GB2510815A

GB2510815A - Wide-angle light sensing device

Info

Publication number: GB2510815A
Application number: GB1302314.8A
Authority: GB
Inventors: Daniele Tommei
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-02-10
Filing date: 2013-02-10
Publication date: 2014-08-20
Also published as: GB201302314D0

Abstract

An alignment system for a heliostat to ensure light from the main mirror 3 is directed to the target includes a sensing mirror 8 and an optical receiver 6 positioned to receive light reflected from the sensing mirror. The sensing mirror includes an inner surface (8a fig 1a) within an outer convex surface (8b fig 1a), the inner surface being less convex than the outer surface. The inner surface may be convex, planar or concave and preferably is continuous with the outer surface. The main mirror may be parallel to the inner surface or the sensing mirror itself may be the main mirror. The detecting means is preferably attached to the stationary structure of the heliostat and positioned along a line intersecting the heliostat target and the inner surface of the sensing mirror.

Description

WIDE-ANGLE LIG FIT SENSING DEVICE

10001] The present invention pertains to au optical-based alignment system for a heliostat according to the preamble of claim 1.

FIELD OF THE INVENTION AND PRIOR ART

10002] As is known, a heliostat is a device used to Ibilow the Sun's route during the span of the day, usually to orient the light thereof towards a precise target thanks to the help of one or more minors (the Main Mirrors).

10003] The simultaneous usc of several heliostats pointing at We sane target is indispensable to obtain the necessary temperature for devices that convert heat into electricity by means of t.hermodynamc processes. The cost of ma.kmg one heliostat is a. significant part of the totaL cost of a thermodynamic solar plant and it is therefore fundamental to be able to make a heliostat at low costs, 100041 Other applications ofheliostats include lightredirection br domestie as well as industrial uses, in which the heliostat redirects sunlight towards an object or room to illuminate, brightcn and warm -up.

10005] Hehostats with optical-based control systems use an optical device to determine what rotation of the Main Mirror is necessary in order to reflect sunlight from the Main Mirror towards a target. To reflect the sunlight towards a target the two aspects that must be taken into consideration are the angular position of the Sun (azimuth and elevation). a.nd the current angular posthon of the Main Mirror of the heLiostat.

10006] Many optical control systems fbr hel.iostats detect th.e angle of th.e sunlight reflected from the Main Minor or a second sensing mirror parallel to the Main Minor --in order to determine which rotation the Main Mirror must effect. These solutions can he highly accurate because the sunlight reflected towards the target is also used to obtain, the correct alignment.

10007] Tn these optical control systems, however, there are situations in which the reflected sunlight mary not reach the optical receiver, such as at sunrise, when the Main Mirror is rotated towards the last position of the Sun at sunset, or during a cloudy day, when the Sun is only visible in a discontinuous manner. For these reasons, supporting systems are added fir -these optical control systems to perform a pre-al.ignment in which. the Main Mirror is moved to a position that allows the reflected sunlight to strike the optical receiver.

100081 For example, in patent JP2004333003 the prc-alignmcnt occurs in two stops: firstly, a mechamcai gear connected to the Main. Mlirror rotates an auxiliary sensor around a first axis towards the direction of the Sun; secondly, the Main Minor rotates around a. second axis until the reflected sunlight strikes the optical receiver. Once the pre-aligninent has occurred, the optical receiver takes control and performs the line---tuning of the alignment.

10009] Patcnt CN1O 1236287 uses a pre-alignment process to direct the reflected sunlight towards the optical receiver. Specifically, the pre-al.ignm.ent occurs by means of -m auxihary optical receiver of less accuracy and greater angular aperture than the main optical receiver.

10010] The present invention pertains to an optical alignment device that does away with the necessity tbr a pre-alignment device or process to help in finding the position of the Sun in the sky.

OOiij In patent W00066947 the USC ofa convex mirror obviates the necessity for a pre-alignment process. i-lowever. this solution is limjtcd by the cxc[ustve use of a. convex mlrror as the Main Minor of the heliostat.

OOi2] The present invention pertains to an optical alignment device that eliminates the need for a supporting pre-alignment device or process, and is not limited to the use of a convex mirror as the Main Mirror of the heliostat, because it provides an accurate and immediate aFignrnent of the reflected sunlight towards the target.

SUMMARY ATD OBJECTS OF THE INVENTION

Thc invention provides an optical alignment system for a heliostat in accordance with independent claim 1. Further preferable features of the nvcnton arc provided in the dependent claims.

The present invention pertains to an optical aliginnent system for a hehostat that allows for the construction of a low-cost heliostat of great accuracy. In order to obtain such construction features, the rotation. of the Main Mirror of the heliostat is eontrofled by an optical alignment system based on sunlight. Other advantages, features and modes of use of the present invention will be evident from the following detailed description of some embodiments, shown by way of example arid not for limitative purposes.

According to an example embodiment, an alignment system for a heliostat includes: a sensing mirror; an optiea receiver; and is characterized in that: the. sensing, mirror is designed to have a first inner zone withi.n a second outer convex surfhce, th.e first inner zone is less convex than the surrounding second convex surface, the optical receiver is positioned in order to receive the sunlight reflected from the sensing mirror.

So. in on.e aspect of th.e present invention, an alignment system for a heliostat comprising a sensing mirror and an optical receiver, is characterized in that: the first inner zone of the sensing minor is less convex than the outer zone, and is preferably planar or less preferabl.y concave; the first inner zone is. preferably contiguous with the second outer convex surface; in another aspect oithe invention the curvatures oI'the first inner zone and the second. outer convex surface arc monotonjeally continuous; the second outer convex zone is preferably spherical in profile (i.e. of constant curvature); in another aspect of the invention the area of the first inner zone may be small compared to the area of the outer convex surface, or very small including the limiting case where the first inner zone effectively becomes a pont; the first inner zone is preferably parallel to the Main Mirror of the heliostat; th.e optical receiver is preferably solidly connected to the stationary structure of the heliostat and preferably positioned along the line that connects the centre of the first inner zone of the sensing mirror to the target of the heliostat, or less preferably' in. case the first inner zon.e is pariar, positioned along the line that connects any point on the planar first inner zone to the target of the heliostat; when the Main Mirror is required to be small (e.g. less than about 10-30cm across) it can he convenient to constnict the Main Mirror in the fbrm described herein fbr the sensing rmrror.

and then use the Main Mirror itself as the sensing mirror too i.e. reflecting sunlight both towards the target, as well as to the optical receiver used to control the steering of the Main Mirror, and so; in another aspect oft!ic invention the sensing mirror is also the Main Mirror of the heliostat, i.e. the sensing mirror serves to also direct sunlight towards the target as well as to the optical receiver, in which ease the receiver optical device is preferably located between the Main Mirror and the target, so that the optical recei\er can always detect the perimeter of the outer convex surfitce olthe Main Mirror (which now also being the sensing mirror, is constructed of a shape as described for the sensing mirror) at any angle of the Main Mirror; all axes of rotation of the sensing mirror are rositioned near the first inner zone so that the central axis of the optical receiver always intersects the first inner zone at any ang]e oFthe sensing: mirror; in the limiting case in which the first inner zone is approximated by a point, all axes of rotation of the sensing mirror intersect at that point; the receiver optical device is an image capture device; the receiver optical device is at minimum a three-sector photosensor array; In the present lnvention a method of automatically steering a heliostat comprises: reflecting light from the sun off a sensing mirror designed to have a first inner zone within a second outer convex surface, where the first inner zone is less convex than the surrounding second convex surface; receiving said reflected light with an optical receiver that is positioned in order to receive the sunlight reflected from the sensing minor; using control signals generated by the optical receiver to control a feedback loop connected to actuators used to steer the heliostat such that the light reflected from its Main Mirror is directed towards a target.

A methodof automatically steering aheliostat, using any of the devices described herein as the present invention to produce control signals generated by the optical receiver to control a feedback loop connected to actuators used to steer the heliostat such that the light reflected from its Main Minor is directed towards a target.

DETAi1ED DESCRIPTION OF THE PREFER. .RED EMBODIMENT 0013l Fig Ia and lb show in detail the parts comprising the sensing mirror according to the present invention; Fig Ic and leshow the resu]ts obtained with. a planar mirror as sensing mirror for two different angles, and Fig Id and If show the results obtained with a sensing mirror according to the present invention for the same two different angles.

0014l Fig 2 shows the f oni-lateral-top pens eetive of a heliostat and the optical alignment system according to the present invention.

00i51 Fig 3 shows the rear-lateral-top perspective ofa hehostat and the optical alignment system according to the present invention, [0016] By referring to Fig 2 and 3 a heliostat with an optical alignment system according to the present invention is designated as a whole with the reference number 100.

100171 The optical alignment system of the heliostat uses a microcomputer that, by means of thc integration of the information coming from all sensors connected to it, drives the movement of two linear actuators. This movement, in turn, enables the Main Mirror of the heliostat to maintain an angle that will always allow the sunlight reflected from it to reach, in a precise and stable manner, a predetermined target that is fixed in position relative to the ground. More specifically, since the Main Mirror will need to be rotated about at least two non-parallel axes, the optical alignment system determines the angles about each axis.

100181 The support mechanism of the heliostat is comprised of a rotating shaft 2 that rotates with respect to a support post around a main axis of rotation a (a-axis) and a secondary axis of rotation (b-axis) that is preferably perpendicular to the main axis of rotation a by means of a two-axis joint.

100191 A small sensing mirror is mounted on the upper extremity of rotating shaft 2 that is integrally and solidly connected to Main Mirror 3. Tn this way, the sensing mirror and the Main Mirror will always rotate around the same axes and with the same angles with respect to the supporting post.

10020] As shown in Fig la and lb. the sensing minorS has a central planar zone Sa that is surrounded by a convex surface Sb. The convex surface will reflect sunlight towards the optical receiver when the angle of the planar zone doesn't allow the sunlight reflected from the planar zone to reach the optical receiver.

10021] The thawing in Fig ft shows a planar sensing minorS that correctly reflects sunlight towards an optical receiver 6. Similarly, the thawing in Fig id shows a sensing mirror 8 according to the invention that correctly reflects sunlight, by means of its planar zone, towards an optical receiver 6. Both drawings in Fig Ic and Id depict a moment in time in which the optical alignment system of the heliostat correctly positions the Main Mirror to send its reflected sunlight towards the target. Thus, optical receiver 6 will detect the movement of the Sun and the angular position of the heliostat may be accordingly corrected.

100221 The drawing in Fig le shows a planar sensing mirrorS that does not reflect sunlight towards an optical receiver 6. By contrast, the drawing in Fig if shows a sensing mirror 8 according to the invention that correctly reflects sunlight, by means of its convex surface, towards an optical receiver 6. Both drawings in Fig le and If depict a misalignment due to.

for example, the Sun reappearing from behind some clouds. In fact, the Sun keeps moving behind the clouds but the heliostat, incapable of detecting this movement, will find itself in a position of misalignment when the Sun will reappear. In Fig le optical receiver 6 is unable to detect the Sun and cannot rotate the sensing mirror in order to send the reflected sunlight towards optical receiver 6. By contrast, in Fig if optical receiver 6 can detect the Sun thanks to the convex surface of the sensing mirror that reflects part of the sunlight towards optical receiver 6, which can now guide the heliostat to the position in which the reflected sunlight received will be reflected from the planar zone of the sensing mirror.

100231 Thanks to convex surfaces reflecting sunlight in a radial mode, unlike planar surfaces that always reflect it in a parallel mode, the sensing mirror according to the invention has the characteristic that it will always reflect part of the sunlight towards the optical receiver and it will do so at every angle of the sensing mirror and/or the Sun.

10024] Furthermore, since the convex surface surrounds the central planar zone, the position of the Sun as a reflection on the convex surfItce will indicate in which direction the sensing mirror must be rotated in order for the optical receiver to receive the reflected sunlight from the planar zone.

100251 The two axes of rotation a and 1 arc positioned near the planar zone of the sensing mIrror, and preferably Intersecting the centre of thjs planar zone, so that the central axis of the optical receiver can always intersect the planar zone of the sensing mirror at any angle of the sensing mirror.

[0026] The optical receiver is located along the line passing between the centre of the planar zone and the heliostat target, and its photosensitive part points towards the planar zone of the sensing muTor.

[0027] The optical receiver is preferably formed by a fourquadrant photosensor array located behind a crossed screen, which is able to measure the angle of incidence of the sunlight reflected from the sensing mirror. The optical receiver could also be less preferahiy formed by a three-sector, or five--or-more--sector photosensor array.

[0028] The microcomputer processes the signals generated from ftc optical receiver fbrming a negaUve tbedback loop, and guides the motors of the heliostat, which in turn move the Main Mirror and the sensing mirror until the sunlight reflected from the sensing mirror produces equa.i signals from each diametrically opposite pa.r of quadrants of the optica] leceiver, which is the condition where the Main Mm-or is directing sunlight towards the target, because the planar section of the sensing mirror is pan] Ic! to the Main Mirror, and the optical leceiver is directed along a line parallel to the direction between Main Mirror and target.

[0029] In Fig 3 the heliostat 100 comprises a. supporting post that comprises a fixed pedestal I a resting upon the ground, a. fixed shaft lb solidly and integrally connected to fixed pedestal la, a support flange Ic solidly and integrally connected-to fixed shaft Ib, a fixed pair of anns id solidly and integrally connected to support flange Ic, and a fixed ann pair Ic solidly and integrally connected to lixed ann pair Id.

100301 In Fig 3 receiver optical device 6 is solidly and integrally connected to fixed arm pair le and the. centie of its photosensitive part roints towards the centre of sensing mirror 8.

[0031] in Fie 2,3, a rotating shaft 2 rotates aroun.d a first axis of rotation a (aaxis) and a second axis of rotation i (b-axis) that intersects preferably perpendicularly to the axis of rotation a. by means of a iwo-axis joint 7. The two-axis joint 7 rotates with respect to fixed arm Id and. therefore, the supporting post, around the axis of rotation a.

[0032] Tn Fig 2, a sensing mirrorS is solidly and integrally connected to the top of rotating shaft 2. Th.e sensing mirrorS is positioned so that th.e two axes of rotation a and 1 intersect near the planar zone of sensing mirror 8, so that the central axis of the optical receiver always intersects the planar zone at any angle of the sensing mirror, [0033] in Fig 2,3 a Main Mm-or 3 is solidly and integ-rally connected to the bottom of rotating shaft 2.

100341 In Fig 3. two linear actuators S are connected bctwce.n the support flange Ic and a horizontal arm 4 1)3-means of spherical joints or suitable fl.exures Sa and 4a, respectively. A suitable ficxurc might combine bending in two orthogonal directions with rotation either through twisting or via a rotating oint. Hereinafter "spherical joint" is to be taken to mean "spherical-joint or suitable tiexure" as described above.

[0035] In Fig 2,3 horizontal aim 4 is solidly and integrally connected to rotating shaft 2.

10036] in. the presen.t cm.hodir.n.ent th. .ere is a. supportng post with a fro.n.t and a back, which supports the rest of the structure of the invention. The supporting post is in turn supported by civ IrauLcal extenial rnecn', licluding directly testing on the gioun1 supported off the ground oy nims of'eet, 01 s oidiry str etui s mcludirg towers o pylor s, a'l noin naly rigid. The supporting post may be implemented by means of a tubular structure that may be slmpiy rested upon the ground or anchored to the ground itdesjred, [0037] The so-implemented structure allows Main Mirror 3 to rotate with respect to the supporting post by mears of horizontal ann 4, in turn moved by means of linear actuators 5 around rotation axes a.

100381 The rotation of Main Mirror 3 around axes a and is controlled in an interderendent manner by linear actuators 5 which can be of electrical or hydraulic nature.

10039] Linear actuators 5 are able to receive control signals to move Main Mirror 3 to the correct orientation, 10040] Finally, the control of the orientation of the Main Mirror 3 with resect to the position of the supporting post, and thus of the ground, can he. implemented by means of the composite movement of the two linear actuators 5, which modifi the geometry of the quadrilateral defined by the two linear actuators 5. the horizontal arm 4 and the support flange ic, and of the two triangles defined by the horizontal ann 4. the support flange Ic, and each of the two Linear actuators 5, and are responsibLe tbr the driving of Main Minor 3.

[0041] While the invention has been described in reference to a preferred embodiment, it will be readily apparent to one otordnary skill in the art that certain modifications may he made to the system without departing from the same inventive core. The following could also be changed without changing the principle of orienting philosophy: 0042] the shape and size of sensing mirrorS; 10043] the connection between the sensing-mirror 8 and the rest of the structure; [0044] the number and position of the axes of rotation of sensing mirror 8; 100451 the mechanical means by which the movement of the sensing minorS is achieved; 100461 the type, size and number of photosensitive elements in the optical receiver 6; [0047] the position and orientation of the optical receiver 6.

Claims

C LA NI S1. An alignment system for a heliostat, comprising a sensing mirror and an optical receiver.eria.racterized in that.the sensing mirror is designed to have a first inner zone within a second outer convex surface, the first inner zone is less convex than the sunonding..second convex surface, the optical receiver is positioned in order to receive the light reflected from the sensing mirror.
2. A device as described in Claim 1 wherein the first inner zone is planar.
3, A device as described in Claim I wherein the first inner zone is concave.
4. A device as described in any ofthc preceding claims, wherein the first inner zone is contiguous with the second outer convex surface.
5. A device as described in any of the preceding daims wherein the curvatures ofthe first inner zone and the second outer convex surfitce are monotonically continuous.
6. A device as described in any of the preceding claims wherein the second outer convex zone is spherical in profile (i.e. of constant curvature).
7, A device as described in any of the preceding claims wheretn the area of the first inner zone is small compared to the area of the outer convex surface, or very small including the hniiting casc where the first inner zone effectively becomes a point.
8. A device as described in any of the preceding claims wherein the first inner zone is parallel to the Main Mirror of the heliostat.
9. A device as described in any of the preceding claims wherein the optical receiver is solidly connected to the stationary structure of the heliostat and positioned along the line that connects the centre of the first inner zone of the sensing mirror to the target of the heliostat.
10. A device as described in any of the preceding claims wherein the optical receiver is solidly connected to the stationary structure of the heliostat and positioned along a line that connects ally point on the planar first inner zone of the sensing mirror to the target of the heliostat.
Ii. A device as described in any of the preceding claims wherein the sensing mirror is the Main Mirror of the heliostat.
12. A device as described in any of the preceding claims wherein all axes of rotation of the sensing mirror arc positioned near the first inner zone so that the central axis of the optical receiver always intersects the first inner zone at any angle of the sensing mirror.B
13. A device as described in any of the preceding claims wherein in the limiting case in which thc first inner zone is approximated by a point, all axcs of rotation of the sensing mirror intersect at that point.
14. A device as described in any of the preceding claims wherein the receiver optical device is an image captum device.
15. A device as described in any of the preceding claims wherein the receiver optical device is at minimum a three-sector photosensor array.
16. A method of automatically steering a heliostat comprising: reflecting light from the sun off a sensing mirror designed to have a fkct inner zone within a second outer convex surface, where the first inner zone is less convex than the surrounding second convex surfisce; receiving said reflected light with an optical receiver that is positioned in order to receive the sunlight reflected from the sensing mirror; using control signals generated by the optical receiver to control a feedback loop connected to actuators used to steer the heliostat such that the light reflected from its Main Mirror is directed towards a target.
17. A method of automatically steering a heliostat using any of the devices described in Claims 1 to 15 to produce control signals generated by the optical receiver to control a feedback loop connected to actuators used to steer the heliostat such that the light reflected from its Main Mirror is directed towards a target.