U.S. patent application number 09/815117 was filed with the patent office on 2002-09-26 for dual input servo coupled control sticks.
Invention is credited to Dyra, Brian, Makhlin, Alex, Szulyk, Zenon.
Application Number | 20020135327 09/815117 |
Document ID | / |
Family ID | 25216914 |
Filed Date | 2002-09-26 |
United States Patent
Application |
20020135327 |
Kind Code |
A1 |
Szulyk, Zenon ; et
al. |
September 26, 2002 |
DUAL INPUT SERVO COUPLED CONTROL STICKS
Abstract
The present invention provides an active control system for
coupling the movements of a pair of independently operated manual
input devices such as dual flight control sticks operated by a
pilot and co-pilot flying an aircraft. Each input device is
configured to receive manual input data in the form of angular
displacement of the device about one or more rotational axes. The
active control system provides desired tactile feedback to an
operator who displaces one of the manual input devices in the form
of a restorative centering force. If an external system such as an
auto-pilot system is engaged, the restorative force may be in a
direction necessary to reconcile manual displacement of the input
device with a position commanded by the external system, rather
than directed toward the center position. The system also acts to
reflect manual displacement of each input device as a force applied
to the other. For example, when a pilot moves his or her control
stick forward, the co-pilot will feel a like force tending to move
the co-pilot's control stick forward.
Inventors: |
Szulyk, Zenon; (Mount
Prospect, IL) ; Dyra, Brian; (Elmhurst, IL) ;
Makhlin, Alex; (Skokie, IL) |
Correspondence
Address: |
LAFF, WHITESEL & SARET, LTD.
Suite 1700
401 North Michigan Avenue
Chicago
IL
60611-4212
US
|
Family ID: |
25216914 |
Appl. No.: |
09/815117 |
Filed: |
March 22, 2001 |
Current U.S.
Class: |
318/34 |
Current CPC
Class: |
G05D 1/085 20130101 |
Class at
Publication: |
318/34 |
International
Class: |
H02P 001/54 |
Claims
What is claimed is:
1. An active control system for applying desired force versus
displacement characteristics to each of a first input device and a
second input device, each input device being configured to receive
a manual torque input for angularly displacing the input device
about a control axis associated therewith, the active control
system comprising: first and second motors coupled to the first and
second input devices for applying a restorative torque to the first
and second input devices about their respective control axes; a
first servo control loop associated with the first motor and a
second servo control loop associated with the second motor, each
servo control loop comprising a position sensor for generating a
position signal indicative of the angular position of the input
device associated therewith, a force profile gain amplifier, and a
servo controller, the force profile gain amplifier receiving and
amplifying a position error signal derived from the position
signal, the gain of the force profile amplifier being a function of
the angular position of the input device, the output of the force
profile gain amplifier comprising a torque error signal input to
the servo controller, the servo controller generating current of
polarity and magnitude to drive the motor in a direction opposite
the direction of displacement of the input device, applying a
restorative torque to the input device having a magnitude
proportional to the magnitude of the error signal input to the
servo controller; and a cross-coupling feedback loop for reflecting
the relative positions of the first and second input devices in the
torque error signal input to the servo controllers associated with
the first and second servo control loops so that the torque applied
to the first and second input devices acts to reconcile the
positions therebetween.
2. The active control system of claim 1 further comprising a
command signal representing an angular position to which the first
and second input devices are being commanded by an external control
system, the position error signals associated with the first and
second servo control loops comprising the angular position signal
associated with each respective input device subtracted from the
command signal.
3. The active control system of claim 2 wherein each of the first
and second servo control loops further comprise a velocity damping
loop wherein an angular velocity signal proportional to the angular
velocity of the input device is amplified by a damping profile
amplifier, and a velocity damping signal output from the damping
profile amplifier is subtracted from the torque error signal.
4. The active control system of claim 3 wherein the damping profile
amplifier has a variable gain output which is a function of the
angular velocity of the input device.
5. The active control system of claim 2 wherein the cross-coupling
feedback loop includes a relative position signal comprising the
difference between the angular position signal of the second input
device and the angular position signal of the first input device,
and a proportional gain amplifier for amplifying the relative
position signal.
6. The active control system of claim 5 wherein the cross-coupling
feedback loop further includes an integrating amplifier for
integrating the relative position signal.
7. The active control system of claim 6 wherein the cross-coupling
feedback loop further comprises a relative velocity signal
comprising the difference between the first input device angular
velocity signal and the second input device angular velocity
signal.
8. The active control system of claim 7 wherein an integrated
relative position signal output from the integrating amplifier is
added to the proportionally amplified relative position signal
output from the proportional gain amplifier and the relative
velocity signal is subtracted from the integrated relative position
signal and the proportionally amplified relative position signal to
form a cross-coupled position signal.
9. The active control system of claim 8 wherein the cross-coupling
feedback loop further comprises a cross-coupled damping amplifier
for amplifying the cross-coupled position signal, the damped
cross-coupled position signal output from the cross-coupled damping
amplifier being added to the torque error signal of one of the
first and second servo control loops and subtracted from the torque
error signal of the other of the first and second servo control
loops.
10. The active control system of claim 1 wherein the cross-coupling
feedback loop comprises a damped proportional integral derivative
signal based on the difference between the position signal
associated with the first input device, and the position signal
associated with the second input device.
11. An active control system for supplying tactile feedback to a
pair of manual input devices comprising: first and second manual
input devices, each adapted to receive input in the form of a
manual torque applied to displace the input device about a control
axis; first and second servo control loops each comprising a servo
motor coupled to a respective one of the input devices to apply a
controlled restoring torque thereto about the associated control
axis, and a servo controller for providing drive current to the
motor of polarity necessary to drive the motor in a direction
reducing the magnitude of a torque error signal and of a magnitude
proportional to the magnitude of the torque error signal; each of
the first and second servo control loops further comprising a
position feedback loop and a velocity feedback loop, the position
feedback loop providing a position error signal proportional to the
difference between the angular position of the input device and a
commanded position, the position error signal being input to and
amplified by a force profile gain amplifier having a variable gain
output dependent on the angular position of the input device; and a
cross-coupling feedback loop comprising a relative position error
signal representing the difference in angular position between the
first and second input devices, the relative position error signal
being added to the error signal input to the servo controller
associated with one of the first and second servo control loops,
and subtracted from the error signal input to the servo controller
associated with the other of the first and second servo control
loops.
12. The active control system of claim 11 wherein the commanded
position is determined by a command signal generated by an external
control device.
13. The active control system of claim 12 wherein the first and
second manual input devices comprise first and second flight
control sticks, and the command signal is generated by an autopilot
system.
14. The active control system of claim 11 wherein the gain of the
force profile gain amplifier increases linearly with increases in
angular displacement of the input device.
15. The active control system of claim 11 wherein the gain of the
force profile gain amplifier comprises a compound force profile,
the gain increasing linearly at a first rate with displacement of
the input device over a first range of displacement angles, and
increasing linearly at a second rate over a second range of
displacement angles.
16. The active control system of claim 11 wherein the
cross-coupling feedback loop comprises a damped proportional
integral derivative signal based on the difference between an
angular position signal associated with the first input device, and
an angular position signal associated with the second input
device.
18. The active control system of claim 11 wherein the velocity
feedback loop comprises a velocity signal representing the angular
velocity of the input device which is input to a velocity damping
profile amplifier having a variable gain output depending on the
magnitude of the velocity signal.
19. An active control system for applying a restorative torque to a
pair of self-centering manual input devices, the system comprising:
a first servo loop configured to apply a restorative torque to a
first input device; a second servo loop configured to apply a
centering torque to a second input device; a cross-coupled feedback
loop wherein a first position signal indicative of an angular
position of the first input device is fed back to the second servo
loop to influence the magnitude of the restorative torque applied
to the second input device, and a second position signal indicative
of an angular position of the second input device is fed back to
the first servo control loop to influence the magnitude of the
restorative torque applied to the first input device; and wherein
each of the first and second servo loops includes a velocity
damping feedback loop comprising a velocity signal indicative of
the angular velocity of the associated input device, and a velocity
profile damping amplifier having a velocity sensitive variable gain
for amplifying the velocity feedback signal.
20. The active control system of claim 19 wherein the cross-coupled
feedback loop includes a relative position signal comprising the
difference between an angular position signal associated with the
second input device and an angular position signal associated with
the first input device, and a proportional gain amplifier for
amplifying the relative position signal.
21. The active control system of claim 20 wherein the cross-coupled
feedback loop further includes an integrating amplifier for
integrating the relative position signal.
22. The active control system of claim 21 wherein the cross-coupled
feedback loop further comprises a relative velocity signal
comprising the difference between a first input device angular
velocity signal and a second input device angular velocity
signal.
23. The active control system of claim 22 wherein an integrated
relative position signal output from the integrating amplifier is
added to a proportionally amplified relative position signal output
from the proportional gain amplifier and the relative velocity
signal is subtracted from the integrated relative position signal
and the proportionally amplified relative position signal to form a
cross-coupled position signal.
24. The active control system of claim 23 wherein the cross-coupled
feedback loop further comprises a cross-coupled damping amplifier
for amplifying the cross-coupled position signal, the damped
cross-coupled position signal output from the cross-coupled damping
amplifier being added to a torque error signal associated with of
one of the first and second servo control loops and subtracted from
a torque error signal associated with the other of the first and
second servo control loops.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an active control system
for providing desired force versus displacement characteristics to
a pair of manual input devices such as the flight control sticks
operated by a pilot and co-pilot flying an aircraft. In addition to
providing a desired force versus displacement profile for the input
devices, the active control system further acts to reflect manual
inputs applied at one of the input devices at the other of the two
input devices. Additionally, inputs from an outside source, such as
an autopilot signal, can be used to reflect motion onto both
control sticks. Variable gain velocity damping is also provided to
reduce oscillations at or near a zero or null position.
[0002] In many applications it is desirable to impart tactile
feedback to users of manually operated input devices. For example,
in mechanically linked systems, tactile feedback to the operator is
provided as a result of the force required to move the mechanical
parts associated with the system. In electronically controlled
systems, however, the physical interrelationship between the input
device and the mechanical components acted upon is replaced by
electrical signals generated by sensors in the input device which
signal actuators to act on the mechanical components. In such
systems, the force versus displacement characteristics of the input
device have no direct relationship to the systems being controlled.
It is thus desirable to generate mechanical forces to be applied to
the input device to emulate mechanically linked systems. Such
emulation provides the operator with tactile feedback regarding the
state of the system and the effects of his or her input actions.
Heretofore, self-centering control sticks having force versus
displacement characteristics that emulate mechanical systems have
employed mechanical spring arrangements or active servo control
systems.
[0003] Aircraft flight control systems are an application where it
is particularly important to provide accurate tactile feedback to
the pilot or co-pilot operating a control stick or yoke which
electrically interfaces with the mechanical systems for controlling
the flight control surfaces of the aircraft. Such "fly by wire"
systems employ various sensors to determine the position of and/or
force applied to the control stick in order to translate the
pilot's input commands into electrical signals for controlling the
flight control surfaces of the aircraft. In many aircraft, dual
control sticks are provided, one to be operated by the pilot and a
second to be operated by a co-pilot. In cases where there are dual
control sticks, it is desirable that actions taken on either one of
the control sticks are reflected in the other control stick in the
form of a force supplied to the second control stick in the
direction of the action taken on the first control stick.
[0004] An active control system for providing variable force feel
characteristics to a pair of manual input control stick is
disclosed in U.S. Pat. No. 5, 291,113 to Hegg et al. According to
the system disclosed there, a desired force versus displacement
profile is provided in which the magnitude of the control stick
displacement is proportional to the force applied in order to
emulate a purely mechanically linked system. The system includes a
pair of control sticks each of which is directly coupled through a
gimble to a motor in a conventional manner. A position signal from
the first input device is fed back and combined with an autopilot
or center position signal to create an error signal. This error
signal is amplified and input to servo control electronics to
generate excitation currents for a motor coupled to the control
stick. Thus, this position feedback loop causes the motor to drive
the control stick in a direction to reduce the amount of error
between the position commanded by the autopilot signal and the
actual position of the control stick. The gain of the amplifier
that acts on the difference between the stick position and the
autopilot reference command in Hegg, et al. is fixed, and serves to
define the mechanical spring rate being emulated, resulting in a
single force-versus-displacement gradient profile.
[0005] A second position signal generated from the position of the
second control stick is also fed back and summed with the position
signal from the first control stick. This signal is also amplified
and summed with the error signal input to the servo controller
driving the motor coupled to the first control stick. The signal
representing the combined position signal from the first and second
control sticks is amplified to a far greater extent than the error
signal between the autopilot signal in the position of the first
control stick. Thus, the position error signal between the first
and second control sticks will dominate over the position error
signal between the autopilot signal and the first control sticks.
The motor coupled to the first control stick will drive the first
control stick to a position intended to eliminate the position
error between the first and second control sticks, as well as
attempting to reconcile the position between the first control
stick and the position commanded by the autopilot signal, with
elimination of the position error between the two control sticks
predominating.
[0006] The position signals from both the first and second control
sticks are also in fed into the servo control electronics driving
the motor coupled to the second control stick. Thus, displacement
of the first control stick will also be reflected back to the
second control stick. Discrepancies between the autopilot signal
and the second control stick are rectified by having the second
control stick follow the position of the first control stick. The
operational characteristics of such a system are poor since the
system relies on the reconciled position of one stick as the signal
to drive the other. This can cause poor frequency response, lag in
position tracking, poor coupling and poor feel.
[0007] A second embodiment disclosed by Hegg et al. further
describes a torque sensor for generating a signal representative of
the torque applied to the first and second control sticks. These
signals are fed back and summed with the position error signals
which are input to the servo control electronics driving the motors
which are coupled to the first and second control sticks.
[0008] Another example of an active control system for controlling
the force feel characteristics of a manual input device such as a
flight control stick is disclosed in U.S. Pat. No. 5,347,2042
Gregory et al. A system is disclosed there for providing variable
damping to a servo control system in order to prevent oscillations
due to motor torque and high gain characteristics at or near the
center position. A signal representing the angular velocity of the
control stick is combined with the position error signal which is
supplied to the servo control electronics driving the motor coupled
to the control stick. The velocity feedback signal is subjected to
position dependent scaling which provides a variable rate gain
which is dependent on the angular position of the control stick.
The position dependent scaling is implemented via an amplifier
inserted in the velocity feedback loop. The gain of the amplifier
is established by a pair of resistors connected in parallel between
one of the inputs and the output of the amplifier. A position
dependent switch is connected in series with one of the resistors
such that when the control sticks is positioned within a first
position range the switch is open, and the gain of the amplifier is
determined by only one of the resistors connected across the input
and output of the amplifier. When the control stick is in a second
position range, the switch is closed and the gain of the amplifier
is determined by the parallel combination of the two resistors.
Thus, a higher gain setting for the feedback amplifier may be
established when the control stick is near the zero position to
provide higher rate damping for the overall servo loop when the
control stick is near the zero position, and less rate damping as
the control stick is moved away from zero in order to improve the
response characteristics of the system.
[0009] The present invention provides significant advantages over
prior art active control systems for dual input control devices.
The active control system of the present invention provides for
multi-shaped force versus displacement profiles in a simpler, less
expensive manner than the prior art. The present system provides
excellent frequency response with little or no lag in position
tracking, strong coupling between the input devices, with whatever
tactile response is desired. All of these features are provided
without the added cost and complexity of single or redundant
multiple force or torque sensors. Thus, the system is less
expensive and more reliable than prior art active control
systems.
SUMMARY OF THE INVENTION
[0010] The present invention relates to an active control system
for tactile feedback to an operator employing a manual input device
such as a flight control stick used for flying an aircraft.
Specifically, the invention provides desired force versus
displacement characteristics to each of a pair of input devices,
such as the pilot's and co-pilot's flight control sticks. In
addition to supplying a centering force to urge the input devices
back toward a predefined center position when the input devices are
manually displaced, the active control system will also act to
reconcile the positions of the two input devices with a command
signal received from an external source such as an autopilot.
Finally, differences in position between the first and second input
devices are reflected back to each other by way of a restoring
torque which tends to force each input device in the direction of
the position of the other. Thus, if one operator, such as a pilot
moves his or her flight control stick, the pilot's action will be
reflected as a force applied to the co-pilot's control stick in the
direction in which the position of the pilot's control stick varies
from the position of the co-pilot's control stick.
[0011] Each input device is configured to receive a manual torque
input for angularly displacing the input device about a control
axis. Each input device may include more than one control axis. For
instance, a single flight control stick may be configured to
receive manual input for controlling the pitch, roll, and yaw of an
aircraft, by moving the control stick relative to three separate
control axes. In cases where the input device comprises multiple
control axes, the active control system of the present invention
may be duplicated on each axis. However, for the sake of brevity
and clarity, the system is described herein as applied to only a
single control axis of each input device.
[0012] A servo motor is coupled to each of the first and second
input devices in a manner whereby the motor can apply torque about
the control axes of the two input devices. As will be described
below, the torque applied by the motors will generally be a
restorative torque directed toward returning the input devices to a
center or null position, or toward reconciling the position of the
input devices with a position command signal supplied by an
external system such as another side stick or the autopilot
system.
[0013] First and second servo control loops are associated with the
first and second motors respectively. Each servo control loop
comprises a position sensor for generating a position signal
indicative of the angular position of the corresponding input
device. A force profile gain amplifier and a servo controller are
also included in the first and second servo control loops. The
force profile gain amplifier receives a position error signal
derived by subtracting the angular position signal output by the
position sensor from the command signal received from an external
system. If the external system is not operable or not present, the
position error signal merely becomes the negative of the position
signal.
[0014] The gain of the force profile amplifier is variable, and is
a function of the angular position of the input device which is fed
back to the force profile gain amplifier from the position sensor.
This technique allows shaping of the force profile to include
multiple segments of different shapes, not limited to, but
including: breakout regions, main gradient, soft stop,
post-soft-stop gradient, and hard stop. All of these features can
be modifiable in real-time in terms of their magnitude and
position.
[0015] A torque error signal is output from the force profile
amplifier and input to the servo controller. The servo controller
converts the torque error signal to current for driving the motor.
The polarity and magnitude of the motor drive current are such as
to drive the motor in a direction opposite the direction of
displacement of the associated input device, with a restorative
torque proportional to the amount of displacement.
[0016] A cross-coupling feedback loop is also provided for
reflecting the relative positions of the first and second input
devices in the torque error signal input to the servo controllers
associated with the first and second servo control loops. This has
the effect of altering the torque applied to the first and second
input devices to reflect a force directed toward reconciling the
positions of the first and second input devices.
[0017] Each of the first and second servo control loops includes a
velocity damping loop. The amount of velocity damping is dependent
on the velocity of the associated input device. An angular velocity
signal proportional to the angular velocity of the input device is
fed back to a velocity damping profile amplifier both as an input
signal, and as the signal to be amplified. The variable gain of the
damping profile increases with the velocity of the respective input
device. Thus, the faster the input device is moved, the greater the
damping applied. The output of the profile damping amplifier is
subtracted from the torque error signal and acts to smooth the
torque characteristics applied to the input device.
[0018] The cross-coupling feedback loop includes a relative
position signal representing the difference between the angular
position signal of the second input device and the angular position
signal of the first input device. A proportional gain amplifier
amplifies the relative position signal, and an integrating
amplifier integrates and amplifies the relative position signal.
Also, a relative velocity signal is included in the cross-coupled
feedback loop. The relative velocity signal is obtained by taking
the difference between the first input device angular velocity
signal and the second input device angular velocity signal. A
signal summing device adds the integrated relative position signal
output from the integrating amplifier to the proportionally
amplified relative position signal output from the proportional
gain amplifier and subtracts the relative velocity signal. The
resultant cross-coupled position signal is input to a cross-coupled
damping amplifier, the output of which is added to the torque error
signal of one of the first and second servo control loops and
subtracted from the other of the first and second servo control
loops.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a block diagram of an active control system for
providing a desired force versus displacement profile to a pair of
manual input devices such as pilot and co-pilot flight control
sticks; and
[0020] FIG. 2 is a force versus displacement curve showing a
typical force profile for the input devices controlled by the
active control system depicted in FIG. 1.
[0021] FIG. 3 is a force versus displacement curve showing an
alternate force profile for the input devices controlled by the
active control system depicted in FIG. 1.
[0022] FIG. 4 is a force versus displacement curve showing another
alternate force profile for the input devices controlled by the
active control system depicted in FIG. 1.
[0023] FIG. 5 is a force versus displacement curve showing yet
another alternate force profile for the input devices controlled by
the active control system depicted in FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0024] The present invention provides an active control system for
coupling the movements of a pair of independently operated manual
input devices such as dual flight control sticks operated by a
pilot and co-pilot flying an aircraft. Each input device is
configured to receive manual input data in the form of angular
displacement of the device about one or more rotational axes. The
active control system of the present invention may be applied
independently to each input axis associated with the manual input
device, such as pitch, roll or yaw when the system is applied to
the flight control sticks of an aircraft. For the sake of clarity
the present description will be limited to a single control axis of
each manual input device with the understanding that the system may
be duplicated on additional control axes.
[0025] The active control system of the present invention provides
desired tactile feedback to an operator who displaces one of the
manual input devices. The system provides a restorative centering
force to the input device when an operator manually displaces the
input device from an arbitrarily defined null position. Preferably
the control system provides a force versus displacement curve or
"force profile" that emulates a mechanical spring system wherein
the restorative force increases with increased displacement of the
input device. However, other force profiles, including compound
force profiles, may also be implemented. Further, if an auto-pilot
system is engaged, the restorative force created by the control
system acts in the direction necessary to reconcile manual
displacement of the input device with an input device position
commanded by the auto pilot signal, rather than forcing the input
device back toward the null position. The system also reflects
manual displacement of each input device as a force applied to the
other. For example, when a pilot moves his or her control stick
forward, the co-pilot will feel a like force moving the co-pilot's
control stick forward.
[0026] FIG. 1 shows a block diagram 100 of an active control system
according to the present invention for controlling a pair of manual
input devices such as a pair of aircraft flight control sticks. A
first control loop 102 shown at the top of the diagram generates
and applies the restorative force applied to a first manual input
device 104. A second servo control loop 106 shown at the bottom of
the diagram generates and applies the restorative force applied to
a second manual input 108. A cross-coupled feedback loop 110 shown
in the center of the diagram provides position feedback from one
input device to the other which is converted to a tactile force
which is applied to either of the two input devices to indicate
that the other input device has been displaced.
[0027] Turning to the first control loop 102, the first manual
input device 104 receives manual input in the form of a torque
signal d applied by an operator, e.g. a pilot pushing a flight
control stick forward. Input device 104 is mechanically coupled to
the output of a servo motor 120 which is capable of delivering
torque to the input device. The torque applied to the input device
104 by the operator is subtracted from the torque output of the
motor 120, as indicated at summing junction 122. The direction of
torque applied by the operator will generally be directed opposite
the torque output by servo motor 120. Therefore, the manually
applied torque signal 142 is shown being subtracted from the output
torque 140 of servo motor 120 at summing junction 122. The combined
torque entered by the operator and applied by the servo motor 120
must overcome various mechanical influences built into the system
in order to actually move input device 104. These mechanical
influences are collectively grouped into the mechanical transfer
function G(s) shown at 124. The mechanical transfer function
includes the gear ratios of a gearbox (not shown) which may be
interposed between the output of the servo motor and the first
manual input device 104, the friction and inertia of the system and
other mechanical influences. All of these mechanical influences
have an impact on how the input device 104 moves, including the
speed and distance of movement for a given torque input. As shown
in FIG. 1, the mechanical transfer function 124 outputs an angular
velocity signal .theta. at signal line 146. A further integration
of the angular velocity results in an angular position signal
.theta. at signal line 148. Position signal 148 may also be used to
control the position or settings of external equipment such as the
flight surfaces of an aircraft which input device 104 is intended
to control.
[0028] The angular position signal .theta. is fed back to summing
junction 112 to create a position feed back loop which is input to
the forward loop gain amplifier 118. The magnitude of the current
for driving servo motor 120 output from the forward loop gain
amplifier 118 is directly related to the position signal .theta.
fed back through the position feed back loop. At summing junction
112, the angular position signal 148 is subtracted from the
autopilot signal 130. The resultant signal 132 comprises a position
signal between where the autopilot is commanding the input device
104 and its actual position. If the autopilot system is not
engaged, the autopilot signal 130 is 0, and the output of summing
junction 112 is simply the negative of the position signal 148.
Therefore, if the autopilot is not engaged, or if the autopilot is
commanding the input device 104 to the null position, the force
applied to the input device 104 by the active control system will
be a restorative force directed opposite the direction of
displacement, and the magnitude of the restorative force will be
proportional to the amount of displacement. Otherwise, in the first
case, with a non-zero autopilot signal the restorative force will
act to correct any discrepancy between the actual position of the
input device 104 and the position to which the autopilot signal is
commanding it to move. In either case, the error signal 132 output
from summing junction 112 is input to force profile gain amplifier
114.
[0029] The force profile gain amplifier 114 defines the force
versus position characteristics of the restorative force applied to
the first manual input device. An example of a force profile for a
flight control stick employing the present system is shown at 300
in FIG. 2. The horizontal axis represents angular displacement of
the control stick, with the origin representing the null position.
The horizontal axis represents the amount of force necessary to
move the control stick, or conversely, the restorative force
applied to the control stick to resist displacement. In this
example, a "breakout" force of 0.75 lbs. is provided. The control
stick will not move from the null position unless a force in excess
of 0.75 lbs. is applied to the input device 104 in either
direction. Thereafter, the force necessary to further displace the
control stick increases linearly as the control stick is further
displaced from the null position. The force profile 300 comprises a
compound profile. Up to approximately 15.degree. of displacement,
the profile emulates a mechanical spring loading the control stick.
The centering force, acting in a direction opposite the direction
of displacement, increases proportionally with the amount of
displacement. At approximately 15.degree., however, an additional
10 lbs. of force is needed to displace the control stick further.
This additional force threshold is provided to alert the pilot that
displacing the control stick further represents an extreme setting
which could result in unsafe flying conditions. The force profile
depicted in FIG. 2 may be achieved by the present active control
system by providing the profile gain amplifier 114 with position
dependent gain characteristics that mirror the force profile curve
300. Alternate force profile curves 300a, 300b and 300c are shown
in FIGS. 3, 4 and 5. These alternate profiles may be obtained by
merely changing the position dependent gain characteristics of the
force profile gain amplifier 114.
[0030] The amplified position error signal 134, output from force
profile gain amplifier 30, is passed through summing junction 116
where it is combined with a damping signal 50 and a cross-coupled
feedback signal 114 and the combined signal 136 output from summing
junction 116 is applied to the forward loop gain amplifier 118. The
signal 134 represents the position error between the actual
position of the input device 104 and either the null position or
the position commanded by the autopilot system. The signal 136
output from summing junction 136 comprises a torque error signal
which is input to the forward loop gain amplifier 118. Due to the
combination with damping signal 50, transients resulting from rapid
changes in position of the input device 104 are attenuated in
torque error signal 136. Signal 136 also reflects manually input
changes to the position of the second input device 108 due to the
addition of the cross-coupled feedback signal 114. The forward loop
gain amplifier 118 converts the torque error signal 136 to a motor
excitation current signal 138 which drives the servo motor 120. The
servo motor 120 in turn converts the current signal 138 to a torque
output 140 applied to the input device 104. As has already been
described, the servo motor output torque 140 is combined with
torque signal d which is manually applied by the operator, and the
combined torque signal 144 acts to move the input device 104. The
current 138 supplied to the servo motor 120 drives the motor in the
direction that reduces the magnitude of the error signal. In other
words, the servo motor 120 drives input device 104 in the direction
that reduces the displacement of the input 104 from either the null
position or the position commanded by the autopilot system. The
greater the displacement error from the null position or the
position commanded by the autopilot system, the greater will be the
restoring force applied to eliminate that displacement.
[0031] The velocity damping feedback loop begins with the input
device angular velocity signal .omega. output from the mechanical
transfer function G(s) at 146. The angular velocity signal is input
to the damping profile amplifier 128, the output of which is fed
back into summing junction 116, where it is subtracted from the
amplified position error signal 134. The amount of gain applied by
the damping profile amplifier 128 is dependent on the angular
velocity of the input device 104 itself and angular velocity signal
127 is separately derived from the position signal 148. In addition
to being fed back to summing junction 112 and profile gain
amplifier 114, the position signal 148 is also fed into derivative
block 129, which takes the derivative of the position signal to
determine the rate at which the position signal is changing. The
damping profile gain amplifier 128 provides an amount of gain that
is dependent on the magnitude of the velocity signal 127. The
larger the magnitude of the velocity signal 127 the more gain that
damping profile amplifier 128 applies to the velocity feedback
signal 146. Thus, the damping signal 50 which is subtracted from
the error position signal 134 at summing junction 116 is much
greater for rapid movements of the input device 104 than it is for
slower, steadier movements. This has the result of smoothing out
the response of the system, eliminating chatter at or around the
null or autopilot commanded position, while maintaining a firm
tactile response to deliberate manual input applied to the input
device 104.
[0032] The second servo control loop 106 is substantially identical
to the first servo control loop 102. The second manual input device
108 receives manual input in the form of a torque signal applied by
an operator, e.g. a co-pilot pushing a flight control stick
forward. Input device 108 is mechanically coupled to the output of
a servo motor 160 which delivers torque to the second input device
108. The torque supplied by the motor and the manually input torque
signal d supplied by the operator are combined at summing junction
162 and act against the mechanical transfer function G(s), the
output from the mechanical transfer function 164 comprising an
angular velocity signal Omega at 164. The angular velocity signal
is input to a position sensor 166 which generates a position signal
.theta. at 188. The position signal 188 is fed back to summing
junction 152 to form a position feedback loop. The position signal
is subtracted from the autopilot signal 130 at summing junction 152
in the same manner described above with regard to the position
signal 148 of the first servo control loop 102. The position error
signal 172 output from junction 152 is input to force profile gain
amplifier 154 which operates in an identical manner to the force
profile gain amplifier 114. As with the first servo control loop
102, the position feedback signal 188 is input to the force profile
gain amplifier 154 to provide a variable gain consistent with the
desired force versus displacement profile established for the
system. The amplified position error signal 174 output from the
force profile gain amplifier 154 is input to summing junction 156
where it is combined with a damping signal 190 output from a
profile damping amplifier 168 and the cross-coupled feedback signal
114. The combined signal 176 output from summing junction 156
comprises a torque error signal which is input to the forward loop
gain amplifier 158. The forward loop gain amplifier converts the
torque error signal into a current signal for driving servo motor
160. The position loop and dampening loop of the second servo
control loop 106 operate in the same manner as the position loop
and damping loop of the first servo control loop 102.
[0033] In addition to forming the position feedback loops of the
first and second servo control loops 102 and 106, the position
output signals 148 and 188 which indicate the position of the first
and second manual input devices 104, 108, respectively, may be used
to drive external equipment such as motors and the like for
manipulating the flight control surfaces of an aircraft in a
conventional manner. The position signals 148 and 188 are further
input to summing junction 192 which forms a part of the
cross-coupling feedback loop 110. At summing junction 192 the
position signal from the second manual input device in 108 is
subtracted from the position signal 148 of the first manual input
device 104 to create a position error signal 204 at the output of
the summing junction. The position error signal 204 is input to a
position gain amplifier 196 and a position integral gain amplifier
198. The output of the position gain amplifier 196 and the position
integral gain amplifier 198, signals 208 and 210 respectively, are
added together at summing junction 200. Additionally, summing
junction 194 subtracts the velocity signal 186 of second manual
input device 108 from the velocity signal 146 of first manual input
device 104 to create a velocity error signal 206. Velocity error
signal 206 is in turn subtracted from the output signals 208 and
210 from the position gain amplifier 196 and position integral gain
amplifier 198 at summing junction 200. The output signal 212 from
summing junction 200 comprises a conventional PID feedback signal
as it is known in the art. This signal 212 is amplified by the
cross-coupling gain amplifier 202 which produces a cross-coupling
signal 114. The cross-coupling-signal 114 is subtracted from the
amplified position error signal 134 of the first servo control loop
102 controlling the force versus displacement characteristics of
the first manual input device 104, and added to the amplified
position error signal 174 of the second servo control loop 106
controlling the force versus displacement characteristics of the
second manual input device 108.
[0034] The position gain amplifier 196 amplifies the position error
between the first input device 104 and the second input device 108.
The position error integral gain amplifier 198 accumulates the
position error over time and outputs a signal proportional to the
magnitude of the position error and the amount of time which the
position error has existed. Thus, the output signal from the
position error integral gain amplifier will compensate for small
position errors which taken alone are too small to overcome the
mechanical influences of the system. The velocity error signal 206
is subtracted from the position error and position error integral
signals to eliminate transients created by small rapid changes in
the position of the first or second input devices 104, 108. The
cross-coupling gain amplifier 202 amplifies the signal 212 to
provide the desired amount of reflected force at each of the first
and second manual input devices 104, 108. It should be noted that
the cross-coupling feedback signal 114 is subtracted from the
position error signal 134 of the first servo control loop 102, and
added to the position error signal 174 of the second servo control
loop 106. This is necessary so that movement of the first input
device 104 results in a force being applied to the second input
device in the direction of displacement of the first input device
relative to the position of the second input device. The converse
is also true. If the second input device is displaced relative to
the first input device, a force is applied to the first input
device in the direction of displacement of the second input device
relative to the first. Of course, the addition and subtraction
operations could be reversed. In other words, signal 114 could be
added to the position error signal 134 at summing junction 116 and
subtracted from the position error signal 174 at summing junction
156 with no net effect on the system. The gain of cross-coupling
gain amplifier 202 may be set very high to provide a very stiff
response to discrepancies between the position of the two input
devices in order to synchronize their position.
[0035] In this manner, the active control system of the present
invention provides desired tactile feedback to the operators of the
two manual input devices 104, 108. The force profile defining the
force versus displacement characteristics of the system may be
established as desired by establishing the proper gain
characteristics of the force profile gain amplifiers 114, 154.
Further, the system provides a restorative force directed in a
direction opposite the direction of displacement from the zero or
null position, or a corrective force directed to reconcile the
actual position of the input devices with the position commanded by
the autopilot system. And finally, the system provides a tactile
indication at each input device of what is occurring at the other
input device, in the form of a force applied to the input devices
reflecting a discrepancy in the position of the two devices.
[0036] It should be noted that various changes and modifications to
the present invention may be made by those of ordinary skill in the
art without departing from the spirit and scope of the present
invention which is set out above and in the appended claims.
Furthermore, those of ordinary skill in the art will appreciate
that the foregoing description is by way of example only, and is
not intended to be limiting of the invention as described in the
appended claims.
* * * * *