System to link the kinematics of neighboring panels in a panel assembly

A panel assembly includes a number of rectangular panels each carrying solar cells or a cooling radiator on one of the two main surfaces, where the panels are interconnected mutually by hinges such that the assembly from a first state, in which the panels are folded into a package, can be brought into a second state in which the package is unfolded and the panels are situated alongside each other. A torsion element substantially extends across the other main surface of each panel from a first position on the hinge axis between the panel and the adjoining panel at one side, to a second position on the hinge axis between the panel and the adjoining panel at the other side, whereby the torsion element at or near the first and second positions is attached to the respective adjoining panel.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a panel assembly comprising a number of 
rectangular flat panels interconnected mutually by hinges such that the 
assembly from a first state, in which the panels are folded upon each 
other into a package, can be brought into a second state in which the 
panels are situated alongside each other. 
2. Description of the Related Art 
Such panel assemblies whereby at least some panels carry solar cells are 
already known, e.g. from U.S. Pat. Nos. 5,487,791 and 5,509,747. In the 
first state the panels of these assemblies are folded zigzag wise into a 
package and in the second state the panels are unfolded and are oriented 
alongside each other in the same plane, forming one larger solar panel 
assembly. 
Instead of solar cells any other suitable devices could be connected to the 
panels such as one or more cooling radiators, a number of mirrors, etc. In 
fact it is not even necessary that other components are attached to the 
panels. The panels as such can be used for instance for reflecting 
electromagnetic energy such as radio or radar waves. 
Other known assemblies are described in U.S. Pat. No. 5,520,747 and EP 
0754626. Wherein a central panel is adjoined by two side panels which in 
the first state both are folded just as window shutters on top of the same 
surface of the central panel and in the second state are unfolded and 
oriented along the central panel under a predetermined angle. In the 
unfolded state the mirrors, carried by the side panels will reflect sun 
light on the solar cells carried by the central panel. 
In fact U.S. Pat. No. 5,520,747 describes a combined assembly whereby all 
central panels are unfolded zigzagwise whereafter the side panels 
connected to each central panel are unfolded window shutter wise. 
Before transport the panels of such a panel assembly are folded into a 
package of which the length and width correspond approximately with the 
length and width of one separate panel and of which the thickness 
corresponds approximately with the thickness of one panel multiplied by 
the number of panels thereby greatly reducing the volume occupied by the 
assembly. In this state the assembly is transported from the earth into an 
orbit in space. In general the transporting vehicle (rocket, space 
shuttle, etc.) is able to transport payloads of rather restricted 
dimensions and restricted weight. Therefore, it is required in general 
that solar panel assemblies have a low weight and dimensions which should 
be within certain limits. To maintain a low weight one could use 
stiffness-efficient constructions having a sufficient strength, such as 
constructions comprising a lot of air and still having a sufficient 
stiffness and strongness, such as for instance honeycomb sandwich panels. 
In general the only way to reduce the dimensions of a solar panel assembly 
in its first state is to reduce the thickness of the actual panels. In 
case honeycomb sandwich constructions are used the only reduction 
possibility is to reduce the dimensions of the core. The surface, i.e. the 
length and width of each panel, will be selected as large as possible to 
obtain a large useful area for locating solar cells. 
A too great a reduction of the weight may lead to a construction having too 
little stiffness, both in a stowed configuration and in the fully deployed 
configuration. During operation, that may lead to harmful bending and 
torsion movements or oscillating movements of the individual panels or of 
the assembly as a whole in its extended second state. Such movements may 
occur for instance in the situation in which the position of the assembly 
in relation to the carrying satellite has to be corrected. 
Structural stiffness can be given to an extended solar panel assembly of 
relatively thin rectangular panels by curving each panel in a direction 
parallel to the panel edges to which the hinges between the panels are not 
attached. Such an embodiment is described in an older European application 
97204099.2 in the name of Fokker Space. 
Among systems to link the kinematics of neighboring panels of the solar 
panel assembly during unfolding from an undeployed position to a deployed 
position are systems employing motors, powered reels comprising cables, 
pulleys or the like. Examples of systems to synchronize the angular 
rotation of all the panels of he solar panel assembly during unfolding are 
those presented by U.S. Pat. Nos. 5,487,791 and 5,509,747. 
In the first mentioned U.S. Pat. No. 5,487,791 a system is described which 
comprises in fact two of the above-mentioned assemblies which in the 
unfolded second state are positioned in the same plane alongside each 
other. Each panel of the first assembly is connected through a pivot hinge 
to an adjacent panel of the second assembly. These pivot hinges extend 
along the central line of the respective panels such that both assemblies 
can be unfolded from the first into the second state simultaneously, 
whereby the unfolding operation of the first assembly takes place in 
counterphase in relation to the unfolding operation of the second 
assembly. Especially because of the presence of the pivot hinges it is 
impossible to get the panels in one plane and consequently curving of the 
panels to provide structural stiffness to the panel assembly as a whole 
cannot be used. 
The assembly described in U.S. Pat. No. 5,509,747 comprises an articulation 
arrangement whereby all hinge axes are mutually coupled by means of gear 
wheels, wire wheels and a number of endless wires running across pairs of 
wire wheels such that an unfolding movement between for instance the first 
two panels in the assembly is transferred to all the other hinges which 
will move simultaneously in the same way and in the same direction. 
Miniaturization of the control mechanisms will undoubtedly lead to very 
high mechanical stresses in the various sprocket wheels or chain wheels. 
SUMMARY OF THE INVENTION 
Considering these prior art configurations as either complicated or 
unreliable, an object of the invention was to provide a rather simple 
configuration specially designed for operating a panel assembly wherein 
the panels are relatively thin. 
In agreement with this object, the invention provides a solar panel 
assembly of the type mentioned in the first paragraph which is 
characterized in that a torsion element extends across at least one of the 
panels from a first position on the hinge line between the respective 
panel and the adjoining panel at one side to a second position on the 
hinge line between the respective panel and the adjoining panel at the 
other side whereby the torsion element at or near said first and second 
positions is attached to the respective adjoining panel. 
In fact the only additional element which has to be present between the 
pile of panels in the folded first state are the various torsion elements. 
These torsion elements in general are embodied as an elongated tube, rod 
or wire made of a resilient material, which is preferably flexible in 
bending and torsionally stiff, and which has a small diameter. In most 
cases the thickness of the whole package will be determined mainly by the 
thickness of the panels themselves as well as the dimensions of the 
various hinges. In general the dimensions of the torsion elements have no 
influence on the thickness of the whole panel. 
In a specific embodiment the assembly comprises three panels of which the 
two outer panels in the said first state are positioned on top of the same 
surface of the middle panel, whereby the torsion element has an inverted 
U-shape. In this embodiment the panels are folded and unfolded just as 
window shutters. 
In another embodiment the assembly comprises three or more panels which, in 
the first state, are folded zigzag wise, whereby each torsion element has 
an S-shape. In this embodiment the panels are folded and unfolded zigzag 
wise. 
In a preferred embodiment a panel assembly is characterized in that at said 
first and second position the torsion element is shaped as an axle and 
functions as hinge axle for one of said parallel hinges. Therewith it is 
guaranteed that the torsion element extends indeed from a first position 
on the hinge axis between the panel and the adjoining panel at one side to 
a second position on the hinge axis between the panel and the adjoining 
panel at the other side.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 7 illustrates an alternative for the torsion element. 
In FIG. 1 four separate panels are visible, i.e. the panels 10, 12, 14, and 
16. The panels are interconnected by means of hinges. Especially the 
panels 10 and 12 are interconnected by the hinges 20 and 22, the panels 12 
and 14 are interconnected by means of the hinges 24 and 26, the panels 14 
and 16 are interconnected by means of the hinges 28 and 30. A flexible 
torsion rod extends across each of the panels and the ends thereof are 
positioned in the central hinge passage such that these torsion rod ends 
function as hinge pins. The torsion rod 32 extends across the panel 12 
and, as is clearly illustrated in FIG. 1, the upper end thereof is 
inserted in the hinge 22 whereas the lower end thereof is inserted in the 
hinge 24. The torsion rod 34 extends across the panel 14, the upper end 
thereof is inserted in the central passage of the hinge 26 whereas the 
lower end of the torsion rod 34 is inserted in the central passage of the 
hinge 28. In the same manner the torsion rods 36 and 38, which are only 
partly visible in the figure, are installed on their panels 10 and 16 
respectively. The upper end of torsion rod 32 extending outside the hinge 
22 is bent parallel to the panel 10 and attached to said panel. The lower 
end of the torsion rod 32 is also bent parallel to the panel 14 and 
attached to said panel 14. The way in which the bent ends are attached to 
the respective panels is not relevant. One could use separate mounting 
means such as bolt and nuts or other appropriate fastener or one could 
rely on for instance a welded or soldered connection. In the same way the 
ends of the other torsion rods 34, 36, and 38 are bent and fastened to the 
surface of the adjoining panel. 
It is assumed in FIG. 1 that the solar cells of the solar panel assembly 
are mounted at the not visible underside of the various panels. 
To avoid vibrations in the rather resilient torsion rods it is preferred to 
use one or more intermediate saddle-shaped fasteners 40, 42 to guide the 
rods at various intermediate places. In FIG. 1 one of such fasteners for 
each torsion rod is illustrated, however, it will be clear that more of 
such guiding fasteners could be used if necessary. 
During transport from the earth into space the panels are folded zigzagwise 
together into a package, which is indicated as the first state of the 
assembly. After reaching its position in space the panels are unfolded 
until they reach a situation in which all panels are positioned in one 
plane as is illustrated in FIG. 1. 
FIG. 2 illustrates an intermediate situation of the unfolding process. In 
the following, the functioning of the torsion rods will be discussed with 
reference to FIG. 2. 
In FIG. 2 only three panels are illustrated indicated by 50, 52, and 54. 
Furthermore, only one of the torsion elements is illustrated indicated by 
56. The upper bent end of torsion element 56 is indicated by 56a and the 
lower bent end of torsion element 56 is indicated by 56b. Just as 
explained with reference to FIG. 1 the end 56a is attached to panel 50 and 
the end 56b is attached to panel 54. The various hinges interconnecting 
the panels 50, 52, and 54 are not illustrated because they do not play a 
role in the functional explanation of the torsion elements. It is only 
important that the torsion element 56 extends through the hinge line as is 
illustrated in FIG. 1. 
It is assumed that the bent ends 56a and 56b are in parallel planes. In the 
illustrated situation in FIG. 2 the angle between the panels 52 and 54 is 
indicated by .alpha.1 and the angle between the panels 50 and 52 is 
indicated by .alpha.2. An important property of the torsion element is 
that it strives to a condition whereby the bent ends 56a and 56b are still 
in parallel planes. That implies that if the panels 52 and 54, by (not 
illustrated) actuating means, are moved in the unfolding direction such 
that the angle .alpha.1 is increasing, then, because of the mentioned 
property of the torsion rod 56, the bent end 56a thereof will act on the 
panel 50 such that the angle .alpha.2 between the panels 50 and 52 is also 
increasing. Because all adjoining panels each have their own torsion rod 
and because in fact all the bent end sections thereof are extending 
parallel, the combined action of all these torsion rods will result into 
an unfolding movement of the whole assembly when only two adjacent panels 
thereof are moved in the unfolding direction. 
The same applies for bringing the assembly back from the unfolded second 
state into the folded first state. By moving the panels 52 and 54 by means 
of suitable actuators such that the intermediate angle .alpha.1 will 
decrease, the panel 50 will also start moving such that the angle .alpha.2 
will decrease under the influence of the torsion rod 56. The combined 
action of all the various torsion rods will lead to a situation whereby 
the whole panel will fold together only by moving the panels 52 and 54 
towards each other. 
In FIGS. 1 and 2 the ends of the torsion wires are bent at an angle of 
about 90.degree.. This is preferred to obtain a long effective force 
transmitting arm. However, smaller angles with resultant smaller effective 
force transmitting arms are certainly within the scope of the invention. 
FIG. 3 illustrates an alternative embodiment of a hinge 28a between the 
panels 14a and 16a. The end of the torsion rod 34a is attached to the 
panel 16a by attaching it to those parts of the hinge 28a which are 
connected to the panel 16a. In FIG. 3 small bolts 60a, 60b, 60c are used 
to fix the end of the torsion rod 34a to the section of the hinge 28a 
which is connected to the panel 16a. The way in which the hinge is 
connected to the panel is not illustrated because it does not play a role 
in relation to the invention. 
A further alternative embodiment is illustrated in FIG. 4. In this figure 
the end of the torsion rod 34b is not extending through the central 
passage of the hinge 28b, acting thereby as hinge pin, but is fastened by 
means of a bracket 70 to the panel 16b. The bracket 70 is constructed such 
that the end of the torsion rod 34b is preferably aligned with the central 
axis of the hinge 28b. The bracket 70 could have a section with a central 
passage in which the end of the torsion rod 34b could be inserted and 
could be fixed by means of bolts in a similar manner as is illustrated in 
FIG. 2. In FIG. 4 another solution is illustrated. The end section of the 
round torsion element 34b is flattened such that locally only half the 
volume of the original round rod remains. The central passage through the 
fastener 70 has a corresponding shape and the torsion rod 34 is fixed to 
the panel 16b by inserting its end into the passage in the fastener 70. 
FIG. 5 illustrates an embodiment in which, in stead of an S-shaped torsion 
element as in FIGS. 1-4, an inverted U-shaped torsion element is used. The 
assembly comprises in this case only three panels 60, 62 and 64. The 
panels are interconnected by parallel hinges which are not separately 
illustrated in FIG. 5. An inverted U-shaped torsion rod 66 extend across 
the middle panel 62. Both bent ends 66a and 66b of the torsion rod 66 are 
attached to the respective adjoining panels in a suitable manner. 
It is assumed that the solar cells are attached to the non visible 
underside of the middle panel 62 and that mirrors are attached to the non 
visible underside of the panels 60 and 64. 
If the side panel 60 is rotated along its hinge line in the direction 
indicated by the arrow 68a, then because of the influence of the torsion 
element 66 the other outer panel 64 will rotate in counterdirection 
indicated by arrow 68b. To obtain the first state this folding operation 
is continued until both outer panels 60 and 64 are on top of the panel 62. 
Dependent on the dimensions the outer panels are in this first state 
alongside each other or (partly) on top of each other, which is completely 
unimportant for the invention. 
From the first state the assembly reaches its second state by rotating one 
of the outer panels, e.g panel 60 in the direction indicated by the arrow 
70a. The other outer panel 64 will rotate in the direction of the arrow 
70b under the influence of the torsion element 66. The panels pass a 
situation in which all three panels are in the same plane and both outer 
panels will rotate further until a predetermined angle with the middle 
pane is obtained in which situation sun light impinging in the figure on 
the (not visible) under surfaces will be reflected from the outer panels 
onto the middle panel. 
In all the illustrated embodiments the various hinges have mutually 
parallel hinge lines. That is, however, not a prerequisite. If in a zigzag 
configuration of panels the various hinge lines in the series determine a 
small mutual angle then, after unfolding the assembly, the various panels 
will determine a fan-shaped surface. With suitable dimensions it is even 
possible to obtain a C-shaped surface or even a completely closed 
ring-shaped surface. 
In the above described embodiments it was furthermore assumed that the 
panels were used for carrying solar cells or mirrors. That is, however, 
not a prerequisite. The unfolded panels can be used also for reflecting 
for instance electromagnetic waves such as radio waves or radar waves onto 
an antenna. If the panels as such are made of a reflecting material then 
no further components have to be attached to obtain the desired goal. 
If the panels as such are made of a light reflecting material, such as 
highly polished aluminium or another suitable material, then special panel 
assemblies which define a large surface in the unfolded second state could 
be used to reflect solar light to one specific light receiver in space or 
even on the earth. 
To illustrate schematically the means for driving a panel from the first 
state into the second state two embodiments of an unfolded panel, attached 
to a satellite, are illustrated in FIGS. 6a and 6b. In FIG. 6a the panel 
assembly, as a whole indicated by 72, comprises the panels 72a, 72b, 72c, 
. . . , each by means of hinges connected to each other in the above 
described manner. Torsion elements 74b, 74c extend across the panels 72b, 
72c, . . . , but not across panel 72a (and also not across the outer panel 
at the other end of the series). The panel assembly 72 is through a boom 
71 attached to the body of the satellite 70. Details about the boom 71 and 
the satellite 70 will not be provided because they are not relevant in 
relation to the invention. 
A drive motor 76 is attached to the free sides of the panels 72a and 72b as 
is schematically illustrated in FIG. 6a. The function of the drive motor 
is to rotate the panel 72b in relation to panel 72a along the hinge line 
between both panels. If the panel assembly is in its first state whereby 
all panels are zigzagwise folded together and are positioned on top of 
each other, and the drive motor 76 is activated then panel 72b starts to 
rotate away from panel 72a. Because of the influence of all the various 
torsion rods 74a, 74b, etc., all the other panels start to rotate along 
their various hinge lines as is described above and the panel as a whole 
will start defolding until the desired end situation is obtained. 
Another way of driving the package from the folded first state into the 
unfolded second state is illustrated in FIG. 6b. In this figure the same 
components 70, 71, 72, 72a, 72b, 72c, . . . , and 74a, 74b, . . . , are 
illustrated. In this figure there is a further tension rod extending 
across panel 72a. The end of this torsion rod 74a positioned on the hinge 
line between panels 72a and 72b is attached as described above. The other 
end is attached to the shaft of a drive motor 78. The house of said drive 
motor 73 is attached to the panel 72a. By rotating the shaft of the drive 
motor 78 a rotational force will act on the attached end of the torsional 
shaft, which rotational force will be transmitted to the other end with 
the result that the panels 72a and 72b will start folding or defolding 
(dependent on the rotational direction of the drive motor 78). It will be 
clear that, because of the influence of the further torsion elements, the 
whole panel assembly will start folding or defolding. 
In all the above illustrated and discussed embodiments it was assumed that 
the torsion element consists of a tube, wire or rod of a resilient and 
torsionstiff material. However, instead of such a rod also a combination 
of stiff and non-resilient rods, interconnected by means of homokinetic 
couplings can be used. Such a combination is schematically illustrated in 
FIG. 7. Therein three stiff and unbendable rods 80, 82, and 84 are 
illustrated interconnected by two homokinetic couplings 86 and 88. As such 
the homokinetic coupling is considered as generally known and no further 
details thereof will be provided. A combination as illustrated in FIG. 7 
will fulfill the same function as a flexible and torsionally stiff tension 
rod, tube or wire as assumed in the previous figures.