Note: Descriptions are shown in the official language in which they were submitted.
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Introduction
This invention relates to position determining systems
and, more particularly, to systems for making linear and angular
position determinations in single degree of freedom, multi-axis
systems.
Background of the Invention
An effective approach to linear and angular position
l determining systems has been shown in my V.S. Patent No. 4,035,762,
issued on July 12, 1977. Such patent describes various embodi~ents
for measuring a position along a line, either straight or curved,
or on a plane or other curvilinear ~urface, with a high degree of
accuracy at a reasonable cost. The embodiments described therein
generally require two relatively movable members. In a particular
lS embodiment one member may comprise a driver transducer and a delay
line, both fixedly positioned, and a second member may comprise a
receiver transducer which is movable with respect to the fixed
driver transducer and the delay line. The resolution of the
displacement measurement depends upon the phase shift experienced
by a continuous elastic wave travelling once along a single delay
line element in one direction only, parallel to, or coincident
with, the distance to be measured. If position with respect to
more than one axis is required, a plurality of such delay elements
I are used for such purpose.
¦ It is desirable to reduce the number of delay elements in
¦ multi-axis systems in order to simplify the structure thereof as
¦ much as possible and to reduce the cost by requiring the use of
¦ fewer precision components while, at the same time, still provid~
¦ high resolution. Moreover, in single-axis applications it is
desirable to obtain much higher resolutions than presently availabl~
while still using the same components without changing either the
frequency of the driver signal or the velocity of propagation
in the del ~ ~ L
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srief Summary of the Invention
This invention provides advantages in multi-axis appli-
cations over that described in my above-mentioned, previously
issued U.S. patent, which advantages are particularly gainea for
special multi-axis embodiments in which each degree of freedom
is orthogonal to each other, the complexity and costs being con-
siderably reduced by the shared use of at least one delay element
in providing position determinations with respect to more than
one axis. In each case, the shared delay element is positioned
at a selected angle with respect to the direction for which a
position determination is to be made. ThuS, in providing for
position determination with respect to two axes, a single delay
element can be positioned at a selected angle with respect to
each axis (e.g., the delay element may be positioned at a 45
angle with respect to each of two orthogonal axes), and linear
or angular position determinations with respect to each axis can
be obtained thereby.
In accordance with the present invention there is pro-
vided a position determining device comprising delay means
mounted at a selected angle greater than 0 with reference to
at least one selected direction; first transducer means fixedly
coupled to said delay means; second transducer means coupled to
said delay means and relatively movable with respect to said
delay means so as to maintain substantially the same coupling
with said delay means throughout its movement; means for acti-
vating one of said first and second transducer means to generate
a signal which traveIs along said delay means, the other of said
~irst and second transducer means detecting said travelling sig-
nal as it travels past said other transducer means; means for
determining the delay of said signal as it travels from the
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activated transducer means to the detecting transducer means
whereby the position of said detecting transducer means relative
to said activated transducer means along said delay means is
determined; and means responsive to said delay determination for
calculating the position of said detecting transducer means
relative to said activated transducer means along said at least
one selected direction.
In accordance with the present invention there is also
provided a device for determining angular positions comprising
three movable gimbal elements each angularly movable with respect
to each other about one of three different axes which are
orthogonally positioned with respect to each other, said gimbal
elements forming an assembly thereof comprising an inner gimbal
element, a middle gimbal element, and an outer gimbal element;
a circular delay element fixedly mounted on said middle gimbal
element at a selected angle with reference to the axis associated
therewith; driver transducer means fixedly coupled to said delay
element; first receiver transducer means fixedly mounted on said
inner gimbal element, said first receiver transducer means being
coupled to said delay element and being relatively movable with
respect thereto so as to maintain substantially the same coupling
with said delay element throughout its movement; second receiver -
transducer means fixedly mounted on said outer gimbal element,
said second receiver transducer means being coupled to said delay
element and being relat~vely movable with respect thereto so as
to maintain substantially the same coupling with said delay
element throughout its movement; means for activating said driver ~:
transducer means to generate a signal which travels along said
delay element, said first and second receiver transducer means
30. each.detecting said travelling signal as it travels past said
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first and second receiver transducer means; means for determininy
the delay of said signal as it travels from said driver trans-
ducer means to each of said first and second receiver transducer
means whereby the positions of said first and second receiver
transducer means relative to said driver transducer means along
said delay element are determined; and means responsive to said
delay determinations for calculating the angular positions of
said inner and outer gimbal elements with respect to said middle
gimbal element.
In accordance with the present invention there is also
provided a position determining device comprising a distributed
sensing means mounted at a selected angle greater than 0 with
reference to at least one selected direction; at least one movable
means coupled to said sensing means and relatively movable with
respect thereto along said at least one selected direction so as
to maintain substantially the same coupling therewith throughout
its movement, said at least one movable means providing an output
representing its position along said sensing means; and means
responsive to said output for calculating the position of said
movable means along sàid at least one selected direction.
Description of the Invention
Particular embodiments of the invention can be better
understood in more detail with the help of the accompanying ~ .
drawings wherein
FIG. 1 shows an embodiment of the invention for determin-
ing a position with respect to a pair of orthogonal axes using a
single delay element;
FIG. 2 shows an alternative embodiment of the invention
for providing angular position determinations with respect to a
3Q multi-axis gimbal system;
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FIG. 3 shows a portion of the embodiment of FIG. 2 in
which the inner gimbal element has been rotated through an angle -
~1 '
FIG. 3A shows a geometric diagram helpful in understand-
ing the operation of the system of FIGS. 2 and 3;
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FIG. 4 shows an alternative embodiment of the system
shown in FIG. 2; and
FIG. 5 shows an embodiment of the invention for impro~ing
resolution in a single axis position determination system.
The embodiment of FIG. 1 can be utilized to provide
position determination with respect to two axes utilizing only a
single delay element. As seen therein, a single element in the
form of a delay line 10 is utilized to provide position
determinations along two orthogonal axes identified as the ~X"
axis 11 and the "Y" axis 12. The delay line which may be,
for example, a magnetostrictive delay line element of the type
discussed in my above-mentioned U.S. patent is preferably position~ ,~
so that it is at a 45 angle with respect to each axis. ~hen
~ using such magnetostrictive delay line elements a magnetic bias
! is required, as is known to the art, such bias being produced
by several techniques, as discussed in my aforementioned U. S.
patent. Delay line element 10 has a damping element lOA mounted
at each end for preventing reflections of signals thereat.
A first driver transducer 13 is excited by a signal generator 14
so as to produce a signal which travels along delay line 10. A
second receiver transducer 15 is arranged for movement along the
X-axis direction as shown by double-headed arrow 15A and a third
receiver transducer 16 is mounted for movement along the direction
l of the Y axis as shown by double-headed arrow 16A.
Transducers 15 and 16 are suitably mounted on mounting
means (not shown) for movement along the X and Y directions,
respectively, and may be in the form of an extended loop of wire,
as shown, which moves along each direction adjacent delay line 10
in a manner so as to provide substantially the same coupling with
¦ the lsy line throughout their entire movements.
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A signal which travels along delay element 10 is picked up
by each of the transducers 15 and 16 and suitably amplified by
amplifiers 17 and 18, respectively, the amplified received signals
l thereupon being supplied to phase detectors 19 and 20, respectively.
! The phases thereof are compared to the phase of the signal rom
signal generator 14 so as to produce a measurement of the distance
between each of said receiver transducers relative to the driver
transducer 13 along delay line element 10. , -
As discussed more fully in my above-referred to
U.S. Patent No. 4,035,762, the position measurements when using
continuous wave signals require both a "coarse" and a "fine"
measurement, the coarse measurement determining the number of
'lintegral cycles of the C-W signal between the activated transducer
l 13 and the receiver transducers 15 and 16 so that a coarse
I determination of the approximate distance therebetween to within
¦one cycle (i.e., one wavelength) is determined. The phase
difference within such one wavelength thereupon provides the
! "fine" measurements of the overall distance bet~een the driver
I and receiver transducers at a desired accuracy determined by the
frequency of the C-W signal which is used. Since suitable
techniques for providing such coarse and fine measurements are
described in such previously issued patent, the details thereof
! need not be given here and, for simplicity, such coarse and fine
measurements are represented by the phase detectors 19 and 20 in
FIG. 1 and also in subsequent figures herein.
The components thereof along the X-axis and Y-axis
¦directions are thereupon appropriately calculated by the scale
factor units 21 and 22, respectively, in each case the scale facto
! being the cosine of the angle between the delay line 10 and the
~correcponding axic involved. Where each angle is 45, ac here,
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the scale factor is ~ . In general, where the X-axis angle is ~,
¦and the Y-axis anyle is ~, the scale factors are cos~ and cos~,
¦respectively
~ Accordingly, a single deiay line element, appropriately
positioned with respect to two angularly related directions, can
¦be utilized to determine the positions along such directions.
¦While the particular embodiment disclosed in FIG. 1 shows a
Iposition determining system with respect to two orthogonal axes,
such directions need not be orthogonally related. Further, the
signal which is supplied from signal generator 14 may be a
continuous wave (C-W) signal for generating a C-W travelling wave I
along delay line element 10, or such signal can be a pulse signal ¦
in which case the delay which is measured is a time delay
~¦representing the time of travel of such pulse from the driver
transducer 13 to the receiver transducers 15 and 16. In the
latter case the phase detectors involved can be replaced by time
¦jdetection measurement devices such as suitable counters, etc.,
i! well known to those in the art, the time measurement representing
la direct measurement of distance so that no "coarse" and "fine"
measurements need be made as in the phase measurement case.
Moreover, while the transducer 13 is utilized as the
driver transducer in such embodiment and the transducers 15 and 16
! as receiver transducers, such roles can be reversed and the
driver signal can be applied to both the latter transducers and
¦ the transducer 13 utilized as the receiver transducer. In the
latter case, for example, appropriate multiplexing techniques can
¦¦be utilized for determining the positions along each of the two
¦¦axes, such measurements being made at different times utilizing
l~the same delay line element 10.
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The concepts discussed above relative to the measurement
of linear distances in FIG. 1 are also applicable to the measure-
ment of angular relationships. Such angular determinations ~ay
be utilized, for example, in multi-axis gimbal systems wherein
the angular relationships between gimbal elements are to be made.
Such gimbal systems are utilized, for example, in inertial gui ~ c
and control systems wherein gimbal angle readouts are essential
for providing the desired control signals therein. In presently
used gimbal inertial measurement systems, several gimbal angular
readout elements are required, all of which adds to the complexity
and cost of the overall system. A gimbal system utilizing the
concepts of the invention, however, can reduce such cost and
¦complexity by eliminating the number of angle sensors which are
normally required therefor.
An embodiment of the invention is applied to a simple
gimbal system for measuring the angular relationship between a
stabilized gimbal element and each of two other gimbal elements
¦which move angularly with respect thereto is shown diagrammatically
i!in FIG. 2. As seen therein, a first inner gimbal element 30
rotates about a first (~X~) axis 31,shown as horizontal in the
figure, a second middle gimbal 32 assumes a stable position as
shown, and a third outer gimbal element 34 rotates about a second !
("Y") axis 33,shown as vertical and orthogonal to axis 31. While
¦ such gimbal elements are often in the form of spheres, for
¦ simplicity they are depicted only diagrammatically in the planar
¦drawing of FIG. 2. In operation, it is desirable to determine
the angular relationship between the first inner and second middle
gimbal elements 30 and 32, respectively, identified by the angle
~1~ and the angular relationship between the second middle and
third outer gimbal elements 32 and 34, respectively, identified
¦ by the angle ~2.
losæls
In accordance with the invention, a delay element 36 is
fixedly mounted on the middle gimbal element 32 at a selected
angle with respect to the vertical axis of rota~ion 33 (in the
. case shown the angle is selected as 45). The delay element 36
may be in the form of a circular delay line having a pair of
damping elements 37 at the ends thereof. A transducer 38 which
may be, for example, a coil of wire is coupled to the delay line
element 36 adjacent one end thereof. Transducer 38 in the
embodiment shown in FIG. 2 may be utilized as a driver transducer
1 for producing a travelling signal in delay element 36 when
appropriately excited from a signal generator 39, substantially
in the same manner as discussed above with reference to FIG. 1.
A second transducer in the form of a wire loop 40 is
, mounted on the outer surface of inner gimbal element 30. Trans- !
¦ ducer 40 in the embodiment shown is utilized as a receiver
i transducer, one end of which is connected to ground and the other
l~of which provides a receiver signal when the travelling signal
¦¦and delay line element 36 pass by transducer loop 40. A second
,Ireceiver transducer 41 is mounted as shown on the outer surface
¦~ of outer gimbal element 34, one end of transducer 41 being
¦¦connected to ground and the other end providing a receiver signal
¦¦when the travelling signal and delay element 36 pass by transducer
loop 41. In order to determine the angular relationship ~
¦¦for example, between the inner gimbal element 30 and middle
1! gimbal element 32, transducer 38 is excited with a continuous wave¦
signal, for example, and such signal is picked up by transducer 40
~and supplied to amplifier 42. The input signal from signal
¦¦generator 39 and the amplifier received signal are applied to a
¦Iphase detector 43 in substantial~y the same manner as discussed above
with reference to FIG. 1. The phase diEference therebe~een
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represents a measurement of the distance along delay line 36 from ¦
the middle gimbal element 32 to the inner gimbal element 30 which
is rotated with respect thereto. The output from phase detector
43 is supplied to calculation unit 44 to provide a determination
of the angle ~1 in accordance with the appropriate spherical
trigonometric relations involved.
In order to understand the trigonometric calculations
involved, FIG. 3 shows middle gimbal 32 and inner gimbal 30
llrotated with respect thereto at an angle ~1 A spherical triangle¦
47 is thereby formed having two sides, "a" (equivalent to the 45
distance which delay line 36 makes with the vertical axis 33)
¦¦and "b" (the distance travelled by the travelling wave along
¦delay line 36 to where it is picked up by receiver transducer 40).
¦The spherical angle at B represents the angle ~1 to be measured
¦and the spherical angle at C is 90. Accordingly, the following
¦known general spherical trigonometric relationship holds:
Il tan b = tan B sin a
!jSuch expression can be rewritten to solve for B as follows: I
l,j B = tan [tan b/sin
~ In the particular case where a is equal to 45, as shown
I in FIG. 3, the relationship reduces to
B = tan 1 ~v~~ tan b~
In FIG. 3 where the angle B is the desired angle ~1 and
l b is the distance ~1 along delay line 36, the above relationship
becomes
~1 = tan~l ~v~- tan ~ ~ !
~ For clarity in understanding the spherical triangular
¦relationships set forth above, the spherical triangle is re-
l produced in FIG. 3A, the sides a and b (where b=~l) and the
¦ angles A,B (where B=~l) and C being suitable identified.
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Such calculation can then be made by calculation unit 44
once the distance ~1 (in degrees) along delay line 36 is
¦determined by phase detector 43.
l In a similar manner the angle between middle gimbal
1 element 32 and outer gimbal element 34 can be determined in
accordance with the phase difference between the signal applied
to driver transducer 38 from signal generator 39 and the signal
which is received at transducer 41, appropriately amplified by
amplifier 45, both of such signals being supplied to phase
detector 46 and thereupon to calculation unit 47 to determine the ¦
angle ~2
Thus, a single delay line element appropriately mounted
on a middle gimbal element at a preselected angle (for simplicity
the angle has been selected in FIG. 2 as 45, although not
limited thereto) permits a measurement of the angular relationship
¦between an inner gimbal element and such middle gimbal element
as well as between an outer gimbal element and such middle gimbal
~l element, without the need for two separate angle sensors and
readout units as is normally required in such a gimbal structure.
` 20 ! While the signal applied to driver transducer 38 has been I
discussed as a continuous wave signal, such signal can also be a
pulse signal and the angular measurements can be determined by
¦measuring the time delays between the signal produced at trans- !
l ducer 38 and the signals picked up at transducers 40 and 41,
l such time delayc and the polarities of the received signals
appropriately indicating the gimbal angles.
¦ While the dual gimbal angle system of FIG. 2 is shown as
used in connection with a two degree of freedom, three gimbal
lelement system, such concept can be extended to a higher degree
1 of freedom system having more than three such gimbal elements,
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in each case a single delay element on a selected gimbal element
being used to determine angular relations with respect to
adjacent inner and outer gimbal elements. Such a system as may
be conventionally used in many applications could comprise,
for example, one stabilized gimbal element and four rotatiny
gimbal elements. In cases where more than one delay element is
required to determine the angular relationships in a system using
four or more gimbal elements, separate signal generators can be
~ used to excite each of the driver transducers involved and the
received signals can be supplied directly to appropriate phase
~jdetectors and calculation units. Alternatively, only a single
I signal generator need be used and the signal therefrom supplied
!I to the driver transducers in a multiplexed fashion, the received
¦¦outputs also being correspondingly multiplexed using well-known
15 ¦¦ multiplexing techniques.
Although the embodiment of FIG. 2 shows the delay line
element 36 supported on gimbal element 32 in a manner such as to
! coincide with the great circle thereof the delay line element
lican be mounted so as to be off the great circle as shown in
IFIG. 4, the necessary spherical trigonometric relationships
being calculated in substantially the same manner as discussed
above.
! While the use of a delay line element which lies at an
angle with respect to the distance being measured along an axis,
as opposed to lying along the direction of the axis itself, has
¦ been discussed in a multi-axis configurationwith respect to FIG. 1
such concept can also be used to improve the resolution in a
¦single-axis o~n~igur~ion as shown in FIG. 5. As seen therein, a
delay element 50 is fixedly mounted with respect to a selected
~0 ~axis directi n 51 identified a~ the "X" direction at a selected
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angle ~. A clriver transducer 5~ i5 fixedly mounted on delay
line 50 and a receiver transducer 53 is mounted for movement
along the "X" direction and may be in the form of an extended
loop of wire, as also shown in FIG. 1, so as to provide substanti~
¦ coupling with the delay line 50 throughout its entire movement.
The distance along the "X" direction can be determined in ¦
the same manner as discussed above in connection with FIG. 1.
Because the delay line is positioned at a selected angle ~ with
reference to the "X" direction, the resolution of the measurement
involved is improved over that obtained when the delay line lies
along the "X" direction since the component of the distance
between transducers 52 and 53 along the "X" direction is
represented by a much longer distance along the delay line itself
! (depending on the selected value of ~) where the phase shift
1 (or time shift if pulses are used) measurements are made. The
resolution improvement is greater the greater the selected value
of ~.
While the invention is discussed above in connection with
the use of delay elements for position determinations, the
¦fundamental concept thereof can also be useful in measurement I -
systems using other distributed sensing elements. Thus, a
ilpotentiometer, for example, uses a distributed resistance element
having a movable contact element coupled thereto, the varying
¦¦resistance at the contact providing a determination of its
¦¦position along the distributed resistance. In conventional
potentiometers the distributed resistance is arranged to be
aligned with the direction, either linear or curvilinear, along
which a position is to be determined.
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I In accordance with the invention, a single distributed
i sensing means te .g ., a distributed resistance element), is
positioned at a selected angle with re~pect to one or more
i selected directions along which a position is to be determined.
5 11 One or more movable elements are coupled to the distributed
! element and move with respect thereto along the one or more
selected directions. The outputs at the one or more coupled
! elements determine the position along the distributed means
and from the known selected angle a determination can then be
o l! made of the position along the one or more selected directions
with a much higher degree of resolution than in conventional
devices of this type.
Other modifications and uses of the invention will occur
Il to those in the art within the spirit and scope of the invention
¦¦ and the invention is not to be deemed limited to the particular
embodiments disclosed herein except as defined by the appended
claims.
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