Sensing apparatus for determining the relative position between two bodies with plural emitters and a shading member

Sensing apparatus for determining the relative position between two bodies located at a distance from one another with respect to a predetermined relative position wherein one of the bodies is provided with a camera having an areal matrix of photosensitive elements arranged in the image plane of the camera and wherein the other of the bodies is provided with a shading member projecting from the surface thereof and with an optically clearly distinguishable reference pattern in the area of the base of the shading member, the reference pattern being formed by means of light sources which emit light patterns which are as punctiform as possible. The reference pattern is partially covered in an asymmetric manner by the shading member during deviation from the reference position and this deviation is sensed by the photosensitive elements in the camera.

The present invention is directed to measuring apparatus for determining 
the relative position between two bodies located at a distance from one 
another with respect to a pregiven reference position. More particularly, 
the invention is directed to apparatus comprising at one body means for 
sensing an optically or visually clear distinguishable reference pattern 
on the other body in order to determine deviation from the relative 
reference position between the bodies. 
Measuring apparatuses used for determining the relative position of two 
bodies with respect to a pregiven reference position are required in 
various branches of technology. For example, robots must be capable of 
bringing parts to be mounted at a body or to be fitted into openings at a 
body to this body in very specific predetermined orientation. Also, in 
submarine technology, such devices may be utilized, for example, in 
automatic or remote-controlled maneuvering of crewless minisubmarines. 
In space travel, the problem can be posed with regard to effecting the 
approach of manned or crewless space missiles or satellites to one another 
and for effecting coupling thereof by means of coupling devices provided 
for this purpose. In this situation, caution must be exercised before 
coupling in order to insure that the actively approaching space missile 
exactly observes and maintains the required reference position with 
respect to the passive space missile. For this purpose, again, deviations 
from the reference position must be quickly and accurately sensed and 
measured, especially for automatic operation, so that the required 
position corrections or adjustments can be effected in due time. 
Such apparatus is known in the prior art from U.S. Pat. No. 3,910,533, by 
means of which the docking of a space vehicle at another space vehicle is 
made possible. For this purpose, a television camera is attached in the 
center of the docking apparatus for the active space vehicle, which 
television camera scans the docking apparatus of the passive space missile 
in its viewing field during the approach of the active space missile to 
the passive space missile. The approach process of the two space missiles 
is ideal when the two axes of symmetry of the docking apparatuses coincide 
continuously. 
However, in most cases, this is not insured from the outset of the docking 
maneuver. In order to be able to determine deviations from this reference 
position, there is provided in the center of the docking apparatus of the 
passive space missile a shading member which projects forwardly from the 
surface of the latter and exactly and completely covers a reference 
pattern located in the area of its base, as seen from the camera of the 
active space missile, when the two space missiles are located in the 
relative reference position. This reference position corresponds to the 
mutual orientation of the space missiles required for docking in which the 
two axes of symmetry coincide with or are coaxial with one another in 
position and direction and a predetermined relative angular position is 
also established with respect to these axes of symmetry. 
The shading member is a square frame attached on supports at whose base is 
located a similarly square-shaped band as a reference pattern with clearly 
visible transverse striping. As seen from a determined point on the axis 
of symmetry of the docking apparatus of the passive space missile, this 
square band is optically completely covered or shaded by means of the 
frame arranged in front of it. If, on the other hand, the active space 
missile with its camera approaches from a lateral position, the square 
band serving as the reference pattern is then only partially covered. The 
image which is outlined or projected by the camera arrives on a monitor 
and can there be observed by the pilot of the active space missile. The 
pilot is then able to carry out correcting or adjusting control movements 
in order to bring the active space missile into the reference position. 
The direction in which these control movements are to be carried out 
results from the perspective mutual displacement of the frame and 
reference pattern visible on the monitor. The result of the control 
command can be followed or tracked on the monitor at any time. 
The apparatus described in U.S. Pat. No. 3,910,533 is designed such that 
correcting movements in the direction of the desired reference position 
are carried out by a pilot controlling the active space missile. An 
approach which is automatically carried out is not possible with this 
apparatus. Moreover, the apparatus gives a visual impression of the 
magnitude and direction of the deviation of the active space missile from 
the reference position. However, this is not a measuring apparatus in the 
true sense. An exact deviation measurement is not intended and is also not 
required because of the presence of a pilot or astronaut. This apparatus 
is, therefore, unsuitable for use in unmanned or crewless space vehicles 
and it requires great experience and absolute concentration on the part of 
the pilot. 
In contrast, the present invention is directed toward providing a measuring 
apparatus of the aforementioned type, which makes it possible to 
automatically measure as accurately as possible the relative position 
between two bodies, particularly space missiles, located at a distance 
from one another, with regard to a relative reference position so that the 
required position corrections can be carried out reliably and 
automatically on the basis of the results obtained. This capability has 
particular importance with regard to the measurement of tilting or 
pitching of the two axes of symmetry relative to one one another, since it 
was not previously possible to measure such tilting with the required 
accuracy, while maintaining justifiable cost limits for the apparatus. 
SUMMARY OF THE INVENTION 
Briefly, the present invention may be described as sensing apparatus for 
determining the relative position between two bodies which are located at 
a distance from each other with respect to a predetermined relative 
reference position between the bodies, comprising camera means provided at 
one of the bodies, a shading member provided at the other of the bodies 
projecting from the surface of said other body, and means for defining an 
optically clearly distinguishable reference pattern in the area of the 
base of the shading member, said reference pattern being formed preferably 
by means of light sources, such as light emitting diodes which emit a 
light pattern which is as punctiform as possible with the light sources 
being linearly or areally distributed outside the base of the shading 
member. The reference pattern which is defined is partially covered in an 
asymmetric manner by the shading member during deviation of the two bodies 
from the reference position. The camera is provided with an areal matrix 
of photosensitive elements arranged in the image plane of the camera 
adapted to sense the light sources defining the reference pattern. 
The proposed operating characteristics of the invention are achieved in 
that an areal matrix of photosensitive elements is arranged in the image 
or focal plane of the camera and the reference pattern is formed by means 
of light sources which emit light in a pattern as punctiform as possible 
and are distributed in a lineal or areal arrangement outside the base of 
the shading member. Instead of a television camera connected with a 
monitor, a CCD or CID camera, for example, is used, in whose image plane a 
CCD or CID array is located, respectively. Such cameras, in contrast to 
television cameras, comprise a coordinate allocation of the image plane 
which can be fixed or determined in an unequivocal manner. In addition, 
the reference pattern, according to the invention, is formed by means of a 
lineal or areal arrangement of light sources which are as punctiform as 
possible, preferably light emitting diodes or LEDs, which are arranged 
outside the base of the shading member. During lateral displacement or 
tilting of the axis of symmetry of one body relative to the axis of 
symmetry of the other body, a part of the light sources is accordingly 
covered by means of the shading member in the image of the reference 
pattern outlined in the image plane of the camera. According to the shape 
of the shading member, which preferably can be circular-cylindrical or 
cubic, as well as to the specific arrangement of the light sources, a 
shading pattern results which is characteristic for the type of deviation 
from the reference position, from which shading pattern the deviation 
magnitudes, such as tilting angle or relative displacement of the axes of 
symmetry, can be determined on the basis of purely geometric 
relationships, possibly by means of comparison with a stored image 
corresponding to the exact reference position. 
The closer the light sources are arranged adjacent one another, the more 
punctiform they are and the smaller and closer together the photosensitive 
elements of the camera matrix are, the more accurate the measuring 
apparatus. 
A particularly simple measuring apparatus is provided by using light diode 
rows of equal lengths arranged in a cruciform pattern. In this case, the 
shading member is advisably constructed as a circular cylinder. During 
tilting of the axes of symmetry relative to one another, one or two of the 
four half-rows are partially covered starting from the base, with more of 
their length being covered as the tilting angle increases. The extent and 
the direction of the relative tilting can also be unquivocally concluded 
from the covering degree of these partially shaded light diode rows. Also, 
pure rotation around the axes of symmetry can be determined with the aid 
of such cruciform light diode row. 
In addition to a cruciform arrangement of light diode rows, other radiating 
or radially extending arrangements of light diode rows are also possible. 
Light sources which are arranged close together and distributed over a 
surface area, i.e., areally, can also serve as a reference pattern, for 
example, light diodes which are preferably uniformly distributed within a 
circular or rectangular surface area. Here, as well, the deviation 
magnitudes can be concluded from the direction and extent of the shading. 
In practice, light diode rows have the advantage that, to the extent that 
they are so arranged, during deviation, particularly during tilting, a 
corresponding shading occurs which can be evaluated in an unequivocal 
manner since the linear arrangement is naturally distinguished, in 
comparison to the areal arrangement, by substantially lower expenditure in 
signal processing. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of this disclosure. For a better understanding of the invention, its 
operating advantages and specific objects attained by its use, reference 
should be had to the drawings and descriptive matter in which there is 
illustrated and described a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, and particularly to FIG. 1, there is shown 
schematically, in side view, apparatus according to the invention 
comprising a cylindrical shading member 5 which is attached on the surface 
of a body 1, for example, a passive satellite. Attached in a symmetrical 
arrangement around the base of the cylindrical shading member 5 are four 
rows 7 of light emitting diodes 6 (LEDs) at an angular distance of 
90.degree. relative to one another, which together accordingly form a 
light diode cross (see also FIG. 2). Shown above the shading member 5 is a 
body 2, e.g., an active second satellite, located in an approach to the 
body 1. The body 2 approaching the passive satellite 1 is equipped with a 
camera 3 arranged to have the shading member 5 and its surroundings on the 
surface of the body 1 in its viewing field. 
Located in the image plane of a lens 8 of the camera 3 is an areal matrix 4 
of readable, photosensitive elements. The latter can be CCD or CID 
sensors, wherein CCD refers to a charge coupled device and CID refers to a 
charge injection device. The camera 3 is thus a solid-state type camera 
whose sensor elements can be electronically directly read out, i.e., 
without the auxiliary means of an electron beam to be guided in a vacuum. 
The lens 8 of the camera 3 preferably has a variable focal length which is 
automatically tracked during the approach to the subject of observation, 
in this case, the surface of the body 1 with the shading member 5, for 
example, on the basis of simultaneous distance measurements. 
FIG. 1 shows a position of the two bodies 1 and 2 relative to one another 
in which the axis of symmetry 9 of the lens 8 of the camera 3 coincides 
with the axis of symmetry 10 of the shading member 5. Accordingly, a 
completely symmetrical image of the shading member 5, as well as of the 
light diode rows 7, appears in the image plane of the lens 8. FIG. 1 shows 
the angle of view or angular field .alpha. of the lens 8 at the distance 
of the two bodies 1 and 2 from one another, shown in the drawing, as well 
as the angle of vision .beta. at which the cylindrical shading member 5 
appears, as seen from the camera 3. Accordingly, a circular shading zone 
11 results, i.e., an area around the base of the shading member 5 which, 
as seen from the camera 3, is covered by means of the latter. However, 
this does not impair the symmetry with respect to the quantity of light 
diodes 6 still visible in the four light diode rows 7, as seen from the 
camera. The circular area 11 increases as the approach of the camera 3 
increases, but an equal quantity of light diodes 6 in each light diode row 
7 is covered by means of this. In this case, the approaching body 2 is 
already in the ideal position provided for possible coupling. The distance 
as well as the approach speed of the body 2 with respect to the body 1 can 
be deduced from the increasing covering degree of the light diode rows 7 
given by the increasing shading zone 11. In addition, the length of the 
still unshaded light diode rows 7 increasing in the image plane of the 
lens 8 can likewise be used, possibly accompanied by a selection of two 
fixed reference diodes whose increasing image distance is measured 
In addition, FIG. 1 shows a second position of the body 2 indicated by 
means of an inclined axis of symmetry 9', in which second position the 
axis of symmetry 9' is tilted relative to the axis of symmetry 10 of the 
shading member 5 at an angle .gamma.. The covering surface 12 of the 
shading member 5 now appears at a somewhat reduced angle of vision .beta.' 
and, above all, there results a shading zone 13 which is asymmetrical 
relative to the axis of symmetry 10, so that, as seen from this new camera 
position, a considerable part of the light diode row 7' shown at the left 
in FIG. 2 appears covered by means of the shading member 5. The tilting 
angle .gamma. is unequivocally deduced from the quantity of covered light 
diodes 6 to the extent that the distance of the camera 3 from the shading 
member is simultaneously known. This, in turn, can be determined from the 
image length of the uncovered light diode rows 7, in particular of the two 
which are oriented perpendicularly relative to the rows 7'. The tilting 
angle .gamma. is then determined on the basis of generally known 
trigonometric relations. 
In the second camera position (axis of symmetry 9') shown in FIG. 1, 
lateral offsettings are already corrected so that during the further 
position correction, only the tilting angle .gamma. must be brought to 
zero. FIG. 2 shows three additional light diodes 14 on the covering 
surface 12 of the shading member 5, which additional light diodes 14 can 
be used as a reference pattern in approaching from greater distances and 
must therefore have a correspondingly greater light-transmitting capacity. 
However, these light diodes 14 can also be used as desired in the closer 
distance range in order to determine lateral offsetting or rotation, i.e., 
bearing or roll angle deviations of the approaching body 2 with respect to 
the ideal reference position. However, in principle, at least rotation 
alone can also be determined by means of the light diode rows 7 arranged 
in a cruciform manner, wherein one of the rows, in particular, is to be 
characterized, possibly by means of omitting individual light diodes 6, 
through color or pulse frequency coding. In order to make these light 
diodes used as light sources particularly visible relative to the 
immediate surrounding, the cylindrical shading member 5, as well as the 
surface of the body 1 surrounding its base and the light diode rows 7, are 
advisably blackened or darkened so that no disturbing light reflections 
can occur. 
In the selected arrangement of the reference pattern as a light diode 
cross, the roll angle deviation, i.e., the rotation of the approaching 
body 2 around the axis of symmetry of the camera 3 with respect to a 
pregiven zero position, the lateral offsetting, as well as the tilting 
angle, can be determined by means of comparison with a stored reference 
image of this reference pattern. In addition, the relative distance can be 
determined, for example, with the aid of a stored distance scale with 
stored images of the reference pattern which differ in dimensioning in 
dependence on the distance, as well as the relative speed, namely by means 
of the determined changes in distance. 
The CCD or CID matrices can be read out in a known manner and the readout 
information can be digitized and evaluated in this form in a conventional 
manner and fed to the required calculating operations. With a suitable 
selection of parameters, such as dimensioning and shape of the shading 
member, length and arrangement of the light diode rows, as well as mutual 
distance of the individual light diodes, camera focal length and quantity, 
as well as closeness of the CCD or CID sensor elements arranged in a 
matrix in the image plane of the camera, angle resolutions or definitions 
of an order of magnitude of 0.05.degree., as well as resolutions with 
respect to the lateral offsetting of less than 1 mm, can be achieved with 
a measuring arrangement, according to the invention, at a distance of the 
camera from the shading member amounting to a few meters. These resolution 
values can be further improved when using suitable interpolation methods. 
It can be advantageous to use the light diodes in pulse operations in order 
to make them unequivocally recognizable relative to a light background. In 
order to be able to determine rotations with respect to the axis of 
symmetry in an unequivocal manner, it is advisable to divide at least one 
of the light diode rows in segments, in the case of a light cross, such 
that the segments can be switched off separately as desired. The 
unambiguity in determining the relative position can also be insured by 
operating one or more of the light diode rows accompanied by a 
predetermination of different frequency codes. 
Accordingly, it will be seen from the foregoing that the present invention 
provides measuring apparatus used for determining the relative position of 
two bodies located at a distance from one another, for example, two 
satellites approaching one another, with reference to a predetermined 
reference position. A camera 3 is provided at one body 2 and a shading 
member 5 is provided at the other body 1. Provided in the base area of 
this shading member 5 is an optically clearly distinguishable reference 
pattern 7 which is partially covered in an asymmetrical manner by the 
shading member during deviation from the reference position. In order to 
automatically measure as accurately as possible the relative position of 
the two bodies relative to one another, particularly with respect to 
tilting of the two axes of symmetry relative to one another, an areal 
matrix 4 of photosensitive elements is arranged in the image plane of the 
camera 3. Moreover, the reference pattern is formed by means of light 
sources, for example, light emitting diodes, which are as punctiform as 
possible and are distributed linearly or areally outside the base of the 
shading member 5. 
While a specific embodiment of the invention has been shown and described 
in detail to illustrate the application of the inventive principles, it 
will be understood that the invention may be embodied otherwise without 
departing from such principles.