Sunshield device

A signal generator equipped with a shading device and two light sensors is arranged on the upper side of a slat equipped with retro-reflective prisms and rotatable about a longitudinal axis. Depending upon the sun's position relative to the slat, the light sensors are variously shaded or illuminated by means of the shading device, and when the slat is rotated about its longitudinal axis, the light sensors supply electrical code values which change in opposing directions. A difference between the code values is fed via an amplifier to a servo-motor which rotates the slat about its longitudinal axis until the plane of incidence of the sun's rays, which passes through the longitudinal axis, is at right angles to the upper side of the slat. This ensures that sun's rays which hit the slat are reflected regardless of the sun's position, the time of year, and the alignment of the facade plane in which the slat is arranged.

BACKGROUND OF THE INVENTION 
The invention relates to a sunshield device for a window opening in a 
facade plane. 
A sunshield device of this kind, which is known from U.S. Pat. No. 
4,517,960, incorporated herein by reference, has a relatively small 
blocking zone. Compared with the previously known, retro-reflective 
sunshield devices, it allows a large amount of Zenith light to enter the 
room behind it, and nevertheless requires only slight adjustment during 
the course of the day and the seasons. 
SUMMARY OF THE INVENTION 
An object of this invention is to alternate this adjustment using simple 
means. 
According to the invention, basically a signal generator is provided 
comprising a shading device and two light sensors arranged on at least one 
slat within a facade plane in such manner that when the slat is rotated 
about its longitudinal axis, the electrical code values of the light 
sensors change in opposing directions. The slat is adjusted by means of a 
servo-motor controlled via an amplifier device in dependence upon the 
difference between the values of a parameter of the two light sensors. 
Here, photo-cells, light-sensitive resistors, photo-transistors, or the 
like can be used as light sensors. Preferably the sensors, together with 
additional resistors, form a bridge circuit whose output is connected to 
the input of the amplifier device. This bridge circuit--and likewise the 
amplifier device and the servo-motor--can be fed by additional photo-cells 
on the slat. 
It is within the scope of the invention that all the slats which are 
arranged in the same facade plane of a building, whose longitudinal axes 
extend parallel to one another, and should be driven by means of 
servo-motors in dependence upon one single signal generator on one of 
these slats. Since these slats are all exposed to the same sun radiation, 
they are also all subject to the same optimum adjustment position. One 
single servo-motor can be provided for all the slats arranged in the same 
window opening, and can be coupled to all the slats, for example, via a 
chain drive. 
The invention obviously easily permits slats of this kind in 
differently-orientated facade planes of a building to be adjusted 
separately from one another in optimum fashion in accordance with the path 
of the sun. Here it is advantageous to arrange a switch-over device 
between the amplifier device, which controls the servo-motors of all the 
slats in a facade plane, and the signal generator assigned to this facade 
plane. In this way it is possible to interrupt the control circuit, and by 
imposing an arbitrarily variable control voltage, to adjust all the slats 
of this facade plane to a specified angle of inclination. The sunshield 
device can then also be adjusted to be such that the sun's rays fully 
enter the room behind the window opening, and thus--for example during 
winter--can also be used to heat the building. 
The shading device preferably comprises a partition wall which extends 
between its top panel and the upper side of the slat and which extends 
between the two light sensors. This serves to increase the sensitivity of 
the signal generator, i.e. the level of the oppositely-directed change in 
the electrical values relative to a specific change in the angle of 
inclination of the slat. Extremely favorable conditions are achieved if 
the partition wall is arranged at right angles to the upper side of the 
slat and to the top panel, and if the shading device is designed to be 
symmetrical with the partition wall. 
The highest level of sensitivity is achieved if the partition wall is 
arranged parallel to the longitudinal axis of the slat and the center 
points of the light sensors are arranged, at an equal distance from the 
partition wall, on a transverse line which is at right angles to the 
longitudinal axis. In this way, the top panel can be flat and can extend 
at a constant distance parallel to the upper side of the slat. However, an 
arrangement of this kind results in the optimum level of sensitivity only 
when the longitudinal axes of the slats extend in the north-south 
direction, i.e. at right angles to the plane of the sun's path. 
In order to always achieve the maximum level of sensitivity regardless of 
the particular alignment of a facade plane to the sun's path, in 
accordance with a further development of the invention, the top panel is 
curved and the transverse edges of the top panel can be brought down to 
the upper side of the slat.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The sunshield device illustrated in FIG. 1 and 2, and which is known per 
se, consists of a plurality of slats 1 arranged in a window opening F so 
as to be rotatable about a longitudinal axis 10. Each slat consists of 
refractive material, for example synthetic material, and has the 
cross-section shown in FIG. 2. It has a flat upper side 11 which faces 
towards the sun's rays S (see FIG. 1). On the underneath side, prisms 100 
are juxtaposed without gaps, which extend parallel to the longitudinal 
axis 10 and are delimited by catheti 120 and the upper side 11 as the 
hypotenuse. Transversely to the longitudinal axis 10, the individual 
prisms have the cross-section of an isosceles triangle, where the inner 
angle .alpha. between the catheti is selected to be such that the sun's 
rays which hit the upper side 11 are re-reflected outwardly--under 
conditions which are yet to be described--and thus cannot enter the room 
behind the window opening F. One of the conditions of this 
"retro-reflection", which is based on the principle of total reflection, 
is that the inner angle .alpha. should be equal to 
90.degree..+-.3.degree., depending upon the material. 
FIG. 3 is the reflection diagram of a slat corresponding to FIG. 1 and 2 
with an inner angle .alpha. of 90.degree.. The radial direction plots the 
angles of "azimuth planes" which extend at right angles to the upper side 
11 of the slat. The azimuth angles X of these planes are calculated from 
the reference line B which extends at right angles to the longitudinal 
axis 10 of the slat. 
The height angles .psi. of 0.degree. to 90.degree. are plotted in 
concentric circles. In the reflection diagram, the blocking zone of the 
slat has been shown shaded and delimited by boundary curves K1 and K2. 
Thus, an azimuth angle X and a height angle .psi. are assigned to each 
point located in the blocking zone. All the beams which hit the upper side 
11 of a slat and whose parameters X and .psi. lie within the blocking zone 
are totally reflected. All those light beams which hit the upper side with 
parameter combinations which lie outside of the blocking zone are allowed 
to pass into the interior of the room. The width of the blocking zone 
decreases in accordance with an increasing deviation of the inner angle 
.alpha. from 90.degree.. 
FIG. 4 is a sun's position diagram represented in the same form as FIG. 3. 
Here the path curves of the sun have been plotted for different days of 
the year. Each path curve results in the associated height angle X for 
each azimuth angle .psi.. 
FIG. 4 also represents, in dash-dot form, the blocking zone of a slat in a 
vertical facade plane which is orientated precisely to the south so that 
the largest possible section of the path curve of the 21st of June falls 
into the blocking zone. For this purpose, the slat is rotated in such 
manner that its reference line B points exactly to the south. A parallel 
displacement towards the south was also necessary, and was achieved by 
rotating the slat about its longitudinal axis by the angle of inclination 
.beta. from the horizontal plane, which also involves some change in the 
boundary curves K1, K2 of the blocking zone. 
It can be seen from FIG. 4 that, in the case of the sunshield device as 
shown in FIG. 1, during the day practically no adjustment is necessary 
since the path curve lies outside of the blocking zone only during the 
early morning hours and in the late evening hours. However, during the 
year a parallel displacement of the blocking zone, and thus a change of 
the angle of inclination .beta. of the slats, is necessary. 
In order to alternate this adjustment with respect to changing the angle of 
inclination .beta., the slats 1 in FIG. 1 are adjustable by a servo-motor 
(not shown), or a plurality of servo-motors assigned to each slat. The 
servo-motor or servo-motors are controlled by an amplifier (likewise not 
shown) which, at its input, receives a different signal from a signal 
generator (2, 31, 32) on the upper side 11 of one of the slats 1. 
The construction of this signal generator is shown in detail in FIGS. 5 to 
7. It is designed to be symmetrical to a plane which is at right angles to 
the upper side 11 of the slat 1 and extends in parallel to the 
longitudinal axis thereof, which it preferably passes through. The signal 
generator fundamentally consists of a shading device 2 having a top panel 
21 which is delimited by longitudinal edges 211 and transverse edges 212, 
and of a partition wall 20 which is at right angles to the top panel and 
which divides the shading device 2 into two identical halves. The top 
panel 21 is curved, preferably in semi-circular fashion, so that its 
transverse edges 212 rest on the upper side 11 of the slat 1 (see FIG. 7). 
In FIG. 5 the top panel 21 has been shown projected at right angles to the 
upper side 11. Thus, the longitudinal and transverse edges 211 and 212 
respectively simultaneously define a rectangular shading zone of the 
shading device on the upper side 11 given light projected from above the 
top panel. 
Two light sensors 31, 32, for example in the form of light-sensitive 
resistors having circular sensor surfaces 300, are arranged on both sides 
of the partition wall 20 in such manner that the center points M of the 
sensor surfaces are located at an equal distance from the partition wall 
20 on a transverse line Q which extends at right angles to the 
longitudinal axis 10. The spacing of these center points M is now selected 
to be such that equal-sized sub-surfaces 310, 320 of the two light sensors 
are located in the shading zone of the shading device 2. 
If it is assumed that the sun's rays S which hit the upper side 11 always 
lie in a reference plane at right angles to the upper side 11 and which 
extends in parallel to the longitudinal axis 10, then the unshaded 
sub-surfaces of the two light sensors receive virtually equal amounts of 
energy and will therefore exhibit the same electrical code values. Thus, 
they will either have the same resistance or will supply the same 
photo-voltage. If, however, the sun's rays travel out of this reference 
plane, then one of the sensors will receive more light than the other, so 
that their electrical values will change in opposing directions, where the 
sign of the change is dependent upon the direction in which the sun moves 
out of the reference plane. This information is now analyzed by difference 
formation--in the case of photo-resistors, by means of a bridge 
circuit--in order to form a control value which is fed to the amplifier 
device in order to control the servo-motor. The servo-motor then changes 
the angle of inclination .beta. of the slat until the two light sensors 
again have the same electrical code values, and therefore the amplifier no 
longer receives a resultant control value. 
The invention is based on the fact that, regardless of the orientation of 
the facade plane, the angle of inclination .beta. of a slat can always be 
adjusted to be such that the sun's rays lie in the reference plane. Here 
attention is drawn to FIG. 8 in which a facade plane E with an azimuth 
angle .gamma., measured from the south direction, is plotted in a 
coordinate system x, y, z whose x-axis is orientated to the south. Also 
shown is a slat 1 with its longitudinal axis 10 in the facade plane E and 
its angle of inclination .beta. to the horizontal plane, and a sun's ray S 
with an azimuth angle X and a height angle .psi.. In order that the sun's 
ray S should lie in the reference plane which passes through the 
longitudinal axis 10 and is at right angles to the upper side 11 of the 
slat 1, the angle of inclination .beta. must be calculated from the 
equation 
##EQU1## 
where X and .psi. are the azimuth angle and height angle respectively of 
the sun's ray S and .gamma. is the azimuth angle of the facade plane E. 
As the explanation of the embodiment with reference to FIGS. 5 through 7 
has shown, with the invention the light components incident upon the two 
light sensors are dependent on the angle of inclination of the light rays 
relative to the upper side 11. The shading device 2 thus acts in practice 
as an angle-dependent "light divider". 
In the exemplary embodiments set forth, the light division is essentially 
based on a shading. In accordance with a further embodiment of the 
invention, however, an active light divider can also be employed, this 
active light divider steering the different light components onto the two 
light sensors dependent on the angle of inclination of the light rays 
relative to the upper side 11. Such an exemplary embodiment shall be set 
forth in greater detail with reference to FIGS. 9 through 11. 
A deflection means in the form of a hemisphere 2.1 of light-refractive 
material, especially of "plastic glass", serves as a light divider in the 
embodiment explained by FIGS. 9-11. This hemisphere has a circular base 
area G comprising the radius r around the center M' of the sphere. A 
center plane ME proceeds through the center M' of the sphere. A center 
plane ME proceeds through the center M' of the sphere at right angles to 
this base area G. A barrier slot 20.1 proceeds at both sides of the center 
plane ME and parallel thereto. This barrier slot 20.1 extends over at 
least 50% of the radius r from the outside surface in the direction toward 
the center M' of the sphere. This parting gap can be additionally filled 
with a light-impermeable material. 
The hemisphere 2.1 is applied to the upper side 11 of the vane or lamella 1 
such that the base area G proceeds parallel to the upper side 11 and the 
center plane ME proceeds at right angles to the upper side 11 and through 
the longitudinal axis 10. 
Two photodiodes 31.1 and 32.1 are arranged equidistant from the center 
plane ME as light sensors. They are arranged such that their centers lie 
on a transverse line Q which proceeds at a right angle to the longitudinal 
axis 10 and through the center M' of the sphere. The light-sensitive 
surfaces of the photodiodes lie against the base area G of the hemisphere 
2.1. In particular, the photodiodes are arranged in corresponding recesses 
in a cylinder section 2.11 which adjoins the base area G of the 
hemisphere. 
Due to the symmetry of the arrangement relative to the center plane ME and 
relative to the transverse line Q (FIG. 9), the two photodiodes receive 
identical light components as long as the light rays proceed parallel to 
the center plane (FIG. 10). The two photodiodes therefore supply 
practically identical signals. 
This symmetry, however, is disturbed as soon as the light rays describe a 
small angle with the center plane ME, as shown in FIG. 11. Here, the 
photodiodes receive different light components and accordingly supply 
different output signals which are used for the re-adjustment of the slats 
1 in the same way as set forth with reference to the exemplary embodiment 
of FIGS. 5 through 7. 
Although various minor changes and modifications might be suggested by 
those skilled in the art, it will be understood that we wish to include 
within the claims of the patent warranted hereon all such changes and 
modifications as reasonably come within our contribution to the art.