Abstract:
A planar reflector is supported on a ball-and-socket joint and can be independently pivoted about X and Y axes by magnetic drives that propel corresponding bail arms hingedly connected to the reflector. Control is achieved using the outputs of a multi-axis magnetic field sensor closely positioned adjacent a spherical magnet embedded in the ball of a ball-and-socket joint that supports the reflector for pivoting motion.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 USC Section 119(e) from the similarly entitled U.S. Provisional Application Ser. No. 61/108,774 filed Oct. 27, 2008. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to systems and methods for utilizing the energy of the Sun, and more particularly, to systems and methods for tracking the Sun to re-direct and concentrate incident solar radiation for lighting, heating and photovoltaic applications. 
     BACKGROUND 
     Increased usage of renewable energy sources such as solar radiation is important in reducing dependence upon foreign sources of oil and decreasing greenhouse gases. Devices have been developed in the past that track the motion of the Sun to re-direct and concentrate incident solar radiation. Prior art includes, for example, the use of a parabolic dish mirror with a central axis that is pointed generally toward the Sun. Incidental solar radiation is received and reflected by the parabolic dish mirror and concentrated at its focus, where a thermal target can be mounted so that it can be heated. Such a parabolic dish mirror has been supported for independent movement by a two-axis tracking support mounted atop a supporting structure such as a tower. In some instances, optical encoders associated with the tracking support provide signals indicative of the direction and amount of rotation of the parabolic dish mirror so that motor drives and a control system can be used to track the Sun and increase the efficiency of the energy transfer. 
     Similar existing devices utilize a parabolic trough mirror whose focal line aligns with the Sun. A tracking support carries the parabolic trough mirror, typically mounted atop a tower. Incident light rays from the Sun are collected and reflected by the parabolic trough mirror and concentrated on a pipe that extends along the focal line effecting a heat transfer to a fluid such as water or liquid sodium. The heating efficiency can be improved by targeting mechanisms that cause the parabolic trough mirror to pivot and track the Sun. 
     Another variation of the prior art utilizes a heliostat flat mirror that receives incident light rays from the Sun and reflects them against a thermal target atop a tower. The flat-mirror heliostat may be supported by a two-axis tracking device which may be elevated on a tower. Drive mechanisms may control the azimuth and elevation of the flat mirror to keep the Sun&#39;s rays focused on the target thermal collector. 
     Cost and complexity of design are frequently encountered disadvantages to the prior art devices in this field. Tracking frames are historically often cumbersome and require significant power to drive in tracking. Additionally, the need for individual tracking sensor units on mirror heliostats in order to keep them individually pointed can significantly add to the expense of the units. 
     SUMMARY OF THE INVENTION 
     The present invention offers an improvement to the prior art in the design of tracking mechanisms and support frames, as well as an advanced method of controlling the orientation of an array. In accordance with the present invention, a solar tracking apparatus is supported by two pivoting arch-shaped bail arms and a central shaft providing optimum range of motion through an advanced magnetic drive and magnetic sensing system. 
     An advantageous use of magnetic linear drives moves the arch-shaped bail-arms in such a way as to position the mirror in any required orientation for maximum directed reflection of solar radiation. 
     An array of multiple reflectors of this design may be coordinated to maximize efficient use of incident solar radiation through a single-sensor central control system. An innovative method of controlling such an array by use of a single focal camera device is revealed, which enables multiple reflectors to be controlled in their orientation from a single control point. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a pair of the bail-arms and a central ball-joint assembly in accordance with an embodiment of the present invention. 
         FIG. 2  is an isometric view from below of a reflector, illustrating the mounting of the central ball-joint assembly, the bail-arms and their respective hinges. 
         FIG. 3  illustrates the components of  FIG. 2  combined with a central shaft, a support frame and a housing that form an embodiment of the solar reflector and drive control system of the present invention. 
         FIG. 4  is an isometric view from above of the system illustrated in  FIG. 3 . 
         FIG. 5  is an enlarged vertical sectional view of the system of  FIG. 4  taken along line  5 - 5  of  FIG. 4 . 
         FIG. 6  is a view similar to  FIG. 5  taken along line  6 - 6  of  FIG. 4 . 
         FIG. 7  is an enlarged cross-sectional view of an individual drive mechanism used in the system of  FIGS. 3-6  to situate the bail-arms and orient the reflector plane. 
         FIG. 8A ,  8 B,  8 C,  8 D,  8 E,  8 F,  8 G,  8 H,  8 J,  8 K, are graphs illustrating sensor outputs for angles of orientation of the system of  FIGS. 3-6  from 22.5° to 157.5° of azimuth and 0° to 90° inclination. 
         FIG. 9  is a diagrammatic illustration of and embodiment of the present invention that includes multiple reflectors and a central array-control system. 
     
    
    
     DETAILED DESCRIPTION 
     The entire disclosures of U.S. Patent Application of Jan. 30, 2006 (U.S. Ser. No. 11/342,396) and U.S. patent application Ser. No. 11/763,267, filed on Jun. 14, 2007, Mark S. Olsson, are hereby incorporated by reference. 
     In an embodiment of the present invention, a mirror or other reflecting surface for collecting and reflecting incident solar radiation is supported for independent motion about a pair of axes. The reflecting surface is supported by a pair of arch-shaped bail-arms, each of which may pivot about one of the x and y plane axes of the mirror. At the intersection of the two plane axes of the reflector, a ball and socket joint is located such that the central vertical (z) axis of the mirror passes through its center. The socket portion of the joint is affixed to the center of the reflector. 
     Turning to  FIG. 1 , the two bail-arms ( 101 ,  103 ) are illustrated in their relative locations. One of the arms ( 101 ) is considered the fixed arm, while the other ( 103 ) is considered the unfixed arm. In  FIG. 1 , the ball component ( 105 ) of the ball-and-socket joint is illustrated to show its spatial relationship to the bail-arms  101 ,  103 . The arch-shaped bail-arms terminate in hinge adaptors (such as  107 ). In the illustrated embodiment adaptor  107  is an Aluminum cylinder. The hinge adaptors  107  serve to connect the bail-arm ends to a rectangular planar reflector  201 . 
     Turning to  FIG. 2 , the reflector assembly ( 200 ) is illustrated from below. In  FIG. 2  the hinge adaptors  107  at the ends of the bail-arms ( 101 ,  103 ) are seen attached to the hinge pieces  207  at each corner of reflector  201 . A mirror housing assembly  203  is centrally attached to the reflector  201  and contains logic circuitry for controlling drive motors (not illustrated in  FIG. 2 ). The ball component  205  of the ball-and-socket joint is visible in  FIG. 2 . The ball component  205  has a threaded receptacle to attach it to a central shaft (not illustrated in  FIG. 2 ). In the illustrated embodiment, the ball component  205  is a Delrin® plastic sphere drilled and tapped to house a composite magnet (not illustrated in  FIG. 2 ) which is used in the magnetic positioning capability of the illustrated embodiment. The center of ball  205  acts as the central point of rotation for reflector  201  and the reflector assembly  200  including the mirror housing assembly  203 , and as the threaded connector of the associated shaft ( 517  in  FIG. 5 ). In the illustrated embodiment, the bail-arms are made of 0.125″ thick round steel stock, bent to an 8″ radius. 
     Turning to  FIG. 3 , the components of  FIG. 2  are seen from below, assembled with a housing structure  305  in a compound assembly  300  comprising the reflector  201 , a housing assembly  305 , and a mirror housing assembly  203 . In  FIG. 3 , bail-arms  101 ,  103  are led through separate slots in the sides of housing  305  so that the fixed bail-arm  101  is confined to rotate about the center of the ball  205  in only a single plane along its major cross-section and perpendicular to the plane created by the two pivot axes. The slots in the housing  305 , through which the unfixed bail-arm  103  is led, allow the unfixed bail-arm  103  to rotate passively about the center of the ball  205  along its major cross-section. As in  FIG. 2 , each bail-arm is attached at its end to a corresponding hinge adaptor  107  which connects to a corresponding hinge component  207  fixed to reflector  201 . The drive motor assemblies  301 ,  303  are located inside the housing assembly  305 , mechanically associated with their respective bail-arms  101 ,  103 . 
     Still referring to  FIG. 3 , within the housing assembly  305 , the slots for the fixed bail arm  101  prevent it from rotating about the vertical axis of the shaft while the slots for the unfixed bail arm  103  do not. Both sets of slots allow for any tolerable irregularities in the radii of the two bail arms. Properly engineered, these slots provide a large amount of stability for both bail arms while allowing for the appropriate amount of rotation. The housing assembly  305  also houses the drive assemblies  301 ,  303 . 
     In  FIG. 3  the central shaft ( 517  in  FIG. 5 ) terminates in ball  205  which supports a socket housing  307 . The socket housing  307  is affixed to the top mirror housing assembly  203  and thus to the reflector  201  and allows the reflector to rotate freely around both x and y axes on the ball-and-socket joint. Only the lower portion of the ball  205  is visible in  FIG. 3 . 
     Referring to  FIG. 4  the compound assembly  300  includes the reflector  201 , bail-arms  101 ,  103 , hinge adaptors  107  and hinge components  207 , connected with the housing assembly  305 . 
     The system illustrated in  FIGS. 3-6  is capable of determining and correcting the angular orientation of the reflector  201  in three dimensions, relative to its fixed base. This is accomplished by the inclusion of a three-axis Hall-effect sensor that generates signals representing the orientation of magnetic fields along the X, Y, and Z axes. In the illustrated embodiment, a magnet  511  is embedded inside the ball  205  of the ball-and-socket joint supporting the reflector  201 , and a sensor capable of determining flux in three axes is located directly above it such that changes in the reflector&#39;s orientation produce detectable changes in the magnetic flux along the three axes detected by the sensor. 
     Turning to  FIG. 5 , a section view of the compound assembly  300  is illustrated along the major plane of the fixed bail-arm  101  and the edge of reflector  201 . Reflector  201  is attached to the mirror housing assembly  203 . Within the mirror housing assembly  203  a chip socket mount  513  supports an integrated circuit board  515  which supports and electrically connects a microcontroller  515   a , a three-axis magnetic sensor  515   b  and associated circuitry. The sensor  515   b  may comprise a commercially available Melexis® 90333 sensor. A ball interface and column assembly  517  supports the ball  205  at the upper end of the housing  509 . Two bearings  507 , retained by clips such as  501 , for example, support a shaft  503 . The magnet  511  is spherical and is mounted within ball  205 . Drive motor assemblies  301 ,  303  are located within the overall housing assembly  305 . The arc of the fixed bail-arm  101  is visible in  FIG. 5 . Rotation of motor assembly  301  governs the motion of bail-arm  101  and thus defines the tilt of reflector  201  relative to the horizontal plane in  FIG. 5 . 
     Still referring to  FIG. 5 , the magnet  511  is generally spherical and is preferably a composite magnet made of two parts. The outer part is a permanently magnetized neodymium ring magnet of 0.5″ outer diameter and 0.5″ in length, with an internal diameter of 0.125″. The inner part of the magnet  511  is an axially magnetized cylinder-shaped neodymium magnet is placed through the center of the ring magnet forming the composite magnet  511 . The axial cylinder-shaped magnet is inserted in such a way as to be flush with the bottom of the ring magnet and to protrude approximately 0.125″ above the top of the ring magnet. The composite magnet  511  is embedded in a cavity formed in ball  205  in such a position that its flux level as detected at the sensor  515   b  for the z-axis approaches the sensor&#39;s maximum detection level for that axis. The composite magnet  511  is aligned such that its axis is centered with the center-point of the reflector  201 . In  FIG. 5 , the three-axis magnetic sensor onboard the IC board  515  is positioned as close as practicable to the surface of ball  205  and with one axis of the sensor (X or Y) aligned with the bearing of the fixed bail-arm  101 . This alignment is important because it facilitates angular calculations from the flux-levels detected by the sensor  515   b.    
     Because the composite magnet  511  in  FIG. 5  remains stationary with the ball affixed to the end of the central axle shaft, the movement of the three-axis sensor within the socket housing  513  causes changes in the flux readings output by the sensor  515   b  along the X, Y, and Z axes of the ball. These values are used to compute the angle of the reflector  201  using software algorithms known in the art and enabled in firmware stored in the memory portion of the circuit supported by the circuit board  515 . The microcontroller  515   a  may have its own memory or it may rely on a separate memory supported on the circuit board  515 . 
       FIG. 6  illustrates the compound assembly  300  along the major plane of the unfixed bail-arm  103  and the edge of reflector  201 . The arc of the unfixed bail-arm  103  is illustrated in  FIG. 6 . Rotation of the drive component  303  governs the motion of bail-arm  103  and defines the tilt of reflector  201  relative to the x-axis of  FIG. 6 . 
       FIG. 7  illustrates the construction of the drive motor assembly  303 . In the illustrated embodiment, a magnetic drive system causes an electric motor to magnetically interface to the steel bail-arms of approximately circular cross-section which comprise the supports of the reflecting panel. A relatively small electric gear-head motor  703  is connected at one end to a molded hinge piece  701  which supports the motor  703  and allows the motor assembly  303  to pivot along one axis of rotation. The other end of motor  703  includes a shaft protruding from the motor. The motor shaft is joined to a medium-carbon steel interface block  705  by a setscrew. Interface block  705  cradles one end of a NdFeB Neodymium washer-shaped magnet  709 . The distal end of magnet  709  is cradled by a 1045-medium-carbon steel drive wheel  707  whose near-end form is essentially a mirror of the interface block  705 . A threaded socket-head machine screw  711  centrally connects the extended drive wheel  707 , the magnet  709 , and the interface block  705 . As can be seen in  FIG. 7 , the combined profile of the interface block  705 , magnet  709 , and drive wheel  707  is such as to form a mechanical guide channel  710  into which one of the bail-arms  101 ,  103  may be drawn by the magnetic force of magnet  709 , thus providing the necessary component of friction for the motor  703  to drive the bail-arm along its length. In the illustrated embodiment, the magnet  709  is a 0.5″OD Neodymium ring magnet. The other drive motor assembly  301  has a construction similar to the drive motor assembly  303 . In an alternate embodiment, the extended drive wheel component  707  may be formed with a leading shaft supporting an adjustable counterweight. 
     The graph of  FIG. 8A  illustrates flux signals output by the three-axis sensor  515   b  as the reflector  201  rotates in the y-plane around the ball  205  (that is, with the reflector&#39;s X-angle at zero while the Y-angle proceeds from 22.5 degrees through 90 degrees to 157.5 degrees relative to the vertical). A peak negative value is shown in the Z-axis when the sensor plane is at 90 degrees relative to the central shaft&#39;s vertical axis. This distinct pattern is a benefit of using the composite magnet assembly described in connection  FIG. 5 , in which a central rod-magnet protrudes above the center of a cylinder magnet forming the composite magnet  511 ). 
     In  FIG. 8B  through  FIG. 8K , the process is repeated with the orientation of the reflector  201  incremented in 10-degree steps from 10 degrees to 90 degrees through the combined effects of the two bail-arms  101 ,  103  being variously positioned. In each case the advantageous distinct peak when the sensor plane is at 90 degrees relative to the vertical can be seen. In combination, the Bx, By, and Bz values provide a unique set of values for each azimuth and inclination orientation of the reflector. 
     In another embodiment of the present invention multiple reflectors provide an advantage over previous art by reducing the number of sensors required to establish correct and complete control of the orientation of all of the reflectors. This benefit is achieved by using a single central intelligent control unit, rather than, in the traditional manner, requiring each reflector in a multiple-reflector array to intelligently direct itself toward the Sun&#39;s location. Referring to  FIG. 9 , a plurality of reflectors such as  901  are situated so as to be within the field of view of a target mirror  903  which reflects to a camera  905  below it. Target reflector  903  also serves to protect the camera  905 , which receives the full field of view of the target reflector  903 . This configuration may be used to reflect light into a skylight from the target reflector  903 . The camera  905  gathers an image of the field of view of the target reflector  903  and detects the individual reflection of the reflectors  901  and differentiates amongst them based on a pattern of individual pixels in the camera&#39;s sensing array which were activated by individual reflectors  901 . Firmware associated with the camera  905  captures the values of the multiple pixels of the camera. In a modification of the embodiment illustrated in  FIG. 9 , camera  905  is placed in front of the first mirror  903 . 
     In the initialization of the embodiment of  FIG. 9 , the individual reflectors  901  are calibrated to flash sunlight to the target camera  905 , establishing an array of points in the camera&#39;s field of view which is mapped into memory as a set of values associated with the individual reflector  901 . An individual set of pixels is then mapped to each individual reflector  901 . A large array of pixels can track a large number of reflectors while still being able to discriminate among them as a result of this initial mapping process. 
     During the day, differences in the values caused by changing light conditions may be processed using stored firmware in order to determine control outputs to the individual reflector&#39;s motor controls. This enables the system of  FIG. 9  to keep individual reflectors optimally directed as the light changes, or to compensate for movement caused by wind-gusts, for example. By a process of averaging and extrapolation, the system of  FIG. 9  can be prevented from causing the reflector array to search futilely under cloudy conditions, but can adjust each reflector  901  for optimum reflection of the Sun&#39;s light during normal operations. The algorithms programmed into the firmware can also accommodate re-positioning each reflector  901  at night to redirect the light from the Sun when it reappears in the morning. Control impulses sent from a microcontroller (not illustrated) associated with camera  905  may be addressed to the drive motor assemblies  301 ,  303  associated with either or both of the bail-arms associated with individual reflectors. Transmission of control data may be through any appropriate network connection, such as Ethernet, 802.11x wireless, or other protocol as best suits the application&#39;s requirements. 
     Alternative embodiments of the present invention may be used to concentrate the reflected light to provide thermal energy transfer to a heat exchange device, rather than illumination of a building interior, for example. Systems for concentrating available sunlight onto photovoltaic surfaces may also incorporate the present invention. 
     Clearly, other embodiments and modifications of the present invention will occur readily to those of skilled in the art, in view of the foregoing teachings. Therefore, the protection afforded the present invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings.