U.S. patent application number 09/733291 was filed with the patent office on 2002-12-19 for guided bullet.
Invention is credited to Brosch, R. Glenn, Lipeles, Jay.
Application Number | 20020190155 09/733291 |
Document ID | / |
Family ID | 26865819 |
Filed Date | 2002-12-19 |
United States Patent
Application |
20020190155 |
Kind Code |
A1 |
Lipeles, Jay ; et
al. |
December 19, 2002 |
GUIDED BULLET
Abstract
A projectile having a plurality of micro electromechanical
(MEMS) devices disposed about the axis of flight for active control
of the trajectory of the projectile. The MEMS devices each form an
integral control surface/actuator. Control circuitry installed
within the projectile housing includes both rotation and lateral
acceleration sensors. Flap portions of the MEMS devices are
extended into the air stream flowing over the projectile in
response to the rate of rotation of the projectile, thereby forming
a standing wave of flaps operable to impart a lateral force on the
projectile. MEMS devices utilizing an electrostatically
controllable rolling flap portion provide a large range of motion
while consuming a small amount of power. The MEMS devices may be
arranged in longitudinal strips along an ogive portion of the
projectile. Packaging concepts for projectiles as small as a 30
caliber bullet are described.
Inventors: |
Lipeles, Jay; (Apopka,
FL) ; Brosch, R. Glenn; (Sorrento, FL) |
Correspondence
Address: |
BEUSSE, BROWNLEE, BOWDOIN & WOLTER, P. A.
390 NORTH ORANGE AVENUE
SUITE 2500
ORLANDO
FL
32801
US
|
Family ID: |
26865819 |
Appl. No.: |
09/733291 |
Filed: |
December 8, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60170192 |
Dec 10, 1999 |
|
|
|
Current U.S.
Class: |
244/3.21 |
Current CPC
Class: |
F42B 10/62 20130101 |
Class at
Publication: |
244/3.21 |
International
Class: |
F42B 015/01; F42B
005/24; F42B 014/06 |
Claims
We claim as our invention:
1. An airborne vehicle comprising: a housing; a plurality of micro
electromechanical (MEMS) devices attached to the housing, each MEMS
device comprising an integral control surface/actuator and having a
flap portion adapted to move between a withdrawn position and an
extended position; and actuator circuitry connected to the MEMS
devices for selectively moving at least one of the flap portions
into and out of an air stream passing over the airborne
vehicle.
2. The airborne vehicle of claim 1, wherein the actuator circuitry
further comprises: a rotation sensor for producing a first signal
corresponding to the rotation of the airborne vehicle about an axis
of flight; a lateral acceleration sensor for producing a second
signal corresponding to acceleration of the airborne vehicle in a
direction normal to the axis of flight; control circuitry connected
to the rotation sensor and to the lateral acceleration sensor for
providing a third signal to the actuators responsive to the first
and the second signals.
3. The airborne vehicle of claim 2, wherein the plurality of MEMS
devices are arranged about the axis of flight, and wherein the
third signal is operable to extend selected ones of the flap
portions to produce a standing wave of extended flap portions
relative to the axis of flight.
4. The airborne vehicle of claim 1, wherein the MEMS devices are
arranged in a plurality of longitudinal strips.
5. The airborne vehicle of claim 4, wherein the plurality of
longitudinal strips are disposed about an ogive portion of the
airborne vehicle.
6. The airborne vehicle of claim 1, wherein the housing has a
diameter no more than that of a 50 caliber bullet.
7. The airborne vehicle of claim 1, wherein the housing has a
diameter no more than that of a 30 caliber bullet.
8. The airborne vehicle of claim 1, wherein the MEMS devices each
comprise: a first fixed electrode; the flap portion comprising a
second moveable electrode disposed on a rolled layer of tentured
material, the layer of tentured material having an end affixed
relative to the first electrode; wherein the second electrode is
caused to roll toward the first electrode to move the flap portion
to the withdrawn position in response to an electrostatic force
between the first electrode and the second electrode; and wherein
the second electrode is caused by residual stress in the tentured
layer of material to roll away from the first electrode to move the
flap portion to the withdrawn position.
9. An airborne vehicle comprising: a housing; a plurality of micro
electo-mechanical (MEMS) devices disposed about an axis of flight
of the airborne vehicle; a rotation sensor for producing a first
signal responsive to a rate of rotation of the airborne vehicle
about the axis of flight; circuitry connected to the rotation
sensor and to the plurality of MEMS devices, the circuitry operable
to actuate at least one of the MEMS devices in sequence about the
axis of flight at a rate of rotation responsive to the first
signal.
10. The airborne vehicle of claim 9, further comprising: a lateral
acceleration sensor for producing a second signal responsive to
acceleration of the projectile in a direction normal to the axis of
flight; the circuitry being connected to the lateral acceleration
sensor and operable to control the sequence of actuation of the at
least one of the MEMS devices in response to the second signal.
11. The airborne vehicle of claim 9, wherein the MEMS devices each
comprise: a first fixed electrode; the flap portion comprising a
second moveable electrode disposed on a rolled layer of tentured
material, the layer of tentured material having an end affixed
relative to the first electrode; wherein the second electrode is
caused to roll toward the first electrode to move the flap portion
to the withdrawn position in response to an electrostatic force
between the first electrode and the second electrode; and wherein
the second electrode is caused by residual stress in the tentured
layer of material to roll away from the first electrode to move the
flap portion to the withdrawn position.
12. A method of controlling the trajectory of an airborne vehicle,
the method comprising the steps of: providing a plurality of micro
electromechanical MEMS devices on an airborne vehicle, each MEMS
device comprising an integral control surface/actuator and having a
flap portion adapted to move between a withdrawn position and an
extended position; determining a desired change in trajectory of
the airborne vehicle relative to an axis of flight; and actuating a
selected portion of the MEMS devices to extend the respective flap
portions into and out of an air stream passing over the airborne
vehicle to achieve the desired change in trajectory.
13. The method of claim 12, further comprising the steps of:
disposing the MEMS devices on the projectile about the axis of
flight; sensing rotation of the airborne vehicle about the axis of
flight; and actuating the selected portion of the MEMS devices in a
sequence responsive to the rotation of the airborne vehicle to form
a standing wave of extended flap portions relative to the axis of
flight.
14. The method of claim 13, further comprising the step of
disposing the MEMS devices in a plurality of longitudinal
strips.
15. The method of claim 13, further comprising the step of
disposing the MEMS devices in a plurality of longitudinal strips
about an ogive portion of the projectile.
Description
[0001] This application claims benefit of the filing date of
provisional U.S. patent application 60/170,192 filed Dec. 10,
1999.
BACKGROUND OF THE INVENTION
[0002] The present invention relates generally to the field of
airborne vehicles, and more specifically to a guidance system
capable of being used on a small airborne projectile such as a
bullet.
[0003] The path of a gun-launched projectile is at the mercy of
gravity, air currents, muzzle accuracy, barrel wear, sighting
accuracy, gun stability, projectile anomalies, charge uniformity,
etc. As with a golfer who leans after a shot to encourage the ball
to travel one way or the other, one would similarly like to
influence the flight path of a bullet to overcome the above
disturbances and to deliver the projectile to its intended target.
The least expensive weapon for the last several centuries has been
a bullet. Although bullets themselves are very inexpensive, they
are not always the most cost effective. That is, the real cost of
using a weapon includes the cost of all the ammunition plus the
cost of delivery necessary to achieve the desired objective. Thus,
a more expensive bullet that has a greater accuracy may actually be
a less expensive bullet to use.
[0004] Most bullets spin about their axis of flight and are thereby
spin stabilized. Equipping such a projectile with guidance vanes or
other control devices would be useless unless the control devices
could be activated only at such times and for an appropriate
duration when they could impose the control force in the
appropriate direction, and then be retracted when their affect
would be inappropriate or counter to the desired flight path
correction. Obviously such operation would mean very rapid
projection and retraction of the guiding aspects, i.e. a wide
bandwidth control system. Traditional control systems are not
capable of such rapid deployment. To avoid the need for such a wide
bandwidth control system, it is known to de-spin the section of the
projectile that houses the control devices. The de-spun section may
then be roll stabilized with respect to inertial space. In such a
state, the control section moving axially through the air could
activate relatively slow moving control devices without subjecting
them to the roll of the bullet.
[0005] Micro electromechanical systems (MEMS) have been developed
based upon a variety of technologies for a variety of applications.
An electrostatic actuator using a rolling electrode is described in
U.S. Pat. No. 4,266 339 issued to Kalt on May 12, 1981, for
application as an electronic window blind.
[0006] MEMS actuators have been tested on military aircraft as part
of a flight control system for reducing the buffeting forces
imposed on the aircraft vertical fin resulting from local flow
condition instability. Piezoelectric actuators were used in this
test. Although the speed of movement of such actuators is
sufficiently high to respond to local flow instabilities, the
effectiveness of such piezoelectric actuators is limited because
the range of motion of a piezoelectric material is relatively
small.
BRIEF SUMMARY OF THE INVENTION
[0007] There is a particular need for a guidance control system
that is small enough and fast-acting enough to be applied to a
projectile as small as a bullet. Accordingly, an airborne vehicle
is described herein as having a housing; a plurality of micro
electromechanical actuators attached to the housing, each actuator
having a flap portion adapted to move between a withdrawn position
and an extended position; and actuator circuitry connected to the
actuators for selectively moving ones of the flap portions into and
out of an air stream passing over the projectile. The airborne
vehicle may further include a rotation sensor for producing a first
signal corresponding to the rotation of the projectile about an
axis of flight; a lateral acceleration sensor for producing a
second signal corresponding to acceleration of the projectile in a
direction normal to the axis of flight; and control circuitry
connected to the rotation sensor and to the lateral acceleration
sensor for providing a third signal to the actuators responsive to
the first and the second signals. The plurality of actuators may be
arranged about the axis of flight, and wherein the third signal is
operable to extend selected ones of the flap portions to produce a
standing wave of extended flap portions relative to the axis of
flight.
[0008] A method of controlling the trajectory of an airborne
vehicle is describe herein as including the steps of: providing a
plurality of micro electromechanical actuators on a projectile,
each actuator having a flap portion adapted to move between a
withdrawn position and an extended position; determining a desired
change in trajectory of the projectile relative to an axis of
flight; and actuating a selected portion of the actuators to extend
the respective flap portions into and out of an air stream passing
over the projectile to achieve the desired change in trajectory.
The method may further include the steps of: disposing the
actuators on the airborne vehicle about the axis of flight; sensing
rotation of the projectile about the axis of flight; and actuating
the selected portion of the actuators in a sequence responsive to
the rotation of the projectile to form a standing wave of extended
flap portions relative to the axis of flight.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The features and advantages of the present invention will
become apparent from the following detailed description of the
invention when read with the accompanying drawings in which:
[0010] FIG. 1 is a perspective view of a projectile having a
plurality of micro electromechanical actuators arranged in strips
along its ogive section.
[0011] FIG. 2 is a cross-sectional view of one of the micro
electro-mechanical actuators of the projectile of FIG. 1.
[0012] FIG. 3 is a cross-section view of the projectile of FIG.
1.
[0013] FIG. 4 is a block diagram of the control system for the
projectile of FIG. 1.
[0014] FIG. 5 illustrates a typical Mach number distribution in the
neighborhood of a single actuator flap portion.
DETAILED DESCRIPTION OF THE INVENTION
[0015] FIG. 1 illustrates a projectile 10 having a housing 12 with
a front ogive section 14 with a tapered thickness relative to an
axis of flight 16. Projectile 10 is illustrative of any sort of
airborne vehicle that may be built in accordance with the present
invention. The term airborne vehicle is used generally herein to
include any of the following types of vehicles: airplane, rocket,
missile, projectile, rocket assisted projectile, bullet, lifting
body, etc. The housing 12 is illustrative of any appropriate
portion of an airborne vehicle to which a control surface may be
attached, for example a fuselage, wing, fin, body, etc. The
projectile includes a plurality rows or strips 18 of flight control
devices disposed about the axis of flight 16. The trajectory of the
projectile may accordingly be affected by actuation of selected
ones of the flight control actuators, as will be described more
fully below.
[0016] FIG. 2 is a partial cross-sectional view of one of the
flight control devices 20 of the projectile 10 of FIG. 1. Flight
control device 20 is an electrostatic flexible film device having a
first fixed electrode 22 disposed on a layer of insulating material
24 supported on a substrate 26. A second flexible electrode 28 is
deposited on a tentured layer of polymer 30. The tentured material
is formed to have internal tensile stresses resulting from the
method of manufacturing use to form the device. The fixed electrode
22 and the flexible electrode 28 are separated from each other by
respective layers 32, 34 of a polymer material. Together, tentured
layer 30, electrode 28 and polymer layer 34 form a flap portion 36
that is adapted to move between an extended position (as
illustrated) and a withdrawn position wherein flexible electrode 28
is drawn toward fixed electrode 22 so that flap portion 36 is
unrolled to lay against the substrate 26. Thus the flight control
device 20 forms an integral control surface/actuator.
[0017] FIG. 3 is a cross-sectional view of projectile 10. Housing
12 contains a control system 38 operable to affect the in-flight
trajectory of the projectile 10. Housing 12 also contains both nose
ballast 40 and aft ballast 42 selected to provide desired flight
characteristics for projectile 10. In one embodiment, projectile 10
may be designed as a replacement for a standard bullet, and since
the electronic components are composed of materials that are less
dense than steel, the ballast 40, 42 is selected to provide
inertial characteristics (center of gravity, weight, etc.) for
projectile 10 that are as close to the original bullet
characteristics as possible.
[0018] FIG. 4 is a block diagram of control system 38 of projectile
10. Control system 38 may be designed upon a flex circuit that may
be rolled/folded to fit within the available housing interior
space. The control system 38 must withstand gun-imposed loads. The
electronics package is small and will be fully potted. Individual
wires and their terminations are most vulnerable to acceleration
loading and should be avoided. A digital signal processor 44
receives input from an inertia motion unit 46 for control of an
array of micro electromechanical systems actuators 20. Control
system 38 also includes power supply 47 including a voltage
regulator and battery 50.
[0019] System Excelerator's (SEI) digital signal processor (DSP)
system currently utilizes a 52 MHz device with on-chip SRAM and a
micro-chip A/D to process up to 16 channels of sensor data in real
time. Coupled with a new operating system resident in internal DSP
memory, the DSP provides both real time computation and control to
process multiple sensors effectively. New 16-bit DSP's now push the
silicon technology envelope, taking advantage of silicon processes
and fabrications, to clock at 75 MHz with up to 250 MB of on-chip
SRAM. These upgraded devices provide the computational power and
memory necessary to compute the precession and nutation
frequencies, to enhance and process the accelerometer signals, and
to carry out the auto-pilot functions that will be described more
fully below. Expected improvements in DSP architecture will quickly
remove computational power from being a limiting design feature for
the projectile 10.
[0020] The inventors believe that the projectile 10 may be packaged
in embodiments as small as a 50 caliber bullet, or even a 30
caliber bullet. The small volume of a rifle bullet is the
overwhelming design constraint for the projectile of the present
invention. There is no room for conventional controls, nor is there
room for a battery large enough to power them. There is no room for
a terminal guidance seeker. There is insufficient area for a GPS
antenna, and even if there were, there is insufficient flight time
to acquire the GPS constellation and to make useful guidance
corrections.
[0021] The inertial motion unit 46 includes an angular rate
rotation sensor 52 and a lateral acceleration sensor 54 consisting
of two COTS accelerometers similar to those developed for the
automobile industry for air bag and roll-over sensors. These
devices are surface mounted MEMS devices and are very small and
relatively inexpensive. They are mounted to a motherboard at the
centerline of the projectile to measure motions in the two
transverse ortho-normal directions to produce a first signal
corresponding to the rotation of the projectile 10 about the axis
of flight 16 and a second signal corresponding to acceleration of
the projectile normal to the axis of flight. Known techniques for
signal processing may be used to improve the accuracy of these
signals.
[0022] Recently introduced integrated circuits that provide
efficient up-conversion of single cell batteries for mobile
personal computers may be used to create a voltage regulator 48.
These micro-powered devices provide 3 or 5 volt operation for cells
that vary all the way down to 1.6 volts during discharge.
[0023] It is expected that the available volume will be too small
for a workable thermal battery, since with such a small volume
there may be insufficient thermal mass for the battery to sustain
temperature. Thin film batteries may be made quite small and offer
a viable alternative. Such batteries can have any shape provided
the electrolyte completely isolates the cathode from direct contact
with the anode. Lithium batteries offer another alternative.
Several thin pouch-like lithium batteries have been stacked
together and gun fired successfully in the United States Army HSTSS
program. Solid lithium-polymer batteries have begun to enter the
mobile PC market and may be another alternative. Another approach
would be to use battery 50 to charge a capacitor, which would
activate actuators 20 through a voltage boosting circuit. Because
MEMS actuators 20 are electrostatic devices, they require
essentially no current and only about 50 volts. Finally,
lithium/manganese dioxide cells offer another alternative source of
the necessary electrical energy. An inertial switch will be
triggered by the firing load imposed on the projectile. An
electronic latch will secure the switch so that power is retained
after the initial launch load and throughout the projectile's
flight.
[0024] The self-compensating disturbance compensating system
described herein includes means to sense accelerations, processing
to extract the amplitude of disturbance accelerations, and a means
of effecting a compensating force with the appropriate spin phasing
relative to the disturbance. The spin and nutation are high in
frequency as compared to the disturbance phenomena. They are also
well behaved harmonics that lend themselves to simple signal
processing. This concept exploits the spin and residual nutation
motion as a carrier signal. A body fixed accelerometer will sense
the aerodynamic acceleration caused by the coning angle. The
direction of the cone angle, and thus the acceleration direction,
rotates in inertial space at the nutation frequency. Additionally,
the sensed acceleration is modulated at the spin frequency. These
two frequencies are simple multiples of one another as determined
by the ratio of the moments of inertia. Simple processing can be
used to extract differences in these modulations due to lower
frequency disturbances. The traditional bane of spinning projectile
guidance is keeping up with the roll angle. Fortuitously, it is not
necessary to determine the direction of the disturbance in inertial
space. It is only necessary to issue the corrections in-phase with
the disturbance in body coordinates. Disturbances due to wind, wind
shear, gust, tip-off, rain and particulates in the atmosphere,
imperfections in the gun or bullet, gravity bias, etc. will excite
precession and nutation. By measuring the amplitude of these
responses and using them as parameters to develop a feedback signal
to the control system actuators 20, the precession and nutation
will be minimized and the trajectory corrected. The device
described herein is a semi-smart bullet; that is, it does not have
command or terminal guidance. Volume limitations preclude such
features. It does, however, have an active guidance and a control
system that will counter the effects of errors or disturbances that
would alter the path of the bullet from its ideal trajectory. The
bullet 10 will go where it was sent.
[0025] Conventional flight control devices are not possible in such
a small application. Methods of flow control include geometric
shaping of the airfoil, vortex generators for separation control,
longitudinal grooves or riblets to reduce drag, and the use of
mechanical flow deflectors to modify the flow field. The MEMS
devices 20 described herein provide low power consumption, fast
response, reliability and low cost. Integral control
surface/actuator 20 may be fabricated with methods developed for
the fabrication of silicon chips. Only five photo-lithographic
steps are required to form a simple actuator. These steps can be
accomplished with conventional, prior generation VLSI equipment,
including contact photolithography. The significance of MEMS
technology is that it becomes possible to provide mechanical parts
of micron size that are batch fabricated in large quantities and
are easily integrated with their associated electronics.
Miniaturization to this scale is necessary for actuators to control
the flow field of a 30 or 50 caliber bullet.
[0026] Device 20 operates on the basis of the electrostatic
attraction of a flexible, curled film to a substrate. Initial work
by the Microelectronics Center of North Carolina (MCNC) has
utilized polyimide films with chrome/gold metallization. The
polyimide/metal films of these structures curl due to the internal
stress caused by the difference in the thermal coefficients of
expansion of the gold and polyimide and the cooling from
400.degree. C. to room temperature during the polyimide cure cycle.
The electrostatic flap 36 is a partially curled flexible film 30
with one electrode 28 in the flap portion 36 and a second electrode
22 fixed to the substrate 26. The flap portion 36 is attached to
the substrate 26 at one edge 56 and there is at least one
insulating film 32, 34 covering the electrodes 22, 28 to prevent
them from coming into contact with one another. The basic operation
of the flap portion 36 is simple. A voltage applied between the two
electrodes 22, 28 establishes an electrostatic attraction. The
force is strongest at the point 56 where the flexible film 30
attaches to the substrate 26. As the electrostatic force overcomes
the material system rigidity, the flexible film 30 begins to
unroll, which in turn creates a new area of high electric field.
This process continues until the entire film 30 has flattened
(unrolled) against the substrate 26. Upon the removal of the
applied voltage, the residual stress in the tentured film 30 curls
the material stack back to its original position as illustrated in
FIG. 2. Because it is electrostatic in operation, the power
requirements are very low compared to thermal and electromagnetic
actuators. With the curled film 30, the separation at the point of
attachment is very small, resulting in large forces, while the curl
also positions the tip of the film 30 far from the substrate 26.
Thus device 20 has a large range of motion, large forces and low
operating voltages relative to other electrostatic actuators.
Because the release of the film 34 from the substrate 26 upon the
removal of the applied voltage is a curling motion, the separation
occurs along a line instead of the entire area of contact. Thus,
stiction is not an issue since the stress of the film 30 is larger
than the attractive surface forces in the small separation area
along the line of contact.
[0027] A plurality of flight control devices 20 may be mounted to
the surface of the forebody ogive of projectile 10 so as not to
interfere with the rifling, or at other locations depending upon
the design of the particular projectile. A longitudinal strip 18 of
actuators 20 may be excited together to extend the respective flap
portions 36 into the stream of air flowing past the projectile 10,
thereby affecting the trajectory of the projectile. By actuating
selected strips 18 in a sequence responsive to the rotation of the
projectile 10 about the axis of rotation 16, the control system 38
will cause a standing wave of extended flap portions 36 to be
formed relative to the axis of flight 16. The excitation will
rotate from one strip to the next at the same speed, but in the
opposite direction to the projectile spin, thereby creating a
standing wave relative to the axis of flight 16. The wave will have
the effect of a de-spun control section that will be stationary
with respect to the flow field and trajectory. The actuators 20
will therefore function much like conventional canard controls.
[0028] Although actuators similar to that illustrated have been
made in a number of sizes and materials, they have not been
designed as aerodynamic control devices, nor have they been wind
tunnel tested. Individual devices 20 will be exposed to
aerodynamic, inertial and electrostatic forces that are a nonlinear
function of actuator displacement and shape. The aerodynamics are
non-linear, the electrostatics are non-linear, because the
deflections are large there are geometric non-linearities, and as
the device rolls its boundary conditions change. Thus, the device
20, unlike conventional aerodynamic control devices, is not subject
to simple approximations that usually initiate the design process.
However, many computational fluid dynamics (CFD) codes include
structural deformation, and one recently published code now
includes electrostatic forces, thereby greatly easing the analysis
problem. Simple CFD calculations of the basic concept of the
projectile 10 has been performed. The model includes a hypothetical
vehicle with a blunt nose and a single actuator. The calculations
assumed 2-dimensional flow, that the flap portion 36 was rigid,
0.099 inches long with the tip at about 60.degree.. Turbulent flow
was not modeled. The results for Mach numbers 3-6 are tabulated
below. The force is that due to an individual actuator and the
control pressure is the force divided by the flap portion area.
1 Mach Force (lbs) Pressure (psi) 3 1.07 274 4 1.14 293 5 1.54 395
6 1.89 486
[0029] These forces are likely greater than that needed for vehicle
control. The pressure variation associated with an actuator is
highly localized relative to the projectile. The flap portion 36
will function must like a conventional spoiler. The pressure load
will be mechanically transferred through the actuator to the
projectile structure.
[0030] FIG. 5 shows a typical Mach number distribution in the
neighborhood of a single actuator flap portion 56. The generally
vertical lines above the actuator illustrate a shock wave emanating
radially from the flap portion 56 and interacting with the bow
shock. Aft of the secondary shock and outside the boundary layer
near surface 58 there is a small disturbance due to the actuator
with the remaining flow field being fairly regular. This implies
that the aerodynamic design of projectile 10 as a whole will not be
seriously affected by an array of such actuators. The flow
immediately forward of the flap portion is at a lower Mach number
than the background flow. This implies that the actuators can be
moved forward toward the nose of the projectile, as they would be
in an ogive nose configuration. Note that the greatest disturbance
is just above the flap portion 56 with the wake flow being much
less disturbed. This suggests that adjacent actuators may be spaced
fairly closely together with a minimum of interaction between
them.
[0031] A method of controlling the trajectory of a projectile may
be appreciated from the above. By providing a plurality of micro
electro-mechanical actuators on a projectile and by actuating a
selected portion of the actuators in coordination with the
rotational speed of the projectile, a desired change in the
trajectory may be achieved. The method may include simply
counteracting a disturbance to correct the projectiles flight,
thereby minimizing its error but leaving it off its intended flight
path. Alternatively, it may be possible to continue the correction
to bring the projectile back to its intended flight path. The
problem with this approach is that while the original correction is
made closed loop under inertial feedback, the over correction is
open loop. There is no feed back sensor to tell the auto-pilot to
stop the correction. The error must therefore be integrated and
remembered and the over correction continued until the integrated
error is zero.
[0032] While the preferred embodiments of the present invention
have been shown and described herein, it will be obvious that such
embodiments are provided by way of example only. Numerous
variations, changes and substitutions will occur to those of skill
in the art without departing from the invention herein.
Accordingly, it is intended that the invention be limited only by
the spirit and scope of the appended claims.
* * * * *