GB2120399A

GB2120399A - Tracking system for celestial bodies

Info

Publication number: GB2120399A
Application number: GB08312014A
Authority: GB
Inventors: Hayder Adam
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-05-06
Filing date: 1983-05-03
Publication date: 1983-11-30
Also published as: GB2120399B; GB8312014D0

Abstract

A tracking system for maintaining in alignment with a celestial body, such as the sun, an object such as a solar panel (6) throughout seasonal variations in the circle of apparent movement of the body comprises a first device (A) for rotating the object (6) about the axis of an extension (20) of the counterweighted driving arm to follow the celestial bodies' movement across the sky between rising and setting and a second device (B) whereby the linear movements of a member (2) in orthogonally related directions as the member (2) is reciprocated along a shaft (1) and the shaft (1) is moved vertically up and down are translated into angular movement of the object (6) such that throughout the year it is normal to incident light rays. The axis of the shaft 1 is aligned with the rotary axis of the first device (A) twice a year at the equinoxes and between them tilts the first device (A) upward or downward. <IMAGE>

Description

SPECIFICATION Tracking system for celestial bodies This invention relates to an improved tracking system for celestial bodies.

Apparatus for automatically tracking the apparent movement of celestial bodies across the sky is needed for such observation equipment as telescopes and for coelostats, heliostats and solar energy collection and conversion devices.

Increasing interest in the exploitation of solar energy has created a demand for a cheap, simple yet reliable solar tracking system which does not require sophisticated engineering either to manufacture or maintain it, so that solar energy converters can be employed in large numbers anywhere in the world at acceptable cost.

The essential problem in devising any such tracking device is that the apparent motion of a celestial body in a plane containing the observer is in a circle the centre of which coincides with the observer twice a year at the equinoxes but between the equinoxes shifts both vertically and horizontally relative to the observer. In the case of the sun this movment of the centre is zero in the vertical direction if the observer is at the equator and its horizontal amplitude is small, but both the vertical and the horizontal amplitude of this movement of the centre increase as the observer moves northward or southward away from the equator.

Various biaxial mountings, e.g. for telescopes, have been proposed in the past whereby an object maintains its orientation relative to a celestial body as the seasons change by rotating about orthogonally related axes. In general, however, such proposals require a high level of precision engineering and the apparatus is both heavy and costly. This is acceptable in the case of astronomical instruments but is not suitable for the mass production and use of large numbers of solar energy converters, where installation and maintenance costs should be kept to a minimum and precision engineering should, if possible, be avoided.

An object of the present invention is to provide a tracking system which fulfils contemporary and foreseeable needs especially, but not exclusively, in the field of solar energy collection or conversion.

The present invention proceeds from the realisation that at any given point on the earth's surface the seasonal movement of the centre of apparent motion of a celestial body such as the sun is a combination of two simple harmonic motions, one vertical and the other horizontal, and that in a simplified and less costly tracking system the biaxial rotary movements previously proposed may be substituted by orthogonally related linear movements.

In accordance with the present invention, therefore, a tracking system for maintaining an object in alignment with a celestial body throughout seasonal variations of the circle in which the body appears to move comprises means linearly movable simultaneously in orthogonally related directions and means for translating said linear movements into an angular movement of said object such that its orientation to the circle of apparent movement of said body remains substantially constant throughout the year.

Said translation means may comprise an articulated connection between said object and means for rotating the same, said rotating means being angularly displaceable about an axis fixed in space at right-angles to its axis of rotation, mounting means for the object which is of variable length between said articulated connection and a member movable toward and away from said rotating means, and means for displacing said member at right-angles to its direction of movement with respect to said rotating means.

Said mounting means preferably comprises relatively telescopic components one of which is fixed relative to the object and another of which is pivotally connected to said member.

Said member is preferably rotatable about and is guided for movement longitudinally of a shaft which is in turn displaceable at right-angles to its axis. The member may be a sleeve surrounding the shaft and means for displacing the sleeve along the shaft may comprise an eccentrically rotatable connecting rod which passes through a tubular element fixed at right-angles to the sleeve so that the sleeve is rotatable but not axially displaceable relative to the tubular element.

The shaft may have an integral collar which surrounds a vertical column so that the shaft is vertically movable without alteration of its horizontal attitude, and means for vertically displacing the shaft may comprise a crank one end of which is engaged in a longitudinal slot in the shaft.

Said means for rotating the object may comprise a generally "T"-shaped driving arm, the stem of the "T" being journalled for rotation about its axis with the crosspiece of the "T" being articulated at one end to said object and having at its other end a counterweight which tends to balance the object about the axis of the stem portion of the "T". A helical spring may be provided for rotating the driving arm about the axis of its stem portion, the spring surrounding said stem portion and at one end engaging the crosspiece of the driving arm at a position spaced from the stem, there being further provided a timing mechanism which permits rotation of the driving arm by the spring at a speed corresponding with the apparent angular velocity of said body.

A preferred embodiment of the invention will now be described with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a view in side elevation of a tracking system in accordance with the invention, Figure 2 is a view in side elevation of support means for the shaft 1, shown in Figure 1, Figure 3 is a view from above of the solar panel 6 of Figure 1 and its mounting 4, 5, Figure 4 illustrates tilting of the driving arm 14 of Figure 1 through an angle 0, Figure 5 is a detail view taken on the line V-V of Figure 1, and Figure 6 diagrammatically illustrates the apparent motion of the sun through an angle 0 at different seasons.

The solar panel 6 of Figures 1 and 3 is to be maintained by the apparatus illustrated in a plane to which the rays of the sun are perpendicular.

The panel 6 may be a single reflector or collector or may be made up of a plurality of cells. To follow the sun in its arcuate path between rising and setting the panel 6 is rotated in a plane at rightangles to the plane of the paper as viewed in Figure 1 by a first device A. This comprises a generally "T"-shaped driving arm the stem portion 20 of which is mounted in bearings 1 6 so as to be rotatable about its axis. One limb 14 of the cross-piece of the "T" is cranked and is articulated by a universal joint 1 5 to the centre of the back of the panel 6. The other limb 19 terminates in a counterweight 1 8 which balances the panel 6 about the axis of the portion 20.As shown, the driving arm is driven in rotation about the axis of its portion 20 by a helical spring 17 which engages one limb 14 of the arm at a position spaced from the portion 20, a timing mechanism (not shown) engaging the driving arm and controlling its rate of rotation by the spring 17 to coincide with the angular velocity of the sun as it apparently moves across the sky.

Alternatively, the portion 20 of the driving arm may be rotated about its axis by a constant-speed motor (not shown). It is optional whether the driving arm is rotated 1 800 and reset to its initial position during the night or whether it is rotated 3600 by a constant-speed motor.

The four arms of a yoke 5 are integral with the back of the panel 6 at positions spaced around the point of articulation 1 5. The arms of the yoke all extend from one end of a rod portion, the other end of which is telescopically received in a tubular element 4. This is pivotally connected at its lower end to a sleeve 2 by means of a pin 3a which extends between lugs 3 upstanding from the sleeve 2 (see Figure 5). The sleeve 2 is rotatable relative to a shaft 1 to follow the arcuate movement of the panel 6 and is also axially displaceable relative to the shaft 1. Axial displacement of the sleeve 2 relative to the shaft 1 is performed by a rotating crank 7 which is connected to the sleeve 2 by a rod 9 which passes through a tubular member 10 at rightangles to the sleeve 2. The latter is rotatable but not axially displaceable relative to the member 10.

The effect of axial displacement of the sleeve 2 relative to the shaft 1 is to alter the angular position of the panel 6, which tilts about the universal joint 1 5. Extension and retraction of the rod portion of the yoke 5 relative to the tubular element 4 allows the tilting movement of the panel 6, and rotation of the crank 7 is so related to the changing attitude of the sun as the seasons change throughout the year that the panel 6 is maintained in an angular attitude such that it is always normal to incident rays of the sun.

Figure 6 is illustrative of the seasonal changes in the duration of time between sunrise and sunset at a given position on the earth's surface.

At the two equinoxes the sun is in the sky each day for 12 hours represented by the angle 02. In winter it is in the sky for less than 12 hours, represented by the angle O and in summer for more than 12 hours, represented by the angle 03.

To accommodate these changes the shaft 1 is vertically movable by a crank 11 while maintained in the same horizontal attitude by a collar at one end of the shaft (Figure 2) which slidably surrounds a fixed vertical support column 1 3a.

One end of the crank 11 engages in a longitudinal slot 13 in the shaft 1 so that the rotary motion of a drive disc 12 for the crank 11 is translated into up-and-down movement of the shaft 1. The arrangement is such that twice a year, at the equinoxes, the shaft 1 is coaxial with the portion 20 of the driving arm, i.e. the rotary axis of the driving arm. In winter the shaft 1 moves downward from this position so that the driving arm is tilted about an axis, fixed in space, at right angles to its axis of rotation through an angle 6 as illustrated in Figure 4. In summer the driving arm is oppositely tilted. The speed of rotation of the driving disc 8 for the crank 7 and of the disc 12 are so related that the combination of vertical movement of the shaft 1 and movement of the sleeve 2 along it produce angular movements of the panel 6 about the universal joint 1 5 such that throughout its arcuate movement each day the panel 6 is maintained in a plane normal to incident rays of the sun throughout the year.

The device "B" thus ensures that daily variation of the attitude of the sun is compensated by suitable tilting of the panel 6 as well as daily variation of the distance from the panel 6 of the plane in which the sun apparently moves between rising and setting.

Annual adjustment of the device B will be necessary to conform to the precesion of the equinoxes. Otherwise the drives 8 and 12 may rotate at a constant speed.

Claims

1. A tracking system for maintaining an object in alignment with a celestial body throughout seasonal variations of the circle in which the body appears to move, said system comprising means linearly movable simultaneously in orthogonally related directions and means for translating said linear movements into an angular movement of said object such that its orientation to the circle of apparent movement of said body remains substantially constant throughout the year.

2. A system as claimed in claim 1, wherein said translation means comprises an articulated connection between said object and means for rotating the same, said rotating means being angularly displaceable about an axis fixed in space at right-angles to its axis of rotation, mounting means for the object which is of variable length between said articulated connection and a member movable toward and away from said rotating means, and means for displacing said member at right-angles to its direction of movement with respect to said rotating means.

3. A system as claimed in claim 2, wherein said mounting means comprises relatively telescopic components one of which is fixed relative to the object and another of which is pivotally connected to said member.

4. A system as claimed in claim 2 or claim 3, wherein said member is rotatable about and is guided for movement longitudinally of a shaft which is in turn displaceable at right-angles to its axis.

5. A system as claimed in claim 4, wherein said member is a sleeve surrounding the shaft and wherein means for displacing the sleeve along the shaft comprises an eccentrically rotatable connecting rod which passes through a tubular element fixed at right-angles to the sleeve so that the sleeve is rotatable but not axially displaceable relative to the tubular element.

6. A system as claimed in claim 4 or claim 5, wherein the shaft has an integral collar which surrounds a vertical column so that the shaft is vertically movable without alteration of its horizontal attitude, and wherein means for vertically displacing the shaft comprises a crank one end of which is engaged in a longitudinal slot in the shaft.

7. A system as claimed in any one of claims 2 to 6, wherein said means for rotating the object comprises a generally "T"-shaped driving arm, the stem of the "T" being journal led for rotation about its axis with the crosspiece of the "T" being articulated at one end to said object and having at its other end a counterweight which tends to balance the object about the axis of the stem portion of the "T".

8. A system as claimed in claim 7, wherein a helical spring is provided for rotating the driving arm about the axis of its stem portion, the spring surrounding said stem portion and at one end engaging the crosspiece of the driving arm at a position spaced from the stem, there being further provided a timing mechanism which permits rotation of the driving arm by the spring at a speed corresponding with the apparent angular velocity of said body.

9. A tracking system for maintaining an object in alignment with a celestial body constructed and arranged to operate substantially as described in the description with reference to and as shown in the accompanying diagrammatic drawings.