HUB-BASED ACTIVE VIBRATION CONTROL SYSTEMS, DEVICES, AND
METHODS WITH OFFSET IMBALANCED ROTORS
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of U.S. Provisional Patent Application
Serial No. 611927,741, filed January 15, 2014, the disclosure of which is incorporated herein
by reference in its entirety.
FIELD OF INVENTION
[0002] This relates to the field of vibration and noise control for any system with an
unwanted vibratory disturbance.
BACKGROUND
[0003] Multiple helicopter original equipment manufacturers (OEMs) are interested in
hub-based active vibration control (AVC). Placing force generators on the helicopter hub
provides the capability of canceling hub loads near the source, thus enabling global vibration
control.
[0004] One type of hub-based force generator comprises two co-rotating motorized
imbalanced rotors. These rotors may rotate in the same direction as the hub such that the
masses are rotating at the blade pass frequency. These rotors create a controllable rotating
force vector that can be controlled to cancel hub loads. Another type of hub-based force
generator comprises two pairs of co-rotating motorized imbalanced rotors - one pair rotating
in the same direction as the hub, and the other pair rotating in the opposite direction.
[0005] One challenge with hub-based AVC, however, pertains to the need to address
certain failure modes such as loss of operation or loss of power in which the imbalanced
rotors will discontinue rotating relative to the hub. They may come to a stop in a statically
balanced condition, in a statically worst case imbalance condition, or in some condition in
between. The static imbalance that results after loss of operation will create 1P hub loads that
will cause vibration on the hub, the gearbox and the engines. The static imbalance condition
that results after such a failure mode may dictate the severity of the failure mode (e.g., minor,
major, hazardous, or catastrophic). For example, if after loss of operation, the rotors come to
rest in a statically mass balanced condition, this may be classified as a Minor failure mode.
On other hand, if after loss of operation, the rotors come to rest in a severely imbalanced
condition, the resulting 1P loads and vibration may be severe enough that this may be
classified as a Hazardous or catastrophic failure mode. If the latter is true, a hub-based AVC
system design is required that will sufficiently mitigate this failure mode. Accordingly, there
is a need for improvements to design and system architecture to address potentially hazardous
and catastrophic failure modes.
SUMMARY OF THE INVENTION
[0006] A hub based AVC design has been conceived that includes at least one pair of corotating
motorized imbalanced rotors that create a controllable rotating force vector that can
be controlled to cancel hub loads on a rotating hub. This control is achievable using a
configuration in which each rotor has an axis of rotation that is offset from the hub axis of
rotation. In this way, in a loss of operation failure mode, the system is designed such that
centrifugal forces will cause the masses to spin to an orientation of low static imbalance.
[0007] In one aspect the hub-based AVC system comprises a hub associated with a rotary
wing aircraft, at least one controller, at least one sensor, and at least one pair of imbalanced
rotors. The hub configured for rotation about a hub axis of rotation at a hub frequency. The
at least one sensor in electronic communication with the at least one controller, the at least
one sensor configured to measure at least one vibration associated with the rotary wing
aircraft. The at least one pair of imbalanced rotors coupled with the rotating hub, the at least
one pair of imbalanced rotors comprising: a first imbalanced rotor having a first axis of
rotation that is offset in a first direction from the hub axis of rotation; and a second
imbalanced rotor having a second axis of rotation that is offset from the hub axis of rotation
in a second direction that is different from the first direction. Wherein the at least one
controller is configured to provide control to at least one of the imbalanced rotors. Wherein
the at least one pair of imbalanced rotors is configured for co-rotation at a controllable rotor
speed. Wherein a phase associated with each imbalanced rotor is adjustable to create a
controllable rotating force vector
[OOOS] In another aspect, a method for active vibration control at a rotating hub of a
rotary wing aircraft is provided. The hub configured for rotation about a hub axis of rotation
at a hub frequency. The method comprises: providing at least one controller and at least one
sensor capable of measuring a vibration in the rotary wing aircraft, wherein the at least one
sensor is in electronic communication with the at least one controller; providing at least one
pair of imbalanced rotors coupled with the hub, the at least one controller controlling the at
least one of imbalanced rotors; during normal operation, co-rotating at least one pair of
imbalanced rotors that are coupled with the hub at a controllable rotor speed, wherein a phase
associated with each imbalanced rotor is adjustable to create a controllable rotating force
vector; and during a loss of operation or loss of power failure mode, rotating the at least one
pair of imbalanced rotors to an orientation of low static imbalance with respect to one
another.
[0009] Although some of the aspects of the subject matter disclosed herein have been
stated hereinabove, and which are achieved in whole or in part by the presently disclosed
subject matter, other aspects will become evident as the description proceeds when taken in
connection with the accompanying drawings as best described hereinbelow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIGS. 1 and 2 are perspective side views of a hub-based AVC system having two
imbalanced rotors with offset axes of rotation according to embodiments of the present
subject matter.
[0011] FIGS. 3 and 4 are top views of a hub-based AVC system having two imbalanced
rotors with offset axes of rotation operating in a normal mode according to an embodiment of
the present subject matter.
[0012] FIG. 5 is a side view of a hub-based AVC system showing two imbalanced rotors
with offset axes of rotation operating in a normal mode according to an embodiment of the
present subject matter.
[0013] FIG. 6 is a side cutaway view of a hub-based AVC system showing two
imbalanced rotors with offset axes of rotation operating in a normal mode according to an
embodiment of the present subject matter.
[0014] FIG. 7 is a schematic of a single imbalanced rotor.
[0015] FIG. 8 a perspective side view of a hub-based AVC system having two imbalanced
rotors with offset axes of rotation after a loss of operation failure according to an embodiment
of the present subject matter.
[0016] FIG. 9 is a top view of hub-based AVC system having two imbalanced rotors with
offset axes of rotation after a loss of operation failure according to an embodiment of the
present subject matter.
[0017] FIG. 10 is a side view of a hub-based AVC system having two imbalanced rotors
with offset axes of rotation after a loss of operation failure according to an embodiment of the
present subject matter.
[OOlS] FIG. 11 is a top schematic view of a hub-based AVC system having two pairs of
imbalanced rotors with offset axes of rotation according to an embodiment of the present
subject matter.
DETAILED DESCRIPTION
[0019] Referring to FIGS. 1 - 11, the following provides for hub-based active vibration
control systems, devices, and methods with offset imbalanced rotors. In representative
embodiments shown in FIGS. 1 and 2, for example, an active vibration control (AVC)
system, generally designated 100, is mounted about a hub 101 that is associated with a rotary
wing aircraft, the hub 101 being configured for rotation about a hub axis of rotation 102 at
one or more selected hub frequency. In addition, although not shown in the figures, those
having skill in the art will appreciate that other elements of a hub-based AVC system may
likewise be provided about the hub 101, including but not limited to a housing and/or wiring
and control electronics (not shown). The controller, programming and associated electronics
are known to those having skill in the relevant art.
[0020] The control electronics include at least one controller (not shown) and at least one
sensor (not shown). The at least one sensor is in electronic communication with the at least
one controller, the at least one sensor configured to measure at least one vibration associated
with the rotary wing aircraft. In one embodiment, the at least one controller is configured to
provide control to at least one of the imbalanced rotors. In one embodiment, each
imbalanced rotor has at least one controller providing control thereto. In another
embodiment, each pair of imbalances rotors has at least one controller providing control
thereto. In another embodiment, the at least one controller is configured to provide control to
at least one pair of the imbalanced rotors. In one embodiment, the at least one controller is
configured to adjust a magnitude of the controllable rotating force vector.
[0021] As illustrated in FIG. 1, the hub 101 is represented as a disk in the center of the
system 100 to illustrate that such an assembly is substantially toroidal (i.e., donut shaped) and
can enable other helicopter systems, such as the slip ring and deice system, to pass thought its
inner diameter.
[0022] The system 100 includes at least one pair of imbalanced rotors coupled with the
rotating hub 101. Referring to the configuration shown in FIGS. 1-6, for example, the system
100 includes two motorized imbalanced rotors with offset centers of rotation. A first rotor
110 includes a first mass 111 that is rotatable about a first axis of rotation 112 that is offset a
first distance 113in a first direction from the hub axis of rotation 102. A non-limiting
example of the first distance 113 is about 0.5 inches (about 1.27 centimeters). The first rotor
110 further includes a first rotor bearing 114 and a first rotor stator 115. In addition, a second
rotor 120 includes a second mass 121, a second rotor bearing 124, and a second rotor stator
125. The second mass 121 is rotatable about a second axis of rotation 122 that is offset a
second distance 123 from the hub axis of rotation 102, but in a second direction that is
different from the first direction. A non-limiting example of the second distance 123 is about
0.5 inches (about 1.27 centimeters). As shown in FIGS. 3-6, in some embodiments, the
second direction in which the second axis of rotation 122 is offset from the hub axis of
rotation 102 is substantially opposite from the first direction in which the first axis of rotation
112 is offset from the hub axis of rotation 102. As shown, both the first direction and the
second direction extend along a common line that is perpendicular to the hub axis of rotation
102, albeit in opposite directions. In addition, as shown in FIGS.5 and 6, in some
embodiments, all of the hub axis of rotation 102, the first axis or rotation 112, and the second
axis of rotation 122 are substantially parallel with one another.
[0023] Regardless of the particular configuration, the at least one pair of imbalanced
rotors is configured for co-rotation at a rotor speed that is controllable to be a multiple of the
hub frequency, and a phase associated with each imbalanced rotor is adjustable to create a
controllable rotating force vector. In particular, in some embodiments, normal operation of
the system 100 can involve the hub 101 spinning at frequency Q, and the at least one pair of
imbalanced rotors being driven to co-rotate at a rotor speed NQ (with respect to the stationary
frame), where N is a multiple of the hub frequency. FIGS. 3-6illustrate the first mass 111 and
the second mass 121 to be nearly aligned, thus creating a rotating force vector of a nearly
maximum amplitude and at frequency NQ. If each imbalanced rotor has an imbalance of mr,
then the amplitude of the output force is between 0 and 2 mr (NQ)~. The magnitude and
phase of this rotating force vector are controlled in order to minimize hub loads at NQ.
[0024] In some embodiments, the system 100 is further configured such that, during a
loss of operation or loss of power failure mode, the at least one pair of imbalanced rotors is
configured to rotate to an orientation of low static imbalance with respect to one another.
FIGS. 8-loillustrate the two motorized imbalanced rotors as configured to spin nominally
with the hub at speed Q during a loss of operation or loss of power. In this condition, the
imbalanced rotors can create forces at frequency Q due to static imbalance at levels between
0 and 2 mr C12 depending on the relative orientation of the masses. Because of the offset axes
of rotation of the imbalanced rotors, centrifugal forces will tend to orient the imbalances
substantially at 180 degrees apart such that static imbalance forces will be near zero.
[0025] To model this force, FIG. 7 shows a single imbalanced rotor with an offset center
of rotation where gis the gravitational force, R is the hub rotational velocity [Radls], R is the
offset of the rotor from the hub center of rotation, mr is the imbalance of the rotor. The
equation of motion for this system is as follows:
where
8 + 2(w,8 + wz sin 8 = a sin(Qt + 0)
( % ) Z = m ~ / ~ and a = m g / J
where J is the rotor inertia. The natural frequency of the pendulum mass in the centrifugal
field is o,. The radius r, in a general sense, is an effective radius defining the location of the
center of mass of the imbalanced rotor. In this case, rotor inertia is J = mr2 and the motion of
the system can be characterized by the following parameters:
3~ = and
R
a = g l r
[0026] Whereas a is only a factor when gravity is present, the non-dimensional ratio
o,/Q affects many design considerations. In particular this affects (a) the speed at which the
imbalanced rotors will achieve a balanced condition upon loss of motor operation, (b) the
amplitude of 1P rotor wobble due to gravity after loss of operation, (c) the additional motor
power resulting from rotor offset, and (d) the parasitic moment during normal operation
resulting from rotor offset.
[0027] The dimensionless ratio o, /Q will dictate the speed at which the offset
imbalanced masses become statically balanced upon loss of operation. The number of hub
rotations M it will take for the system to settle out to the static balance condition is
proportional to the following:
where ( is the torsional damping ratio of the system.
[0028] When gravity is present, the right hand side term involving a imposes an
oscillatory torque on the imbalanced rotor. The rotor responds with an oscillation at
frequency Q and steady state magnitude O:
[0029] Because the dynamics of the system are inherently non-linear when the
gravitational disturbance is applied, the analytical expression for the steady-state magnitude
of the disturbance oscillation is only an approximation.
[0030] In view of these considerations, in some embodiments, it can be advantageous for the
offset distances R for each imbalanced rotor to be sized such that a ratio of the offset distance
R to the radius r has a value that is within a range that provides desired performance. For
example, the ratio of Wr can be less than a upper limit at which an expected centripetal field
(e.g., about 4g) would yield uncontrollable imbalances and/or very steep power increases.
Additionally, the ratio of Wr can be selected to be greater than a lower limit below which the
settling time RzSettle is undesirably large (e.g., number of hub rotations M is greater than
about 4). For example, in some embodiments, the system 100 may provide desirable
functionality with values of Rlr between 0.02 and 0.2.
[0031] During typical operation of the system (e.g., while motors are running), there is
additional power required due to the offset radius of the rotors. Per rotor, there is an
additional sinusoidal power required PR due to the offset R which occurs at frequency
(N - l ) R at an amplitude:
2
PR = (N - 1) (2) ]R3
where N - 1 is the multiple of R at which the imbalanced rotor is spinning in the rotating
frame.
[0032] A parasitic torque during normal operation will result from the rotor offset. The
maximum parasitic torque zmax occurs when the imbalanced rotors are spinning at NQ and
are neutralized.
[0033] The requirement of this additional sinusoidal power PR and the presence of this
parasitic torque is tolerated, however, because the offsets of the imbalance rotors allow the
system 100 to better address potentially hazardous and catastrophic failure modes as
discussed above.
[0034] In other embodiments, additional imbalanced rotor pairs are added. In the nonlimiting
embodiment shown in FIG. 11, a second pair of imbalanced rotors are coupled with
the rotating hub lOlIn the embodiment shown in FIG. 11, the second pair of imbalanced
rotors has a third imbalanced rotor 130 that is rotatable about a third axis of rotation 132,
which is offset in a third direction from the hub axis of rotation 102. The second pair of
imbalanced rotors further includes a fourth imbalanced rotor 140 that is rotatable about a
fourth axis of rotation 142, which is offset from the hub axis of rotation 102 in a different
direction (e.g., opposite) of the third axis of rotation 132. As illustrated in FIG. 11, third
direction and fourth direction are substantially perpendicular both to the first direction (i.e.,
the direction to which the first rotor 110 is offset) and the second direction (i.e., the direction
to which the second rotor 120 is offset) and to the hub axis of rotation 102. Those having skill
in the art will recognize, however, that other orientations and configurations can be used to
achieve the static force balancing during a loss of operation or loss of power failure mode.
[0035] Other embodiments of the present invention will be apparent to one skilled in
the art. As such, the foregoing description merely enables and describes the general uses
and methods of the present invention. Accordingly, the follow claims define the true
scope of the present invention.
CLAIMS
What is claimed is:
1. A hub-based AVC system comprising:
a hub associated with a rotary wing aircraft, the hub configured for rotation about a
hub axis of rotation at a hub frequency;
at least one controller;
at least one sensor in electronic communication with the at least one controller, the at
least one sensor configured to measure at least one vibration associated with the rotary wing
aircraft;
at least one pair of imbalanced rotors coupled with the hub, the at least one pair of
imbalanced rotors comprising:
a first imbalanced rotor having a first axis of rotation that is offset in a first
direction from the hub axis of rotation; and
a second imbalanced rotor having a second axis of rotation that is offset from
the hub axis of rotation in a second direction that is different from the
first direction; and
wherein the at least one controller is configured to provide control to at least one of
the imbalanced rotors;
wherein the at least one pair of imbalanced rotors is configured for co-rotation at a
controllable rotor speed, and
wherein a phase associated with each imbalanced rotor is adjustable to create a
controllable rotating force vector.
2. The hub-based AVC system of claim 1, wherein during a loss of operation or loss of
power failure mode, the at least one pair of imbalanced rotors is configured to rotate to an
orientation of low static imbalance with respect to one another.
3. The hub-based AVC system of claim 1, wherein the at least one controller is
configured to adjust a magnitude of the controllable rotating force vector.
4. The hub-based AVC system of claim 1, wherein each imbalanced rotor has at least one
controller providing control thereto.
5. The hub-based AVC system of claim 1, wherein each pair of imbalanced rotors has at
least one controller providing control thereto.
9
6. The hub-based AVC system of claim 1, wherein the first axis of rotation is offset from
the hub axis a first distance and the second axis of rotation is offset from the hub axis a
second distance; and
wherein the first distance and the second distance are substantially the same.
7. The hub-based AVC system of claim 6, wherein a magnitude of each of the first
distance and the second distance is sized such that a ratio of the magnitude to an effective
radius of a center of mass of either of the first imbalanced rotor or the second imbalanced
rotor has a value between 0.02 and 0.2.
8. The hub-based AVC system of claim 1, wherein the second direction in which the
second axis of rotation is offset from the hub axis of rotation is substantially opposite from
the first direction in which the first axis of rotation is offset from the hub axis of rotation.
9. The hub-based AVC system of claim 1, wherein the at least one pair of imbalanced
rotors comprises a second pair of imbalanced rotors coupled with the rotating hub, the second
pair of imbalanced rotors comprising:
a third imbalanced rotor having a third axis of rotation that is offset in a third direction
from the hub axis of rotation; and
a fourth imbalanced rotor having a fourth axis of rotation that is offset from the hub
axis of rotation in a fourth direction that is different from the third direction.
10. The hub-based AVC system of claim 9, wherein the fourth direction in which the
fourth axis of rotation is offset from the hub axis of rotation is substantially opposite from the
third direction in which the third axis of rotation is offset from the hub axis of rotation.
11. A method for active vibration control at a rotating hub of a rotary wing aircraft, the
hub being configured for rotation about a hub axis of rotation at a hub frequency, the method
comprising:
providing at least one controller and at least one sensor capable of measuring a
vibration in the rotary wing aircraft, wherein the at least one sensor is in electronic
communication with the at least one controller;
providing at least one pair of imbalanced rotors coupled with the hub, the at least one
controller controlling the at least one of imbalanced rotors;
during normal operation, co-rotating at least one pair of imbalanced rotors that are
coupled with the hub at a controllable rotor speed, wherein a phase associated with each
imbalanced rotor is adjustable to create a controllable rotating force vector; and
during a loss of operation or loss of power failure mode, rotating the at least one pair
of imbalanced rotors to an orientation of low static imbalance with respect to one another.
12. The method of claim 11, wherein co-rotating the at least one pair of imbalanced rotors
at a controllable rotor speed comprises co-rotating the at least one pair of imbalanced rotors
at a speed that is controllable to be a multiple of the hub frequency.
13. The method of claim 12, wherein the at least one pair of imbalanced rotors comprises:
a first imbalanced rotor having a first axis of rotation that is offset in a first direction
from the hub axis of rotation; and
a second imbalanced rotor having a second axis of rotation that is offset from the hub
axis of rotation in a second direction that is different from the first direction.
14. The method of claim 13, wherein the first axis of rotation is offset from the hub axis a
first distance and the second axis of rotation is offset from the hub axis a second distance;
wherein the first distance and the second distance are substantially the same.
15. The method of claim 13, wherein the second direction in which the second axis of
rotation is offset from the hub axis of rotation is substantially opposite from the first direction
in which the first axis of rotation is offset from the hub axis of rotation.
16. The method of claim 13, wherein co-rotating the at least one pair of imbalanced rotors
that are coupled with the rotating hub comprises co-rotating a second pair of imbalanced
rotors that are coupled with the rotating hub.
17. The method of claim 16, wherein the second pair of imbalanced rotors comprises:
a third imbalanced rotor having a third axis of rotation that is offset in a third direction
from the hub axis of rotation; and
a fourth imbalanced rotor having a fourth axis of rotation that is offset from the hub
axis of rotation in a fourth direction that is different from the third direction.
18. "Hie method of claim 17, wherein the fourth direction in which the fourth axis of
rotation is offset from the hub axis of rotation is substantially opposite from the third
direction in which the third axis of rotation is offset from the hub axis of rotation.