U.S. patent number RE35,016 [Application Number 07/831,257] was granted by the patent office on 1995-08-15 for three-axis force measurement stylus.
This patent grant is currently assigned to SRI International, Inc.. Invention is credited to Larry S. Gullman, Roy Kornbluh, Thomas P. Low, Peter M. Newgard, Eric J. Shrader.
United States Patent |
RE35,016 |
Gullman , et al. |
August 15, 1995 |
Three-axis force measurement stylus
Abstract
A three-axis force measurement stylus includes a housing and a
cartridge and an interface between the housing and the cartridge
wherein the interface comprises a plurality of pressure sensitive
sheets, preferably of variable resistance pressure sensitive Mylar
films which sense the force between the cartridge and the housing.
The cartridge and the housings are disposed at a skew angle
relative to the axis of the stylus to be able to sense forces in
three dimensions. In a specific embodiment, the cartridge forms a
conical section which mates with a complimentary conical section of
the housing. Membranes of the force sensitive material are provided
along three fingers from an apex of the conical section. The
cartridge is preloaded against the conical section by a spring
between the housing and the cartridge. Alternatively to the force
sensitive film, a sheet of a piezoelectric pressure-sensitive
material may be substituted. In each instance, direct pressure
between the conical section of the cartridge and the conical
section of the housing is sensed by the sensor mounted
therebetween.
Inventors: |
Gullman; Larry S. (La Honda,
CA), Kornbluh; Roy (Palo Alto, CA), Low; Thomas P.
(La Honda, CA), Newgard; Peter M. (Rainier, WA), Shrader;
Eric J. (La Honda, CA) |
Assignee: |
SRI International, Inc. (Menlo
Park, CA)
|
Family
ID: |
23034825 |
Appl.
No.: |
07/831,257 |
Filed: |
January 30, 1992 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
271254 |
Nov 15, 1988 |
04896543 |
Jan 30, 1990 |
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Current U.S.
Class: |
73/862.041;
73/862.043; 382/119; 73/865.4; 401/194; 345/179 |
Current CPC
Class: |
B43K
8/22 (20130101); G01L 5/161 (20130101); G06F
3/03545 (20130101); G01L 5/167 (20130101) |
Current International
Class: |
B43K
8/22 (20060101); B43K 8/00 (20060101); G01L
5/16 (20060101); G06F 3/033 (20060101); G01L
005/16 (); G06K 009/00 () |
Field of
Search: |
;73/862.043,862.042,862.044,862.045,862.046,862.05,862.041,862.541,865.4,862.06
;382/3 ;401/194 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Goldstein; Herbert
Attorney, Agent or Firm: Townsend and Townsend Khourie and
Crew
Claims
I claim:
1. An apparatus for generating signals representing direction and
magnitude of force on a shaft in a stylus comprising:
a housing, wherein said housing comprises a funnel portion;
a pickup .Iadd.coupled to said shaft.Iaddend., wherein said pickup
comprises a cone portion; and
means disposed between said housing and said pickup and abutting
said housing and said pickup at an interface skewed from said shaft
for sensing pressure between said housing and said pickup in a
plurality of directions wherein said sensing means further
comprises a first pad, a second pad and a third pad constructed on
a common elastomeric backing material, each said pad including at
least a pair of conductive traces having a surface exposed for
electrical connection thereto and a coating of conductive material
over said traces, said conductive material being in contact with
said traces varying conductivity between said traces in proportion
to pressure between said coating and said traces.
2. The apparatus according to claim 1 wherein said pickup further
comprises an ink-carrying cartridge, said cartridge being removably
mounted to said cone portion.
3. The apparatus according to claim 2 further including means for
biasing said funnel portion against said cone portion.
4. The apparatus according to claim 1 further including means for
biasing said funnel portion against said cone portion.
5. An apparatus for generating signals representing direction and
magnitude of force on a shaft in a stylus comprising:
a housing, wherein said housing comprises a funnel portion;
a pickup .Iadd.coupled to said shaft.Iaddend., wherein said pickup
comprises a cone portion; and
means disposed between said housing and said pickup and abutting
said housing and said pickup at an interface skewed from said shaft
for sensing pressure between said housing and said pickup in a
plurality of directions, wherein said funnel portion and said cone
abut one another in a complementary relationship forming said
interface, and wherein said sensing means comprises planar pads
which are disposed at said interface between said funnel portion
and said cone portion and which are distributed around a central
axis through said cone portion for sensing directionality of
force.
6. The apparatus according to claim 5 wherein said pickup further
comprises an ink-carrying cartridge, said cartridge being removably
mounted to said cone portion.
7. The apparatus according to claim 6 further including means for
biasing said funnel portion against said cone portion.
8. The apparatus according to claim 5 further including means for
biasing said funnel portion against said cone portion.
9. An apparatus for generating signals representing direction and
magnitude of force on a shaft in a stylus comprising:
a housing, wherein said housing comprises a first pressure
means;
a pickup .Iadd.coupled to said shaft.Iaddend., wherein said pickup
comprises a second pressure means; and
a sensing means disposed between said housing and said pickup and
abutting said housing and said pickup at an interface wherein said
first and second pressure means exert pressure on said sensing
means for sensing pressure of said pickup abutting said housing in
a plurality of directions wherein said first pressure means
comprises a funnel portion and wherein said second pressure means
comprises a cone portion, said cone portion abutting said funnel
portion in a complementary relationship forming said interface, and
wherein said sensing means comprises planar pads which are disposed
at said interface between said funnel portion and said cone portion
and which are distributed around a central axis through said cone
portion for sensing directionality of force.
10. The apparatus according to claim 9, wherein said sensing means
further comprises a first pad, a second pad and a third pad
constructed on a common elastomeric backing material, each said pad
including at least a pair of conductive traces having a surface
exposed for electrical connection thereto and a coating or
conductive material over said traces, said conductive material
being in contact with said traces varying conductivity between said
traces in proportion to pressure between said coating and said
traces.
11. The apparatus according to claim 10, wherein said pickup
further comprises an ink-carrying cartridge, said cartridge being
removably mounted to said cone portion.
12. The apparatus according to claim 11, further including means
for biasing said funnel portion against said cone portion.
13. The apparatus according to claim 10, further including means
for biasing said funnel portion against said cone portion.
14. The apparatus according to claim 9, wherein said pickup further
comprises an ink-carrying cartridge, said cartridge being removably
mounted to said cone portion.
15. The apparatus according to claim 14, further including means
for biasing said funnel portion against said cone portion.
16. The apparatus according to claim 9, further including means for
biasing said funnel portion against said cone portion. .Iadd.
17. A stylus comprising:
a) a pickup, said pickup coupled to a shaft;
b) a housing for holding said pickup; and
c) a sensor connected to and between said pickup and said housing,
said pickup comprising a funnel portion and a cone portion, said
funnel portion and said cone portion defining a substantially
common vertex, each of said cone portion and said funnel portion
defining interfaces skewed from an axis of said pickup, said sensor
further comprising:
i) a first substantially planar pad;
ii) a second substantially planar pad; and
iii) a third substantially planar pad, each of said pads varying a
conductivity in proportion to pressure between said coating and
said traces when pressure is applied to said shaft in said stylus.
.Iaddend. .Iadd.
18. The stylus as recited in claim 17 wherein said pads each
further comprise a conductive trace having an exposed surface for
electrical connection thereto, and a coating of conductive material
over said traces, said conductive material varying said
conductivity. .Iaddend. .Iadd.19. The stylus as recited in claim 17
wherein said pickup comprises an ink cartridge. .Iaddend. .Iadd.20.
Apparatus for generating signals representing direction and
magnitude of force on a shaft in a stylus comprising:
a) a housing, wherein said housing comprises a funnel portion;
b) a pickup coupled to said shaft, wherein said pickup comprises a
cone portion, said funnel portion and said cone portion defining a
substantially common vertex, each of said funnel portion and cone
portion defining abutting interfaces skewed from a central axis of
said pickup; and
c) means disposed between said housing and said pickup for sensing
pressure between said housing and said pickup when pressure is
applied to said shaft in said stylus. .Iaddend. .Iadd.21. Apparatus
as recited in claim 20 wherein said means for sensing comprises at
least three planar pads arranged between said funnel portion and
said cone portion. .Iaddend.
.Iadd.22. Apparatus as recited in claim 20 wherein said pickup
further comprises an ink-carrying cartridge, said cartridge
removably mounted to said cone position. .Iaddend. .Iadd.23.
Apparatus as recited in claim 20 further comprising means for
biasing said funnel portion against said cone portion. .Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a stylus or writing instrument which
generates electrical signals representative of the force applied in
the direction of motion taken in writing. A particular application
of the apparatus is for use as a computer input device wherein the
forces sensed by the stylus are used for recognizing ciphers,
selecting colors, or establishing line widths and densities of
lines. The apparatus can also be used in connection with signature
analysis. Still further, the apparatus may be used in connection
with a tablet or sensing x-y position for various applications
related to graphics and computer aided design.
2. Description of Prior Art
The prior art of force-sensitive stylae is represented by
inventions described in for example, U.S. Pat. Nos. Re. 29,765 to
Crane et al. entitled "Strain Gauge Transducer System," 4,111,052
to Sniderman entitled "Pressure-Sensitive Writing Stylus,"
3,986,403 to Hurd et al. entitled "Writing Instrument Employing
Adjustable Housing carrying Strain Gage and Removable Reservoir"and
3,906,444 to Crane et al. entitled "Special Pen and System for
Handwriting Recognition."
The Crane et al. reissue patent discloses a strain gauge based
transducer system employing a diaphragm on which strain gauges are
mounted. The strain gauges in accordance with standard strain gauge
technology produce a signal proportional to the stretching of the
sensor with the deformation of the diaphragm. The Sniderman
reference discloses a pressure sensitive pen employing a thin film
strain gauge array in connection with a elongated tubular member.
The strain in tubular member in sensed and translated into a signal
representative of pressure along the axis of the pen.
In addition, a pen is marketed by Summagraphics in connection with
its graphics technology which employs a force sensitive film
mounted at the end of a tube to sense change of pressure along the
axis of the tube with a stylus. A user's manual for the
Summagraphics pen describes its relevant features.
What is needed is a stylus which can be inexpensively manufactured
and yet sense pressure in multiple axes at the tip of the stylus.
What is also needed is a stylus of sufficiently rugged construction
to withstand the riggers of heavy and abusive use.
SUMMARY OF THE INVENTION
According to the invention, a three-axis force measurement stylus
comprises a housing and a cartridge and an interface between the
housing and the cartridge wherein the interface comprises a
plurality of pressure sensitive sheets, preferably of variable
resistance pressure sensitive Mylar films which sense the force
between the cartridge and the housing. The cartridge and the
housing are disposed at a skew angle relative to the axis of the
stylus to be able to sense forces in three dimensions. In a
specific embodiment, the cartridge forms a conical section which
mates with a complimentary conical section of the housing.
Membranes of the force sensitive material are provided along three
fingers from an apex of the conical section. The cartridge is
preloaded against the conical section by a spring between the
housing and the cartridge. Alternatively to the force sensitive
film, a sheet of a piezoelectric pressure-sensitive material may be
substituted. In each instance, direct pressure between the conical
section of the cartridge and the conical section of the housing is
sensed by the sensor mounted therebetween.
The invention will be better understood by reference to the
following detailed description in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view of the stylus with a partial cross-section of
the housing.
FIG. 2 is a view along the axis of the stylus along the axis of the
stylus.
FIG. 3 is a peel-away of one of the pressure sensitive sensors used
in connection with the invention.
DESCRIPTION OF SPECIFIC EMBODIMENTS
Referring to FIG. 1, there is shown a stylus 10 comprising a
housing 12 and a pick-up 14. The housing 12 comprises a tip cover
16, a barrel 18 and a pressure funnel 20.
The pick-up 14 comprises a pressure cone 22 juxtaposed to pressure
funnel 20 and a cartridge 24, such as a standard ball point pen
cartridge having a tip 26 and a shaft 28. The pick up 14 is biased
against the housing 12 by means of a preloading spring 30, such as
a coil spring disposed between the inner wall 32 of the tip cover
16 and the back 34 of the pressure cone 22, thereby forcing the
pressure cone 22 against the surface of the pressure funnel 20. A
suitable elastomeric O-ring 36 is disposed between barrel 18 and
the shaft 28 to provide a degree of flexibility to the shaft 28
within the barrel 18.
Referring to FIG. 2 in connection with FIG. 1, there are a
plurality of sensors 38, 40 and 42 distributed around the central
axis of the pressure cone 22 such that they rest in juxtaposition
between the pressure cone 22 and the pressure funnel 20. The
sensors 38, 40 and 42 comprise pads having interconnections 44 (not
shown in FIG. 2) between active sensing areas in the pads to
fingers 46, 48, 50, which terminate in connectors 52, 54, 56, to
suitable electronic processing circuitry. In a specific embodiment
of the invention, the fingers are held in place by a pressure
interface between the barrel 18 and a tube portion 58 of the
pressure funnel 20.
In operation, a user grasps the stylus 10 to apply pressure to the
tip 26 which in turn transmits the pressure to the interface
between the pressure cone 22 and the pressure funnel 20. The
sensors 38, 40 and 42 detect the pressure upon the pad surface
between the face of the funnel 20 and the cone 22, there typically
being a differential pressure depending on the direction and amount
of pressure at the tip 26. The resultant pressure is transformed
into a change in conductance through the interconnections 44 which
can be measured through appropriate circuitry connected at the
connectors 52, 54 and 56. A suitable signal processing can be used
to interpret the variations in conductance and provide a suitable
output signal or sequence of signals to a suitable utilization
device.
FIG. 3 is an illustration of one specific embodiment of a suitable
sensor 38 for use in accordance with the invention. The sensor 38
has two interconnections 44, each of which is connected to one set
of trace 60 and 62 which are intersticed on the surface of a
suitable elastomeric film 64. Juxtaposed to the surface 66 of the
elastomeric film bearing the traces 60 and 62 is a second
elastomeric film 68 having on its facing surface is a coating 70 of
a suitable conductive material. Conductivity varies directly with
pressure. A suitable pad having the appropriate coating is
manufactured by Interlink of Santa Barbara, Calif.
The sensors for use in accordance with the invention have the
advantage of relative ease and economy of manufacture, making it
possible to provide a stylus of potentially low-cost and
high-volume production. In addition, the stylus employing sensors
in accordance with the invention can be made to be extremely rugged
because of the inherent reliability of parts as well as their
resistance to abuse and environmental factors.
Alternatively, piezoelectric transducers may be used for pressure
sensing, however, these are not preferred for two reasons. First,
piezoelectric transducers may be constructed of brittle material
which could be broken. However, some piezoelectric transducers are
known which are composed of extremely thin material on a pliant
backing. Second, piezoelectric transducers generally generate a
signal only under changing conditions. Thus, they do not generate a
steady state signal directly proportional to pressure. Hence, a
sensor capable of generating a signal directly proportional to
pressure is preferred for applications contemplated for the
invention.
The invention has now been explained with reference to specific
embodiments. Other embodiments will be apparent to those of
ordinary skill in the art. Therefore, it is not intended that this
invention be limited, except as indicated by the appended
claims.
* * * * *