U.S. patent application number 10/158592 was filed with the patent office on 2003-05-22 for stylus input device utilizing a permanent magnet.
Invention is credited to Brian, Taylor, Glad, Paul, Gyori, Benjamin, Harney, Michael, Lee, Daniel, Woolley, Richard.
Application Number | 20030095115 10/158592 |
Document ID | / |
Family ID | 29709645 |
Filed Date | 2003-05-22 |
United States Patent
Application |
20030095115 |
Kind Code |
A1 |
Brian, Taylor ; et
al. |
May 22, 2003 |
Stylus input device utilizing a permanent magnet
Abstract
A stylus that operates utilizing magnetic fields, wherein a
permanent magnet is disposed within a passive stylus that is
detectable by a plurality of magnetic sensors that remove the
magnetic field of the stylus from the earth's relative magnetic
field to thereby obtain vectors that are used in a triangulation
equation to determine the location of the stylus in two or three
dimensions, depending upon the number of magnetic sensors that are
used, wherein one set of magnetic sensors can be used as a
reference for earth's magnetic field, and wherein each of the
magnetic sensors includes a polarizing coil to change direction of
sensitivity, a null coil and a flipping coil.
Inventors: |
Brian, Taylor; (Salt Lake
City, UT) ; Woolley, Richard; (Orem, UT) ;
Glad, Paul; (Taylorsville, UT) ; Lee, Daniel;
(Salt Lake City, UT) ; Harney, Michael; (Layton,
UT) ; Gyori, Benjamin; (Farmington, UT) |
Correspondence
Address: |
MORRISS, BATEMAN, O'BRYANT & COMPAGNI
136 SOUTH MAIN STREET
SUITE 700
SALT LAKE CITY
UT
84101
US
|
Family ID: |
29709645 |
Appl. No.: |
10/158592 |
Filed: |
May 29, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10158592 |
May 29, 2002 |
|
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|
09993394 |
Nov 22, 2001 |
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Current U.S.
Class: |
345/179 |
Current CPC
Class: |
G06F 3/03545 20130101;
G06F 3/0383 20130101; G06F 3/0346 20130101; G06F 3/0354 20130101;
G06F 3/046 20130101 |
Class at
Publication: |
345/179 |
International
Class: |
G09G 005/00 |
Claims
What is claimed is:
1. A passive stylus system for providing input to an electronic
appliance, wherein the passive stylus utilizes a permanent magnet
to provide location information to a magnetic sensor system, said
passive stylus comprising: a passive stylus including at least one
permanent magnet; a magnetic sensor system for detecting a location
of the at least one permanent magnet disposed within the passive
stylus, wherein the magnetic sensor system further comprises a
plurality of magnetic sensors that are capable of (1) detecting the
at least one permanent magnet, (2) determining a location of the at
least one permanent magnet relative to a reference point, and (3)
transmitting the location of the at least one permanent magnet; and
a display system, wherein the display system utilizes the location
of the at least one permanent magnet to display data on the display
system that represents movement of the passive stylus within a
field of operation.
Description
BACKGROUND
[0001] 1. Cross Reference
[0002] This application claims priority to a co-pending application
Ser. No. 09/993,394, filed Mar. 22, 2002.
[0003] 2. The Field of the Invention
[0004] This invention relates generally to input devices for
electronic information devices. More specifically, the present
invention provides a sensing system and a stylus that is operable
in two or three dimensions, and which is utilized to provide input
such as lines that represent movement of the stylus within a field
of operation, or cursor control for computers and portable
information appliances such as laptops, PC tablets, personal
digital assistants (PDAs) or other types of electronic appliances
such as mobile telephones.
[0005] 3. Background of the Invention
[0006] The state of the art of input devices utilizing a stylus is
generally characterized by digitizing tablets or a touchpad. A
digitizing tablet is generally a large surface that is used to
input data with a stylus that is coupled to the tablet or touchpad.
For example, a cable connects the stylus to the tablet, and
movement of the stylus is detected or tracked as it moves across
the surface of the tablet. The movement is typically portrayed as
lines on a display.
[0007] The basis of operation for most stylus-based tablets is
reliance upon electromagnetic sensors. A magnetic field is formed
by electric current that is flowing in a loop. The pen has a coil
that picks up this magnetic field and sends it back to a convertor
that determines the X and Y position from this data. This type of
pen generally requires a tether between the pen and a base device
to transfer the data, or the use of an active pen that is battery
powered and generates some type of signal that is detectable by the
touchpad.
[0008] It would therefore be an advantage over the prior art to
provide a pen or stylus-based system for data input or cursor
control which does not require a tethered stylus or an active pen.
It would also be advantageous if the stylus did not require an
internal power source to operate.
[0009] The prior art also describes using a stylus with personal
digital assistants (PDAs). When a stylus requires pressure in order
to be detectable, the writing surface of the PDA can be damaged. In
addition, the writing area for the stylus is typically very small.
It is also difficult to use a stylus when there is no visual
feedback or "inking trail" to show the writer what has been
written. Inking can also be difficult if there is a delay between
stylus movement and the appearance on a display screen of what is
being written.
[0010] Accordingly, it would be an advantage over the prior art to
provide an off-screen inking surface to prevent damage to a PDA
screen. It would also be an advantage to provide a larger writing
surface for the PDA, as well as visual feedback that is rapid.
[0011] The prior art also fails to teach any type of stylus which
can operate without making contact with a surface that can detect
the presence of the stylus. In other words, the surface being
written on is some surface that is capable of detecting the stylus.
Accordingly, it would be an advantage to be able to detect and
track movement of a stylus on a surface, where the surface is not a
stylus detection surface.
[0012] The prior art also teaches that some type of sensing surface
must be used with a stylus. Accordingly, it would be an advantage
over the prior art to provide a stylus which does not require any
sensing surface in order to be detectable. It would also be an
advantage to therefore enable a stylus to be detectable as it moves
within three dimensions.
[0013] Another aspect to be addressed is the ability to turn
writing on and off. Typically, this type of function has required a
sensitive surface, possibly a tether from the pen to another
device, or an active pen. Accordingly, it would be an advantage
over the prior art to provide a stylus that can be actuated to turn
on and off writing on an associated display, where the stylus is a
passive device that does not write on a special sensing surface,
and is not physically tethered to another device.
[0014] A final aspect of the invention is the ability to implement
a stylus for use in a very small area. Consider the mobile
telephone user that wants to input and email message and send it.
It is a tedious and time consuming task with state of the art input
options on cell phones. It would be an advantage over the prior art
to provide a very small keyboard that is actuated by the stylus so
that it can be used in mobile situations, and with relatively small
devices.
SUMMARY OF INVENTION
[0015] It is an object of the present invention to provide a
passive stylus that operates in two or three dimensions.
[0016] It is another object to provide a passive stylus that only
requires a permanent magnet disposed therein.
[0017] It is another object to provide a passive stylus that can
provide signals indicative of touchdown and pressure.
[0018] It is another object to provide a passive stylus that can
provide "start" and "stop" writing signals to a display device,
wherein the signals are actuated by normal writing movements and
actions.
[0019] It is another object to provide a passive stylus that can
include an inking cartridge that provides real inking of the stylus
on paper when used off-screen.
[0020] It is another object to provide a passive stylus that can
operate in three dimensions by providing a sufficient number of
sensors to provide a three dimensional detection volume.
[0021] It is another object to provide a passive stylus that
increases magnetic field strength to thereby function as an
indicator of a changing signal.
[0022] It is another object to provide a passive stylus that
rotates a permanent magnet stored within a pen body to thereby
change polarity and provide a digital "on" and "off" signal.
[0023] It is another object to provide a passive stylus that can
detect rotation of the stylus.
[0024] It is another object to provide a passive stylus that can be
turned over to perform an erasing function on a display device.
[0025] It is another object to provide a passive stylus that can be
incorporated into a mechanical pencil as well as with an inking
cartridge.
[0026] It is another object to provide a passive stylus that can be
utilized with a small keypad, wherein the keypad detects contact of
the passive stylus with keys on the keypad.
[0027] It is another object to provide an active stylus that
provides a signal to a display device to thereby provide pressure
information so as to be able to draw with varying degrees of
shading.
[0028] In a preferred embodiment, the present invention is a stylus
that operates utilizing magnetic fields, wherein a permanent magnet
is disposed within a passive stylus that is detectable by a
plurality of magnetic sensors that subtract the magnetic field of
the stylus from the earth's relative magnetic field to obtain
vectors that are used in a triangulation equation to determine the
location of the stylus within a writing area.
[0029] In a first aspect of the invention, each pair of magnetic
sensors provides a vector, wherein two pairs provides vector
information for two dimensions, and three pairs provide vector
information for three dimensions.
[0030] In a second aspect of the invention, the three pairs of
magnetic sensors are disposed in three of four corners in the plane
of a virtual rectangle.
[0031] In a third aspect of the invention, one of the three pairs
of magnetic sensors functions as a reference for earth's magnetic
field.
[0032] In a fourth aspect of the invention, each of the magnetic
sensors includes a polarizing coil to change direction of
sensitivity, a null coil and a flipping coil.
[0033] In a fifth aspect of the invention, a "start" and "stop"
signal generated by the passive stylus are detectable by the
magnetic sensors by rapid movement of a permanent magnet within the
stylus body.
[0034] These and other objects, features, advantages and
alternative aspects of the present invention will become apparent
to those skilled in the art from a consideration of the following
detailed description taken in combination with the accompanying
drawings.
DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 is a top elevational view of magnetic field sensors
set out in sets to provide an area of sensitivity that is two
dimensional when two sets are used, and three dimensional when
three sets are used.
[0036] FIG. 2A is an example of an area of sensitivity of the
present invention.
[0037] FIG. 2B is an example of another area of sensitivity of the
present invention.
[0038] FIG. 2C is an example of another area of sensitivity of the
present invention.
[0039] FIG. 3 is a profile cut-away view of a stylus.
[0040] FIG. 4 is circuit diagram of a magnetic field sensor.
[0041] FIG. 5 is schematic diagram of components of the present
invention.
[0042] FIG. 6 is a profile cut-away view of two views of a stylus
showing an alternative embodiment.
[0043] FIG. 7 is a profile cut-away view of an alternative
embodiment of a stylus.
[0044] FIG. 8 is a profile cut-away view of an alternative
embodiment of a stylus.
[0045] FIG. 9 is a close-up view of the drive coils of FIG. 9.
[0046] FIG. 10 is a profile cut-away view of an alternative
embodiment of a stylus.
[0047] FIG. 11 is a cross-sectional profile view of another
embodiment of a passive stylus.
[0048] FIG. 12 is a cross-sectional profile view of the passive
stylus of FIG. 11.
[0049] FIG. 13 is a close-up cross-sectional view of the passive
stylus of FIG. 11, with the stylus actuated to write on a
display.
[0050] FIG. 14 is a block circuit diagram that can be used to
determine the degree of pressure being applied by a stylus tip on a
writing surface.
[0051] FIG. 15 is a circuit diagram of a transmitter utilized in an
active stylus that is performing pressure sensing described in FIG.
14.
[0052] FIG. 16 is a see-through view of the components in an
improve tilt stack pen embodiment.
[0053] FIG. 17A is a top view of three round magnets.
[0054] FIG. 17B is a profile view of the magnets in FIG. 16A.
[0055] FIG. 17C is a profile view of the magnets being rotated.
[0056] FIG. 17D is a profile view of the magnets being rotated.
[0057] FIG. 17E is a profile view of the magnets having completed a
rotation of 180 degrees.
[0058] FIG. 18 is a see-through perspective view of an assembled
stylus using the magnets of FIG. 17.
[0059] FIG. 19 is a perspective view of half of the housing for the
three magnets.
[0060] FIG. 20 is a perspective view of a lever arm that is pushed
by the pen tip, causing the first magnet to rotate.
[0061] FIG. 21 is a perspective view of a holder for the first
magnet.
[0062] FIG. 22 a first circuit diagram that illustrates the layout
of a sensor system that can be utilized in the present
invention.
[0063] FIG. 23 a first circuit diagram that illustrates the layout
of a sensor system that can be utilized in the present
invention.
[0064] FIG. 24 a first circuit diagram that illustrates the layout
of a sensor system that can be utilized in the present
invention.
[0065] FIG. 25 a first circuit diagram that illustrates the layout
of a sensor system that can be utilized in the present
invention.
DETAILED DESCRIPTION
[0066] Reference will now be made to the drawings in which the
various elements of the present invention will be given numerical
designations and in which the invention will be discussed so as to
enable one skilled in the art to make and use the invention. It is
to be understood that the following description is only exemplary
of the principles of the present invention, and should not be
viewed as narrowing the claims which follow.
[0067] The presently preferred embodiment of the invention is a
plurality of magnetic sensors that are capable of determining a
location and orientation of a passive stylus that generates a
magnetic field without using a power source. In the presently
preferred embodiment, the plurality of magnetic sensors are
directionally sensitive devices. For example, the magnetic sensors
can be a magnetic field sensor such as one sold having part number
KMZ51 from Philips Semiconductors. However, any similar magnetic
sensor can be substituted and create the same results. It is noted
that the magnetic file sensor KMZ51 is relatively inexpensive, and
is thus desirable for the applications herein.
[0068] In the presently preferred embodiment, the magnetic field
sensors are disposed in pairs, stacked one on top of the other or
arranged side-by-side, and separated by a non-conductive material
such as PC board when they are stacked. Each pair of magnetic field
sensors provides a vector to the stylus. Thus, two pairs of
magnetic field sensors are sufficient to provide two vectors, and
thus determine the location of the stylus in two dimensions.
[0069] In an alternative embodiment, a third magnetic field sensor
is added to each pair, thus making two groups of three magnetic
field sensors each. The third magnetic field sensor provides
up-down sensitivity to give the configuration three-dimensional
sensitivity.
[0070] It is noted that in the preferred embodiment, three magnetic
field sensor sets will be arranged so as to have a straight line
between them. For example, FIG. 1 shows a first magnetic sensor set
10, and a second magnetic sensor set 12, each set comprised of
three magnetic field sensors 8. The directional sensitivity of each
of the magnetic field sensors 8 is identified by the arrows 14.
Note that the dot representing an arrow 14 in each set 10, 12
indicates that sensitivity is directed out of the page. The
approximate area of sensitivity is identified by dotted line
16.
[0071] Unfortunately, a stylus cannot be detected when it is
disposed along the straight line 18 that lies directly between the
first and second magnetic sensor sets 10, 12. To be detectable, it
is preferable in an alternative embodiment to include a third set
20 of magnetic field sensors. This third set 20 makes detection of
a stylus in three dimensions much simpler, and also eliminates the
"blind spot" represented by line 18.
[0072] It is noted that in the alternative embodiment of three sets
10, 12, 20 of three magnetic field sensors each, the sets are
preferably arranged as three corners of a square or rectangle. This
area is represented by area 16.
[0073] It is important to recognize that the area of sensitivity
can be varied according to the desired placement of the magnetic
field sensor sets. This means that the area of sensitivity is a
relative area that is based upon the needs of the application. For
example, if the application is for a cursor control input device,
then the area of sensitivity 22 could be as shown in FIG. 2A
relative to three magnetic field sensor sets 24, or as in FIG. 2B
or 2C. What is important to realize is that the area of sensitivity
is very approximate, and will extend beyond the sharply defined
lines of the figures. However, it is the practical realization that
some arbitrarily defined area must be selected to give a user a
feel for the area to operate in to write, draw, or cause cursor
movement in a defined area on a computer screen when that is the
application of a stylus and sensors.
[0074] FIG. 3 illustrates that the presently preferred stylus 30 is
a generally pen-like object, having a permanent magnet 32 disposed
near the tip 34 thereof. The stylus 30 preferably has a magnetic
field whose strength is approximately equal to that of the earth's
magnetic field.
[0075] In order to understand operation of the stylus 30, it must
be considered in context with an understanding of the operation of
the magnetic field sensors. Each magnetic field sensor of the
preferred embodiment includes a polarizing coil. The polarizing
coil allows a user to swap the direction in which a magnetic field
sensor is sensitive. This feature enables a user to cancel out
offsets, drift, etc. Generally, a user will only swap directions in
order to occasionally "zero-out" the magnetic field sensor, but
will generally not perform this operation before every measurement.
The magnetic field sensors generally have good bandwidth, from
about 1 volt DC to about 1 MHZ.
[0076] As shown in FIG. 4, the magnetic field sensor is essentially
a bridge 40, which also includes a nulling coil 42 and a flipping
coil 44. In order to get a good dynamic range, it is best to avoid
flipping before each measurement because as the magnetic field
grows higher and higher, it starts saturating the magnetic field
sensor. At that point, the magnetic field sensor begins to lose
linearity.
[0077] Accordingly, the preferred magnetic field sensor includes
the nulling coil 42. The output of a differential amplifier 46 is
fed back into the nulling coil 42. This allows obtaining a "zero"
magnetic field on the magnetic field sensor, to thereby increase
gain immensely while maintaining linearity.
[0078] It is important to realize that if the sensor system is to
be accurate, the sensor system should not try to maintain a linear
circuit. Instead, the user should select a null point, and then
feed a linear DAC into it to maintain a null point. That provides
the sensor system with a tremendous dynamic range. By using the
nulling coil 42, it is possible to maintain linearity and better
range.
[0079] It is also noted that the range of the magnetic field sensor
is a function of several factors. An analog-to-digital (A/D)
converter used in the presently preferred embodiment is 14 bits.
This A/D convertor is sufficient to obtain an area of sensitivity
that is approximately 8.5 by 11 inches, or a regular sheet of
paper. This area of sensitivity is obtained when the sets of
magnetic fields sensors are separated by approximately 4 or 5
inches. Using a 16 bit A/D converter would obtain an even greater
range, and thus provide a larger area of sensitivity.
[0080] Assume that a sensor system is operated in the configuration
as shown in FIG. 1, with three sets 10, 12, 20 of three magnetic
field sensors. When the sensor system is first turned on, the
system will be assumed to be stationary and coupled to a desktop
computer or other stationary device. The first action is to
calibrate the sensor system so that it can determine its position
relative to the earth's magnetic field. This information is
preferably stored in a driver, RAM or other memory device. This
information is used for sensitivity and correction factors. Each
magnetic field sensor set 10, 12, 20 provides a vector to a stylus
that is disposed within the identified area of sensitivity 16. It
is important to determine an absolute vector, then subtract out a
calibration vector.
[0081] If all of the magnetic field sensor sets 10, 12, 20 give
vectors that are parallel to each other, then it is assumed that
there is no magnet within the area of sensitivity 16. Because the
earth's magnetic field is also known, that is also subtracted out
to thereby obtain a null space within the sensor system's field of
sensitivity.
[0082] When the stylus is introduced into the null space (field of
sensitivity), the threshold for the presence of the stylus is
simply a determination that the vectors are no longer parallel. By
subtracting out the magnetic field of the permanent magnet disposed
within the stylus from the earth's relative magnetic field, the
user obtains two vectors that point to the stylus. By
triangulation, the location of the stylus is then determined.
[0083] FIG. 5 is a schematic diagram of the presently preferred
sensor system. As shown, a MUX 50 goes to all the magnetic field
sensors 8 of the three magnetic field sensor sets 10, 12, 20. The
signal from the MUX 50 goes to an A/D converter 52, which is then
passed to a CPU 54. The presently preferred embodiment utilizes an
A/D converter card disposed in a slot of a personal computer. The
input to the A/D converter 52 is accessed by a program executing on
the personal computer to process a triangulation formula to thereby
provide stylus position determination. A good example of an A/D
converter with adequate properties is an 8051 processor.
[0084] Some details on triangulation methods are useful to an
understanding of implementing the present invention. Triangulation
is usually done in one of two ways, neither of which is adequate
for the present invention. The first method will not work because
when either an x or y sensor has a value close to zero, it becomes
for difficult to determine accurate coordinates. Furthermore, if
the user is inclining the stylus, incorrect coordinates are again
given.
[0085] The second method requires an alternating signal from the
source of a fixed frequency and uses two sensors at a fixed
distance from each other. This method is not useful for tracking
the stylus of the present invention because the magnetic sensors
look at non-alternating magnetic fields and frequency information
is not available.
[0086] Thus, the present invention looks to the
circular-triangulation method. This method uses a knowledge of how
magnetic fields drop off in distance. As a magnetic source moves
away from it's sensor, the sensor records a value that is
proportional to the inverse cube of the distance between the source
and sensor. This information enables a hypothetical circle to be
drawn around the sensor at a radius that is calculated from the
sensor value and the inverse-cube formula. This circle projects all
the possible points the stylus can be on.
[0087] A second sensor at a fixed distance away projects another
circle of a different radius. The circles intersect in at most two
points, with one of the points being behind the sensors in a
non-drawing area, which means that this point can be eliminated as
a solution. The remaining point's coordinates are thus calculated
by solving for the intersection of the two circles and using the
positive solution as the coordinates of the stylus.
[0088] This method has the advantage of only requiring two x or two
y sensors separated at a distance, as opposed to the four sensors
required for the angle methods described above.
[0089] Advantageously, changes in the pen's angle with respect to
the writing surface do not influence the calculation of the stylus'
coordinates if two x and y sensors are used at each sensing
location. A decrease in x from one set of sensors will be
compensated for by an increase in the corresponding y from that
set. The magnitude between the two sensors can be determined as the
square root of (x{circumflex over (2)}+y{circumflex over (2)}).
This eliminates angle disturbances because of low x and y values,
and eliminates the effects of pen angle with respect to a writing
surface.
[0090] This method also allows for increased distance because of
the use of raw sensor magnitudes instead of angles calculated from
these magnitudes. The same concept can be applied to
electromagnetic fields, which lose energy in their fields by the
inverse of the distance-squared, as opposed to inverse of
distance-cubed for magnetic dipoles. Spheres can be drawn from each
antenna to the source and the solution of the source's coordinates
is found be solving for the intersection of the spheres. By
triangulating electromagnetic sources with this method, dependence
on the angle that the object is facing with respect to the antennas
of the magnetic sensors can be eliminated.
[0091] The stylus 30 used with the presently preferred and
alternative embodiments has been described as a passive device with
a permanent magnet 32 disposed therein. However, the present
invention also teaches alternative designs for the stylus that
include modifications to the passive configuration, and the
addition of active elements that enable the user to do more than
just determine the location thereof.
[0092] For example, to enhance the passive stylus, it can be
advantageous to alter the strength of the magnetic field generated
by the stylus. If this change in strength can be detected, the
stylus is able to provide more input information to a receiving
device. An embodiment that provides a changing magnetic field
relies on applying pressure to a stylus tip.
[0093] In FIG. 6, the increased pressure pushes a stylus tip 60
inwards until the first permanent magnet 62 makes contacts with a
second permanent magnet 64. The magnetic field of the combined
permanent magnets 62, 64 is larger than the individual magnets, and
this increase in magnetic field strength is detectable. Releasing
pressure on the stylus tip 60 enables a spring 66 to push the
permanent magnets 62, 64 apart, returning the magnetic field
strength to an initial state. This is all done without the use of a
power source.
[0094] In an alternative embodiment, it is possible to introduce
active elements that go beyond the basic stylus design above. For
example, FIG. 7 is an alternative embodiment of an active stylus
70. In this embodiment, the inner detail of the stylus 70 is
illustrated to show that a permanent magnet 72 is oriented in a
first orientation when at rest. Shown here, the south pole of the
magnet is toward the stylus tip. When pressure is applied to the
stylus tip 74, a rod 76 pushes on the permanent magnet 72, causing
it to rotate. The rotation reverses the polarity of the permanent
magnet 72, causing the south pole to be on the opposite side, away
from the stylus tip 74. Thus, the stylus again provides a signal to
an input device. The signal could be a digital 1 changing to a
digital 0, or vice versa. The spring 78 pushes the rod 76 back
towards the stylus tip 74 and thus causes the permanent magnet to
rotate back to an original orientation when pressure is removed
from the stylus tip.
[0095] Generally, a stylus does not need to provide "Z" to an input
device. However, "Z" orientation is useful when using an electronic
paintbrush because it provides an infinite range of pressure
values.
[0096] The next alternative embodiment of an active stylus is shown
in FIG. 8. The stylus 80 is shown having a coil configuration 82
near the tip 84 of the stylus. The coil configuration 82 comprises
three coils 86, 88, 90 disposed about a sphere 92 as shown in
close-up in FIG. 9. The coils 86, 88, 90 are drive coils having
three different frequencies, from 250 KHz to 1 MHZ. Each of the
magnetic field sensor sets would be tuned to be sensitive to a
different drive coil. In this way, the sensor system would not only
be able to track the location of each drive coil in three
dimensions, but it would also enable the detection of rotation. The
only drawback to this embodiment is that the drive coils would
require power to drive them at the required frequencies. However,
the tradeoff is obtaining not only XYZ position, but pitch, roll,
and yaw. Thus, the sensor system would have six (6) degrees of
freedom. It is noted that it would be possible to transmit the
signals from each coil 86, 88, 90 to another device, such as a
personal digital assistant (PDA), because each coil functions as an
antenna of its own signal, thus providing a wireless
connection.
[0097] Accordingly, the present invention enables the use of static
magnetic fields instead of dynamic fields. This fact provides a way
to use permanent magnets that do not require power when using the
basic features of the invention, and only requires power when
trying to do provide more features to the user.
[0098] FIG. 10 is provided as an illustration of another means for
increasing magnetic field strength. The stylus tip 100 is coupled
to a permanent magnet 102 and to a cylindrical coil 104 (shown in
cross-section). When the spring 106 is compressed by the tip 100
until making contact with another cylindrical coil 108, the
magnetic field strength is increased.
[0099] FIG. 11 is a cross-sectional profile view of an alternative
embodiment of a passive stylus 110 in an exploded view. This
passive stylus 110 provides "start" and "stop" signals to the
magnetic sensors through a novel use of a tilting magnet. The
components of the passive stylus 110 are a plastic housing 112 or
other material that will not interfere with magnetic fields. The
housing 112 has a plastic or ferrous housing cap 114 that can be
removed in order to replace an ink cartridge 116. The ink cartridge
116 includes an interference fit threaded ferrous component 118
with the housing 112. The threaded ferrous component 118 is
threaded in order to couple the plastic housing cap 114 to the
plastic housing 112. A spring 120 is disposed between the
interference fit threaded ferrous component 118 and the inside of
the plastic housing cap 114. Above the interference fit 118 are
disposed circular ceramic magnets 122 that have a hole through the
middle for the ink cartridge 116 to pass through. The number of
ceramic magnets 122 depends upon the sensitivity of the magnet
sensors that are being used to detect the location of the ceramic
magnets. More or stronger magnets will improve detection of the
passive stylus 110.
[0100] On the top of the ink cartridge 116 is disposed a plastic
actuator 124. This plastic actuator is used to more uniformly push
on the rare earth magnet 126. Whereas the top of the ink cartridge
might be dented or otherwise made irregular, the plastic actuator
124 presents a consistent interface to the magnet 126. Between the
plastic actuator 124 and the rare earth magnet 126 are disposed a
ceramic trigger magnet 128, and a ferrous washer 130 with pitched
ID. The last two components are a ferrous cylinder 132 that extends
along most of the length of the plastic housing 112, and a plastic
housing cap 134 that is screwed into the plastic housing 112.
[0101] FIG. 12 is a cross-sectional profile view of the passive
stylus 110 shown in FIG. 11, but put together in an operable
mode.
[0102] Operation of the passive stylus 110 is novel in its system
for enabling the magnetic sensors to determine when a user wants to
begin writing on a display, and to stop writing. A user will begin
to write with the passive stylus 110. After gentle and nominal
pressure is applied, as when a person presses down on paper to
write with ink, the passive stylus 110 actuates the "start" signal,
indicating that an associated display device is to begin "inking"
or writing on a display.
[0103] This "start" signal is generated by the pressure on the ink
cartridge 116. This pressure causes the ink cartridge 116 to move
approximately {fraction (1/16)} to 1/8 of an inch upwards into the
plastic housing 112. The ink cartridge 116 is coupled to the
plastic actuator 124, which is turn moves through a whole in the
ceramic trigger magnet 128, and then partially into the pitched ID
of the ferrous washer 130. Movement of the ink cartridge 116 is
stopped because of the plastic actuator 124 that cannot move past
the ceramic trigger magnet 128 when a lower shelf 136 meets the
bottom 138 of the ceramic trigger magnet.
[0104] FIG. 13 is provided as a close-up view of how the
above-described process will appear when the user is writing. The
figure shows the plastic housing 112, the rare earth magnet 126
that is now in an upright position, the ferrous washer 130 with the
pitched ID, the ceramic trigger magnet 128, and the plastic
actuator 124. A tip 140 of the plastic actuator 126 is pushing up
on a bottom surface of the magnet 126. The magnet 126 is now
resting on a small lip 142 of the ferrous washer 130.
[0105] It may not be obvious why tipping the rare earth magnet 126
from an inclined position to an upright position will provide a
"start" signal. However, the magnetic sensors that are tracking the
position of the passive stylus 110 are also detecting the rare
earth magnet 126. When the rare earth magnet 126 is at rest in the
inclined position shown in FIGS. 11 and 12, the magnet 126 is
actually being held in place by magnetic attraction to the ferrous
washer 130. The force required to break the rare earth magnet 126
free is relatively small, approximately 80 to 100 grams of force.
However, when the rare earth magnet 126 breaks free, it accelerates
rapidly and moves to the upright position to which it is also
magnetically attracted on the lip 142 of the ferrous washer 130.
Even though the distance moved by the rare earth magnet 126 is very
small, it is very detectable. Fortunately, the movement is also
very rapid, which is the key to distinguishing this movement from
ordinary movement of the passive stylus 110 when writing. This
movement is so fast that it will not be accidentally caused through
normal use of the stylus.
[0106] Likewise, the release of pressure off the ink cartridge 116
will enable the stronger attraction of the rare earth magnet 126 to
be in the inclined position to occur. The amount of force is
approximately 45 to 50 grams, but can be varied as desired, as can
the actuation force. The rare earth magnet is trying to be in the
inclined position because the lip 142 is small as compared to the
broader surface of the pitched ID of the ferrous washer 130.
[0107] The movement of the ink cartridge 116 that is necessary to
send the start and stop signals is barely detectable, enabling the
passive stylus 110 to function well as a normal inking pen. The
movement of the rare earth magnet as it snaps into an actuated
upright position, and then snaps back to the released inclined
position does not interfere with use of the stylus. Furthermore,
various methods of dampening any outward indication of this motion
is possible by modifying the plastic housing 112.
[0108] Another aspect of the present invention is to provide
pressure sensing utilizing an active stylus. Varying degrees of
pressure applied to the stylus tip are difficult to detect with the
magnetic sensors. Accordingly, a resistive rubber is used to detect
pressure. The rubber changes resistance for small changes in
compression. The force of the stylus' ink cartridge on a writing
surface is used to compress the rubber against the case of the
stylus. This change in resistance is used to change the frequency
of an RC oscillator. This information is then sent to a frequency
modulated transmitter. The data is transmitted to a receiver on a
controller board. A microcontroller on the controller board
determines the frequency of the signal, or the change from a given
frequency, to thereby determine the degree of pressure that is
being applied to the stylus tip on a writing surface. Ultimately,
the pressure data can be displayed in two different ways. Either
the width of line being drawn can be varied, or an inking gray
scale is displayed on a computer display.
[0109] The resistive rubber acting as a pressure transducer for the
present invention is operating in the circuit described in FIG. 14.
FIG. 14 shows the resistive rubber 150 coupled to an RC circuit
152. For example, a 555 chip can receive inputs from the resistive
rubber 150. Output from the RC circuit 152 is sent to an RF
modulator 154 for transmission via antenna 156. Output from the RF
modulator 154 is utilized to determine the degree of compression of
the resistive rubber 150, and thus the degree to which pressure is
being applied. A conversion table can be used to relate the amount
of pressure being applied to a value for the width of a line being
drawn, or the shade of gray that should be applied.
[0110] A resistive rubber that can be used in the present invention
is sold under the brand name of ZOFLEX ZF40(.TM.).
[0111] FIG. 15 is provided as an example of a circuit that can be
utilized to transmit the pressure data from the stylus to the
controller board. This is a sample only, and should not be
considered limiting. However, it is noted that this type of
transmitter can be disposed within the space limitations of a
stylus.
[0112] It is noted that the present invention has many
applications, especially with mobile appliances such as cell
phones, digital phones, PDA's and other similar electronic
appliances that need simple yet efficient ways of inputting data to
an electronic device.
[0113] Another aspect of the invention is the ability to detect
very small and precise positioning of the passive stylus. This
enables the passive stylus to be used in a very small area that is
defined as a keyboard. The keys of the keyboard are actuated by the
small tip of the passive stylus. For example, consider a small
keyboard that is coupled to a mobile telephone. The keyboard
contains the magnetic sensors of the present invention, and can
determine what key is being touched by a tip of the passive stylus.
This detection ability can enable rapid input of text to a mobile
phone, for example, to send email messages.
[0114] By providing the keyboard with its own memory, the keyboard
could also be provided with a small display screen, such as one
line of text on an LCD display. The keyboard could then even be
used when not attached to the mobile telephone, for example, to
take notes during a call. Afterward when the keyboard is attached
to the mobile telephone, the memory of the keyboard is uploaded or
synchronized with the memory in the mobile telephone, so that a
user can input data that has been stored by the keyboard. For
example, a user can take notes on the keyboard while talking on the
mobile telephone. After the conversation is over, the user attaches
the keyboard to the mobile telephone, and uploads whatever data was
typed into the keyboard memory into the memory of the mobile
telephone. Typically, this action is performed in order to send the
data in an email message from the mobile telephone.
[0115] However, the keyboard does not have to be used apart from
the mobile telephone. The keyboard can be used when attached to the
mobile telephone. The user may be able to take advantage of the
larger display of the mobile telephone, or just continue to use the
built-in LCD display of the keyboard. This may depend on the
visibility of the LCD display when the keyboard is attached to the
mobile telephone.
[0116] Two additional stylus embodiments have been developed which
are an improvement over the previous embodiments. The first new
stylus embodiment has much in common with the earlier designs.
Before describing the embodiment shown in FIG. 16, it is useful to
understand that the algorithms being used in a two sensor system
work best when there is a single magnetic dipole being seen in the
stylus. But a single magnet creates weaker magnetic field lines.
Thus, a balance has been reached, where a small stack of magnets
170 is used. The stack of magnets 170 is large enough so that their
signal can be tracked over a larger area, but small enough that the
critical tilting of the stack of magnets 170 is still detectable
within the stylus.
[0117] Another factor in the design is the diameter of the stylus
body 172. If the stylus body 172 has a large diameter, the stack of
magnets 170 can tilt further within the stylus, which is more
detectable by the sensor system. But a large stylus diameter 174 is
not desired because it can become too large to feel comfortable in
the average user's hand. Accordingly, the stylus diameter 174 must
be balanced against the height of the stack of magnets 170, which
must be balanced against the need for a detectable tilt of the
stack of magnets when changing from a non-inking mode, to an inking
mode, and back again. Furthermore, the stack of magnets 170 has
been moved as close as possible to the inking end 176 of the stylus
172. This is helpful to the sensor system.
[0118] The next embodiment is a substantial departure from the
tilting stack of magnets shown in the previous embodiment. In this
new embodiment shown in a top view in FIG. 17A, three magnets 200,
202, 204 are separated some distance that allows them to rotate
without touching each other, but to still be close enough to have a
strong magnetic attraction. The magnets 200, 202, 204 are disks
having the same height and diameter. Height and diameter can be
varied, even within the same pen if the mechanical structure within
the stylus compensates. To operate properly, they are also aligned
coaxially along common axis 206. Coaxial alignment is critical for
the algorithms currently in use because the magnets will appear as
a single magnetic dipole.
[0119] This new embodiment operates on the principle of using
magnetic attraction between magnets to enable the on/off inking and
non-inking signal from a stylus. Consider three magnets which are
coaxially aligned, but are spaced apart. Three magnets are used to
increase the strength of the magnetic field lines of the stylus.
However, two magnets could be used, as well as more than three. The
magnets 200, 202, 204 are free to rotate along parallel axes 208,
210, 212.
[0120] FIG. 17B is a profile view of the same set of magnets as
shown in FIG. 17A, but the profile view is necessary to see the
rotation of the magnets.
[0121] FIG. 17C is a profile view of the magnets 200, 202, 204,
where the first magnet 200 is beginning to be rotated. If rotated
slowly, it is easy to see that the second magnet 202 begins to
rotate in a somewhat delayed fashion because of the inescapable
effects of friction between a magnet casing or holder, and the
physical pins being used as the axis along which the magnet is
turning. The third magnet 204 rotates in a more pronounced delayed
manner.
[0122] FIG. 17D shows that when the first magnet 200 is turned
(rotated about an axis) some amount greater than 90 degrees, the
first magnet 200 will then rapidly continue the movement, if
unimpeded, until it has turned a full 180 degrees because of the
attraction to the second magnet 202 which is also being caused to
turn. Thus, by turning the first magnet 200, the second magnet 202
also turns in order to maintain attraction between the North and
South poles of the magnets 200, 202. The third magnet 204 will
likewise be caused to turn because of the rotation of the second
magnet 202. If the first magnet 200 is turned very rapidly, the
second and third magnets 202, 204 also turn very quickly so as to
be virtually simultaneous. Slowly turning the first magnet 200
results in a delay down the line of magnets. Yet, once the first
magnet 200 is turned beyond 90 degrees, it rapidly snaps over if
movement is unimpeded, along with the second and third magnets 202,
204. FIG. 17E shows that the magnets 200, 202, 204 have completed
rotation 180 degrees, and form a single magnetic dipole.
[0123] This embodiment requires all of the magnets to operate about
parallel axes 206, 208, 210. The space between the magnets must be
large enough to allow free rotation, and small enough to enable
strong attraction between the magnets that results in the rapid
"snapping" rotation. It is this rapid rotation that is recognized
by the magnetic sensors as a signal for a change of state between
inking and non-inking. It is also an advantage that the magnets are
changing polarity by 180 degrees. The change in magnetic field
lines is more recognizable to the sensors than the change in the
field lines from a stack of tilting magnets.
[0124] The reason for trying to make the motion of the magnets
rapid is because it desirable to have a signal that is recognizable
to the sensor system and virtually instantaneous so that the on/off
inking action of the stylus can occur without any visible delays.
This is one of the advantages of using an active instead of a
passive stylus. The active stylus can transmit a signal, such as an
RF signal, that travels virtual instantaneously to a sensor system,
and inking can be turned on an off rapidly. But a passive stylus
must try to make its inking signal as rapid as possible without
using power from an electrical source. Of course, the passive
stylus does not need to have a battery replaced.
[0125] FIG. 18 is a see-through profile view of the assembled
components of this stylus embodiment to be described
hereinafter.
[0126] FIG. 19 is a perspective view of one half of the housing 220
for the magnets within a stylus body. The view illustrates the
holes 222, 224, 226 for the axis pins of the magnets 200, 202, 204.
The other half of the housing would have the other corresponding
holes for the other axis pins.
[0127] A mechanism must be in place to push on the first magnet 200
so that it is caused to rotate. In this embodiment, pushing down on
a stylus tip (not shown) will cause a lever arm to push against a
magnet casing (FIG. 21). FIG. 20 shows the lever arm 230 that is
pushed upward in the stylus to cause the casing of the first magnet
200 to rotate. In order for the first magnet 200 to rotate back 180
degrees when the user is no longer pushing on the stylus tip and
therefore does not want to ink, the lever arm 230 compresses a
spring (not shown) within the stylus body. When the user removes
the stylus tip from a writing surface, the spring pushes the lever
arm down toward the stylus tip, which pulls the casing of the first
magnet 200 and causes the first magnet to rotate. Back to its
original position.
[0128] FIG. 21 is a perspective view of a magnet casing 240 in
which the first magnet 200 is disposed. The two axis pins 242, 244
about which the first magnet 200 rotates within the casing 240 are
shown. The cut-away 246 in the casing 240 enables the lever arm 230
to push on the casing and cause it to rotate. The casings for the
second and third magnets 202, 204 do not have the cut-away 246.
They simply rotate about their axis pins.
[0129] Some comments about algorithms used by the sensor system to
detect the stylus are useful to discuss in more detail to enable
those skilled in the art to practice the invention. Several
algorithms have been implemented, each with its advantages and
disadvantages.
[0130] The first algorithm to be developed is the angular
triangulation method that used vectors. The problem with this
method is that when an angle becomes small, the error in the
equations increases rapidly. Thus, when the stylus is near one of
the sensors, the error increases to the point that determination of
the position of the stylus tip becomes very inaccurate. The method
works well when the stylus stays away from the sensors, and remains
between them. This method is also very sensitive to pen tilt
because there is very little if any 3D capability in the
equations.
[0131] The next method uses Maxwell's equations. An element of the
equations is a magnetic constant for the magnets being used in the
stylus. This magnetic constant is the dipole moment. The dipole
moment is fixed as a constant in the equations to make them easier
to use. But the value is only an estimate. This next method can be
referred to as the magnitude method. The magnitude method generates
an equation for a circle, the center of the circle being the
location of the sensor, and the stylus tip being defined as a point
on the circle. Two sensors means that equations for two circles are
generated that must intersect. The two equations are solved for two
unknowns to determine the location of the stylus tip.
Advantageously, there are some 3D elements in the equations that
make this method less sensitive to tilting of the pen. In addition,
when the stylus gets too close to one of the sensors, the equations
for the other sensor become highly accurate and can compensate for
errors. But when the stylus is closer than one half inch to a
sensor, the equations begin to break down. This is because the
circles are supposed to intersect, and because this method uses
estimates in Maxwell's equations, it is sometimes the case where
one circle is completely within another circle. With no
intersection, the equations fail completely. This method also does
not work well when the stylus is tipping toward the sensors.
[0132] The next method is a modification of the magnitude method.
In this case, the method includes mathematical compensation for
when the stylus is tipped toward the sensors. Otherwise, the method
is the same.
[0133] The next method is a substantial increase in complexity over
the previous methods, but it yields surprisingly more accurate
results. This method will be referred to as the field line method,
or the 3D dipole triangulation method, and it also uses two
equations to solve two unknowns. This method uses the full 3D
equations of Maxwell. The full equations are more difficult to
solve because they require more steps. In this method, the
equations are trying to determine the shape or surface of the field
lines of the stylus in order to determine the location of the
stylus tip. In other words, the algorithm is trying to find a best
fit curve. Because the equations are not closed, an iterative
answer is obtained in a method similar to a binary search that
closes in on the correct values. In this embodiment, the algorithm
utilizes approximately 50 iterations at most to close in on the
solution to the equations.
[0134] This embodiment has used a neural net as well as a Fourier
series to solve the equations. The more elements used in the
Fourier series, the faster the solution is reached. The tradeoff is
the number of calculations that must be performed. Using a neural
net, the algorithm finds a best case approximation of the field
lines to create a function that describes them. The algorithm
converges on a solution using a gradient descent.
[0135] Unfortunately, this method can often get trapped in a local
minima. However, it is possible to simply throw out these wrong
answers using an error checking routine. In other words, if the
stylus tip location suddenly jumps to a new one that is beyond a
certain distance, the answer is thrown out and recalculated using
new data. It should be realized that there is no approximation in
this method. It can be used to find the location of the stylus tip
down to a very small margin of error. While the algorithm may take
50 iterations, it sometimes gets lucky and finds the correct answer
earlier as well. This method can give the 3D location of the stylus
tip, and handles any type of stylus tipping.
[0136] Alternatively, this method can use the last calculated
position as a beginning point for the next set of calculations. If
the calculations get trapped in a local minima, then they can be
thrown out and the position can be determined without using the
last known position.
[0137] The last method is similar, but relies on three sensors
instead of two sensors used in the algorithms above. Three sensors
will increase the cost of the system, but the equations become
extremely simple. With three sensors, the system now has the
intersection of three planes at the stylus tip. Thus, the algorithm
is the planar method that doesn't use Maxwell's equations. Instead,
the algorithm utilizes linear algebra to find the intersection of
three planes. This method is not iterative, and is of a closed
form.
[0138] It is observed that these methods all assume that the Z
plane is fixed as the writing surface. This works well when the
user writes, for example, in front of a PDA or laptop. But when the
user wants to write on an LCD screen of the laptop and have the
inking appear, compensation must be used to fix the Z plane a
certain distance above the assume writing surface. The LCD screen
of the laptop or PDA would have to be level. This may be a
calibration issue that is used to solve this distance problem.
[0139] FIGS. 22, 23, 24, and 25 are provided as detailed schematic
circuit diagrams that illustrate the sensor system in great
detail.
[0140] It is noted that by turning the stylus upside down, the
permanent magnet(s) in the stylus change polarity. This change in
polarity can be detected as a relatively slow movement, not
interpreted to be a signal indicating inking and non-inking. The
software can use this to erase what was written in the vicinity of
the erasing end of the stylus.
[0141] It is to be understood that the above-described arrangements
are only illustrative of the application of the principles of the
present invention. Numerous modifications and alternative
arrangements may be devised by those skilled in the art without
departing from the spirit and scope of the present invention. The
appended claims are intended to cover such modifications and
arrangements.
* * * * *