, and a controller,
fastened on the housing and coupled with the plurality of PD
receivers, (i) for controlling the at least one LED selector, (ii)
for controlling the at least one PD selector, and (iii) for
determining therefrom position and velocity of an object crossing
at least one of the substantially parallel planes, based on output
currents of the plurality of PD receivers.
[0017] There is additionally provided in accordance with an
embodiment of the present invention a method for a light-based
touch screen, including controlling a plurality of light-emitting
diodes (LEDs) to select and deselect at least one of the LEDs,
whereby a selected LED emits infra-red light beams, controlling a
plurality of photodiode (PD) receivers to select and deselect at
least one of the PD receivers, whereby a selected PD measures
received light intensity, and determining position and velocity of
an object obstructing light from at least one of the PD receivers,
based on output currents of the plurality of PD receivers.
[0018] There is further provided in accordance with an embodiment
of the present invention a touch screen, including a housing for a
display screen, a plurality of sensors, fastened on the housing,
for sensing location of an object touching the display screen, and
a controller, fastened on the housing coupled with the plurality of
sensors, for receiving as input locations sensed by the plurality
of sensors, and for determining therefrom positions of two or more
objects simultaneously touching the display screen.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The present invention will be more fully understood and
appreciated from the following detailed description, taken in
conjunction with the drawings in which:
[0020] FIG. 1 is a diagram of a touch screen having 16 LEDs and 16
PDs, in accordance with an embodiment of the present invention;
[0021] FIGS. 2A-2C are diagrams of a touch screen that detects two
objects that touch the screen simultaneously, in accordance with an
embodiment of the present invention;
[0022] FIGS. 3A and 3B are diagrams of a touch screen that detects
a two finger glide movement, in accordance with an embodiment of
the present invention;
[0023] FIGS. 4A-4C are diagrams of a touch screen for a piano
keyboard simulator, that detects multiple keys of a displayed piano
keyboard that are touched simultaneously, in accordance with an
embodiment of the present invention;
[0024] FIG. 5 is a circuit diagram of the touch screen from FIG. 1,
in accordance with an embodiment of the present invention;
[0025] FIG. 6A is a simplified block diagram of electronics for a
touch screen, in accordance with an embodiment of the present
invention;
[0026] FIG. 6B is a simplified block diagram of alternate
electronics for touch screen, in accordance with an embodiment of
the present invention;
[0027] FIG. 7 is a simplified circuit diagram of an exemplary
central processing unit for use with the touch screens of FIGS. 6A
and 6B, in accordance with an embodiment of the present
invention;
[0028] FIG. 8 is a diagram of a shift register for an array of 16
LEDs, in accordance with an embodiment of the present
invention;
[0029] FIG. 9 is an illustration of a waveform for activating LEDs,
in accordance with an embodiment of the present invention;
[0030] FIG. 10 is a diagram of a touch screen with four LEDs placed
in the four corners of the screen, and plural PDs are arranged
along the four sides of the screen, in accordance with an
embodiment of the present invention;
[0031] FIG. 11 is a diagram of an LED driver matrix for a touch
screen, in accordance with an embodiment of the present
invention;
[0032] FIG. 12 is a diagram of LED switches, in accordance with an
embodiment of the present invention;
[0033] FIG. 13A is a diagram of a current limiter, used for
limiting and directing current to LEDs, in accordance with an
embodiment of the present invention;
[0034] FIG. 13B is a diagram of an alternative current limiter,
used for limiting and directing current to LEDs, in accordance with
an embodiment of the present invention;
[0035] FIG. 14 is a diagram of a shift register for an array of 16
PDs, in accordance with an embodiment of the present invention;
[0036] FIG. 15 is an illustration of a waveform for activating
selected PDs, in accordance with an embodiment of the present
invention;
[0037] FIG. 16 is a diagram of a photodiode matrix for a touch
screen, in accordance with an embodiment of the present
invention;
[0038] FIG. 17 is a diagram of a PD output selector for use in a
touch screen, in accordance with an embodiment of the present
invention;
[0039] FIG. 18A is a diagram of a resistor-based current integrator
used in conjunction with PD receivers in a touch screen, in
accordance with an embodiment of the present invention;
[0040] FIG. 18B is a diagram of a transistor-based current
integrator used in conjunction with PD receivers in a touch screen,
in accordance with an embodiment of the present invention;
[0041] FIG. 19 is an illustration of current integration over time,
in accordance with an embodiment of the present invention;
[0042] FIG. 20 is a simplified flowchart of a method for PD
sampling, in accordance with an embodiment of the present
invention;
[0043] FIG. 21 is an illustration of measuring ambient light by
summing pulses when an LED is on and subtracting pulses when the
LED is off, in accordance with an embodiment of the present
invention;
[0044] FIG. 22 is a simplified flowchart of an alternative method
for PD, in accordance with an embodiment of the present
invention;
[0045] FIG. 23A is a circuit diagram of a signal filter and
amplifier, used for PDs arranged along one edge of a touch screen,
in accordance with an embodiment of the present invention;
[0046] FIG. 23B is a circuit diagram of an alternative signal
filter and amplifier circuit, using an OP amplifier, in accordance
with an embodiment of the present invention;
[0047] FIG. 24 is a diagram of a prior art lens assembly for an LED
and PD;
[0048] FIG. 25A is a diagram of a lens assembly for use with LEDs
and PDs for a touch screen, in accordance with an embodiment of the
present invention;
[0049] FIG. 25B is a diagram of a lens assembly for distributing
two groups of light beams, in accordance with an embodiment of the
present invention;
[0050] FIGS. 26A and 26B are diagrams of simplified lens assemblies
corresponding to the respective lens assemblies of FIGS. 25A and
25B, in accordance with an embodiment of the present invention;
[0051] FIG. 27 shows three-dimensional measurements of light
intensities over the surface of a touch screen, in accordance with
an embodiment of the present invention;
[0052] FIG. 28 is an illustration of a touch screen with
three-dimensional sensing functionality, in accordance with an
embodiment of the present invention;
[0053] FIG. 29 is a graph illustrating different light intensities
measured by a PD receiver corresponding to proximity of an object
to a touch screen surface, in accordance with an embodiment of the
present invention;
[0054] FIG. 30A is a simplified illustration of a handset with a
touch screen, in accordance with an embodiment of the present
invention;
[0055] FIG. 30B is a simplified illustration of a pattern of dots
projected into the space above a touch screen, in accordance with
an embodiment of the present invention;
[0056] FIG. 30C is a simplified illustration showing how the
density of a pattern projected by a projector in the space above a
touch screen, and reflected by an object, is dependent upon the
distance of the object from a projector, in accordance with an
embodiment of the present invention;
[0057] FIGS. 30D and 30E are simplified illustrations of patterns
of digits projected into the space above a touch screen, in
accordance with an embodiment of the present invention;
[0058] FIG. 31 is an illustration of use of a touch screen for
processing finger motions as input to a computer, in accordance
with an embodiment of the present invention; and
[0059] FIG. 32 is a simplified illustration of a touch sensitive
display case containing items of merchandise, in accordance with an
embodiment of the present invention.
DETAILED DESCRIPTION
[0060] Aspects of the present invention relate to light-based touch
screens. According to embodiments of the present invention, a
light-based touch screen includes a plurality of infra-red
light-emitting diodes (LEDs) and a plurality of photodiodes (PDs)
arranged along the perimeter surrounding the screen. The LEDs
project light substantially parallel to the screen surface, and
this light is detected by the PDs. An object, such as a finger,
placed over a portion of the screen blocks some of the light beams,
and correspondingly some of the PDs detect less light intensity.
The geometry of the locations of the PDs, and the light intensities
they detect, suffice to determine screen coordinates of the object.
The LEDs and PDs are controlled for selective activation and
de-activation by a controller. Generally, each LED and PD has I/O
connectors, and signals are transmitted to specify which LEDs and
which PDs are activated.
[0061] In one embodiment of the present invention, plural LEDs are
arranged along two adjacent sides of a rectangular screen, and
plural PDs are arranged along the other two adjacent sides. In this
regard, reference is now made to FIG. 1, which is a diagram of a
touch screen 100 having 16 LEDs 130 and 16 PDs 140, in accordance
with an embodiment of the present invention. The LEDs 130 emit
infra-red light beams across the top of the touch screen, which are
detected by corresponding PD receivers that are directly opposite
the LEDs. When an object touches touch screen 100, it blocks light
from reaching some of PD receivers 140. By identifying, from the PD
receiver outputs, which light beams have been blocked by the
object, the object's position can be determined.
[0062] Reference is now made to FIGS. 2A-2C, which are diagrams of
a touch screen that detects two objects, 10 and 20, that touch the
screen simultaneously, in accordance with an embodiment of the
present invention. Objects 10 and 20, which are touching the
screen, block light from reaching some of PD receivers 140. In
accordance with an embodiment of the present invention, the
positions of objects 10 and 20 are determined from the crossed
lines of the infra-red beams that the objects block. In
distinction, prior art resistance-based and capacitance-based touch
screens are unable to detect more than one object simultaneously
touching the screen.
[0063] When two or more objects touch screen 100 simultaneously
along a common horizontal or vertical axis, the positions of the
objects are determined by the PD receivers 140 that are blocked.
Objects 10 and 20 in FIG. 2A are aligned along a common vertical
axis and block substantially the same PD receivers 140 along the
bottom edge of touch screen 100; namely the PD receivers marked a,
b, c and d. Along the left edge of touch screen, two different sets
of PD receivers 140 are blocked. Object 10 blocks the PD receivers
marked e and f, and object 20 blocks the PD receivers marked g and
h. The two objects are thus determined to be situated at two
locations. Object 10 has screen coordinates located at the
intersection of the light beams blocked from PD receivers a-d and
PD receivers e and f; and object 20 has screen coordinates located
at the intersection of the light beams blocked from PD receivers
a-d and PD receivers g and h.
[0064] Objects 10 and 20 shown in FIGS. 2B and 2C are not aligned
along a common horizontal or vertical axis, and they have different
horizontal locations and different vertical locations. From the
blocked PD receivers a-h, it is determined that objects 10 and 20
are diagonally opposite one another. They are either respectively
touching the top right and bottom left of touch screen 100, as
illustrated in FIG. 2B; or else respectively touching the bottom
right and top left of touch screen 100, as illustrated in FIG.
2C.
[0065] Discriminating between FIG. 2B and FIG. 2C is resolved by
either (i) associating the same meaning to both touch patterns, or
else (ii) by associating meaning to only one of the two touch
patterns. In case (i), the UI arranges its icons, or is otherwise
configured, such that the effects of both touch patterns FIG. 2B
and FIG. 2C are the same. For example, touching any two diagonally
opposite corners of touch screen 100 operates to unlock the screen.
In case (ii), the UI arranges its icons, or is otherwise
configured, such that only one of the touch patterns FIG. 2B and
FIG. 2C has a meaning associated therewith. For example, touching
the upper right and lower left corners of touch screen 100 operates
to unlock the screen, and touch the lower right and upper left of
touch screen 100 has no meaning associated therewith. In this case,
the UI discriminates that FIG. 2B is the correct touch pattern.
[0066] Reference is now made to FIGS. 3A and 3B, which are diagrams
of a touch screen that detects a two finger glide movement, in
accordance with an embodiment of the present invention. The glide
movement illustrated in FIGS. 3A and 3B is a diagonal glide that
brings objects 10 and 20 closer together. The direction of the
glide is determined from changes in which PD receivers 140 are
blocked. As shown in FIGS. 3A and 3B, blocked PD receivers are
changing from a and b to PD receivers 140 more to the right, and
from c and d to PD receivers 140 more to the left. Similarly,
blocked PD receivers are changing from e and f to PD receivers 140
more to the bottom, and from g and h to PD receivers 140 more to
the top. For a glide in the opposite direction, that moves objects
10 and 20 farther apart, the blocked PD receivers change in the
opposite directions.
[0067] When objects 10 and 20 are aligned in a common vertical or
horizontal axis, there is no ambiguity in identifying glide
patterns. When objects 10 and 20 are not aligned in a common
vertical or horizontal axis, there may be ambiguity in identifying
glide patterns, as illustrated in FIGS. 3A and 3B. In case of such
ambiguity, and as described hereinabove with reference to FIGS. 2B
and 2C, discriminating between FIG. 3A and FIG. 3B is resolved by
either (i) associating the same meaning to both glide patterns, or
else (ii) by associating meaning to only one of the two glide
patterns.
[0068] It will be appreciated by those skilled in the art that the
present invention also identifiers three or more objects that are
simultaneously touching touch screen 100. Reference is now made to
FIGS. 4A-4C, which are diagrams of a touch screen for a piano
keyboard simulator, that detects multiple keys of a displayed piano
keyboard that are touched simultaneously, in accordance with an
embodiment of the present invention. The touch screen in FIGS.
4A-4C has a different layout than the touch screen in FIGS. 1-3.
Piano keys are displayed along a horizontal axis. As such, touch
positions along the horizontal axis correspond to keys of the
keyboard. The black keys are identified by their positions that
straddle two white keys.
[0069] The hand shown in FIG. 4A is playing three white keys, and
correspondingly the PD receivers denoted a-f are blocked. The hand
shown in FIG. 4B is playing two white keys and one black key, and
correspondingly a different plurality of PD receivers, also denoted
a-f, are blocked. The hand shown in FIG. 4C is playing four white
keys with three fingers. The same PD receivers a-f as in FIG. 4B
are blocked in FIG. 4C. In this case, the PD receivers along the
right edge of touch screen 100 discriminate between FIG. 4B and
FIG. 4C; namely, PD receivers g, h and are blocked in FIG. 4B,
where PD receivers g and h are blocked in FIG. 4C. Blocked PD
receiver i in FIG. 4B indicates a depth corresponding to a black
piano key.
[0070] Reference is now made to FIG. 5, which is a circuit diagram
of touch screen 100 from FIG. 1, in accordance with an embodiment
of the present invention. The LEDs 130 and PDs 140 are controlled
by a controller, shown in FIG. 6A. The LEDs receive respective
signals LED00-LED15 from LED switches A, and receive current from
VROW and VCOL through current limiters B. Operation of LED switches
A is described with reference to FIG. 12. Operation of current
limiters B is described with reference to FIGS. 11A and 11B. The
PDs receive respective signals PD01-PD15 from shift register 120.
PD output is sent to controller 150, via signals PDROW and
PDCOL.
[0071] According to one embodiment of the present invention, the
LEDs are controlled via a first serial interface, which transmits a
binary string to a shift register 110. Each bit of the binary
string corresponds to one of the LEDs, and indicates whether to
activate or deactivate the corresponding LED, where a bit value "1"
indicates activation and a bit value "0" indicates deactivation.
Successive LEDs are activated and deactivated by shifting the bit
string within shift register 110. Operation of shift register 110
is described with reference to FIG. 8.
[0072] Similarly, the PDs are controlled by a second serial
interface, which transmits a binary string to a shift register 120.
Successive PDs are activated and deactivated by shifting the bit
string in shift register 120. Operation of shift register 120 is
described with reference to FIG. 14.
[0073] According to another embodiment of the present invention,
shown in FIG. 11, the LEDs are logically arranged in a matrix with
signals controlling each row and each column in the LED matrix.
Each LED matrix signal is connected to a separate pin of a
controller. Similarly, as shown in FIG. 16, the PDs may be
logically arranged in a matrix with signals controlling each row
and each column in the PD matrix.
[0074] The ensuing description addresses (1) the electronics, (2)
the optics, and (3) applications of touch screen 100.
[0075] 1. Electronics of Touch Screen 100
[0076] Reference is now made to FIG. 6A, which is a simplified
block diagram of electronics for touch screen 100, in accordance
with an embodiment of the present invention. As shown in FIG. 6A,
touch screen 100 includes light-emitting diodes 130, which emit
pulses of infra-red light, and photodiodes 140, which detect light
intensity. LEDs 130 are selectively activated in a controlled
manner by a controller 150, via LED selectors 160 and LED switches
A. Current is supplied to LEDs 130 by current limiters B shown in
FIGS. 5 and 6A. Each LED requires approximately 2 amps of current,
whereas each LED selector 160 only supplies a few milliamps. As
such, each LED selector activates an LED switch A that supplies
sufficient current. Operation of LED switches A is described with
reference to FIG. 12. Operation of current limiters B is described
with reference to FIGS. 13A and 13B.
[0077] Controller 150 also selectively filters PDs 140 in a
controlled manner, via PD selectors 170. PDs 140 are selectively
activated by PD selectors 170, which activate one of the PDs. The
signal from the activated PD is transmitted back to controller 150
via a current integrator 180, which then determines whether or not
one or more objects are placed over touch screen 100 and, if so,
the positions of the objects. According to an embodiment of the
present invention, the signal from the activated PD is transmitted
to a signal filter and amplifier 175. The output of signal filter
and amplifier 175 is transmitted back to controller 150, which then
determines whether or not one or more objects are placed over touch
screen 100 and, if so, the positions of the objects. Operation of
signal filter and amplifier 175 is described with reference to
FIGS. 23A and 23B. Operation of current integrator 180 is described
with reference to FIGS. 18A and 18B.
[0078] Reference is now made to FIG. 6B, which is a simplified
block diagram of alternate electronics for touch screen 100, in
accordance with an embodiment of the present invention. The diagram
of FIG. 6B includes an optional multiplexer 171, used to select one
from among several PD output signals. In the absence of multiplexer
171, inactive PD signals may affect the signal entering controller
150 and optional filter and amplifier 175. Multiplexer 171
eliminates these effects. Operation of multiplexer 171 is described
with reference to FIG. 17.
[0079] i. Controller 150
[0080] As used herein, the term "controller" includes inter alia
programmable processors, RISC processors, dedicated hardware, field
programmable gate arrays (FPGA) and application-specific circuits
(ASIC). Although FIGS. 6A and 6B show current integrator 180,
signal filter and amplifier 175, PD selectors 170, LED selectors
160 and other functional blocks as being external to controller
150, such implementation is for purposes of clarity and exposition.
However, it will be appreciated by those skilled in the art that in
other implementations of the present invention some or all of these
blocks, or portions thereof, may be integrated within controller
150.
[0081] Reference is now made to FIG. 7, which is a simplified
circuit diagram of an exemplary controller 150 for use with touch
screen 100, in accordance with an embodiment of the present
invention. The exemplary controller shown in FIG. 7 includes 64 I/O
pins, some of which connect to LED selectors 160 and PD selectors
170, and some of which receive touch signals.
[0082] Controller 150 shown in FIG. 7 may be an MSP
microcontroller, manufactured by Texas Instruments Incorporated of
Dallas, Tex.
[0083] ii. LED Selector 160 and Shift Register 110
[0084] Reference is now made to FIG. 8, which is a diagram of shift
register 110 for an array of 16 LEDs 130, in accordance with an
embodiment of the present invention. Shift register 110 is
connected to controller 150 via the LED_CTRL signal shown in FIG.
7. Integrated circuit IC1 drives 8 LED switches A via corresponding
push-pull drivers denoted LED_D00 thru LED_D07; and integrated
circuit IC2 drives another 8 LEDs switches A via corresponding
push-pull drivers denoted LED_D08 thru LED_D15.
[0085] In accordance with the embodiment shown in FIG. 8, shift
register 110 is implemented in IC1 and IC2, wherein the lower 8
bits of shift register 110 are stored in IC1, and the upper 8 bits
are stored in IC2. Bits are shifted from IC1 to IC2 via the
connection shown in FIG. 8 exiting IC1 at Q7S and entering IC2 at
DS.
[0086] Referring to the LED_CTRL signals, when L_SCLR_N is low, all
LEDs 130 are turned off. In accordance with an embodiment of the
present invention, L_SCLR_N resets shift register 110; i.e., resets
circuits IC1 and IC2.
[0087] Reference is now made to FIG. 9, which illustrates a
waveform for activating LEDs, in accordance with an embodiment of
the present invention. FIG. 9 illustrates the use of LED_CTRL
signals L_SI, L_SCK, L_RCK, L_SCLR_N and L_EO_N from FIG. 7.
[0088] As shown in FIG. 9, at time t1 a low L_SCLR_N signal turns
off all LEDs by resetting shift register 110. At time t2, a bit
value of 1 is entered into shift register 110 by signal L_SI.
Thereafter, at each cycle of L_SCK the data in shift register 110
is shifted one position further into the register, and a new L_SI
bit is entered into the first bit of shift register 110. After six
L_SCK cycles, corresponding to time t3, the bit value of 1 arrives
at bit position 6, corresponding to LED06. A high L_RCK signal
activates the LED drivers using the data in shift register 110,
driving push-pull driver LED_D06 high, and thereby activating a
respective one of switches A and turning on LED06. A subsequent
L_SCK cycle, corresponding to time t4, advances the bit value of 1
one bit position further. A subsequent high L_RCK signal activates
the LED drivers again, with the bit value of 1 at position 7 and a
bit value of 0 at position 6, thereby turning on LED07 and turning
off LED06 via respective switches A.
[0089] In distinction to the embodiment shown in FIG. 1, in
accordance with another embodiment of the present invention, four
LEDs 130 are placed in the four corners of a touch screen, and
plural PDs 140 are arranged along the four sides of the screen, as
shown in FIG. 10. When an LED 130 is lit, it projects an arc of
light substantially parallel to the surface of the screen. The PDs
140 detect respective portions of this light, according to the
positions of the LED 130 and the PDs 140. The four LEDs 130 suffice
to determine the screen coordinates of an object, such as a finger,
placed over a portion of the screen, based on the light intensities
detected by the PDs 140.
[0090] In yet another embodiment of the invention, the LEDs are
inter-connected with the topology of a matrix, and each I/O
connector transmits a signal to an entire row or an entire column
of LEDs. Such a topology provides an advantage in reducing the
total number of I/O connectors required, thereby reducing the cost
of the electronics. In this regard, reference is now made to FIG.
11, which is a diagram of an LED driver matrix 200 for a touch
screen, in accordance with an embodiment of the present invention.
FIG. 11 shows how 16 LEDs are controlled by using only 4 VROW
signals and 4 VCOL signals. Each VROW signal controls a respective
one of four connections via switch 210, and each VCOL signal
controls a respective one of four connections via switch 220.
Switches 210 and 220 are connected to respective pins in controller
150. Switches 210 and 220 are similar to LED switches A shown in
FIG. 12.
[0091] Matrix 200 includes 16 LEDs and 8 IO connectors. More
generally, matrix 400 may include an m.times.n array of mn LEDS and
m+n IO connectors. In distinction, prior art LEDs required two IO
connectors apiece. As such, it will be appreciated by those skilled
in the art that matrix 200 reduces the number of IO connectors
required from 2 nm to m+n. In turn, this reduces the cost of touch
screen 100, since the IO connectors are a significant part of the
bill of materials.
[0092] As shown in FIG. 11, each LED is accessed by selection of a
row and a column IO connector. Four push-pull drivers are used for
selecting rows, and four push-pull drivers are used for selecting
columns. A designated LED is activated by driving the appropriate
push-pull driver for its row to high, and driving the appropriate
push-pull driver for its column to low. FIG. 11 shows the second
from left push-pull driver driven low, and the second from top
push-pull driver is driven high. Correspondingly, the LED circled
in FIG. 11 is activated.
[0093] It will be appreciated by those skilled in the art that the
row and column coordinates of the LEDs are not related to the
physical placement of the LEDS and the push-pull drivers. As such,
the LEDs do not need to be physically positioned in a rectangular
matrix.
[0094] In another embodiment of the present invention, current
source drivers are used instead of push-pull drivers. In yet
another embodiment of the present invention, current sink drivers
are used instead of push-pull drivers. In yet another embodiment of
the present invention, some of the push-pull drivers are combined
with current source drivers and others of the push-pull drivers are
combined with current sink drivers.
[0095] iii. LED Current Switches A
[0096] Reference is now made to FIG. 12, which is a diagram of LED
switches A, in accordance with an embodiment of the present
invention. LED switches A are push-pull drivers that control LEDs
130. These push-pull drivers control gates of power transistors in
each of the LED circuits LED00-LED15. In systems where the LED
drivers supply sufficient current to operate LEDs 130, switches A
may be removed, and LEDs 130 may be controlled directly by LED
selectors 160.
[0097] iv. LED Current Limiters B
[0098] Reference is now made to FIG. 13A, which is a diagram of
current limiters B, used for limiting and directing current to LEDs
through VROW and VCOL, in accordance with an embodiment of the
present invention. As shown in FIG. 13A, a transistor 300 controls
the current issued via VROW to the row LEDs 0-7 along the top of
touch screen 100 (FIG. 5), by a signal denoted ROW_EN_N. Similarly,
a second transistor (not shown) controls the current issued via
VCOL to the column LEDs 8-15 along the right side of touch screen
100, by a signal denoted COL_EN_N. When ROW_EN_N is low, any of the
row LEDs whose corresponding bit in shift register 110 is set,
issue a light pulse. Similarly, when COL_EN_N is low, any of the
column LEDs whose corresponding bit in shift register 110 is set,
issue a light pulse. Transistor 300 may be a low saturation voltage
type transistor, such as the transistors manufactured by NXP
Semiconductors of The Netherlands.
[0099] The magnitude of the current gated by transistor 300, and
issued by VROW, is determined by resistors R1, R2 and R3.
Specifically, the current limit VROW, ignoring the base current,
are given by:
I row = + 3 V R 2 R 2 - R 3 - Ube R 1 ##EQU00001##
Where +3V is the input voltage to controller 150 (FIG. 6), and Ube
is the base-to-emitter voltage on transistor 300.
[0100] Reference is now made to FIG. 13B, which is a diagram of
alternative current limiters B, used for limiting and directing
current to LEDs through VROW and VCOL, in accordance with an
embodiment of the present invention. As in FIG. 13A, only one
current limiter is shown in FIG. 13B, receiving input ROW_EN and
controlling current sent over VROW, and a similar current limiter
(not shown) receives input COL_EN and controls current sent of
VCOL. The dotted portion of circuit 400 represents LED circuits,
and the dotted line connected to the solid line corresponds to
VROW.
[0101] Shown in FIG. 13B is a bandgap voltage stabilizer, D2, or
such other voltage stabilizer, which has a contact voltage drop
across it irrespective of the current flowing through it. As long
as the current is above a holding current, the voltage across D2 is
constant. Resistor R1 supplies a diode current and a base current
of NPN transistor Q1. The constant diode voltage, denoted by VZ,
applies across the base of Q1 and emitter resistor R2.
[0102] When circuit 400 is operational, the voltage across R2,
denoted by VR2, is given by VR2=VZ-VBE, where VBE is the
base-emitter drop of Q1. The emitter current of Q1, denoted by IE,
which is also the current through R2, denoted by IR2, is given
by
I R 2 = V R 2 R 2 = VZ - VBE R 2 ##EQU00002##
Since VZ is constant, and VBE is approximately constant for a given
temperature, it follows that VR2 is constant and IE is constant.
Due to transistor action, current IE is approximately equal to the
collector current of the transistor, denoted by IC, which is the
current through the load. Thus, neglecting the output resistance of
the transistor due to the Early effect, the load current is
constant and the circuit operates as a constant current source.
[0103] Provided the temperature does not vary significantly, the
load current is independent of the supply voltage, denoted by VR1,
and the transistor's gain, R2, allows the load current to be set at
any desired value. Specifically, R2 is given by
R 2 = VZ - VBE IR 2 .apprxeq. Vz - 0.65 IR 2 ##EQU00003##
Since VBE is generally 0.65V for silicon devices.
[0104] VBE is temperature dependent; namely, at higher
temperatures, VBE decreases. VZ is also temperature dependent;
namely, at higher temperatures, VZ also decreases. As such, circuit
400 is self regulating as both voltages grow or decline
simultaneously, resulting in a substantially constant voltage
VR2.
[0105] When issuing a light pulse, signal ROW_EN is initially set
to low. Capacitor C1 is also low, and begins to accumulate charge.
Subsequently, ROW_EN is briefly set to high, to activate the light
pulse, and the charge on C1 rises accordingly. The presence of
bandgap diode D1 ensures that the charge on C1 drops quickly when
ROW_EN is again set to low. As such, the presence of diode D1
protects circuit 400 from excessive charge that would otherwise
result over the course of multiple pulses.
[0106] Resistance R1 is given by
R 1 = VS - VZ IZ + K IB ##EQU00004##
where IB is given by
IB = IC hFE ( min ) = IE hFE ( min ) = IR 2 hFE ( min )
##EQU00005##
and hFE(min) is the lowest acceptable current gain for the specific
transistor type being used. The parameter K ranges between 1.2 and
2.0, to ensure that R1 is sufficiently low and that IB is
adequate.
[0107] v. PD Selector 170 and Shift Register 120
[0108] Reference is now made to FIG. 14, which is a diagram of
shift register 120 for an array of 16 PDs 140, in accordance with
an embodiment of the present invention. The PD shift register shown
in FIG. 14 is similar to the LED shift register in FIG. 8. In
contrast to LEDs 130, PDs 140 are activated directly without
intermediate switches such as switches A used with LEDs 130. Shift
register 120 is connected to controller 150 via the PD_CTRL signal
shown in FIG. 7. A description of the PD_CTRL signal now
follows.
[0109] Initially, the PD outputs are set to high. A value of 1 in
at least one bit of shift register 120 (FIG. 5) activates at least
one corresponding PD by setting its output low. The PD output
signal is sent back to controller 150 via signal PDROW or
PDCOL.
[0110] Reference is now made to FIG. 15, which illustrates a
waveform for activating selected PDs, in accordance with an
embodiment of the present invention. FIG. 15 illustrates the use of
signals SI, SCK, RCK, SCLR_N and OE_N from FIG. 7.
[0111] At time t1, a low SCLR_N signal sets all PD outputs low and
clears shift register 120. At time t2, a low SI signal enters an
activation value of "1" into the beginning of shift register 120.
At each rising high edge of signal SCK, the data in shift register
120 is shifted further into the register, and a new bit value is
entered in the beginning of the register. A rising high edge of
signal RCK transfers data from shift register 120 into IC3 and IC4,
selecting or deselecting corresponding PDs, depending on the bit
values at corresponding positions within the bit string. Thus, a
first high RCK signal selects a first PD based on data in shift
register 120, followed by an SCK cycle shifting the data in shift
register 120, followed by a second RCK signal that deselects the
first PD and selects a second PD based on the shifted data. Thus at
time t3, PD06 is selected, and at time t4, PD06 is deselected and
PD07 is selected.
[0112] As described above for the matrix of LED drivers shown in
FIG. 11, a similar matrix of PD receivers may be used in
embodiments of the present invention. In this regard, reference is
now made to FIG. 16, which is a diagram of a photodiode matrix 500
for a touch screen, in accordance with an embodiment of the present
invention. Matrix 500 as shown in FIG. 16 includes a 4.times.4
array of PDs. In general, matrix 500 may include an array of
m.times.n PDs. Matrix 500 requires only m+n IO connectors. In
distinction, prior art systems require two IO connectors per PD to
scan a plurality of PDs, and thus matrix 500 represents a savings
of 2 nm-m-n connectors. Each PD in matrix 500 is accessed by
selecting an appropriate row connector and an appropriate column
connector, corresponding to the row and column of the PD.
[0113] Shown in FIG. 16 are four 1-to-2 analog switches 510, and
four push-pull drivers 520. Analog switches 510 are used to select
a row, and push-pull drivers 520 are used to select a column. For
each analog switch 510, one terminal connects to GND and the other
terminal connects to receiver electronics 530, including an
amplifier 540 and an ADC 550. Opening one of analog switches 510 to
receiver electronics 530 and putting the remaining switches to GND
serves to select an active receiver row. Driving one of push-pull
connectors 520 low and driving the remaining connectors to high
serves to select an active column. For matrix 500 shown in FIG. 13,
the second from top analog switch is open and the second from left
push-pull connector is low. The PD corresponding to the active row
and column is shown circled in matrix 500.
[0114] It will be appreciated by those skilled in the art that the
row and column coordinates of the PDs are not related to the
physical placement of the PDs on touch screen 100. The row and
column coordinates are only used for controlled selection of the
PDs.
[0115] In accordance with an embodiment of the present invention,
each PD receiver includes a photodiode 560 and a blocking diode
570. Blocking diodes 570 are used to prevent disturbances between
neighboring diodes 560. According to an embodiment of the present
invention, blocking diodes 570 are low backwards current and low
backwards capacitance type diodes.
[0116] Further according to an embodiment of the present invention,
the voltage +V at push-pull drivers 520 is greater than or equal to
the voltage +Vref at receiver electronics 530. A slightly higher
voltage +V at push-pull drivers 520 than +Vref improves
performance, since all blocking diodes 570 are in reversed state,
except for the blocking diode of the PD receiver corresponding to
the active row and column.
[0117] vi. PD Receivers 140
[0118] In accordance with embodiments of the present invention,
multiple configurations are described herein for PD receivers used
with touch screen 100. In each configuration, the PD output is sent
to an analog-to-digital converter (ADC). The ADC matches the
expected output range, and the output range differs from one
configuration to another. The accuracy of touch screen 100 depends
to a large extent on the accuracy of the ADC.
[0119] The PD receiver configuration is determined by three
parameters: (1) the number of PD signals that enter controller 150,
(2) the type of integrator circuit used to bias and sample PD
current as it enters controller 150, and (3) the type of signal
filter and amplifier circuit used, if any.
[0120] Regarding (1) the number of PD signals that enter controller
150, in a first PD receiver configuration, the PDs along each edge
of touch screen 100 have separate outputs. Thus, at least one
circuit is provided for PDs that are arranged along one edge of
touch screen 100, and at least one other circuit is provided for
PDs arranged along the other edge. In this regard, reference is
made back to FIG. 5, which shows all PD outputs along one edge
channeled into signal PDROW, and all PD outputs along a second edge
channeled into signal PDCOL. A capacitor and a biasing resistor are
coupled to each of the ADC input signals to control the current and
to set a voltage amplitude range.
[0121] In a second PD receiver configuration, a limited number of
PDs are connected to each ADC input. PDs may be grouped, for
example, into sections of up to four PDs per section. Each output
thus integrates four PDs. An advantage of this second configuration
is less capacitance and less disturbance from non-selected
neighboring PDs.
[0122] In order to further reduce capacitance and disturbance from
non-selected neighboring PDs, an embodiment of the present
invention adds at least one multiplexer that outputs only the
selected PD signal. In this regard reference is now made to FIG.
17, which is a diagram of multiplexer 171, which operates as a PD
output selector, in accordance with an embodiment of the present
invention. FIG. 17 shows two parallel multiplexers 171, which each
receives eight PD signals as input, and generates a single output
signal. As described hereinabove with reference to FIG. 6, the PD
output is processed by signal filters and amplifiers 175. For a
touch screen with 64 PDs, in a configuration using eight
multiplexers 171, each multiplexer taking eight PD input signals
and outputting to a signal filter and amplifier 175, eight such
filters and amplifier 175 are used.
[0123] The dotted line shown in FIG. 17 separates components
internal to controller 150, which are shown to the right of the
dotted line, from components external to controller 150, which
appear to the left of the dotted line. Controller 150 includes a
multiplexer 151, which connects to an analog to digital converter
152. The signals entering multiplexers 171 from the top are control
signals from controller 150. Each such control signal uses three
bits, to control selection of one of the eight input PDs. In
general, n control bits suffice for controlling selection of up to
2.sup.n input PDs.
[0124] In addition to the three control bits used to control
selection of the input PDs, each multiplexer 171 receives an output
enable control bit, OE_NOT, from controller 150. When OE_NOT is set
to zero, the PD driver outputs the selected PD signal. When OE_NOT
is set to one, the PD driver outputs a high impedance signal.
[0125] TABLE I summarizes the logical input-output relationships
used with each PD multiplexer 171.
TABLE-US-00001 TABLE I Logical input-output relationship for PD
multiplexers Control Control Control Bit 1 Bit 2 Bit 3 OE_NOT
Output 0 0 0 0 In1 0 0 0 1 HighZ 1 0 0 0 In2 1 0 0 1 HighZ 0 1 0 0
In3 0 1 0 1 HighZ 1 1 0 0 In4 1 1 0 1 HighZ 0 0 1 0 In5 0 0 1 1
HighZ 1 0 1 0 In6 1 0 1 1 HighZ 0 1 1 0 In7 0 1 1 1 HighZ 1 1 1 0
In8 1 1 1 1 HighZ
[0126] It will be appreciated by those skilled in the art that the
first and second configurations, with and without optimal
multiplexers 171, are based on providing PD_ROW and PD_COL signals,
each signal corresponding to a signal-generating circuit, or to a
plurality of signal-generating circuits.
[0127] In accordance with the second configuration, separate
current integrator cells are assigned to subgroups of column PDs
and to subgroups of row PDs. E.g., one current integrator may be
assigned to eight PDs. In this embodiment, multiple inputs to
controller 150 are provided, one input for each subgroup.
Controller 150, as shown in FIG. 7, may be used this way to
accommodate 64 PDs grouped into eight subgroups, via eight input
signals to controller 150. Specifically, the eight inputs are
PD_ROW.sub.--1, PD_ROW.sub.--2, PD_ROW.sub.--3, PD_ROW.sub.--4,
PD_COL.sub.--1, PD_COL.sub.--2, TOUCH_SIGNAL and
TOUCH_SIGNAL.sub.--2, where TOUCH_SIGNAL and TOUCH_SIGNAL.sub.--2
are used as PD_COL.sub.--3 and PD_COL.sub.--4, respectively.
[0128] vii. PD Current Integrator 180
[0129] With regard to the type of integrator circuit used to bias
and sample PD current as it enters controller 150, several
alternative configurations and methods of operation are
provided.
[0130] According to a first configuration, each of the PD_ROW and
the PD_COL signals entering controller 150 is coupled to a biasing
resistor that sets the linear amplification, and to a capacitor
that integrates the PD current over time. In this regard reference
is now made to FIG. 18A, which is a diagram of a resistor-based
current integrator 180 used in conjunction with PD receivers 140 in
a touch screen 100, in accordance with an embodiment of the present
invention. The dotted line shown in FIG. 18A separates components
internal to controller 150, which are shown to the right of the
dotted line, from components external to controller 150, which
appear to the left of the dotted line.
[0131] According to a second configuration, the biasing resistor is
removed, and a transistor is used to set a voltage amplitude
range.
[0132] In this regard, reference is now made to FIG. 18B, which is
a diagram of a transistor-based current integrator 180 used in
conjunction with PD receivers 140 in a touch screen 100, in
accordance with an embodiment of the present invention. The dotted
line shown in FIG. 18B separates components internal to controller
150, which are shown to the right of the dotted line, from
components external to controller 150, which appear to the left of
the dotted line. A transistor T1 is located within controller 150,
and is used to efficiently control current sampled by a selected
PD. In alternative embodiments of the present invention, components
external to controller 150 are used to control the current.
[0133] When transistor T1 is open, capacitor C charges, and
integrates the current, i, flowing through the photodiode. The
voltage over C is given by
V=.intg.Cidt
When transistor T1 is closed, capacitor C discharges, and the
voltage over C is reduced to 0 volts. In order to obtain a precise
measure of the current, the sample and hold (S/H) element in FIG.
18B is discharged before sample integration begins, and S/H is open
through sample integration time. In this embodiment, the analog to
digital converter ADC in FIG. 18B is not active during integration
time.
[0134] In an alternative embodiment, S/H is configured to sample at
the end of the integration period, without previously having
discharged the S/H internal capacitors. In this embodiment, there
may be a voltage differential between the capacitor associated with
S/H and the integrator circuit.
[0135] As indicated hereinabove with reference to controller 150,
elements illustrated in the figures as being external to controller
150 may, in other implementations, reside internal to controller
150.
[0136] Reference is now made to FIG. 19, which illustrates current
integration over time, in accordance with an embodiment of the
present invention. As shown in FIG. 19, when transistor T1 is
turned on, the current in capacitor C is reset to zero. When
transistor T1 is turned off, capacitor C begins integrating current
over time. The measurement used is the current value at the end of
the sample window.
[0137] The transistor-based circuit offers several advantages over
the use of resistors for setting the linear amplification of the PD
signal. The resistors have a higher bias to low frequency noise,
such as ambient light and, as such, the ambient light is amplified
more than the light pulse. Moreover, the system measures the
ambient light sensed by a designated PD prior to issuing a light
pulse from a selected LED, in order to establish a baseline value.
Thus resistor bias to low frequency ambient light amplifies the
ambient light measurement more than the light pulse measurement. By
eliminating these resistors, the system registers similar levels of
bias for both ambient light measurements and light pulse
measurements.
[0138] Another advantage of the transistor-based circuit is that
the resistors in the resistor configurations require longer time to
completely discharge between measurements, than transistor T1. In
turn, this enables use of shorter intervals between measurements of
successive PDs, as well as between successive measurements of the
same PD. In particular, in cases in which a successive PD senses
less ambient light, or other such noise, than a previous PD, a
relatively long discharge interval is required to fully discharge
the circuit below the ambient level of the previous PD with the
resistor configurations. This problem is overcome in the
transistor-based circuit, in which the resistors are eliminated.
Since the current measurement is linearly integrated over time,
with little residual current present in the measuring circuit, the
transistor-based circuit requires uniform measuring intervals. As
such, this configuration requires precise timing to ensure that the
measurement be integrated over the same amount of time. In
distinction, when resistors are used, because they are inherently
less precise, sampling has less stringent timing requirements.
Clock jitter, for example, impairs performance of a system with
transistor-based circuits, more so that for systems with
resistors.
[0139] Reference is now made to FIG. 20, which is a simplified
flowchart of a method for PD sampling, in accordance with an
embodiment of the present invention. The method shown in FIG. 20
relates to the transistor-based circuit of FIG. 18B, used to sample
PDs.
[0140] At step 1000 all transistors, T1, T2 and T3, are turned off.
At step 1005 a PD is selected by turning on transistor T2. At step
1010 the S/H circuit is opened, and transistor T1 is turned on.
This causes capacitor C and the capacitor inside the S/H circuit to
discharge. If the S/H circuit is not discharged, then residuals
from previous measurements may arise. At step 1015 the S/H circuit
is closed, for holding. At step 1020 transistor T1 is turned off,
in order to begin current integration. At step 1025 the method
waits a designated amount of time, such as 10 .mu.s. At step 1030
the S/H circuit is opened. At step 1035 the method waits for at
least the minimum amount of time required by the S/H circuit; e.g.,
1 .mu.s. At step 1040 the S/H circuit is closed, and the analog to
digital conversion begins.
[0141] At step 1045 transistor T1 is turned on, in order to
discharge capacitor C. At step 1050 the method waits 1 .mu.s for
the capacitor for discharge. At step 1055 the LED is turned on, by
turning on transistor T3.
[0142] At step 1060 transistor T1 is turned off, to begin a new
integration/measurement. At step 1065 the method waits for a
designated amount of time, generally the same amount of time as in
step 1025. Step 1065 is done for performance. At step 1070 the S/H
circuit is opened. The conversion from step 1040 must be ready and
stored. At step 1075 the method waits for at least the minimum
amount of time required by the S/H circuit; e.g., 1 .mu.s. At step
1080 the S/H circuit is closed, and the analog to digital
conversion begins. At step 1085 the LED is turned off, by turning
off transistor T3. At step 1090 transistor T1 is turned on, in
order to discharge capacitor C. Finally, at step 1095 the method
waits 1 .mu.s for the capacitor for discharge.
[0143] In accordance with an embodiment of the present invention,
steps 1000-1095 of FIG. 20 are repeated several times, e.g., 5-20
times, in order to obtain a plurality of measurements when the LED
is on, and a plurality of measurements when the LED is off. The
background ambient light is then measured by accumulating values
when the LED is on and subtracting values when the LED is off.
[0144] In this regard, reference is now made to FIG. 21, which
illustrates measuring ambient light by summing pulses when an LED
is on and subtracting pulses when the LED is off, in accordance
with an embodiment of the present invention. In terms of samples A
thru J shown in FIG. 21, the accumulated signal is
B-A+D-C+F-E+H-G+J-I. A signal to noise ratio is given by
S N = signals noise 2 ##EQU00006##
The signal is accumulated based on a voltage metric that is a
square of power. The noise is accumulated by a power metric that is
the square root of the voltage. In case the signal is significantly
less than the background light, then DC blocking is used.
[0145] It will be appreciated by those skilled in the art that the
method of FIG. 20 affords many advantages, including inter alia:
[0146] quick switch between measurements of different PDs, and
short settle time; [0147] substantially equal amplification of
background (AC) and light pulses (DC); and [0148] ability to
measure pulse trains.
[0149] In an alternative embodiment of the present invention,
integration and analog to digital conversion are performed in
sequence. This alternative embodiment has the advantage that the
capacitor in the S/H circuit is discharged prior to each current
integration, providing for more accurate measurement. Thus if this
alternative embodiment is implemented using an ASIC, then the
integrator and the S/H may be in the same function block. However,
if analog to digital conversion of a first signal is to be done
simultaneous with integration of a second signal, then the
integrator and the S/H should be in separate function blocks.
[0150] Reference is now made to FIG. 22, which is a simplified
flowchart of an alternative method for PD sampling, in accordance
with an embodiment of the present invention. The method shown in
FIG. 22 relates to the transistor-based circuit of FIG. 18B, used
to sample PDs.
[0151] At step 1100 all transistors, T1, T2 and T3, are turned off.
At step 1105 a PD is selected by turning on transistor T2. At step
1110 the S/H circuit is opened and transistor T1 is turned on. This
serves to discharge capacitor C and the capacitor inside the S/H
circuit. If the S/H circuit is not discharged, then residuals from
previous measurements may arise. At step 1115 the method waits 1
.mu.s for the capacitor to discharge. At step 1120 transistor T1 is
turned off, to begin current integration. At step 1125 the method
waits a designated amount of time; e.g., 10 .mu.s. At step 1130 the
S/H circuit is closed, and the analog to digital conversion begins.
At step 1135 the method waits for the conversion from step 1130 to
complete.
[0152] At step 1140 transistor T1 is turned on, to discharge
capacitor C, and the S/H circuit is opened. At step 1145 the method
waits 1 .mu.s for the capacitor to discharge. At step 1150 the LED
is turned on, by turning on transistor T3. At step 1155 transistor
T1 is turned off, to begin a new integration/measurement. At step
1160 the method waits a designated amount of time, generally the
same amount of time as from step 1125. Step 1160 is done for
performance.
[0153] At step 1165 the S/H circuit is closed, and the analog to
digital conversion begins. At step 1170 the LED is turned off, by
turning off transistor T3. At step 1175 the method waits for the
conversion to complete.
[0154] As with the method of FIG. 20, steps 1105-1175 of FIG. 22
are repeated for a plurality of pulses. Values when the LED is on
are accumulated, and values when the LED is off are subtracted, in
order to measure the ambient light.
[0155] viii. PD Signal Filter and Amplifier 175
[0156] Discussion now turns to the type of signal filter and
amplifier circuit used, if any. FIG. 23A is a circuit diagram of
signal filter and amplifier 175 used for PDs arranged along one
edge of touch screen 100, in accordance with an embodiment of the
present invention. The input to signal filter and amplifier 175,
denoted PD_COL, is the output current from a selected column PD.
The output current of signal filter and amplifier 175 is sent to
controller 150 via the TOUCH_SIGNAL signal shown in FIG. 7. A
similar circuit (not shown), used for PDs arranged along the other
edge of touch screen 100, processes current from a selected row PD,
and sends the output current to controller 150 via one of the
PD_ROW_n signals shown in FIG. 7. In this embodiment, the remaining
PD_ROW and PD_COL signals are not used. Additional filter and
amplifier circuits are used when PDs along one edge are grouped
into subgroups as described above with respect to the second PD
receiver configuration. In this case additional PD_ROW and PD_COL
signals are used as required by the number of ADC inputs to
controller 150.
[0157] The circuit shown in FIG. 23A includes two filter and
amplifier paths. One path ends at TOUCH_SIGNAL in the middle of
FIG. 23A, and another path, which performs a second filter and
amplification, ends at TOUCH_SIGNAL.sub.--2 at the right of FIG.
23A. In one embodiment of the present invention, both outputs
TOUCH_SIGNAL and TOUCH_SIGNAL.sub.--2 are connected to controller
150, and firmware running on controller 150 is used to select one
of the two signals. In another embodiment of the present invention,
only one of the outputs is connected to controller 150.
[0158] Signal filter and amplifier 175 includes passive
sub-circuits that have two resistors, such as resistors R10 and
R11, and one capacitor, such as capacitor C10. Resistors such as
R12 and R13 are pass-through zero-ohm resistors.
[0159] PD_COL connects with the ADC input via resistors R10, R12,
R13 and R14, and via capacitors C10 and C11. According to an
embodiment of the present invention, capacitor C11 is a zero-ohm
capacitor. The signal level is set by resistor R13 and capacitor
C1. R13 sets the voltage amplitude range entering the ADC, and C1
integrates the current to generate voltage input to the ADC.
According to this configuration, the signal does not have to be
biased to within a predetermined range, such as between V and VCC,
because open collectors are used to read the active PD output
value. It is noted in FIG. 23A that the signal is in the range of
+3V and below.
[0160] An alternative signal filter and amplifier circuit is shown
in FIG. 23B, in accordance with an embodiment of the present
invention. In this embodiment, an OP amplifier acts like a low
impedance current to a voltage amplifier; i.e., a trans-impedance.
This configuration results in less sensitivity to capacitance and
truer current sensing. For this embodiment, the relationship
between light and current is substantially linear.
[0161] Referring to FIG. 23B, signal filter and amplifier 175
receives as input the output current from a selected column PD,
denoted PD_COL. The output current of signal filter and amplifier
175 is sent to controller 150 via the TOUCH_SIGNAL signal shown in
FIG. 7. A similar circuit (not shown), used for PDs arranged along
the other edge of touch screen 100, processes current from a
selected row PD, and sends the output current to controller 150 via
the TOUCH_SIGNAL.sub.--2 signal shown in FIG. 7
[0162] This embodiment uses a large phase margin in order to
eliminate high amplification grade that causes the amplifier to
oscillate.
[0163] The discrete transistor amplifier circuits of FIG. 23A are
of advantage in having high frequency response and low cost.
However, they are of disadvantage in having non-linear integration
over time.
[0164] A feature of the discrete transistor amplifier circuits of
FIG. 23A is that DC amplification is reduced, and the PD receiver
may thus be made entirely AC current. However, problems may arise
when shifting between PDs having a large signal difference between
them. E.g., suppose a first PD receives little light and is
amplified by the transistor-based amplifier to be within a
designated range, and a second PD receives substantially more
light, based on its position relative to ambient light sources.
Then the transistor-based amplifier, having greatly amplified the
first signal, will also greatly amplify the second AC signal, and
also the rising edge of the difference between signals, including
the second signal DC values. The combination of these amplified DC
values, together with the AC of the second PD, may amplify the
resulting signal beyond the maximum voltage, say, 3V.
[0165] 2. Optics of Touch Screen 100
[0166] Reference is now made to FIG. 24, which is a diagram of a
prior art lens assembly for an LED and PD.
[0167] Reference is now made to FIG. 25A, which is a diagram of a
lens assembly for use with LEDs and PDs for a touch screen, in
accordance with an embodiment of the present invention. Shown in
FIG. 25A are four optical surfaces for the LED lens side, and four
optical surfaces for the PD side. The focal length, f, is not
necessarily the same as the distance from the LED to the last lens
surface, LENS SURFACE 2. It may be larger or smaller than such
distance. If the focal length is smaller than such distance, then
the light spreads over a larger receiving area, and the receiving
side scans a larger area and thus receives more background light.
Nevertheless, there is an advantage to having a focal length
slightly smaller than the distance from the LED to the last lens
surface, because an optimized design is able to sense for
tolerances of the optical elements.
[0168] Reference is now made to in FIG. 25B, which is a diagram of
a lens assembly for distributing two groups of light beams, denote
by X and Y, in accordance with an embodiment of the present
invention. Shown in FIG. 25B is a lens assembly aligned
substantially parallel with the surface of the touch screen, and a
second lens assembly skewed at an angle with the surface of the
touch screen. The second lens assembly is arranged so that a finger
or stylus positioned near the touch screen, reflects some or all of
light beams Y to the PD receivers.
[0169] It will be appreciated by those skilled in the art that
although FIGS. 25A and 25B illustrate convex lenses, concave and/or
convex lenses may be used to achieve the dual foci.
[0170] The lens assembly shown in FIG. 25A is designed with the
following objectives: [0171] as much as possible of the LED light
arrives at the PD; [0172] as little as possible of the sounding
background light arrives at the PD; [0173] the horizontal
components of the light beams should be as wide as the distance
between LEDs, which improves performance in interpolating position
between light beams; and [0174] the vertical components of the
light beams are limited by the height of a frame over the LCD
screen.
[0175] Reference is now made to FIGS. 26A and 26B, which are
diagrams of simplified lens assemblies corresponding to the
respective lens assemblies of FIGS. 25A and 25B, in accordance with
an embodiment of the present invention. The simplified lens
assembly in FIG. 26A resembles that of a camera lens, and is useful
for determining LED and PD die sizes, denoted by d, focal length,
denoted by f, PD lens aperture, denoted by a, and distance between
LED and PD lens surfaces, denoted by s. The PD lens aperture is
approximately equal to the distance between neighboring PDs and to
the distance between neighboring LEDs. Ideally, the LED projects
over the PD lens aperture, which corresponds to the relationship
d/a=f/s. Sample design parameters for a horizontal lens and for a
vertical lens are provided in TABLE II. It is noted that the
horizontal and vertical foci are significantly different. Ideally,
the horizontal and vertical foci are directed away from the LED
center, and towards the target PD, so that all light emanating from
the LED lens arrives at the PD.
TABLE-US-00002 TABLE II Design parameters for touch screen optics
parameter symbol horizontal lens vertical lens LED die size d 0.3
mm 0.3 mm PD die size d 0.3 mm 0.3 mm aperture a 5 mm 1 mm distance
between s 30 mm 30 mm LED and PD edges focal length f 1.8 mm 9
mm
[0176] 3. Applications of Touch Screen 100
[0177] Aspects of the present invention relate to applications for
the touch screen described hereinabove. The ensuing discussion
includes (i) user input based on finger motion, (ii) mobile phone
handset, (ii) touch-screen as mouse-type input device for a
computer, and (iii) touch-based storefront window.
[0178] i. User Input based on Finger Motion
[0179] As indicated in FIGS. 6A and 6B, the output of PD receivers
140 is processed by controller 150, to determine, from the measured
light intensities, if one or more objects are positioned over touch
screen 100. The optical assembly of FIG. 25 enables measurements of
light intensities at several heights above touch screen 100; i.e.,
three-dimensional measurements at various heights over the surface
of the touch screen 100. In this regard, reference is now made to
FIG. 27, which shows three-dimensional measurements of light
intensities over the surface of touch screen 100, in accordance
with an embodiment of the present invention. The top chart
corresponds to measured light intensities at seven locations, when
no finger is positioned on touch screen 100. The bottom left chart
corresponds to measured light intensities at the seven locations,
when a finger is positioned over touch screen 100. The bottom right
chart also corresponds to measured light intensities when the
finger is positioned over touch screen 100. The bottom right chart
corresponds to measurements taken slight after the measurements
used for the bottom left chart were taken. The difference in charts
indicates that the finger is moving downward, closer to the touch
screen. As a result, light intensity is being blocked at lower
z-values, i.e., heights.
[0180] It will thus be appreciated by those skilled in the art that
the measurements of light intensities at various heights above
touch screen 100 enables determination of both position and motion
of an object on touch screen 100. Referring to FIG. 27, the
distance between the finger positions from the bottom left chart
and the bottom right chart, denoted by DIST, may be determined from
the light intensity readings. Knowing the time difference between
the measurements for the two charts enables determination of a
finger velocity vector. If the velocity vector is substantially
downward, then the magnitude of the velocity vector is an
indication of how hard the finger is pressing on touch screen 100.
If the velocity vector is substantially rightward, then the finger
is making a rightward gesture.
[0181] By determining motion information, touch screen 100 is able
to distinguish between a variety of user inputs, including inter
alia tap, press, and directional finger gesture, and to process
them accordingly.
[0182] Reference is now made to FIG. 28, which is an illustration
of a touch screen with three-dimensional sensing functionality, in
accordance with an embodiment of the present invention. Touch
screen 100 functions as a three-dimensional sensor. Increases or
decreases in light intensities measured by PD receivers are used to
sense the presence of a finger or other object above the screen
surface. As shown in FIG. 28, a lens or array of lenses,
distributes light emitted by an LED in a plurality of directions.
Two groups of light beams are identified in FIG. 28; namely, light
beams denoted by X, which are directed along a plane substantially
parallel to the screen surface, and light beams denoted by Y, which
are directed diagonally across and upward to the screen
surface.
[0183] When no object is near the screen surface, the PD receiver
measures all of light beams X. When a finger or other object is
positioned above the screen surface, it reflects a portion of light
beams Y to the PD receivers, via a second lens or array of lenses.
The PD receiver accordingly senses an increased light intensity
corresponding to the sum of light beams X and Y. It will be
appreciated by those skilled in the art that use of a reflective
object, such as a silver pen, to point at the touch screen,
enhances reflection of light beams Y.
[0184] Reference is now made to FIG. 29, which is a graph
illustrating different light intensities measured by a PD receiver
corresponding to proximity of an object to a touch screen surface,
in accordance with an embodiment of the present invention. The
middle portion of the graph corresponds to light beams X,
indicating that no object is obstructing light beams X, and none of
light beams Y are reflected to the PD receiver. This portion of the
graph is the default PD receiver intensity when no object is near
the screen surface.
[0185] The signals shown in FIG. 29 rise and decline. When the PD
current is activated, as shown at the bottom of FIG. 29, the
signals rise. When the PD current is terminated, the signals
decline.
[0186] The highest portion of the graph corresponds to a finger or
object reflecting a large portion of light beams Y to the PD
receiver. As the finger or object is moved closer to the screen
surface, the magnitude of measured light intensity changes, based
on the amount of light beams Y directed to the PD receiver by the
finger or object. The effect of increasing intensity of reflected
light beams Y is similar to the effect of increasing intensity when
a finger is brought close to a light bulb. Namely, as the finger
approaches the light bulb, the intensity of light on the fingertip
increases; i.e., more light is reflected by the fingertip.
[0187] When a finger or object is brought very close to the screen
surface such that it blocks a portion of light beams X, the
measured light intensity at the PD receiver drops to below its
default value, and approaches zero as the object touches the screen
and substantially completely blocks light beams X. Referring back
to FIGS. 25A, 26A and 27 it is seen that the light intensity
detected by a PD receiver is a function of a finger's proximity to
the screen surface, when the finger blocks a portion of light beams
X.
[0188] ii. Mobile Phone Handsets
[0189] The touch screens of the present invention are particularly
suitable for small mobile phones. Phones that have these touch
screens do not required keypads, since the screens themselves may
serve as touch-based keypads. The touch screens serve as input
devices, for receiving touch-based user inputs, and as output
devices, for displaying data generated by a phone modem.
[0190] US Publication No. 2008/007533 A1 entitled INFORMATION
MANAGEMENT SYSTEM WITH AUTHENTICITY CHECK by Ericson et al.
describes a system for identifying the location of a pen above a
sheet of paper, whereby the pen includes a camera that captures
images of a varying pattern on the sheet of paper. A computer unit
analyzes a captured image and determines therefrom the location of
the pen. Further, by analyzing a sequence of images captured by the
camera as the pen is moved over the pattern, the computer unit
identifies strokes made by the pen.
[0191] In one embodiment, the present invention provides a similar
system for a touch screen. Instead of providing a pattern on a
sheet of paper, a light pattern is projected over the touch screen.
When a finger or other object is positioned above the touch screen,
the finger or other object reflects a portion of the projected
light pattern. Only the reflected portion of the projected pattern
is substantially visible.
[0192] A camera communicatively coupled with the touch screen
captures an image of space above the touch screen. The captured
image shows the pattern reflected by the finger or other object.
The captured image is transmitted to a controller that determines
the location of the finger or other object over the touch screen by
analyzing the captured image. Further, by providing a sequence of
images captured as the finger or other object moves over the touch
screen, the controller identifies a stroke or gesture made by the
finger or other object.
[0193] Reference is now made to FIG. 30A, which is a simplified
illustration of a handset 600 with a touch screen 100, in
accordance with an embodiment of the present invention. Handset 600
includes a projector 610, a barrier 613 that blocks portions of
light projected by projector 610, and a lens 617 that spreads the
light over a specific angle, denoted by .theta.. Barrier 613 may be
implemented as an etched metal plate that only allows light to
penetrate through the etched openings. Barrier 613 may
alternatively be implemented as a material that has transparent
portions and non-transparent portions. The transparent portions may
be in the form of digital, letters, dots, or such other shape.
Barrier 613 may alternatively be a grating, with openings through
which light projected by projector 610 passes. When projector 610
projects light at barrier 613, a light pattern 620 is generated
above touch screen 100.
[0194] Handset 600 further includes a camera 630 which captures
images of projected pattern 620. When an object, such as a user's
finger 640, is within range of projected pattern 620, portions of
pattern 620 are reflected by finger 640. In turn, the images
captured by camera 630 show the reflected portions of pattern 620,
from which distance and position information of finger 640 is
derived. Since finger 640, or such other reflecting object such as
a stylus or pen, is not a flat surface, the reflected portion of
pattern 620 is warped or otherwise distorted when viewed from an
angle other than the angle of projection. By aligning camera 630
with projector 610, the images of finger 640 are captured at
substantially the angle of projection, as a result of which the
reflected portion of pattern 620 is not significantly
distorted.
[0195] Reference is now made to FIG. 30B, which is a simplified
illustration of a pattern of dots projected into the space above
screen 100, in accordance with an embodiment of the present
invention. The pattern of dots shown in FIG. 30B may be generated
by a barrier 613 that is implemented as a metal plate having holes
etched therein. A portion of the dot pattern, shown as black dots,
is reflected by finger 640; and a portion of the dot pattern, shown
as white dots, is not reflected by finger 640. By analyzing the
pattern of dots reflected by finger 640, the touch screen
controller determines the three-dimensional position of finger 640
relative to touch screen 100.
[0196] Finger 640 in FIG. 30B reflects a pattern of seven dots. As
finger 640 moves to the right or to the left, different dot
patterns appear on finger 640, based on the dots shown in FIG. 30B
to the right and to the left of finger 640, respectively.
Similarly, when finger 640 moves up or down, different dot patterns
appear on finger 640, based on the absence of dots above finger 640
and the dots shown below finger 640. As such, the dot pattern on
finger 640 determines the height of finger 640 above touch screen
100, along the z-axis, and the position of finger 640 along the
width of touch screen 100, along the x-axis.
[0197] The position of finger 640 along the length of touch screen
100, along the y-axis, is determined from the scale of the image
reflected by finger 640 or, equivalently, by the sizes of the
elements of the projected pattern. Since projector 610 projects the
pattern across a wide angle, as shown in FIG. 30A, the closer
finger 640 is to projector 610, the denser is the reflected
pattern. As such, the density of the reflected image determines the
distance between finger 640 and projector 610. In turn, this
distance determines the position of finger 640 along the length of
touch screen 100, along the y-axis.
[0198] Reference is now made to FIG. 30C, which is a simplified
illustration showing how the density of pattern 620 projected by
projector 610 in the space above touch screen 100, and reflected by
finger 640, is dependent upon the distance of finger 640 from
projector 610, in accordance with an embodiment of the present
invention. It is noted that the reflected pattern 620, signified in
FIG. 30C by a "1" digit, scales larger the further it is from
projector 610. The protected pattern 620 is spread over an angle
.theta. by lens 617. The angle .theta. and the sizes of the
captured pattern elements are used to determine the distance of the
reflected pattern 620 from projector 610.
[0199] In an alternative embodiment of the present invention, a
second projector and barrier is situated along a second edge of
touch screen 100. The two sets of relative (x, z) position
coordinates of finger 640, determined by the two cameras, suffice
to determine the y coordinate of finger 640.
[0200] In accordance with an embodiment of the present invention,
the distance and position information of finger 640 is used to
further derive the location 650 on touch screen 100 where finger
640 is aimed. Touch screen 100 highlights location 650 so that a
user can see the location to which finger 640 is aimed, and to
adjust the position of finger 640 if necessary.
[0201] Reference is now made to FIG. 30D, which is a simplified
illustration of a pattern of digits projected into the space above
screen 100, in accordance with an embodiment of the present
invention. The pattern of digits shown in FIG. 30D may be generated
by a barrier 613 that is implemented as a metal plate having the
digits "1", "2" and "3" etched thereon lithographically, or by such
other etching process. When projector 610 projects light at barrier
613, the digits "1", "2" and "3" are projected above screen 100.
When finger 640 is positioned over screen 100 to the left of
projector 610, as shown in FIG. 30D, the digit "1" appears on the
finger, and is captured by camera 630. The digits "2" and "3" are
not visible.
[0202] Similarly, when finger 640 is positioned in front of
projector 610 (not shown), the digit "2" appears on the finger, and
is captured by camera 630; and when finger 640 is positioned to the
right of projector 610 (not shown), the digit "3" appears on the
finger, and is captured by camera 630.
[0203] Reference is now made to FIG. 30E, which is a simplified
illustration of another pattern of digits projected into the space
above screen 100, in accordance with an embodiment of the present
invention. The pattern of digits shown in FIG. 30E may be generated
by a barrier 613 that is implemented as a metal plate having two
rows of digits etched thereon. When projector 610 projects light
through barrier 613, the digits "1", "2" and "3" are projected
closer to the surface of screen 100, and the digits "4", "5" and
"6" are projected further from the surface of screen 100. When
finger 640 is positioned over screen 100 to the upper left of
projector 610, as shown in FIG. 30E, the digit "4" appears on
finger 640, and is captured by camera 630. The remaining digits are
invisible.
[0204] Similarly, when finger 640 is positioned over screen 100 to
the lower left of projector 610 (not shown), the digit "1" appears
on finger 640, and is captured by camera 630.
[0205] FIGS. 30B-30E illustrate that the location of finger 640
relative to touch screen 100 is determined by analyzing images
captured by camera 630. As the number of unique patterns, such as
digits, is increased in barrier 613, the position of finger 640 may
be determined more accurately.
[0206] iii. Touch Screen as Mouse-Type Input Device for a
Computer
[0207] Aspects of the present invention apply to a touch screen
which serves as a mouse-type input device for a computer. Reference
is now made to FIG. 31, which is an illustration of use of touch
screen 100 for processing finger motions as input to a computer, in
accordance with an embodiment of the present invention. Shown in
FIG. 31 is a finger motion that is detected by touch screen 100.
Controller 150 (FIGS. 6A and 6B) recognizes the finger motion and
converts the motion to mouse pointer coordinates, for input to a
computer. Thus it may be appreciated that touch screen 100 is able
to emulate mouse movement.
[0208] Additionally, left and right mouse clicks may also be
emulated by displaying two objects on touch screen 100. Touching a
first one of the objects corresponds to a left mouse click, and
touching a second one of the objects corresponds to a right mouse
click.
[0209] Further single and double clicking may be emulated by
velocities of approach of touch screen 100. As described above with
respect to FIG. 27, measurement of light intensities at different
heights above touch screen 100 enables determination of finger
velocity. A slow approach, made by a light tap, corresponds to a
single click, and a fast approach, made by a hard press,
corresponds to a double click.
[0210] Referring to FIG. 31, it will be appreciated by those
skilled in the art that the path of finger motion shown involves
relative motion between a finger and touch screen 100. The path
shown may be generated by a moving finger and a stationary touch
screen. It may also be generated by a moving touch screen and a
stationary finger, or other stationary object.
[0211] As such, a dual embodiment of the present invention operates
by moving touch screen 100 over a stationary object. The relative
motion of touch screen 100 generates the path shown in FIG. 31 and,
in turn, the path information is converted into mouse
coordinates.
[0212] iv. Touch-based Storefront Window
[0213] Aspects of the present invention relate not only to use of
touch-based position and motion information for input to a
computing device, but also to use of this information for data
processing purposes. In general, the sensed position and motion
information for touch screen 100 may be transmitted to a data
processor for further analysis. An application of such data
processing is a touch-sensitive interactive storefront window,
which enables passersby to interact with a display showcase or a
video display. The storefront window system responds to passersby
touch inputs, and also records and analyzes their touch inputs.
[0214] In this regard, reference is now made to FIG. 32, which is a
simplified illustration of a touch sensitive display case 700
containing items of merchandise 710, in accordance with an
embodiment of the present invention. In accordance with an
embodiment of the present invention, the perimeter of an opening in
the display case is fitted with light sensors and light emitters,
thereby providing the display case with touch screen functionality.
Additionally, display case 700 includes mechanical apparatus to
automatically move, rotate or otherwise manipulate a displayed item
710, in response to a passerby 720 touching the display case at a
location corresponding to the displayed item.
[0215] A passerby 720 may interactively manipulate selected items
by touching and making gestures with his finger on display case
700. For example, touching display case 700 causes a corresponding
item 710 to be selected. A rotating gesture on display case 700
causes item 710 to be rotated. A swipe on display case 700 in one
direction causes item 710 to be moved closer to passerby 720, and a
swipe in display case 700 in the opposite direction causes item 710
to be moved away from passerby 720. An x-shaped gesture on display
case 700 causes item 710 to be de-selected.
[0216] In the foregoing specification, the invention has been
described with reference to specific exemplary embodiments thereof.
It will, however, be evident that various modifications and changes
may be made to the specific exemplary embodiments without departing
from the broader spirit and scope of the invention as set forth in
the appended claims. Accordingly, the specification and drawings
are to be regarded in an illustrative rather than a restrictive
sense.
* * * * *