Note: Descriptions are shown in the official language in which they were submitted.
38706 L /G ~
~ V~ll iele Cuidance and ~ em
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~ l~his invention relates to a vehicle control and
guidance system in which one or more vehicles each haviny
its own motive power and steering capability can be
S accurately moved within a predetermimed area of space.
In the present case, the vehicles are of a free
ranging nature and the invention seeks to provide a
system in which the vehicles can be guided over paths
which are not of a predetermined nature but with a very
high degree of positional accuracy.
According to a first aspect of this invention a
vehicle guidance and control system includes a vehicle
having motive power and steering and means for
transmitting a directional laser beam which is scanned
in a predetermined sense; a plurali-ty of
reflectors spaced apart from each other, each incorporating
an optical code which identifies that reflector, and which
is located so as to be capable of intercepting said laser
beam; and means utilising light reflected back to said
20 vehicle by at least two reflectors for controlling the I
movement and heading of said vehicle.
Aceording to a second aspeet of this invention
a vehicle guidance and control system includes a
plurality of controllable vehicles each having individually
controllable motive power and steering and having means
for transmitting a directional laser beam which is
continuously scanned in azimuth in the same sense; a
base station for allocating destinations for the vehicles;
a plurality of reflectors spaeed apart from each other,
each incorporating an optical code which identifies that
reflector, and which is located so as to be capable of
intercepting said continuously scanning laser beam; and
means utilising light reflected back to said vehicle by
at least two reflectors for controlling the movement
and heading of said vehicles towards their respective
destinations. ~
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Thus tlle laser beam can be scanned continuously
in a clockwise or anticlockwise direction.
Preferably the nature of each reflector, and t~
disposition of the means which serve to identify it,
s are dependent on the sense of the azimuth direction in
which the laser beam is scannedr i.e. clockwise or
anticlockwise.
Preferably again the reflector comprises an
array of stripes disposed transversely to the direction
of the scanning, with the stripes having predetermined
reflection characteristics which differ from their
background or a second interleaved array of stripes.
In this way the stripes constitute an optical pattern
representing a binary code which uniquely identify the
reflector and distinguishes it from all other of said
reflectors. Preferably, at least one of the stripes
defines a precisely determined position in said system,
and the instant at which light is reflected by it back
to the vehicle is utiLised by the vehicle to determine
its own angular position relative to that of the stripe.
The directional laser beam could be one which is
extremeLy narrow in the azimuth direction, or ~~
fan-shaped in elevation, so that the beam will strike
each reflector even if they are mounted at different
heights, and if the platform on which the scanning laser
beam is mounted is not always exactly horizontal.
Alternatively, a narrow pencil laser could be projected
in an exactly horiæontal direction if all reflectors are
carefully placed at the correct height - this results in a
more efficient use of the available laser light.
The means for transmitting the directional laser beam
preferably comprises an arrangement for directing a
~,encil ïi~e beam upwards upon an inclined mirror which is
rotatable about a nominally vertical axis. Conveniently,
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a lens is positioned just below the mirror surface so as
to convert the pencil-like beam into a fan-shaped beam if
required before it is incident upon the mirror.
In another aspect, the invention consists of an optical
positional sellsing apparatus comprising: a mobile assembly
for mounting about a mobile unit adapted for shuttling
between two locations; a fixed assembly for mounting about
a station to which said mobile unit will shuttle; light
source means for providing to the mobile as.sembly discrete,
spaced apart, light beams; photodetection means mounted on
the mobile assembly for detecting the angular position of
each of said light beams relative to a central axis of said
mobile assembly; rotary means, mechanically coupled to the
photodetection means for sweeping the photodetection means
about an arc relative to the central axis of the mobile
assembly, the rotary means including an encoder coupled
thereto for sensing the angu].ar position of the photo-
detection means relative to the central axis of the mobile
assembly; and electronic circuit means, electrically
coupled to the photodetection means and to said encoder
for receiving data therefrom, the electronic circuit means
adapted for interpreting said dataO
In a still fwrther aspect, the invention consists of
an optical positional sensing apparatus comprising: a
mobile assembly, including a supporting framework for
mounting about a mobile transport unit adapted for
shuttling between a plurality of stations within a
particular environment; a fixed optical reflector assembly
for mounting about a station, and positioned remotely from
said mobile assembly; light source means attached to said
supporting framework for directing said beam of light to
the fixed optical reflector, optical coupling means
attached to said framework for directing said beam of light
to the fixed optical reflector, the optical coupling means
further including rotary means for sweeping the beam in an
arc relative to a central axis of the mobile assembly,
encoder means for sensing the angular position of the
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rotary means, and photodetector means coupled to the
rotary means for detecting a light beam reflected by the
fixed optical reflector; and electronic circuit means;
electrically coupled to the photodetector means for
receiving data therefrom, the electronic circuit means
being adapted for interpreting said data~
The invention is further described by way of example
with reference to the accompanying drawings in which:
Figure 1 is a schematic plan view of a vehicle
guidance and control system in accordance with the
invention,
Figure 2 shows a vehicle,
Figure 3 shows a reflector,
Figure 4 shows part of a vehicle-mounted laser beam
scanning head, and
Figure 5 shows circuits associated therewith.
Referring to Figure 1 there is shown in schematic form
an area defined by a perimeter shown in broken line 1
within which two mobile trucks 2 and 3 are to be controlled
2~ and guided under the overall control of a base station 4.
In practice, the trucks 2 and 3 are utilised to transfer
material between a store area 5 and a work position 6.
The store area can, for example, accommodate raw material
which is to be machined at the work position into a
required shape, or otherwise processed in accordance with
a particular requirement. The finished work pieces are
transferred by rneans of one of the trucks to a further
holding area 7 for removal and utilisation as required.
The base station 4 allocates required destinations to
each of the trucks 2 and 3 via any convenient form of
communication link. For example, a short range radio
communications link can be provided, or, alternatively, an
optical communication system utilising infra-red trans-
mitters and detectors mounted in the ceilings of the area
defined by the perimeter 1. In this latter case each
vehicle contains a co-operating infra-red sensor and
transmitter directed upwards. Once each vehicle has been
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allocated a particular destination it navigates
autonomously utilising transmitted instructions and relying
on reflector boards 8 located around the area of movement
to achieve a high degree of positional accuracy. Each
reflector board contains a unique code which indicates
its identity and precise position. The reflector boards are
described in greater detail subsequently with reference
to Figure 3.
Each vehicle contains a scanning laser beam which
rotates in azimuth so that it scans across each of those
reflector boards which are within its field of view. The
reflector board is composed of a retro-reflective material
which is such that a narrow bearn is reflected in the same
direction from which the original illumination is incident
upon it. Thus each vehicle is able to determine the
precise direction of at least two reflector boards relative
to its own position, and using triangulation techniques
the vehicle is therefore able to determine its own
position relative to any location within the perimeter 1,
such as the store area 5, the work position 6 and the
holding area 7.
The vehicle continuously monitors its own position
as it moves along a path which takes it to its required
destination. Its own position i5 continuously transmitted
2~ back to the base station so that the base station is
aware of the location of all trucks to enable it to assume
overall command to avoid a collision between two trucks.
Particularly precise control is required in the region of
the store area 5, the work position 6 and the holding area
7 and for this reason additional reflectors are positioned
around these locations as indicated in Figure 1. In
practicej the store area and the holding area may be much
larger than illustrated, and of complex configurations.
For example, each may consist of a large number of bays
divided into separate sections by means of alley-ways
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down which the trucks can navigate. In this case
additional reflector boards are re~uired so as to ensure
a truck is always able to communicate with at least two
of them whilst in any position.
A truck is illustrated diagramatically in ~igure 2,
and it will be seen that it comprises a small vehicle
having a load carrying su.rface 10 and a raised portion
11 at one end of which support a rotating scanner head
lZ. As the scanner head rotates in azimuth a very narrow
fan-shaped laser beam 14 is transmitted, although it may be
desired to use ]ust a narrow horizontal pencil-like beam The
fan beam has an appreciable vertical spread which is.deter~ined by
the apex angle of the fan so as to ensure that at least a
portion of the laser beam 14 is incident upon a reflector
board 8 regardless of significant variations in the height
of the reflector board above ground level. It will be seen
that the reflector board 8 contains an array of the ver~ically
disposed striped referred to previously. Assuming that
the laser beam is rotating in a clockwise d.irection as
indicated by the arrow 13, the beam sweeps across the board
8 shown in Figure 2 from left to right. The reflector
board 8 there~ore returns an amplitude modulated beam of
light having a pattern whi.ch varies in time which corresponds
to the bright (reflective) and dark (absorbin-g) portions of
the reflector board. The returned signal is received by a
detector located within the scanning head, and from this
information the vehicle can determine its precise bearing
relative to that of the reflector board 8 and by utilising
returns from two or more boards it can make minor
corrections to its path to compensate for any positional
errors.
A reflector board is illustrated in greater detail
in Figure 3. It will be seen that it contains reflective
stripes, which are indicated by cross-hatching, which
are spaced apart by dark stripes, i.e. non-reflective
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regions. The width of the reflective stripes and the
associated non-reflective stripes together determine the
nature of the coded signal which is obtained. Thus in
Fiyure 3 a digital "1" is represented by a rela-tively wide
reflective stripe followed by a narrower non-reflective
stripe, and a digital "O" is represented by the inverse
combination of these stripes.
Assuming still that the reflector board 8 is scanned
from left to right in this exarnple, the first few stripes
serve to indicate unambiguously that a reflector board has
been found. It is important to distinguish a reflector
board from other reflective bodies within the field of
view which could produce a confusingly similar reflector
pattern, such as a metal grid or mesh having a number of
vertically disposed wires. Once the initial pattern of
l's and O's has been found which identify a reflector
board, a unique code follows, idQntifying that particular
reflector board so as to distinguish it from all other
reflector boar~s which are mounted within the area. The
final vertical stripe in this example is a position stripe
which indicates the position of the end of the reflector
board with a very high degree of accuracy, typically to
within one cm, aLthough-any ~redetermined stripe could be
designated as the position member. As a stripe could have
an appreciable width, in a system requiring very high
positional accuracy, the boundary edye of the stripe will
be used to define the position of the reflector board.
Thus, the angular bearing of the vehicle can be determined
relative to that of the reflector board at the instant
that the rotating scanning head receives a reflected signal
from the end stripe.
~ Along a corridor, conveniently two reflector boards can
be associated with a particular reflector position such
that each can be easily seen by trucks approaching in
3S ither Aire~e~on. In thi~ ~ase ~he s'rip~s at t~
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abutting ends of the two boards serve to define a common
position relative to which the truck orientates itself.
An accurately calibrated optical encoder keeps
track of the angular position of the rotating scanner
head 12 relative to that of the vehicle. An angular
bearing of this kind received from at least two reflector
boards enables the absolute position of the vehicle to be
determined accurately. The angular offset of the vehicle
from the reflector boards indicate its actual heading and
can be used to permit navigation of the vehicle to proceed
to a required destination.
The nature of the scanning head 12 is illustrated
in greater detail of the sectional view of ~igure 4.
Referring to this drawing, a laser 21 generates a very
narrow beam of intense coherent light which is expanded
by means of an optical system 23 into a parallel sided
pencil~like beam of about 5 mm width. This laser may be
a conventional gas-filled type consisting of a mixture
o helium or neon, or it may be a semi-conductor source
such as a gallium arsenide laser diode. The narrow pencil
beam is emitted by the optical system 23 and is reflected
at a mirror 24 upwardly on to a further mirror 25 which
is fixed relative to the vehicle. The beam~is then
reflected on to a further small mirror 26 which is carried
by the centre of a plate, the remaining annular region of
which constitutes a very large area light sensor 27. The
transmitted beam is passed via a cylindrical lens 28 on
to the reflecting surface of an inclined mirror 29. The
lens in combination with the mirror produce a very wide
angle fan beam defined by the lines 30 and 31. The fan
typically has an apex angle of about 40. The mirror 29 has
a flat planar surface and is supported by a rotating frame
32 which is secured to a base diode 33 supported by
bearings 34 and 35 and which are driven hy means of a
small motor 36 so that the mirror 29, and hence the laser
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beam, are rotated in azimuth at a rate of about three
revolutions per second.
Light reflected by a reflector board is returned in a
parallel beam, represented by the lines 38 and 39, which
is incident upon the inclined mirror surface 29 and
directed downwardly on to the very large area of the
light sensor 27. The use of retroreflective stripes on
the target boards ensures that a vexy high proportion of
the incident light is returned to the sensor 27, as retro-
reflective material returns incident illumination back alongits original path largely independently of the angle of
incidence. Typically, the sensor 27 comprises a photo
diode. An interference filter can be placed immediately
above the sensor 27 to reduce the effect of ambient light.
The information is extracted in electrical form via
an interface device 40 and fed to an analysing circuit for
utilisation as required.
If the gallium arsenide diode laser is used to produce
the beam, the light output can conveniently be pulsed at a
high predetermined fre~uency, typically above 1 MHz, and the
use of a band pass filter tuned to the same frequency in
the output path of the sensor 27 provides positive
discrimination against inter~erence by ambient light~ By
modulating the beam in an amplitude pulsed manner, a direct
indication of the distance of a truck from a reflector
board can ~e obtained. One could simply measure the transit
time of a pulse reflected back to the sensor, hut preferably
the phase of the modulated reflection is compared with that
of the emitted beam.
An arrangement of this kind is indicated diagramatically
in Figure 5, in which an oscillator 41 running at about
100 MHz is used to drive the gallium arsenide diode laser
21 so as to amplitude modulate it. The output from the
sensor 27 is fed via the interface device 40 to a narrow
band pass filter 42 tuned to the frequency of oscillator 41.
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The filtered signal is fed to a phase comparator 43 where
it is compared with the output of the oscillator. The phase
difference (or phase shift) is directly related to the
distance of the truck from the reflector board, and is
10 converted into a measure of distance at a converter 44.
~ince -the approximate position of the truck is ~nown by
monitoring its movement from a location at which it can
access two reflector boards, use of a single reflector board
need only give a fine adjustment of position, and hence
15 the use of a very high optical frequency modulation having
a short effective wavelength, will not result in
ambiguity in the calculated position of the truck.
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