U.S. patent application number 09/746452 was filed with the patent office on 2002-06-27 for inductive joystick.
Invention is credited to Berton, Andrew, Hohl, G. Burnell.
Application Number | 20020080050 09/746452 |
Document ID | / |
Family ID | 25000905 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020080050 |
Kind Code |
A1 |
Hohl, G. Burnell ; et
al. |
June 27, 2002 |
Inductive joystick
Abstract
A multi-dimensional position sensor includes at least three
curved triangular-shaped sense inductors and a movable shaft that
incorporates a conductive material. The distance of the movable
shaft from the sense inductors varies as the shaft is moved in a
two-dimensional plane. The variation in distance causes a variation
in the inductance of each of the triangular-shaped inductors and
this variation in inductance may be used to determine the physical
position of the movable shaft through means of triangulation
calculations.
Inventors: |
Hohl, G. Burnell; (New
Canaan, CT) ; Berton, Andrew; (Minneapolis,
MN) |
Correspondence
Address: |
PATTERSON, THUENTE, SKAAR & CHRISTENSEN, P.A.
4800 IDS CENTER
80 SOUTH 8TH STREET
MINNEAPOLIS
MN
55402-2100
US
|
Family ID: |
25000905 |
Appl. No.: |
09/746452 |
Filed: |
December 21, 2000 |
Current U.S.
Class: |
341/20 |
Current CPC
Class: |
Y10T 74/20201 20150115;
G01D 5/202 20130101; G05G 9/047 20130101 |
Class at
Publication: |
341/20 |
International
Class: |
H03M 011/00; H03K
017/94 |
Claims
What is claimed:
1. A multi-dimensional position sensor, said sensor comprising: at
least three curved triangular-shaped sense inductors; a movable
shaft containing a conductive material, wherein said at least three
curved triangular-shaped inductors are fixedly positioned about
said movable shaft, and wherein a distance of said movable shaft
from said at least three triangular-shaped sense inductors varies
as said movable shaft is moved in a two-dimensional plane, the
variation in distance causing a variation in the inductance of each
of said at least three triangular-shaped sense inductors, said
variation in the inductance usable to determine a physical position
of said movable shaft.
2. The sensor of claim 1, wherein said movable shaft comprises a
handle and a conductive cone.
3. The sensor of claim 1, wherein said conductive material
comprises a silver paint.
4. The sensor of claim 2, wherein said at least three curved
triangular-shaped sense inductors are mounted to a cylinder that is
fixedly positioned about said movable shaft.
5. The sensor of claim 4, wherein said at least three
triangular-shaped sense inductors are equidistantly spaced about
said cylinder.
6. The sensor of claim 4, wherein said at least three
triangular-shaped sense inductors incorporate a non-linear sensing
portions, and wherein said at least three triangular-shaped sense
inductors are mounted proximate one another such that said
non-linear sensing portion of each of said at least three
triangular-shaped sense inductors overlaps at least one of the
adjacent triangular-shaped sense inductors
7. The sensor of claim 1, wherein said movable shaft comprises a
handle and a conductive cylinder, and wherein said at least three
curved triangular-shaped sense inductors are mounted to a cone that
is fixedly positioned about said movable shaft.
8. A multi-dimensional position sensor, said sensor comprising: a
reference sense inductor; a plurality of curved triangular-shaped
sense inductors; a movable shaft containing a conductive material,
wherein said plurality of triangular-shaped sense inductors are
fixedly positioned about said movable shaft; an oscillator
connectable to said reference sense inductor and said plurality of
triangular-shaped sense inductors; a comparator, wherein upon said
oscillator being connected to each of said plurality of
triangular-shaped sense inductors, a state of each of said
plurality of triangular-shaped sense inductors is compared by said
comparator against a plurality of precision thresholds to determine
the change in inductance of said plurality of triangular-shaped
sense inductors, wherein the change in inductance of said plurality
of triangular-shaped sense inductors corresponds to a position of
said movable shaft.
9. The sensor of claim 8, further comprising an analog-to-digital
converter, wherein said analog-to-digital converter digitizes said
state of each of said plurality of triangular-shaped sense
inductors, wherein the digitized states are usable to determine the
position of said movable shaft.
10. The sensor of claim 8, wherein said movable shaft comprises a
handle and a conductive cone.
11. The sensor of claim 8, wherein said conductive material
comprises a silver paint.
12. The sensor of claim 10, wherein said at least three curved
triangular-shaped sense inductors are mounted to a cylinder that is
fixedly positioned about said movable shaft.
13. The sensor of claim 12, wherein said at least three curved
triangular-shaped sense inductors are equidistantly spaced about
said cylinder.
14. The sensor of claim 12, wherein said at least three
triangular-shaped sense inductors incorporate a non-linear sensing
portions, and wherein said at least three triangular-shaped sense
inductors are mounted proximate one another such that said
non-linear sensing portion of each of said at least three
triangular-shaped sense inductors overlaps at least one of the
adjacent triangular-shaped sense inductors.
15. The sensor of claim 8, wherein said movable shaft comprises a
handle and a conductive cylinder, and wherein said at least three
curved triangular-shaped sense inductors are mounted to a cone that
is fixedly positioned about said movable shaft.
16. The sensor of claim 9, wherein the digitized states are usable
to determine the position of said movable shaft through use of
triangulation calculations.
17. The sensor of claim 16, wherein said triangulation calculations
include comparison of the digitized states with a table of nominal
states for a plurality of discrete shaft positions, and
determination of the nominal state of the shaft position that most
closely matches the digitized states with minimum error.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to joysticks and, more
particularly, to a two-dimensional position sensor using a movable
shaft, incorporating a conductive material, surrounded by at least
three, curved triangular-shaped sense coils. The physical position
of the shaft is determined by triangulation, by detecting the
change in the self-inductance of the sense coils as the shaft
moves.
BACKGROUND OF THE INVENTION
[0002] Joysticks are used in many military, industrial, and
commercial applications to control movement of an aircraft,
vehicle, object on a video screen, etc. Most joysticks convert the
angular movement of a control shaft into movement along an X and Y
axis, using a mechanical linkage to translate the motion. The
displacement of the shaft in each direction is detected by means of
mechanical switches, variable resistors, or optical sensors.
Usually the greater the resolution required in detecting the shaft
position, the greater the cost of the precision sense elements,
such as optical sensors, required to detect tiny changes in the
shaft position.
[0003] A number of joystick systems using inductive sense elements
have been developed. U.S. Pat. No. 4,685,678 describes a joystick
system where position is determined through use of a pair of
inductors that operate with a movable slug. The movement of the
slugs, by the joystick handle, causes a change in inductance. The
inductors produce signals proportional to the position of the slugs
in two dimensions.
[0004] U.S. Pat. No. 4,855,704 describes a system that utilizes two
induction coils, and a spherical induction body secured to the
joystick. As the joystick is moved, the location of the induction
body relative to the sensors changes the inductance of the
sensors.
[0005] Finally, U.S. Pat. No. 5,598,090 describes a joystick system
that uses biasing springs as inductors. The biasing springs
position the joystick in a neutral position. Movement of the
joystick compresses or extends the springs, changing their
inductance. All of these approaches incorporate multiple, movable
components, or mechanical elements to translate the joystick
position into two dimensions.
[0006] U.S. Pat. No. 5,949,325 describes a joystick system where
the joystick is secured to a conductive rubber transducer. As the
joystick is moved about, the curved rubber transducer is deflected
and contacts conductors on a printed circuit board. This approach
eliminates many of the mechanical moving parts required to
translate angular motion into two axes, however, it uses direct
contact between the joystick and sensing elements.
[0007] In view of the above, there is a need in the art for a
joystick with no moving parts other than the joystick shaft.
Further, it would be desirable to eliminate the need to
mechanically translate the motion of the shaft into an X and Y
direction. It would be further desirable to detect the position of
the joystick shaft without physical contact to the shaft which, in
combination with the elimination of moving parts, provides improved
reliability and durability. It is also desirable to detect the
joystick shaft position with significant precision to provide
increased resolution using low cost sensors.
SUMMARY OF THE INVENTION
[0008] The needs described above are in large measure met by an
inductive joystick of the present invention. The inductive joystick
has no moving parts other than the joystick shaft, and utilizes
low-cost printed sense inductors. The shaft position is detected by
use of a triangulation algorithm that can detect at least 72
discrete positions within the sphere of movement of the shaft.
There is no physical contact with the joystick shaft.
[0009] Specifically, the inductive joystick of the present
invention includes a shaft that is provided at a first end with a
layer of a cone-shaped conductive material. A tubular housing
surrounds the first end and contains at least three curved sense
inductors that surround the movable shaft. The sense inductors are
preferably triangular in shape. The distance of the movable shaft
from the sense inductors varies as the shaft is moved in a two
dimensional plane. The variation in distance between the conductive
material and the sense inductors causes variation in the inductance
of each of the triangular shaped inductors and this variation in
inductance is used to determine the physical position of the
movable shaft through use of triangulation calculations.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a diagram showing the construction of an inductive
joystick incorporating a plurality of triangular-shaped sense coils
surrounding a movable shaft fitted with a conductive cone.
[0011] FIG. 2 is a block diagram of the inductive joystick that
incorporates an inductive sensory apparatus and a microprocessor
controlled successive approximation A/D converter.
[0012] FIG. 3 is a detailed circuit diagram of the inductive
joystick electronics.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0013] Construction of an inductive joystick 200 of the present
invention is shown in FIG. 1. In this particular configuration,
three triangular sense coils 100 (only two may be seen) are curved
about and evenly spaced around the circumference of a
non-conductive cylinder 202. Each of triangular sense coils 100 is
preferably printed with conductive ink, as a flex circuit, onto
mylar or other suitable material that allows the coils 100 to be
curved about the cylindrical shape of cylinder 202. Sense inductors
100 are triangular shaped because the self inductance of such coils
varies linearly in proportion to the position of proximate
conductive material along the coil axis.
[0014] It should be noted that the apex 108 of each of triangular
sense coils 100 overlaps the area of the adjacent triangular sense
coil 100 where the coil turns run perpendicular, designated by
dashed line 110, to imaginary coil axis, designated by dashed line
102, which is the non-linear sensing portion of each triangular
sense coil 100. Alternatively, a portion of each triangular sense
coil 100 may be bent at a right angle, such that the non-sensing
area of each triangular sense coil 100 extends perpendicularly to
the side of cylinder 202 and only the linear sensing portions of
each of triangular sense coils 100 are evenly spaced, without
overlap, around the circumference of cylinder 202.
[0015] Cylinder 202 is maintained in a stationary position about a
movable shaft 204 that is preferably comprised of a shaft handle
206 and a cone 208. Cone 208 is covered in a conductive material,
preferably a highly conductive silver paint. The angle of cone 208
is such that as shaft 204 of joystick 200 is rotated about at its
maximum extremity, the edge of cone 208 becomes parallel to the
wall of cylinder 202. Shaft 204 is centrally supported by a base
210 that allows shaft 204 to pivot and rotate 360 degrees. Base 210
is preferably of a configuration to enable storage of the circuitry
that comprises the inductive joystick sensory system.
[0016] While cylinder 202 is preferably fitted with three
triangular sense coils 100, depending upon the signal strength from
sense coils 100 when shaft 204 is in its idle, center position, it
is usually desirable to use a fourth external coil as a reference
coil (the signal strength while in the idle, center position is
dependent upon the conductivity of the cone material and the
diameter of cylinder 202 surrounding shaft 204). The reference coil
is preferably identical in inductance to triangular sense coils
100. Alternatively, in certain configurations, any of the three
triangular sense coils 100 fitted about cylinder 202 may be used as
the reference coil.
[0017] FIG. 2 shows a block diagram of the inductive joystick
sensory system. The three position sensing triangular sense coils
100 and one reference coil 102 are used as inductors in an LC
oscillator 22 circuit. The negative excursion of the oscillator 22
output is clamped to ground and the positive peak detected by a
peak detector 28, to convert the oscillation amplitude to a DC
level. When the microcontroller 26 selects the reference coil 102
through a coil multiplexor 24, a feedback control loop 32 adjusts
the drive voltage to the LC oscillator 22, by means of a voltage
comparator 34 and peak detector/buffer 36, to clamp the signal from
the reference coil to a fixed amplitude. This allows the system to
compensate for changes in oscillation amplitude due to temperature,
supply voltage, and component tolerance variations. The software
within microcontroller 26 than samples the signals from each of the
three triangular sense coils 100 which are digitized by a low cost
successive approximation A/D converter 32.
[0018] Referring to the detailed inductive joystick electronic
circuit diagram of FIG. 3, operational amplifier 60 forms part of
the successive approximation A/D converter 32 comprising a
comparator whose reference voltage is set by microprocessor 26,
through a D/A converter 200. D/A converter 220 utilizes a summing
amplifier 222, feedback resistor 223, and a precision resistive
ladder network 224. The microcontroller 26 outputs digital words to
the inputs of precision resistive ladder network 224 feeding
summing amplifier 222 using a binary search algorithm until the
output of the D/A converter matches the coil signal. The software
of microcontroller 26 triangulates the position of shaft 204 by
comparing the digitized signals from each of the three triangular
sense coils 100 against a stored table of nominal signal values for
various shaft positions, and runs a closeness of fit algorithm to
determine the current position of shaft 204. The purpose of the
closeness of fit algorithm is to find the nominal shaft position
which most closely matches the measured coil signals with minimal
error. The position of shaft 204 may then be output by
microcontroller 26 to control a video game, machine, etc. It is
possible to detect at least forty-eight (48) discrete positions
around the perimeter of the largest circle circumscribed by the
rotation of shaft 204 of joystick 200, with a proportional number
of intermediate positions also detectable.
[0019] The inductive nature of operation of joystick 200 provides
desirable advantages over that of mechanical, resistive, or optical
joystick approaches. Specifically, joystick 200 provides excellent
resolution at low cost and high reliability because there are no
moving parts other than center shaft 204, and sensing of the
joystick position requires no mechanical or physical contact with
center shaft 204.
[0020] An alternative embodiment of joystick 200 comprises mounting
three triangular sense coils 100 around the surface of an inverted
cone surrounding shaft 204. In this case, the conductive portion of
shaft 204 can be cylindrical in shape, rather than cone shaped; the
operation of joystick 200 remains as substantially described
above.
[0021] The present invention may be embodied in other specific
forms without departing from the spirit of the essential attributes
thereof; therefore, the illustrated embodiments should be
considered in all respects as illustrative and not restrictive,
reference being made to the appended claims rather than to the
foregoing description to indicate the scope of the invention.
* * * * *