# Patent

## Title
System and method for producing modular photovoltaic panel assemblies for space solar arrays

## Abstract

An automated system provides automated manufacturing of photovoltaic standard power modules for utilization in a space solar array, in both rolled blanket and z-folded configurations. The automated system provides robotically controlled systems for CIC-ing, glassing, stringing, laydown and acceptance testing of interconnected photovoltaic devices. A method of manufacturing the photovoltaic standard power modules includes the steps of robotic positioning of diodes, interconnects and busbars onto a SPM stringing tray followed by the robotic positioning of bare cells into position adjacent to the diodes, interconnects and busbars to form strings. The SPM stringing tray is thereafter robotically positioned adjacent to an integral welder for welding of the front side of the string. Cover glass is thereafter robotically placed over the cells. The string is flipped and the backside of the string is robotically positioned for welding.

## Background
RELATED APPLICATIONS
This is a divisional application of U.S. application Ser. No. 14/702,704 which claims priority to Provisional Patent Application No. 61/988,102 filed on May 2, 2014.


BACKGROUND OF THE INVENTION
The present invention relates to photovoltaic arrays and methods of manufacturing photovoltaic arrays. More particularly, the present invention relates to a method and a system for the manufacture of power modules for solar arrays that require less time and labor than required for presently known methods and systems. Various space craft and man-made satellites utilize photovoltaic (“PV”) arrays for recharging of batteries and/or operation of various systems. The PV arrays are a collection of solar cells formed into a unit referred to as a “CIC” (solar cell—interconnect—coverglass). The completed CICs are assembled into strings which are configured into standard power modules (SPMs). The SPMs include interconnected solar cell assemblies, frontside and rearside shielding/coatings, substrate structure, mechanical attachment interfaces, and electrical interconnection interfaces. A number of SPMs are thereafter mechanically and electrically connected to create various blanket architecture aspect ratios, allowing for seamless adaptability to a variety of flexible blanket solar array systems. SPMs manufactured with the disclosed system and according to the disclosed method may be utilized as building blocks to form an Integrated Modular Blanket Assembly (“IMBA”).
U.S. Pat. No. 6,555,739 by Kawam describes a known method of manufacturing a photovoltaic array. According to this method, a CIC is formed by welding or soldering one or more interconnect members (made of a thin ribbon of silver or similar metal) to the solar cell's top surface metal layer. Thereafter, a liquid, translucent silicone adhesive is applied to the solar cell's top surface to bond a layer of doped glass to the cell and interconnect. After all of the solar cells have been formed into CICs, the CICs are assembled into strings. As further described by Kawam, as part of this assembly process, all of the CICs are placed, one at a time, on an alignment tool or jig, with their glass sides down, interleaving the CICs such that the interconnect member from one CIC is resting on the bottom side of an adjacent CIC. The interconnect members are then attached to the bottom side of adjacent CICs by a soldering and/or a welding process. After a desired number of CICs have been so arranged and attached to form a string, the string is transferred to a substrate, which embodies the final solar array configuration. This transfer process is accomplished by first attaching masking tape or similar non-permanent adhesive to the backside of the string, and transporting the taped string, glass side down, onto a transfer device that is fabricated from a sheet of mylar. The transfer device, fabricated from mylar or similar material, allows the array of modules to be handled and lifted into position.
As the next step, the surface of the substrate to be laminated with the string of solar cells is primed by painting a silane material on the substrate surface. As noted by Kawam, the backsides of each of the solar cells are also primed with this material to promote subsequent silicone adhesion. A thin layer of liquid silicone adhesive is then applied to the primed substrate. While the adhesive is still wet and uncured, the string is quickly set into place atop the adhesive applied to the substrate. The string is aligned and individual weights applied to the cells while the adhesive cures, which may take up to a week. After curing, excess adhesive is removed from the PV array.
Kawam notes that the above process was developed in an effort to create a batch process. As noted, first the CICs are assembled, then strings are assembled, and then the strings are transferred to substrates to form the PV arrays. Kawaam notes this manufacturing process involves the handling of the solar cells during at least four separate operations, which results in excessive cost and cycle time. He further notes that the process permits only portions of the assembly to be automated and that this process results in damage to 5% to 8% of the solar cells.
Kawam directs his attention the need to eliminating the need to solder or weld the interconnects to the solar cells, where his solution is to construct strings by bonding the solar cells and interconnect members to the array surface of a substrate with double-sided and pressure sensitive adhesive, and electrically coupling the interconnect members and end members to the solar cells via a dry electrical contact. However, Kawam does not disclose any automated device for the assembly of the strings he discloses. He specifically teaches against a single automated method which produces strings with welded interconnects.
Thus, while there have been some efforts to automate the process, there is not a known system or method which provides for the assembly of an SPM suitable for a space solar array by a single automated device.
SUMMARY OF THE INVENTION
The present invention provides an automated manufacturing system and method for CIC-ing, glassing, stringing, laydown and acceptance testing of interconnected photovoltaic devices to assemble photovoltaic standard power modules for assembly onto an ultra-lightweight photovoltaic flexible blanket (IMBA) for utilization in a space solar array, in both rolled blanket and z-folded configurations. The automated manufacturing system disclosed herein provides high performance and repeatable high quality photovoltaic panels/modules at a cost which is significantly lower than the known devices.
The system comprises the following subassemblies: (1) end effector tools consisting of: SPM tray carrier, adhesive dispenser, preload bar pickup and cell/interconnect vacuum chuck tools; (2) enclosure assembly; (3) adhesive system assembly; (4) carousel system assembly; (5) gravity feed system assembly; (6) preload stabilizer assembly for glass bonding; (7) SPM assembly tray; (8) SPM/Kapton substrate bonding tray; (9) vacuum manifold interface tray assembly; (10) interconnect liner weld assembly; (11) cell interconnect reel feeder assembly; (12) diode interconnect reel feeder assembly; (13) SCARA robotic system; (14) integrated circuit inverter/flipper assembly; (15) cell or integrated string flipper assembly; (16) X-Y-Z welding assembly stage; (17) vision and sensor system assembly; and (18) interconnect weld strength test stand assembly.
A method of manufacturing power modules for solar arrays generally comprises the following steps: (1) robotic positioning of diodes, interconnects and busbars onto a SPM stringing tray; (2) robotic positioning of bare cells into position adjacent to the diodes, interconnects and busbars to form strings; (3) robotic positioning of the front side of the string adjacent to an integral welder and welding the front side of the string; (4) robotic placement of cover glass over the cells; (5) robotic positioning of a weight assembly on the cover glass to apply a load to maintain the coverglass bond line; (6) flipping the string; (7) robotic positioning of the string adjacent to the integral welder and welding the back side of the string; (8) robotic placement of a kapton substrate over the string. Embodiments of the method include: (a) a method of utilizing prefabricated CICs in the fabrication of SPMs; (b) a method of utilizing bare cells in the fabrication of SPMS; (c) a method of utilizing inverted metamorphic multi-junction (“IMM”) cells in the fabrication of SPMS.



BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1-27 depict an embodiment of the manufacturing system in the process of fabricating an SPM, specifically:
FIG. 1 depicts an embodiment of the SCARA robotic system selecting a tool from the end erector tools.
FIGS. 2-3 depict the robotic system of FIG. 1 selecting a SPM tray carrier tool.
FIGS. 3-4 depict the carrier gripping tool picking up a SPM assembly tray.
FIG. 5 depicts the SPM assembly tray being loaded onto an X axis linear motor.
FIG. 6 depicts the robotic system of FIG. 1 exchanging the SPM carrier tool for a vacuum assisted pickup mechanism.
FIGS. 7-8 depicts the vacuum assisted pickup mechanism in position to pick up diodes, interconnects and busbars from respective reel feeder assemblies for each component for placement on the SPM assembly tray.
FIGS. 9-10 depicts diodes, interconnects and busbars as positioned on the SPM assembly tray by the vacuum assisted pickup mechanism.
FIGS. 11-14 depict bare cells being picked up from a carousel assembly, and placement of the bare cells on the SPM assembly tray.
FIG. 15 depicts the welder welding the interconnects on the front side of the string.
FIG. 16 depicts the robotic positioning of an adhesive dispenser for dispensing adhesive onto the cells in preparation of placement of cover glass.
FIGS. 17-20 depict cover glass member being picked up from the carousel assembly and placed on each cell.
FIGS. 21-23 depict the robotic positioning of calibrated weights over the coverglass.
FIG. 24 depicts the external reorientation of the string.
FIG. 25 depicts the welding of the backside interconnects.
FIG. 26 depicts the application of the kapton substrate.
FIG. 27 depicts a competed SPM.
FIG. 28 depicts an embodiment of the manufacturing system showing the various subassemblies.
FIG. 29 shows a plan view of the manufacturing system depicted in FIG. 28.
FIG. 30 shows an embodiment of a robotic system which may be utilized with the manufacturing system.
FIG. 31 depicts an embodiment of an X-Y-Z string welding station which may be utilized with embodiments of the invention.
FIG. 32 depicts a single IC'ing station which may be utilized with embodiments of the present invention to enable the weld qualification and characterization of each welded cell. The single IC'ing station consists of a single Y-axis linear motor stage, a Unitek weld head, a power supply, and a weld load cell pull tester.
FIG. 33 depicts an interconnect weld force tester assembly which may be utilized with the IC'ing station in embodiments of the invention.
FIG. 34 depicts a cell flipper mechanism which may be utilized with the IC'ing station in embodiments of the invention.
FIG. 35 depicts an embodiment of a carousel mechanism which may be utilized to house bare cells, cover glass, ICs or CIC's, this embodiment having sufficient storage to manufacture four full-sized 91-cell SPMs.
FIG. 36 depicts an embodiment of a SPM stringing vacuum tray assembly, showing, from left to right below the full figure, the SCP interface, vacuum, and assembly trays.
FIG. 37 depicts an embodiment of a SPM pick-up tool.
FIG. 38 depicts an embodiment of a preload bar pickup tool.
FIG. 39 depicts an embodiment of an adhesive dispenser.
FIG. 40 depicts an embodiment of a cell, interconnect, and diode pick-up tool.
FIG. 41 depicts an embodiment of the tool stand-off brackets for parking of the various tools during operations.
FIG. 42 depicts an embodiment of a string flipping assembly which is used external to the manufacturing system for turning an SPM.
FIG. 43 is a flow chart showing a process for manufacture of CICs to SPMs utilizing embodiments of the disclosed system.
FIG. 44 is a flow chart showing a process for manufacture of bare cells to SPMs.
FIG. 45 is a flow chart showing a process for manufacture of IMM ICs to SPMs.



DETAILED DESCRIPTION OF THE EMBODIMENTS
Referring now to the Figures, an embodiment of the manufacturing device 10 is depicted in FIGS. 1-27 in the process of fabricating an SPM 500, shown as completed in FIG. 27. FIGS. 28-29 show, respectively, a perspective view and a plan view of an embodiment of the assembly work station showing the major subassemblies. FIGS. 30-41 show close-up views of some of the components of the subassemblies. FIG. 42 shows an embodiment of a flipping assembly, used external to the work station, for turning over an SPM which is in the process of being completed. FIGS. 43-45 show flow charts for assembling SPMs from, respectively, CIC's, bare cells, and IMM ICs.
The manufacturing device 10 is configured to process both standard ZTJ/XTJ PV and emerging IMM PV. The manufacturing device 10 is also designed to manufacture interconnected cells (CIC's), and fully CIC'd cells (glassed) during periods of SPM fabrication downtime. The manufacturing device (also referred to herein as “work station”) 10 may be housed within a safety enclosure 300, best depicted in FIG. 28, to protect personnel from the moving assemblies, although certain components, such as reel feeders 302 which provide consumable materials during the manufacturing process, may extend beyond the envelope of the safety enclosure 300 to facilitate the replenishment of the consumable materials. For additional safety, an indicator light 304 may extend above the safety enclosure 300 to communicate the operating status of the work station 10.
The manufacturing device 10 is configured to assemble bare cells, interconnects, diodes and cover glass into CICs—independently or at string level—to qualified flight standards. The manufacturing device provides front and backside welding of CICs and bare cells, controlled dispensation of adhesive onto the front of bare cells, and to accommodate the current, state of the art, ZTJ cell configuration and future PV sizes and technology. The possible PV options include, but not limited to, IMM, Super Cell, Microlink and Single Cell per wafer designs.
The manufacturing device will place and weld CICS, bus-bars and turn-arounds in variable string configurations (length and shape), because of the flexible nature of the utilized robotics and controlling software, including a string design up to seven cells wide and thirteen cells deep.
The manufacturing device is capable of adhering completed strings to a multitude of substrate materials, such as Kapton with pressure sensitive adhesive, Kapton with dispensed and metered adhesive, and Mylar employing a weak adhesive for transfer to a rigid panel.
The manufacturing device is capable of performance validation of CICs, strings and SPMs by employing various means of investigating cell, string, or SPM integrity. One such means of validation utilizes either InfraRed or the visible spectrum to identify structural issues within the CIC, string or SPM. Visual cameras may be utilized to verify the positional accuracy of features within these same assemblies. For example, proper diode location, cell spacing, bus-bar and turn-around location, interconnect placement and bonded coverglass tolerance.
Embodiments of the manufacturing device 10 utilize a robot 120 as a pick-and-place machine. An acceptable robot 120 is the Epson SCARA type robot because of its inherent circular work space area and accommodation of conveyor applications. The robot utilizes an effector tool interface 122 with pneumatic tool changers to allow the use of a single robot 120 with multiple tools to execute multiple operations. The robot 120 will typically have a predetermined “safe position” which places the arm 122 of the robot away from all cell, interconnect, SPM and coverglass materials, testing equipment, linear motors and sensors. The safe position is, instead, directly over the tool changers and with the Z-axis fully retracted to eliminate possible interference issues with surrounding hardware should a failure occur. Robot 120 works in conjunction with a collection of end effector tools, which are necessary to perform all necessary automated tasks within the work station. The collection of end effector tools may comprise the following: (1) SPM tray carrier 12, preload bar pickup 14, adhesive dispenser 16, and cell/interconnect vacuum assisted pickup mechanism 18, which allows the robot 120 to pick up and position diodes, interconnects and busbars onto the SPM assembly tray 400. FIGS. 37-40 depict embodiments of the end effector tools in greater detail.
FIG. 31 depicts a string welding station 200 which enables loose cells, interconnects, diodes, bus-bars and turnarounds to be welded into fully functional string in situ. Following automatic placement of the of these various components by the robot 120, utilizing vacuum assisted pickup mechanism 18, X and Y linear motors position the required weld points beneath the weld head 202. X-axis translation of the SPM welding tray may be achieved with a Parker 412LXR Linear Motor Stage. Y-axis translation of the weld head may be controlled with a Parker 406LXR Linear Motor Stage.
The inventors herein have determined that the Unitek 72 weld head unit and the associated UB-25 power supply provide acceptable service for weld head 202. The weld head 202 is mounted to a Z axis linear motor for vertical positioning. An acceptable Z axis linear motor is a Parker 404XR 500 mm travel ballscrew stage. Weld head 202 and the Z axis linear motor are in turn mounted to the Y axis linear stage. An optional, battery powered, absolute encoder may be utilized with both the X and Y linear motors to prevent the possibility of the system losing its positional awareness along its axis should power be lost.
As depicted in FIG. 32, an embodiment of the manufacturing device 10 may comprise a single IC'ing station 600. The single IC'ing station 600 takes advantage of the SPM manufacturing down time and allows the weld qualification and characterization of each welded cell. The single IC'ing station comprises a single Y-axis linear motor stage, a weld head assembly (Unitek 72 with UB-25 power supply is acceptable), weld load cell pull tester, and a cell flipping mechanism.
FIG. 33 depicts an interconnect weld force tester assembly 700. The purpose of the weld force tester assembly 700 is to verify that the cell to interconnect weld strength exceeds the applicable standard. The weld force tester 700 comprises a single axis ballscrew stage, a cell plate with integrated vacuum, a load cell, a ball slide and rail, and a pneumatic gripper. In action, the robot 120 places an cell C onto a vacuum plate 702 with the interconnects positioned off the edge of the plate and on the side of gripper 704. The single axis stage then moves the interconnects between the retracted jaws of the gripper 704. The gripper 704 is actuated and pinches the interconnects to restrain the IC while undergoing in-plane loading. The stage 706 moves away from the gripper 704 until a predetermined load is registered on the load cell. Upon conclusion of the test, the stage 706 relaxes, the gripper 704 is released and the stage 706 moves back to its original position of the robot 120 may access the IC for the next step in the process.
FIG. 34 depicts an embodiment of a cell flipper 800. During the IC'ing process, it is necessary to flip the cell C 180 degrees so that the diode may welded onto the back of the cell. Cell flipper 800 provides this service. Cell flipper utilizes an actuator and a vacuum tray to hold the cell. The actuator (which may be a SMC CRJU1-180-M9NWL actuator) has a 180 degree rotary configuration with a hardstop-to-hardstop motion. FIG. 34 shows two view of the cell flipper 800, showing an IC on the vacuum tray with opaque rendering on the left side and as transparent on the right side, so that the underlying vacuum port detail of the interface plate 802.
FIG. 35 depicts an embodiment of a carousel 900 to support the various SPMs and individual ICs, and cover glass. The embodiment of carousel 900 depicted in FIG. 35 may utilize a Parker RT212 worm drive rotary stage and removable storage cassettes 902. The cassettes may be configured to hold bare cells, cover glass, ICs or CICs. For example, the cassettes 902 may hold sufficient components to manufacture four full-sized 91-cell SPMs. Ample clearance is provided to allow the robot end effector tools access to the entire cassette during loading and unloading events. Robot 120 may utilize vacuum assisted pickup mechanism 18 for placing each of these components.
FIG. 36 depicts the various components of SPM assembly tray 400. The SPM assembly tray 400 is utilized to locate and stabilize free cells, interconnects, diodes, busbars and turnarounds during the stringing process. Each of these components is deposited onto SPM assembly tray 400 utilizing robot 120 in conjunction with vacuum assisted pickup mechanism 18. The SPM assembly tray 400 comprises three separate plates, which are shown in the figures below the top portion of FIG. 36. These three components are the linear motor interface plate 402, the vacuum manifold plate 404, and the string assembly plate 406. The linear motor interface plate 402 bolts directly to the X-axis linear motor and is equipped with locating pins for accurate placement of the vacuum manifold plate 404.
The manifold plate 404 is furnished with elbow fittings to enable quick connect/disconnect with the vacuum system. The manifold plate 404 is subdivided into channels to permit staged vacuum application and release. Staggering the vacuum channel application decreases the overall required vacuum system capacity by limiting the number of air ports exposed to the atmosphere at any given time. The manifold plate 404 may also be equipped with locating pins for restraining the stringing tray.
The stringing tray 406 is perforated in specific locations to hold cells, interconnects, diodes, busbars and turnarounds in place. The stringing tray 406 also contains machined locating features for the cells and cover glass to ensure accurate relative placement and repeatability. The stringing tray 406 has pins at the ends of all string columns for positioning of the coverglass preload bars 1000.
During the CICing process it is necessary to hold the coverglass slides stationary with respect to the ICs. In addition to the relative inplane position—governed by machined features in the stringing tray 406—the bond line thickness between the cells and coverglass is equally critical. To achieve accurate bond lines across the entire SPM, a calibrated preload bar 1000 is utilized, which has a low-pressure spring driven, adjustable mechanism. Each preload bar 1000 is positioned by utilizing preload bar pickup 14. The preload bars 1000 are delivered via a gravity feed ramp 1002, which has integrated feed rollers and utilizes actuators, which may be located on either side of the feed ramp. After the preload bars 1000 are utilized during the stringing process, following the complete cell adhesive curing, the preload bars 1000 may be replaced by hand on the gravity feed ramp 1002.
The last automated step in the SPM manufacturing process is the application of the substrate to the backside of the cells. Whether the substrate is bare Kapton, Kapton with pressure sensitive adhesive, or a mylar transfer sheet, the material must be restrained and applied in a controlled manner. This is accomplished with bonding platen 1100 depicted in FIG. 26. The bonding platen 1100 has locating holes for registration on pins embedded in the perimeter of the stringing tray 400.
FIGS. 43-45 are flow charts showing processes for fabricating SPMs utilizing CICs, bare cells, and IMM ICs using embodiments of the work station 10 disclosed herein. FIG. 43 is a flow chart showing a process for manufacture of CICs to SPMs utilizing embodiments of the disclosed system. FIG. 44 is a flow chart showing a process for manufacture of bare cells to SPMs. FIG. 45 is a flow chart showing a process for manufacture of IMM ICs to SPMs.
While the above is a description of various embodiments of the present invention, further modifications may be employed without departing from the spirit and scope of the present invention. Thus the scope of the invention should not be limited according to these factors, but according to the following appended claims.

## Claims

1. A method of manufacturing standard power modules for solar arrays comprises the following steps:
positioning, via a robotically manipulated effector tool, a diode, an interconnecting electrical conductor and a busbar onto a stringing tray configured to receive a plurality of components for a standard power module in a preconfigured arrangement;
placing a bare cell into position adjacent to the diode, interconnecting electrical conductor, and the busbar to form a string, the string having a front side and a back side;
positioning, via a robotically manipulated effector tool, the front side of the string adjacent to a welder;
welding the front side of the string;
positioning, via a robotically manipulated effector tool, a cover glass over the string;
weighting the cover glass; and
turning the string over and welding the back side.

2. The method of claim 1 further comprising the step of applying a substrate to the back side of the string.

3. The method of claim 2 wherein the substrate comprises Kapton.