Vision-Guided Robotics Responds to Changes in Photovoltaic Manufacturing

Economic sluggishness and a need for developed countries to compete with manufacturing costs from low-cost labor markets means that customers want smaller, more flexible vision guided robotic assembly workcells for photovoltaic manufacturing. Vision is helping to make that happen.

When a U.S. company called on manufacturing solutions provider Comau Inc. (Southfield, Michigan) to develop a vision-guided robotic workcell proof-of-concept for manufacturing specialty solar cells, Comau was responding to several trends affecting the photovoltaic industry.

First, economic sluggishness and low petroleum prices have softened solar cell markets, despite a growing interest in renewable energy sources around the globe. U.S. companies are particularly challenged because, despite being a leader in the development of photovoltaic product designs, the country has considerably higher labor prices than many emerging or developing markets in Asia and Europe. Companies are responding to both of these challenges by requesting smaller, more flexible manufacturing solutions that can do more production, assembly and quality control functions in a small footprint and at lower cost than traditional manufacturing that depends heavily on specialized tooling and skilled labor. As the economy returns to health, manufacturers can then simply add addition workcells and ramp up production without having to recreate the ‘wheel.’

“Comau’s biggest role is as an integrator, but since we also manufacture robots, we can do everything ourselves under one roof,” explains Comau’s Tony Ventura, Product Line Manager for Robotics and Vision. “We developed the workcell using 7 different robots that included a new ‘hollow-wrist’ design that allowed us to run the cables inside the robot, allowing the robot to rotate up to 400 degrees without straining the cables. This enabled each robot to do an average of 5 different assembly steps.”

For the beta test, Comau used machine vision to confirm the position and placement of solar modular components. “Since this wasn’t a full production workcell, we didn’t use as much vision-guided robotic assembly as we would normally. The client is really happy with the results, and if we get the contract, we’ll be using vision for numerous applications, including Comau’s RecogniSense™ system, which currently has over thirty installations in production today running on COMAU, FANUC, KUKA, and Motoman robots - and inspection, along with more robots to increase the workcell’s throughput.”

Melding Vision and Robotic Control

“One of FANUC Robotics biggest advantages in solar manufacturing is that we offer our Integrated Robot iRVision as an option to our robot controllers, which speeds up integration and manufacturing,” notes FANUC Robotics America, Inc. (Rochester Hills, Michigan) National Distribution Group account manager, Chris Blanchette. “And improving throughput has been one of the biggest issues facing solar manufacturing.”

While some solar manufacturing processes require specialized vision systems that use ultra high resolution cameras and specialty processes, FANUC’s iRVision platform has helped the company meet several important needs of the photovoltaic manufacturing industry.

“While the main purpose of our 2D and 3D iRVision offerings are for robotic guidance, handling, and tracking of the product, we can also handle several types of quality inspection through our iRVision Error Proofing tool, including chips, cracks, bows, and other gross defects.”

Like semiconductors, solar modules and their components are often very small, delicate and located in complex assemblies requiring careful, precise handling. Precise tracking of products on conveyors, tables, and trays often challenges the repeatability and precision of today’s cutting-edge robotic systems. According to FANUC’s Blanchette, Vision helps the robot achieve greater accuracy and repeatability than a robot controller could achieve without vision corrected guidance.

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“When it comes to robotic guidance, interlacing the robot and vision coordinate frames is one of the greatest challenges,” continues Blanchette. “By having the two systems housed in the robot controller, this simplifies integrating the two coordinate systems while speeding throughput.”

To use physical product tracking through conveyor encoders alone would require additional tooling and fixtures to precisely hold the component in place, which adds time and additional handling of the component. “Every time you touch a part, there’s a chance you might damage it,” notes Blanchette. “The benefit of using vision rather than fixtures is that precision fixtures are expensive, and require more handling than vision guided robotics alone.”

FANUC’s iRVision 3D, in particular, which uses laser triangulation to determine the location of objects in three dimensions, has been particularly useful for FANUC Robotics’ latest M-3iA robot. The M-3iA, which is finding wide use in the solar manufacturing industry, is a delta-type robot (see image) that allows six degrees of freedom rather than the standard four degrees. “The M-3iA gives solar manufacturers more flexibility than 4-axis delta robots, which then allows them to create smaller work cells with greater flexibility when it comes to feeding parts,” says Blanchette. “In solar concentrators, for instance, lenses have to be fixed at specific angles. The junction box on a solar panel is another example. Typically, a manufacturer would use a separate tool to bend the leads under the box to a specific angle, and then use a 4-axis delta robot to place the junction. With 6-degrees of freedom, you can do it all with one robot, which simplifies the work cell and speeds throughput.” Finally, by going to smaller workcells, manufacturers can install automated systems that meet lower volume requirements while maintaining low cost-per-Watt metrics. When demand increases, manufacturers can simply add another workcell.

Finally, through iRVision’s Calibration Master and Tool Center Point options, the vision system allows the operator to verify exact tool location and placement before starting production. “Precision is crucial for many solar manufacturing applications,” concludes Blanchette. “By using Calibration Master to determine the exact position of the frame, you maintain higher precision than the robot could accomplish on its own, while avoiding expensive precision fixtures.”

While FANUC declined to comment on future hardware and software enhancements to its iRVision line, Blanchette did confirm that the company is always looking for ways to improve the processing capabilities for next generation machine vision robotic guidance systems. “Today, we have the ability to integrate with third party high resolution cameras and PCs to handle the extra data, but we’re always exploring ways to add intelligence to our product line. It’s a key objective,” Blanchette says.

As robotic controllers continue to take advantage of the latest microprocessor designs, convergence of vision with robotic technology is likely to accelerate while the breadth of vision-guided applications expands. The photovoltaic industry - a promising growth solution for tomorrow’s renewable energy needs - will certainly benefit as a result, reducing cost-per-Watt metrics and making sunlight collection and conversion a serious player in tomorrow’s energy markets.