Machine vision cuts PV module assembly time
Manufacturers of photovoltaic (PV) modules are using more automation to increase competitiveness. Perfectly soldered joints contribute to the efficiency of PV modules. Consistently high product quality and shorter cycle times lead to a permanent cost reduction. As in other industrial sectors, image processing is becoming an important function for more companies. In a fully automated soldering system from Mondragon Assembly of Stockach, Germany, the intelligent vision system optimizes the process of soldering the cross-links between photovoltaic modules.
Important factors in creating a perfect soldered joint are the largest possible contact area, the high strength of the compound, and a small contact resistance. These three criteria largely determine the conductivity and current flow, thus ensuring a high degree of efficiency in the completed solar module.
Parallel workflow saves time
Before the vision system can set the precise positioning of the soldered joints, the cross-links made of galvanized copper are inserted into the system as approximately 5 mm wide strips. A stretching station prevents formation of wave-shaped and crescent-shaped deformations. Using a pneumatic string cutter, they are cut down to match the typical product specifications. A vacuum pad gripper then successively places the cross-link strips individually on a clipboard, until they form the completed connection diagram of the circuits. Then the cross-links as a whole are in turn transferred by means of pneumatic grippers to the photovoltaic module. This approach offers the advantage of parallel soldering and positioning and thus saves more time.
Soldered joints reliably detected
The process takes place simultaneously on the front and back of the module. On each side, two induction soldering heads equipped with the intelligent vision system move over the work areas. Supported by red dome lighting, they recognize the predefined soldered joints. Simultaneously, the vision systems inspect the individual target positions, which are stored in type-specific recipes. The actual and target positions are compared and the deviation is transmitted to the control. If the tolerance limits have been complied with, the flux material is sprayed on and soldered, whereas rejected sites are reworked manually. The quality inspection of the soldered joints themselves is performed by the automated soldering machine.
Vision accelerates production
With machine vision, Mondragon Assembly achieved cycle times of 80 seconds for cells with three busbars and modules with six strings, much faster than manual production. In addition to the rapid functioning as a stand-alone system, the easy handling of the compact image processing system speeds up equipment use.
Even without detailed knowledge in the field of image processing or programming, it can be configured easily and quickly for pending tasks in production. Using its spreadsheet interface, the implementation of simpler applications can be done especially quickly. Complex applications are solved by powerful vision tools. A wide range of development, management, and monitoring tools is offered by the graphical development platform in the machine-vision software. Based on the familiar Microsoft Windows environment, it provides for shorter development cycles for vision applications, increased functional reliability, and high system flexibility.
Advantage of worldwide availability
Mondragon Assembly also receives global services and logistics. The system is easy to use so even less well-trained employees can operate the equipment without knowledge in the field of image processing systems.
The systems are flexible and can be used as a stand-alone solution, without central control. Use of a central server becomes unnecessary, making is possible to do repair and maintenance work even without specialist IT personnel. In this way, the vision-based soldering system for cross-links of photovoltaic modules ensures especially application-oriented operation, in addition to fast cycle times and consistently high quality in the soldered joints.
– John Lewis is market development manager, Cognex Corp. Edited by Mark T. Hoske, content manager, CFE Media, Control Engineering.