U.S. patent application number 11/942176 was filed with the patent office on 2008-03-13 for harmonic propulsion and harmonic controller.
This patent application is currently assigned to The Trustees of Columbia University In The City Of New York. Invention is credited to Michael R. Treat.
Application Number | 20080061644 11/942176 |
Document ID | / |
Family ID | 37865706 |
Filed Date | 2008-03-13 |
United States Patent
Application |
20080061644 |
Kind Code |
A1 |
Treat; Michael R. |
March 13, 2008 |
Harmonic Propulsion And Harmonic Controller
Abstract
A device and method for propelling objects using periodic or
harmonic vibrations is described. The device comprises a flexible
substrate or surface and a source of vibrational energy that is
applied to the substrate or surface. Specific embodiments include a
device which can move along a flat surface, which can climb a
smooth vertical or slanted wall, which can move along a ceiling
while suspended upside down, which can climb up a smooth hollow
tube, or which can move through liquids.
Inventors: |
Treat; Michael R.; (New
York, NY) |
Correspondence
Address: |
WOLF, BLOCK, SHORR AND SOLIS-COHEN LLP
250 PARK AVENUE
10TH FLOOR
NEW YORK
NY
10177
US
|
Assignee: |
The Trustees of Columbia University
In The City Of New York
New York
NY
|
Family ID: |
37865706 |
Appl. No.: |
11/942176 |
Filed: |
November 19, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10536479 |
Oct 3, 2005 |
7317275 |
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PCT/US04/32702 |
Sep 30, 2004 |
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11942176 |
Nov 19, 2007 |
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60507667 |
Sep 30, 2003 |
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Current U.S.
Class: |
310/81 |
Current CPC
Class: |
H02N 2/0065 20130101;
B60L 50/00 20190201; B63H 1/30 20130101; H02N 2/026 20130101; B63H
19/00 20130101 |
Class at
Publication: |
310/081 |
International
Class: |
H02K 7/06 20060101
H02K007/06 |
Claims
1. A device comprising: a flexible substrate or first surface and
at least one source of vibrational energy attached to or in
communication with the flexible substrate or first surface, wherein
vibrational energy is applied to the flexible substrate or first
surface to cause periodic motion in the flexible substrate or first
surface and the device is capable of translational motion along a
second surface or through a fluid.
2. The device of claim 1, wherein the vibrational energy is
harmonic.
3. The device of claim 2, wherein the vibrational energy causes the
substrate or surface to flex in a harmonic fashion.
4. The device of claim 2, wherein at least one of the at least one
source of vibrational energy imparts vibrations to said substrate
or first surface to cause said device to move in a translational
fashion.
5. The device of claim 1, wherein the second surface is other than
horizontal.
6. The device of claim 1, wherein a change in frequency of the
vibrational energy causes the direction of the motion of the device
to change.
7. The device of claim 1, which also comprises an asymmetry
element.
8. The device of claim 7, wherein the asymmetry element comprises
bristles, spines or spicules embedded in a flexible matrix, regular
or irregular projections, fins, or a conformable mat.
9. The device of claim 8, wherein the asymmetry element comprises
bristles.
10. The device of claim 1, wherein the flexible substrate is
circular, rectangular, oval, square, or hemispherical.
11. The method of claim 1, wherein the flexible substrate has first
and second substantially parallel planar surfaces.
12. A method for imparting translational motion to an object on a
first surface or in a fluid, the object comprising a flexible
substrate having at least one substantially flat surface and a
source of vibrational energy attached to or in communication with
at least one of the at least one substantially flat surface to
apply vibrational energy to the flexible substrate, said method
comprising the steps of: (a) vibrating the object to produce
harmonic vibration; and (b) coupling the vibration to the first
surface or fluid in an asymmetric way to produce translational
motion by the object.
13. The method of claim 12, wherein an asymmetry element produces a
net force in one direction when averaged over the entire vibratory
cycle.
14. A method for imparting translational motion to an object having
a flexible substrate or a first surface and a source of vibrational
energy on a second surface or in a fluid, said method comprising
the steps of: (a) applying vibrational energy to the object to
produce harmonic vibrations in the flexible substrate or first
surface; and (b) coupling the vibrations to the second surface in
an asymmetric way to produce translational motion by the
object.
15. The method of claim 14, wherein a force in one direction during
one part of the wave cycle is not counterbalanced by an equal and
opposition force in the other direction.
16. The method of claim 14, wherein an asymmetry element produces a
net force in one direction when averaged over the entire vibratory
cycle.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of co-pending, commonly
assigned U.S. patent application Ser. No. 10/536,479, filed Oct. 3,
2005, which is a National Phase filing of PCT Patent Application
No. PCT/US2004/032702, filed Sep. 30, 2004, which is based upon
commonly assigned U.S. provisional patent application Ser. No.
60/507,667, filed Sep. 30, 2003, all of which are incorporated
herein in their entirety.
FIELD OF THE INVENTION
[0002] The present invention generally relates to a method for
moving objects. The present invention specifically is directed to
propelling objects by using periodic or harmonic vibrations.
Embodiments of the present invention include a method to move an
object along a flat surface (translating horizontally), to move an
object up a smooth vertical wall (climbing vertically), to move an
object along a ceiling while the object is upside down relative to
its position in normal horizontal translation, to climb inside a
smooth hollow tube, to swim through liquids, and to rotate. The
present invention is also directed to devices which execute the
various movements.
BACKGROUND OF THE INVENTION
[0003] Historically, the usual means for propelling objects along
the ground has been by employing wheels. Typically at least one
wheel is made to move by means of a motor. The wheel so driven
exerts force on the ground as it turns, and the object to which the
wheel is attached will move forward. A common example of such a
method is that of propulsion of automobiles. Another means for
propelling or moving objects is a propeller. A propeller will push
against a fluid in which an object is immersed and thereby propel
the object forward. Simple examples would be the motion of an
airplane propeller against the fluid air or the motion of a boat
propeller against the fluid water. A different means of propulsion
is inertial reaction in which mass is expelled in one direction,
causing an object expelling the mass to move in the opposite
direction, by virtue of conservation of linear momentum. A simple
example of such motion would be the motion of a rocket or a jet
airplane.
[0004] Although there are numerous examples of the use of wheels,
propellers, and reaction engines to impart translation motion,
there appear to be relatively few examples of the use of vibrations
to induce motion. Of the few vibratory examples, most involve the
use of vibrations imparted to the entire surface on which the
moving object is travelling. One such example is the use of
vibratory conveyor belts to move grain or small parts in
manufacturing operations. There is also a toy sports game in which
miniature football players are moved along a playing field, which
is a sheet of metal, by vibrations to the entire playing field
induced by an electromechanical motor (such as a buzzer). However,
there are no devices wherein there is a self-contained and mobile
source of vibrations that cause an object to move translationally
in a directable manner.
OBJECTS OF THE INVENTION
[0005] It is an object of the invention to provide a method and
device for harmonic propulsion.
[0006] It is also an object of the invention to provide a method
and device for propelling and/or controlling objects by use of
periodic or harmonic vibrations.
[0007] It is a further object of the invention to provide a method
and device for imparting translational motion to an object.
[0008] It is a yet further object of the invention to provide a
method and device for imparting translational motion to an object
on a surface by vibrating the object to produce harmonic motion and
coupling the vibration to the surface in an asymmetric way
[0009] It is a yet further object of the invention to provide a
method and device to move an object along a flat surface, to move
an object up a vertical wall, to move an object along a ceiling, to
move an object through a smooth hollow tube, to move an object
through a liquid or fluid, or to cause an object to rotate.
[0010] These and other objects of the invention will become more
apparent from the discussion below.
SUMMARY OF THE INVENTION
[0011] According to one aspect of the invention, vibratory motion
is used to perform the functions of devices described herein,
namely, to move along a level surface, to climb up a smooth
vertical or slanted wall, to move upside down on a ceiling, or to
climb up a hollow tube. Another aspect of the invention comprises a
solution to the problem of controlling the direction of such moving
devices. Without directional control, the utility of a moving
device is much reduced; and, with directional control, the method
and device for which is taught by the present invention, it becomes
possible to build devices which can be used for exploration of
intricate spaces, under either remote control or control based on
an on-board set of sensors and decision-making circuits. A device
according to the invention is expected to be have various
applications. One potential use is in the in the medical field, for
example, in or with a partly or wholly self-propelled endoscope or
other invasive medical device.
[0012] A great advantage of vibratory or harmonic propulsion is
that such devices may be very small and simple compared to more
conventional devices, such as wheeled devices. This is because this
form of propulsion does not require axles, bearings, transmissions,
or even wheels, as are needed for wheeled devices. This form of
propulsion does not require propellers or jet engines. The present
invention requires a system with a source of vibrations and a
driving surface, which comes in contact with the surface upon which
the device is moving.
[0013] Also, unlike wheels or treads (as in a tank), harmonic
propulsion can be effected on any or all surfaces of the device,
instead of being limited to the aspects of the device (the driving
surface of the wheels or treads). Therefore, it becomes very easy
using harmonic propulsion to build devices which can, for example,
ascend the inside of hollow pipes since the device can obtain
propulsion from the entire circumference of the pipe. Also, the
surface of vibration can be adjusted as to its stiffness and
texture so that the device can move on a great variety of terrain
(for example, hard, smooth, dry ground versus softer wet ground).
In one embodiment, it is envisioned that this technology will allow
for the development of a practical self-propelled endoscope to
explore a patient's gastrointestinal tract or another corporeal
channel or site.
[0014] In its simplicity and with few moving parts, the present
invention overcomes the problems of the prior art. The present
invention describes a device and method to cause an object to move
translationally by impartation of vibrational energy.
[0015] One embodiment of the invention is generally directed to
imparting translational motion of an object by application of
vibrations, preferably harmonic vibrations.
[0016] Another embodiment of the invention is a device to effect
translational motion that comprises a source of harmonic or
periodic mechanical or acoustic vibrations, a vibrating surface
whose modes of vibration are excited by the source of vibrations,
and a symmetry breaking element.
[0017] Another embodiment of the invention concerns a method to
effect translational motional comprising the steps of applying
harmonic or periodic vibration to an object, exciting modes of
vibration in a surface, and directing the translational motion of
the object by using symmetry breaking elements. The present
invention specifically discloses types of vibration sources, types
of vibrating surfaces, and types of antisymmetry elements.
[0018] Other embodiments of the present invention include methods
to effect translational motion from traveling waves, translational
motion from standing waves, wall climbing motion, directional
control using vibrating surfaces ("focusing surfaces") which
interact with obstacles, and directional control using
eigenmodes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a plan view of one embodiment of the
invention;
[0020] FIG. 2 is a perspective view of an embodiment of the
invention on a vertical surface; and
[0021] FIG. 3 is a schematic cross-sectional view of an embodiment
of the invention having a distinct antisymmetry element.
DETAILED DESCRIPTION OF THE INVENTION
[0022] In general, the present invention represents a novel
approach to effect translational motion by application of
vibrations. More particularly, aspects of the invention are
directed to a device to effect such motion and a method to produce
such motion.
[0023] A device according to the invention employs vibratory motion
emanating from the device itself, to effect translational motion.
Such a device comprises a source of harmonic or periodic mechanical
or acoustic vibrations. This vibration source must be energetic
enough to produce amplitudes of vibration which can actually cause
movement of the device. Suitable vibration sources include, for
example, the following:
[0024] (1) an electric motor which is fitted with an eccentric cam.
A preferred aspect of a motor which rotates an eccentric weighted
cam is that traveling waves can be produced, since the motor-cam
combination tends to produce a rotating or twisting motion in
addition to an up-down and side to side motion;
[0025] (2) an electromechanical buzzer consisting of an
electromagnet and a springy steel vibrating reed. Such devices are
preferred for producing standing waves;
[0026] (3) an electromagnetic audio speaker;
[0027] (4) a piezoelectric speaker or bending element; and
[0028] (5) a gas under pressure escaping from a nozzle, which is
used to vibrate a reed or drive some sort of oscillating device
such as a piston-cylinder combination. If the source of the gas is
some sort of combustion process, then it is possible to obtain a
much greater power to weight ratio than is possible with battery
powered motors. Another method of obtaining gas under pressure
would be to exploit a phase change of a particular substance, e.g.,
the change of solid CO.sub.2 ("dry ice") into a gas at room
temperature. Yet another means of obtaining a gas under pressure
would be some sort of chemical reaction, e.g., the breakdown of
acetic acid and sodium bicarbonate into CO.sub.2 (gas) and
water.
[0029] A device according to the invention comprises a vibratable
or vibrating substrate whose modes of vibration are excited by the
source of vibrations. The vibrating substrate needs the correct
stiffness (modulus of elasticity) and mass density to vibrate. It
will also need to have the correct size and shape so that its
normal modes of vibration can result in forward, left, and right
motion of the device. Size and shape of the device are selected to
optimize outcome. Typical shapes include circular, rectangular,
oval, and square, circular being preferred. It has been found
empirically that plates with these shapes have normal modes of
vibration which lend themselves to forward motion with the ability
to be directed to the right or to the left as desired. Some
particular embodiments are a thin plastic sheet, a thin brass
sheet, and a thin Styrofoam sheet, having a thickness from about
0.02 to about 0.20 inches thick, preferably from about 0.05 to
about 0.15 inches thick. In a preferred embodiment of the invention
the substrate will be flat or substantially flat where the surface
of the substrate facing a horizontal, slanted, or vertical surface
may have a slightly angled outer periphery or "lip", which will
extend all, or substantially all, the way around the outer
periphery of the substrate.
[0030] Preferably a device according to the invention comprises an
"antisymmetry element" (or symmetry breaking element) which will
break the symmetry of the vibrating motion relative to the ground
and thereby produce a net translational movement. This antisymmetry
element can be an arrangement of projections or bristles situated
at an angle to the vibrating surface which functions to break the
symmetry of the vibrating motion relative to the ground and thus
produce a net translational movement. The antisymmetry elements
are, in general, at an angle to the vibrating surface, which angle
will preferably be other than perpendicular to the vibrating
surface. The elements may consist of bristles, semi-stiff pins,
bumps, or any textured projection. The purpose of these
antisymmetry elements is to convert the symmetrical standing waves
of the vibrating surface into propulsive movements of the device.
Specific examples of such embodiments include, for example,
flexible brush bristles, which are curved backward; small spines or
spicules embedded in a flexible matrix; fins; and a conformable
mat.
[0031] In addition to providing translational movement, the
antisymmetry element contributes to a control mechanism whereby
changing the frequency of the harmonic vibratory motion will cause
direction of the device to change. In addition, in other
embodiments of the invention, the vibrating surface may be
segmented and/or there could be more than one source of vibratory
energy, so that there could be translational movement as well as
directional control.
[0032] There are at least five distinct aspects to the
invention:
[0033] Translational Motion from Travelling Waves
[0034] Traveling waves, which are produced in the vibrating
surface, can obviously produce translational motion as these waves
progress from one end of the device to the other end. By alteration
of the direction of these traveling waves, steering or directional
control can be produced.
[0035] Translational Motion from Standing Waves
[0036] Vibrations or waves in a solid or liquid medium can be
either standing waves or travelling waves. From everyday experience
one knows that traveling waves, such as ocean waves, can be used to
propel objects such as, for example, boats or surfers. Standing
waves, however, produce only repetitive motion, which does not
result in any net displacement of material, or translational
motion. An example of this would be the standing waves produced on
the string of a musical instrument. If a standing wave is made to
impinge on the ground, there would be no net motion in any
direction since the displacements of the wave tending to produce
motion in one direction would be cancelled out in the next half
cycle by the return motion of the wave in the opposite direction.
However, it is possible to use standing waves to effect net
translational motion if the waves can be coupled to the ground in
antisymmetric way so that a force in one direction during one part
of the wave cycle that is not counterbalanced by an equal and
opposite force in the other direction during the next part of the
cycle. This asymmetry is produced by the antisymmetry elements on
the vibrating surface, which are at an angle to the surface.
[0037] This translational motion may be used to propel the device
on a flat surface (one surface of contact between device and
substrate), in a walled channel without a roof (three surfaces of
contact), in a hollow tube (contact on all lateral surfaces), and
in liquids either on the surface or submerged.
[0038] Wall Climbing Motion
[0039] Certain standing waves, particularly those with circular
symmetry, can produce a suction or vacuum effect as the vibrating
surface is lifted away from the surface during one part of the
vibratory cycle and slightly pushed into the surface during another
part of the cycle. When the surface is being accelerated towards
the wall, a slight positive pressure is produced under the plate,
which is more than overcome by the inertial forces, which are
pressing the plate against the wall. The motion of the plate
relative toward the wall may also simultaneously produce some net
translational motion. In the next part of the cycle when the plate
is being accelerated away from the wall, a vacuum is produced under
the plate, which tends to hold it to the wall but now the inertial
force tends to pull the plate away from the wall. A new wall
holding effect depends on the correct balance between the vacuum
producing part of the cycle with the inertial forces, which try to
remove the plate from contact with the wall. If the motion when the
plate is being accelerated away from the wall is not too violent,
there will be production of a vacuum between the plate and the
wall, which will more than compensate for the inertial force, which
tends to throw the plate away from the wall.
[0040] Directional Control Using Vibrating Surfaces ("Focusing
Surfaces") which Interact with Obstacles
[0041] The essential understanding here is that focusing surfaces
which are concave relative to the obstacle encountered will tend to
steer the device toward the obstacle, while focusing surfaces which
are convex focusing surfaces tend to steer the device away from the
obstacle. This steering ability is enhanced by the vibrating nature
of the basic motion of the device, as the vibrations tend to
re-align the device toward (or away) from the obstacle.
[0042] Directional Control Using Eigenmodes
[0043] Directional control can be achieved by using certain normal
modes of the vibrating surface. The best combination of normal
modes to produce the ability to turn left or right would be two
modes which are mirror images of one another and which are
asymmetric around the longitudinal axis of the vibrating surface.
When the vibrating surface is equipped with appropriate
antisymmetry elements, the device will turn either to the left or
to the right depending on which normal mode is active. A normal
mode ("eigenmode") can be selected by vibrating the surface at the
specific frequency corresponding to that mode ("eigenfrequency").
The fact that there is a one to one correspondence between each
eigenfrequency and each normal mode is known from the physics of
wave motions and the solutions of the wave equation.
[0044] Embodiments within the scope of the invention include:
[0045] (1) a device which propels itself by means of its own
vibratory motion; [0046] (2) a device which can move on a flat
surface; [0047] (3) a device which can move on a channeled surface;
[0048] (4) a device which can move by adhering to a wall or other
vertical or slanted surface; [0049] (5) a device which can move by
adhering to a ceiling or other horizontal surface; [0050] (6) a
device which uses a vibrational source to create standing waves in
the device; [0051] (7) a device which uses a vibrational source to
create traveling waves in the device; [0052] (8) a device which
uses "antisymmetry" texturing of the vibrating surface to effect
translational motion from standing waves; and [0053] (9) a device
which can use a balance of inertial and suction forces to adhere to
a wall or ceiling and also translate (move) along that wall or
ceiling.
[0054] In another embodiment of the invention, the
vibration-producing element of the device comprises an
electromechanical buzzer, a rotating eccentric cam on an electric
motor, an escaping gas which vibrates a reed, an element which
produces standing waves in the device, an element which produces
traveling waves in the device, a device wherein standing
(stationary) waves can produce translational motion by means of
elements at an angle to the vibrating surface of the device, or a
combination of two or more thereof, or the functional equivalent of
one or more thereof.
[0055] Antisymmetry elements, as discussed above, produce a net
force in one direction when averaged over the entire vibratory
cycle. Such elements may be, for example, bristles, periodic
elevations, regular or irregular projections, or conformable
surfaces.
[0056] A device according to the invention can be controlled or
steered by means of special surfaces called "focussing surfaces",
by means of varying the frequency of vibration to select a
particular eigenmode, by means of selective damping of the
vibrating plate at a nodal line of a desired eigenmode in the case
of a standing wave vibrational source, by changing the direction of
rotation of the vibrating device in the case of traveling
waves.
[0057] The invention can perhaps be better appreciated by making
reference to the drawings. FIG. 1 represents an embodiment of the
invention which comprises a circular substrate 10 having a source
of vibratory harmonic motion or motor 12 centered thereon. Adjacent
motor 12 is a battery holder 14 containing two AA batteries 18. Two
wires 20 lead from battery holder 14 to a switch 22, which switch
22 is electrically connected through wires 24 to motor 12.
Activating switch 22 closes the electrical circuit comprising
batteries 18 and motor 12 and causes motor 12 to vibrate.
[0058] Motor 12 can comprise any known or future source for
imparting vibrational energy, to cause harmonic motion. Motor 12
has to be sufficiently small and efficient to impart vibrational
energy but not weigh too much that it negates the vibrational
effect or causes the device to slide or fall off a non-horizontal
surface. A representative motor 12 is a commercially available
pager motor, which provides vibration in the frequency of from
about 5 to 20 cycles per second.
[0059] Substrate 10 should be a flexible but rigid surface that can
vibrate in response to the vibrations from motor 12. Typical
materials useful for substrate 10 include polymers, metal,
ceramics, and the like. Substrate 10 should be thick enough to
support motor 12 but thin enough to vibrate.
[0060] Substrate 10 can be of almost any shape or size, dependent
upon the strength or power of motor 12. The weight of motor 12 plus
the batteries would also be a factor. The bottom surface 30 of
substrate 10 is preferably substantially flat, although a slightly
concave or pie-plate or FRISBE-shape surface will work as well.
[0061] FIG. 2 is a cross-sectional view of the device shown in FIG.
1 in position on a vertical surface 32. With the motor 12
activated, the device 34 will either remain in approximately one
position, or it may slowly move in a direction along surface 32. If
an external lateral force is applied to motor 12 or substrate 10,
device 34 will tend to go in that direction. Also, device 34 may be
configured as discussed above so that vibratory action may result
in directional control.
[0062] FIG. 3 is a schematic view of an embodiment of the invention
where the device 40 comprises a housing 42 containing a vibrational
energy source (not shown specifically) and a power supply (not
shown specifically), such as one or more batteries, and a substrate
44. Extending from the lower surface 48 of substrate 44 are
bristles 50, which are shown at an angle of about 30.degree. from
normal to horizontal surface 52. Preferably bristles such as
bristles 50 will be from about 45 to 85.degree. from normal.
Optionally bristles 50 could be slightly curved and are preferably
comprised of a suitable flexible polymeric material.
EXAMPLES
Example 1
[0063] The device comprises a Styrofoam pie plate (9 inches in
diameter, of central depth 3/4 inch, with an edge at the
circumference of width approximately one-half inch), an electrical
motor with an eccentric weight, and 2 Ni--Cd batteries (AAA size).
The motor and batteries are placed on the underside of the pie
plate.
[0064] In one use, the device, with the pie plate upside down,
translated with the circumferential edge in contact with a surface.
This device translated in a vertical direction along a wall, in an
embodiment termed "wall crawling pie plate."
[0065] In another use, the motor and batteries can be placed in an
enclosure, such as a film can. The device, with the pie plate
upside down, translated with the circumferential edge in contact
with a surface. Specifically, the device can translate along a
surface, such as a porcelain tub surface, underneath water.
Example 2
[0066] The device comprises an approximately flat 3 inch diameter,
approximately 1 mm thick, circle or approximate circle of material
(which can be cut, for example, from the bottom of the 9'' diameter
Styrofoam pie plate), a pager motor, and a power source. The power
source can be wires connected to the motor which lead to a battery
remote from the 3 inch diameter circle.
[0067] On energizing the motor and creating vibrations, the device
translated along a surface.
Example 3
[0068] The device comprises a ping pong ball with a hole, a motor,
and a power source. The motor and power source can be placed within
the ping pong ball. On energizing the motor and creating
vibrations, the device spins when placed in a cup of water. It is
believed that this is through rotational traveling waves.
Example 4
[0069] The device comprises a foam wheel with a motor and a power
source. On energizing the motor and creating vibrations, the foam
wheel revolved.
Example 5
[0070] The device comprises a piece of scrub brush with a motor and
a power source. The motor is attached to the portion of the scrub
brush opposite the bristles. On energizing the motor and creating
vibrations, the scrub brush moved forward.
Example 6
[0071] The device comprises a motor, potted in a container, with a
power source or leads to a power source, wherein bristles are
attached to the scrub brush. This device climbed vertically in a
cardboard tube even carrying its own battery.
Example 7
[0072] The device comprises a motor with a power supply, a brass
sheet, and bristles attached to the brass sheet on the side
opposite to the side with the motor. Depending on the frequency of
the motor, the device, when placed on a surface, turned left,
turned right, or went straight ahead. The bristles are used to
break symmetry.
[0073] The preceding specific embodiments are illustrative of the
practice of the invention. It is to be understood, however, that
other expedients known to those skilled in the art or disclosed
herein, may be employed without departing from the spirit of the
invention or the scope of the appended claims.
* * * * *