GB2506846A

GB2506846A - Heliostat with optical control by means of a rotating sensing mirror

Info

Publication number: GB2506846A
Application number: GB1215892.9A
Authority: GB
Inventors: Daniele Tommei
Original assignee: Individual
Current assignee: Individual
Priority date: 2012-09-06
Filing date: 2012-09-06
Publication date: 2014-04-16
Also published as: GB201215892D0

Abstract

A heliostat 100 driven by a control system comprises a moveable main mirror 3 for directing sunlight at a target device, a moving means, such as linear actuators 5, 6, for moving the main mirror about an axis of rotation (b-axis), one or more rotating sensing mirrors (13a, 13b; fig.3), one or more photosensors 17, a photosensor direction-sensing controller, and an angular sensor (14, fig.3). The axis of rotation of the one or more sensing mirrors is parallel to the axis of rotation of the main mirror and positioned along a line connecting the axis of rotation of the main mirror to the target device. The axis of rotation of the one or more sensing mirrors may be coaxial with the axis of rotation of the main mirror. A heliostat with a support and drive mechanism may incorporate the above optical control system such that, in use, the azimuth angle and vertical inclination of the heliostat main mirror can be varied in order to track the movement of the Sun.

Description

HELIOSTAT WITH OPTICAL CONTROIL BY MEANS OF ROTATING MIRROR

0001] The present invention pertains to a heliostat support and drive mechanism controlled by-an optical-based system for target alignment according to the preamble of claim 1.

FIELI) OF HE INVENTION ANT) PRIOR ART

10002] As is known, a heliostat is a device used to follow the sun's route during-the span of the day, usually to orient ftc light thereof towards a precise target thanks to the help of one or more rmrrors.

10003] The simultaneous use of several heliostats pointing at the same target is indispensable to obtain the necessary temperature for devices that convert heat Into electricity by means of thermodynamic processes. However, when severa.i heliostats are pointed towards the same target the distance from the target needs to increase to ensure that the hetiostats don't cast shadows on each other. As a result, it is necessary for each heliostat to have a higher precision and meehanica.1 stability that will guarantee the correct illumination of the target in the presence of disturbances such as wind.

10004] Many heliostat so]utions have been patented that use two serarate gearboxes, one on each axis of a two-axis system to rotate their reflective member. This type-of solution has the disadvantage that it gathers all torque forces on the two gearhoxes, which need to be large enough to sustain these forces. Also, the high degree of accuracy needed for the proper functioning of a heliostat, results in expensive gearboxes, In US patent 2010/0024802 and German patent 102008053247. to reduce this problem a proposition is made that uses a rotating minor flame attached to a pedestal by means of linear actuators. However, to determine the movement of the linear actuators that will result in high targeting precision, this type of solution necessitates the use of expensive rotating or linear shaft encoders to trace the position of the mirror, as well as astronomical computations to reveal the position of the sun.

0005] An alternative method to obtain high targeting precision is the use of art optical sensor closed-loop system. Such systems work by detecting the position of the sun and that of the heliostat's mirror with respect to the target, and. by moving the mechanical actuators to the optimal position.

0006l However, an optical sensor closed-loop system works properly offly when the optical sensors are installed on the heliostat in a position where they are illuminated by sunlight at all times and are never shadowed by other parts of the heliostat In any combination of positions of the sun and the heliostat. Moreover, this optical sensor closed-loop system must he capable of detecting lEe angular error with respect to the direction olthe target. An ideal position that encompasses all of these requirements does not exist on the heliostats described by US patent 2010/0024802 and German patent 102008053247.

0007] The present. invention uses a novel optica] system to controL the two linear actuators and has the advantage over the mentioned patents that it can be installed on the top of the heliostat's support allowing for an economical closed-loop system.

BRIEF DESCRIPTION OF THE. DRAWINGS

10008] Fig I shows a. rear perspective of the support and drive mechanism of the heliostat according to the invention.

[0009] Fig 2 shows a rear perspective of the optical control system of the heliostat according to the invention.

10010] Fig 3 shows a top perspective olthe optical control system of the heliostat according to the iflvelltiOfl, 00ii] Fig 4 shows a side perspective of the optical control system of the heliostat according to the invention.

10012] Fig 5 shows a detailed perspective of the mirror shaft on the optical control system of the heliostat according to the invention.

SUMMARY AND OBJECTS OF THE INVENTION

100131 The present invention pertains to a heliostat support and drive mechanism controlled by a microcomputer connected to an optical based system that allows the construction of a low-cost heliostat of. great accuracy. In order to obtain such construction features, the orientation of the mirror support frame of the heliostat is achieved by an optical. alignment system based on sunlight. Other advantages, fbaures and modes of use ofthc present invention will he evident from the following detailed description of some embodiments, shown by way of example and not for limitative purposes.

According to art example embodiment, a heliostat support arid drive mechanism controlled by a microcomputer connected to an optical based system includes: a moveahic main mirror for directing sunlight at the target device; a moving means for moving that main mirror; one or more rotating sensing mirrors; one or more photosensors; a photosensor position controlling means; arid an. angular sensor: ciiara,cterised in that: the axis of rotation of the one or more sensing mirrors must be parallel to the axis of rotation of. the main mirror and positioned along the l.in.e thta.t connects the axis of rotation of th.e main mirror to the target; the one or more photosensors are maintained in a position, independently oldie vertica' inclination of the heliostat, along the line that connects the target to at least one intersection of the borders of the sensing mirrors with the axis of rotation of the sensing mirrors, said tnterseeton referred to as central sensing point; the height and position of the one or more sensing, mirrors must bc such that, during a 3600 rotation of said one or more sensing mirrors, at least oiie of the photosensors will receive the reflected sunlight from at least one of the sensing mirrors, independently of the inclination of the heliostat and the position of the sum during the rotation of the sensing mirrors, the angular sensor gives the value of the angular difkrence between one of the sensing niirmrs and the main mirror, Sc) that when the reflected sunlight hits one of the photosensors, the value of the angular difference at that moment will indicate the extent and orientation of the rotation needed to move the main mirror so that it will reflect sunlight so as to hit the target; the sunlight reflected from the central sensing point and detected by one of the photosensors, allows detection of the correct vertical inclination of the heliostat due to it being reflected only partially iion a mirror border with an intensity that changes a.s a function of the vertical inclination of the sensing mIrrors.

So in one aspect of the present invention, a heliostat driven by a control system, comprising a moveabie main mirror for directing sunlight at the target device, a moving means for moving that main mirror, and one or more rotating sensing mirrors, and one or more photosensors, and a photosensor sensingdireetion controlling means, and an angular sensor, is eharacterised in that: the axis of rotation of the one or more sensing mirrors is parallel to the axis of rotation of the main mm-or and positioned along a line connecting the axis of rotation of the main mirror to the target.

The axis of rotation of the one or more sensing mnors may preferentially be coaxial with one of the axes of rotation of the main mirror.

The position of one or more photosensors may preferentially be maintained, independently of the vertica] inclination of the heliostat, along the line that connects the target to at least one intersection of the borders of the sensing mirrors with the axis of rotation of the sensing mirrors, said intersection referred to as central sensing point.

The height and position of the one or more sensing mirrors may preferentially be arranged such that, during a 3600 rotation ot said one or more sensing mirrors, at least one of the photosensors wilD receive reflected sunlight irom at east one of the sensing mirrors, independently of the inclination of the heliostat and the position of the sun.

During the rotation of the sensing mirrors, the angular sensor may preferentially provide signals allowing, the determination of the value of the difference in angle of the normal to the surface of one of the sensing mirrors and the normal to the surface of the main mirror.

When the sunlight reflected by one of the sensing mirrors reaches one of the photosensors, the value ofthe difference hi angle of the nonnats to the mirror surfitces at that moment may preferentially indicate the extent and orientation of the rotation of the main mor required in order for the reflected sunlight from the main mirror to hit the target; Sunlight reflected from the central sensing point and detected by one of the photosensors.

may preferentially allow the detection of the correct vertical inclination of We heliostat required for the main mirror to reflect sunlight towards the target.

Detection of the correct vertical inclination of the heliostat may preferentially he achieved by sensing partial reflection with a reflection intensity that changes as a function of the vertical inclination of the sensing mirrors.

Partial reflection may preferentially be achieved by reflection from a region of minor bordering a region with a]owreflection unmirrored surface.

A heliostat driven by a control system according to the present invention, has a First Shaft capable of rotation around a mant axis of rotation with respect to a resting post, a Second Shaft capable of rotation around a secondary axis of rotation that is preferably perpendicular to the main axis of rotation, and a Third Shaft that is coaxial to the Second Shaft.

The Second Shaft preferentially extends above the Third Shah and the moveable main mirror of the heliostat, and is preferentially integrally and solidly connected at the top to a fixed support.

A revolving support is preferentially attached to the fixed support by ajoint so that said revolving support is able to revolve with respect to the secondary axis and is preferentially maintained in constant rotation by an electric motor.

A First sensing mirror a.nd a Second sensing mirror, the latter of shorter height than the former, are solidly arid integrally connected to the rcvolving support and the highest border of the longest sensing minor is preferentially aligned with the highest border of the shortest sensing mirror.

A First sensing mirror and a Second sensing mirror, the Ia tier of shorter height than the former, are solidly and interally connected to the revolving support and the lowest border of the longest sensing, minor is. pretérentially aligned with the lowest hc rcer of the shortest sensing minor.

One sensing mirror is solidly and integrally connected to the revolving support and one photoscnsor preferentially lies along the line connecting the highest or lowest border of the sensing mirror to the target, whie another photosensor Lies fhcing the sensing mirror The planes defined by the First and Second sensing mirrors preferentially both contain the secondary axis. th.e reflective surfaces of the sensing mirrors do not have the same angle, and the reflective surface of the First sensing mirror is preferentially opposite the reflective surface of the Second sensing mirror.

Preferentially a rotating arm is' attached to the fixe.d support by a joint so that said rotatin.g arm is able to rotate around a third axis that is preferentially parallel to the main axis of rotation, perpendicular to the secondary axis of rotation, and aligned with the lowest or highest border of the shortest sensing mirror.

Preferentially a rotating arm is attached to the fixed support by a joint so that said rotating is able to lorate around at urd a> is that is referential l pcal Eel to the mair axis jf rotation, preferentially peroendicular to the secondary axis of rotation, and preferentially aligned with the border of the sensing mirror that prefirrentially has -ci photosensor lying along the line connecting said border to the target.

The rotating arm is preferentially maintained at a constant inclination with respect to the ground, independently of the rotation of the Second Shaft around the main axis of rotation.

preFerentially by a counterweight solidly and integrally connected to said rotating arm.

The rotating arm may alternatively be maintained at a constant inclination, with respect to the ground, independently of the rotation of the Second Shaft around the main axis oirotation, by a servo-motor controlled by an accelerometer sensor attached to s-aid rotating arm.

The rotating arm may alternatively he maintained at a constant inclination with respect to the ground, independently of the rotation of the Second Shaft around the main axis of rotation, by a. mechanicaL system that connects said rotatlng ann. to the resting post.

One or more ph.otosensors are solid]y and integrally connected to the rotating arm. and are preFerentially oriented towards the axis cf rotation of one or more sensing mirrors as well as preferentially positioned to the front of one or more sensing mnTors.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIE.MENT

10014] By referring to Fig 1,2,3,4 and 5 a heliostat with a support and drive mechanism according to the present invention, is designated as a whole with the reference number 100, and an optical control system according to the present invention is designated as a whole with the reference number 101 - 100151 The optica] control system of the heiios.at uses a microcomputer that, by means of the integration of the information coming from all sensors connected to it, drives the movement of two linear actuators. This movement, in turn, enables the reflecting member (the Main Mirror) of the heliostat to maintain a-n 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 specificai]y, since die reflecting member w'il need to be rotated about at least two non-parallel axes, the optical control system determines the angles about each axis by means of two different processes.

[0016] The support mechanism ot' the heliostat is comprised ot'a First Shaft that rotates around a main axis of rotation a with respect to a resting post, a Second Shaft that rotates around a secondary axis ofrotation f that is preferably perpendicular to the main axis: of ot Jion a and Thu. Shal that s coaxurl to thc Sc cond Shaft 10017] A small minor-shaft constitutes the core element of the optical control system of the heliostat. This mirror-shaft is coaxial with the Third Shafl of the heliostat support structure and is mounted on the upper extremity of the Second Shaft, as well as being maintained in constant rotation relative to the Second Shaft by an electric motor, An angular reference signal is produced by a sensor (the Angle Sensor) whenever the mirror-shaft rotates through a specific absolute angle relative to the Second Shaft, 00i8j Two juxtaposed mirrors, with their non-reflecting sides touching, constitute the mjrrorshatt: the First Mirror extends the entire length of the shaft and is used for azimuth alignment, the Second Minor extends from the top of the rninorshaft to a point near the middle of the mirrorshaft and is used thr vertical alignment.

[0019] The process of azimuth alignment uses the minor extending the entire length of the mirror-shaft, he. the First Mirror.

10020] During the process of azimuth alignment the First Minor rotates continuously around the main rotating axis of the reflecting member of the heliostat to simulate all possible directional outcomes and verify all possible azimuth angles. During the rotation of the First Minor, two different signals are received: the first from a photosensor that is positioned-along the direction of the target, and detects the intensity of the sunlight reflected from the First Mirror; the se-.ond from the Angle Sensor which detects the moment of coincidence when the angular difference between the reflecting surFace of the reflecting member of the heliostat (i.e. the Main Mirror) and the reflecting surface of the First MirTor is zero (or some other well defined and fixed relative angle). The absolute angle at which the reflected sunlight detected by the photosensor reaches its maximum value during a 360° rotation of the First MilTor about the mirror-shaft axis, corresponds to the absolute angle that the Main Minor of the heliostat should have in order to correctly send the sunlight towards the target. By measuring the time passed between the reception of the Angle Sensor coincidence signal, and the photosensor maxitnurn signal, the microcomputer in the optical control system can determine the rotation, which when applied to the reflecting member of the heliostat (i.e. the Main Mirror) will position said reflecting member at the correct angular value that will allow optimal target illumination.

100211 Since the optical control system is mounted on the upper extremity of the heliostat, and its inclination with respect to the ground changes as a function of the inclination of the heliostat. the photosensor is mounted on a rotating ann, rotating about an-axis that is parallel to the main axis of rotation, perpendicular to the secondary axis of rotation, and aligned with the lowest or highest border of the Second Mirror. The purpose of'this rotating ann is to maintain the pfiotoscnsor always aligned along the line that connects the lower oordcr of the Second Mirror and the target. A variety of techniques can he used to maintain the angle of the rotatmg ann constant with respect to the ground. so as to compensate fbr variations jn inclination of the heliostat during its functioning. One technique uses a counterweight coimected rig:id]y to and placed below the rotating arm since the force of gravity is always perpendicu]ar with respect to the ground. Another technique uses an accelerometer/inclinometer mounted on the rotating arm that, by detecting the angle with respect to the ground, can regulate the inclination of the rotating arm by means ofa servomotor. Other techniques can use mechanical levers or cables to ilupiement the same rotation a.s the one on the horizontal axis at the base of the heliostat, the First Shaft that changes with the vertical inclination of the heliostat, thus maint-ThJng the nclination of the rotating arm constant with respect to the ground.

[0022] The process of vertical alignment uses the Second Minor.

1002.3] To obtain infbrmation on the vertical alignment, the optIcal control system uses the Second Mirror that is positioned on the rear of and rotated 180° with respect to the First Mirror of the mirrorshaft. The part of the mirrorshaft he]ow the Second Mirror is Trlade as non-ref-'lective as possible so as to maximally reduce its specular reflection, by for example, coating it with a low reflectivity material, such as matt-blaek paint, or by making it diffusely reflective, or both. Due to the difference in length of the two mirrors constituting the mirror-shall, during a 360° rotation the sunlight reflected from the First Mirror will always he detected by the photosensor. Instead, the sunlight reflected from the Second Mirror will only he detected by the photosensor when the angle between the sun, the Second Mirror and the photosensor wIll allow the ref iectiori to come fain the Second Mirror, generating, together with the refLection from the First Mirror, two signals for the photosensor to detect, that are 80° apart with respect to the rotation of the mirror-shaft. When the sunlight strikes the bottom half of the mirror-shaft, little or no signal will be generated due to the absence of a good reflective surface and the photosensor wilt detect only one signal per rotation, that due to reflection of sunlight from the First Mirror.

10024] The infomiation on the presence or absence of a second signal coming from the Second Mirror of the mirror-shaft, enables the microcomputer to distinguish where in the vertical plane the sunlight is coming from and correct the vertical inclination of the heliostat until the angle is reached at which the intensity of the signal from the Second Mirror is half that of the signal from the First Minor. This happens because the sunlight ret'lected from a region centred, on the lower border of the Second Mirror of the mirror-shaft comprises half' mirror suifacc and half the aforesaid low reflectivity surface (which in practice may have reflectivity of only a. few percent of that of' the runror surfltcc) and therefore has only half the total intensity of the signal coming from the First i\4irror, which instead reflects completely, and this difference in light level is detected by th.e photosen.sor, 10025] hi Fig 1, the heliostat support and drive mechanism 100 comprises a restiiig post I resting upon the ground and connected by aloirit to revolving shaft 8, the First Shaft, that is integrally and solidly connected to shaft 7, the Second Shaft, and is also preftrablv perpendicular to shaft 7. An additional revolving shall 2, the Third Shaft, is coaxial to shaft 7 and externally placed en shaft 7. Specifically, revolving shaft 2 can rotate around its own central and parallel axis 13, and around axis a, which is preferably rarallel to the ground and preferably perpendicular to axis 13. Revolving shaft 2 rotates around shaft 7 hut cannot shift along axis j3 on shaft 7. Unlike revolving shaft 2, shaft 7 and revolving shaft 8, that are integrally and soidiy cern ected to each. other, can rotate only around axis a that is preferably parallel to the ground and preferably perpendicular to axis 13- 10026] Revolving shaft 2 is integraliy and solidly connected to an arm 4. Ann 4 is not parallel to revolving shaft 2 and is preferentially substantially orthogonal to it, Together with arm 4, revolving shaft 2 constitutes the mirror support frame supporting reflecting member 3, the Main Mirror.

[0027] In Fig 2 & 4. the use of external revolving shaft 2 that can rotate about shaft 7, allows for the easy installation of optical control system 101 positioned in the upper extremity of the heliostat surport and drive mechanism 100, for the purpose of sun-tracking and re-directing the reflected sunlight towards a fixed target in an accurate and stable manner. The great advantage of having an optical control system installed above the mirror support frame of a heliostat is that it will always be exposed' the sun and never shadowed by other parts of the heliostat, independentLy of th.e conibination of positions that the sun and the heliostat may have.

[0028] In Fig 2,3 & 4 the optical control system 101 is composed of motor 9 that is.' intealiy and solidly connected to a support platform 18 that is in turn integrally and solidly connected to the upper extremity of' shaft 7. The axis of' rotation of motor 9 is parallel to and coaxial with the axis of rotation of revolving sha.ft 2.

B

100291 A flywheel 11 is integrally and solidly connected at its centre to the axis of rotation of motor 9. A small angular reference magnet 12 is integrally and solidly connected to flywheel 11 and positioned along the perimeter of flywheel 11.

10030] In Fig 2,3,4 & S a mirror-shaft 13, integrally and solidly connected to the centre of the upper side of flywheel 11 and parallel to and coaxial with the axis of rotation of flywheel 11, has two parallel mirrors 13a, the First Mirror, and 13b. the Second Mirror, that are parallel to and equidistant from the axis of rotation oirrirror-shart 13. Whilst the First Mirror, mirror 13a, spans the entire length of mirror-shaft 13, the Second Mirror, mirror 13b, snails only the upper half of mirror-shaft 13.

10031] A hall-effect proximity magnetic sensor 14, integrally and solidly connected to rotating shaft 2, is positioned adjacent to flywheel 41 in order to sense the passing of small angular reference magnet 12, connected to flywheel 11, every 360° of rotation of the flywheel relative to Shaft 2.

10032] In Fig 2 & 4 a rotating arm 15, to which a counterweight lóis solidly connected, rotates around an axis that passes near to the centre of mtrror shaft 13 and is parallet to the axis of rotation of revolving shaftS and is located on one side of mirror shaft 13, rotating within a bearing in a support structure connected solidly and integrally with support platform 18.

[0033] A photosensor 17, integrally and solidly connected to rotating am-i 15 along an axis that is perpendicular to rotating arm 15 and passes by the centre of mirror-shaft 13, thees the centre of mirror-shall 13, [0034] A microcomputer is used for the integration of the signals received by the sensors connected to it as well as the control of the motors.

100351 In order to establish the azimuth alignment necessary for reflecting member 3 to correctly reflect the light towards its target, motor 9 rotates mirror-shaft 13 arid flywheel 11 at a constant angular velocity. The small angular reference magnet 12 is positioned on flywheel 11 so as to produce an electrical signal from the Hall sensor 14 to the microcomputer each time mirror 13a on mirror-shaft 13 is parallel to reflecting member 3 that is integrally and sohcity connected to revolvIng shaft 2. In this way, the electric signak generated during the rotation of mirror-shaft 13 will indicate that the plane of mirror 13a on mirror shaft 13 and the plane of reflecting member 3 are parallel.

[0036] Photosensor 17, integrally and solidly connected to rotating arm 15, is placed along the line defined by the centre of mirror shaft 13 and the target. The goal of rotating: arm iSis to maintain photosensor 17 always positioned along this line. This is achieved by means of a counterweight 16 that maintains constant the vertical inclination of the rotating arm 15, independently of the vertical inclination of rotating shaft 2 to which rotating arm 15 and motor 9 are integrally and soldiv connected.

[0037] Photosensor 17, given its position, will indicate by means of an electric signal to the microcomputer, the exact tune at which the reFlection of the light coming from the centre oF mirror 13a on mntr shaft 13 is directed towards the target. If the two electrical signals coming: from the hail-effect proximity magnetic sensor 14 and photoscnsor 17 are simultaneous, then the microcomputer will not correct the azimuth angle ot reflecting member 3. On the contrary, if the two signals are not simultaneous, then the microcomputer will correct the azimuth angle of reflecting member 3 lw means of the two linear actuators S and 6.

In practice, the signals generated by the Hail-effect sensor and the photosensors will not be very narrow impulses, but instead will have finite rise and fall times ard even. suL)stanti*al width in practice the microcomputer will estimate the maxima of each of these signals and use the flu xima as the reference poInts tor the decson as to whether or not, dnd how, to move the main minor so as to track accurately the target.

0038] In order to establish the vertical alignment necessary for reflecting: member 3 to correctly reflect the sunlight towards its target, photosensor 17 transmits to the microcomputer the intensity value of the sunlight reflected from mirror 13a and 13b at each 3600 rotation of mirror shaft 13. However, when the vertical inclination of fixed shaft 7 needs to be reduced, photosensor 17 will not receive sunlight reflected from mirror 13b, which only extends along the upper half of mirror-shaft 13, hut instead the [hr weaker light reflected by the unmirrored portion of the mirror-shaft. On the contrary. the presence of a fil-va1ue.signal indicates that the inclination of fixed shaft 7 needs to be increased. When the intensity of the signal generated from the reflection of mirror 13b is around half that of the signal generated by the reflection of mirror 13a, then the sunlight is' being reflected from a region centred on the lower border of minor 13b and the vertical angle of fixed shaft 7 will not need to be changed.

[0039] In the present embodiment there is a resting post I with a front and a back, which supports the rest of the structure of the invention. The resting post 1 is in turn supported by any practical external means, inciuding directly resting on the ground, supported. off the ground by means of feet, or subsidiary structures including towers or pylons, all nominally rigid. The resting post 1 may be implemented by means ofa. tubular structure that may be simply rested upon the ground or anchored to the ground if desired.

[0040] The lower extremities of linear actuators S & 6 are connected to the rear of resting post I by means of spherical joints or suitable fiexures. A suitable flexure might combine bending in two orthogonal directions with rotation either through twisting or via a rotating joint. Hereinafter "spherical joint" is to he taken to mean "spherical-joint or suitable flexure" as described above.

[00411 the upper extremities of linear actuators 5, 6 are each connected to one of the extremities of aim 4 by means of spherical joints.

100421 The so-impLemented structure allows reflecting member 3 to rotate with respect to resting post 1 by means of arm 4, in turn moved by means of linear actuators 5,6, around rotation axes a, [0043] The rotation of reflecting member 3 around axes a, F is controlled in an intcrdependent manner by linear actuators 5,6, which can be of electrical or hydraulic nature.

[0044] Linear actuators 5,6. are ab]e to receive control signals to move reflecting member 3 to the correct orientation.

004Sl Finally, the control of the orientation of the mirror support frame with respect to the postori of rest!ng post 1, aria thus of the ground, can be irnpleniented by means of the composite movement of the two linear actuators 5,6, which modify the geomctnr of the quadrilateral defined by the two linear actuators 5.6, the mirror support frame and the resting post 1, and of the two triangles defined, by the mirror support frame, the resting post 1, and each of the two linear actuators 5,6 and are responsible for the driving of reflecting member 3 without afkcting the sturdiness of the heliostat support structure.

[0046] While the invention has been described in reference to a preferred embodiment, it will be readily' apparent to one ofordinarv 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 c i&'ecd \kl'hout changing Vie nimerole of onenung philosophy 0047j the insertion order of shafts 2 and 7: 10048] the position of shafts 2 and 7 next to each other instead of coaxiaHy; 10049] the shape and orientation of the arm 4 and the rotating shaft 2; O050] the connection between ann 4 and rotating shall 2; [0051] the number and dimension of the minors comprising the minorshaft; [0052] the number and orientation of the photosensors attached to rotating ann 15: 10053] the type of angukr sensor; [0054] the means of maintaining ilie rotating arm 15 a.t a constami inclination with respect to the ground.

[0055] it is not essential that the motor rotates the revolving platform continuously. Instead, the platform may be rotated through 360°, often enough that any significant ofThet of the Main Mirror from its desired direction (i.e. reflecting sunhght directly at the targeti can he corrected in a timely manner. Given that the Sun rotates roughly.360° in a 24hr time span (or equivalently at a rate of approximately 0.25° per minute). it is only necessary to correct the Main Mirror pointing direction when the error in pointing is significant compared to tfie accuracy of the whole system. So for example, if al° accuracy is required then a motor rotation and sensor scanning cycie carried out every 2 minuLes would ensure thaL the Sun's reflection had not sirayedby more than 1° off the target (the Sun's reflection moves at twice the angular rate of the Sun itself), However, in practice there are other sources of targeting disturbance, such as wind, arid the actual rate of performing a sensing cycle (by means of a complete rotation. of the motor), may be chosen to suit the required put-noses.

Claims

C LA NI S1. A hehosta.t driven by a control system, comprIsing a moveabie main mirror tor directing sunlighi at the target device, a moving means for moving that main minor, and one or more rotating sensing mirrors, and one or more photosensors, and a photosensor sensingdirection eontroi ing means, and an angular sensor, characterised in that the axis of rotation of the one or more sensing mirrors is parallel to the axis ofrotation of Lhe main mirror and positioned along a line connecting the axis of rotation of the main nurror to the tareet.
2. A hehosta.t and control system as described in (Ilaim 1, wherein the axis of rotation of the one or more sensing mirrors is coaxial with one of the axes of rotation of the main minor.
3. A heliostat and control 5)stem as desenbed in Claims i or 2, such that the position of one or more photosensors is maintained, independently of the vertical inclination of the heliostat, along the line that connects the target to at least one intersection of the borders of the sensing mirrors with the axis of rotation of the sensing mirrors, said intersection referred to a.s central sensing point.

*
4. A heliostat and control system as described in Claims U 2 or 3, such that the height and position of the one or inure sensing mirrors is such that, during a 360° rotation of said one or more sensing nurrors, at least one of the photosensors will receive reflected sunhghu from at least one of the sensing mirrors, independently of the inclination of the heliostat and the position of the sun.
5. A heliostat and control system as described in any of the previous Claims, such that during the rotation of the sensing mirrors, the angular sensor provides signals allowing the determination of the value of the difference in angle of the nonnal to the surface of one of the sensing mirrors and the normal to the surface of the main mirror.
6. heliostat and control system as described in Claim 5, arranged such that when the sunlight reflected by one of the sensing mirrors reaches one of the photosensors, the value of the difference in a1i4ic of the normals to the mirror surfaces at that moment will indicate the extent and orientation of the rotation of the main mirror required in order for the reflected sunlight from the main mirror Lo hit the target:
7. A heliostat and control system as described in any-of the previous Claims, arranged such that sunlight reflected from the central sensing point and detected by one of the photosensors, allows the detection of the correct vertical inclination of the heliostat required for the main mirror to reflect sunlight towards the target.
8. A heliostat and control system as described in Claim 7, wherein detection of the correct vertical nciina.t!on of the heliostat is achieved by sensing parha.l reflection with a reflection intensity that changes as a ftmction of the vertical inclination of the sensing mirrors.
9. A heliostat and control system as described in Claim 8, wherein partial reflection is achieved by reflectionfioni a region of mirror bordering a region with a lowrefleetion un mirrored surface.
10. A heliostat driven by a control system according to any of the prevIous Claims, wherein a First Shaft rotates around a main axis of rotation with respect to a resting post, a Second Shaft rotates around a secondary axis of rotation that is preferably perpendicular to the main axis of rotation, and a Third Shaft that is coaxial to the Second Shaft.
11. A heliostat driven by a control system according to any oithe previous Claims, -Thcrein the Second Shaf extend1⁄4 al o e the Ehird Shaft CULJ the mo c<ible main rnirwr ot the heliostat, and is integrally and solidly connected at the top to a fixed support.
12. A heliostat driven by a control system according to any of the previous Claims, wherein a revolving support is attached to the fixed support by a joint so that said revolving support is able to revolve with respect to the secondary axis and is maintained in constant rotation by an electric motor.

]3. A heliostat driven by a control system according to any of the previous Claims, wherein a First sensing mirror and a Second sensing mirror, the latter of shorter height than the former, are solidly and integrally connected to the revolving support arid the highest border of the longest sensing mirror is aligned with the highest border of the shortest sensing-mirror.

] 4.A heliostat driven by a-control system according to any of the previous Claims, wherein a First sensing mirror and a Second sensing mirror, the latter of shorter height than the former, are solidly and integrally connected to the revolving support and the lowest border of the longest sensing mirror is aligned with the lowest border of the shortest sensing mirror.5. A heliostat driven by a control system according to any of the previous Claims wherein one sensing mirror is solidly and integrally connected to the revolving support and one photose-nsor lies-along the line connecting the highest or lowest border of the sensing mirror to the target. while another photosensor lies facing the sensing mirror.16. A heliostat driven by-a control system according to any of the previous Claims, wherein the planes defined by the First ni-id Second sensing mirrors both contain the secondary axis, the-reflective surfaces of th ensing minors do not have the same angle, and the reflective surface of the First sensing mirror is opposite the reflective surface of the Second sensing mirror.17 A heliostat driven by a control system ac-cording to any of the previous Claims, wherein a rotating arm is attached to the fixed support by a joint so that said rotating arm is able to rotJe aiound a thud axis tnar s patadel to the nu.in axis ofrotation, pet nercicular r0 the secondary axis of rotation, and aligned with the lowest or highest border of the shortest sensing mIrror.18. A heliostat driven by a control system according to any of the previous Claims, wherein a rotating arm is attached to the fixed support by a joint so that said rotating arm is able to rotate around a third axis that is parallel to the main axis of rotation, perpendicular to the secondary axis of rotation, and aligned with the border of the sensing mirror that has a photosensor lying along the line connecting said border to the target.19. A heliostat driven by a control system according to any olthe previous Cairns, wherein the rotating arm is maintained at a constant inclination with respect to the ground, independenty o the rotation of the Second Shaft around the main axis of rotation, by a counterweight solidly and integrally connected to said. rotating arm.20. A hehosta.t driven by a controL system according tc any of the prevIous Claims, wherein the rotating arm is maintained at a constant inclination with respect to the ground.independently of the rotation of the Second Shaft around the main axis of rotation, by a servornotor controiled by an accelerometer sensor attached to said rotating arm.21. A heliostat driven by a. control system according to any of th.c prcvious Claims, wherein the rotating ann is! 1naintained at a con.stan.t inclination with respect to th.e ground.independently of the rotation of the Second Shaft around the. main axis' of rotation, by a mechanical system that connects said rotating arm to the resting post.22, A heliostat driven by a controL system according to any of the previous Claims, wherein one or more photosensors are soiidl.y and integrai].y connected to the rotating ann and are oriented towards the axis of rotation of one or more sensing mirrors as wefl as positioned to the front of one or more sensing mirrors.