Note: Descriptions are shown in the official language in which they were submitted.
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CONTROL STICK ADAPTED FOR USE
IN A FLY-BY-WIRE FLIGHT CONTROL
SYSTEM, AND LINKAGE FOR USE THEREIN
[0001] This is a divisional application of Canadian patent application
No. 2,669,919, filed
August 8, 2007.
Technical Field
[0001a] The present invention relates generally to the field of control
sticks (e.g., joysticks,
side-sticks, etc.) that are adapted for use in sensing and transmitting manual
operator
commands to an object-to-be-moved (e.g., airfoil surfaces, etc.) in response
to such
commands, to improved linkages for use in mounting such control sticks on
suitable supports,
and to improved compound springs that are particularly adapted for use
therein. One
= particular application contemplates the transmittal of pilot or co-pilot
commands to various
airfoil surfaces by a fly-by-wire flight control system.
Background Art
[0002] Joysticks are well-known devices to transfer a pilot's manual input
commands to
various aircraft flight control surfaces. In their early forms, joysticks were
usually mounted
on the cockpit floor between the pilot's legs. They were typically mounted so
as to enable
compound pivotal movement of the stick about two mutually-perpendicular axes,
representing the pitch and roll axes of the aircraft. However, the position
and size of these
joysticks often interfered with other devices and freedoms, and required
considerable space to
accommodate the range of permissible movement of the handle.
[0003] Originally, such joysticks were connected to various airfoil surfaces
by mechanical
linkages and cables. These couplings were unnecessarily heavy and bulky, and
did not
readily allow for redundancy.
[0004] As the performance, control and sophistication of aircraft have
increased, fly-by-
wire systems have been developed. In these systems, various manual inputs to
the joystick
handle are first transduced into electrical signals, and these are then
transmitted along various
redundant paths to one or more computers, and then to remotely-located motors
and drivers
that control movement of the various airfoil surfaces. Thus, mechanical
transmittals from
joysticks and column wheels have given way to electrical transmittals from
transducers
associated with the sticks.
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[00051 In more recent years, side-sticks have been developed. These are
typically mounted
ahead of an arm rest located on the outboard sides of the pilot's and co-
pilot's seats. The pilot
is typically seated in the left seat, and the co-pilot in the right seat.
Thus, the pilot's side-stick
us usually to his left, and the co-pilot's side-stick us usually to his right.
Hence, the pilot will
typically rest his left arm on his left arm rest, and will control his side-
stick with his left hand,
while the co-pilot will typically rest his right arm on his right arm rest,
and will control his
side-stick with his right hand. In many cases, the tilting of the stick about
the appropriate
axis was sensed as a function of position (see, e.g., U.S. Pats. No. 5,125,602
and 5,291,113).
In other cases, it was sensed as a function of force or torque (see, e.g.,
U.S. Pats. No.
6,028,409; 5,694,010 and 5,347,204).
[0006] Some of these side-sticks have been mounted on gimbals to allow for
omni-
directional or compound pivotal movement about the pitch and roll axes (see,
e.g., U.S. Pats.
No. 5,291,113 and 5,694,014).
[00071 Side-sticks are typically thought of as being either "passive" or
"active". A
"passive" side-stick unit ("PSSU") senses the pilot's or co-pilot's pitch and
roll commands as
functions of the tilting displacement of the associated control stick about
the appropriate axes.
These commands are then supplied to one or more flight control computers,
which, in turn,
control the movement of various airfoil surfaces to control the pitch and roll
of the aircraft.
The control stick may supply redundant command signals to the computer. Some
of these
devices use various springs to apply various force-feel gradients to the
handle of the control
stick to afford the pilot and copilot a tactile sensation and feel of various
conditions (see,
e.g., U.S. Pat. No. 5,125,602).
[0008] An "active" side-stick unit ("ASSU") is similar to a PSSU, but further
incorporates
motors to couple the positions of the pilot's and co-pilot's side-sticks. If
the pilot is actively
controlling the aircraft, and the co-pilot has his hand off his stick, the co-
pilot's stick will be
back-driven to follow and duplicate the various positional movements that the
pilot supplies
to his stick. Thus, the pilot's and co-pilot's sticks will tilt simultaneously
in parallel and in
unison, as if one were slaved to the other. Conversely, if the co-pilot is
actively controlling
the aircraft, and the pilot has his hand off his stick, the pilot's stick will
follow and duplicate
the positional commands supplied by the co-pilot to his stick. This is
sometimes known as
"position recopying" (see, e.g., U.S. Pat. No. 5,125,602), or an "electrical
cross-cockpit
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interconnect" (see, e.g., U.S. Pat. No. 5,456,428), or simply "cross-coupling"
(see, e.g., U.S.
Pat. No. 5,694,014).
[0009] If the aircraft is provided with an autopilot, the autopilot may
generate electrical
signals that are supplied to the motors associated with the pilot's and co-
pilot's control sticks
to back-drive both of these sticks.
[0010] It is also known to provide such side-sticks with various feedback
force sensations
that simulated the "feel" of the resistance of the airfoil surfaces to the
various input
commands, or the transitions between various operational conditions, or even a
vibration in
the case of an emergency. It is also known to damp such control sticks so as
to impede the
stick from freely moving from a manually-commanded position if the operator
were to let go
of the stick (see. e.g., U.S. Pats. No. 5,125,602; -6,459,228 and 4,069,720).
[0011] However, the column wheels, joysticks and side-sticks developed
heretofore have
involved various mechanical linkages and couplings that have introduced
friction, backlash,
and the like into the movement of the control stick. These designs are
believed to have been
heavy and bulky. They are believed to have interfered with the smooth
continuous
transmission of manual pilot input signals from the control stick to the
flight control
computer, and with the smooth continuous transmission of various electrical
signals to back-
drive the control stick in accordance with the electrically-commanded
movements and forces.
[0012] Accordingly, there is believed to be a demonstrated and long-felt need
to provide
improved control sticks that are adapted for use in 'both "passive" and
"active" fly-by-wire
flight control systems, and for improved linkages for use with such improved
control sticks,
and for improved compound torsional springs for possible use therein.
Disclosure of the Invention
[0013] With parenthetical reference to the corresponding parts, portions or
surfaces of the
disclosed embodiment(s), merely for purposes of illustration and not by way of
limitation, the
present invention broadly provides an improved control stick (20), an improved
linkage
(27)for use in a control stick, and an improved compound spring (38).
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10013a1 According to one aspect of the invention, there is provided in
a control stick
mounted on a support and adapted to control the movement of an object, the
improvement
comprising: a handle mounted on said support for compound pivotal movement
about two
mutually-perpendicular axes for providing an input of the desired movement of
said object; a
compound spring acting between said support and handle, said compound spring
including a
first tubular portion having a longitudinal axis, having a first wall
extending between a first
end and a second end, and having at least one first slot extending through
said first wall and
defined between opposing first slot walls such that if said first and second
ends are torsionally
rotated relative to one another, said first tubular portion will have one
force-to-displacement
characteristic when said first slot walls are spaced from one another and will
have another
force-to-displacement characteristic if said first slot walls contact one
another, and such that if
said first and second ends are flexed relative to one another in said common
plane, said first
tubular portion will have a third force-to-displacement characteristic; and a
linkage responsive
to movement of said handle for selectively applying a relative torsional force
between said
first and second ends about said longitudinal axis, or a flexure force between
said first and
second ends; whereby said compound spring may provide a simulated feel of said
object to
said handle.
[0014] In one aspect, the invention provides an improvement in a
control stick (20)
mounted on a support (21) and adapted to control the movement of an object
(not shown). The
improvement broadly includes: a support (21); and a linkage (27) for mounting
a handle
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(24) on the support for selective compound pivotal movement about two mutually-
perpendicular axes (X411-XU!, X(12-XU2) to provide an input to the control
stick. The linkage
includes: a first gimbal .(22) mounted on the support; an upper member (23)
mounted on the
first gimbal, the upper member having a handle (24) arranged above the first
gimbal, and
having a lower portion (25) arranged below the first gimbal; an intermediate
member (26); a
second .gimbal (28) connecting the upper and intermediate members; and a lower
member
(29), one Of the intermediate and lower members being movably mounted on the
other of the
intermediate and lower members to permit relative movement therebetween when
the handle
is moved relative to the support; a third gimbal (30) connecting the lower
member to the
support; and a resilient member (31), such as a column spring, arranged to
bias the direction
of relative movement between the intermediate and lower members. The handle
may be
grasped and selectively moved relative to the support to provide an input to
the linkage.
[0015] The resilient member (31) may be arranged to exert a force that
substantially
removes all backlash from the linkage. The resilient member may urge the
handle to move
toward a null position relative to the support.
[0016] The improvement may further include an object-to-be-moved (e.g., an
airfoil
surface), and at least one transducer (32, 32, 32) mounted on the support to
sense the position
of a portion of the linkage and to produce an electrical signal proportional
to such sensed
position. The handle is adapted to be moved relative to the support to cause
the transducer to
provide a command signal for moving the object.
[0017] The improvement may further include a plurality of springs (33, 33, 34,
34) acting
between the support and the linkage. These springs have different force-to-
deflection
characteristics. At least one of the springs may be a compound spring (38).
[0018] In
the improved control stick, the extent of movement between the intermediate
and lower
members when the handle is moved off null may be a function of the ratio of
(a) the distance between
the pivotal axes of the first and second gimbals (i.e., dimension a in Fig.
4), and (b) the distance
between the pivotal axes of the second and third gimbals (i.e., dimension b in
Fig. 4). The angle of
deflection between (i) an imaginary line joining the pivotal axes of the first
and second gimbals, and
(ii) an imaginary line joining the pivotal axes of the second and third
gimbals (i.e., angle C in Fig. 4),
may be substantially equal to the sum of (a) the angle of deflection of the
upper member relative to an
imaginary line joining the pivotal axes of the first and third gimbals (i.e.,
angle A in Fig. 4), and (b)
the angle of deflection of the lower member relative to the imaginary line
joining the pivotal axes of
the first and third gimbals (i.e., angle B in Fig. 4).
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[0019] The improvement may further include a magnetic detent (35) acting
between the
support and the linkage for requiring that a force be exerted on the handle to
move the handle
off null.
[0020] The improvement may further include a damper (36) acting between the
support
and linkage for damping the velocity of the handle. This damper may be an eddy
current
damper.
[0021] The improvement may further include a motor (not shown) acting between
the
support and linkage for causing the linkage to move as a function of a signal
supplied to the
motor."
= [0022] The improved control stick may be mounted on an aircraft having a
fly-by-wire
control system, and the improved control sticks may be mounted at the pilot's
station and at
the co-pilot's station. The pilot's and co-pilot's control sticks may be cross-
coupled to move
together. The aircraft may have an autopilot, and the pilot's and co-pilot's
control sticks may
be moved together in response to a signal supplied by the autopilot.
- [0023] In another aspect, the invention provides an improvement in a control
stick (20)
adapted to control the movement of an object. The improvement includes: a
support (21); an
upper member (23) pivotally mounted on the support, the upper member having a
lower
portion (25) arranged below its pivotal connection with the support; an
intermediate member
(26) having an upper portion pivotally connected to the upper member lower
portion, and
having a lower portion; and a lower member (29) having a lower portion
pivotally mounted
on the support, and having an upper portion; and wherein the intermediate
member lower
portion is movably mounted on the lower member such that pivotal movement
of the upper member upper portion relative to the support will produce pivotal
movement of
the intermediate and lower members relative to the support; and a resilient
member (31)
arranged to bias the direction of relative movement between the intermediate
and lower
members.
[0024] The upper member may be mounted on the support for pivotal movement
about an
axis (xui-xur, or xu2-xu2) intermediate the length of the upper member, the
upper member
may have an upper portion arranged above the axis and arranged to function as
a handle (24),
and the handle may be grasped and selectively manipulated to provide an input
to the linkage.
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100251 The upper member may be mounted for compound pivotal movement about two
mutually-perpendicular axes (xui-xui, xu2-xu2) relative to the support.
[0026] The force exerted by the resilient member may urge the upper member to
move
toward a null position relative to the support. The resilient Member may be
arranged to exert
a force that substantially eliminates all backlash from the linkage. The force
exerted by the
resilient member may be adjustable.
[0027] The extent of movement between the intermediate and lower members when
the upper
member is moved off null may be a function of the ratio of (a) the distance
between the pivotal axis
between the upper member and the support and the pivotal axis between the
intermediate member and
= the support (i.e., dimension a in Fig. 4), and (b) the distance between
the pivotal axis between the
intermediate member and the support and the pivotal was between the lower
member and the support
(i.e., dimension b in Fig. 4). The angle of deflection between (i) an
imaginary line joining the pivotal
axes of the first and second gimbals, and (ii) an imaginary line joining the
pivotal axes of the second
and third gimbals (i.e., angle C in Fig. 4), may be substantially equal to the
sum of (a) the angle of
deflection of the upper member relative to an imaginary line joining the
pivotal axis between the upper
member and the support and the pivotal axis between the lower member and the
support (i.e., angle A
in Fig. 4), and (b) the-angle of deflection of the lower member relative to
the imaginary line joining
the pivotal axis between the upper member and the support and the pivotal axis
between the lower
member and the support (i.e., angle B in Fig. 4).
[0028] The upper member and the support may be connected by a universal joint,
such as a
gimbal mechanism (22).
[0029] The intermediate member (26) may be mounted for compound pivotal
movement
about two perpendicular axes (xmi-xitm xm2-xm2) relative to the upper member.
[0030] The upper and intermediate members may be connected by a universal
joint, such
as a gimbal mechanism (28).
[0031] The lower member (29) may be mounted for compound pivotal movement
about =
two mutually-perpendicular axes (xLi-xm, xa-xL2) relative to the support.
[0032] The lower member and the support may be connected by a universal joint,
such as a
gimbal mechanism (30).
[0033] The intermediate member lower portion may be slidably received in the
lower
member upper portion.
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[0034] The resilient member may contribute to the force-feel gradient of the
handle
portion.
[0035] The improvement may further include at least one first position sensor
(32, 32, 32)
mounted on the support and engaging the upper member lower portion for
providing a first
output signal as a function of the position of the upper member lower portion
about one of the
axes, and possibly at least one second displacement sensor (32, 32, 32)
mounted on the
support and engaging the upper member lower portion for providing a second
output signal as
a function of the position of the upper member lower portion about the other
of the axes.
[0036] The improvement may further include a first upper spring (33), such as
a compound
spring, acting between the upper member and support for affecting the force
required to move
the handle about one of the axes, and possibly a second upper spring (33),
such as a
compound spring, acting between the upper member and support for affecting the
force
required to move the handle about the other of the axes.
[0037] The improvement may further include a first intermediate spring (34),
such as a
compound spring, acting between the intermediate member and support for
affecting the
force required to move the handle about one of the axes, and possibly a second
intermediate
spring (34), such as a compound spring, acting between the intermediate and
support for
affecting the force required to move the handle about the other of the axes.
The first
intermediate spring provides a distinct change in the force-feel gradient to
alert an operator of
a change in the displacement of the handle.
[0038] The improvement may further include a breakout device (35)for exerting
a small
force on the intermediate member that is required to be overcome for an
operator grasping the
handle to break out of the null position. The breakout device may include a
plurality of
magnets mounted on the support and intermediate member.
[0039] The improvement may further include a damper (36) acting on the lower
member to
damp the velocity of the handle. The damper may be an eddy current damper.
[00401 In another aspect, the invention provides a control stick (20) which
broadly
includes: a support (21); a linkage (27) having a handle (24) and being
mounted on the
support; and a plurality of position sensors (32, 32, 32)mounted on the
support and engaging
the linkage at various locations thereon, each of the position sensors being
adapted to produce
an output signal as a function of the position of the linkage locations
relative to the support; a
plurality of springs (33, 33, 34, 34) acting between the support and linkage
for affecting the
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force-feel characteristics of the linkage; a magnetic detent (35) acting
between the support
and linkage for requiring an operator to apply a force to the handle to move
the handle off
null; and a damper (36) acting between the support and linkage for damping the
velocity of
the handle. '
[0041] Each of the springs may have its own individual force-to-deflection
characteristic,
and the force-feel characteristic of the linkage may be a function of the
various individual
force-to-deflection characteristics of the springs. In the preferred
embodiment, the force-feel
characteristic of the linkage is a function of the sum of the various
individual force-to-
deflection characteristics of the springs and the geometry of the linkage.
[0042] The springs may urge the handle to move toward a null position relative
to the
support, and one of the springs may be arranged to exert a force that
substantially removes all
backlash from the linkage.
[0043] In still another aspect, the invention provides a compound spring (38),
which
broadly includes: a first tubular portion (40) having a first wall extending
between a first end
(41) and a second end (42); at least one first slot (43) extending through the
first wall and
defined between opposing slot walls such that when the first and second ends
are rotated
relative to one another, the spring will have one force-to-displacement
characteristic when the
slot walls are spaced from one another and will have another force-to-
displacement
characteristic when the slot walls contact one another; and a third force-to-
displacement
characteristic when the first and second ends are flexed relative to one
another in a common
plane.
[0044] The first slot may be elongated in a direction parallel to the
longitudinal axis of the
first tubular portion. There may be a plurality of the first slots, and these
may be spaced
circumferentially from one another about the first tubular portion.
[0045] The spring may further include a second tubular portion (44) arranged
within the
first tubular portion and having a second wall extending between the second
end (42) and a
third end (45). The second tubular portion may have at least one second slot
(46) extending
through the second wall and defined between opposing slot walls. The second
slot may be
elongated in a direction parallel to the longitudinal axis of the second
tubular portion, and a
plurality of the second slots may be spaced circumferentially from one another
about the
second tubular portion.
[0046] The third end (45) may be arranged proximate the first end (41).
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[0047] Accordingly, the general object of some aspects of the invention is to
provide an improved
tontrol stick.
[0048] Another object of some aspects of the invention is to provide an
improved linkage for use in
a control stick. = =
[0049] Still another object of some aspects of the invention is to provide an
improved compound
spring that is particularly adapted for use in a control stick..
= [0050] These and other objects and advantages will become apparent from
the foregoing and
ongoing written specification, the drawings and the appended claims.
Brief Description of the Drawings
[0051] Fig. 1 is a schematic view of one form of mechanical linkage of an
improved
control stick, this view showing the positions of the upper, intermediate and
lower members
when the handle is in its null position relative to the support.
[0052] Fig. 2 is a schematic view of the structure shown in Fig. 1, but
showing the
. positions of the upper, intermediate and lower members after the handle has
been moved to
an off-null position.
[0053] Fig. 3 is a simplified schematic showing the angles between the various
linkage
members when the handle has been moved to an off-null position. =
[0054] Fig. 4 is a simplified schematic showing the forces and moments acing
on the
various linkage members when the handle has been moved to an off-null
position.
[0055] Fig. 5 is a simplified schematic of the control stick linkage, showing
the various
springs, sensors and dampers acting between the support and the various
members.
[0056] Fig. 6 is a series of -plots of force (ordinate) vs. rotation angle
(abscissa)
. characteristics of the basic spring, the soft-stop and differential
functions of the secondary
springs, the column spring, and further showing the added or superimposed
function of all of
the foregoing springs.
[0057] Fig. 7 is an isometric view of one form of an improved compound
torsional spring.
[0058] Fig. 8 is a side elevation of the spring shown in Fig. 7.
[0059] Fig. 9 is a horizontal sectional view thereof, taken generally on line
9-9 of Fig. 8.
= [0060] Fig. 10 is an isometric view of a commercial form of the improved
control stick
with the handle shown as having been tilted to an off-null position, this view
showing the
compactness of the packaging of this particular embodiment.
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Description of the Preferred Embodiments
[0061] At the outset, it should be clearly understood that like reference
numerals are
intended to identify the same structural elements, portions or surfaces
consistently throughout
the several drawing figures, as such elements, portions or surfaces may be
further described
or explained by the entire written specification, of which this detailed
description is an
integral part. Unless otherwise indicated, the drawings are intended to be
read (e.g., cross-
hatching, arrangement of parts, proportion, degree, etc.) together with the
specification, and
are to be considered a portion of the entire written description of this
invention. As used in
the following description, the terms "horizontal", "vertical", "left",
"right", "up" and "down",
as well as adjectival and adverbial derivatives thereof (e.g., "horizontally",
"rightwardly",
"upwardly", etc.), simply refer to the orientation of the illustrated
structure as the particular
drawing figure faces the reader. Similarly, the terms "inwardly" and
"outwardly" generally
refer to the orientation of a surface relative to its axis of elongation, or
axis of rotation, as
appropriate.
[0062] Referring now to the drawings, the present invention provides certain
improvements in a control stick. Such a control stick might be a joystick, a
side-stick, or
some other type of control device for remotely controlling an object. In the
accompanying
drawings, the improved control stick is depicted as being a being a side-stick
for use with an
aircraft to control the various airfoil surfaces thereon. However, this is
only illustrative and is
not limitative of the scope of the appended claims.
[00631 One form of the mechanical linkage of the improved control stick is
shown
principally in Figs. 1, 2 and 5.
[0064] Referring now to Figs. 1 and 2, the improved control stick, generally
indicated at
20, is shown as being mounted on a suitable support, generally indicated at
21. In an aircraft
environment, the control stick 20 would typically be mounted in the cockpit of
an aircraft,
and used to control the movement of a remote object, such as the flaps,
rudders and ailerons.
[0065] The arrangement in shown in Figs. 1 and 2 schematically depicts the
linkage (27) as
including a three-gimbal mechanism. As used herein, a "gimbal" is a device
having two rings
mounted at right angles to one another so that an object may remain suspended
therein,
regardless of movement of the support on which it is mounted. It is one
particular species of
a broader class of joints and connections that allow compound pivotal movement
about two
mutually-perpendicular axes. Other joints and connections of this class
include universal
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joints, ball-and-socket jbints that allow for omni-directional pivotal
movement of one
member relative to another, and the like. More particularly, the improved
linkage broadly
includes a first or upper gimbal 22. An upper member 23 is mounted on the
first gimbal
mounted on the support for compound pivotal movement about mutually-
perpendicular axes
xtir-xu, and xu2-xu2. The upper member has a handle 24 arranged above the
first gimbal, and
has a lower portion 25 arranged below the first gimbal. The linkage is shown
as further
including an intermediate member 26, and a second gimbal 28 connecting the
upper marginal
end portion of the intermediate member with the lower marginal end portion of
the upper
member for compound pivotal movement about mutually-perpendicular axes xmi-
xA,II and
x,v12-xA/2. The device is further shown as having a lower member 29. One of
the lower and
intermediate members is movably mounted on the other of the intermediate and
lower
members. In the arrangement shown, the lower marginal end portion of
intermediate member
26 is slidably and telescopically received in lower member 29, but this
arrangement could be
reversed if desired. The lower marginal end portion of lower member 29 is
mounted on the
support by a third gimbal 30 for compound pivotal movement about mutually-
perpendicular
axes xm-xLi and xL2-xL2. A coil spring 31 is arranged to act between the lower
and
intermediate members. This spring is in constant compression, and continually
urges the
intermediate member to move downwardly relative to the lower member. This has
the
practical effect of removing substantially all backlash from the three-member
linkage.
[0066] The mechanical linkage is shown in Fig. 1 as being in a centered or
null position
relative to the support. In this position, the longitudinal axes of all three
members 23, 26 and
29 are vertically aligned. In Fig. 2, the uppermost handle is shown as having
been tilted
leftwardly relative to the support, with a concomitant rightward movement of
the lower
marginal end portion of the upper member. Note also that this motion is
accommodated by
pivotal movement of the intermediate and lower members about axis xL2-xL2, and
by axial
movement of the intermediate member relative to the lower member, and by
additional
compressive displacement of spring 31.
100671 As noted above, while the present invention has been shown as being
implemented
in the form of a side-stick for a pilot and co-pilot, persons skilled in this
art will readily
appreciate that such a mechanism might be implemented in the form of a
joystick, or some
other type of control stick for controlling an object. The object itself might
be the airfoil
surfaces of an aircraft, or some other object.
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[00681 Fig. 3 is a further simplified schematic of the linkage when the handle
has been
displaced off null. While a gimbal mechanism allows for compound pivotal
movement about
two mutually-perpendicular axes, the embodiment schematically shown in Fig. 3
depicts
motion in about only one such axis for each gimbal. The upper pivot point of
the first gimbal
is indicated at xw , the intermediate pivot point of the second gimbal is
indicated at x,142, and
the pivot point of the lower gimbal is indicated at xi..2, so as to be
consistent with the
foregoing nomenclature. The link between intermediate and lower pivots xm2 and
xL2 is
indicated by reference numerals 26, 29 when in the null position, this being
the combined
effective length of the intermediate and lower members, and by reference
numerals 26', 29'
when in the illustrated off-null position.
[00691 When the handle is in its null position, the linkage is vertically
aligned, as shown
more clearly in Fig. 1. In Fig. 3, the distance between the upper and
intermediate pivots 31,
32 is indicated by distance A, and the distance between the intermediate and
lower pivots x,w2,
xL2 is indicated by distance B. When the handle is displaced from the null
position to an off-
null position, as indicated at 24', the lower end of the upper member will
swing to the
position indicated at 25', and the intermediate and lower members will move to
the alternative
positions indicated by 26', 29'. Angle A represents the included angle of the
displaced handle
off null. Angle B represents the included angle of the axis of intermediate
and lower
members 26', 29' off null. Angle C is the sum of angles A and B. Dimension dx
represents
the extension of the intermediate member relative to the lower member when
these two
members move from the null position to the off-null position, as accommodated
by further
compression of spring 31. The equations for Angles B and C, and distance dx
are as follows:
sin(AngleA) x A
AngleB = tan -1[ B + (A ¨ cos(AngleA) x A
AngleC = AngleA + Ang1 eB
[sin(AngleA) x A]¨ B
clx ¨
sin(AngleB )
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[0070] Referring now to Fig. 4, a force Fu exerted by the pilot's hand through
the arm
distance, GRP, of the grip, will create an upper moment Mu about upper pivot
point xu2. The
force exerted at the second pivot point will be a function of distances a and
b. The moment
about the middle pivot, xm2, is calculable. Similarly, the force exerted on
the intermediate
pivot point is also calculable. These relationships are expressed by the
following equations:
M
¨ ____________________________________ GRp-
= F M u xa
L GRP xb
MM =¨F x(GRP -F A) ¨F m x A
M =¨Fu[(GRP + A)+ A]
M
Fki =
(GRP x A)
[0071] Thus, the extent of movement between the intermediate and lower members
when the
handle is moved off null is a function of the ratio of (a) the distance
between the pivotal axes of the
first and second gimbals (i.e., dimension a in Fig. 4), and (b) the distance
between the pivotal axes of
the second and third gimbals (i.e., dimension b in Fig. 4). The angle of
deflection between an
imaginary line joining the pivotal axes of the first and second gimbals and an
imaginary line joining
the pivotal axes of the second and third gimbals (i.e., angle C in Fig. 4) is
substantially equal to the
angle of deflection of the upper member relative to an imaginary line joining
the pivotal axes of the
first and third gimbals (i.e.,. angle A in Fig. 4), and the angle of
deflection of the lower member relative
to an imaginary line joining the pivotal axes of the first and third gimbals
(i.e., angle B in Fig. 4).
[0072] Fig_ 5 is a schematic view of the improved control stick 20, but
further showing the
various springs, sensors and dampers attached thereto. In Fig. 5, the linkage
27 is again
shown as including an upper member 23 having an upper handle 24 and a lower
arm 25, an
intermediate member 26, and a lower member 29. The lower marginal end portion
of the
intermediate member is depicted as being telescopically received in lower
member 29. Coil
spring 31 continuously urges the intermediate member to move downwardly
relative to the
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lower member. In Fig. 5, the linkage is shown as being mounted for movement in
only one
plane, this being for simplicity of illustration. Upper member 23 is mounted
on the support
21 for pivotally movement about axis xu2. The upper marginal end portion of
the
intermediate member is pivotally connected to the lower marginal end portion
of the upper
member for pivotal movement about axis XA,f2. Finally, the lower member 29 is
pivotally
mounted on the support for movement about axis xL2. It should be clearly
understood that
this arrangement may include the three-gimbals, although the details of such
gimbals is not
fully shown.
[0073] In Fig. 1, movement of the upper member 23 is sensed by three redundant
position
sensors, severally indicated at 32. Three of these position sensors are
located at diametrically
opposite positions. There would also be three additional positions sensors on
either side of
the upper member in a plane coming out of the paper as well. The function of
these position
sensors is to sense and determine the extent of tilting movement of the upper
member relative
to the support. There are three of such position sensors to provide triple
redundancy.
[0074] Within the position sensors, there are a plurality of opposing compound
torsional
springs, severally indicated at 33. Here again, two opposing torsional springs
are depicted in
Fig. 5, and there are an additional two opposing springs in the plane coming
out of the paper.
The function of these springs is to provide some force-feel resistance to
tilting movement of
the handle. The structure and operation of these compound torsional springs is
shown more
clearly in Figs. 7-9, and described infra.
[0075] Certain additional torsional springs, indicated at 34, 34 are active
between the upper
and intermediate members to provide certain secondary spring functions, and
soft stops. This
arrangement may also include a magnetic detent, indicated at 35 that would
affirmatively
require that the 'pilot exert some force to move the linkage off null.
[0076] Still referring to Fig. 5, opposed eddy current dampers, severally
indicated at 36,
are arranged to act between the support and the lower member to damp the
velocity of
movement of the linkage. Here again, there are actually four velocity dampers,
arranged in
opposing pairs.
[0077] Fig. 6 illustrates the individual functions of the various springs
shown in Fig. 5, and
illustrates graphically the net function attributable to their summation. The
basic spring
function is depicted as being a straight line between the ordinate (force) and
the abscissa
(rotation). The secondary springs 34 provide the soft-stop and differential
functions as
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indicated in Fig. 6. The column spring 31 has the illustrated force-to-
displacement
characteristics shown. The curve labeled "net function" is obtained by
superimposing the
other four curves shown in Fig. 6. Fig. 6 illustrates that the various springs
may be carefully
selected so that their properties, when superimposed may give whatever net
function is
desired.
[00781 Referring now Figs. 7-9, one of the compound torsion springs is
generally indicated
at 38. This spring is shown as having a mounting flange 39 which is adapted to
be connected
to suitable structure, depending upon its application. The spring further has
a first tubular
portion, indicated at 40, which is connected to the flange which has a first
end 41 connected
to the flange and extends rightwardly therefrom to a second end 42. This first
tubular portion
is shovvn as having at least one longitudinal slot, indicated at 43. In the
form shown, the first
tubular portion has a plurality of such slots, and these are spaced
circumferentially about the
first tubular portion.
[00791 The spring may also have a second tubular portion 44 within the first
tubular
portion 40. The second tubular portion is physically connected to the first
tubular portion at
second end 42, and extends leftwardly within the first tubular portion to a
third end 45.
Second tubular portion 44 has at least one longitudinally extending slot 46.
In the form
shown, there are a plurality of such slots 46, these are circumferentially
spaced from one
another about the second tubular portion. The reason for the slots is to
afford the capability
of having one force-to-displacement characteristic when a torsional force is
exerted on the
spring between the first end and the third end before the opposing slot walls
physically
contact one another, and a second force-to-displacement characteristic after
such slot walls do
contact with one another. In effect, the two tubular portions are mechanically
connected in
series, although the second is arranged within the first. The
circumferentially spacing
between the opposed longitudinally extending walls of the slots may be the
same or different
between the two tubular portions, depending on the particular force-to-
displacement
characteristics desired. Moreover, one unique feature of the improved spring
is that it is not a
pure torsional spring. Rather, it may act as a torsional spring, and may also
be subjected to
flexure in a plane, such as the plane of the paper. The various torsional
springs shown in Fig.
may be selectively designed to afford the particular force-to-displacement
characteristics
desired, so as to contribute to the overall net function of the device.
Another unique feature
of the compound spring is that by having the inner tube positionally reversed
on the outer
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tube, the spring is axially compact. This affords great advantages, because it
allows the
capability of providing the control stick within a small package or envelope,
as shown in Fig.
10.
[0080] Therefore, the present invention provides an improved control stick, an
improved
linkage for use therein, and an improved compound spring.
Modifications
[0081] The present invention contemplates that many changes and modifications
may be
made. For example, while one form utilizes a three-gimbal mechanical linkage
with the
various members, other types of connections might alternatively be used.
Indeed, the
connection could be simplified to a type of socket joint, a universal joint,
or some other joint.
Indeed, while the principal advantage of these forms is that such joints and
connections allow
for compound pivotal movement of the handle about mutually perpendicular axes,
in
alternative arrangements other types of linkages might be used. In some cases,
the linkage
may be affected by the geometry of the links.
[0082] The column spring is deemed particularly useful for removing
substantially all of
the backlash from the linkage. In effect, it continuously biases the linkage
so as to remove
the feeling of backlash. However, such column spring, while desired, is not
absolutely
critical.
[0083] Shown in Fig. 6, different types of springs, sensors and dampers may be
associated
with different parts of the linkage. While the primary springs 33 are
associated with the
upper member and a secondary springs are associated with the intermediate
member, this
arrangement is not invariable, and may be changed. Also, the position of the
eddy current
dampers may be changed. Similarly, the location of the breakaway detents 35
may also be
changed or modified, as desired.
[0084] The compound torsional spring is also deemed to be unique. This spring
is deemed
to be a compound spring in the sense that it is operatively arranged to resist
both torsion
about its axis x-x, and flexure in a particular plane, such as (but not
limited to) the plane of
the paper. In its simplest form, the torsional spring simply has one tubular
portion provided
with at least one, but preferably a plurality of circumferentially-spaced
longitudinally-
extending slots. The fiinction of these slots is so that the spring will have
one force-to-
displacement characteristic when the second end is rotated relative to the
first end and before
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the slot walls contact one another, and a second and different force-to-
displacement
characteristic after the slot walls contact one another. By spicing the slots
circurriferentially
about the first tubular portion, the spring is more symmetrical, and has
similar properties to
= resist flexure in any particulat direction. The spring may also have a
reversed second portion
= within the first portion. Persons skilled in this art will readily
appreciate that the first and
second portions, being commonly connected at the second end, are mechanically
connected
in series with one another. However, the reversed inner or second portion
allows for a
compact arrangement, and this is deemed particularly useful where the size of
the envelope is
constrained, such as in an aircraft.
[0085] Therefore, while several simplified and progressively-more detailed
embodiments
of the invention have been shown and described, and several modifications and
changes
thereof discussed, persons skilled in this art will readily appreciate that
various additional
changes and modifications may be made without departing from the scope of the
invention, as
defined and differentiated by the following claims.
