U.S. patent application number 11/327302 was filed with the patent office on 2007-02-08 for capturing handwriting.
Invention is credited to Ethan A. Funk, Andrew M. Goldman, Sergey Liberman, Arkady Pittel, Leonid Reznik, Ilya Schiller, Vladimir V. Subach.
Application Number | 20070030258 11/327302 |
Document ID | / |
Family ID | 34397237 |
Filed Date | 2007-02-08 |
United States Patent
Application |
20070030258 |
Kind Code |
A1 |
Pittel; Arkady ; et
al. |
February 8, 2007 |
Capturing handwriting
Abstract
Motion of a writing instrument is tracked from sensors located
in the vicinity. The signals generated from the sensors are
processed and used in a wide variety of ways.
Inventors: |
Pittel; Arkady; (Brookline,
MA) ; Schiller; Ilya; (Brookline, MA) ;
Liberman; Sergey; (Bedford, MA) ; Funk; Ethan A.;
(Boston, MA) ; Subach; Vladimir V.; (Lexington,
MA) ; Goldman; Andrew M.; (Wakefield, MA) ;
Reznik; Leonid; (Sudbury, MA) |
Correspondence
Address: |
FISH & RICHARDSON PC
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Family ID: |
34397237 |
Appl. No.: |
11/327302 |
Filed: |
January 6, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10623284 |
Jul 17, 2003 |
|
|
|
11327302 |
Jan 6, 2006 |
|
|
|
09698471 |
Oct 27, 2000 |
|
|
|
10623284 |
Jul 17, 2003 |
|
|
|
09376837 |
Aug 18, 1999 |
6577299 |
|
|
10623284 |
Jul 17, 2003 |
|
|
|
60161752 |
Oct 27, 1999 |
|
|
|
60195491 |
Apr 10, 2000 |
|
|
|
60230912 |
Sep 13, 2000 |
|
|
|
60142200 |
Jul 1, 1999 |
|
|
|
60142201 |
Jul 1, 1999 |
|
|
|
60096988 |
Aug 18, 1998 |
|
|
|
Current U.S.
Class: |
345/179 |
Current CPC
Class: |
Y02D 10/00 20180101;
Y02D 10/155 20180101; G06F 1/3259 20130101; G06F 3/0386 20130101;
G06F 1/3203 20130101; G06F 3/03545 20130101; G06F 3/0428 20130101;
G06F 3/04886 20130101; G06F 3/03542 20130101 |
Class at
Publication: |
345/179 |
International
Class: |
G09G 5/00 20060101
G09G005/00 |
Claims
1. A method comprising: receiving light from a moving writing
instrument at an array of sensing elements of a sensor; reading the
sensing elements in sequence to generate a sequence of signals
indicative of light sensed by the elements of the array; and
resetting each elements after it is read and before at least some
of the other elements in the array are read.
2. The method of claim 1 in which the array comprises a CMOS or CCD
position sensor.
3. The method of claim 1 in which each of the elements is reset
before the next element in the sequence is read.
4. The method of claim 1 in which all of the elements are read
before all of the elements are reset.
5. A method comprising: conveying light from a moving hand-held
instrument; sensing the light at two or more sensors, each of the
two or more sensors comprising a two-dimensional array of sensing
elements; generating signals representing the two-dimensional
locations on the arrays of light that is sensed; and determining a
sequence of three-dimensional positions of the moving writing
instrument based on the signals.
6. Apparatus comprising: a writing instrument system that can track
three-dimensional motion of the writing instrument.
7. The apparatus of claim 6 in which the system includes sensors
having 3 linear arrays.
8. The apparatus of claim 6 in which the system includes sensors
that are a two-dimensional array or a one-dimensional array.
9. A method comprising: sending light from a moving writing
instrument, the light being indicative of a position and path of
the writing instrument; and directly sensing, at one or more
sensors spaced from the writing instrument, angles from which light
is received from the writing instrument.
10. The method of claim 9 in which the angles are directly sensed
by an array of sensitive elements of a sensing device.
11. The method of claim 10 in which the sensing device comprises a
CMOS or CCD device.
12. The method of claim 10 in which the sensing device comprises a
PSD.
13. Apparatus comprising: a writing instrument; an element that
enables wireless transmission of a signal associated with motion of
the writing instrument and tracking of the writing motion based on
the signal; and the element being built into a cell phone, a PDA, a
webpad, or a clipboard.
14. Apparatus comprising: two optical sensors separated by a known
distance and arranged to, receive light from a source associated
with a writing instrument, determine directions from which the
light is received relative to a known direction, and provide
signals representing the directions for use in determining a
sequence of locations of the writing instrument; and at least one
of the two sensors comprising a CMOS of CCD array.
15. The apparatus of claim 14 in which the CMOS or CCD array
comprises a linear array of sensor elements.
16. The apparatus of claim 14 in which the CMOS or CCD array
comprises a two-dimensional array of sensor elements.
17. Apparatus comprising: a holder for a writing instrument, the
writing instrument including electronic circuitry configured to be
used in conjunction with tracking writing motion of the writing
instrument, the writing instrument including a rechargeable battery
connected to power the electronic circuitry, and the holder
including a receptacle for the writing instrument and a recharging
circuit connected to recharge the battery when the writing
instrument is in the receptacle.
18. Apparatus comprising: a CMOS sensor adapted to receive light
associated with motion of a writing instrument and to provide
signals indicative of an angle of receipt of the light with respect
to a known direction; and a lens aligned to direct the received
light to the CMOS array.
19. The apparatus of claim 18 in which the lens comprises a
half-ball lens.
20. The apparatus of claim 18 in which the lens comprises an
aspherical lens.
21. The apparatus of claim 18 in which the lens is optimized for
collection of light from an area in which the motion of the writing
instrument occurs.
22. The apparatus of claim 18 in which the lens comprises a flat
field lens.
23. The apparatus of claim 18 in which the lens comprises a Fresnel
lens.
24. The apparatus of claim 18 in which the lens system is
configured to collect light in a dimension normal to a plane of
motion of the writing instrument and to project the light onto the
sensor in a direction parallel to the plane of motion.
25. A method comprising: modulating light that is conveyed from a
moving writing instrument to light sensors spaced from the writing
instrument at a predetermined frequency; and using a phase locked
loop associated with the sensors to lock onto the phase of the
modulated light.
26. Apparatus comprising: circuitry for tracking writing motion of
a writing instrument using wireless transmission of signals between
the writing instrument and a stationary element, the stationary
element including a main processor and a separate preprocessor, the
preprocessor being connected to perform at least data capture with
respect to motion of the writing instrument, and the main processor
being connected to perform at least data communication with respect
to the tracking.
27. The apparatus of claim 26 in which the preprocessor is also
connected to perform user interface functions and sub-pixel data
storage.
28. The apparatus of claim 26 in which the main processor is also
connected to perform background cancellation and sub-pixel
calculation.
29. The apparatus of claim 26 in which the main processor is also
connected to perform conversion of sub-pixel data into paper
coordinates.
30. The apparatus of claim 27 in which data storage is done in the
form of paper coordinates.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 10/623,284, filed Jul. 17, 2003; which is a continuation of
U.S. application Ser. No. 09/698,471, filed Oct. 27, 2000, now
abandoned, which claims the benefit of U.S. Provisional Patent
Application Ser. No. 60/161,752, filed Oct. 27, 1999, U.S.
Provisional Patent Application Ser. No. 60/195,491, filed Apr. 10,
2000, and U.S. Provisional Patent Application Ser. No. 60/230,912,
filed Sep. 13, 2000, and is a continuation-in-part of Ser. No.
09/376,837, filed Aug. 18, 1999, now U.S. Pat. No. 6,577,299, which
claims the benefit of U.S. Provisional Patent Application Ser. No.
60/142,201, filed Jul. 1, 1999, U.S. Provisional Patent Application
Ser. No. 60/142,200, filed Jul. 1, 1999, and U.S. Provisional
Patent Application Ser. No. 60/096,988, filed Aug. 18, 1998.
[0002] The disclosures of the prior applications are considered
part of and are incorporated by reference in the disclosure of this
application.
BACKGROUND
[0003] This invention relates to tracking motion of a writing
instrument.
[0004] By tracking the motion of a pen, for example, as it is used
to write or draw on paper, it is possible to capture and reproduce
electronically what is being written or drawn. Motion of a stylus
that does not leave a mark on a writing surface can also be
tracked.
[0005] In some proposed approaches, the surface on which the pen is
moving may have an array of pixels or other sensing locations each
of which responds when the pen is at that location.
[0006] In other techniques, the pen tracking is done entirely by
electronics mounted in the pen. In some schemes, the moving pen
communicates with stationary sensors that are separate from the
pen, and triangulation algorithms are used to track the motion.
SUMMARY OF THE INVENTION
[0007] In general, in one aspect, the invention features a method
that includes conveying light from a moving writing instrument as
an indication of the location and path of the writing instrument on
a two dimensional writing surface; sensing the light at two or more
sensors and generating a sequence of signals representative of the
sensed light; and applying a technique to reduce the effect of
variations of the light intensity in a third dimension with respect
to the generated signals.
[0008] Implementations of the invention may include one or more of
the following features. The technique may be based on optics that
are configured to enhance the uniformity of signal response of the
sensors. The lens may be a spherical lens or an aspheric lens. The
sensors may be arrays of sensitive pixel elements or analog
sensors. The technique may be based on algorithmic processing of
the generated signals. The algorithmic processing may include
linearizing the signal response of the sensors based on parameters
associated with the writing instrument. The technique may be
implemented in digital hardware or in analog circuitry. The
algorithmic technique may reduce the effect of variations of the
light intensity based on other than dimensional effects. The
signals may be grouped in frames, and the signal processing
technique may include processing of multiple frames to cancel
noise. The light conveyed from the moving writing instrument may be
modulated at a frequency related to the rate at which the signals
are generated by the sensors, and the sensor signals may be chopped
at the frequency of modulation. Opposite gains may be applied to
each of the chopped signals depending on the on or off state of the
light conveyed from the writing instrument that corresponds to the
signals. The frame rate may be varied. The chopped signals may be
integrated over time. The light conveyed from the writing
instrument may include a strong short pulse imposed at on the
modulation frequency, a phase lock loop may determine the
modulation frequency from the sensor signals, and the sensor signal
may be sampled at the times triggered by the phase lock loop during
the duration of the strong short pulse. The characteristics of the
conveyed light may be used for synchronization between the writing
instrument and the sensors. The conveyed light may include periods
of lower frequency modulation and bursts of higher frequency
modulation, and the sensor signal associated with the higher
frequency bursts may be used to lock onto a modulation clock.
[0009] In general, in another aspect, the invention features a
method that includes conveying light from a moving writing
instrument in a time-changing pattern of directions, sensing the
light at two or more sensors located at two or more different
locations spaced from the writing instrument, and determining the
location of the writing instrument by detecting a phase difference
between signals measured at the two or more sensors.
[0010] Implementations of the invention may include one or more of
the following features. The time-changing pattern of directions may
include a rotating pattern with respect to an X-Y plane on which
the writing instrument is moving. The signal radiated in the
positive X direction may be in phase quadrature to the signal
radiated in the Y direction.
[0011] In general, in another aspect, the invention features
apparatus that includes sensors configured to receive light from a
writing instrument moving across an X-Y writing surface, the light
having variations in intensity along a Z-axis normal to the writing
surface, and optics configured to enhance optical power of the
light received from the writing instrument.
[0012] Implementations of the invention may include one or more of
the following features. The optics may be a ball lens or an
aspherical lens. The optics may include a single spherical lens and
the lens and the corresponding sensor may be together configured to
enhance the optical power of light received at large angles or
longer distances or at disadvantageous positions of the writing
instrument. The optics may include a special lens configured to
enhance optical power of the light received from a location on the
X-Y surface that is beyond a predetermined position. The optics may
include two cylindrical lenses, one nearer the sensor to project
light horizontally onto sensor, and the other positioned to collect
light in the Z-axis dimension, the other lens having a body that is
bent around the first lens. The algorithmic processes may enhance
the immunity of the signals to variations in the intensity of the
received light caused by distance from or tilt of the writing
instrument. The processes may determine the integral power of the
overall signal distribution on the sensor and calculate a subpixel
position based on half of the integral power position. The
processes may use a polynomial approximation on the signal
distribution and calculate a subpixel position as a position of
approximated maximum. The calibration procedure may produce
parameters to be used in combination with data from the sensors.
The calibration parameters may correct for manufacturing
deficiencies of the optics and the sensors, and the algorithmic
processes may use a straight triangulation technique to determine a
position of the writing instrument. The calibration parameters may
correct for manufacturing deficiencies of the optics and sensors
and the algorithmic processes may determine the position of the
writing instrument using polynomial series, where coefficients in
these polynomials are determined during the calibration
procedure.
[0013] In general, in another aspect, the invention features a
method that includes receiving light from a moving writing
instrument at a an array of sensing elements of a sensor, reading
the sensing elements in sequence to generate a sequence of signals
indicative of light sensed by the elements of the array, and
resetting each of the elements after it is read and before at least
some of the other elements in the array are read.
[0014] Implementations of the invention may include one or more of
the following features. The array may include a CMOS or CCD
position sensor. All of the elements may be read before all of the
elements are reset.
[0015] In general, in another aspect, the invention features a
method that includes determining a sequence of three-dimensional
positions of the moving writing instrument based on the
signals.
[0016] In general, in another aspect, the invention features the
combination of a writing instrument having an elongated housing
configured to be hand-held, a light source in the housing, and a
lens in the housing configured to receive light from the light
source and to convey the light through a free-air path to optical
sensors spaced from the writing instrument, the lens being
configured to be semi-reflective.
[0017] In general, in another aspect of the invention, the light
source includes an array of light sources arranged around an axis
of the writing instrument and configured to emit light in a
direction normal to the axis.
[0018] Implementations of the invention may include one or more of
the following features. The lens may be configured to internally
reflect and concentrate the light and to emit it by reflection from
a reflective external surface of the lens. The lens may have a
cylindrical body having an upper surface that receives the light
and a lower annular surface that reflects the light toward the
optical sensors. The reflective external surface may include a
conical surface oriented at a 45 certain degree angle to a
longitudinal axis of the writing instrument. The light source in
the pen may include LEDs arranged in a ring.
[0019] In general, in another aspect, the invention features a
device configured to turn the light source on and off in response
to a user applying pressure from the writing instrument to a
writing surface, the device being configured so that an amount of
pressure required to trigger the device is not so large as to
disrupt normal writing motion of the writing instrument on the
writing surface.
[0020] Implementations of the invention may include one or more of
the following features. The writing instrument may include a
ballpoint cartridge having a writing point and the device may be
positioned at the opposite end of the cartridge from the writing
point. The device may be a switch or a pressure sensor.
[0021] In general, in another aspect, the invention features a
holder having a receptacle for receiving at least a portion of the
writing instrument for storage of the writing instrument,
[0022] the writing instrument and the holder containing respective
elements that enable wireless transmission of signals associated
with motion of the writing instrument and tracking of the writing
motion based on the signals.
[0023] In implementations of the invention the holder may be a pen
cap and may include a clip configured to attach the holder to a
stack of pages or to a notebook. The holder may include at least
two light sensors and a processor that processes signals from the
light sensors to determine a sequence of positions of the writing
instrument. The holder may include a receptacle for holding the
writing instrument and for enabling recharging of batteries in the
writing instrument.
[0024] In general, in another aspect, the invention features an
element that enables wireless transmission of a signal associated
with motion of the writing instrument and tracking of the writing
motion based on the signal, the element being built into a cell
phone, a PDA, a webpad, or a clipboard.
[0025] In general, in another aspect, the invention features, a
holder that has a mechanism for attaching the holder to a writing
substrate in an orientation that enables the elements to be used in
conjunction with the wireless transmission. The clipping mechanism
may include a switch to activate functions of a processor in the
holder when the clipping mechanism is manipulated.
[0026] In general, in another aspect, the invention features, a
holder that includes a receptacle for the writing instrument and a
recharging circuit connected to recharge the battery when the
writing instrument is in the receptacle.
[0027] In general, in another aspect, the invention features a CMOS
sensor adapted to receive light associated with motion of a writing
instrument and to provide signals indicative of an angle of receipt
of the light with respect to a known direction, and a lens aligned
to direct the received light to the CMOS array.
[0028] In implementations of the invention, the lens may be
optimized for collection of light from an area in which the motion
of the writing instrument occurs. The lens may be a field lens or a
Fresnel lens. The lens system may be configured to collect light in
a dimension normal to a plane of motion of the writing instrument
and to project the light onto the sensor in a direction parallel to
the plane of motion.
[0029] In general, in another aspect, the invention features
calibrating by positioning a writing instrument at a succession of
positions on a writing surface, generating signals at sensors from
light received from the writing instruments at the succession of
positions, and determining calibration parameters for the writing
instrument for use in calibrating a process that determines the
positions of the writing instrument as it is being moved.
[0030] In implementations of the invention, the calibration
parameters may include coefficients used in polynomial series that
are part of the position determining process.
[0031] In implementations of the invention, the positions do not
lie on a regular rectangular grid.
[0032] In general, in another aspect, the invention features (1)
identifying locations on a writing surface that correspond to input
elements to be entered into an electronic device, the writing
surface being non-electronic and separate from the electronic
device, (2) using a writing instrument to point to selected ones of
the identified locations corresponding to input elements to be
entered, and (3) sensing the locations at which the writing
instrument is pointing and entering the corresponding data into the
electronic device.
[0033] In implementations of the invention, the writing surface
includes a sheet of paper, the input elements comprise characters
of language or commands that are printed on the writing
surface.
[0034] In general, in another aspect, the invention features moving
a writing instrument across a non-electronic writing surface to
indicate a path, and remotely sensing the path and generating
signals for use in entering the path into an electronic device that
is separate from the writing surface.
[0035] In general, in another aspect, the invention features
modulating light that is conveyed from a moving writing instrument
to light sensors spaced from the writing instrument at a
predetermined frequency, and using a phase locked loop associated
with the sensors to lock onto the phase of the modulated light.
[0036] In general, in another aspect, the invention features,
circuitry for tracking writing motion of a writing instrument using
wireless transmission of signals between the writing instrument and
a stationary element, the stationary element including a main
processor and a separate preprocessor, the preprocessor being
connected to perform at least data capture with respect to motion
of the writing instrument, the main processor being connected to
perform at least data communication with respect to the tracking.
In implementations of the invention the preprocessor may also be
connected to perform user interface functions and sub-pixel data
storage and the main processor may also connected to perform
background cancellation and sub-pixel calculation.
[0037] In general, in another aspect, the invention features a
reflective element configured to reflect light received from
outside of the writing instrument to the sensor for use in tracking
motion of the writing instrument.
[0038] In implementations of the invention, the reflective element
may reflect light to the sensor when the writing instrument is
being used for writing and disable the reflective element from
reflecting light to the sensor when the writing instrument is not
being used for writing.
[0039] In general, in another aspect, the invention features
receiving light from a moving writing instrument at a light sensor
having an array of sensitive pixel elements, and determining the
location in the array at which the maximum intensity of light has
been received from the writing instrument, the location being
determined with sub-pixel accuracy.
[0040] In implementations of the invention, the sub-pixel location
is determined by determining the integral pixel location that is
closest to the subpixel location, and finding a fractional center
of gravity of a subarray that is centered on the integral pixel
location.
[0041] In general, in another aspect, the invention features
indicating locations on a non-electronic surface that correspond to
inputs to an electronic device, and detecting the locations and
inputting them into the electronic device.
[0042] In general, in another aspect, the invention features a clip
for clipping paper on which the writing instrument is to be moved
to the sensor.
[0043] In implementations of the invention the mechanism may be
part of a clipboard or a notebook, the clip may include a mechanism
that enables a user to cause the clip to grip or to release the
paper. The clip may include an activation button and a spring and a
lever operated by the button. The lever may be configured to rotate
in response to the button. The button may be configured to be
pushed or pulled. Other advantages and features will become
apparent from the following description and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] FIG. 1 shows pen tracking.
[0045] FIG. 2 shows a pen.
[0046] FIG. 3 shows a lens in a pen.
[0047] FIG. 4 shows a lens in a pen.
[0048] FIGS. 5 and 6 show reflection of light in a pen.
[0049] FIG. 7 shows a tracking method.
[0050] FIG. 8 shows a pen.
[0051] FIG. 9 shows a pen.
[0052] FIG. 10 shows a holder.
[0053] FIG. 11 shows a lens in front of a sensor.
[0054] FIG. 12 shows a holder.
[0055] FIG. 13 shows a holder.
[0056] FIGS. 14 and 15 show half of a holder.
[0057] FIG. 16 shows another half of the holder.
[0058] FIG. 17 shows a field of view.
[0059] FIG. 18 shows a block circuit diagram.
[0060] FIG. 19 shows a state diagram.
[0061] FIG. 20 shows a timing diagram.
[0062] FIG. 21 shows a timing diagram.
[0063] FIG. 22 shows geometry of tracking.
[0064] FIG. 23 shows a circuit diagram.
[0065] FIG. 24 shows a timing diagram.
[0066] FIGS. 25 and 26 shows a rotating beam technique.
[0067] FIG. 27 shows a channel diagram.
[0068] FIG. 28 shows a channel circuit.
[0069] FIG. 29 shows a paper keyboard.
[0070] FIG. 30 shows a spherical lens.
[0071] FIG. 31 shows an aspherical lens.
[0072] FIG. 32 shows a two-lens arrangement.
[0073] FIG. 33 shows a clip.
[0074] FIG. 34 shows a clip.
[0075] FIG. 35 shows a sliding belt clip.
[0076] FIG. 36 shows two views of a clip.
[0077] FIG. 37 shows two views of a clip.
DETAILED DESCRIPTION OF THE INVENTION
[0078] We describe an electronic wireless pen that in addition to
its regular function of leaving a visible trace on the writing
surface also emits infrared (IR) light that is collected by
external IR sensors to measure pen position with respect to the
sensors. The sensors are CMOS or CCD linear or 2D arrays, Position
Sensitive Detectors (PSD) or other light sensitive detectors. The
sensors can be clipped to the edge of writing surface allowing
reconstruction of writing on that page. The position of the pen is
determined by mapping the sensor reading to the actual XY position
of the pen on paper.
[0079] This electronic input device looks like a regular pen with a
holder. The user writes with it just as with any ordinary pen on
paper, notebook or any other flat surface. It is used to capture
handwriting text or drawings. The pen stores all its movements
during its use by recording sensor measurements into its memory.
The pen then downloads it to a computer, personal digital
assistant, handheld computer or cellular phone. The handwriting, as
it appears on a page, is then automatically reconstructed from
sensor information.
[0080] As shown in FIG. 1, a pen or other writing instrument 10
that leaves a visible trace 12 of writing or drawing in the usual
way on a sheet of paper or other writing surface 14 may also have a
source 16 that emits infrared (IR) light 18 for use in
automatically tracking the motion of the pen. The light is detected
by IR sensors 20, 22 that are held stationary relative to the pen
at a nearby location, for example, near the edge 23 of the
paper.
[0081] The sensors deliver sequences of signals that represent the
position of the pen on the writing surface (e.g., angle 24) at
which the light is received from the pen for each of a succession
of measurement times. Circuitry associated with the sensors uses an
algorithm to process the directional information (and the known
distance 26 between the sensors) to determine a succession of
positions of the pen as it is moved across the writing surface. The
algorithm can use a mathematical model that translates pixel
signals of the sensors into positions on the writing surface. The
algorithm could be a quasi-triangulation algorithm using calibrated
parameters (distance from lens to sensor and horizontal offset
between their centers of refractive index) or it could be a
polynomial approximation.
[0082] The tracked motion of the pen can be used to recognize
handwriting or capture drawings created using the pen or used in a
wide variety of other applications. The tracked motion information
can be sent to a local personal computer or to a central computer
through a personal digital assistant, a handheld computer, or a
cellular phone for central storage and processing.
Tracking of Light Source with a Two or One Dimensional Sensor
[0083] The problem of tracking XY bearing of a pen can be
formalized as follows.
[0084] The pen carries a finite source of light close to the tip.
This source emits light which intensity in the test point depends
on the XYZ position of a test point with the source in the
origin.
[0085] A multichannel detector is located at another location. It
collects some portion of the light emitted by the source on a pen.
Intensity delivered to different channels varies depending on the
XYZ position of channel inputs with respect to the location of this
source. Intensity data are sufficient to calculate the XYZ position
of a source relative to the detector. Intensity data are also
subject to noise including source instability, detector noise, and
other kinds.
[0086] We are interested in obtaining the XY bearing of the pen
only. In fact, all three coordinates will vary due to thickness
irregularities on a writing surface and due to varying tilt of a
pen during writing. Along with noise this will cause complex
variations in channels reading.
[0087] There are different ways of processing such signals:
weighted average ( center of gravity), median computation,
thresholding, etc. They mostly address noise cancellation and treat
Z motion of a source as noise also.
[0088] Our goal is to establish such a property of the detected
signal that would be invariant to the motion of a pen in Z
direction and to some sources of noise.
[0089] For this purpose, we introduce an aperture between a
detector and the source. This aperture may contain a lens, for
example. Thus we obtain a spatially limited signal. This means that
there is a closed group of detector channels that is excited by
both the signal and the noise (a segment in case of a linear array
detector). This group is surrounded by channels that are excited by
the noise only. In the absence of an aperture, all channels are
excited by both the signal and the noise.
[0090] After creating such a signal we establish a specific point (
e.g. maximum) and define a processing window around this point in
such a way that it extends beyond a spatially limited signal. Then
a cumulative distribution function of data inside the processing
window is calculated versus channel numbers. The projection of this
function's half magnitude point on channel numbers produces the
invariant property. While channel numbers are integers, the
invariant property value may be fractional.
[0091] There are basically two types of detectors, whether 2D or
1D. Each detector can be a two channel detector, like a PSD, or a
"multichannel" detector like a CMOS and CCD device. PSD detectors
have two output signals whose ratio defines a relative position of
incident light spot. CMOS and CCD detectors have a number of
pixels. Each pixel defines a particular space on the detector and
has an analog output. These analog outputs can be digitized for
later processing in firmware or software, or can be processed by
analog means. Algorithms used in software can alternatively be
implemented in hardware in the same way.
One Calibration Procedure
[0092] There is no need to achieve a linear response of the
detectors to pen motion as has been proposed in other known
approaches. A linear response would be required if simple
triangulation were to be used to interpret a detector reading as an
XY position of a pen.
[0093] An unambiguous dependency exists between the XY position of
a pen and left and right detector (L and R) readings as follows:
X=Fx(L,R); Y=Fy(L,R). (1)
[0094] These functions can be expressed as polynomial series.
Coefficients in these polynomials can be determined during the
calibration procedure.
[0095] During the calibration procedure, the pen is positioned in
different known XY locations on the paper and readings of both
detectors are taken and stored for future processing. After a
sufficient number of points has been accumulated, common linear
algebra methods are used to calculate the coefficients in (1).
[0096] We know that system (1) is substantially non linear. It is
important to locate calibration points in such a way that a
necessary resolution is achieved across the entire writing area. We
do not locate the calibration points in the nodes of a regular
rectangular grid. Instead, we use mathematical models to match a
calibration grid to particular nonlinear properties of our
detectors.
Another Calibration Procedure
[0097] If simple triangulation is used to calculate an XY pen
position from detector data, we intentionally introduce an error
into the geometrical parameters of our detectors to allow for the
nonlinear properties discussed above.
[0098] We know exactly the refractive index of the lenses in our
detectors and distances between the lenses and sensors by virtue of
our design. At the same time it has been proved that varying these
values in triangulation computation one can effectively compensate
the nonlinear properties of detectors.
[0099] To obtain effective values for refractive index and
distances between the lenses and sensors we run another calibration
procedure. The different XY location calibration points are
necessary for proper resolution across the writing area. Locations
of calibration points for this disturbed triangulation are obtained
through mathematical models.
The Pen
[0100] As shown in FIG. 2, in one example, the IR source in the pen
can be an LED 13 that emits IR light 15 at the tip 17 of the pen
when pressure is applied during writing. In this example, the LED
source 13 is formed by a ring of LEDs 19 arranged around the
longitudinal axis 21 of the pen (only two LEDs are shown).
[0101] Light from the LEDs is project downward toward the pen point
and into a body/lens of acrylic material 18 that operates as a
light pipe. The acrylic lens diffuses and transmits the received
light so that light emitted from the pen is delivered along optical
paths in all directions around the pen.
[0102] As shown in FIG. 3, the pipe 18 is polished and reflective
and concentrates light 502 from the LEDs 19 inside by not allowing
the light to escape sideways. The bottom part of the pipe is also
polished at the 45 degree conical surface 504 at the bottom of the
pipe. A reflective cylindrical shell 506 helps to confine and cause
mixing of the light that is emitted from the LEDs. A conical body
508 supports the light pipe. Downwardly directed light within the
pipe is reflected from the conical surface 504 and delivered to the
air at all angles around the pen.
[0103] FIGS. 5 and 6 illustrate side and top views of internal
reflection of light in the light pipe. Most light from the LEDs
passes along the length of the body of the pen and is reflected at
a 90 degree angle toward the sensors. Some other light finds its
way out of the pen at angles different from 90 degrees.
[0104] As shown in FIG. 2, the light that is emitted from the pen
is confined to a vertical space 11 that is near to the writing
surface 13 so that as much of the light as possible can reach the
sensors (not shown), which are also positioned within a small
distance of the writing surface.
[0105] Other configurations having different shape light
pipes/lenses could be used, including the one shown in FIG. 4,
which may have a better coupling between the LED and the light pipe
and more effective splitting and directing of light toward the
reflective surface at the bottom of the pipe.
[0106] The pen in this example (FIG. 2) includes a ball-point pen
cartridge 23 that terminates in a writing point 25. When the user
bears down on the writing point during writing, a pressure switch
26 delivers a signal that can be used to turn on the LEDs and to
trigger functions of circuitry 28 also mounted in the pen.
Circuitry 28 and LEDs 19 are powered by a battery 30. The
components are all held in a housing 15.
[0107] As shown in FIG. 7, the pen position in an x-y coordinate
system 40 parallel to the writing surface is determined from two
angles alpha and beta that are sensed by the two sensors 20, 22,
and the known distance 26 between sensors.
[0108] In another example, shown in FIG. 8, the pen is powered by
three miniature AAA-like NiCd rechargeable batteries 51 that are
held in the back of the pen (For better weight distribution the
batteries will be moved closer to the tip, with the circuitry
placed at the back). The batteries power the electronic circuitry
28 directly without any DC-to-DC converter. The power is delivered
only when the pressure switch 26 is activated. The light activation
switch travels only a short distance (e.g., 0.25 mm). The switch is
preloaded by a spring mechanism to minimize refill travel, which
should not exceed 0.008-0.010 inches.
[0109] Pressure sensors would be an way to effectively match
pressure on the pen refill with activation of LED, as many
off-the-shelf switches have an activation pressure above the
desired level of 20 to 30 g.
[0110] The electronic board 28 positioned behind the battery
generates modulation frequency pulses at approximately 100 Hz and a
50% duty cycle for the IR LEDs along with the bursts of 1 to 10 kHz
to generate pen on and pen off signals for sleep mode.
[0111] The light emitted from the pen is visible in all directions
to enable the pen to be used in any orientation in the hand. The
closer the emitted light is to the tip of the pen, the less is the
error due to the variations of pen angel to paper, and the more
accurate is the tracking of the tip of the pen. The LED light
should be in an IR region away from the visible light spectrum so
that ambient light from the sun and light fixtures does not
interfere excessively with the IR emission and is not visible to
the human eye.
[0112] The IR source at the pen and the orientations of the sensors
in the holder are arranged to assure that as the pen tilts and
rotates during normal writing or drawing, its IR beam reaches the
sensors.
[0113] FIG. 9 shows a more detailed isometric view of a partially
assembled pen.
Pen Holder
[0114] As shown in FIGS. 1 and 10, the sensors can be housed in a
typical pen cap 70 in which the pen can be held when not in use.
When the pen is being used, the pen is removed from the cap and the
cap is positioned at a stationary location near the writing surface
and in the vicinity of the pen. In some examples, the sensors are
linear CMOS arrays (available, for example, as 1024 pixel arrays
from Photo Vision Systems, LLC (PVS) (P.O Box 509, Cortland, N.Y.
13045) (part number LIS1024)). Other linear CMOS sensors from PVS
or other companies with the same or a different number of pixels
could also be used. The analog output of each sensor is a sequence
of 1024 analog signals, one from each sensor pixel.
[0115] A shown in FIG. 10, the holder may include a clip 62 to
attach the holder to the edge of a pad of paper or a notebook.
[0116] A third sensor in the form of a photodiode 56 in the middle
of the holder is used (among other things) to wake up the processor
from a sleep mode (described below) when writing begins (e.g., the
pen begins to emit light).
[0117] The third sensor signal may also be used to synchronize the
circuitry in the pen with the circuitry in the sensor system. All
three sensors are covered by IR filtering windows that face the
writing surface.
[0118] As shown in FIG. 11, in one example, the front surface 100
of each of the main sensors has a vertical height 104 of 125
micrometers and a distance 106 from the front surface 108 of the
lens 110 of four millimeters. The FOV 112 is 10 degrees. The pen
tip 114 directs IR light into the FOV when the pen tip is on the
paper 116.
[0119] As shown in FIG. 17, the two sensors 88, 90 are positioned
100 mm apart. Each of the sensors has a field of view (FOV) 94, 96
centered on an FOV axis 195, 197. The axes of the FOVs are not
parallel but are toed in by an angle 199 to increase amount of
overlap of the FOVs. The FOV of each sensor has a breadth of
150.degree. in the horizontal (x-y) plane and a height of
+/-5.degree. in the vertical plane.
[0120] The FOVs do not cover some locations 101 on the writing
surface that are close to the edge of the paper 303, and the FOVs
are arranged so that the dead zone 98 does not extend more than 25
mm from the holder.
[0121] In another example of a pen holder, shown in FIG. 12, the
sensors 117 and the lenses 119 are mounted on a holding bracket 121
with the IR filter 123 in front. The bracket is mounted on a
printed circuit board 125 and is held in a housing 127. The centers
of two main sensors are separated by 100 mm.
[0122] The light from the pen is collected from two sensors in
order to identify the linear position of a modulated light source
within a defined area (8.5.times.11 inches). The linear position
may be computed by triangulation, a lookup table, polynomial
approximation, or a combination of any of these.
[0123] The sensors are flat, linear, multi-pixel sensors. Different
pixels of each of the sensors are illuminated when the light source
is in different locations within the field. As the light source
moves across the field, the corresponding movement of the light
across the pixels of the sensors may not be linear, but the lack of
linearity can be handled because the linear position may be
computed by math and knowledge of optics combined with calibration
data from the pair of sensors.
[0124] Instead of seeking a linear response from the sensors, we
seek to maximize the light from within writing area that falls onto
the sensors. Correct reproduction of writing is achieved by using
parameters saved from the prior calibration procedure. The system
uses, in some implementations (in the polynomial example shown
below, the number of parameters can be greater)and supplied in a
separate file) only four parameters to be passed from each pen to a
host or server to process the data and linearize it. The particular
calibration parameters for a pen are stored in the memory of the
pen during production test and calibration. The parameters can also
be stored on the server or on a PC used by the user instead of
being passed on from the pen during downloads.
[0125] A lens or a set of lenses accompanies each sensor. The goals
of the optical system are to maximize the efficiency of the light
delivery, cover the entire field of view of the field, provide a
uniform signal response across the entire field, and make the
optical system as small and as cheap as possible. These goals are
met in part by the following steps:
[0126] As shown in FIG. 30, a spherical lens 753 is used to focus
the light on the sensor 755. The focal plane has a shape of a
semicircle. The distance 759 from the lens to the sensor is
optimized as are the other optical and mechanical properties of the
lens including focal length, diameter, thickness, and material.
[0127] As shown in FIG. 31, an aspheric lens 760 may be designed
with a focal point positioned on the sensor as the light source
travels around the periphery of our field where the total power of
the light source delivered to the sensor will be the weakest. Thus,
this aspherical lens is designed to have a focal plane, which
coincides with the plane of the sensor for only the points that are
on the periphery of the page. Points within the page will be out of
focus, but the amount of light falling onto the sensor will be
significantly larger (closer to sensor or better angle), and the
signal stronger.
[0128] As shown in FIG. 32 (which includes a top view above and a
side view below), two perpendicular cylindrical lenses 770, 771 may
be used instead of one lens. The length of the sensor limits the
focal length of the lens in the horizontal axis. Therefore the lens
diameter must be small and the lens must be located close to the
sensor. In the vertical axis the lens may be located further from
the sensor so the diameter can be larger. The larger diameter will
allow for the collection of more light from the light source. The
first cylinder (closer to the lens) will focus the light in the
horizontal axis. This lens may be spherical because the spot size
is not very important in the horizontal axis and will not vary that
much within our given field. The second cylinder will have power in
the vertical axis. It is important to focus as much light as
possible on the sensor in the vertical dimension. For this to be
true, the light must travel an equal distance from the cylinder to
the sensor for all angles. To accomplish this, the second cylinder
should be bent into an aspheric shape. Any of these two cylindrical
lenses can be Fresnel lenses in order to save space.
[0129] In a more detailed example of a pen holder shown in FIGS.
13, 14, 15, and 16 the sensor system is held in a housing 79 that
has a bottom 80 and a top 82. The bottom 80 holds a clip 62 (not
shown). Paper can be inserted between the clip 62 and the bottom of
the pen holder when a clip button 86 is depressed. When the button
is released, the clip grasps the paper. The pen clip holds a 7
mm-thick stack of paper sheets or a standard notepad 83. The clip
positions the pen holder on the paper so that the side 87 that
faces the pen is vertical with a tilt of no more than +/-1.degree.,
thus assuring that the sensors will receive IR light from the pen
when it is being used to write on the surface.
[0130] The holder can also just sit on top of paper or notebook
without use of clip.
[0131] In the holder shown in FIGS. 13 through 16, the two sensors
are mounted behind IR filtering windows 89, 91, and the photodiode
93 is mounted in the middle. An "ink well" 95 can receive the tip
of the pen 97 for temporary storage, and a tube 99 provides a place
to store the pen. The pen can be fully inserted into the tube and
the batteries in the pen can be recharged during storage.
[0132] Various mechanisms for operating the clip are possible
including the example shown in U.S. patent application Ser. No.
09/376,837, filed Aug. 18, 1999.
[0133] In one arrangement, the clip mechanism shown in FIG. 33 is
used. The figure shows the steps in operating the mechanism, as
follows.
[0134] Step 1: Mechanism is not activated.
[0135] Step 2: When the push button 780 presses on a spring 782,
the latter releases the bracket 733, and lets the hinge spring 784
unfold the clip 785.
[0136] Step 3: Paper 786 is inserted between the clip and the body
787 of the pen holder.
[0137] Step 4: Lever 785 (the clip) is against the paper, and
spring 788, which is significantly weaker than the hinge spring
gives in and starts collapsing. The clip rotates around rotating
point 789.
[0138] Step 5: The clip presses the paper against the bottom of the
holder. Spring 788 collapses, and both levers move down by the
amount of paper inserted.
[0139] A clip button can be used to transfer horizontal motion to
vertical motion by a lever, which lowers the clip. Or, the button
can push against a lever that rotates, transferring horizontal
motion to vertical movement, which lowers a clip.
[0140] This mechanism is shown on FIG. 34. The clip has two
vertical sliding bars 790, 791 connected to a horizontal bar 792.
There is a spring 793 between the horizontal bar and the body of
the holder. There are two vertical guides 794, 795 for the vertical
bars to go up and down.
[0141] In the side view at the bottom of the figure, when the
button is not depressed, the spring is all the way up and the clip
is pressed against the penholder body (left side of the figure).
When the button is depressed (right side of the figure), the spring
is depressed and the clip (see the front view now), goes down
between the slides. After paper is inserted and the button
released, the spring pushes the clip up and the mechanism grabs the
paper between the clip and the penholder body.
[0142] The button may move a lever in multiple axes to lower the
clip. The button can activate a lever that rotates and moves
linearly to lower the clip.
[0143] In another arrangement, shown in FIG. 36, the operator
pushes down on a sliding panel (button) 901. The sliding button
contacts the center of two spring-loaded levers 903, 905 moving
these fulcrums down in the same direction of the button/panel. The
bottom ends of the levers are fixed about rotating pins 907, 909
and thus the bottom? ends move downward about twice the distance of
the button. The top ends of the levers are fitted with pins 911,
913, which ride in guide slots 915, 917 and in two tabs that are
bent up vertically from the bottom clip. The end result is a
movement vertically downward of the clip, which is about twice the
distance as the button/panel travel.
[0144] Alternatively, as shown in FIG. 35, the sliding panel 930
may be placed in a horizontal orientation and, by means of a rigid
flexible belt, achieve the desired result with a horizontal pushing
motion as opposed to the vertical motion of the button.
[0145] As shown in FIG. 37, another approach may be achieved by a
pulling motion of the button 951 if the forces acting on the two
levers 953, 955 in the mechanism is moved from the middle of the
levers to the bottom ends, and the fulcrums of the levers are moved
to a point 1/3 the distance from the top? ends to the bottom? ends.
This would provide the necessary mechanical advantage to maintain
the 2:1 ratio of the distance the clip moves to the travel of the
button.
[0146] In both mechanisms, the location of pivoting points to
points of applying force on levers can be used to increase
mechanical displacement of the clip.
Pen Holder Circuitry
[0147] A circuit block diagram of the holder is shown in FIG. 18.
An ASIC 205 is powered by a battery 511, or from an AC adaptor 513,
or from a USB connection to a host computer 211. The two CMOS
sensors 201, 203 have outputs that are connected 165, 167 through
operational amplifiers 169, 171 through a multiplexer 180 and a
12-bit A-to-D converter to the ASIC.
[0148] The analog output of the CMOS sensor is subjected to signal
processing in the form of offset cancellation and automatic gain
control. The signal-to-noise ratio requirements of the processing
implies use of 5V power for the CMOS sensors and all analog signal
processing circuitry. Some A/D converters are operated at a 2.5v
reference, and the signal from the CMOS sensor may scaled down by
factor of 2 using a resistive divider.
[0149] The ASIC could be model Clarity 2B from Sound Vision,
located in Framingham, Mass.) and is based on an ARM7 core. The
ASIC firmware implements data acquisition, data storage, file
system management, I/O service (LEDs and switches), RS232, and USB
communications, power management for idle and sleep modes, optical
calibration, and test mode.
[0150] The multiplexer enables the A-to-D converter 182 to
alternate between the two CMOS arrays 201 and 203 to minimize the
time skew between the two sensors. The clock frequency of the
A-to-D converter is 1.2 MHz. Each CMOS sensor is clocked at 600
kHz. Data acquisition uses the ASIC's direct memory access (DMA)
facility.
[0151] A wakeup input of the ASIC is driven by a PLL 513 that
receives an input signal from the photodiode 515. The photodiode is
driven by modulated light from the pen.
[0152] The ASIC is clocked by a 48 MHz crystal and a clock divider
517. I/O features are provided through a USB port 211 and an
RS232/IrDA port 209. Firmware and data are processed in SDRAM 207
and stored in a flash memory 519. An optional LCD 172 can be
provided for user display.
[0153] USB provides two data transfer modes from the holder to a
PC: bulk and real-time. Real time transfer is interrupt driven and
is used for keyboard and mouse replacement applications.
[0154] A dual function transceiver is used to implement both RS232
and IrDA communication. The RS232 communication is used as a dial
up connection to the server over cellular phone.
[0155] The holder can support different types of external
connections, including USB, Serial, Parallel, IrDA, Bluetooth,
Firewire, or any kind of communication port. When powered down, if
the holder is connected to any external device, it has a capability
to automatically power itself up. It also has a capability to power
itself down when an external device is disconnected. There are two
types of connections for the holder:
[0156] One connection is an external storage type of connection.
Such a connection is made with a computer, or other device, called
host, that is capable of displaying graphics and has an adequate
user interface. While connected to a host device, the holder
behaves as an external storage device. A user of the host device
can browse through the holder file system, copying, viewing, and
editing files previously collected by the holder. The software
residing on the host is capable of converting, displaying,
printing, and editing on the host screen files stored on the holder
or copied from the holder to the host. While connected to the host,
the pen can also behave as a real-time input device.
[0157] The other type of a connection is with a portable internet
or modem enabled device, such as a cellular phone. Upon detecting
such a connection, the pen holder automatically initiates
transmission of all the data previously collected to be sent as
e-mail or fax.
[0158] The optional LCD display notifies a user of the pen's
status, for example, with respect to connections and downloads over
Internet-ready cellular phones where communications are not
reliable. This display can be mounted on top of the holder. If an
LCD is used, the LED may not be needed.
[0159] A single three-color (green, yellow, red) LED 170 (see also
FIG. 18) indicates normal acquisition of writing data, downloads to
a PC and over cellular phone, and monitoring of battery and memory
status.
[0160] Pen, clip, and inkwell switches 141, 143, and 145 are used
to control the ASIC and a reset switch 147 is used to reset the
ASIC.
[0161] FIG. 19 shows a state diagram of the states of operation of
the invention. Shaded blocks indicate study states. Clear blocks
indicate transition states. Among other things, the figure
identifies the manner in which the multicolor LED is used to
indicate the state of operation.
[0162] At power up, the green light blinks as many times as there
are pages in memory. The green light is not on at power up when the
memory is empty, and stops blinking after 30 seconds or sooner if
the user starts to write.
[0163] During writing, when data acquisition is proceeding
properly, the LED is pale green. The green light goes off for
faulty acquisition triggered by, for example, obstructed light, a
pen that is off the writing surface, or a discharged battery.
[0164] Low battery status is indicated by a blinking yellow light
when no writing is occurring. However, when writing, the yellow
light blinks intermittently with pale green if the battery is
low.
[0165] Memory nearly full status is indicated by a double-blink of
the yellow light when writing is not occurring and a yellow light
blinking intermittently with pale green when writing is
occurring.
[0166] Download status (which may start independently whether the
pen is in or out of the holder or ink well) is indicated by a
bright green light after successful download. Blinking green,
signifies that download is in progress. When no service is
available for downloading or the download signal is week, a red
light blinks. The red light double blinks for an Internet problem,
for example when a server is down. A triple blinking red light
indicates a wrong setup for communication including a wrong user ID
or server address. This requires a code sent back to pen from
server after unsuccessful match of data from pen with account on
database.
[0167] Battery recharge status is indicated by a solid green light
after a successful recharge and by a multiple blinking green light
when the holder is plugged into the AC adapter and charging. A
combination of signals from the battery monitoring circuitry and
the fast charge signal from a charger (high when not charging) can
identify the state, whether charge in process or trickle
charge.
[0168] The pen can be used during recharging. If the pen is removed
from the ink well and is used during recharging, the yellow light
is replaced with all normal indicator lights described above.
[0169] Writing to flash status is indicated by a continuous yellow
light.
[0170] All errors are reset by activation of any of the two pen or
ink well switches mentioned later. The only exception is when a
download was successful, and the user started writing. Then the
constant bright green light will switch to a pale green light.
[0171] In sleep mode, all trouble indications, low memory, and low
battery continue as in the normal mode. All download troubles stay
on also.
[0172] If the ASIC needs to indicate low memory or low battery
conditions during power up, the power up indications take the
priority. Then the trouble indications are displayed up after a 30
second timeout. If the ASIC needs to indicate low memory or low
battery conditions during download, the download indications take
precedence. After a reset of download status, the trouble
indications are displayed.
[0173] Of the four switches on the holder, the clip switch 141
indicates that the clip is being opened and closed as a way to
notify the circuitry that the user is beginning a new page. The pen
switch 143 indicates when pen is in or out of the holder. An ink
well switch 145 indicates when the pen is in or out of the ink
well. The reset switch 147 is hidden but accessible through a hole
in the bottom using a paper clip.
[0174] The pen switch and the inkwell switch indicate when the pen
is in the holder or the inkwell and remove power from the data
acquisition and storage electronics when the pen is in the holder
or the inkwell. The pen switch also opens new files (or pages) on
activation, while the ink well switch does not.
[0175] The clip switch indicates when the clip is activated, as
well as a new page and beginning of a new file (each page is a
file).
[0176] The reset switch resets the ASIC if the software freezes.
The switches are normally ON as follows:
[0177] Pen ON when the pen is out of the holder.
[0178] Ink Well ON when the pen is out of the ink well.
[0179] Clip ON when the clip button is released.
[0180] Reset ON when switch is depressed.
[0181] The holder also includes a miniature connector for USB and
RS232 interfaces as well as an antenna for use with Bluetooth or
other wireless technology. The USB and RS232 connector are also
connected to the wake-up power circuitry so that pen holder can
power itself up when cable is plugged into the miniature
connector.
[0182] Angle signals generated by the sensors are processed by the
ASIC and stored in flash for later transmission to other devices
such as cellular phones, PDAs, and PCs (not shown) where they can
be used for handwriting recognition or to capture drawings. The
transmission can be done using, for example, USB, RS232, IrDA, or
Bluetooth protocols. File System
[0183] The flash memory is structured as a FAT (file allocation
table)-compatible file system, where each file represents one page
of handwritten information. Each file has a unique name of 12
characters, including 3 characters of extension and a separating
"dot".
Data File Creation
[0184] When a user brings the pen into writing mode by taking the
pen out of the holder, or by pressing the new page clip button if
the pen is already in the writing mode, a new file is created, and
the subsequent writing is saved in a new file. If the user does not
actually do any more writing after new file was created, the newly
created file is deleted, and the next time pen is brought to the
writing mode, the same file name will be reused.
[0185] During data acquisition, uncompressed data is stored in a
temporary buffer in SDRAM and compressed by a data store task
before being stored into a file in flash memory. Each page is
stored in a separate file. A previous page is compressed before new
page acquisition is started.
Data File Format
[0186] We use a binary compressed format based on a variable rate
Huffman encoding with cubical appoximation. Such a format comprises
encoded data coordinates and timestamps.
[0187] Before being compressed, the file has the following
format:
[0188] The file is structured in four byte segments. Each segment
corresponds to either one pixel or one timestamp. Each pixel has a
most significant bit (MSB) of zero, and consists of two 15-bit
numbers that are the sub coordinates of corresponding CMOS sensors.
Timestamps are distinguished by a MSB of one, and can store either
full date and time of the next pixel (called full timestamp), or
incremental counter of pixels since the last full timestamp.
[0189] Each file begins with the full timestamp. An incremental
timestamp is inserted in the end of every written stroke. Because
all pixels are scanned evenly in time, such a combination of
timestamps enables efficiently recover the whole history of
handwriting in the future processing.
Downloading of Data
[0190] When the holder is connected to a PC using a USB cable, the
PC automatically recognizes the holder as a PC-compatible USB
device, and the contents of the holder file system becomes visible
for the PC through the PC-file system extension. The user can
browse through it and view the files using a handwriting
viewer.
[0191] When an RS232 cable is connected between the holder and, for
example, a cellular phone, the holder automatically powers itself
up, and starts transmission of data files from the memory of the
holder to the phone. IR transmission of data to the phone could
also be done.
[0192] The data is sent in the compressed form to the server and is
kept there until requested for an addressee. Then it is
decompressed and translated into one of the following formats: tif,
.pdf, gif, ps specific to e-mail or FAX service.
Sensor Signal Preprocessing
[0193] In some examples, a preprocessor (not shown) can be used for
background cancellation, and storage into flash memory, while the
ASIC processor performs all communication and I/O functions. The
preprocessor can be implemented as a programmable device such as
PLD, FPGA or digital ASIC or a DSP. In this example, a frequency
multiplication is performed to generate a high-frequency pixel
clock and a clock for the preprocessor from the pen LED modulation
frequency that is recovered by the PLL.
[0194] The second processor can be a processor of another portable
device such as a cellular phone or PDA.
Data Acquisition
[0195] Position data is collected in a succession of samples spaced
10 milliseconds apart to adequately capture writing motion at a
typical speed of 5 cm per seconds for a resolution of 0.5 mm. The
ASIC operates as a master, generating the clock and all necessary
signals for the sensors.
[0196] The sensors in the holder use the pixel clock from the ASIC.
A frame signal is generated by each sensor and read back into the
ASIC. Thus, the LED pulses from the pen and the signal acquisition
performed on the holder are not synchronized in some
implementations. In other examples, the data acquisition is
synchronized with the pen modulation frequency. Synchronization
significantly improves angle resolution.
[0197] In each sampling cycle in which the pen position coordinates
are obtained, data is captured from both sensors. One version of
the background cancellation algorithm (asynchronous with pen)
requires capturing three consecutive frames at each sensor. An
additional frame is used by the ASIC architecture for sensor
reset.
[0198] To minimize any skew between coordinates from the two
sensors, the multiplexer data acquisition alternates between the
two sensors for each pixel.
[0199] Operating the A-to-D converter at a sampling rate of 1.2 MHz
maximum and alternating between the two sensors allows for a pixel
sampling frequency up to 600 kHz. Each CMOS array has 1024+4
pixels, which produces a frame rate of approximately 600 Hz. A
slower rate of 300 Hz might be used to achieve more pixel exposure
to light and accordingly better signal-to-noise ratio.
[0200] Each sensor operates in a mode in which each pixel is reset
after being read into A/D converter.
[0201] The IR LED duty cycle is 50% out of three frame intervals.
For that duty cycle, the LED frequency cannot exceed 200 Hz.
[0202] For purposes of cancellation of background noise and low
frequency interference without synchronization, three data frames
of 1024 pixels are required, as described below.
[0203] In addition to the main analog output each CMOS delivers
END_FRAME signals. From each CMOS the acquisition cycle for each of
the three sequential frames of data is started by the END_FRAME
signal, which coincides with the last pixel of the frame. Each
A-to-D conversion occurs on the falling edge of the PIXEL_CLOCK
pulse. The total number of points is essentially (1024+4)*3, where
1024 is the length of the CMOS array, 4 is the number of clock
pulses between the END_FRAME signal and the beginning of the next
frame, and 3 is the number of sequential frames needed to implement
background compensation.
[0204] From the acquired waveform, the ASIC extracts three arrays,
each corresponding to 1024 pixels. The arrays must be correctly
aligned so that the i-th element in each of them corresponds to the
i-th pixel of the CMOS.
[0205] Let us call the arrays A1, A2, and A3. Background
compensation is based on the fact that the LED in the pen is
modulated with a frequency equal to 1/3 of the frame rate and with
a 50% duty cycle. To achieve background compensation, the following
calculations are performed element-wise on the arrays:
A12=abs(A1-A2); A23=abs(A2-A3); A13=abs(A1-A3). Then arrays A12,
A13 and A23 are added element-wise to form a new array called A.
This array A is 1024 elements long and carries the beam information
with the background removed.
[0206] To reliably get rid of the large peaks appearing in the
pixel waveform during the END_FRAME pulses, subarrays shorter than
1024-elements long can be extracted, for example, three
1020-element long subarrays, that start at pixels 3, 1032 and 2061
(base 0).
[0207] The readouts of the two sensors are digitized simultaneously
(or quasi-simultaneously when using only one A-to-D converter with
a multiplexer).
Finding Peak Position Along CMOS Array with Subpixel Resolution
[0208] Determining the angle of receipt of the light at each of the
sensors depends on determining the pixel location of the peak light
intensity along the array of the sensor. The algorithm to find peak
position with subpixel resolution uses two parameters: T, the
intensity threshold in volts and W, the window width in pixels.
Typical values of these parameters are T=0.1 V and W=15.
[0209] As an initial step, the peak value and its index in the
array A are found, call them Amax and M. If either of the two Amax
values (corresponding to the two sensors) is smaller than T, then
the point is discarded. In that instance the LED is considered to
be off with the pen not touching the paper. If M<W/2 or
M>(1024-W/2), the point is discarded as being too close to the
edge of the field of view.
[0210] From A, extract a W-element-long subarray starting from
element M-W/2. Find its fractional center of gravity as follows:
create an array of running sum of elements of the extracted
subarray (call it S). Take the value of its last element. Divide it
by 2. Find the fractional index of the position of this value in S
using linear interpolation/lookup. Add M-W/2 to this value. This
will be the fractional index of the center of gravity of the beam
in the original 1024-element array. Invert its sign and add 512 (in
the case of an A that is 1024 elements long or 510 in the case of
an A that is 510 elements long). The result, P, is the fractional
position of the beam with respect to the axis of the sensor (in
pixels).
[0211] The use of a subpixel algorithm permits an increase of the
pixel resolution by a factor of 8 to 10.
Calculating Light Source Angle with Respect to Sensor Axis
[0212] As a result of the previous calculation, we have the angular
position of the beam for each sensor (in pixels). We call them
Pleft and Pright (looking at the sensors from the pen point of
view). We recalculate the Ps in radians based on the sensor
geometry. In one example, the pixel pitch L=7.77 microns, the
distance from the lens to the CMOS is D=4800 microns (typical), the
refraction coefficient of the lens material is N (1.5 for glass,
1.4 for plastic, 1.8 for SF6). Parameters, distance D, index of
refraction N, and horizontal offset, Off, will be adjusted using
calibration data for correct mapping of writing.
[0213] Then the angle (in radians) is calculated as
F=arcsin(N*sin(arctan((P*L)/D))).
[0214] As illustrated in FIG. 22, the following parameters are
required for calculating the light source position in Cartesian
coordinates: Sensor convergence angle (toe-in) C (radians),
typically 30/57 Base B, the distance between sensors (mm);
typically 150 Left sensor: Kleft=tan(C-Fleft) Right sensor:
Kright=tan(C+Fright) X(mm)=B*Kright/(Kleft+Kright); Y(mm)=Kleft*X.
Criteria for Accepting a Point as Valid
[0215] Points are stored as coordinate pairs (X,Y). When saving
points into the memory, coordinates are saved continuously, except
as follows:
[0216] If the signal is found to be below the threshold (as
described above), then a marker (a pair of unique values) is
written into the memory, for example (NaN,NaN) which will signify
later that the pen was lifted (NaN stands for not-a-number as
defined in the IEEE arithmetic standard). After that, no new points
are added to the file until the signal is detected again. This
approach allows the pen to tell the playback program exactly where
to interrupt the restored trajectory line.
[0217] If the signal is significant, but the pen position did not
change significantly as compared to the previous position, then no
new point is added to the memory, but unlike the case of no signal,
no markers are written to the memory. The size of the move squared
is calculated as (X1-X0).sup.2+(Y1-Y0).sup.2.The typical value for
the significance of the move squared is 0.04 mm.sup.2.
[0218] No timestamps are included in a file because this
information is not required for restoration of the pen
trajectory.
[0219] Coordinates are stored in the temporary buffer and are
compressed only before storing in flash memory. Each page is stored
in a separate file. Therefore, there is no need for an end of page
mark. Full time stamps will be inserted before the first valid
pixel. All other timestamps on a page (file) will be incremental
and inserted whenever the pen is lifted off the paper. Only one
time stamp is inserted regardless of how long the pen was off the
paper.
Sleep Modes
[0220] When the pen is taken out of the holder or the ink well for
writing, the ASIC turns on in the sleep mode and waits until an
optical signal is detected from the pen.
[0221] When the holder is awake and it detects that writing is
interrupted for a predefined period of time, the holder returns to
the power-saving sleep mode. The ASIC enters sleep mode by reducing
its normal 48 MHz clock frequency to 750 kHz. SDRAM update refresh
rate also changes accordingly to keep data intact.
[0222] The holder power is almost entirely off when the pen is
inside the holder or in the inkwell. RS232 receiver and USB
monitoring circuits consume very little standby current. These
circuits wake up and enable power to the rest of the electronics on
detection of active levels for RS232 or USB, when connected to a
cellular phone over the cable or by USB cable to a PC. The pen
holder is completely off when the pen is inside the holder.
[0223] In sleep mode, the only function of the holder electronics
is to watch for a WAKEUP input from photodiode and associated PLL
circuitry indicating that the pen is active. In sleep mode, the pen
consumes little power between the time intervals when it checks the
photodiode.
[0224] During writing, the pen transmits modulated IR pulses. The
pulses are detected at the holder causing the PLL to wake up the
processor, which starts normal acquisition mode as soon as the ASIC
switches back to the 48 MHz system clock.
Phase Lock Loop (PLL)
[0225] When the modulated IR light from the pen is being detected,
the modulation clock of the pen LED (represented by 1 kHz bursts in
the output light) is extracted using PLL circuitry 132 tuned to the
modulation frequency of the IR light.
[0226] All acquired data is initially stored in SDRAM 134 using
DMA. The update rate of the SDRAM remains unchanged when going from
acquisition mode to sleep mode. The memory requirement is 1 Mbyte
for 50 pages of compressed or 10 pages of uncompressed data. The
5:1 compression algorithm must have fast and computationally simple
coding with no limitation on decoding.
[0227] The acquired data is initially stored in SDRAM during
writing. When the pen is returned to the ink well or the pen, or
when the new page switch 136 is activated, the ASIC writes all data
from SDRAM into flash memory 138. Only a short time is needed to
write a full page of hand-written text data into flash. The
transfer is indicated to the user by lighting a yellow LED 140 on
the holder.
[0228] 8 Mbit flash memory stores compressed files representing a
maximum of 50 pages of handwritten text. The compression algorithm
allows at least 6-to-1 compression without observable distortion of
text.
Power for the Holder
[0229] The holder is powered by two AA NiMH batteries connected in
series to provide 3.0V. When the pen is in the ink well or the
holder, the pen's three NiCd batteries are recharged by a trickle
current. The pen batteries have a large capacity and are almost
never recharged completely. The trickle current charging is enough
to maintain the battery charge. A special mode is provided when the
pen and the pen holder are both in the charger to charge all the
batteries including the pen batteries with the full charging
current.
[0230] Battery life is ten handwritten pages or a week of average
use without compression of data for storage in memory. An average
user may write 2 characters per sec, or 120 char/min, or 7200
char/hr. The average handwritten page is approximately 700
characters. To produce ten pages, the battery must work for 5
hours.
[0231] When connected to a USB port, the holder can get power from
the USB host. The charge on batteries is maintained at a high
enough level to start the circuitry prior to switching to USB
power. Power from the USB connector is provided only after the ASIC
establishes communication over the USB link and notifies a PC on
the other end of the USB link that the connection is "high power".
In response, the PC provides up to 0.5 A. Battery charging current
is set at 0.4 A and is monitored to switch the charger into trickle
charge.
[0232] The holder circuitry is activated when the pen is taken out
of the holder or the ink well. Some holder circuitry, like the
RS232 driver and wake-up power circuitry take power directly from
the battery. Other circuitry takes power from a 3.3v supply
generated by an on-board switching regulator from the battery
voltage of 2 to 3 volts. When connected to a USB link, the 3.3v is
generated from USB power.
[0233] 5v is generated for the analog circuitry from the 3.3v
supply.
Synchronization of Pen and Holder
[0234] Synchronization of the pen and the pen receiver can produce
a better signal resolution and correspondingly better angle
resolution and resolution of writing.
[0235] As shown in FIG. 20, for synchronization, the pen produces
periodic bursts 401 of higher frequency pulses, such as pulses at
1-10 kHz (suggest we show some timing diagrams) that can be easily
detected by the PLL. The PLL will detect not only the actual
modulation clock but also its phase, which enables a signal to be
generated to start data acquisition and synchronize it with the pen
LED.
[0236] As shown in FIG. 21, the control signals, LED_ON and
LED_OFF, trigger signal acquisition. In such a case, only two
frames will be required for background cancellation, one for the IR
signal when the pen LED is on, and the other, when the LED is off.
For a CMOS sensor, a shutter mode is provided that resets all
pixels at one time.
[0237] Having only two frames per sample raises the sample rate and
resolution and may allow the processor to go into idle mode in
between the samples to save power.
Use of 2-D CMOS Arrays
[0238] Vendors to manufacturers of digital sensors produce small
power-saving sensors and sensors along with the image processing
circuitry that can be integrated into the pen on paper or 3-D pen
applications.
[0239] 3-D positioning of a light spot is possible using two 2-D
photo arrays. Projection of a point of light onto two planes
defines a single point in 3-D space. When a trajectory of 3D
positions is available, motion of an IR pointer-pen can control a
3-D object on a PC screen. When the pen moves in space, it drags or
rotates the object in any direction.
Slave Mode
[0240] In other implementations, using the ARM7 based ASIC in a
slave mode, the DMA can handle the data acquisition, but the
vertical synchronization signals are provided by the pen light
detection circuitry (PLL).
Two Analog Channels Alternative
[0241] Two separate channels can be used for analog signal
processing and A-to-D conversion. Such an implementation could use
more economical parts that do not require fast settling times,
frequency bandwidth and slew rate.
Frame Varying Alternative
[0242] CMOS sensors have a limited dynamic range. Although an
adjustable electronic gain may be used for both CMOSs
simultaneously after the output of the CMOSs, this arrangement may
be not be ideal, for two reasons.
[0243] First, the signals for the two CMOSs may be different in
magnitude when the pen is being moved in certain areas of the
paper, so changing the gain for both may fix one signal while
degrading another signal to an unacceptable level. To get suitable
signals across the page, it is useful to have separate gains for
each CMOS. Second, using an electronic gain does not do anything to
prevent saturation of the actual CMOS, which is unavoidable with
the area that the sensors must cover.
[0244] The gain of the CMOS can be changed by changing the exposure
rate for each CMOS independently. As shown in FIG. 21, the pen
transmission rate remains 100 Hz, while the frame rate 601 of the
CMOS is shifted among 300 Hz, 600 Hz, and 1200 Hz. At 300 Hz, the
background cancellation is straightforward. For 600 Hz, the
algorithm uses every other frame (frames 1, 3, and 5). For 1200 Hz,
the algorithm uses every fourth frame (frames 1, 5, and 9). The
pixel rates are 300 kHz, 600 kHz, and 1.2 MHz. Changing the frame
rate can be accomplished by the ASIC without any additional
hardware.
[0245] Each CMOS may be connected directly to its own ADC or both
could be connected to one ADC that would be able to handle 1.5
megasamples/sec and have a 4V reference voltage. The ADCs then may
feed into a digital multiplexer so that the signals can be fed into
the ASIC.
PSD Based Approach
[0246] Instead of CMOS arrays, two PSDs may be used to detect the
IR light from the pen. Each PSD determines the angle between the
page and a line of sight between the pen and the PSD. The two
angles from the two PSDs and the distance between the PSDs are
sufficient to compute the location of the tip of the pen.
[0247] Even with IR filters, ambient light will introduce errors in
PSD positioning measurements. To reduce the errors, the IR light at
the pen is modulated to generate pulses at a modulation frequency
and with a 50% duty cycle, as described above.
[0248] Two analog techniques may be used to discriminate the PSD
signal that is translated into the angle for use in
triangulation.
[0249] In one approach, called synchronous demodulation and used in
instrumentation electronics, the incident synchronous light pulses
are chopped at the light modulation frequency, and opposite gains
(+1 and -1 respectively) are applied to those signals, depending on
whether the LED is on or the LED is off. This allows for
subtraction of background noise. Then the signal is integrated
using a time constant that it is responsive to the signal
variations on one hand and averages out noise on the other. In one
example, the modulation frequency could be 3 kHz, and the pulse
amplitude could be ILEDpeak=Xma.
[0250] A second approach to discrimination uses a sample and hold
technique. The shape of the optical signal has a 50% duty cycle at
the 3 kHz modulation frequency, as before, but also has a
significantly stronger short pulse imposed on the modulation
frequency. The modulation frequency is discriminated using a PLL
and is used to trigger the sample and hold circuitry, while the
strong optical pulse is actually sampled. The pulse amplitude is
ILEDpeak=Xma and the pulse duration T=Y usec.
[0251] PSDs are extremely accurate in sensing and measuring the
position of light on their photosensitive surfaces. They are
inexpensive and require very little power consumption. The PSD
implementation is also simpler than the CMOS one.
[0252] As shown in FIG. 23, current-to-voltage transformation is
done on each of four channels, two for each PSD. The four analog
signals pass through low frequency filtering 605, synchronous
detection 607, integration 609, and digitization 611 by
microcontroller 613 (12-bit A/D converters). A-to-D conversion is
performed at a 100 Hz sampling rate. The processor is active when
the pen is making a trace on paper. The processor performs signal
acquisition and periodic storage into flash memory. FIG. 24 shows a
system timing diagram. When no trace is being made, the
microcontroller enters the idle mode, and after an arbitrary period
of time, the sleep mode.
[0253] The microcontroller is awakened from idle mode or sleep mode
by either an interrupt or polling (TBD) of the following inputs:
one of the four analog channels, when the signal at its modulation
frequency exceeds a certain threshold of the comparator; an
interrupt from a USB port when presence of activity from a host is
detected; one of its key buttons is pushed.
[0254] When the RAM becomes full or/and the boundary of a flash
memory page is reached, the processor writes data from RAM to flash
memory. If acquisition continues and the page is full, the
microcontroller start writing to flash. However, most of the flash
operations should be done during idle cycles when there is no
writing.
[0255] Each PSD has two channels of analog signal processing. Each
channel has a current-to-voltage converter whose output is AC
coupled into the first gain amplifier. The signal is chopped with
the modulated frequency of the pulsing IR LED (on pen), currently 1
kHz.
[0256] When LED emits light, the chopper has a gain of +1. When
there is no light, the gain is -1, therefore the signal is
synchronously demodulated. The last stage is an integrator, whose
output is close to DC. More precisely, it is a saw-tooth waveform
due to charging and discharging of the integrating capacitor in the
feedback of the amplifier.
[0257] The A/D converter, either a PC-based DAQ or an A/D of the
microcontroller, samples the output at specified time intervals
synchronously with the modulation frequency to cancel errors due to
saw-tooth waveforms.
[0258] To use all 12 bits of the A/D converter resolution, a
dynamic change in reference voltage for the converter is used. The
microcontroller always starts reading the A/D channels with the
highest range and then divides it in half until the range is the
most optimum for the signal.
[0259] The chopper amplifier uses a replica of the modulation
frequency detected with an analog circuitry on each channel (four
channels altogether). This signal is taken after the second gain
stage, processed for detection of signal transitions, and then the
recovered modulation pulses pass through OR gate to drive the
chopper amplifier analog switch to change its gain between +1 and
-1.
Phase Shift using Photo Diodes, Rotating Pen Tip
[0260] As shown in FIG. 25, if a rotating light source 617 is used
at the tip of the pen, it is possible to measure the phase
difference among signals on three photodiodes 619, 620, 621 on the
holder to find the pen position.
[0261] The rotating light on the pen tip can be realized using
several (e.g., eight) LEDs 623 that are triggered at times spaced
apart by T/N, where T is the overall time period of the LED cycle,
and N (e.g., 8) is the number of LEDs.
[0262] The signal source is at some location on an X-Y plane. Two
signal detectors 619, 620 are located at two other fixed locations
on the same plane. If the signal source has a radiation pattern
such that the signal radiated in the positive X direction is in
phase quadrature to the signal radiated in the Y direction
(spatially rotating at the signal frequency), and the propagation
delay is negligible compared to the signal period, then the angle
A1, formed by two intersecting lines 637, 639 drawn from the
detectors to the signal source will be the same as the phase
difference between the signals measures at the detectors.
[0263] If a third fixed location detector 621 is added, then a
second angle A2 will be formed as three lines intersect at the
signal source. Again, the angle A2 between the lines at the
intersection will be the same as the phase difference of the signal
measured between the detectors. By applying some basic
trigonometry, it becomes possible to find the location of the
signal source in the X-Y plane by knowing the fixed locations of
the detectors and measuring the phase differences of the signals at
the detectors. If the three detectors are arranged in a straight
line with equal distances between them, the computation becomes
trivial.
[0264] Referring to FIG. 26, the calculation of B and A angles
based on the angles measured by the sensors, "a" and "b" is as
follows:
[0265] Having: a/A=d/R (1) and b/B=d/R (2) and B+A+b+a=180.degree.
(3),
[0266] from basic geometrical theorems,
We get: B/A=b/a, (4), and accordingly B=A.times.b/a (5)
A=B.times.a/b (6);
[0267] Now plugging (3) into (5) and (6) we get:
A.times.b/a+A+b+a=180.degree. (7) and B.times.a/b+B+b+a=180.degree.
(8);
[0268] We solve them for A and B: A=a.times.(180.degree.-b-a)/(a+b)
(9) B=b.times.(180.degree.-b-a)/(a+b) (10)
[0269] The rotating light on the pen tip can be realized using
several (e.g., eight) LEDs 623 that are triggered at times spaced
apart by T/N, where T is the overall time period of the LED cycle,
and N is the number of LEDs. For example, eight light emitting
diodes (LED) could be arranged in a circle pointing outward, spaced
45 degrees apart and driven by an signal oscillator with a 45
degree phase difference between adjacent LEDs.
[0270] As shown in FIGS. 27 and 28, the three detectors 641 could
be Positive Intrinsic region Negative (PIN) diode optical detectors
driving a signal processing chain 642 consisting of a
trans-impedance amplifier 643 and a high gain limiter 645 to remove
any amplitude modulation in the detected signals.
[0271] Phase detection could be accomplished with two
edge-triggered one bit Up-Down counter type phase detectors 649,
two binary counters and a clock running several decades above the
signal frequency. If the counters are connected such that they
count up with every clock cycle where the one sensor leads the
phase of the other and count down when the phase lags, and a third
counter is set to count up continuously, then a microprocessor can
periodically read and reset all the counters, scaling the reading
from the two counters connected to the phase detectors (dividing
by) by the reading from the continuously running counter. This
number is the phase difference (in gradients) between the three
sensors and as such, the angles between the intersection of the
lines from the sensors to the source. It is then a trivial task to
calculate the location of the source relative to the sensors.
Pen Light Activation Switch Alternatives
[0272] Different pen light activation methods can be used,
including conductive rubber, pressure sensitive materials or strain
gauges.
[0273] Pressure sensitive material allows for a variable pressure
threshold and coordination of the switching point with the ink
flow. This would prevent loss of data when the ink is making a
trace while the pen is not active yet. Most ball point refills
release ink at 20 to 30 gf +/-30%, while an off-the-shelf switch
activates at 50 to 100 gf and +/-40 gf, for example, making a
reliable coordination of ink flow and data capture impossible.
Special refills can be also designed to prevent ink flow below 50
gf that might enable the use of off-the-shelf chip switches.
Pen Optics Alternatives
[0274] Other approaches for emitting light from the tip of the pen
are possible. Optical fibers could be used to collect light from an
LED and emit it in a 360.degree. pattern around the tip of the pen.
Individual LED chips could be located around the tip of the pen and
emit light through a half reflective lens/window, such that 50% of
light is emitted and the other 50% is reflected internally to be
mixed with other light, ultimately producing uniform 360.degree.
illumination. Light could be mixed from a single LED using special
rings that redistribute the light for uniformity.
Passive Pen Alternative
[0275] The pen may be completely passive if the IR light source is
located next to the sensor. A reflective surface would be provided
near or at the tip of pen. The sensors would see reflection of IR
light from the tip of the pen and compute angles as described
above.
[0276] The tip of the pen must be reflective only when pressed
against paper and ink is forming traces. Otherwise there will be
erroneous traces in digital form with no corresponding traces on
paper.
[0277] Activation of the reflective mechanism can be mechanical or
electrical. In a mechanical implementation, pressure on the tip
will open up a sheath and expose reflective surface around the tip.
In a electrical implementation, pressure on the tip will activate
liquid crystals or other photo technology that will make that
material reflective to light. Reflection from other objects, like
fingernails and rings, can be handled by using polarized IR
light.
Passive Pen Holder
[0278] Conversely, the holder may have two reflectors, while the
pen both emits light and receives reflections. The sensing element
on the pen could be a 2-dimensional PSD or CMOS array. If flat 2-D
sensors are used, the pen would not be omni-directional, but it
would be possible to make a custom circular 2-D sensor that would
have 360.degree. coverage.
Keyboard and Mouse Replacement Architecture
[0279] The pen described above can be used to replace standard PC
input devices such as a mouse and a keyboard.
[0280] When used as a replacement for a keyboard or a mouse, the
sheet of paper, plastic or other flat surface, may bear a printed
keyboard pattern that will serve as a keyboard and mouse pad for,
e.g., PC's, handheld computers, and cellular phones.
[0281] Users today are, for the most part, limited to keyboards,
keypads or stylus input on screens when inputting data into PC's,
handheld computers or cell phones. Keyboards are efficient and
convenient when they are full size but do not lend themselves to
portable devices such as palm computers and cellular phones. Cell
phone keypads, while efficient for dialing phone numbers, require
excessive keystrokes when trying to generate ASCII letters and
symbols, making any type of data input a very tedious and
time-consuming process. Styli on screen input with palm devices
requires either that the user use unique writing styles such as
"graffiti" in order to minimize the amount of handwriting
recognition needed on the device or that the user tap on small
virtual keyboards represented on the screen. Both styli approaches
often result in incorrect input, which limits the functionality of
these devices.
[0282] An electronic pen can be used in a mode that provides a
highly reliable method for inputting text characters in addition to
recording handwritten images and lines. A sheet of paper or any
other surface (with or without a printed pattern of a keyboard) is
all that users need to type with a pen.
[0283] The spatial transcription capabilities of the electronic pen
together with the keyboard template are used to substitute for the
mouse or keyboard.
[0284] The paper keyboard can be multiple sizes based on the user's
needs. The size can range from an 81/2.times.11 sheet of paper to
the size of a cell phone cover. The user first selects the size of
keyboard he desires and then calibrates by touching the pen to
specified characters on the keyboard. To type a message, the user
touches the tip of the pen on the appropriate keys. When the pen
touches the square area of the paper that corresponds to a certain
letter the location of the tip of pen is computed and the
designated letter is determined. This approach allows the user to
generate text on a computing device with an electronic pen without
any dependency on handwriting recognition software.
[0285] This approach is an improvement over the built in keypads,
software keyboards or styli on screen input approaches currently
used on ever-shrinking personal appliances. The paper keyboard
allows the user to enter messages on handhelds and cellular phones
faster and more reliably than with alternative approaches. The
paper can also be used in other modes to record drawings and
handwritten notes and images. When done, the paper keyboard can be
discarded or folded for future use.
[0286] In addition to characters, the keyboard can also contain
shortcut keys and function keys that enable more efficient
interaction with a small device. Short cut keys can minimize the
number of keystrokes required to enable commands. Short cut keys
can be customized based on the type of device being input into.
[0287] The keyboard can also incorporate a section that serves as a
paper mouse pad. Using the electronic pen's spatial transcription
capabilities, the user can move the pen within a designated square
space on the paper that in turn moves a pointer on the screen of a
device. The paper mouse thus serves as an alternative to keys and
styli on screens as a means for navigating on the screen of a
handheld or cellular phone.
[0288] The paper keyboard also enables flexibility in inputting
foreign characters. Keyboards can be created for several languages
such as Japanese, Korean, Spanish, French and Russian. A user can
simply print out a new keyboard if they desire to input a different
alphabet.
[0289] As shown in FIG. 29, to type a message, the user touches the
tip of the pen 701 on the appropriate keys 703 printed on a paper
keyboard 705. The positions at which the pen is touched are tracked
by tracker 707, converted to text and then sent to a portable
device such as a cellular phone 711 or a palm computer 709.
[0290] The keyboard can be folded or discarded after the use.
[0291] In other implementations, there is no printed paper
keyboard; rather the tracked motions of the pen can be used through
handwriting recognition to derive text, commands, and drawings as
the pen is used for writing on any surface.
[0292] In one implementation of this approach, the mouse and
keyboard can continue to be used and the pen serves as an
alternative. The pen can operate in either a "pointing device"
(mouse) or a "character input" (keyboard) mode. The mode can be
selected by a dedicated hardware switch or button, on a pen holder
or pen, or by sending a command from PC to a holder.
[0293] In mouse mode, pen operation is indistinguishable from that
of a secondary (USB) mouse. It is a relative positioning pointing
device moving the cursor on the screen. In keyboard mode, pen input
can be received by a specially designed application using an
available character recognizer to convert graphical input (strokes)
into characters. Other applications are not aware of the pen
presence and continue to operate using the regular (legacy)
keyboard.
[0294] In another approach, the pen is the only input device to the
system. In this case, a software driver stack is modified to
provide keyboard functionality system-wide. Mouse-mode operation is
not affected and is identical to the first-described approach. When
operating in keyboard mode, pen input is recognized by available
handwriting recognition software built into a keyboard filter
driver and then delivered to system input queue in a similar way to
traditional keyboard input.
[0295] This second approach requires a platform usability model and
(most likely) modification of certain system components such as
Basic Input/Output System (BIOS).
[0296] Both approaches raise human factor and usability issues. In
particular, there are two basic approaches to handwriting
recognition: discrete (single character at a time) and continuous
(word, phrase or page at a time). In the former case, the user must
continuously rely on computer screen output for feedback. This may
be awkward, because the handwriting process must be constantly
interrupted by looking at the computer screen for feedback. In
latter case, the user must only look at the screen once in a while,
when a writing unit (word or phrase) is completed and correct it as
necessary.
[0297] Switching from mouse to pen input mode could be done by
retractable pen refill action. When the refill is inside the pen
(pen cannot write), it is used as a mouse. When writing is
activated, the pen acts as a keyboard.
[0298] Other embodiments are within the scope of the following
claims.
[0299] The holder need not be of the kind that includes an inkwell
as described above but can be any kind of device that can hold the
sensors. The holder can be a simpler pen cap, as shown earlier, or
could be any other kind of device whether or not it mates with or
caps the pen and whether or not it includes a clip or not. The
holder could be incorporated into a clipboard or a notebook, for
example.
[0300] The light in the pen can be fiber optics that deliver light
to the tip and convey it in all directions around the pen in a
disk-like pattern.
* * * * *