Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
57~
POSITIONING SYSTEM
The present invention relates to a system for
detection and determination of a relative position
between a first unit arranged in a first plane and
a second unit arranged in a second plane parallel
to said first plane and spaced therefrom, said units
being mutually movable parallel to said planes, and
said first unit having a radiation source for trans-
mitting a beam of rays directed against said second
unit, and a radiation detector for detecting a beam
of rays retransmitted from said second unit, said
second unit having a passive means adapted, when said
relative position lies within specific limits, to
receive the beam of rays transmitted from said radiation
source and to retransmit the radiation received towards
said radiation detector which is adapted, in response
to the retransmitted beam of rays, to provide position
information corresponding to said relative position.
Positioning systems of this type may be used
for example when one wishes to establish a desired
position of a movable first unit relative to a sta-
tionary second unit, to detect that the desired posi-
tion has been attained, or that this position lies
within specific limits. In this connection, drive
means for controlling the movable first unit prefer-
ably are adapted to receive the position informationprovided by said radiation detector in order to inter-
rupt, in response to this information, the movement
of said first unit when the desired position has been
attained, or to direct said fir~st unit towards a dif-
ferent position relative -to said stationary second
unit.
One field of application of such positioning
systems is the positioning of automatically controlled
trucks of the type which are caused -to follow a path
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or a loop on a factory floor or the like and which
are stopped at predetermined positions or stations
located along said path. It is especially important
that the truck can be accurate:Ly positioned in rela-
tion to a given station if the truck supports a robotor the like whose movement pattern, when the truck
has stopped at the station at issue, is dependent
on a reference system which is stationary relative
to the station or the floor. If the truck is posi-
tioned incorrectly by means of the above-mentioned
positioning system at the station, the subsequent
movements of the robot will be correspondingly in-
correct.
Another application is the relative alignment
of mutually movable machine components.
A third application is the alignment of a vehicle
drawhook with a trailer or the like. In this instance,
the source of radiation and the radiation detector
preferably are mounted on the vehicle adjacent the
drawhook thereof, the passive radiation receiving
and retransmitting means being provided adjacent the
trailer coupling member. When the driver has reversed
the vehicle up against the trailer such that the draw-
hook takes up the correct position relative to the
trailer coupling member, the said passive means re-
ceives radiation transmitted by the source of radia-
tion and retransmits it to the radiation detector
which, in response thereto, provides information to
the driver that the vehicle is in correct position,
whereupon the vehicle and the trailer can be coupled
up .
Swedish Patent 366,127 discloses a system which
is adapted to indicate a predetermined position be-
tween a first and a second object, said system being
characterised in -that the first object comprises a
light transmitter and a light receiver with parallel
optical axes, that the second object comprises a light
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reflector which, when the predetermined position be-
tween the said two objects has been attained, is adapted
to received light from the transmitter and to reflect
said light in parallel with the received light towards
the light receiver on the first unit, and that said
light receiver is adapted to indicate the said prede-
termined position. The light reflector here is a so-
called retroreflector, and the reflected light is
transmitted from the reflector at substantially the
same point where the reflector receives the correspond-
ing light, which means that a turn of the reflector
about an axis perpendicular to the main plane of said
reflector does not affect the indication result. Like
the present invention, this system thus comprises
a source of radiation and a radiation detector on
the first unit and a radiation receiving and retrans-
mitting means on the second unit.
The system disclosed by Swedish Patent 366,127
is not, however, suited for the determination and
detection of a relative position between a first unit
arranged in a first plane and a second unit arranged
in a second plane parallel to said first plane and
spaced therefrom, which units are mutually movable
in a direction of movement parallel to the said planes.
More particularly, the system according to Swedish
Patent 366,127 is arranged to detect a relative position
between two objects approaching one another substan-
tially in parallel with the optical axes of the radia-
tion source and the radiation detector, whereas the
present invention aims at solving the problems encoun-
tered when the two units are moving relative to one
another in planes perpendicular to the said optical
axes. Furthermore, the system according to the present
invention provides possibilities of fine positioning,
which is not the case with the system of Swedish Patent
366,127.
DE 2,617,797 discloses a system for optical measure-
ment of a relative position between two units mu-tually
movable in parallel planes, said first unit having
a radiation source and a radiation detector, and said
second unit having a passive means adapted to receive
radiation transmitted from the radiation detector
and to retransmi-t said radiation towards said radiation
detector which is adapted, in response to the retrans-
mitted radiation, to provide position information cor-
responding to said relative position. The radiationdetector here consists of two photocells arranged
closely adjacent one another, the position indicating
information being calculated on the basis of how great
a part of the retransmitted radiation impinges upon
each of said photocells. The passive means consists
of a reflective planar surface or a V-shaped prism,
-the base of which is facing said first unit.
The system disclosed by DE 2,617,797 thus merely
permits position determination in one direction, which
for instance in the positioning of automatically con-
trolled trucks does not give sufficient accuracy,
especially if the truck supports a robot or the like
whose movements are calculated on the basis of a refe-
rence system which is stationary relative to the floor
and which requires position determination in two dimen-
sions in order to achieve adequate accuracy.
In the event that the passive means according
to DE 2,617,797 is a planar reflective surface, a
turn of the second unit about an axis perpendicular
to said plane cannot be detected, and in the event
that said passive means is a V-shaped prism, a turn
of said second unit about said axis will cause the
radiation retransmitted from said prism to fall ou-t-
side the two photocells, such that there will be no
position information even if the two units are close
to one another.
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A number of difficulties are encountered in the
event that the positioning system of the type mentioned
by way of introduction is used for interrupting the
movement of a movable unit when this has been moved
into such a position relative to a stationary unit
that radiation is transmitted from said movable unit
to said stationary unit and back to said stationary
unit.
In the first place, the detection area of the
system may be so large that satisfactory accuracy
in the positioning of the first unit is obtained only
within a limited part of the detection area. In the
second place, the means provided for driving and con-
trolling the movable unit may respond slowly to the
position information given by the radiation detector,
such that the movable unit is not stopped at the point
where detection is obtained. In the third place, prior
art positioning systems of the type here concerned
offer no or but limited correction possibilities,
in the event a position indication has been obtained,
but an inccorrect relative position has been attained
in response to this position indication. In the fourth
place, most systems of this type offer no possibility
of detecting whether the unit carrying the radiation
receiving and retransmitting means is turned about
an axis extending through said means in parallel with
the path of rays, i.e. detecting relative turning
of the units about the said axis.
The invention aims at solving the above-mentioned
difficulties, and this is achieved if use is made
of a positioning system of the type disclosed by way
of introduction, said system being further charac-
terised in that the passive means has a separate radia-
tion receiving portion which is extended in said second
plane and within which the transmitted beam of rays
impinges when said relative position lies within said
limits, and a separate radiation retransmitting por-
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tion which is in optical communication with and, asseen in a direction parallel to said second plane,
is spaced a distance from said radiation receiving
portion; and that said radiation detector has a two-
dimensionally position sensitive detection area, thebeam of rays retransmitted from said radiation retrans-
mitting portion having a convergence such that it
impinges on a limited part of the detection area when
said relative position lies within said limits, said
radiation detector being further arranged such that
the position information provided contains information
about where the retransmitted beam of rays impinges
in the two-dimensionally extended detection area.
The positioning system according to the invention
thus comprises both a distance between the receiving
location and the retransmitting location of the second
unit and a distance between the radiation source and
the radiation detector of the first unit and, further-
more, a detection area extended in two dimensions,
for which reason the positioning and/or position deter-
mination of said first unit in relation to said second
unit can be carried out on the one hand in two dimen-
sions and, on the other hand, with far higher accuracy
than is possible in prior art positioning systems.
To be able to utilise the entire detection area of
the radiation detector in the direction of movement,
the extent of the receiving location in this direction
is at least as large as the extent of the detection
area in the same direction.
In an especially preferred embodiment of the
invention, the radiation detector is a semiconductor
detector which is position sensitive in one or two
dimensions and has a detection area extended conti-
nuously in two dimensions in the first plane. (A semi-
conductor detector of this type, which is position
sensitive in two dimensions, is commercially available
under the tradename Sitek. A detailed description
a trade mark
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of the function and construction of this detector
is given in, for example, the publica-tion "Elteknik
med aktuell elektronik", 1983, No. 17, pp. 96 and
97.)
In another embodiment of the positioning system
according to the invention, the radiation detector
may comprise a plurality of separate radiation sen-
sitive elements, such as photocells or the like, which
are distributed in two dimensions, for example in
parallel with the first plane. The fine positioning
accuracy is, in this instance, directly dependent
on the number or denseness of the radiation sensitive
elements.
In an especially inexpensive, compact and simple
variant of the invention, the passive means consists
of at least one optical fibre, one end of which is
attached at the receiving location and the other end
at the retransmitting location on the second unit.
In a preferred embodiment of the invention, the
radiation source and the radiation detector, arranged
in the first plane, of said first unit are spaced apart
essentially the same distance as the said distance
between the receiving and retransmitting locations of
said second unit, whereby the directions of the trans-
mitted and the retransmitted radiations will be essen-
tially parallel.
A particular advantage of the system according
to the invention is that it can be provided with spe-
cific identification means with which it is possible,
on the basis of the position information provided
by the detector, to distinguish the second unit from
similar units with other identification means. Such
an identification means may consist of, for example,
a screen which is mounted at the retransmitting loca-
tion of the passive means and has a pattern specificfor the second unit. The radiation detector is here
adapted to sense different radiation patterns and
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to provide identification information corresponding
to these patterns. This possibility is of special
interest in the above-mentioned application for auto-
matically controlled trucks where each station can
be provided with such identification means.
To prevent functional disorders due to dirt and
the like on the radiation receiving and retransmitting
surfaces in the system, the frequency of the radiation
transmitted by the radiation source, and thus the
radiation retransmitted by the passive means, prefer-
ably lies within the infrared range of the spectrum.
The design of the positioning system according
to the invention, and its mode of application, as
well as its specific application to automatically
controlled trucks, will now be described in more detail
below, reference being had to the accompanying drawing
in which Fig. 1 is a schematic perspective view of
an especially preferred embodiment of a positioning
system according to the invention, Figs. 2A and 2B
are lateral views of the system shown in Fig. 1 and
illustrate an especially preferred mode of application
thereof, and Fig. 3 is a schematic view of the applica-
tion of the positioning system according to the inven-
tion to automatically controlled trucks.
Fig. 1 which illustrates the basic design of
a positioning system according to the invention, shows
a movable first unit 1 and a stationary second unit
2. The units 1 and 2 are arranged each in one XY plane
which are mutually parallel and spaced apart in the
Z direction, as indicated by the coordinate system
in Fig. 1. The movement of the first unit 1 in relation
to the stationary unit 2 is accomplished by control
and drive means not shown. In the embodiment illu-
strated, it is assumed that the first unit 1 is movable
in at least the X direction and the Y direction in
the first plane. On its side la facing the second
unit 2, the first unit 1 is provided with a radiation
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source 3 and a radiation detector 4 spaced therefrom
and sensitive to radiation of the same frequency as
the radiation frequency of the source 3. Depending
upon the field of application, the frequence may lie
in, for example, the visible or infrared range of
the spectrum.
The second unit 2 which is spaced from -the first
unit 1 in the Z direction, is provided on its side
2a facing the first unit~l with a radiation receiving
location 5 and a radiation retransmitting location
6 disposed at a distance A from the location 5. These
locations will be referred to hereinafter as the re-
ceiving location and the retransmitting location,
respectively. Furthermore, the second unit 2 is provided
with a passive means 7 which, in the embodiment illu-
strated, is constituted by at least one U-shaped optical
fibre, one end 8 of which is located at the receiving
location 5, while the other end 9 is located at the
retransmitting location 6. The second unit 2 is pro-
vided at its receiving location 5 with a collectinglens (not shown) or the like for directing incident
radiation Sl at the receiving location 5 against the
input end 8 of the optical fibre 7, and at its retrans-
mitting location 6 with a screen tnot shown) or the
like, the function of which will be explained in more
detail below.
As will appear from Fig. 1, the receiving location
5 and the retransmitting location 6 of the second
unit 2 are spaced apart a distance A equalling the
distance between the radiation source 3 and the radia-
tion detector 4 of the first unit 1, and the optical
axis of the radiation source 3 is parallel to the
optical axis of the retransmitting location 6, where-
by the radiation Sl transmitted by the source of radia-
tion 3 is parallel to the radiation S2 transmittedfrom the retransmitting location.
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The body of the second unit may be made of any
suitable material, and the optical fibre 7, the collect-
ing lens and the screen may be incorporated with said
body during the production thereof, such that an inte-
grated and robust unit is obtained.
As is shown schematically by dash lines in Fig. 1,
the radiation detector 4 of the first unit 1 is extended
in both the X direction and the Y direction in the
first plane, and the receiving location 5 of the second
unit is extended both in the X direction and in the
Y direction in the second plane, for reasons that
will be explained below.
The radiation detector 4 is adapted to provide
position information signals when the radiation S2
retransmitted from the second unit is directed against
the detection area of the detector 4.
In the preferred embodiment as herein described
and shown in the drawing, the radiation detector 4
which thus has a detection area extended in the first
plane, consists of a position sensitive semiconductor
detector which provides electrical signals indicating
where on the detection area of the radiation detector
4 the retransmitted radiation S2 impinges.
In Fig. 1, the point of incidence of the retrans-
25 mitted radiation S2 is designated P. `
The application of the positioning system desc-ribed
above with reference to Fig. 1 to position detection
and position determination will now be explained in
more detail, reference being had to Figs. 2A and 2B
and like components being identified by like reference`
numerals in, respectively, Fig. 1 and Figs. 2A and
2B. For the sake simplicity, the mode of operation
of the system will be explained only in that case
when the first unit 1 is moving and positioned in
the X direction, but it will be appreciated that the
system operates in the same manner whether the movement
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occurs in the Y direction or in both the X direction
and the Y direction.
In a first stage, the movable unit 1 is spaced
from the stationary unit 2 a distance such that the
radiation Sl transmitted by the radiation source 3
is not directed against the receiving location 5 of the
second unit 2. In other words, the first unit has as
yet not been positioned in this stage.
In a second stage, coarse positioning of the first
unit 1 relative to the second unit 2 is carried out.
This coarse positioning is accomplished in that the
first unit 1 is moved by means of the above-mentioned
control and drive means towards the second unit 2
up to the location where the radiation Sl transmitted
by the radiation source 3 impinges at the receiving
location 5 of the second unit 2, passes through the
collecting lens (not shown) and through the optical
fibre 7, and is retransmitted (S2) towards the detec-
tion area of the detector 4. On receiving the retrans-
mitted radiation S2, the detector 4 supplies positioninformation which indicates that coarse positioning has
been established and also where on the detection area
the retransmitted radiation S2 impinges. In Fig. 2A,
the "point of incidence" on the detection area is
designated Pl, and the position information supplied
in Fig. 2A thus contains information corresponding
to the point Pl. In Fig. 2A, the first unit has been
moved to a position which deviates by ~X from the
desired position shown in Fig. 2B.
In a third stage in which fine positioning of
the first unit 1 relative to the second unit 2 is
carried out, the first unit is caused, in response
to the position information corresponding to the point
Pl, to move towards the desired position shown in
Fig. 2B, i.e. to the right in Fig. 2A, by means of
said control and drive means. It should here be noted
that the po:int of incidence of the retransmitted radia-
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12tion S2 will lie within the detection area of the
detector 4 during the entire fine positioning, and
that the position information provided by the detector
4 is continuously supplied to said control and drive
means during the entire fine positioning. Relative
movement of the units 1 and 2 during fine positioning
obviously is restricted on the one hand by the extent
of the detection range in the direction of movement
and, on the other hand, by the extent of the receiving
location 5 of the second unit 2 in the same direction.
When the first unit has been moved, by means of said
control and drive means, to the position shown in
Fig. 2B, in which the point of incidence of the re-
transmitted radiation S2 has now been displaced from
Pl to P2, the provided position information which
now corresponds to the point P2, is compared with
the desired position. Since the first unit 1 has now
been positioned in the desired position relative to
the second unit 2, the first unit is now caused to
stop in the position shown in Fig. 2B.
The above-mentioned positioning process comprising
a coarse positioning and a subsequent fine positioning,
may be especially preferred in those cases when it
is desired to move the movable unit 1 at high speed
between the positions in which it is intended to stop.
After coarse positioning has been accomplished (Fig. 2A),
the speed can be reduced, whereupon fine positioning
can be carried out at a low speed and with high accu-
racy.
The present invention is especially suitable
for the positioning of automatically controlled trucks
or the like which are controlled automatically along
a path, loop or the like laid out on a factory floor.
This particular use of the positioning system according
to the invention will now be described in more detail,
reference being had to Fig. 3 which from above and
schematically illustrates an automatically controlled
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13
truck 10 which on wheels 11 is guided along a path
12. The truck 10 is intended to stop at a plurality
of stations 13 along the path 12. In order to achieve
the desired positioning of the truck 10 in relation
to the stations 13, the truck is provided with a first
first unit 1 supporting a radiation source 3 and a
radiation detector 4, the stations being provided
each with one second unit 2 having a radiation receiv-
ing location 5 and a radiation retransmitting location
6. The said second, stationary and passive units 2
preferably are let into the floor, such that the upper
side 2a of the units lies in the plane of the floor
surface. In this application of the positioning system
according to the invention, the frequency of the ra-
diation transmitted preferably lies within the infraredrange of the spectrum.
The positioning system according to the invention
also offers a possibility of identifying different
stations 13. Such identification can be accomplished
for e~ample by providing, at the radiation retrans-
mitting location 6 of the station 13, a pattern specific
for that station. In this instance, the radiation
detector 4 on the truck 10 is adapted to detect the
retransmitted radiation S2 influenced by the screen
and to provide information corresponding to the speci-
fic screen pattern.
As an alternative to the screen, the passive
means of the second unit 2 may consist of a plurality
of optical fibres 7, the ou-tput ends 9 of which are
arranged in a specific pattern at the retransmitting
location 6. For detecting such a pattern a two-dimen-
sional set of photocells may be utilised for the detec-
toi 4 on the truck 10.
The positioning of the truck 10 in relation to
the respective stations 13 may be accomplished by
the coarse positioning and subsequent fine position-
ing described above with reference to Figs. 2A and
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2B. However, the positioning system according to -the
invention is especially applicable to the case where
the truck 10 supports a robot or the like which is
movable relative to the truck and adapted, when the
truck 10 has been arranged in position at a station
13, to perform a movement pattern in relation to a
reference system which is stationary relative to said
station 13. In this case, fine positioning of the
truck 10 may be omitted. More particularly, positioning
can be carried out such that the truck 10 is caused
to move towards a station 13 to a position in which
radiation Sl transmitted by the radiation source 3
falls within the receiving location 5 of the station
13, and the retransmitted radiation S2 falls within
the detection area of the detector 4. After coarse
positioning of the truck 10 in this manner relative
to the station 13, the truck is caused to stop, where-
upon a reference system for the robot movement pattern
is calculated on the basis of the position information
provided by the detector ~, said reference system
being dependent on the exact position of the truck
10 relative to the station 13, i.e. dependent on the
point of incidence P of the retransmitted radiation
S2 on the detection area of the detector 4. Thus,
a complicated and time-consuming fine positioning
of the truck 10 relative to the station 13 is not
necessary in this case.
The invention is, of course, not restricted to
the embodiment which has been described above and
illustrated in the drawing and which merely constitu-tes
an example, but may be modified in several ways within
the scope of the protection claimed which is limited
only by that stated in the appended claims.
For example, the two units 1 and 2 may be mounted
on two objects which also are movable in the Z direc-
tion, in which case it may sometimes be interesting
also to provide a positioning in the Z direction.
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Such positioning can be achieved if the optical axes
of the radiation source 3 and the radiation detector
4 are inclined relative to one another, for example
by making the distance between the source 3 and the
detector 4 sreater than the distance between the re-
ceiving location 5 and the retransmitting location
6. Such a system wi-th inclined optical axes gives
a closed radiation path only if the distance in the
Z direction between the first unit 1 and the second
unit 2 lies within specific limits.
Finally, it should be mentioned that the passive
means 7 in the second unit 2 need not consist of op-
tical fibres; it may also be, for example, a mirror
system or the like.
