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BACKGROUND OF THE INVENTION
While the invention is subject to a wide range of applications, it is
particularly suited for a moving vehicle requiring bumpers. In particular,
a vehicle such as a mobile robot which incorporates the bumper of the
present invention is able to navigate by sensing both the force and the
position of a collision with an object.
Bumpers for obtaining tactile sensory information from the perimeters of
associated autonomous mobile robots or platforms, for the purpose of
impact detection and collision avoidance, are well known in the prior art.
The prior art tactile bumpers for accomplishing the foregoing generally
consist of independent and discrete elements arranged in a discontinuous
fashion around the mobile robot or platform being protected.
One such prior art bumper, disclosed in U.S. Pat. No. 3,599,744, is
connected by a hinge to a vehicle. The bumper is formed of an elastically
deformable material. When the bumper contacts an obstruction, it pivots
about hinge pins and opens a switch causing the vehicle to decelerate or
brake. This bumper is not able to distinguish the location or force of
contact with the bumper.
It is also known in the prior art to provide a bumper which is able to
determine the position of an obstacle relative to the vehicle. For
example, U.S. Pat. No. 4,546,840 discloses a metal bumper having an
obstacle contact sensor comprising a conductive rubber member sandwiched
between a protective thin metal film and an electrode plate. The electrode
plate has a plurality of electrode surfaces in contact with the metal
bumper. Compression of the rubber member electrically grounds the
corresponding electrode surface through the conductive rubber having a
reduced electrical resistance whereby the electrical potential of the
electrode surface is lowered. A resulting electrical signal enables the
presence of an obstacle to be sensed. In addition, the location of where
the obstacle contacts the vehicle body can be sensed with the switch
mechanism on the electrode surface. The '840 patent does not disclose a
means to determine the force of contact between the bumper and the
obstacle.
Another prior art bumper for a mobile robot is disclosed in U.S. Pat. No.
4,596,412. The prior art bumper disclosed therein is configured to obtain
sensory information for impact detection and collision avoidance from the
entire perimeter of an associated autonomous mobile robot or platform.
The prior art, as indicated hereinabove, includes some advancements in
bumpers for impact detection and collision avoidance. However, insofar as
can be determined, no prior art tactile bumper incorporates all of the
features and advantages of the present invention.
It is a problem underlying the present invention to determine both the
position and force of impact on a bumper attached to a vehicle.
It is an advantage of the present invention to provide a bumper for impact
detection which obviates one or more of the limitations and disadvantages
of the described prior arrangements.
It is a further object of the present invention to provide a bumper for
impact detection which can sense the location of contact with an obstacle.
It is a still further object of the present invention to provide a bumper
for impact detection which can sense the force of impact with an obstacle.
It is yet another advantage of the present invention to provide a bumper
for impact detection which can sense a very low force of impact.
It is a still further advantage of the present invention to provide a
bumper for impact detection which is relatively inexpensive to
manufacture.
Accordingly, there has been provided a bumper for impact detection with an
object. An electrically conductive member has a compressible, electrically
conductive material mounted thereto. An insulator formed of mesh material
is sandwiched between the electrically conductive member and the
electrically conductive material for electrically insulating the
conductive member from the conductive material when the material is in a
non-compressed state and for providing electrical conduction between the
conductive member and the conductive material when the conductive material
is in a compressed state.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention and further developments of the invention are now elucidated
by means of preferred embodiments shown in the drawings:
FIG. 1 is a perspective view of a bumper for impact detection attached to a
vehicle;
FIG. 2 is a schematic illustration of a top view of the bumper for impact
detection;
FIG. 3 is a schematic top view of the bumper for impact detection
illustrating a collision with an obstacle;
FIG. 4 is a schematic top view of the bumper for impact detection
illustrating a hard collision with an obstacle;
FIG. 5 is a schematic top view of the bumper for impact detection
illustrating a slight collision with an obstacle;
FIG. 6 is a schematic illustration of a conventional potentiometer;
FIG. 7 is a schematic of an electrical equivalent of a bumper in accordance
with the present invention; and
FIG. 8 is a perspective view of a second embodiment of a bumper for impact
detection.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, there is illustrated a bumper 10 for impact detection
with an obstacle. The bumper comprises an electrically conductive member
14. A compressible, electrically conductive material 16 is mounted to the
conductive member 14. A component 18 electrically insulates the conductive
member 14 from the conductive material 16 when the conductive material 16
is in a non-compressed state and provides electrical conduction from said
conductive member 14 to said conductive material 16 when the conductive
material 16 is in a compressed state.
Referring again to FIG. 1, a physical representation of the bumper 10 in
accordance with the present invention is provided. The bumper can be
attached to a vehicle 12 by any desired means such as a weldment 20. Also,
the bumper is illustrated as having a U shape. However, it is within the
terms of the present invention to shape the bumper 10 in any desired
configuration and to surround any portion or the entire perimeter of the
vehicle 12 with the bumper.
The bumper 10 includes an inner, electrically conductive member 14 which
forms an inner (back) plate that can be attached to the vehicle 12. The
plate can be constructed of any rigid conductive material such as a metal
or alloy selected from the group comprising iron, steel, copper, brass,
aluminum alloys thereof, as well as metal impregnated plastic and a
plastic having a metallized surface coating.
A compressible, electrically conductive material 16 is mounted to the
electrically, conductive back plate 14. The conductive material 16 is
preferably a low density foam which serves as both an electrical conductor
for sensing the position and force of impact with an obstacle or object,
as well as a mechanical force-absorber for stopping the vehicle. The foam
has resistive properties in the range of about 10 to about 1000 kilohms
per foot, such as anti-static, conductive foam packaging CP 105 from
Charles Water Products, Inc., Newton, MA. Other materials which will
provide anti-static control and function as the conductive material are
conductive polyethylene CP 501 from Charles Water Products, Inc.,
conductive foams No. 1927T71 to 1927T76 from McMaster-Carr Supply Company
of New Brunswick, New Jersey, and electrically conductive paper No.
2094T41 from McMaster-Carr Supply Co. Although the present invention is
discussed in terms of the foam, it is within the terms of the present
invention to substitute any anti-static, compressible, electrically
conductive material.
The insulating means 18 comprises a mesh material having openings sized to
prevent accidental contact between the conductive member 14 and the
conductive material 16 while allowing contact between the conductive
member and the conductive material from a light impact. The openings in
the mesh can be of any desired shape including but not limited to circles,
triangles, squares and oblong openings. The mesh can have a resolution
from about 0.01 inches (the center-to-center repetition rate) to about 1
foot or more. The dimension of the mesh openings is preferably on the
order of 1/10 of the mesh thickness. The mesh can be formed of any
insulating material selected from the group comprising polyethylene,
nylon, plastic, fiberglass, and rubber.
The conductive foam 16 has a protective cover sheet 21 formed of a flexible
material to protect the underlying foam from physical damage and may be
formed from electrically insulative material. The cover sheet 21 can be
constructed of various materials such as polyethylene, nylon, plastic,
natural latex, fiberglass, nitrile and silicone rubber. The conductive
foam 16 and the cover sheet 21 project outward from an edge 23 of the back
(inner) plate 14. The section of conductive foam 16 which is not supported
by the back plate 14 provides sensitive position detection as will be
discussed hereinafter.
To better understand the operation of bumper 10 illustrated in FIG. 1, a
general and then more detailed explanation of its operation follows.
Two ohmmeters 36 and 38 are illustrated as connected to points A and B at
opposite ends of the conductive material 16. The ohmmeters are also
commonly connected to the conductive member 14 at a common, or ground,
point 25. The ground point 25 can be at any suitable location on the
conductive back plate 14. By measuring the resistance between the points A
and B on the foam material 16, a collision of the bumper with an object
can be detected and the point 27 (see FIG. 5) of impact on the bumper 10
determined. Before the bumper 10 is impacted, the insulating mesh 18
separates the foam sheet 16 from the back plate 14 and an open circuit or
an infinite resistance exists between the points A and B. When impact
occurs, the foam material 16 is forced to make contact at the point 29
(see FIG. 5) with the back plate 14 through the holes of the insulating
mesh 18. Measured resistances R.sub.A and R.sub.B correspond to the
resistance of the length of foam material 16 between the points A and B on
the foam material and the point 29 of impact, respectively. The resistance
varies linearly across the length of the bumper, R.sub.A being lowest when
the impact point 27 is closest to the point A and highest when the impact
point 27 is at the point B. Similarly, R.sub.B being lowest when the
impact point 27 is closest to the point B and highest when the impact
point 27 is at the point A. The position of the impact point 27 can be
determined from R.sub.A and R.sub.B. In addition, by measuring the
absolute resistances, R.sub.A and R.sub.B, the force (F) of impact can be
determined.
The foam 16 used in bumper 10 has a relatively high impedance. The basic
principle associated with this bumper corresponds to the operation of a
conventional potentiometer as schematically represented in FIG. 6. Under
normal circumstances, when the bumper 10 has not contacted an obstacle,
the resistance to ground at the opposite ends 22 and 24 of the bumper 10
is very high. At that time, only a very high leakage resistance can be
measured as indicated by the resistor 26, see FIG. 2. At impact with an
obstacle, the portion of foam 16 near the point of impact is grounded
against the plate 14 as illustrated in FIG. 3. A resistance change will be
effected and indicated (a signal produced) at points A and B. Assuming a
collision with an obstacle indicated by arrow 28 (see FIG. 3), the
resistance to ground value at point A will be lower than the value
indicated at point B.
In the case of a collision in the middle of the bumper, as illustrated in
FIG. 4, an equal resistance to ground values at point A and B will be
registered.
The conventional potentiometer 30 illustrated in FIG. 6 operates under the
same principle and the sliding part 32, known as the glider, is equivalent
to the point of contact of the conductive back plate 14 with foam 16.
It should be understood that the resistances R.sub.A and R.sub.B at the
points A and B, respectively, may be represented by signals, as shown in
FIG. 7, discussed hereinafter.
Another aspect of the present invention relates to the measurement of the
force of impact with the obstacle. A light impact of the bumper with an
obstacle is represented in FIG. 5. Here, the total area of contact between
the foam 16 and the back plate 14 is small. Hence, the absolute value of
the resistances R.sub.A and R.sub.B to ground is relatively high.
On the other hand, as illustrated in FIG. 4, when a hard collision occurs,
the area of contact between the foam 16 and back plate 14 is much greater.
Then, the absolute value of the resistances R.sub.A and R.sub.B to ground
is much lower since a larger portion of the foam is grounded. Therefore,
by measuring the absolute value of resistance at points A and B, the force
(F) of impact caused by the collision can be determined. This principle is
illustrated in FIG. 7.
An electrical equivalent of the physical structure of the bumper 10 is
illustrated in FIG. 7. A voltage (+5v) is applied to the ends A and B of
the foam through pull-up resistors 42 and 44. The conductive foam 16 now
acts as a voltage divider with respect to the voltage developed across
points A and B insofar as the contact point of the foam to ground is
concerned.
To locate the point of impact on the bumper, the signals at A and B are
analyzed. Analog-to-digital (A/D) converters 46 and 48 corresponding to
the ohmmeters 36 and 38 (FIG. 1) are connected to the points A and B
respectively. In addition, the A/D converters 46, 48 are connected to the
grounding arrow 50. As the arrow 50, corresponding to the point of
collision moves closer to the A end of the circuit, the voltage signal in
the A/D converter 46 will increase while the voltage signal in the A/D
converter 48 will proportionately decrease. If the pointer 50 moves
towards the point B, the signal from A/D device 48 will increase while the
signal in A/D device 46 will proportionately decrease. The outputs of the
A/D devices 46, 48 are provided to a microprocessor 51.
In the example of the circuit illustrated in FIG. 7, the voltages V.sub.A
and V.sub.B of 0-5 volts DC correspond to digital outputs for the A/D
converters 46 and 48 of 0-255. In the case of no collision, a +5 volt
signal picked up by the A/D converters 46 and 48 indicate a value of 255.
For noise immunity reasons, the top 10% of the maximum value, i.e. 230-255
will indicate that no collision has occurred.
From a force point of view, the absolute value resistance of the foam is
decisive for force indication. The foam can be looked upon as a volume
resistor, or consisting of several small resistors in parallel. The more
the foam is compressed, the lower its resistance. The compression reduces
the parallel path cross section. This is illustrated by a plurality of
resistors 52 illustrated in FIG. 7. By adding more resistors in parallel
which corresponds to compressing the foam, the absolute values of the
resistances R.sub.A, R.sub.B are decreased, and the voltages V.sub.A,
V.sub.B are increased.
The microprocessor 51 receives the signals from the A/D devices 46 and 48
to calculate the position and the force of impact. Although the
microprocessor 51 can be mounted in any convenient location with respect
to the bumper 10, it is within the terms of the present invention to bury
it within the conductive foam.
Referring again to FIG. 1, the points A and B discussed hereinbefore, are
represented at the opposite ends of the conductive foam 16. Connected to
each of these points are ohmmeters 36 and 38 which correspond to the
analog/digital converters 46 and 48, respectively, illustrated in FIG. 7.
The ohmmeters are connected to the ground point 25 on plate 14. The meter
readings corresponding to resistance signals at A and B which in turn
correspond to the position and force of impact with an obstacle, as
discussed hereinbefore.
The sensitivity of the bumper is determined by the impact absorbing
characteristics of the protective cover as well as the mesh size and
strand thickness of the insulating mesh. If a thin mesh and a thin, highly
flexible protective cover is used, the bumper will respond very quickly to
a light impact. Increasing the thickness of protective cover and/or the
insulating mesh will decrease the bumper's sensitivity since a harder
impact will be required to press the conductive foam into contact with the
back plate. The bumper disclosed herein is generally responsive to an
impact force of a fraction of an ounce to several hundred pounds.
Preferably, the bumpers disclosed herein are responsive to a force of less
than one ounce to about 100 pounds.
Referring to FIG. 8, there is illustrated a second embodiment of the
present invention. A bumper 60 is provided with a back plate 62 which can
be contructed of any rigid, insulator material such as molded plastic. The
back plate can be attached to any component such as a vehicle by a plate
66. Although a particular configuration for the plate 66 is illustrated,
it is within the terms of the invention to use any conventional means of
connecting the bumper to a desired structure. Adjacent to back plate 62 is
conductive foam 68 of the type described hereinbefore in conjunction with
the first embodiment. A conductive mylar sheet 70 is provided with an
electrical conductor on the surface 74 facing the conductive foam 68. For
example, the mylar sheet can have an aluminized surface 74, although any
conductive material will suffice.
Sandwiched between the conductive mylar sheet 70 and the foam 68 is a mesh
material 76 which is substantially the same as the mesh material described
hereinbefore in conjunction with the first embodiment. Finally, a
protective cover 78 is provided on the outer surface of the mylar sheet.
The protective cover 78 is preferably formed of a moderately compliant
material such as polyethylene or any of the cover materials described with
respect to the embodiment illustrated in FIG. 1. The cover sheet 78
extends outward from the mylar sheet 70 in order to provide protection for
the materials forming the other components of the bumper.
The bumper 60 operates in essentially the same manner as the bumper 10
described hereinbefore. An impact with an obstacle presses the conductive
surface 74 of the mylar sheet through the mesh 76 and against the foam 68
whereby the position and amount of force can be determined in accordance
with the principles described hereinbefore.
The bumpers 10 and 60 are advantageously employed as contact sensors for
mobile robots. The position information can be used in navigation
algorithms to plan a path around an obstacle based on the detected
location. The high sensitivity afforded by the mylar 70 allows the robot
to react as quickly as possible to a collision, minimizing the force of
impact.
Advantages of the bumpers 10 and 60 include their low-cost design which
enables them to be used in autonomous ground vehicles as well as in toy
robots, their ruggedness because they consist of so few parts, their
simplicity of design, and their construction from readily available parts.
The general principle of operation for the bumper is applicable to any form
of use, where position and/or force are important to measure. Some
applications include fencing where security surveillance can locate an
intruder climbing over the fence, and measuring the force and position of
a machine tool or industrial robot hand.
The patents set forth in this application are intended to be incorporated
by reference herein.
It is apparent that there has been provided in accordance with this
invention a bumper for impact detection and the method of detecting impact
which satisfies the objects, means, and advantages set forth hereinabove.
While the invention has been described in combination with the embodiments
thereof, it is evident that many alternatives, modifications, and
variations will be apparent to those skilled in the art in light of the
foregoing description. Accordingly, it is intended to embrace all such
alternatives, modifications, and variations as fall within the spirit and
broad scope of the appended claims.
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