GB2499655A

GB2499655A - Triangular structured heliostat support and drive mechanism

Info

Publication number: GB2499655A
Application number: GB1203286.8A
Authority: GB
Inventors: Daniele Tommei
Original assignee: Individual
Current assignee: Individual
Priority date: 2012-02-24
Filing date: 2012-02-24
Publication date: 2013-08-28
Also published as: GB201203286D0

Abstract

A heliostat 100 support and drive mechanism comprises a fixed pedestal 11, a shaft 12 attached to the pedestal by a joint 12a, such as a spherical joint or flexure, so that the shaft is able to rotate with three degrees of freedom, an arm 13 and a mirror frame solidly connected to the shaft, and three linear actuators 15, 16, 17. A first linear actuator 15 connects between one end of the arm and the pedestal in a position on the pedestal that is distant from the connection of the shaft to the pedestal. A second linear actuator 16 connects between the other end of the arm and the pedestal in a position on the pedestal that is distant from the connection of the shaft to the pedestal and is also distant from the connection of the first linear actuator to the pedestal. A third linear actuator 17 connects between the arm and the pedestal, in a position on the arm adjacent to the point of connection of the arm and the first linear actuator and in a position on the pedestal adjacent to the point of connection of the second linear actuator and the pedestal.

Description

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TRIANGULAR STRUCTURED SUPPORT AND DRIVE FOR HELIOSTAT

[0001] The present invention pertains to a triangular structured support and drive mechanism for a three-axis heliostat according to the preamble of claim 1.

FIELD OF THE INVENTION AND PRIOR ART

[0002] As is known, a heliostat is a device used to follow the sun's route during the span of the day, usually to re-orient the light thereof towards a precise target thanks to the help of one or several mirrors.

[0003] The simultaneous use of several heliostats pointing at the same target is indispensable to obtain the necessary temperatures for devices that convert heat into electricity by means of thermodynamic processes. However, when several heliostats are pointed towards the same target, the distance from the target needs to increase. Therefore, a higher number of heliostats re-orienting the light towards the same target require that each heliostat have a higher precision and mechanical stability that can guarantee the correct illumination of the target at a distance in the presence of disturbances such as wind.

[0004] Many heliostat solutions have been patented that use two axes each connected to a separate gearbox to rotate their reflective member. This solution has the disadvantage that it gathers all torque forces on the two gearboxes that need to be large enough to sustain them. Also, the high degree of accuracy needed in a heliostat results in expensive gearboxes. In US patent 2010/0024802 a proposition is made to reduce this problem by using two linear actuators that drive a mirror frame attached to a pedestal by means of a central joint. However, the use of two linear actuators is not enough to free the entire support structure from all torque forces.

[0005] The present invention has the advantage over the existing devices that it eliminates all torques and bending forces from all parts of the heliostat support thanks to its triangularly shaped structure. By using three linear actuators to increase or decrease the lengths of the sides of the triangles defining the support structure of the heliostat, a rotation about three axes is obtained for the mirror support frame. Since all joints used in the present invention are three-degrees-of-freedom joints, such as spherical joints or suitable flexures, no torque forces can be generated on any part of the triangular structured support of the heliostat.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Fig 1 shows a perspective view of the heliostat according to the invention.

SUMMARY AND OBJECTS OF THE INVENTION

[0007] The present invention is a triangular structured support that allows for the building of a low-cost heliostat of great sturdiness and stability. As is known, triangular shapes are the most stable supporting units of construction, all else being equal, because all forces in action are stretching and compressive forces without any torque or bending. In order to obtain the construction features of sturdiness and stability, the orientation of the heliostat's mirror support frame is achieved by changing the geometry of the triangles constituting its

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structure. This, in turn, is achieved by the use of at least three linear actuators that drive the rotation of the mirror support frame about the three axes. Other advantages, features and modes of use of the present invention will be evident from the following detailed description of one embodiment, shown by way of example and not for limitative purposes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIEMENT

[0008] By referring to Fig 1, a heliostat according to the present invention is designated as a whole with the reference number 100.

[0009] The heliostat 100 comprises a fixed pedestal 11 resting upon the ground and connected to a revolving shaft 12 by means of a spherical joint or suitable flexure 12a. Specifically, thanks to joint 12a, the revolving shaft 12 can rotate around its own central and parallel axis P, around axis y pointing towards the target, and around axis a parallel to the ground and perpendicular to axis y. 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 be taken to mean "spherical joint or suitable flexure" as described above.

[0010] In the present embodiment, there is a rigid base or pedestal 11 with a front and a back, which supports the rest of the structure of the invention. The base 11 is in turn supported by any practical external means, including directly resting on the ground, supported off the ground by means of feet, or subsidiary structures including towers or pylons, all nominally rigid. The lower extremity of revolving shaft 12 is connected to the front of fixed pedestal 11 by means of a spherical joint 12a. Revolving shaft 12 is integrally and solidly connected to an arm 13. Arm 13 is not parallel to shaft 12.

[0011] Together with arm 13, revolving shaft 12 constitutes the mirror support frame of reflecting member 2. The fixed pedestal 11 may be implemented by means of a tubular structure that may be simply rested upon the ground or anchored to the ground if desired.

[0012] The lower extremities of linear actuators 15,16,17 are connected to the rear of the fixed pedestal 11 and more specifically, linear actuator 15 is connected to the fixed pedestal 11 by means of spherical joint 11a, and linear actuators 16 and 17 are connected to the fixed pedestal 11 by means of spherical joints lib and 11c, so that there is a substantial fraction of the width of the rear of the base between the mounting positions of, on the one hand joint 11a, and on the other hand, joints lib and 11c, which latter pair may preferentially be mounted close together.

[0013] The upper extremities of two linear actuators 15 and 17 are connected to the one extremity of arm 13 by means of two spherical joints 13a and 13c. The upper extremity of linear actuator 16 is connected to the other extremity of arm 13 by means of spherical joint 13b.

[0014] Joints 13a and 13b respectively are positioned on the arm 13 on the same side of the front-back centerline of the whole structure as are joints 11a and lib respectively on the base.

[0015] The so-implemented structure allows reflecting member 2 to rotate with respect to fixed pedestal 11 by means of arm 13, in turn moved by means of linear actuators 15,16,17 around rotation axes a, P, y.

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[0016] The rotation of reflecting member 2 around axes a, P, y is controlled in an interdependent manner by linear actuators 15,16,17, which can be of electrical or hydraulic nature.

[0017] Linear actuators 15,16,17 are able to receive control signals to move reflecting member 2 to the correct orientation.

[0018] Such an embodiment allows for the rotation of revolving shaft 12, and reflecting member 2 integrally and solidly connected to it, around the three axes of rotation a, P, y with a composite and interdependent movement of the three linear actuators 15,16,17. More specifically, rotation around axis P is obtained when linear actuators 15 and 17 work in the same direction as each other, and linear actuator 16 works in the opposite direction to that of actuators 15 and 17. Rotation around axis a is obtained when linear actuators 15,16,17 all work in the same direction. When linear actuator 17 works alone, it regulates the rotation around axis y.

[0019] Dominant rotations around any of the three axes produced by changing the actuator lengths as previously described, can also produce unwanted secondary rotations around the other two axes. These unwanted secondary rotations can be corrected by adding angular position sensors to one or more of the rotation axes to provide negative feedback to the control system by means of error minimization processes that perform successive approximations. Alternatively, by adding a linear position sensor to one or more linear actuators, the structure's geometry and kinematics may be pre-computed to provide open-loop corrections (e.g. via a look-up table) and determine correction factors for the movement performed by each linear actuator to position the mirror frame in the correct angular position.

[0020] Finally, the control of the orientation of the mirror support frame with respect to the position of fixed pedestal 11 and thus of the ground, can be implemented by means of the composite movement of the three linear actuators 15,16,17, which modify the geometry of the triangles constituting the support structure in its entirety without affecting its sturdiness.

[0021] It will be appreciated that the omnipresence of spherical joints allows for the absence of any torque or bending forces throughout the support structure, aside from the mirror support frame, constituted by rotating shaft 12 and arm 13 that are solidly connected to each other.

[0022] While the invention has been described in reference to a preferred embodiment, it will be readily apparent to one of ordinary skill in the art that certain modifications may be made to the system without departing from the same inventive core. The following could also be changed without changing the principle of orienting philosophy:

[0023] the sizes and technologies of each linear actuator 15,16,17

[0024] the position where each linear actuator 15,16,17 is attached to fixed pedestal 11

[0025] the position where each linear actuator 15,16,17 is attached to arm 13

[0026] the shape and orientation of the arm 13 and the rotating shaft 12

[0027] the connection between arm 13 and rotating shaft 12

[0028] the shape and implementation of the fixed pedestal 11, preferably triangular.

[0029] the spherical joints or flexures may be replaced with some other device that allows for the required degrees of freedom while providing adequate thrust rigidity.

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Claims

1. A heliostat support and drive mechanism comprising:

a fixed pedestal;

a shaft attached to the fixed pedestal by a joint so that the shaft is able to rotate with three degrees of freedom with respect to the fixed pedestal;

an arm solidly connected to the shaft and not parallel to the shaft;

a mirror frame solidly connected to the shaft;

a first linear actuator that connects between one end of the arm and the fixed pedestal in a position on the pedestal that is distant from the connection of the shaft to the fixed pedestal;

a second linear actuator that connects between the other end of the arm and the fixed pedestal in a position on the pedestal that is distant from the connection of the shaft to the fixed pedestal and distant from the connection of the first linear actuator to the fixed pedestal;

a third linear actuator that connects between the arm close to the point of connection of the arm and the first linear actuator, and the fixed pedestal in a position close to the point of connection between the second linear actuator and the fixed pedestal.

2. A heliostat support and drive mechanism according to claim 1, wherein the joint between the shaft attached to the fixed pedestal comprises a spherical joint or flexure.

3. A heliostat support and drive mechanism according to claim 1, wherein the three linear actuators attached to the fixed pedestal comprise spherical joints or flexures.

4. A heliostat support and drive mechanism according to claim 1, wherein the three linear actuators attached to the arms comprise spherical joints or flexures.