U.S. patent number RE39,881 [Application Number 10/667,242] was granted by the patent office on 2007-10-16 for surface position location system and method.
This patent grant is currently assigned to LeapFrog Enterprises, Inc.. Invention is credited to Mark Flowers.
United States Patent |
RE39,881 |
Flowers |
October 16, 2007 |
Surface position location system and method
Abstract
An electrographic sensor unit and method for determining the
position of a user selected position thereon. The electrographic
sensor unit includes a layer of a conductive material having an
electrical resistivity and a surface, at least three spaced apart
contact points electrically interconnected with a layer of
conductive material, a processor connected to the spaced apart
contacts and disposed to selectively apply a signal to each of the
contact points, and a probe assembly, that includes either a stylus
of a flexible conductive layer spaced apart from the layer, coupled
to the processor with the stylus disposed to be positioned by a
user in vicinity of a user selected position on the surface of the
layer, or that position being selected with a user's finger on the
flexible layer and to receive signals from the layer when the
contact points have signals selectively applied thereto. The user
selected position is determined by the processor from signals
received from the stylus, or flexible layer, each in relation to a
similar excitation of different pairs of the contact points under
control of the processor. The conductive layer may be either two or
three dimensional and may be closed three dimensional shape. There
may also be multiple layers with the processor being able to
discern on which of those layers the user selected position is
located. Further, provision is made to correct the calculated
coordinates of the selected position for variations in contact
resistance of each of the contact points individually.
Additionally, a nonconductive skin having selected graphics printed
thereon, such as a map, can be placed over the layer and the
proces-sor further convert the calculated coordinates of the
selected position to coordinates that relate to the graphical
information printed in the skin, and even electro-nically (e.g.,
audio or visual) present information to the user relative to the
graphical location selected as the selected position.
Inventors: |
Flowers; Mark (Los Gatos,
CA) |
Assignee: |
LeapFrog Enterprises, Inc.
(Emeryville, CA)
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Family
ID: |
29254731 |
Appl.
No.: |
10/667,242 |
Filed: |
September 18, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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09796685 |
Feb 28, 2001 |
Re. 38286 |
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08601719 |
Feb 15, 1996 |
5686705 |
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Reissue of: |
08754310 |
Nov 21, 1996 |
05877458 |
Mar 2, 1999 |
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Current U.S.
Class: |
178/18.01;
178/18.03; 178/19.01; 345/173; 345/174 |
Current CPC
Class: |
G06F
3/045 (20130101) |
Current International
Class: |
G09G
5/00 (20060101) |
Field of
Search: |
;345/173-180
;178/18.01-18.07,19.01,19.02-19.06 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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539053 |
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Sep 1993 |
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EP |
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S57-038486 |
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Mar 1982 |
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JP |
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S61-46516 |
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Mar 1986 |
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JP |
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H5-137846 |
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Jun 1993 |
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JP |
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H5-217688 |
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Aug 1993 |
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JP |
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Other References
British Micro, "Operating Guide to Grafpad", 1982, 28 pp. cited by
other.
|
Primary Examiner: Shankar; Vijay
Attorney, Agent or Firm: Townsend and Townsend and Crew
LLP
Parent Case Text
This application is a .[.Continuation-In-Part.]. .Iadd.continuation
application of U.S. Reissue patent application Ser. No. 09/796,685,
filed Feb. 28, 2001, now RE 38,286 which is a reissue patent of
Ser. No. 08/754,310, filed on Nov. 21, 1996, now U.S. Pat. No.
5,877,458, which is a continuation-in-part .Iaddend.application of
an earlier filed co-pending patent application with the same title
filed on Feb. 15, 1996, and given Ser. No. 08/601,719 which
.[.includes as an inventor the inventor of the present invention.].
.Iadd.is now U.S. Pat. No. 5,686,705, all of which are herein
incorporated by reference in their entirety.Iaddend..
Claims
What is claimed is:
.[.1. An electrographic sensor unit for use in determining the
position of a selected point, which comprises: a layer of a
conductive material having an electrical resistivity and a surface;
K spaced apart contact points electrically interconnected with said
layer of conductive material; a processor connected to said K
spaced apart contacts and disposed to selectively apply a signal to
N of said K contact points relative to a signal neutral point, and
where N has an integer value of 3 to K; and a probe assembly
comprising: a cable having a first conductor and a second conductor
with the proximate end of said one conductor coupled to said
processor and the proximate end of said second conductor connected
to said signal neutral point; and a stylus coupled to said cable
and incorporating therein distal ends of said first and second
conductors with the distal end of said first conductor disposed to
receive signals from said layer when said contact points have
signals selectively applied thereto and said user positions said
stylus in vicinity of a user selected point on said surface, and
with the distal end of said second conductor disposed to be
contacted by said user when holding said stylus to connect said
user to said signal neutral point; wherein said position of said
stylus relative to said surface of said layer is determinable by
said processor from signals received from said first conductor of
said stylus each in relation to a similar excitation of J different
pairs of said K contact points under control of said processor,
where J is an integer between 2 and (N-1)..].
.[.2. An electrographic sensor unit as in claim 1 wherein: said
processor selectively applies AC signals to selected ones of said K
spaced apart contact points; said distal end of said first
conductor detects signals radiated from said layer of conductive
material as an antenna without making physical contact with said
layer; and said distal end of said second conductor when contacted
by said user connects said user to said signal neutral point to
minimize any noise radiated by said user from being received by
said distal end of said first conductor and being delivered to said
processor..].
.[.3. An electrographic sensor unit as in claim 1 wherein said
stylus further includes an electrically conductive contact making
electrical contact to said distal end of said second conductor, and
located externally and positioned to be contacted by the user
during use of said stylus..].
.[.4. An electrographic sensor unit as in claim 3 wherein said
electrically conductive contact is a flexible conductive polymer
that encircles said stylus at a position to maximize the user's
comfort when holding said stylus..].
.[.5. An electrographic sensor unit for use in determining the
position of a selected point, which comprises: a layer of a
conductive material having an electrical resistivity and a surface;
three spaced apart contact points electrically interconnected with
said layer of conductive material; a processor connected to said
three spaced apart contacts and disposed to selectively apply a
signal to each of said three contact points relative to a signal
neutral point; and a probe assembly including: a cable having a
first conductor and a second conductor with the proximate end of
said one conductor coupled to said processor and the proximate end
of said second conductor connected to said signal neutral point;
and a stylus coupled to said cable and incorporating therein distal
ends of said first and second conductors with the distal end of
said first conductor disposed to receive signals from said layer
when said contact points have signals selectively applied thereto
and said user positions said stylus in vicinity of a user selected
point on said surface, and with the distal end of said second
conductor disposed to be contacted by said user when holding said
stylus to connect said user to said signal neutral point; wherein
said position of said stylus relative to said surface of said layer
is determinable by said processor from signals received from said
first conductor of said stylus each in relation to a similar
excitation of two different pairs of said three contact points
under control of said processor..].
.[.6. An electrographic sensor unit as in claim 5 wherein: said
processor selectively applies AC signals to selected ones of said
three spaced apart contact points; said distal end of said first
conductor detects signals radiated from said layer of conductive
material as an antenna without making physical contact with said
layer; and said distal end of said second conductor when contacted
by said user connects said user to said signal neutral point to
minimize any noise radiated by said user from being received by
said distal end of said first conductor and being delivered to said
processor..].
.[.7. An electrographic sensor unit as in claim 5 wherein said
stylus further includes an electrically conductive contact making
electrical contact to said distal end of said second conductor, and
located externally and positioned to be contacted by the user
during use of said stylus..].
.[.8. An electrographic sensor unit as in claim 7 wherein said
electrically conductive contact is a flexible conductive polymer
that encircles said stylus at a position to maximize the user's
comfort when holding said stylus..].
.[.9. An electrographic sensor unit in the form of a globe for use
in determining the position of a user selected point on the surface
thereof, which comprises: a sphere formed of a layer of a
conductive material having a substantially uniform electrical
resistivity and an outer surface; a set of four spaced apart
contact points electrically interconnected with said layer of
conductive material of said sphere; a processor connected to said
set of four spaced apart contacts and disposed to selectively apply
a signal to each of said four contact points relative to a signal
neutral point; and a probe assembly including: a cable having a
first conductor and a second conductor with the proximate end of
said one conductor coupled to said processor and the proximate end
of said second conductor connected to said signal neutral point;
and a stylus coupled to said cable and incorporating therein distal
ends of said first and second conductors with the distal end of
said first conductor disposed to receive signals from said layer
when said contact points have signals selectively applied thereto
and said user positions said stylus in vicinity of a user selected
point on said surface, and with the distal end of said second
conductor disposed to be contacted by said user when holding said
stylus to connect said user to said signal neutral point; wherein
said position of said stylus relative to said surface of said
sphere is determinable from three signals received from said stylus
by said processor each in relation to a similar excitation of three
different pairs of said four contacts on said sphere by said
processor..].
.[.10. An electrographic sensor unit as in claim 9 wherein: said
processor selectively applies AC signals to selected ones of said
four spaced apart contact points; said distal end of said first
conductor detects signals radiated from said layer of conductive
material as an antenna without making physical contact with said
layer of said sphere; and said distal end of said second conductor
when contacted by said user connects said user to said signal
neutral point to minimize any noise radiated by said user from
being received by said distal end of said first conductor and being
delivered to said processor..].
.[.11. An electrographic sensor unit as in claim 9 wherein said
stylus further includes an electrically conductive contact making
electrical contact to said distal end of said second conductor, and
located externally and positioned to be contacted by the user
during use of said stylus..].
.[.12. An electrographic sensor unit as in claim 11 wherein said
electrically conductive contact is a flexible conductive polymer
that encircles said stylus at a position to maximize the user's
comfort when holding said stylus..].
.[.13. An electrographic sensor unit for use in determining the
position of a selected point, which comprises: a first layer of
conductive material having an electrical resistivity and a first
surface; a first set of three spaced apart contact points
electrically interconnected with said first layer of conductive
material; a second layer of a conductive material having an
electrical resistivity and a second surface; a second set of three
spaced apart contact points electrically interconnected with said
second layer of conductive material; a processor connected to each
of said first and second sets of three spaced apart contacts and
disposed to selectively apply a signal to each of said three
contact points in each of said first and second sets thereof; and a
probe assembly including: a cable having a first conductor and a
second conductor with the proximate end of said one conductor
coupled to said processor and the proximate end of said second
conductor connected to said signal neutral point; and a stylus
coupled to said cable and incorporating therein distal ends of said
first and second conductors with the distal end of said first
conductor disposed to receive signals from said layer with said
user selected point when said corresponding set of contact points
have signals selectively applied thereto and said user positions
said stylus in vicinity of a user selected point on one of said
first and second surfaces, and with the distal end of said second
conductor disposed to be contacted by said user when holding said
stylus to connect said user to said signal neutral point; wherein
identification of which of said first and second surfaces said
stylus is adjacent to is accomplished by said processor by
independently measuring two signals from each of said first and
second layers received by said stylus, combining said signals from
the same layer independent of the signals received from the other
layer to form a first and a second comparative value with each said
comparative value associated with a different one of said first and
second layers, and independently comparing each of said first and
second comparative values to a preselected threshold value with the
layer associated with the one of said first and second comparison
value that is greatest and is greater than said threshold being the
layer said stylus is closest to and therefore an identified layer
of said first and second layers; and wherein said position of said
stylus relative to said identified one of said first or second
layers is determinable by said processor from signals received from
said stylus each in relation to a similar excitation of all of said
three contact points on the identified one of said first and second
layers and two different pairs of said three contact points on the
identified one of said first and second layers under control of
said processor..].
.[.14. An electrographic sensor unit as in claim 13 wherein: said
processor selectively applies AC signals to selected ones of said
four spaced apart contact points; said distal end of said first
conductor detects signals radiated from said layer of conductive
material as an antenna without making physical contact with said
layer of said sphere; and said distal end of said second conductor
when contacted by said user connects said user to said signal
neutral point to minimize any noise radiated by said user from
being received by said distal end of said first conductor and being
delivered to said processor..].
.[.15. An electrographic sensor unit as in claim 13 wherein said
stylus further includes an electrically conductive contact making
electrical contact to said distal end of said second conductor, and
located externally and positioned to be contacted by the user
during use of said stylus..].
.[.16. An electrographic sensor unit as in claim 15 wherein said
electrically conductive contact is a flexible conductive polymer
that encircles said stylus at a position to maximize the user's
comfort when holding said stylus..].
.Iadd.17. An electrographic sensor unit comprising: a) a surface;
b) a processor; c) a signal neutral point; d) a probe assembly
including (i) a first conductor with a proximate end and a distal
end, the proximate end of the first conductor coupled to the
processor, (ii) a second conductor with a proximate end and a
distal end, the proximate end of the second conductor coupled to
the signal neutral point; and (iii) a stylus incorporating at least
a portion of the first and second conductors, wherein the stylus is
free of active circuit elements; and e) a speaker coupled to the
processor, wherein the position of the stylus relative to the
surface is determinable by the processor..Iaddend.
.Iadd.18. The electrographic sensor unit of claim 17 wherein the
signal neutral point is ground..Iaddend.
.Iadd.19. The electrographic sensor unit of claim 17 further
comprising a random access memory coupled to the
processor..Iaddend.
.Iadd.20. The electrographic sensor unit of claim 17 further
comprising a memory coupled to the processor, wherein the memory
comprises a database containing sound data for features of interest
and their corresponding coordinates..Iaddend.
.Iadd.21. The electrographic sensor unit of claim 17 wherein the
distal end of the first conductor is an antenna that is capable of
receiving signals from the surface..Iaddend.
.Iadd.22. The electrographic sensor unit of claim 17 wherein the
distal end of the first conductor forms an antenna..Iaddend.
.Iadd.23. The electrographic sensor unit of claim 22 wherein the
surface is two-dimensional..Iaddend.
.Iadd.24. The electrographic sensor unit of claim 22 wherein the
surface is three-dimensional..Iaddend.
.Iadd.25. The electrographic sensor unit of claim 17 wherein the
stylus further comprises an electrically conductive contact
comprising a conductive polymer coupled to the second
conductor..Iaddend.
.Iadd.26. The electrographic sensor unit of claim 17 wherein the
stylus further includes a tip, wherein the distal end of the first
conductor is closer to the tip than the distal end of the second
conductor..Iaddend.
.Iadd.27. The electrographic sensor unit of claim 17 wherein the
surface is two-dimensional..Iaddend.
.Iadd.28. The electrographic sensor unit of claim 17 wherein the
surface is three-dimensional..Iaddend.
.Iadd.29. The electrographic sensor unit of claim 17 wherein the
processor is a microprocessor..Iaddend.
.Iadd.30. The electrographic sensor unit of claim 17 further
comprising a demodulator coupled to the first
conductor..Iaddend.
.Iadd.31. The electrographic sensor unit of claim 17 further
comprising an analog to digital converter coupled to the first
conductor..Iaddend.
.Iadd.32. The electrographic sensor unit of claim 17 wherein the
second conductor surrounds the first conductor..Iaddend.
.Iadd.33. The electrographic sensor unit of claim 17 wherein the
surface is in the form of a globe..Iaddend.
.Iadd.34. The electrographic sensor unit of claim 17 further
comprising an audio/video card coupled to the
processor..Iaddend.
.Iadd.35. The electrographic sensor unit of claim 17 further
comprising an AC signal generator coupled to the
processor..Iaddend.
.Iadd.36. The electrographic sensor unit of claim 19 wherein the
signal neutral point is ground..Iaddend.
.Iadd.37. The electrographic sensor unit of claim 20 wherein the
signal neutral point is ground..Iaddend.
.Iadd.38. The electrographic sensor unit of claim 21 wherein the
signal neutral point is ground..Iaddend.
.Iadd.39. The electrographic sensor unit of claim 22 wherein the
signal neutral point is ground..Iaddend.
.Iadd.40. The electrographic sensor unit of claim 23 wherein the
signal neutral point is ground..Iaddend.
.Iadd.41. The electrographic sensor unit of claim 24 wherein the
signal neutral point is ground..Iaddend.
.Iadd.42. The electrographic sensor unit of claim 25 wherein the
signal neutral point is ground..Iaddend.
Description
FIELD OF THE INVENTION
The present invention relates to a system and method for
determining a location selected by a user on a surface and
providing information to the user that has been determined to be
relative to that location. In particular the present invention
relates to position detection devices that are able to detect
positions on a surface of two and three dimensional objects that
have complex shapes. Additionally it relates to position detection
devices in which the object may be turned, rotated or otherwise
manipulated relative to the rest of the position detection system.
Further, the present invention relates to provision of a ground
point on the pointing device to ground the user to the system to
minimize noise input to the system processor and potential error in
position identification.
BACKGROUND OF THE INVENTION
A variety of technologies exist to determine the position of a
stylus, or even a finger, placed on a surface. One technology is a
grid of horizontal and vertical wires that are placed below the
surface of a flat tablet or over the surface of a display device
and emit position indicating signals which are detected by a
stylus. Two devices using this type of technology are described in
U.S. Pat. Nos. 5,149,919 and 4,686,332 to Greenias, et al.
Applications using these devices are computer input drawing (or
digitizing) tablets, and touch-screen display devices.
In another technology, surface acoustic waves are measured at the
edges of a glass plate and are used to calculate the position on
the plate that was selected by a finger or a stylus. Applications
include high use touch screen kiosk displays where a conductive
overlay technology would wear out.
Yet other technologies include the use of light pens as optical
detectors. Additionally a frame around a flat display with an array
of light emitters and detectors around the edge of the frame, may
be used to detect when a finger or stylus is near the display
surface. These technologies are limited to displays or flat
surfaces.
Position detectors such as the devices disclosed in the Greanias
patents, that use many conductors arranged in a grid, are not well
suited to a complex shaped surface of either two or three
dimensions. There are, at a minimum, difficulties in positioning
and shaping the conductors to fit the contours of a complex
shape.
Another similar device is a grid of horizontal and vertical wires
placed over or beneath the surface of a flat display device that
uses capacitive coupling of a stylus or finger. In this device, the
capacitive coupling transfers position indicating signals from one
wire to another which can be used to calculate the position of the
coupling. Computer input tablets, as well as finger pointing mouse
replacement tablets, use this technology.
In another technology, a rectangular homogeneous transparent
conductor is placed over the surface of a display device and bar
contacts on the edges of the transparent conductor charge the
conductor. Capacitive coupling of a stylus or a finger to the
transparent conductor causes the conductor to discharge while
sensors attached to the bar contacts measure the amount of current
drawn through each of the contacts. Analysis of the ratios of the
currents drawn from pairs of contacts on opposing sides of the
rectangle provide an X-Y position on the panel that was selected by
the user. A device of this type is described in U.S. Pat. No.
4,853,498 to Meadows, et al. An application of this device is a
touch-screen display.
A similar technology uses a rectangular piece of extremely uniform
resistive material with a series of discrete resistors along the
edge and is mounted on a flat surface. A voltage differential is
applied to the row of resistors on opposing sides of the rectangle
and in a time-division manner the voltage differential is applied
to the row of resistors of the other two opposing sides. The
position indicating signals are either received by a stylus, or by
a conductive overlay which can be depressed to contact the surface
of the resistive material. One variety of this device is described
in U.S. Pat. No. 3,798,370 to Hurst.
The devices described in U.S. Pat. Nos. 4,853,498 (Meadows, et al.)
and 3,798,370 (Hurst) drive a homogenous rectangular resistive
overlay with bar contacts or a string of resistors along each edge.
These approaches rely upon the regular shape of a rectangle in
order to work. The shape and placement of the contacts provide the
means to detect portions of the surface within a rectangular
subsection of the resistive material of the surface. Other simple
shapes may also be feasible with bar and resistor string contacts
but in complex shapes they can create areas that cannot be
distinguished (e.g., shapes with concave edges such as a circle or
ellipse can not be accommodated by either the Meadows or the Hurst
approaches). The use of bar contacts or strings of resistors along
substantially the entire edge of an object limits their usefulness
on objects where the position on the entire surface needs to be
detected. The locations directly beneath each bar electrode and
between each bar or spot electrode and the edge of the object are
not detectable in these devices.
The devices described in U.S. Pat. Nos. 4,853,499 (Meadows, et al.)
and 3,798,370 (Hurst) do not take into consideration the effects of
contact resistance. The resistance between the contacts and the
homogenous resistive material may be substantial relative to the
resistance of the homogenous material. Additionally the contact
resistance may vary from electrode to electrode or change due to
mechanical or environmental stress. The Meadows and Hurst devices
rely on contacts of known, or constant resistance, which constrains
the use of materials and contact approaches. Any variation in
contact resistance or changes in contact resistance due to
environmental factors are not accounted for and result in detection
errors.
Further, Meadows loads the surface with a capacitively coupled
stylus and determines position by measuring the current drawn from
the driving circuits. The Meadows device requires four receiver
circuits to accomplish this.
The Meadows device is susceptible to the effects of unwanted
phantom styluses coupling to the surface. Phantom styluses such as
rings or fingers may couple to the active surface instead of, or in
addition to, the actual stylus. These phantom styluses cause
detection errors because the changes that they also produce cause
changes in the driving circuit.
In applications where the object containing the grid needs to be
rotated, or the electronics and the object are physically
spaced-apart from each other, a large number of conductors must be
coupled to the system, or between the elements of the systems,
through connection mechanisms that may allow rotation or other
movements. Such cables for the systems of the prior art would be
rather large and cumbersome. Further, connectors with a large
number of contacts are expensive and reduce the overall reliability
of any system that requires them. Contacts that allow rotation,
such as slip rings or commutators, become prohibitively complex and
expensive as the number of connections rises above a small number.
Additionally, the multiple circuits required to drive grid arrays
are complex and costly to manufacture. Acoustic wave detectors
provide a rugged position detection mechanism but are costly to
implement. Light wave detection mechanisms are limited to flat
surfaces and are susceptible to dust and insects blocking the light
paths. It is believed, however, that the present invention solves
these problems.
In today's modern environment there are many sources of
electro-magnetic energy, both naturally occurring and man-made.
Some examples of the sources of such energy in the earth's
atmosphere are static electricity, electrical storms, heat
lightning, radiation from outer space, and man-made radio waves.
Each of these acts and interacts with each other causing
interference and background noise to each other, depending on the
intensity of the background or interfering signal. Thus, as is well
known in devices that utilize an antenna as a device to detect an
input signal, these atmospheric signals may interfere with the
ability to detect and receive a signal of interest. It is also
known that in systems with a hand-held antenna probe, the human
body acts as a larger antenna with a signal from the person holding
that probe added to the signal of interest detected by the
hand-held probe. That added signal, and the multiple frequencies
that it includes is also known to potentially add a level of
inaccuracy in such a system, if the desired signal can be detected
at all. To overcome that unwanted interference many elaborate
circuits have been devised to suppress those interference signals
"picked-up" by the human user from impacting the performance of the
system.
SUMMARY OF THE INVENTION
The present invention includes various apparatus and methods for
determining a user selected position on an electrographic sensor
unit. In the most general terms the electrographic sensor unit of
the present invention includes a layer of a conductive material
having an electrical resistivity with K spaced apart contact points
electrically interconnected therewith, a processor connected to the
K spaced apart contacts and disposed to selectively apply a signal
to N of the K contact points where N has an integer value of 3 to
K, and probe assembly, including a stylus or a flexible conductive
layer placed over the layer, coupled to the processor, the stylus
disposed to be positioned by a user in vicinity of the user
selected position on the layer, or the user to point a finger at
the flexible conductive layer. In turn, the stylus, or the flexible
conductive layer receives signals from the layer when the contact
points have signals selectively applied thereto by the processor
with the user selected position being determinable by the processor
from the signals received from the stylus, or flexible layer, each
in relation to a similar excitation of (N-J) different pairs of the
K contact points under control of the processor, where J is an
integer of 2 to (N-1).
Additionally, where the electrographic sensor includes more than
one conductive layers that are each electrically isolated from each
other, in the most general sense M conductive layers, the present
invention is also able to discern which of those layers contains
the user selected position. Here, each layer has K spaced apart
contact points electrically interconnected with the corresponding
layer of conductive material where N of the K contact points on
each layer are used to locate the user selected position and where
N has an integer value of three to K. The processor is similarly
disposed to selectively apply a signal to each of the N contact
points of each of the M layers and to determine which of the M
layers and position coordinates of the user selected position on
the corresponding one of the M layers in cooperation with a means
for detecting and delivering a signal from the user selected
position on the selected layer of the electrographic sensor unit to
the processor.
The identification of the selected layer is accomplished by
sequentially applying a first selected signal to all of the K
contact points on each of the M layers in turn and measuring a
first measured signal at said user selected position for each of
the M layers individually with the first measurement corresponding
to each one of the M layers being the signal received by the means
for detecting and delivering when all of the contact points on that
layer has the first selected signal applied to that layer's contact
points.
Next, a second measured signal is measured at the user selected
position on the user selected layer for each of the M layers with
each of the K contact points on each of the M layers open
circuited, followed by the subtraction of the second measured
signal from the first measured signal for each of the M layers to
form M difference values.
Those M difference values are then each compared against a
preselected threshold value to determine which one of those M
difference values is both greater than that selected threshold and
which exceeds it by the greatest value. The layer associated with
the difference value that satisfies those conditions is then
identified as the layer that contains the user selected position.
Then once that determination is made the coordinates of the user
selected position on that layer can be determined as discussed
above.
The present invention also includes techniques for compensating for
contact resistance in each of the contact points on the conductive
layer, as well as forming the conductive layer into a two or three
dimensional shape which may be open or closed. Further, the present
invention includes the placement of a conductive skin over the
outer surface layer with that skin having a graphical
representation thereon and the present invention having the
capability to convert the position coordinates of the user selected
position from the coordinates of the conductive layer to those of
the graphical representation. Such a graphical representation may
be that of a map or a globe, even a mythical map or one of a star
or another planet. Carrying this one step further, those graphical
coordinates may also be used to electronically deliver information
that has been prestored in memory relative to the selected
graphical coordinates to the user.
In actual application the present invention can take many forms
from a conductive layer with or without a non-conductive layer
thereon and a stylus for use by the user to select a position on
the layer, to a multi-layer structure with a conductive bottom
layer, a non-conductive compressible inner layer, and a flexible
conductive top layer where the user presses the top layer toward
the bottom layer and the point at which the top and bottom layers
are closest together is determined to be the user selected
position. Further, various designs are proposed wherein the
actuation and measured signals are either AC of a selected
frequency or DC.
The present invention also includes a probe assembly with a cable
with two conductors. The proximate end conductor is coupled to the
processor and the proximate end of the other conductor is connected
to a signal neutral point. The stylus in turn is coupled to the
cable and incorporates therein the distal ends of two conductors
with the distal end of the conductor coupled to the processor
disposed to receive signals from the layer when the contact points
have signals selectively applied to them and the user positions the
stylus in vicinity of a selected point on the surface. The distal
end of the other conductor is disposed to be contacted by the user
when holding the stylus to connect the user to the signal neutral
point. To maximize the probability that the user holds the stylus
making contact with the contact point, it is located externally and
positioned to be contacted by the user during use of the stylus.
Further improve that probability, and to increase the comfort of
holding the stylus, an electrically conductive contact of a
flexible conductive polymer is placed to encircle the stylus at a
position to maximize the user's comfort when holding the
stylus.
Thus, to fully explain the scope of the present invention, a
detailed discussion of various embodiments is offered in the
Description of the Preferred Embodiments below. However it must be
kept in mind that that discussion is not an exhaustive discussion
and variations on the many themes that are presented are also
considered to be part of the present invention.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a simplified block diagram of a generalized embodiment of
the system of the present invention.
FIG. 2 is an illustration of the position location algorithm of the
present invention for a two dimensional surface shape.
FIG. 3 is similar to FIG. 2 however the illustration is for a three
dimensional shape.
FIG. 4 is a block diagram of a first embodiment of the present
invention.
FIG. 5 is a block diagram of a second embodiment of the present
invention.
FIG. 6 is a block diagram of a third embodiment of the present
invention.
FIG. 7 is a block diagram of a fourth embodiment of the present
invention.
FIG. 8 illustrates the restrictions on the placement of contact
points to be able to determine position with only three
contacts.
FIG. 9 illustrates three contact points that can not be used to
determine position on the surface.
FIG. 10 is a partial embodiment wherein a multi-layer compressible
touch surface is disclosed in lieu of the use of a stylus as, for
example, in FIG. 4.
FIG. 11 is a schematic representation of an embodiment of the
present invention adapted to be an interactive globe that
incorporates a spherical conductive surface.
FIG. 12 is a schematic representation of an embodiment of the
present invention adapted to be an interactive globe that
incorporates two hemispherical conductive surfaces.
FIG. 13 is a prior art embodiment of how a potential interfering
signal, from the user holding the antenna stylus is suppressed.
FIG. 14a is a simplified diagram of the stylus and shielded cable
of the present invention.
FIG. 14b is another embodiment of the stylus and shielded cable of
the present invention that grounds the user to the system of the
present invention.
FIG. 14c is still another of the stylus and shielded cable of the
present invention that grounds the user to the system of the
present invention.
FIG. 14d is a partial cut-away view of the stylus design of FIG.
14c to illustrate the internal positioning of the cable shield and
the conductive grip of the stylus.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to a system and method for
determining a location on a two or three dimensional surface of any
shape selected by a user, as well as providing access to data
storage locations or information stored therein that is relative to
that location. More specifically, the present invention determines
the location information in the form of coordinates on a predefined
coordinate system. That location information then serves as an
address to locations within the memory of an associated
microprocessor subsystem. That location, or address may in-turn be
used to retrieve previously stored data pertaining to the
corresponding location on the surface, to store data pertaining to
the corresponding location on the surface, to modify the behavior
of the system incorporating the present invention, or to be
presented to the user on a conventional display or printer
device.
In simple shaped surfaces, such as a rectangle, a minimum of three
small electrical contacts mounted on the edge of the surface are
needed. On more complex shaped surfaces the minimum number of
electrical contacts may increase to enable the system to determine
between multiple locations on the surface as to which one that the
user is indicating. In each configuration of the surface, the
contacts need to be positioned such that all locations on the
surface can be individually identified.
Through the use of small contacts and driver/receiver techniques,
the present invention is able to compensate for differences in the
contact resistance of each of the contacts. The differences that
can be compensated for include differences between contacts on the
same surface, differences between the contacts on one surface
versus those on another surface using the same electronics, as well
as changes in the contact resistance of individual contacts over
time due to mechanical and environmental stresses.
The present invention determines a user selected position on the
surface by measuring the unique position indicating signals with a
receiver as discussed below. For either two or three dimensional
objects, the present invention only requires a single receiver
circuit.
In the various embodiments of the present invention, the stylus
does not load, or negligibly loads, the transmitters and a signal
level at the point on the surface that is touched by the stylus is
measured rather than the changes in the driving circuit as in the
Meadows device. Additionally, potentially phantom styluses such as
fingers and rings, that have a dramatic effect on the operation of
the prior art, only have a negligible loading effect on the
transmitter of the present invention. Thus the present invention is
immune to phantom styluses.
In the present invention the active surface can be made of a
conductive polymer composite (conductive plastic), or a conductive
coating on a non-conductive material. This has substantial cost
advantages over the prior art since no overlays or embedded wires
are needed, and since the surface itself provides the necessary
structural support. Devices incorporating the present invention
would typically include a surface of a conductive polymer composite
molded or vacuum formed that does not require any additional
structure thus resulting in an additional cost of only the
carbon-polymer material, or the applied conductive coating.
Furthermore, the formation of the sensitive surface by injection
molding allows for easy creation of touch sensitive complex shapes.
The use of a carbon-polymer composite material as both an element
in the position location system and the structural support provides
a rugged and reliable system. Carbon-polymer composite materials
are inherently rugged and the system of the present invention
employs a single layer of such material, rather than a multi-layer
system where the bonding between the layers may deteriorate and the
layers separate.
A minimum of three contacts are needed to drive an entire surface
of a simple object (e.g., a rectangle, circle or ellipsoid).
Additionally contacts may be used for complex objects or to provide
increased resolution for simpler shapes rather than increasing the
sensitivity of the circuitry. The low number of contacts and
therefore wire count, leads to low cost, ease of manufacturing, and
enables remote or moveable surface applications (e.g., a rotating
globe).
An advantage to the use of a conductive polymer material for the
surface is that it allows the contacts to be mounted to the back or
inside of the surface, and to thereby achieve a 100% active front
or outside surface.
Additionally, the present invention includes unique surface drive
techniques that can compensate for unknown and variable contact
resistance. Various contact types and mechanical connection
mechanisms create contact resistances which vary substantially
between contacts, and vary over time with mechanical and
environmental stresses such as movement, temperature and aging.
Other technologies rely on contacts of known, or constant, contact
resistance with any uncompensated change in contact resistance
resulting in position detection errors.
The present invention permits the use of various mechanisms to
compensate for differences and variations in contact resistance.
Each of those mechanisms may be used and each provides its own
advantages. One possible mechanism involves using two electrodes as
each contact, with those electrodes being close together and
electrically interconnected but not touching. The first of those
electrodes in this configuration is attached to the signal drive
source and the second of those electrodes provides a high impedance
feedback path. In this configuration the signal drive source is
adjusted so that the signal level at the second electrode is of a
desired value thus providing a known signal level at a known point
on the surface independent of the contact resistance. The drive
method here also provides automatic adjustment for changes in the
resistive material over time and temperature, as well as variations
in contact resistance.
A second possible mechanism has just one electrode per contact and
measures the value of the resistance of each contact to the
resistive material of the surface. In such a system having three
contact points, A, B and C, a signal level measurement is made at
point C through a high impedance path while a signal of a known
level is applied between point A and point B. Similar measurements
are then made at point B with the signal applied between point C
and point A, and at point A with the signal applied between point B
and point C. Thus, knowing the positions of the contacts on the
surface and the resistivity of the surface material, the contact
resistance between points A, B, and C and the surface material may
be calculated as discussed below with respect to FIG. 6.
Additionally, the present invention incorporates the use of a
multi-state drive sequence to provide quick measurement and
on-the-fly calibration for improved accuracy. The stylus is used to
make several signal measurements at a point on the surface of the
object selected by the user. First a measurement is made with no
signals applied to the contacts to determine a baseline DC offset
and ambient noise level for the surface, for purposes of discussion
here this is called DC-OFFSET. A second measurement is made with a
signal applied to all of the contacts to determine the full-scale
signal value, for purposes of discussion here this is called
FULL-SCALE. Another measurement is then made by applying a signal
to one pair of contacts to create a signal level gradient across
the surface between those two points, for purposes of discussion
here call this the X axis and the measured value X. A signal is
then applied to another pair of contacts to create a signal level
gradient in another direction, for purposes of discussion here call
this the Y axis and the measured value Y. The following
calculations are then made by the system to determine the selected
location along the so defined X and Y axes on the surface.
P.sub.x=(X-DC-OFFSET)/(FULL-SCALE-DC-OFFSET) (1)
P.sub.y=(Y-DC-OFFSET)/(FULL-SCALE-DC-OFFSET) (2)
The actual position on the surface can then be determined from
P.sub.x and P.sub.y by using a mathematical, or empirically
determined, model of the signal level gradients for the surface
material.
In the present invention the basic items required (i.e., the
algorithm and conductive material) have been around for quite some
time. The basis for the algorithm dates back centuries. Materials
similar to what is suggested for the surface material here, having
similar electrical properties have also been around for
decades.
The basis of the algorithm of the present invention is the use of
triangulation to determine the location of the point on the surface
of the object. Triangulation is defined as "The location of an
unknown point, as in navigation, by the formation of a triangle
having the unknown point and two known points as the vertices."
(The American Heritage Dictionary of the English Language, Third
Edition)
Triangulation is a basic tenet of trigonometry and its use in
finding the location of a point on the surface of an object has
been used for centuries. It is used in applications such as
celestial navigation, surveying, the global positioning system
(GPS), and seismology.
In the present invention, as is the case in triangulation, position
is determined by measuring the relationship at a point of interest
to two known points. The relationship is determined from the
received signal level at the stylus while injecting signals of
known levels at the first two fixed points. All points on the
surface that would have that signal level create a line of possible
positions. Another relationship is determined using another two
fixed points (a different pair of contacts however one contact can
be one of those that was included in the first pair of contacts)
and another received signal level from the stylus. The intersection
of the two lines of possible positions from the two measurements
thus tells us where the stylus touched the surface. For some
surfaces this may be unique, such as a two dimensional surface or a
hemisphere with the contacts mounted on the edge or at the
equator.
In theory any position in three dimensional space can be uniquely
identified by its distance from four non-coplanar known points,
while the number of known points required may be reduced in some
cases if the possible positions in three dimensional space are
constrained. For the purposes of the present invention the position
of interest is constrained to lie on the surface of the known shape
of the surface. For a shape such as a rectangle or a circle, a
position on the surface may be defined by its distance from three
known points on that surface, provided the known points are either
all on the edge of the surface shape or not collinear. For the
continuous surface shapes of spheres or ellipsoids, a position on
the surface of the shape can be defined by its distance from three
known points, provided the plane defined by the three known points
does not include the center point of the shape. For a cylindrical
shape a position on the surface can be defined by its distance from
three known points, provided the plane defined by the three known
points does not cross the center line of the cylinder.
For a relationship to be determined between a contact and a point
on the surface, the point must be in the field of view of a contact
pair. That is, as shown in FIG. 8, for any point X to be in the
field of view for a pair of contacts A and B, the included angle
A.sub.i, between vectors drawn between A and B, and A and X, as
well as the included angle B.sub.i, formed by vectors drawn between
B and A, and B and X, must both be less than 90.degree..
Additionally the surface must contain electrically conductive
material between points A and X and between X and B. FIG. 9
illustrates a situation where point X is not in the field of view
of points A and B since included angle B.sub.i is greater than
90.degree. even though included angle A.sub.i is less than
90.degree..
In practice more contact points may be used due to the finite
resolution of real measurement devices. Another factor that may
increase the number of contacts is cost. A trade off may be made
between the resolution of the receiver and transmitter circuits,
and the number of contacts between which the signal is applied to
the surface for the measurements. If more contacts are used that
are closer together then the resolution of the transmit/receive
circuit may be reduced.
The use of resistivity in materials to measure distance or position
has been around for a number of years. An early example is the use
of rotating, or sliding, potentiometers to determiner the position
of a knob or a slide.
Conductive polymers that could be employed by the present invention
have been around at least since 1974 when CMI, an early producer of
Conductive Polymer Composites, was acquired by the 3M Company.
At a minimum the materials and algorithms utilized by the present
invention have been readily available for 20 years, and in all
likelihood longer. However, the literature does not teach or
suggest the combination of those elements to produce a device like
the present invention, in fact all of the known references teach
away from this technique.
In FIG. 1 the basic components of the user selected position
locating system of the present invention are shown. They include a
two or three dimensional conductive surface 10 (e.g., carbon loaded
plastic or a conductive coating applied to a non-conductive
surface) having a selected resistivity with three conductive
contacts 12, 14 and 16 affixed thereto. Each of contacts 12, 14 and
16 are connected via conductors 24, 26 and 28, respectively, to
processor 30. Also connected to processor 30 is conductor 18 with a
stylus 20 having a tip 22 affixed to the other end thereof for the
user to use to indicate a position on surface 10 that is of
interest to that user.
Then, as in FIG. 2 when a user selects a point on surface 10 with
stylus 20, a series of measurements as described in general terms
above are made.
First, without any signals applied to contacts 12, 14 and 16,
processor 30 measures the DC-OFFSET value of the system with stylus
20;
Next an equal amplitude signal is applied to all three of contacts
12, 14 and 16, and processor 30 measures the FULL-SCALE signal
value with stylus 20;
The third measurement is made by applying a signal of the amplitude
used in the full-scale measurement to one of the three contacts,
say contact 12 with a second contact grounded, say contact 14, and
the signal measurement made with stylus 20 which will be somewhere
along an equipotential line between those two contacts (i.e., line
X in FIG. 2);
A fourth measurement is made by applying the signal to, and
grounding, a different pair of contacts, say 12 and 16, and the
signal measurement made with stylus 20 which will be somewhere
along an equipotential line between those two contacts (i.e., line
Y in FIG. 2), with the position of stylus 20 being the intersection
of lines X and Y; and
The values of P.sub.X and P.sub.Y are then calculated as in
equations 1 and 2 above.
In actual operation, each of those steps can be automated by
processor 30 without requiring the user to initiate specific
measurements or to switch signals.
The values of P.sub.X and P.sub.Y can then be used as an address to
a memory within processor 30 from which information relative to the
position indicated with the stylus may be obtained. This same
technique can also be used to determine the address in memory where
data is to initially be stored for later retrieval, or as an
address on a remote display that is to be activated for whatever
purpose.
Each unique position on the surface is defined by a unique
combination of values of P.sub.X and P.sub.Y. From the series of
measurements described above, the position of the stylus on the
surface may be expressed in terms of P.sub.X and P.sub.Y which will
be called the equipotential coordinates. Additional calculations
may also be made to convert the position from the equipotential
coordinates to another coordinate system, if desired. The
conversion requires a known mapping of the equipotential
coordinates to the desired coordinate system. The mapping may be
determined mathematically for an object made from a homogenous
conductive material or one where the resistivity distribution is
known. For objects in which the resistivity distribution is not
known, the mapping of equipotential coordinates to the desired
coordinates may be determined empirically. In either case, the
mapping may be stored in the microprocessor's memory and the
conversion calculations performed by the microprocessor.
FIG. 3 illustrates the same approach for determining the values of
P.sub.X and P.sub.Y on the surface having a defining equation that
is continuous over the entire surface, for example a hemisphere as
shown.
Surface 10 of the present invention uses materials such as carbon
loaded polymers or conductive coatings (e.g., 3M Velostat 1840 or
1801) that can be easily molded into, or applied to, two or three
dimensional surfaces, including surfaces having complex shapes. A
minimal number of drive circuits and connections between that
surface and the detection electronics further will reduce the
complexity in both the electronics and the mechanical aspects of
coupling the surface to the electronics.
More specifically, several embodiments of the present invention are
described in the following paragraphs and illustrated starting with
FIG. 4.
The embodiment, shown in FIG. 4, includes a rectangular piece of
conductive material as sheet 100 (e.g., 12 inches.times.12
inches.times.0.125 inches sheet of a carbon loaded polymer such as
3M Velostat 1801). The conductive material may also be composed of
a non-conductive material with a conductive coating such as Model
599Y1249 from Spraylat Corp.
Affixed near the edge of sheet 100, and making electrical contact
thereto, are contacts 102, 104, and 106. Connected between contacts
102, 104 and 106 on sheet 100 and contacts 126, 128 and 130 of
signal generator 122, respectively, are electrically conductive
leads 108, 110, and 112.
Signal generator 122 includes a 60 KHz AC signal generator 124 that
feeds amplifier 134 with the non-inverting output terminal of
amplifier 134 connected to three separate terminals (one
corresponding to each of contacts 102, 104 and 106) of switch 132,
and the inverting output terminal of amplifier 134 connected to
three terminals (one corresponding to each of contacts 102, 104 and
106) of switch 136. Then each of contacts 126, 128 and 130 are each
connected to different terminals of each of switches 132 and 136.
In FIG. 4 each of switches 132 and 136 are shown in the open
position (i.e., no signal applied to any of contacts 126, 128 and
130).
In turn, the position of each of switches 132 and 136 is controlled
via cables 138 and 140, respectively, from microprocessor 142 to
permit microprocessor 142 to select which of contacts 102, 104 and
106 receive a 60 KHz signal through switch 132 via the associated
control lead and which of contacts 102, 104 and 106 receive an
inverted 60 KHz signal through switch 136 via the associated
control lead.
When a 60 KHz AC signal is connected to one or more of contacts
102, 104 and 106 that signal radiates through the conductive
material of sheet 100 and stylus 116 acts as an antenna when
brought within proximity of surface 100. A signal detected by
stylus 116 is in turn conducted to the signal measurement stage 120
via shielded cable 118. In this embodiment stylus 116 is completely
passive and could be fabricated as simply as consisting of a
plastic shell enclosing the end of shielded cable 118 with the
final 1/8 inches of cable 118, at the distal end of stylus 116,
having the shielding removed to allow the center conductor of cable
118 to be exposed to receive radiated signals. Thus, when the tip
of the stylus is near the surface of conductive material 100, the
radiated signal is received by the stylus antenna and provided as
an input signal to signal measurement stage 120.
Signal measurement stage 120 includes a demodulator 144 that is
connected to cable 118 where the signal received by stylus 116 is
demodulated and the demodulated signal is then in turn presented as
a signal level to an analog-to-digital converter (ADC) 146. ADC 146
then digitizes that signal level and presents it to microprocessor
142.
The use of an AC signal in this embodiment makes it possible for
stylus 116 to receive signals radiated from the conductive material
of sheet 100 without being in direct contact with the conductive
material of sheet 100. This allows the conductive material of sheet
100 to be covered with a layer of a non-conductive material for
protection from inevitable striking of the surface of sheet 100
with stylus 116, or for placement of application specific graphics
over the touch surface, and still allow stylus 116 to act as an
antenna to receive a signal from sheet 100 at a selected point that
is to be measured by the signal measurement stage 120.
Microprocessor 142 is encoded to direct the performance of a series
of measurements with different sets of contacts 102, 104 and 106
connected to receive the 60 KHz signal, or the inverted 60 KHz
signal.
Once a user has selected a position on sheet 100 of interest, the
system of the present invention performs a series of measurements
in rapid succession (e.g., by time-division multiplexing) to
determine the location to which stylus 116 is pointed and to
provide the user with the information that is sought.
The first measurement, as outlined above, is here called
Signal.sub.OFFSET, and involves setting switches 132 and 136 to the
all open positions. Microprocessor 142 then reads the signal level
from signal measurement stage 120 and assigns that value to
Signal.sub.OFFSET and saves that value in RAM 144.
The second measurement, as outlined above, is here called
Signal.sub.FULL, involves connecting a 60 KHz AC signal to all of
contacts 102, 104 and 106 at the same time by the closure of all
three sets of contacts in switch 132. Microprocessor 142 then reads
the signal level from signal measurement stage 120 and assigns that
value to Signal.sub.FULL and saves that value in RAM 144.
Next, microprocessor 142 selects a pair of contacts, say 102 and
104, for use in the next measurement. Contact 102, for this
discussion is point A and is connected to receive the 60 KHz AC
signal via switch 132. The other of those two contacts, contact
104, which for this discussion is point B is connected to receive
the inverted 60 KHz AC signal via switch 136. The third contact 106
is merely connected to open switch sections in both of switches 132
and 136. Microprocessor 142 then stores the signal level from
signal measurement stage 120 in RAM 144 and assigns that value the
name Signal.sub.RAW-AB.
Between the energized contacts 102 and 104, a signal level
equipotential map 114A could be drawn due to the effect of the
distributed resistance in the conductive material of sheet 100.
Signal equipotential maps such as 114A, 114B, and 114C, including
the shape and values of the equipotential signal level lines, are
stored in ROM 146. As discussed in Electromagnetics, by John D.
Kraus and Keith R. Carver, McGraw-Hill, 1973, pp 266-278, these
signal equipotential maps are created by finding the unique
solution to Laplaces equation (.gradient..sup.2V=0) that satisfies
the boundary conditions of sheet 100 and each pair of contacts.
There are many methods of finding the solution to Laplace's
equation for an object, including, but not limited to, direct
mathematical solutions, graphical point-by-point computer
modelling, and empirical determination. For homogenous conductive
material and simple shapes, a direct mathematical solution may
easily be obtained. For materials whose homogeneity, shape or
contact placement do not lend themselves to other methods,
empirical determination may be used.
In the empirical determination method, a coordinate system is
chosen and overlaid on the device. To determine the map for a
specific pair of contacts, such as 102 and 104, the contacts are
energized in the same manner as for measuring Signal.sub.RAW AB
above. At each cross point on the chosen coordinate system the
value of Signal.sub.RAW AB is measured. If the chosen cross point
granularity is sufficiently fine the equipotential map may be
extracted directly by finding the points that contain the same
measured value. Otherwise the equipotential lines may be calculated
by interpolating between measured points.
For the third measurement, microprocessor 142 selects another pair
of contacts, such as 102 and 106. Contact 102, as discussed above
will again be referred to as point A, is connected to receive the
60 KHz AC signal via switch 132 and is the only one of the contacts
so connected. The other contact 106, which for this discussion is
referred to a point C, is connected to the inverse 60 KHz signal
via switch 136. Microprocessor 142 then records the signal level
from signal measurement stage 120 and assigns that value the name
Signal.sub.RAW-AC.
The two signals, Signal.sub.RAW-AB and Signal.sub.RAW-AC, are
affected not only by the material resistance between the contacts
but by a number of other factors including the altitude of stylus
116 from the surface of the conductive material of sheet 100, the
attitude or angle of stylus 116, and changes in the circuitry from
environmental changes, aging, or other factors. The signal,
signal.sub.FULL, is similarly affected by altitude, attitude, and
circuitry changes but has a constant signal equipotential map, thus
the value of Signal.sub.FULL may be used to normalize the values of
Signal.sub.RAW-AB and Signal.sub.RAW-AC to remove the effects of
altitude, attitude, and circuitry changes using the following
formula. Signal.sub.NORM=Signal.sub.RAW/Signal.sub.FULL (3)
Both Signal.sub.RAW and Signal.sub.FULL are affected by certain
changes in the circuitry that produce a DC offset in the final
values. Equation 3, if desired, may be modified to remove those
effects as shown in equation 4 below.
Signal.sub.NORM=(Signal.sub.RAW-Signal.sub.OFFSET)/(Signal.sub.FULL-Signa-
l.sub.OFFSET) (4)
Applying either formula of equations 3 and 4 to each of
Signal.sub.RAW-AB and Signal.sub.RAW-AC, the normalized signals,
Signal.sub.NORM-AB and Signal.sub.NORM-AC, can be derived.
For example, using the predetermined signal map 114A and the value
Signal.sub.NORM-AB, the position of stylus 116 may be resolved to a
single signal level line, such as 115, between contacts 102 and
104.
Using the predetermined signal map 114B and the value
Signal.sub.NORM-AC, another signal level line in the signal map
114B can be determined between contacts 102 and 106. The position
of stylus 116 is then resolved to the point, P, where the signal
level line selected by Signal.sub.NORM-AB in 114A crosses the
signal level line selected by Signal.sub.NORM-AC in 114B.
The use of the resolved point, P, is qualified by microprocessor
142 by comparing the value of Signal.sub.FULL to a predetermined
threshold level to determine if the received signal is valid. This
threshold is generally determined empirically to satisfy the
resolution requirements of the application or the user. As the
altitude of stylus 116 from the surface of the conductive material
of sheet 100 is reduced, the received signal is stronger and the
resolution of the position is more precise. Some applications such
as drawing tablets, may want a specific altitude threshold in order
to match user expectations of operation. In these applications,
users do not expect the system to acknowledge the stylus position
until the tip is in contact with the surface. Other applications
may desire a higher or lower degree of resolution. The application
may select the altitude threshold that best matches it's
requirements. When a Signal.sub.FULL threshold for a particular
application is satisfied the resolved point, P, is considered
valid.
The measurements outlined above are made in succession and each
measurement can typically be made within 4 msec so the entire
sequence is completed in 12-16 msec. This is important since the
measurement sequence needs to be completed quickly so that any
stylus position changes between the measurements are minimized.
Substantially faster sample times may be used provided that the
capabilities of the signal measurement device are selected
accordingly.
To support an application that requires a series of stylus
locations in quick succession to be measured, a sample time that is
substantially faster than the movement of the stylus needs to be
chosen. An application that would require successive stylus
location detection would be an electronic drawing pad where the
succession of points would form a line. An application of this type
may require sample times on the order of 200 microseconds.
In the embodiment discussed above, signal generator 122 produces a
60 KHz AC signal, however, a DC voltage level could alternatively
be used. With a DC signal level in lieu of the 60 KHz signal the
ability to detect the position of the stylus without making contact
between stylus 116 and the conductive material of sheet 100 is
eliminated. Since direct contact is made between the stylus and the
material, the effects of the altitude and attitude of the stylus no
longer contribute to the measurement of Signal.sub.RAW since stylus
altitude and attitude are the dominant source of variation in the
measurement of Signal.sub.RAW. The elimination of stylus altitude
and attitude from the measurement reduces, or eliminates, the need
to normalize Signal.sub.RAW with Signal.sub.FULL.
More measurements (contacts 104 to 106, i.e., B to C) may also be
made to refine/confirm the point to which stylus 116 is being
pointed with a minimum number of measurements. Microprocessor 142
could also be programmed to filter measurements to dampen changes
made by movement of stylus 116 and to increase resolution.
Synchronous detection technique in the receive demodulator
substantially improve noise immunity. The received signal is
multiplied by the transmitted signal with a FET switch (e.g.,
DG441). The resulting multiplied signal is then integrated to
determine the DC component. It is the integrated signal that is
presented to the ADC for conversion. The net effect of the
multiplication and integration is that only received signals of the
same frequency and phase to the transmitted signal are seen. Such
signals are considered to be synchronous with the transmitter, and
therefore the name synchronous demodulation. Effective noise
immunity is accomplished since, in general, sources of noise will
not be synchronized to the transmitter, and therefore will not be
seen after multiplying and integrating. Only the desired portion of
the transmitted signal that has been detected by the receiving
stylus will be measured.
Special techniques can be used to enhance the accuracy near the
edges of a conductive surface. On surfaces of certain shapes, the
lines of equipotential may be nearly parallel near the edges, which
tends to reduce the positional accuracy. Distance to the edge can
be estimated from Signal.sub.FULL alone, since Signal.sub.FULL
tends to fall off somewhat near the edge. Applying an estimate of
the distance from the edge to point determined by the intersection
of two equipotential lines near the edge can help improve
positional accuracy in some cases.
In cases where two electrically isolated surfaces terminate along
the same edge, such as the equator on a globe made of isolated
Northern and Southern hemispheres, similar techniques can be used
to improve positional accuracy near the edge. In such cases
distance from the edge can be estimated by comparing
Signal.sub.FULL from both surfaces, and using the ratio of
Signal.sub.FULL-A to Signal.sub.FULL-B to help eliminate the
effects of altitude and attitude.
Once the position indicated by the user is determined, the system
might be employed in an application where information relative to
that position has been prestored, or is to be stored, in the
overall system. To enable that application, RAM 144, ROM 146,
audio/video card 150 and CD ROM drive 156 are shown interfacing
with microprocessor 142 via a data bus. For example, if surface 100
has an overlay of a map there may be information prestored in ROM
146 or on a CD in CD ROM drive 156 that can be delivered to the
user in either audio or visual form via audio/video card 150 and
speaker 154 or monitor 152.
The contact resistance of the connections between contacts 102, 104
and 106 and the conductive material of sheet 100 may play a
significant role in defining the absolute signal levels in the
signal maps (114A, 114B and 114C). That contact resistance affects
the absolute value of the signal level but has only a minor effect
on the shape or distribution of signal lines. In some cases the
contact resistance between one contact and the conductive material
of sheet 100 may be of a similar, or a higher, value than the
resistance through the conductive material between different
contacts. The resistance between a single contact and the
conductive material is also subject to change over time due to
chemical, or mechanical factors. Contact to conductive material
resistance may also differ from unit to unit in a manufactured
product.
To automatically compensate for contact-to-conductive material
resistance differences, which is addressed in the embodiment of
FIG. 4 by calculation, another embodiment of the present invention
is shown in FIG. 5. As can be seen by the comparison of FIGS. 4 and
5 many of the elements of the two circuit embodiments are the same
and connected together in the same way, in particular, sheet 100,
the signal measurement stage 120, microprocessor 142 and associated
components, signal generator 124, amplifier 134, and switches 132
and 136. The additional elements in FIG. 5, which are described
below, have been added to provide the automatic compensation for
resistance differences mentioned above.
The first difference between the two figures is in the structure of
the contacts affixed to sheet 100. In FIG. 5, stated in simple
terms, a single contact as shown in FIG. 4 is replaced with a
connected pair of contacts. A first contact of each connected pair
is used as the point to which connection of the signal generator is
made, while the second contact of the connected pair is used as the
point at which measurements of the signal level is made and at
which adjustments of the signal level being injected at the first
contact in that connected pair is made so that the signal level at
the measured point is at a known level.
For example, contact 102 in FIG. 4 is replaced with connected pair
202a and 202b in FIG. 5. In this embodiment contact 202a could be a
0.0625 inches diameter contact positioned at the same point on
sheet 100 as contact 102 in FIG. 4, and is used as the injection
point of a signal into the conductive material of sheet 100.
Similarly, contact 202b could be a 0.0625 inches diameter contact
positioned 0.25 inches from contact 202a and used as the point at
which the signal level is measured at the associated point on sheet
100.
The second difference from the embodiment of FIG. 4 is the
connection of the output terminal of each of two input terminal
amplifiers 220, 224 and 228 (e.g., MC4558) to contacts 202a, 204a
and 206a, respectively. Each of amplifiers 220, 224 and 228 has the
positive input terminal connected to a different one of the output
terminals of switches 132 and 136. Each of amplifiers 220, 224 and
228 has the negative input terminal connected to a different one of
the "b" contacts of each connected pair attached to sheet 100
(i.e., contacts 202b, 204b and 206b).
When the input signal passes through the resistance of the contact,
the signal level decrease. If the resistance of the contact
changes, the signal level changes inversely proportionally to the
change in resistance of the contact. Therefore if such a change in
the input signal level is inversely compensated for in another way,
any change of signal level resulting from a change in the
resistance of a contact is negated. Persons skilled in the art of
closed loop feedback theory will recognize that the "b" contacts of
sheet 100 provide feedback to the "a" contact drive amplifier 202A,
204a and 206a, such that those amplifiers can sense any decrease in
signal level due to contact resistance, and provide the necessary
signal boost to compensate for loss.
An alternate mechanism for compensating for contact resistance is
to determine the current value of the contact resistance and adjust
the absolute values in the signal map based on any change in
contact resistance value. The embodiment shown in FIG. 6 performs
that function.
Again comparing the embodiments of FIGS. 4 and 6, several
similarities can be noted which include sheet 100 with contacts
102, 104 and 106, stylus 116 and shielded cable 118, signal
measurement stage 120, microprocessor 142 and associated
components, and signal generator 122. The new component here is
four position switch 301 which provides selectability as to which
signal is input to the input terminal of demodulator 144 of the
signal measurement stage 120 under control of microprocessor 142
via line 302. The four potential signal input sources are stylus
116 and any one of contacts 102, 104 and 106 on sheet 100.
For any position in the signal map between two points, any change
in the resistance of any contact through which current is flowing
will modify the signal value observed. For example, for a
predetermined, or calculated, signal map such as 114A between
contacts 102 and 104 in FIG. 4, a change in the contact resistance
at contact 102 will change the absolute values in the signal map
but not the distribution or shape of the signal map. If the contact
resistance at 104 were to change and the new contact resistance
measured, the microprocessor could adjust the predetermined, or
calculated, signal map to compensate for the changed contact
resistance.
To measure and calculate the contact resistance changes at the
three contacts 102, 104, and 106 in FIG. 6, three additional
measurements are made. These measurements may be added to the
sequence of measurements of Signal.sub.FULL, Signal.sub.OFFSET,
Signal.sub.RAW-AB and Signal.sub.RAW-AC. For this discussion the
contacts will be designated A, B, and C for contacts 102, 104, and
106. For the first additional measurement the microprocessor
selects contact 102 to be connected to the 60 KHz AC signal via
switch 132, and contact 104 to be connected to the inverted 60 KHz
AC signal via switch 136. The signal measurement device is
connected to a fixed location, contact 106, via switch 301. The
microprocessor then stores the signal level from the signal
measurement stage in RAM as Signal.sub.C.
The second additional measurement is made with contact 102
connected to the 60 KHz AC signal and contact 106 connected to the
inverted 60 KHz AC signal. The fixed point, contact 104, is
connected to the signal measurement device. The microprocessor then
stores the signal level from the signal measurement stage in RAM as
Signal.sub.B. The third measurement is made with contact 104
connected to the 60 KHz AC signal and contact 106 connected to the
inverted 60 KHz AC signal terminal of amplifier 134. The fixed
point, contact 102, is connected to the signal measurement device.
The microprocessor then stores the signal level from the signal
measurement stage in RAM as Signal.sub.A.
Thus, the measured signals levels can be defined by equations
5a-5c:
Signal.sub.C=Signal.sub.IN[(XR.sub.AB+R.sub.A)/(R.sub.A+R.sub.AB+R.sub.B)-
] (5a)
Signal.sub.B=Signal.sub.IN[(YR.sub.AC+R.sub.A)/(R.sub.A+R.sub.AC+R-
.sub.C)] (5b)
Signal.sub.A=Signal.sub.IN[(ZR.sub.BC+R.sub.B)/(R.sub.B+R.sub.BC+R.sub.C)-
] (5c) where: Signal.sub.IN is the signal level injected between
two contacts; R.sub.AB, R.sub.AC and R.sub.BC are the bulk
resistances of the material between contacts A and B, A and C, and
B and C, respectively; X, Y, and Z define the distribution of the
bulk resistance as seen at the measurement point, between the two
drive contacts; and R.sub.A, R.sub.B, and R.sub.C are the contact
resistances at contacts A, B, and C, respectively.
The values of Signal.sub.IN, X, Y, Z, R.sub.AB, R.sub.AC, and
R.sub.BC are constant values that may be measured and/or calculated
for a particular device and stored in the microprocessors memory.
That leaves a series of three simultaneous equations with three
variables, i.e., R.sub.A, R.sub.B, and R.sub.C. The microprocessor
then can solve those simultaneous equations for the values of
R.sub.A, R.sub.B, and R.sub.C, and then the microprocessor can
adjust the signal value tables based on the new values of R.sub.A,
R.sub.B, and R.sub.C.
An alternate mechanism to driving a pair of contacts and sensing
with a receiver connected to the stylus is to use the stylus and
one of the contacts as the driving mechanism and to perform sensing
with one of the other contacts. A sequence of measurements could be
made where another contact is selected as the drive contact and yet
another contact is selected as the sense contact.
An alternate drive and measurement method is provided by the use of
frequency division multiplexing. Previously discussed methods
include a series of measurement steps separated in time. In a
frequency division multiplexing method, pairs of contact points are
driven simultaneously with different frequency signals. Therefore
the signal received by the stylus is a composite of those different
frequency signals and thus is distributed to multiple independent
signal measurement devices (i.e., sorted by frequency) that each
measure the corresponding signal simultaneously. The multiple
measurement devices in this embodiment are designed to measure
signals within narrow frequency bands. This measurement method
offers the possibility of measuring the position in less time
however with a more complicated signal drive and measurement
detection system.
Several design tradeoffs may be made in the implementation of the
present invention for use in a specific device. To enhance
resolution a higher resolution signal generation and measurement
scheme may be used. Alternately the number of contact points may be
increased and an enhanced algorithm implemented that uses subsets
of the contact points to resolve stylus touches on different areas
of the surface. Another alternative might be the selection of a
conductive material and manufacturing method that provides a more
homogenous resistivity in the surface. This increases the
resolution and allows for calculated, rather than measured signal
maps. If the material used is not homogenous, another way that
higher resolution may be accomplished is by measuring a more
comprehensive signal map that is stored in the microprocessor
memory.
The embodiments described in FIGS. 4, 5, 6, and 7 include a stylus
that is tethered to the rest of the detection system by conductor
118. This conductor may be replaced with a communications link that
does not require tethering the stylus to the system with a
conductor. A low power RF transmitter could be embedded or attached
to the stylus and a compatible RF receiver attached to the signal
measurement means. The RF transmitter and receiver would then
implement the communications link that conductor 118 provided.
The present invention may be extended to include other two and
three dimensional shapes, both with a surface shape that smoothly
changes slope (e.g., a sphere or a saddle shape) and shapes with
sharp edges (e.g., a cube or a pyramid) so long as the resistive
surface is continuous through those changes of slope and around
those sharp edges.
In another embodiment as shown in FIG. 7, the position of stylus
116 on a sphere may be detected. In this embodiment a sphere 400,
molded from a conductive material of the same type discussed for
each of the other embodiments, has four contacts 401, 402, 403 and
404 attached to it. In order to be able to individually distinguish
each point on the surface of a closed three dimensional shape
(e.g., a sphere) the contacts must be positioned such that each
plane defined by each possible combination of any three of those
contact points does not pass through the center of the sphere. How
close these imaginary planes can come to the center of the sphere
(i.e., the placement of the contacts) is determined by the
resolution of the signal measurement device and the precision of
the predetermined, or calculated, signal equipotential map that
determines the point to which the stylus is pointed.
The calculation of position is therefore substantially the same as
discussed with respect to a pair of contacts thus that discussion
and the claims also include this variation.
To resolve the position of stylus 116 on the two dimensional area
of the rectangular sheet 100 in the embodiment of FIG. 4, three
measurements, Signal.sub.FULL, Signal.sub.RAW-AB, and
Signal.sub.RAW-AC were required since, as described above with
respect to FIG. 2, the equipotential lines for each of the AB and
AC measurements can only cross in one point. For a sphere as in
FIG. 7, however, four measurements are required to fully resolve
this position. For example, if contact 401 is point A, contact 402
is point B, contact 403 is point C and contact 404 is point D, a
measurement Signal.sub.FULL with all four points driven
simultaneously is one measurement, and three measurements from the
six possible pair combinations of the four contacts must be made,
namely three of the possible measurements Signal.sub.RAW-AB,
Signal.sub.RAW-AC, Signal.sub.RAW-AD, Signal.sub.RAW-BC,
Signal.sub.RAW-BD, or Signal.sub.RAW-CD. Calculating the three
Signal.sub.NORM values as in equation (3) above and plotting those
values on the applicable signal maps will uniquely resolve all
points on the sphere. When two Signal.sub.NORM values are plotted,
the equipotential lines intersect in two places on opposite sides
of the sphere. The third Signal.sub.NORM value is used to determine
which of the two intersect points is the one to which the stylus is
being pointed. Specifically, if the signal measured at the fourth
point where used with the signal from one of the other two points
that were used to locate the first two alternative points, that
combination would also result in two possible points on the sphere,
however, one of those two points would correspond with one of the
two previously determined points and it is that corresponding point
that is the actual point of interest on the sphere.
An alternative to using a stylus as the pointing device is the use
of a finger as the pointing device. To enable this, a multi-layer
material constructed with the inner layer being similar to the
conductive material discussed in the previous embodiments may be
used. Such a surface is illustrated in FIG. 10 with conductive
layer 100 on the bottom, a flexible conductive layer 501 on top
(e.g., a metal foil or a thin layer of a conductive polymer), and a
compressible non-conductive layer 502 (e.g., silicon rubber or
plastic foam) in-between layers 100 and 501. Outer layer 501 may be
metal, or some conductive material.
In this configuration, outer conductive layer 501 replaces the
attached stylus 116 as in FIG. 4 with outer layer 501 connected to
the signal measurement device by conductor 118 (e.g., see FIG. 4).
Thus, when a user touches outer layer 501, the middle
non-conductive layer 502 compresses and conductive outer layer 501
is brought closer to conductive inner layer 502. In that situation,
the signal level received by outer layer 501 from the radiated
signals on inner layer 100 increases in much the same way as the
signal level received by stylus 116 increases as the altitude of
stylus 116 is decreased relative to surface 100 in FIG. 4. In the
embodiment that utilizes the multi-layer surface, the position of
the user's finger would be calculated in the same way as the
location of the stylus with a threshold value chosen for
Signal.sub.FULL in the signal valid determination step that
corresponds to a fully depressed outer layer.
As mentioned briefly above with respect to FIG. 4, one application
of the present invention might be an interactive globe of the
earth, the moon, one of the planets, one of the stars, or even an
artificial body or planet for an interactive game. Two potential
implementations of such a globe are illustrated in FIGS. 11 and 12.
The primary differences between the embodiments of those figures is
that in FIG. 11 the conductive surface is a sphere, and in FIG. 12
the conductive surface is implemented with two hemispheres.
FIG. 11 illustrates the system disclosed above with respect to FIG.
7 being modified to be a world globe. Thus, the electronics in the
lower portion of FIG. 11 have the same reference numbers as, and
operate in the same way described, in FIG. 7. In FIG. 11 there is a
conductive sphere 603 with four contact points 604, 605, 606 and
607 on the inside of sphere 603, with each of the contact points
connected, respectively, to one of the four insulated conductors of
cable 608 at one end of those conductors. Cable 608 exits sphere
603 through a small hole in the bottom of sphere 603 with the other
end of the conductors of cable 608 interconnecting with the
corresponding sections of switches 422 and 432.
To provide the geographic details of the globe, two vinyl skins 601
and 602, shown here as representing the northern and southern
hemispheres of the earth, are placed over sphere 603. Thus when a
user uses stylus 116 to point to a location on the globe, the
electronics determines the coordinates of that selected location as
described above in the discussion with respect to FIG. 7 since the
electronics here are as described there. The unique location on the
surface of the globe is thus defined by the equipotential
coordinates which can then be mapped by microprocessor 142 (e.g.,
by means of a look-up table) into global coordinates (e.g.,
longitude and latitude) that correspond to the selected position on
the globe.
A database containing features of interest in the world, such as
country locations and names, capitals, and populations can be
prestored in RAM 144 relative to what ever coordinate system is
desired. Thus, when a user selects a point on the globe with the
stylus 116, microprocessor 142 determines the coordinates of that
position and causes the retrieval of information relative to that
position from the database to be presented to the user via, for
example, audio/video card 150 and speaker 154.
An alternative implementation of a world globe is illustrated in
FIG. 12 where conductive hemispheres 701 and 702, that are
electrically isolated from each other, provide the conductive
surfaces for the globe. Here hemispheres 701 and 702 are bonded
together with their edges in close proximity to each other with one
continuous, or several (e.g., three) rigid, non-conductive
spacer(s) affixed to the edges of each of hemispheres 701 and 702
to maintain the spaced-apart relationship and the electrical
isolation. Alternatively a non-conductive adhesive can be used
between the edges of hemispheres 701 and 702. Then vinyl skins 601
and 602 with the geographical information are mounted over the two
hemispheres as discussed above with respect to FIG. 11.
In this embodiment each hemisphere has three contact points affixed
to the inner edge of each, with hemisphere 701 having contact
points 710, 711 and 712, and hemisphere 702 having contact points
740, 741 and 742. Here, each hemisphere is shown with a small hole
through the polar cap to permit three insulated conductor cables
730 and 750, respectively, to pass through and have one end of each
insulated conductor connect to the three points on the inner edge
of the corresponding hemisphere. The other end of each of cables
730 and 750 in-turn are connected to a separate pair of switches in
signal generator 722. The upper hemisphere 701 has cable 730
connected to switches 770 and 771, while the lower hemisphere 702
has cable 750 connected to switches 772 and 773.
By comparing FIG. 12 with FIG. 4 it can be seen that while the
embodiment of FIG. 4 is for a single surface and FIG. 12 is for a
pair of surfaces, the only wiring change between the signal
generator of each embodiment is the addition of a second pair of
switches for the second surface for the embodiment of FIG. 12. The
remainder of the signal generator in each instance is the same with
amplifier 134 connected to both pair of switches 770 and 771, and
772 and 773. This is possible since there is only one stylus 116
and only one point on the globe can be selected at one time (i.e.,
the selected point can only be on one hemisphere at a time). Thus,
each hemisphere is treated as an independent location detection
surface.
To make a determination as to which of hemispheres 701 and 702 the
user has pointed stylus 116, microprocessor 142 is programmed to
make a series of measurements. First, as in many of the embodiments
discussed above, with stylus 116 pointing at the selected point on
one of the hemispheres, Signal.sub.FULL and Signal.sub.OFFSET are
measured for each hemisphere independently, and then the difference
between those measured values for each hemisphere (i.e.,
Signal.sub.FULL-701-Signal.sub.OFFSET-701, and
Signal.sub.FULL-702-Signal.sub.OFFSET-702) is determined and stored
in RAM 144. In short, Signal.sub.FULL is measured by applying the
60 KHz AC signal to all of the contact points on the surface, and
Signal.sub.OFFSET is measured will all of the corresponding switch
contacts in signal generator 722 for that surface open. Once those
difference values are determined, each of those difference values
is compared to a pre-selected threshold value. The threshold value
is determined empirically and typically are the value measured when
the stylus tip is within 0.10 inches from the surface. It is then
noted which, if any, of those difference values exceeds the
threshold and does so with the greatest margin with the
corresponding hemisphere being identified as the one to which
stylus 116 is being pointed.
Once the hemisphere of interest has been determined, microprocessor
142 then calculates the position selected by the sequence of
calculations outlined above with respect to FIG. 4. Thus, four
measurements, Signal.sub.FULL, signal.sub.OFFSET, Signal.sub.RAW-AB
and Signal.sub.RAW-AC are made on the identified hemisphere and the
values of Signal.sub.NORM-AB and Signal.sub.NORM-AC are calculated
as in equation 4 with those values defining a unique location on
that hemisphere.
The unique location provided by the values of Signal.sub.NORM-AB
and Signal.sub.NORM-AC, together with the results of the threshold
test to determine which hemisphere is of interest to the user, may
then be mapped into a location on the globe by means of a look-up
table for the selected hemisphere, if necessary, to obtain the
longitude and latitude of the point selected, in a standard globe
coordinate system. Then, as discussed with respect to FIG. 11,
microprocessor 142 can present the user with information relative
to the selected point from memory via audio video card 150 and
speaker 154, or by any other desired media (e.g., printer, monitor,
etc.) or combinations of media.
In addition to the user acting as an antenna and picking up
atmopsheric noise and signals as described in the Background of the
Invention above, there is another secondary effect that can
potentially occur if the user is not grounded with respect to the
system of the present invention. Since in the present invention the
surface to which the user points the probe, in the AC mode, is
radiating a different signal at different surface coordinates, a
portion of the user's hand, perhaps a finger or thumb, while
holding the probe at the desired location may pick-up a different
signal from another location spaced away from the location of
interest. In such a situation the antenna of the probe can
potentially be influenced by that secondary signal capacitively
coupled from the surface to the user and then coupled to the
antenna of the probe. That secondary signal could result in a
modified signal being received by the signal measurement stage 120.
That modified signal from the surface might then be processed to
identify a location other than the actual location to which the
user has pointed the probe tip.
For example, assume that the user has pointed the probe tip at
Chicago on the surface of a globe of the present invention. In
holding the probe tip at that location the user's thumb might
extend east and be close to Detroit while several of the user's
fingers extend west of Chicago toward Quincy, Ill. on the
Mississippi River. What indeed might happen is that a mix of
signals from the location to which the probe is pointed, together
with a signal from each finger and the thumb of the user could be
received by the signal measurement stage 120 as an averaged signal
resulting in the identification of the selected point as a location
between Detroit and Quincy, or even somewhere else on the surface
that is not even close to the location selected by the user,
perhaps Tokyo. Even worse, the signal received by the antenna of
the probe may be so complex as a result of all of the various
signals coupled to it that the signal measurement stage is unable
to identify any location that corresponds to the combined signal.
By inclusion of the mechanism to ground the user with respect to
the system, as discussed below, this potential problem, as well as
any influence created by atmospheric noise as discussed in the
Background of the Invention will be resolved by virtually
eliminating the other signals coupled to the antenna of the probe
from the user.
In each of the embodiments wherein a radiated AC signal is detected
by stylus 116 acting as an antenna (see FIGS. 4, 5, 6, 7, 11 and
12), stylus 116 is coupled to demodulator 144 with a shielded cable
118. Shielded cable 118 has been included in an effort to prevent
the length of cable 118 from acting as an antenna, in addition to
stylus 116, and picking-up signals some distance from and not
emanating from the corresponding surface of interest (i.e., 100,
400, 603, 701 or 702).
In prior art situations that require an antenna at the distal end
of a cable to use as a pointer in a system for locating the point
to which the stylus is pointed, the internal circuit configuration
of that stylus is very complex. FIG. 13 is a schematic
representation of such a stylus 916 used with the SEGA PICO
interactive story book toy. Note that even in an industry, the toy
industry in this example, where it is imperative to keep costs low
to not price a product out of an intended marketplace, a relatively
complex circuit has been used. The only saving grace, expense wise,
is that the product was probably assembled by low paid workings in
a third world country.
There are several differences that can be seen between this design
of stylus 916 and stylus 116 of the present invention. First, and
foremost is the active circuit design of the prior art that
includes two transistors, and specialty design IC, numerous
capacitors, inductors and resistors, a power switch and a
potentiometer requiring extensive assembly, as opposed to the
passive circuit design of the present invention. In addition to the
active circuit design there is the necessity of a formed metal
shield 920 at the antenna end of stylus 916 to exclude spurious
responses from interfering with the signal received from the
antenna. There is also a labor-intensive step of calibrating stylus
916 to the system with which it is to be used by means of
potentiometer 922. Another added cost item is the use of a four
wire cable 918 that is necessary to perform several functions; a
shield; a line to carry the received signal back to the main
chassis of the product; and two wires to carry power to stylus 920.
Finally there is the power switch 912 that needs to be depressed
during use to power stylus 916 which can present a problem if the
intended user is a child, as is the case with the SEGA product.
FIG. 14a illustrates one embodiment of the combination of stylus 11
and shielded cable 118. In this view the distal end of stylus 116
is shown in dotted outline to illustrate the end of cable 118 in
the interior of the distal end of stylus 116. In this embodiment
shielded cable 118 continues to near the extreme distal end of
stylus 116 with the shield intact and then a selected length of
center conductor 802' is exposed to act as the antenna. At the
proximate end of shielded cable 118, shield 800 is grounded in
signal measurement stage 120 and center conductor 802 is connected
to demodulator 144 to provide the input signal thereto. Thus, in
this embodiment an signal that impinges along the length of
shielded cable 118 will not contribute to the signal detected by
the antenna length of center conductor 802'. However, if the person
holding stylus 116 is inadvertently also acting as antenna and
radiates some of the received signal to center conductor 802', that
signal adds to the desired signal from the surface of interest
(e.g., surface 100). Then, depending on many factors including the
ability of demodulator 144 to reject unwanted signal frequencies
and noise, the position of stylus 116 that is ultimately determined
by the position location system of the present invention may not be
as accurate as desired.
A first embodiment of this aspect of the present invention is
illustrated in FIG. 14b. In this view the connections at the
proximate end of shielded cable 118 are the same as in FIG. 14a. At
the distal end of stylus 116 there are some changes that have been
made to effect the grounding of the user when holding stylus 116 to
eliminate the parallel antenna effect inadvertently created by the
user holding stylus 116 near center conductor/antenna 802'. Here it
can be seen that the distal end of shielded cable 118, in addition
to having center conductor 802' exposed, has a portion of shield
800' exposed. In addition, stylus 116 defines a hole 804
therethrough so that when a user holds stylus 116 a portion of one
of the user's fingers must extend through hole 804 and make contact
with shield 800', thus grounding the user.
A second embodiment of this aspect of the present invention is
illustrated in FIGS. 14c and 14d with FIG. 14d showing a cut-away
view of the distal end of stylus 116 to illustrate the internal
configuration of this embodiment. In these views the connections at
the proximate end of shielded cable 118 are the same as in FIGS.
14a and 14b. In FIG. 14c stylus 116 includes three portions: tip
810; main body 812; and conductive grip 806 that extends around
stylus 116 at the point of the user's grasp. In FIG. 14d a portion
of tip 810 and conductive grip 806 have been cutaway to illustrate
the internal structure of the distal end of stylus 116. The
internal arrangement is similar to that of FIG. 14b with the
exception of the length of shield 800' that has been exposed and
dressing of a pig-tail 808 of shield 800' back beneath conductive
grip 806. Thus, when the user grasps stylus 116 with conductive
grip 806 the user is grounded by the electrical interaction of
conductive grip 806 and shield 800' and pig-tail 808. Various
structures and materials could be used to conductive grip 806
varying from spring loaded metal rings to conductive polymers. One
such conductive polymer might be a carbon impregnated Kraton D-2104
polymer (e.g., RTP 2799X66439).
Additionally, it is well known by those skilled in the art how one
would store data relative to points on any surface that might be
employed with the present invention, as would be look-up tables to
convert one coordinate system for a surface to another coordinate
system.
While the discussion of the various embodiments of the present
invention presented above address a variety of shapes and
applications for the present invention, the shapes and applications
addressed are clearly not an exhaustive list. One could easily
extend such lists to many other shapes and applications and the
techniques discussed above could easily be extended to each of
them. Thus, the present invention is not limited solely to the
scope of what has been discussed above, but rather is only limited
by the scope of the claims appended hereto.
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