Heliostat.

The present invention relates to a novel structure of heliostat.

It recalls that a heliostat is essentially a mirror whose orientation is permanently controlled for reflecting solar radiation toward a focal point always fixed (where there is placed a recovery boiler energy radiated) despite the variation of position of the sun throughout the day.

, ' The structures of heliostats are known are of several types.

Is connaitla altazimuth mounting conventional, capable of performing the orientation of a panel both in azimuth that in altitude by designing it with two perpendicular axes (horizontal axis disposed on a fork, it, mounted on an upright pivot).

This structure has the drawback of being particularly sensitive deflections caused especially by wind which exerts a horizontal thrust on the reflective surface (which is large). The radiation is therefore not always reflected in the correct direction; in particular a large deflection in altitude can be produced. In addition, the torsional stresses on the pins which serve to control the orientation are very important, primarily due to the wind pressure. It is duct sizing very largely the structure to withstand these forces. Finally, the movement of the axes to position 1' heliostat to be very accurate, it would have to be very advanced systems gear ratio to transmit a very high torque.

It is also known to use ball mounts which on the one hand it is difficult to obtain good accuracy because all mechanical forces are reported to the ball, and which on the other hand have the drawback of making more difficult the orientation by motors since there may be used a system to ring gears to transmit motion.. these mounts are often used for ^ · radar.

Finally, it-is known for forming an array of small mirrors on a turntable (for azimuth orientation), each mirror being orientable at altitude through a system of linkages. The drawback of this is that the reflecting surface of the mirrors is incorrectly used;

indeed, for certain positions of the sun, the mirrors distributed in rows will carry shadow upon each other.

To overcome the drawbacks of the known structures, the present invention provides a heliostat pyramidal structure, with a horizontal base pivoting rigid for orientation in azimuth and a tilt support relative to the base, the support having a variable length for the orientation at altitude a reflector panel fixed on one hand on the horizontal base and support obliqued.

This structure has the advantage of good mechanical rigidity to the efforts under which 1' heliostat it is to say the weight of the reflective panel resting on the pyramidal structure as well as the action of the wind on this surface. * therein.

Are removed the torsion stress by triangulating rigid reflective panel of the base, the reflective panel is bonded to the base by a hinge with a horizontal axis. _•

Stresses caused by wind acting on the oblique support which works in compression and not in bending and the rigidity of the structure, is therefore optimized.

Attaching the reflector panel to a slash variable length further allows the complete erasure of the panel under wind too strong.

A further advantage of the arrangement according to the invention is that it minimizes the amount of material used to form a heliostat of given size. Indeed, the support structure 1 'heliostat is limited to a base constituted by three welded tubes, ' a slash support and connecting parts at each end.

More specifically, the heliostat according to the invention comprises a tubular frame with triangular base, pivotally mounted about a substantially vertical axis and provided with an oblique support mounted at a point of the triangular base pivotally about a horizontal axis, means for pivotally attaching a reflector panel on the base, an attachment means sliding on the slash to secure the panel and thereby orient the altitude, and support means rolling chassis along a circular track for orientation in azimuth.

The reflective panel is made of a metal beams assemblagede, trellis for example.

Other features and advantages of the invention " will appear in the detailed description which follows and which is made with reference to the attached drawing which represents perspective the heliostat according to the invention.

Fig. on this, see the structure of the heliostat, consisting essentially in the form of a tetrahedron, whose summit height is adjustable to provide an inclination at altitude to the reflective surface and whose base may - __;

pivot about a vertical axis to provide a variable orientation in azimuth.

The reflecting surface of the heliostat is that of a mirror 20 includes either a panel - silver glass, either, if it is desired that the reflecting surface is not flat, by a mosaic of silver glass plates individually oriented to provide a reflective surface slightly convergent (spherical surface where parabolic).

The plates are mounted on. a frame of metal grid or three-dimensional grid, capable of supporting their weight. This frame is not shown in detail.

The tetrahedral structure supporting the mirror comprises a triangular base having three vertices, b and c are located substantially in a horizontal plane. The apex a is a fixed pivot while the vertices b and c are movable and mounted on bearings 22 and 24 which are ' guided along a-_ D.^{the R} a rail or a circular track 26 to allow HAS'azimuth orientation of the heliostat.

The fourth vertex'd, is movable along a slant support bar 28, to allow the orientation at altitude. This mobility is achieved by sliding, the mirror being secured at its top to a string (or cable) that moves along the bar 28 and which is driven by a motor located IBD bottom of that bar.

The panel 20 is further supported by two bearings a and b about which it can pivot when the apex d varies along the bar 28.

The structure of the heliostat is therefore the following:

three joined tubes 30, 32, 34 and forming a base, a pivot with a vertical axis and a horizontal axis has bearing, a bearing 22 and another bearing in b, for supporting the frame 20 of the reflective surface, a bearing 24 in c and lifting means of the top of the mirror along a tube 28. One of the bearings for example 24, is motor for driving the base around the circular track.

The heliostat means further comprises an auxiliary mirror 36, whose orientation is slightly offset from the primary mirror 20, so as to reflect solar radiation in a direction that is not exactly that of the boiler. The auxiliary mirror 36 is attached to the framework which supports the main mirror, such that its orientation is always representative of the orientation of the main mirror. Thus the light spot reflected by the auxiliary mirror can be used to drive the heliostat of into so the boiler.

The three tubes of the base 30, 32, 34 are square or circular and are soldered to connection (for example cast iron injected): a-frame, the workpiece comprises a clevis 40 (for a vertical pivot 42 fixed to the floor), and a bearing support of the mirror. In b, " an identical bearing 44 is provided, and is more visible; these two bearings allow for rotation of the reflective surface 20 of the heliostat for its orientation at altitude. A; rolling axle of the wheel 22 is also provided in the assembly part in b, and this is the case also of the part c which carries further articulation of the rod 28.

The running track 26 of the base of the heliostat is preferably of concrete and it includes an encoder 45 for tracking the azimuth orientation of the structure.

The utility of this. encoder occurs when it is desired to know the exact position of the heliostat in azimuth.

The encoder is for example optical, with a pitch of 4 cm if it is desired to know the position to near 0, 5 x 10 radians for HEU tube length 34 of about 8 meters. An optical reader 46 moves with one of the wheels (wheel 22 in b for example) to locate the position of the heliostat.

The encoder is in practice consisting of multiple tracks encoded, printed or painted along the raceway. Cettcett.e arrangement ' which allows an absolute code (and not relative or incremental position) is necessary if it is desired to avoid positioning errors due to counting errors.

The optical scanner is a set of photocells located at each track.

In c, a drive wheel 24 is. adapted to move the assembly by pitch, the pitch value is dependent on the positioning accuracy desired.

Always in c, is fixed the oblique support bar 28 which allows 1' attitude, at altitude. This bar 28 comprises a chain or endless cable that slides along the bar, with the wine storehouse néné .est (d) the fixed frame supporting the reflective surface 20.

In the same manner as for positioning in

•azimuth, positioning at altitude is made by not, of 3 mm if the height of the reflecting surface is of 6 meters,

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for the accuracy of 0, 5 x 10 radians.

The.' positioning motors in altitude and azimuth are asynchronous motors followed by appropriate reducing pourpour.qu'a not matches, several revolutions of the engine (e.g. 200).

An optical reader 47 mark the movement in elevation relative to an optical encoder 48 inscribed along the length dede.la bar 28; as the azimuth encoder 45" the encoder at altitude 48 is inscribed or printed on the bar 28 in the form of several parallel tracks for an absolute code..

Finally, it may be necessary to locate in c a counterweight (concrete) for the case where the mirror 20 is substantially vertical and where the wind comes from the rear of the mirror.

THE C?

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